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The H-function and the acidity of aromatic amines. O'Donnell, Joseph Patrick 1962

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( i ) THE H- FUNCTION AND THE ACIDITY OF AROMATIC AMINES by Joseph Patrick- OTtonnell A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOOTOR OF PHILOSOPHY in the Department of Chemistry We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA December, 1962 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of The University of B r i t i s h Columbia, Vancouver 8, Qasjada. Date PUBLICATIONS Reaction of syn-Benzaldoxime with Carbon-Monoxide and Hydrogen to Y i e l d Substi-tuted Ureas. Can. J. Chem. 38, 457, 1960 A. Rosenthal and J.P. O'Donnell. The H- Scale and the Acidity of Aromatic Amines. J. Amer. Chem. Soc. 84, 493, 1962 R. Stewart and J.P. O'Donnell. Rate-equilibrium Correlation for Dis-sociation of a Carbon Acid Tetrahedron 18, 917, 1962 R. Stewart, J.P. O'Donnell, D.J. Cram and B. Rickborn. The University of British Columbia FACULTY OF GRADUATE STUDIES PROGRAMME OF THE FINAL ORAL EXAMINATION FOR THE DEGREE OF DOCTOR OF PHILOSOPHY of JOSEPH P. O'DONNELL B.Sc, University of Alberta, 1949 M.Sc., The University of B r i t i s h Columbia, 1959 WEDNESDAY, DECEMBER 19, 1962, AT 10:30 A.M. IN ROOM 261, CHEMISTRY DEPARTMENT COMMITTEE IN CHARGE . Chairman; F.H. Soward A. Bree CA. McDowell J.N. Butler R.E. Pincock J.P. Kutney R. Stewart G.M. Tener External Examiners R.P. B e l l , F.R.S. The University of Oxford THE H- FUNCTION AND THE ACIDITY OF AROMATIC AMINES ABSTRACT Our present knowledge of the a c i d i t y constant J of acids which are weak with respect to the pH scale i s limited. The present work uses the Hammett a c i d i t y function concept to develop the H-function for the following systems: aqueous benzyl trimethylammonium hydroxide, pyridine-water contain ing tetraalkylammonium hydroxides, and sulfolane-' water and dimethyl sulfoxide-water containing tetra methyl ammonium hydroxide. In addition to these results, adjustments are made to previously published scales for hydrazine-water and ethylenediamine water.' The corrected values range from 12.76 for 9.2 mole percent ethylenediamine i n water to 15.48 for 31.0 mole percent and 13.06 for 23.2 mole percent hydrazine in water to 15.08 for 51.1 mole percent These results are obtained using the Hammett ac i d i t y function concept from the spectroscopic de-termination of the ionization e q u i l i b r i a of 24 sub-s t i t u t e d anilines and diphenylamines. pKa values are reported for these compounds ranging from 2.63 for symmetrical hexanitrodiphenylamine to 18.37 for paranitroaniline. A l l previous H- determinations have been based on paranitrobenzyl cyanide. This indicator i s shown to be unsuitable for this purpose. Results which have been reported by other investigators are adjusted by eliminating the use of paranitrobenzyl cyanide and assigning another indicator as a start-ing point. This procedure results i n a good cor-r e l a t i o n of a l l reported H- data so that the larg-est discrepancy between results reported in this work and those reported previously i s found to be 0.26 pKa units. A limited amount of data i s obtained which permits correlation with sigma-zero substituent constants. For diphenylamines carrying n i t r o groups i n one ring, the a c i d i t y change resulting from varying a substituent i n the second ring follows closely .the.result expected on the basis of sigma-zero values. A good correlation i n obtained between the a c i d i t i e s reported here and the a c i d i t i e s of the conjugate acids of the same indicators which have been determined through the Hammett technique i n s u l f u r i c acid systems. A summary i s presented of much of the available information on the relationship between the . f i r s t and second dis s o c i a t i o n constants of dibasic acids. An explanation of the enhanced b a s i c i t y of the solutions studied i s presented which states that the competition of added solvent for available water molecules reduces the amount of water a v a i l -able for hydration of the hydroxy1 ion and thus greatly increases i t s thermodynamic a c t i v i t y . GRADUATE STUDIES F i e l d of Study? Physical Organic Chemistry S t a t i s t i c a l mechanics . . . . . R.F. Snider Molecular structure C. Reid R. Hochstrasser Recent synthetic methods . . . R.A. Bonnett D.E. McGreer Surface chemistry : J . Halpern Chemical k i n e t i c s . . . . . . . D.G.L. James Physical organic chemistry . . . R. Stewart R.B. Moodie Related Studies: Functions of a complex variable . W.H. Simons Theory and applications of d i f f e r e n t i a l equations . . . CA. Swanson Atomic physics . . . . . . . . . . M. Bloom ( i i ) ABSTRACT Our present knowledge of the a c i d i t y constants of acids which are too weak to "be measured with respect to the pH scale i s l i m i t e d . In t h i s work discrepancies ex i s t i n g among the results published by previous i n v e s t i -gators are reconciled by a reinterpretation of thei r data. No accepted b a s i c i t y values are available for concentrated aqueous a l k a l i solutions (greater than 0.1 Molar) f since measurements of pH are unreliable i n such solutions. The extreme i n s o l u b i l i t y of compounds which might be used as indicators has prevented evaluation of the b a s i c i t y of these solutions by spectrophotometric measurement of indicator e q u i l i b r i a . ' ' The present work uses the Hammett a c i d i t y function concept to develop the H- function for the following systems: For water containing benzyltrimethylammonium hydroxide H- varies from 11.98 for 0.01 Molar to 16.20 for 2.38 Molar; For pyridine-water containing 0.011 Molar tetramethyl-ammonium hydroxide H- varies from 12.27 for water which contains 1.0 mole percent pyridine to 15-43 for water containing 64.7 mole percent pyridine; For a solution of 30 mole 'percent pyridine and 70 mole percent water H-varies from 14.06 when the concentration of benzyltrimethylammonium hydroxide i s 0.03 Molar to 17-65 when the concentration of the base i s 2.19; For a solution 5,0 mole .percent pyridine and 50 mole percent water H- varies from 15»67 when the base concentration i s 0.01 Molar to 18.91 when the base concentration i s 2.12 Molar; For sulfolane-water containing 0.011 Molar tetramethylammonium hydroxide H- varies from 12=39 for 1.79 mole percent sulfolane to 19.18 for 93°4 mole percent sulfolane; For dimethylsulfoxide-water containing 0.011 Molar tetramethylammonium hydroxide H- varies from 12.17 for 5 mole percent dimethylsulfoxide to 18.61 for 70 mole percent dimethylsulfoxide: For\aqueous solutions of lith i u m hydroxide H-( i i i ) varies from 13.4-3 for 1 normal l i t h i u m hydroxide to 14.31 for 5 normal. In addition to these r e s u l t s , adjustments are made to previously published scales for hydrazine-water and ethylenediamine water. The corrected values range from 12.76 for 9.2. mole percent ethylenediamine i n • water to 15.48 for J l . O mole percent and I3.O6 for 23-2 mole percent hydrazine i n water to 15.08 for 51-1 mole percent. These results are obtained using the Hammett a c i d i t y function concept from the spectroscopic determination of the ionization e q u i l i b r i a of 24 substituted anilines and diphenylamines. pKa values are reported for these compounds ranging from 2.63 for symmetrical hexanitrodiphenylamine to 18.37 for paranitroaniline„ A l l compounds which are accepted as indicators i n t h i s work ionize instantaneously. These compounds for which a slow change i n spectrum i s observed are rejected as indicators on the basis that some other process, such as nucleophilic addition, could be occurring. The ionization reaction for a l l compounds accepted as indicators i s instantaneously reversible by suitable adjustment of the acid i t y of the solvent system. ' A l l previous H- determinations have been based on paranitrobenzyl cyanide. This indicator i s shown to be unsuitable for t h i s purpose. Results which have been reported by other investigators are adjusted by eliminating the use of paranitrobenzyl cyanide and assigning another indicator as a st a r t i n g point. This procedure results i n a good correlation of a l l reported H- data so that the largest discrepancy between results reported i n t h i s work and those reported previously i s found to be 6.26 pfCa u n i t s . ( i v ) A l i m i t e d amount of d a t a i s obta ined which permits c o r r e l a t i o n w i t h s i g m a - z e r o ' s u b s t i t u e n t c o n s t a n t s . F o r diphenylamines c a r r y i n g n i t r o groups i n one r i n g , the a c i d i t y change r e s u l t i n g from v a r y i n g a s u b s t i t u e n t i n the second r i n g f o l l o w s c l o s e l y the r e s u l t expected on the b a s i s of s igma-zero v a l u e s . A good c o r r e l a t i o n i s ob ta ined between the a c i d i t i e s r e p o r t e d here and the a c i d i t i e s of the conjugate a c i d s of the same i n d i c a t o r s which have been determined through the Haramett technique i n s u l f u r i c a c i d systems. The pKa v a l u e of a n i l i n e i s not measurable , but a p r e d i c t i o n of ) 21.2 i s made on the b a s i s of the a d d i t i v i t y r e l a t i o n s h i p of the Hammett I s u b s t i t u e n t constants i n the a n i l i n e s a c t u a l l y measured. J A summary i s presented of much of the a v a i l a b l e i n f o r m a t i o n on the r e l a t i o n s h i p between the f i r s t and second d i s s o c i a t i o n constants of d i b a s i c a c i d s . An e x p l a n a t i o n of the enhanced b a s i c i t y of the s o l u t i o n s s t u d i e d i s presented which s t a t e s t h a t the c o m p e t i t i o n of added s o l v e n t f o r a v a i l a b l e water molecules reduces the amount of water a v a i l a b l e f o r h y d r a t i o n of the h y d r o x y l i o n and thus g r e a t l y i n c r e a s e s i t s thermodynamic a c t i v i t y . (v) Acknowledgment The writer wishes to express his thanks to Dr. Ross Stewart for his patience, advice and i n s p i r a t i o n i n the di r e c t i o n of t h i s research project. ( v i ) T a b l e o f C o n t e n t s o p a g e I I n t P O d . U C t X On o . 0 0 0 0 0 0 o . o o o o o . o a . o o 1 A D e f i n i t i o n o f t h e t e r m A c i d . . . . . . . . . . . 1 B M e a s u r e m e n t o f A c i d - B a s e - S t r e n g t h s . » . . . . . . 2 C Summary o f P r e v i o u s W o r k b y E q u i l i b r i u m M e t h o d s . . 7 D U s e o f K i n e t i c ' M e t h o d s . . . . . . . . . . . . . . . 13 I I O b j e c t s o f t h e P r e s e n t R e s e a r c h . . . . . . . . . . . 17 I I I M e t h o d s o f A p p r o a c h . . . . . . . . . . . . . . . . . 18 I V E x p e r i m e n t a l . . . . . . . . . . . . . . . . . o . . . 19 A , P r e p a r a t i o n o f S o l v e n t S y s t e m s . . . . . . . . . . . 19 B P r e p a r a t i o n o f I n d i c a t o r s . . . . . . . . . . . . . 22 C M e a s u r e m e n t o f S p e c t r a . . . e . . . . . . . . . . 25 D T r e a t m e n t o f D a t a . . . . . . . . . . . . . . . . 28 E P r o b a b l e E r r o r , . c o . . . . . . . . . . . . . . 31 V R e s u l t s a n d D i s c u s s i o n . . . . . . . . . . . . . . . . 3 3 A E s t a b l i s h m e n t o f ' . t h e H _ F u n c t i o n a n d A c i d i t y C o n s t a n t s . . . 3 3 B . U s e o f A c i d i t y C o n s t a n t s t o E s t a b l i s h H ~ f o r o t h e r S o l v e n t S y s t e m s . . . . . . . . ]±5 G C r i t i c a l D i s c u s s i o n o f R e s u l t s . . . . . . . . . . 50 D C o r r e l a t i o n o f R e s u l t s w i t h t h o s e o f o t h e r I n v e s t i g a t o r s . . . . 52 E C o r r e l a t i o n o f M o l e c u l a r S t r u c t u r e o f I n d i c a t o r s w i t h p K V a l u e s . . . . . . . . . 66 ( v i i - ) Table of Contents ( c o n t o ) o ' page V F I n t e r p r e t a t i o n of S o l u t i o n Basicity« » . . . » . . 87 G Study of Presumed N u c l e o p h i l i c A d d i t i o n s , » . * . 9 5 VI Suggestions f o r Future Research, 0 0 0 0 . 0 0 0 0 0 IOI4. A Experimental Data on Compounds used as Indicators.107 B C a l c u l a t i o n of the H_ F u n c t i o n f o r the Solvent Systems used, o o , lii 6 C Experimental Data on Compounds not used as I n d i c a t o r s . . . 163 ( v i i i ) Number of Figure T i t l e Page 1 S p e c i f i c Gravity of Sulfolane-Water Mixtures 23 2 S p e c i f i c Gravity of Dimethyl-Sulfoxide Water 24 Mixtures 3 H- A c i d i t y Function for Pyridine-Water Mixture 35 Containing 0.011 Molar Tetramethylammonium Hydroxide 4 Pyridine-Water Solutions Containing Tetramethyl- 36 Ammonium Hydroxide 5 H- Ac i d i t y Function for Sulfolane-Water Mixtures 37 Containing 0.011 Molar Tetramethylammonium Hydroxide 6 Sulfolane-Water Solutions Containing 0.011 Molar 38 Tetramethylammonium Hydroxide Part I 6 Sulfolane-Water Solutions Containing 0=011 Molar 39 Tetramethylammonium Hydroxide Part I I 7 H- Aci d i t y Function for' Aqueous Benzyltrimethyl- 40 Ammonium Hydroxide 8 H- A c i d i t y Function for Pyridine-Water Mixtures 47 Containing Benzyltrimethylammonium Hydroxide 9 H- A c i d i t y Function for Water-Dimethylsulfoxide 48 Mixtures Containing ,0.011 Molar Tetramethyl-Ammonium Hydroxide 10 H- A c i d i t y Function for Aqueous Lithium Hydroxide 49 11 Paranitrobenzyl Cyanide i n Varying Concentrations of 53 Benzyltrimethylammonium Hydroxide i n Water 12 Paranitrobenzyl Cyanide i n Some Basic Solvents 54 13 Recalculation of Schaal's Data i n Ethylenediamine 59 14 Recalculation of Schaal's Data for Hydrazine-Water 60 15 H- A c i d i t y Function for Ethylenediamine Water by 64 Recalculation of Schaal's Data (ix) 16 H- A c i d i t y Function for Hydrazine Water by 65 Recalculation of Schaal's Data 17 Correlation of Diphenylamine A c i d i t i e s with the 68 Hammett Equation Using ,Sigma-Minus Values 18 Correlation of Diphenylamine A c i d i t i e s with the 69 Hammett Equation Using Sigma-Zero Values 19 Correlation of A c i d i t y of Nitrogen Acids with the 70 A c i d i t y of th e i r Protonated Species 20 Relation Between pKi and plfe for Some Dibasic Acids 7^ 21 Hammett -Correlation of Ac i d i t y of Substituted Phenols 78. 22 Prediction of pKa of Aniline Using Hammett Correlations 79 23 H- A c i d i t y Function for Some Aqueous Solvent .Systems 89 2h H- A c i d i t y Function as a Function of the Spe c i f i c 90 Gravity of Sulfolane-Water-Tetramethylammonium Hydroxide Mixtures U ) Number of Ta b l e , page l o o o o o # 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3-0 X (C O l l t ) o o o o o o o o o o o o o o o o o o o o o o 11 I ( c O T l t ) o o o o o o o o e o o o o o o o o o o o o o 12 XX o o o o o o o o o o o o o o o o o o o o o o o o © 4^*3 I X ( C O T l t ) o o o o o o o o o o o o o o o o o o o o o i-jJ {• I I I o o o o o o o o o o o o o o o o o o o o o o o o 62 X I X ( C O r i t ) o o o o o o o o o o o o o o o o o o o o ' O 6 3 1 v o 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 *Z ^ V^  o o o o o o o ' 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 * ^ ^ ) v i 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 83 V I ( C O X l t ) o • o o o o 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 8l_|-V I I o o o o o o o o o o o o o o o o o o o o o o o o 8 ^ V I I (cont ) o 0 0 0 0 0 o 0 0 0 0 0 0 0 0 0 o 0 0 0 0 86 V I I I 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 2 "T /C 0 0 0 0 0 0 0 0 0 0 0 0 0 o 0 0 0 0 o 0 0 0 0 o o o l O ^ 1 I INTRODUCTION A D e f i n i t i o n of the-Term A c i d . The Bronated d e f i n i t i o n of a c i d s and bases can be expressed by the scheme I A ^ ± B -f- H* where A and B are a conjugate acid-base p a i r ( l a ) . There i s no r e s t r i c t i o n aa to the charge on A or B but there muat be a u n i t d i f f e r e n c e of charge between the membera of a conjugate acid-base p a i r . T h i a d e f i n i t i o n has been employed throughout the preaent work. Prom the viewpoint of the w r i t e r simple p r o t o n a c i d a are not a c i d a i n the Lewis sense, t h a t i s , they are not able to accept a p a i r of e l e c t r o n s . I t would seem beat t o . c o n a i d e r the bonding i n the probable hydrogen bonded i n t e r m e d i a t e aa being d i f f e r e n t i $ k i n d from the uaual c o v a l e n t bond ( l a ) . Attempta which have been made to f o r c e p r o t o n a c i d s auch aa HCI to f i t the Lewis p i c t u r e do not seem s a t i a f a c t o r y . For inatance, Luder and Z u f f a n t i (2) atate "Probably i t would be b e t t e r to r e p r e a e n t the f o r m a t i o n of the c o o r d i n a t e bond aa t a k i n g p l a c e aimultaneoualy w i t h i o n i z a t i o n " . S u r e l y t h i a statement i m p l i e s the o p p o s i t e of what the authora i n t e n d e d . One muat deduce t h a t the p r o t o n never a t any time poasesaed more than i t a o r i g i n a l share of a p a i r of e l e c t r o n a . S ince i t d i d not, i t can h a r d l y be c o n s i d e r e d an e l e c t r o n a c c e p t o r . 2 B Measurement of Acid-Base Strengths The simple scheme of e q u a t i o n I cannot be r e a l i z e d i n p r a c t i c e s i n c e observable p r b t o l y t i c r e a c t i o n s must i n v o l v e the t r a n s f e r of a proton between two acid-base p a i r s . The e q u i l i b r i u m constant of r e a c t i o n I I II A i + B 2 ^ A 2 + B i serves as a measure of the r e l a t i v e s t r e n g t h s of the two a c i d s Ax 4-and A 2• I t i s u s u a l to choose the acid-base p a i r H3O - H2O as a standard and express a l l acid-base s t r e n g t h s r e l a t i v e t o the standard so t h a t f o r r e a c t i o n I I I I I I A -f- H2O -—> B H30 + we w r i t e IV K e • — and note t h a t the c o n c e n t r a t i o n of water has been i n c l u d e d i n K Q. The negative l o g a r i t h m i s a convenient e x p r e s s i o n of a c i d s t r e n g t h s i n c e K e values vary by many powers of t e n V pK a -logic-Kg so that M VI pK a = pH - l o g — M 3 We note t h a t the pK a of an a c i d i s the pH of a s o l u t i o n c o n t a i n i n g equal c o n c e n t r a t i o n s of A and Bo Thus any method of measuring the a c t u a l c o n c e n t r a t i o n of A or B (or both) may be used to determine a c i d s t r e n g t h s . These c o n c e n t r a t i o n s ,have u s u a l l y been measured bv p o t e n t i o m e t r i c ( 3 ) conductometrie ( 3 ) or spectrophotometric me thods (I4O0 The range of a c i d s t r e n g t h s t h a t can be measured i n any one s o l v e n t i s l i m i t e d by the l e v e l l i n g e f f e c t of the s o l v e n t . T h i s means t h a t the s t r e n g t h of an a c i d whose conjugate base i s much stronger as a base than the a n i o n of t h a t s o l v e n t cannot be measured i n t h a t s o l v e n t . T h i s means that the u l t i m a t e i n b a s i c i t y a t t a i n -a ble i n any s o l v e n t is, the most concentrated a v a i l a b l e s o l u t i o n of the a n i o n . Of course, f o r an a p r o t i c s o l v e n t no l i m i t of t h i s k i n d e x i s t s . For aqueous s o l u t i o n s of h y d r o x y l i o n the l i m i t f o r p r a c t i c a l pK a measurements i s near 12.3 . T h i s r e s u l t s from at l e a s t three c o n t r i b u t i n g f a c t o r s . F i r s t , pH measurements above 12.88 are u n r e l i a b l e (note t h a t 12.88 i s the accepted value of 0.1N sodium hydroxide at 2^°). (£) Second, the very l a r g e s a l t i n g out e f f e c t on i n d i c a t o r s which occurs i n more conc e n t r a t e d a l k a l i hydroxide has prevented i n d i c a t o r measurements. T h i r d , no;accepted b a s i c i t y ' s c a l e f o r other s o l v e n t s mixed w i t h water,has been developed. I t i s important to note here t h a t no r e l i a b l e estimate of the b a s i c i t y of concentrated hydroxide s o l u t i o n s i n water i s a v a i l a b l e . For our purposes t h i s l i m i t of 12 w i l l serve as a working d e f i n i t i o n of a very weak a c i d . That i s , a very weak a c i d i s one 1* whose pK a cannot be determined by r e f e r e n c e to the c o n v e n t i o n a l pH s c a l e . Three approaches have been used to measure the stre n g t h s of a c i d s , weaker than 12. F i r s t , the d i r e c t approach of Stearns and Wheland (6) c o n s i s t s of measuring the sma l l amount of i o n i z a t i o n which i s d e t e c t a b l e i n aqueous a l k a l i or a l c o h o l i c a l k a l i s o l u t i o n s and assumes t h a t t h i s i s the b e g i n n i n g of an i d e a l i o n i z a t i o n curve. The weakness of t h i s approach i s w e l l i l l u s t r a t e d by the s i t u a t i o n f o r p a r a - n i t r o b e h z y l cyanide. T h i s w i l l be developed f u l l y i n the d i s c u s s i o n s e c t i o n . . Values obtained by Stearns and Wheland, as w e l l as measurements by other i n v e s t i g a t o r s , are c o l l e c t e d i n Table I . Second, an e q u i l i b r i u m method based on a Hammett type a c i d i t y f u n c t i o n has been used, and t h i r d , a k i n e t i c approach based on, f o r example, hydrogen-deuterium exchange r a t e s . In d e v e l o p i n g the e q u i l i b r i u m approach one may' w r i t e the thermo-dynamic d i s s o c i a t i o n constant i n terms of a c t i v i t i e s where A and A are a conjugate acid-base p a i r . a H + a A -VII K a — aA V I I I pK a - l o g — — and then separate the a c t i v i t y c o e f i c i e n t r a t i o s - aH+ fA~ [ A " J IX pK a = - l o g - l o g — f A Now f o l l o w i n g Hammett (7 ) and Paul and Long (2£) we d e f i n e a H + f A ~ X H_ = - l o g . and w r i t e fAH [A - J XI H_ = pK a + l o g [AH] An experimental check on whether H_ i s a unique f u n c t i o n of so l v e n t composition i s r e a d i l y a v a i l a b l e . Let AiH and A^~ be a second conjugate acid-base p a i r and s u b t r a c t the e x p r e s s i o n f o r pKa]_ from t h a t f o r pKa so that pK a - p K a l = - l o g - l o g _ _ -f l o g -F A H f A x - [A H] f A i H ] The l a s t two terms on the r i g h t c o n t a i n only e x p e r i m e n t a l l y measureable c o n c e n t r a t i o n s . Thus, i f measurement of these c o n c e n t r a t i o n s i n a so l v e n t s e r i e s of d i f f e r i n g composition and a p p l i c a t i o n of the equation shows a constant pK a d i f f e r e n c e , fA- f A i H l o g : — i s shown to be n e g l i g i b l e . One may then say fAH f A T -t h a t H_ i s i n d i c a t o r independent and t h a t i s the same, f o r as fAH many i n d i c a t o r s as obey the above r e l a t i o n . In p r a c t i c e one p l o t s [A-] l o g a g a i n s t s o l v e n t composition f o r two or more i n d i c a t o r s [AH] 5 6 w h o s e r e g i o n s o f i o n i z a t i o n o v e r l a p . Now i f H _ i s i n d e p e n d e n t o f t h e a c i d u s e d i n i t s m e a s u r e m e n t , a s e r i e s o f p a r a l l e l , t h o u g h n o t n e c e s s a r i l y s t r a i g h t , l i n e s s h o u l d b e o b t a i n e d . I f one c a n now m e a s u r e i n d e p e n d e n t l y t h e p K a f o r a n y o f t h e a c i d s u s e d a n H _ f u n c t i o n f o r t h e s o l v e n t s y s t e m c a n be c o n s t r u c t e d . ' A p r e f e r a b l e p r o c e d u r e i s t o d e d u c e , f r o m a k n o w l e d g e o f t h e p K a o f t h e f i r s t i n d i c a t o r a n d e q u a t i o n X I , H _ v a l u e s f o r t h e s o l u t i o n s i n w h i c h [ A " ] i t s i o n i z a t i o n was m e a s u r e d . Now i f t h e q u a n t i t y l o g f o r • [AH] t h e s e c o n d o v e r l a p p i n g i n d i c a t o r i s p l o t t e d a g a i n s t t h e s e k n o w n H_ v a l u e s a s t r a i g h t l i n e o f u n i t s l o p e s h o u l d b e o b t a i n e d . T h i s a p p r o a c h i s n o t d i f f e r e n t f u n d a m e n t a l l y b u t l e a d s t o m o r e a c c u r a t e c u r v e f i t t i n g s i n c e one i s now c o m p a r i n g s t r a i g h t l i n e s . f A " We m u s t n o t e h e r e t h a t h a s b e e n s h o w n t o b e a f u n c t i o n f A H o f t h e d i e l e c t r i c c o n s t a n t o f t h e m e d i u m . H a m m e t t (7) h a s s t a t e d t h a t a d i e l e c t r i c c o n s t a n t n e a r 80 i s n e e d e d t o k e e p t h e e f f e c t s o n t h e v a l u e o f t h i s a . c t i v i t y c o e f f i c i e n t r a t i o b e l o w e x p e r i m e n t a l e r r o r . B e l l ( l b ) h a s d i s c u s s e d t h i s q u e s t i o n . I t seems r e a s o n a b l e t o e x p e c t e r r o r s g r e a t e r t h a n 0.1 i n p K a v a l u e s w h e n t h e d i e l e c t r i c o f t h e s y s t e m i s i n t h e JiO t o £0 r a n g e d u e t o t h e e f f e c t o n t h e a c t -i v i t y c o e f f i c i e n t r a t i o . I n p r a c t i c e t h i s may r e p r e s e n t t h e l o w e r l i m i t a t w h i c h a c c e p t a b l e H _ f u n c t i o n s may b e d e v e l o p e d . 7 C S u m m a r y o f P r e v i o u s W o r k b y . E q u i l i b r i u m M e t h o d s P i o n e e r m e a s u r e m e n t s o f t h e s t r e n g t h o f v e r y w e a k a c i d s u s i n g a n e q u i l i b r i u m a p p r o a c h w e r e m a d e b y C o n a n t a n d W h e l a n d .(8) a n d M c E w e n (9)» T h e y u s e d e t h e r s o l u t i o n s o f c a r b a n i o n s p r o d u c e d by r e a c t i o n w i t h m e t a l l i c p o t a s s i u m t o d e t e r m i n e t h e r e l a t i v e s t r e n g t h o f w e a k a c i d s t h r o u g h t h e e q u i l i b r i u m HA]_ + A2 ^ A l + " H A 2 T h e y d e d u c e d t h e p o s i t i o n o f e q u i l i b r i u m b y c o l o r i m e t r i c m e t h o d s a n d s o w e r e a b l e t o d e t e r m i n e a c i d i t y c o n s t a n t s , T h e y u s e d m e t h a n o l a n d p y r r o l e a s s t a n d a r d s a s s i g n i n g b o t h o f t h e s e a v a l u e o f l 6 . M a n y o f t h e i r v a l u e s a r e c o l l e c t e d i n T a b l e I. I t s h o u l d b e n o t e d h e r e t h a t a p p a r e n t a c i d s t r e n g t h s a n d e v e n t h e o r d e r o f a c i d i t y o f a c i d s c a n b e d i f f e r e n t i n s o l v e n t s o f l o w d i e l e c t r i c . S c h w a r t z e n b a c h a n d S u l z b e r g e r (10) t a c k l e d t h e p r o b l e m o f d e t e r m i n i n g v t h e b a s i c i t y o f c o n c e n t r a t e d a l k a l i e s . T h e y f o u n d t h a t t h e e x t r e m e i n s o l u b i l i t y o f i n d i c a t o r s p r e v e n t e d a n o r m a l s p e c t r o -p h o t o m e t r i c a p p r o a c h . T h e y t h e n a d d e d solvents, w h i c h c o n t a i n e d i n d i c a t o r s , t o t h e v a r i o u s a q u e o u s h y d r o x i d e s o l u t i o n s a n d d e t e r m i n e d t h e f r a c t i o n i o n i z e d i n t h e solvent l a y e r . A n a t t e m p t t o e v a l u a t e t h i s p r o c e d u r e w i l l b e m a d e l a t e r . I n 1952 D e n o (11) m a d e t h e f i r s t a t t e m p t t o c o n s t r u c t t h e H_ f u n c t i o n i n a m i x e d s o l v e n t s y s t e m . H e u s e d w a t e r c o n t a i n i n g v a r i o u s c o n c e n t r a t i o n s o f h y d r a z i n e u p t o 65$ h y d r a z i n e i n w a t e r a n d d e t e r m i n e d t h e H _ s c a l e f o r t h i s s y s t e m w h i c h r e a c h e d 16.0 f o r 65$ h y d r a z i n e . 8 Deno's pK a values are a l s o found i n Table I. A p r i o r i , hydrazine seems to be the b e s t choice of s o l v e n t f o r t h i s type of work from the standpoint of i t s p h y s i c a l p r o p e r t i e s , low a c i d i t y , h i g h d i e l e c t r i c , s u i t a b l e o p t i c a l c l a r i t y , f r e e z i n g p o i n t , b o i l i n g p o i n t and v i s c o s i t y . I t i s , however, d i f f i c u l t to f i n d i n d i c a t o r s f o r t h i s system. Hydrazine r e a c t s r a p i d l y w i t h many n i t r o compounds which are u s e f u l i n d i c a t o r s i n other systems. For some' anions very l a r g e s h i f t s i n the wavelength of l i g h t a b s o r p t i o n are observed. For example, S h a t e n s t e i n (12) has observed a wavelength s h i f t of 120mu f o r the meta-nitro-phenol anion between 0 . 0 0 5 N sodium hydroxide and anhydrous hydrazine w i t h l e s s e r but s t i l l troublesome s h i f t s f o r other a n i o n s . In g e n e r a l , S h a t e n s t e i n found the comparable s h i f t s i n l i q u i d ammonia to be much l e s s and concluded that the s h i f t s i n h y d r a z i n e were probably due to the f o r m a t i o n of molecular compounds. The present work shows s p e c i f i c s t a b i l i z a t i o n of c e r t a i n anions i s p o s s i b l e . In a l l , i t w i l l be d i f f i c u l t to improve Deno's o r i g i n a l choice of i n d i c a t o r s f o r the hydrazine system. Schaal and co-workers entered t h i s f i e l d i n 1955 u s i n g s o l u t i o n s o f - e t h y l e n e diamine i n water as the b a s i c system (13) and s i n c e then have p u b l i s h e d many papers (lli-21) c o v e r i n g the systems, ethanolamine i n water, hydrazine i n water and t e r t i a r y amyl a l c o h o l c o n t a i n i n g i t s sodium s a l t . They pr o v i d e d pK a values f o r many weak a c i d s . We have l i s t e d many of t h e i r values i n Table I. Schaal and h i s coworkers obtained l i m i t i n g values of l5°35 for,anhydrous e t h a n o l -amine, 18.2 f o r ethylenediamine and 19.1+ f o r the t e r t i a r y amyl a l c o h o l s o l u t i o n s . 9 B u r w e l l and Langford (22) (23) r e c e n t l y i n v e s t i g a t e d s u l f o l a n e water mixtures c o n t a i n i n g phenyltrimethylammonium hydroxide. They obtained an H_ value near 20 f o r a s o l u t i o n 95 mole percent s u l f o l a n e , 5 mole percent water and 0 . 0 1 3 molar i n p h e n y l t r i m e t h y l -ammonium hydroxide. S u l f o l a n e appears to be a good s o l v e n t i n which to study a wide range of a c i d i t i e s . B u r w e l l p o i n t s out that a 0.01M s o l u t i o n of s u l p h u r i c a c i d i n s u l f o l a n e i s a much stronger a c i d than the same c o n c e n t r a t i o n of s u l p h u r i c a c i d i n water. S i m i l a r i l y , s u l f o l a n e c o n t a i n i n g 5$ water i s a m i l l i o n times more b a s i c than pure water when both c o n t a i n 0.01M h y d r o x y l i o n . B u r w e l l suggests that most of the d i f f e r e n c e i s due to the i n c r e a s e d a c t i v i t y c o e f f i c i e n t of the h y d r o x y l i o n . His r e s u l t s show that a moderate r a t e of i n c r e a s e i n b a s i c i t y i s found as the s u l f o l a n e i n water c o n c e n t r a t i o n i s g r a d u a l l y i n c r e a s e d f o l l o w e d by a much l a r g e r r a t e of i n c r e a s e b e g i n n i n g at the composition where i | moles of water are present f o r each mole of h y d r o x y l i o n . T h i s can be r a t i o n a l i z e d by s t a t i n g t h a t each h y d r o x y l i o n i s i n t i m a t e l y s o l v a t e d by four water molecules i n a s i m i l a r manner to that accepted f o r protons i n aqueous s o l u t i o n s . [see B e l l (lb) and E i g e n and De Maeyer (21^)7] A c r i t i c a l comparison of the values l i s t e d i n Table I shows th a t our knowledge of the pK a values of weak a c i d s i s indeed i n a s t a t e o f c o n f u s i o n . Paul and Long ( 2 5 ) have s t a t e d , concerning a comparison o f values r e p o r t e d by Schaal and Deno "Th i s l a r g e d i s c r e p a n c y c a s t s c o n s i d e r a b l e doubt on the assumption that these H_ s c a l e s are independent of the i n d i c a t o r used and'makes i t P ro ro c t ro P, o oo 3 O -P- 2 ro w H* [ 13 «. o » f-j. \« P 8 p. | « i ! ef er H« 4=. •"d H-f* »d 4> rr - hi 3 ct- cf P 2 c t -i> ef er p - H- H 3 P* J 52 »» P H* o - i ef er © c t fj. O-i CD P . 0 1 P c t O Q H' c t P ^ O CJ\ CD 3 hS 3 H« 3 i 3 P. tsi hi P g Pi <-i N H» P i P «<J O 0 3 « i 3 CD c t « i W o o 3 O 0 o O 3 3 c t o CD H 1 H- H H* H 3 H 1 H- I o* P • c t P e t ' H" P W 0 H ro 0 0 C t H H* 13 3 e+ H° « w O H» O H- 3 -> N O S 1 3 1 c t 3 O 0 ! ! 0 CD CD 0 i H O ! « CO «! w CD » A l - 1 r—1 H H H t—1 V 4 ^ O l O J OO ro OO I—1 « « O o o g O o 9 03 uo H 4 ^ o ro H O O l O l —J O O l O l ' -4> H H M H H H H O l OO OO O l • 1 0 0 o a o o a CT\ 4 ^ o H Ul O l - j O o n o n CTi H h-> h-' 1-J -£> - o i OO - J 0 I 1 o o o 0 4 a a v> OH UO o H o O O l 00 1 1 1 1 a a M t—1 M H (—1 H O l -r> o o o o » 5 a 1 o 0 9 • a H 4 ^ 4=> H O H 03 CT\ OO - O H H H H ro 0~1 OO ro • • i I 8 a O 9 I a OO 4*- ro H OO . o o 00 1 ! 3 t a i 1 g » 8 U5 1 I B 1 i 1 i . a ! OO H ro M M M o 03 -] OO • • e a 1 8 1 o 8 0 CT\ —j -> CTl H i ! i a I 0 i a OO Ethylene diamine water amine water Hydrazine T e r t i a r y p amyl & a l c o h o l 0 Hydrazine water E t h e r formamide cr> E t h a n o l ro 01 O ct i\3 ct- ro p, ro VjJ ro 0 ^ ch -£> t t P i -£» ix) Cfl ^ *<! O O "> H« D 8 0 ] H« I 4 H» i - 1 * CD ^ *"> 4 H O I H4!> 3 3 3 p r t O H« 0) <Xi -P> H) co H o £ : C o pr K - H * (->• H « 4 ? w * c t p* ~ 2 £ O H CD <n, CD p, CD c l - c t c t c l - O H P** p* CD i 2 g • d H P H ' P F° P 4 4 4 hi P O C D ^ 1 ^ 3& H rf 0 CD 0 p 0 p «! c o o o P 4 i d s H ^ H " o P H° F - H a P p p F - O ^ B S H p C D . r+ c t • c t g p 3 3 H B H c t S» P F* P 4 4 3 H« F» F° F« ro 3 4 H Ct) c t P i O O F« H H H 2 3 CD F» , O rt' 4 • W« ! D 3 H " H» • r*> CD C t 2 3 p* O CD 0 P P P P !D | P C D C D C D P c t Ct P CD P 4 CD CD V ^ v v V V Q ? M HEthylene 1 i H • H H H H I ' V J I O >» diamine vo H vo vo vo vo ' V, £water 4*» Vjl co V H E t h a n o l -i i i « » o i i O D i i B o n * amine VJI -j en water VJl i—' o i a i II Q Q o Q ii o o ^ Hydrazine H 00 & co* Co T e r t i a r y & a i i i • • o • o i i s H amvl CD C O V O 45- • VO -, n H o V J I o alcohol H o ^ Hydrazine 2 n o o n J 0 • H . P vo H water c t o • — H H' H ro oo _ _ v_n ro S u l f o l a n e • co ^ water ro —J H ro vjq oo E t h e r H -O VJJ Dimethyl H f ormamide H cnEthanol t i n i i a n a s i a a ^ C a l c u l a t e d ro I T O H» 4 P H" 3 P" H- p" H P*~ o ro ^ H *d H* 0 p" »d CD 0 p* H- C D P ^ j c t ^ H J ^ O O ) B P P C D P P C I > H P " r J C I > r J l d P 0 <<! P CD <<! F) <<< g £ 53- O H t) •X ! > p F* P * P  "H« • d P* 0 »-» 0 0 0 H 0 P 0 P O P cl-" D P «! c t «1 H O P P 0 H P" b1 0  « i f-b « i .3 p 03 P* H H H 0' 0 o • 0 £ M c t CD P 3 O p* c t o F« *<? P P 0 H) H H 0 0 ne oxide sulf O. ene HJ • cn CD c+ 4 CD L_J c<< u-i I_J i • " <T> • en n . 'm CD 0 B c t 0 P* c t P P* P P 0 P . . . . © P - t-b i-- E t h y l e n e O U J X i 8 i <• diamine pi £ water 0 0 0 D j a a a 3 a a a J II 0 ii a 8 0 a a ! a H o i s i CO P* o g 11 0 ii a o i a 8 P a J> P CQ 09 *d 0 0 o a 11 0 a a 0 0 a 8 0 a ro ro ro H H ui ro O V D oo J a " ! a « 0 0 0 • e CO H — j ro o H U l U J U J U J ro ro ro ro a I ro ro H U I U J —0 H VJ1 H V D H Ethanol-y 1 amine H w a t e r CT\ » Hydrazine H CO 1-3 T e r t i a r y o-H a m y 1 0 So a l c o h o l o ^ Hydrazine o H water (Ti-ro S u l f o l a n e "ro water U J CO ^ E t h e r Dimethyl uj f ormamide cr, E t h a n o l UJ i i a a a i a a o a i ui C a l c u l a t e d — j ro ST 13 I m p e r a t i v e t h a t t h i s be t e s t e d by s t u d i e s w i t h o t h e r i n d i c a t o r s . " D Use of K i n e t i c Methods L e t us now c o n s i d e r b r i e f l y the k i n e t i c method and ask whether the r e l a t i v e r a t e s of r e m o v a l of a p r o t o n from two a c i d s can be c o n s i d e r e d a measure of t h e i r r e l a t i v e a c i d i t y . T h i s q u e s t i o n has been d i s c u s s e d by B e l l ( l ) , L e f f l e r ( 2 7 ) ( 2 8 ) and . S h a t e n s t e i n ( 2 9 ) . F o l l o w i n g B e l l we. can p i c t u r e a p r o t o n t r a n s f e r between two atoms A and B. The p r o t o n has no a t t e n d a n t s h e a t h of e l e c t r o n s so t h a t the o n l y i m p o r t a n t r e p u l s i o n i n the system i s t h a t between A and B. We can t h e n p i c t u r e a s i m p l e two d i m e n s i o n a l r e a c t i o n c o o r d i n a t e diagram. / pisr A fc o . , We may t h i n k of E ( a c t i v a t i o n energy) as determining the r a t e of p r o t o n removal k r = Ae and £° as determining the e q u i l i b r i u m p o s i t i o n K e q = Be £ T I t can be seen that c o n d i t i o n s may e x i s t where k r and K e q w i l l be l i n e a r l y r e l a t e d . The dotted l i n e r e p r e s e n t s the p o s s i b l e e f f e c t of a s t r u c t u r a l change i n e i t h e r A or B. In g e n e r a l , i f the shape of t h i s p o t e n t i a l energy curve i s not much changed (by the s t r u c t u r a l change) from t h a t r e p r e s e n t e d by A + BH then l i n e a r r e l a t i o n s h i p s of.the type of the Bronsted c a t a l y s i s law or the Hammett |0£3' f u n c t i o n w i l l h o l d . These statements imply that entropy changes d u r i n g the i o n i z a t i o n process are e i t h e r n e g l i g i b l e or are l i n e a r l y r e l a t e d to the enthalpy changes. T h i s idea has been phrased by L e f f l e r ( r e f . 2 8 page 188) i n the f o l l o w i n g manner. The l i n e a r f r e e energy r e l a t i o n s h i p can p l a u s i b l y be expected whenever the t r a n s i t i o n s t a t e resembles both the a c i d and the i o n . T h i s i m p l i e s t h a t , f o r those a c i d i o n i z a t i o n processes where no e x t e n s i v e e l e c t r o n d e l o c a l i z a t i o n i s involved,' we'may expect a r a t e - e q u i l i b r i u m c o r r e l a t i o n . L e f f l e r ( 2 7 ) has summarized the experimental evidence concerning the r e l a t i o n between enthalpy and entropy changes. No r e l a t i o n of t h i s type i s p r e d i c t e d by thermodynamic theory and at 1 5 p r e s e n t must be c o n s i d e r e d e m p i r i c a l . E x p e r i m e n t a l l y where b o t h pK a measurement and r a t e of i o n i z a t i o n measurement i s p o s s i b l e a l i n e a r c o r r e l a t i o n e x i s t s f o r compounds of c l o s e l y s i m i l a r s t r u c t u r e . The main p o i n t t o note here i s t h a t changes i n s t r u c t u r e w h i c h a f f e c t the shape of the energy c u r v e s may d e s t r o y the l i n e a r r e l a t i o n s h i p . T h i s comparison between r a t e s and e q u i l i b r i u m c o n s t a n t s i s u s u a l l y the o n l y one p o s s i b l e i n p r a c t i c e . A v e r y l i m i t e d amount of d a t a i s a v a i l a b l e f o r a c i d i o n i z a t i o n a c t i v a t i o n e n e r g i e s . Examples of the use of k i n e t i c methods t o compare a c i d i t i e s are numerous i n the l i t e r a t u r e ( 3 0 ) = These have i n c l u d e d measuring the r a t e of p r o d u c t i o n o f methane when the weak a c i d i n q u e s t i o n was a l l o w e d t o r e a c t w i t h m e t h y l magnesium i o d i d e ( Z e r e w i t i n o f f method), the r a t e of p r o d u c t i o n of hydrogen when l i t h i u m aluminum h y d r i d e r e a c t e d , w i t h the a c i d a*nd the r a t e o f p r o d u c t i o n o f n i t r o g e n when diazomethane r e a c t e d i n a s i m i l a r manner. A r e c e n t l y used t e c h n i q u e has been d e u t e r i u m i s o t o p e exchange i n v a r i o u s systems. The r a t e of f o r m a t i o n of C-D bonds can o f t e n be c o n v e n i e n t l y f o l l o w e d i n the i n f r a r e d . For example, Dessy ( 3 1 ) has p u b l i s h e d r e l a t i v e a c i d i t i e s f o r a s e r i e s of weak a c i d s u s i n g d imethylformamide as a s o l v e n t , a t r i e t h y l a m i n e c a t a l y s t , and d e u t e r i u m o x i d e as a d e u t e r i u m s o u r c e . Many of Dessy's r e s u l t s are I n c l u d e d i n T a b l e I . These have been computed from h i s r e l a t i v e v a l u e s by a s s i g n i n g a v a l u e of 1 7 t o c y c l o p e n t a d i e n e . T h i s v a l u e has not been measured but was t a k e n from the c a l c u l a t i o n s 16 of S t r e i t w e i s e r (32). Dessy r e p o r t s dimethyl s u l f o x i d e to be 7 unit's weaker than c y c l o p e n t a d i e n e . In the l i g h t of the previous c o n s i d e r a t i o n s one must view t h i s comparison of two such d i f f e r e n t molecules w i t h some r e s e r v e . In c o n s i d e r i n g r e s u l t s from any k i n e t i c method we are not e n t i t l e d to expect good agreement w i t h e q u i l i b r i u m methods or w i t h a second k i n e t i c method s i n c e changes i n e l e c t r o n d e l o c a l i z a t i o n i n the anion or changes i n mechanism can s e r i o u s l y a f f e c t the r e s u l t s . Hart and Crocker's work (33) ma7 be quoted as an example of the l a r g e amount of m e t a l l a t i o n work found i n the more r e c e n t • l i t e r a t u r e . They used c c-deuteroethylbenzene (as a deuterium source) and measured the r a t e of deuterium t r a n s f e r to other r e l a t e d hydrocarbons i n the presence of potassium. They concluded that cumene was 13 times more a c i d i c than 2,2-dimethyl-3-phenylbutane•> T h i s r e p r e s e n t s a departure from the c o n v e n t i o n a l h e t e r o l y t i c acid-base r e a c t i o n s i n c e the bond b r e a k i n g mechanism here i s c l e a r l y h o m o l y t i c . I t i s t h e r e f o r e d i f f i c u l t to s t a t e that one has measured the r e l a t i v e base s t r e n g t h s . , -• . . . S h a t e n s t e i n (30) concludes that there i s a d i r e c t c o n n e c t i o n between the p o i n t of e q u i l i b r i u m i n p r o t o l y t i c ' r e a c t i o n s and i t s r a t e of attainment and t h a t the r a t e of hydrogen exchange may serve as one method of determining the strengths of very weak a c i d s , p r o v i d e d a t t e n t i o n i s p a i d to the f a c t o r s d i s c u s s e d above. 17 I I O b j e c t s of the P r e s e n t R e s e a r c h An e x a m i n a t i o n of T a b l e I shows t h a t e x i s t i n g measurements of the a c i d i t y c o n s t a n t s of v e r y weak a c i d s have l e d t o many d i f f e r i n g r e s u l t s . The agreement f o r l i - n i t r o b e n z y l c y a n i d e w i l l be shown t o be o n l y a p p a r e n t . The prime purpose of t h i s work, t h e r e f o r e , was t o d i s c o v e r whether c o n s i s t e n t v a l u e s f o r these weak a c i d s c o u l d be found and • i n so d o i n g determine the H_ f u n c t i o n f o r as many systems as p o s s i b l e . I t was d e c i d e d t o use i n d i c a t o r s as c l o s e l y a l l i e d i n m o l e c u l a r s t r u c t u r e as p o s s i b l e . The s u b s t i t u t e d a n i l i n e s and d i p h e n y l a m i n e s p r o v i d e d a s e r i e s of compounds of v a r y i n g a c i d i t y w e l l s u i t e d t o our p u r p o s e . A p a r a l l e l s t u d y was t h e r e f o r e i n i t i a t e d on the r e l a t i o n between s t r u c t u r e and a c i d i t y I n t h e s e compounds. Because of the c o n f l i c t s i n v a l u e s r e p o r t e d by o t h e r i n v e s t i g a t o r i t was n e c e s s a r y t o re-examine t h e i r systems i n o r d e r t o p i n p o i n t s o u r c e s of d i s a g r e e m e n t . 18 I I I .Methods of Approach The a c i d i o n i z a t i o n of d i p h e n y l a m i n e s and a n i l i n e s i n g e n e r a l l e a d s t o l a r g e changes i n the v i s i b l e and u l t r a v i o l e t a b s o r p t i o n s p e c t r a . Thus these compounds are i d e a l l y s u i t e d f o r s p e c t r o p h o t o -m e t r i c d e t e r m i n a t i o n of t h e i r i o n i z a t i o n e q u i l i b r i a . These i o n i z a t i o n e q u i l i b r i a have t h e n been used w i t h the I-T_ concept t o determine the pK a v a l u e of the a c i d i n v o l v e d and the b a s i c i t y of the s o l u t i o n s concerned. The work of p r e v i o u s i n v e s t i g a t o r s has been checked and expanded by use of d i f f e r e n t i n d i c a t o r s . T h i s approach a l l o w e d the p i n -p o i n t i n g of s o u r c e s of disagreement between the i n v e s t i g a t o r s . E v i d e n c e of the v a l i d i t y of the H_ f u n c t i o n was sought from t h r e e s o u r c e s . 1 A c i d i t y c o n s t a n t s f o r the same i n d i c a t o r s h o u l d agree when det e r m i n e d i n d i f f e r e n t s o l v e n t systems. 2 The use o f the Hammett r e l a t i o n K l o g — — p 6~ h e l p e d to i n d i c a t e t h a t the t r a n s i t i o n from the pH r e g i o n t o the mixed s o l v e n t systems had been made i n a r e a s o n a b l e manner. 3 C e r t a i n r e g u l a r i t i e s i n a c i d i t y changes w i t h s t r u c t u r a l f e a t u r e s p r o v i d e e v i d e n c e of the s u b s t a n t i a l c o r r e c t n e s s of the v a l u e s r e p o r t e d . 19 IV E x p e r i m e n t a l . A P r e p a r a t i o n of Solvent Systems (a) S u l f o l a n e (tetramethylene Sulfone) was purchased from the S h e l l Development Company and d i s t i l l e d over sodium hydroxide a c c o r d i n g to the procedure of Langford ( 2 3 ) . -The b o i l i n g p o i n t o ^ o was 112 at 1mm. T h i s s o l v e n t was o p t i c a l l y c l e a r above 2 5 0 0 A. (b) D i m e t h y l s u l f o x i d e was Baker analyzed reagent and was d i s t i l l e d over sodium hydroxide p e l l e t s b e f o r e use. (c) P y r i d i n e - F i s c h e r reagent grade p y r i d i n e was d i s t i l l e d over barium oxide to remove water - B o i l i n g p o i n t - 1 1 5 ° at 7b0mm. (d) Hydrazine - 9 5 ^ Eastman White L a b e l hydrazine was used without f u r t h e r p u r i f i c a t i o n . The percentage hydrazine was determined by i o d i n e t i t r a t i o n u s i n g a procedure g i v e n by A u d r e i t h and Ogg (3l+) o (e) Ethylenediamine. Eastman 9Q% ethylenediamine was d i s t i l l e d over sodium to remove water. T h i s s o l v e n t does not remain o p t i c a l l y c l e a r d u r i n g storage even i f p r o t e c t e d from s u n l i g h t , moisture and oxygen. (f) _ Ethanolamine . Eastman White Label was used without f u r t h e r p u r i f i c a t i o n . (g) Anhydrous methanol was prepared by d i s t i l l a t i o n over magnesium. 20 (h) Potassium a c i d p h t h a l a t e b u f f e r s were prepared c o v e r i n g the pH range from 2.2 to 6.2 a c c o r d i n g to Vogel ( 3 5 ) > and potassium dihydrogen phosphate b u f f e r s from £ . 8 to 8.0. For the range 8.J4.5 to 12.77 g l y c i n e b u f f e r s were used. These b u f f e r s were d i l u t e d so that the i o n i c s t r e n g t h was not g r e a t e r than 0.1. 0.1N sodium hydroxide, prepared from commercial standard sodium hydroxide, was used as a 12 . 8 8 pH standard. A l l pH measurements were made u s i n g a Beckrnann model G pH meter, equipped with a calomel r e f e r e n c e e l e c t r o d e and a standard g l a s s e l e c t r o d e . The Beckrnann E 2 amber g l a s s "blue" e l e c t r o d e was used f o r a l l measurements above pH 11. Benzyltrimethylammonium hydroxide (lj.0% i n water) was used as purchased from B r i t i s h Drug Houses. Tetramethylammonium hydroxide (10% i n water), t e t r a n - p r o p y l -ammonium hydroxide (10% i n water) and phenyltrimethylammonium hydroxide (20% i n methanol) were Eastman White L a b e l . Benzyl t r ime thylammonium hydroxide (Ij-0% i n p y r i d i n e )was * prepared a c c o r d i n g to the method of Sprinzak ( 3 6 ) from a methanol s o l u t i o n of b e n z y l t r i m e t h y l ammonium hydroxide which was purchased from Columbia Organic Chemicals. The s o l v e n t systems needed were prepared i n the f o l l o w i n g manners:-Aqueous b e n z y l t r ime thylammonium hydroxide (li0%) was d i l u t e d w i t h f l e s h l y d i s t i l l e d water to o b t a i n a s e r i e s of ten s o l u t i o n s c o n t a i n i n g v a r i o u s c o n c e n t r a t i o n s of the base. These were then t i t r a t e d w i t h standard s u l p h u r i c a c i d to a p h e n o l p h t h a l e i n endpoint. 2 1 A s e r i e s of s i m i l a r s o l u t i o n s were th e n p r e p a r e d by m i x i n g these w i t h v a r y i n g amounts of p y r i d i n e t o o b t a i n a s e t whose p y r i d i n e t o water mole r a t i o was $0:^0 and a second s e t i n w h i c h the p y r i d i n e t o water mole r a t i o was 30:70« I n o r d e r t o keep the base c o n c e n t r a t i o n as h i g h as p o s s i b l e a l\.0% b e n z y l t r i m e t h y l -ammonium h y d r o x i d e s o l u t i o n i n p y r i d i n e was p r e p a r e d . The p y r i d i n e t o water r a t i o was c a l c u l a t e d from a knowledge of the amounts of p y r i d i n e and water added and the f i n a l base c o n c e n t r a t i o n was determined by t i t r a t i o n . P y r i d i n e - w a t e r m i x t u r e s were p r e p a r e d by w e i g h i n g c a l c u l a t e d amounts of the components as were the s u l f o l a n e - w a t e r m i x t u r e s and the d i m e t h y l s u l f o x i d e -water m i x t u r e s . S o l u t i o n s of l i t h i u m and sodium h y d r o x i d e s were p r e p a r e d u s i n g weighed amounts of the h y d r o x i d e s and f i l t e r i n g t o remove carb o n a t e a f t e r s o l u t i o n i n the c a l c u l a t e d amount of water-. Weighed a l i q u o t s of these s o l u t i o n s were t h e n t i t r a t e d t o determine the c o n c e n t r a t i o n of h y d r o x i d e . The p o t a s s i u m h y d r o x i d e s o l u t i o n s were a l r e a d y c l e a r so no carbonate r e m o v a l s t e p c o u l d be e a s i l y c a r r i e d o u t . The d e n s i t i e s of t h e s u l f o l a n e - w a t e r and the d i m e t h y l s u l f o x i d e m i x t u r e s were determined and are shown i n F i g u r e s 1 and 2 . 22 B P r e p a r a t i o n of I n d i c a t o r s . R e f e r e n c e s t o syn t h e s e s of i n d i c a t o r s a re l i s t e d i n Appendix A. A l l o t h e r compounds were a v a i l a b l e c o m m e r c i a l l y . N - t e r t i a r y - b u t y l - p i c r a m i d e has not-been p r e p a r e d p r e v i o u s l y and was o b t a i n e d by r e f l u x i n g f o r one hour i n e t h a n o l 0.02 moles of t e r t i a r y b u t y l a m i n e w i t h 0.01 moles of p i c r y l c h l o r i d e . The p r o d u c t , a f t e r s e v e r a l r e c r y s t a l l i z a t i o n s from e t h a n o l , was orange n e e d l e s of m e l t i n g p o i n t 9 U - 9 5 ° . A n a l y s i s . C H N Found lj.2.26 l i . l 6 19-71 C a l c u l a t e d 1+2.56 1+..22 19-31 The o t h e r N - a l k y l compounds were p r e p a r e d by the same g e n e r a l method (79) ( 8 0 ) . . 2 5 C Measurement of S p e c t r a . A sample of each i n d i c a t o r was weighed and d i s s o l v e d i n -3 acetone to make a 10 molar stock s o l u t i o n . From t h i s a l i q u o t s were p i p e t t e d d i r e c t l y i n t o a one cm. quartz c e l l , equipped w i t h a ground stopper. The acetone was then evaporated at an a s p i r a t o r and 2ml. amounts of the s o l v e n t under examination were added by means of a volumetric s y r i n g e . T h i s technique was e a s i l y adaptable to an oxygen f r e e method. The c e l l was sea l e d w i t h a s i l i c o n e rubber stopper of the type used i n vapour phase chromatography. The c e l l was then f l u s h e d w i t h dry n i t r o g e n by means of an i n l e t and o u t l e t p a i r of syringe n e e d l e s . The so l v e n t under c o n s i d e r a t i o n could then be added through the s i l i c o n e stopper. T h i s stopper proved s a t i s f a c t o r i l y l e a k p r o o f even a f t e r s e v e r a l puncturings by small gauge need l e s . Provided the s o l u t i o n s used are degassed p r e v i o u s l y t h i s technique prevents oxygen from e n t e r i n g the system. I t was found that the bases employed r e a c t e d r e a s o n a b l y r a p i d l y w i t h s u l f o l a n e to produce a species which showed a p p r e c i a b l e l i g h t a b s o r p t i o n below I+OOmu. T h i s r e a c t i o n was accompanied by a drop i n the b a s i c i t y of the s o l u t i o n s . Because of t h i s , stock s o l u t i o n s of s u l f o l a n e c o n t a i n i n g the base could not be kept and the f o l l o w i n g procedure was adopted. The i n d i c a t o r sample was f i r s t d i s s o l v e d i n a s o l u t i o n of known sul f o l a n e - w a t e r c o n c e n t r a t i o n and the base added i n water s o l u t i o n immediately before t a k i n g the s p e c t r a l measurements. For c o n s i s t e n c y , t h i s same procedure was adopted f o r p y r i d i n e - w a t e r systems and dimethyl s u l f o x i d e - w a t e r systems. 2 6 A l s o , i t was not considered a d v i s a b l e to keep the h i g h l y b a s i c s o l u t i o n s f o r any l e n g t h of time. C a l c u l a t i o n , based on known d e n s i t i e s of the mixtures, then p r o v i d e d the f i n a l mole percent values as r e p o r t e d . For these systems i t was p o s s i b l e to r e c o r d the molecule spectrum and the anion spectrum i n s o l u t i o n s of n e a r l y I d e n t i c a l composition. For other systems ( b u f f e r s , benzyltrimethylammonium hydroxide i n water or hydrazine) the u n i o n i z e d spectrum was r e c o r d e d i n at l e a s t two s o l u t i o n s below the p o i n t at which a s p e c t r a l change was noted and a g a i n i n at l e a s t two s o l u t i o n s above the p o i n t where i o n i z a t i o n appeared complete. These s o l u t i o n s were proven to be of g r e a t e r b a s i c i t y by t h e i r e f f e c t on a weaker a c i d . In t h i s way i t was p o s s i b l e to be c e r t a i n that a l l compounds were f u l l y i o n i z e d and to o b t a i n e x t i n c t i o n c o e f f i c i e n t s f o r both the molecular and a n i o n i c form i n s o l u t i o n s of r e a s o n a b l y s i m i l a r composition. A l l s o l v e n t s were t e s t e d f o r o p t i c a l c l a r i t y i n the r e g i o n s used and a s o l v e n t blank of the same c o n c e n t r a t i o n as that c o n t a i n i n g the i n d i c a t o r was used. The spectrum of the i n d i c a t o r s employed v a r i e d l i t t l e over the s o l v e n t composition range necessary to f u l l y i o n i z e the molecule. T h i s was checked by making measurements at two d i f f e r e n t p o s i t i o n s on the anion spectrixm. A good check of t h i s p o i n t i s the agreement of the i o n i z a t i o n e q u i l i b r i a of one i n d i c a t o r w i t h the next. I f an i n d i c a t o r shows s e r i o u s anomalies the d i f f e r e n c e i n the q u a n t i t y [ A - ] l o g — between i t and the next i n d i c a t o r w i l l not be constant -[ A H ] 27 that i s the Hammett p o s t u l a t e w i l l f a i l . ( p a g e 5) Some s i g n i f i c a n t d i f f e r e n c e s , however, were found f o r both e x t i n c t i o n c o e f f i c i e n t s and wavelength maxima from one s o l v e n t system to another. A l l data of t h i s type are l i s t e d i n the appendix under the I n d i v i d u a l compound. V i s i b l e and u l t r a v i o l e t a b s o r p t i o n s p e c t r a of the- i n d i c a t o r s were measured with a Gary ModeJ l i i r e c o r d i n g spectrophotometer to l o c a t e the wavelengths of maximal a b s o r p t i o n of both the molecular and a n i o n i c forms. The a c t u a l o p t i c a l d e n s i t y measurements were c a r r i e d out at two or more wavelengths u s i n g a Beckrnann DU spectrophotometer whose c e l l compartment was maintained at 25° by means of thermospacers. Room temperature v a r i e d very l i t t l e from 25° d u r i n g the measurements. A l l s p e c t r a l changes were checked f o r r e v e r s i b i l i t y . 2 8 D Treatment of D a t a . The c a l c u l a t i o n o f H_ and pK a i s c a r r i e d out u s i n g e q u a t i o n X I H. = pK a + l o g i [ A H ] [*-] The e x p e r i m e n t a l problems encountered i n d e t e r m i n i n g l o g [AH] have been d i s c u s s e d by Y a t e s ( 3 7 ) ° He examines the t h e o r e t i c a l c u rve method and the l i n e a r method of Hammett as w e l l as t h a t of D a v i s and Geismann ( 3 8 ) . The l a t t e r two methods are d e s i g n e d t o m i n i m i z e e r r o r s i n t r o d u c e d by s o l v e n t e f f e c t s on s p e c t r a . I n t h i s work the good agreement of one i n d i c a t o r w i t h a n other ( p a r a l l e l s t r a i g h t l i n e s of u n i t s l o p e were o b t a i n e d ) has been t a k e n as an i n d i c a t i o n t h a t no s e r i o u s media e f f e c t s were b e i n g e n c o u n t e r e d . I n aqueous s o l u t i o n c a l c u l a t i o n s i n t h i s work were based on the t h e o r e t i c a l curve method because most of the i n d i c a t o r s used i n the pH range showed c o n s i d e r a b l e a b s o r p t i o n by the m o l e c u l e a t the w a v e l e n g t h of maximal a b s o r p t i o n f o r the i o n . T h i s method s t a t e s t h a t , [A~] /AD - A D U l o g _ =• l o g — -logf [ A H ] 1 -CC \ A^i where the symbols have the f o l l o w i n g s i g n i f i c a n c e , oC i s the f r a c t i o n i o n i z e d . A D u i s the d i f f e r e n c e between the o p t i c a l d e n s i t y a t the wave-l e n g t h of maximal a b s o r p t i o n f o r the a n i o n and the o p t i c a l d e n s i t y 29 at the wavelength of maximal a b s o r p t i o n of the molecule when measure-ments are made i n a s o l u t i o n where the amount of i o n i z a t i o n i s e f f e c t i v e l y zero. A D i i s t h i s same d i f f e r e n c e measured i n a s o l u t i o n where i o n i z a t i o n i s e f f e c t i v e l y complete. AD i s t h i s same d i f f e r e n c e measured i n some intermediate t e s t s o l u t i o n . For many of the i n d i c a t o r s In the mixed s o l v e n t systems used i n t h i s work the a b s o r p t i o n of the molecule at the anion wavelength was n e g l i g i b l e , or very s m a l l . In these cases the method d e s c r i b e d by Schaal ( 1 3 ) was used. In t h i s procedure a l l measurements are made at the anion wavelength and the f r a c t i o n i o n i z e d i s , • , D ~ Dmol cC =" —; D i o n " ^ mol where the symbols have the f o l l o w i n g s i g n i f i c a n c e , D_,^ n i s the o p t i c a l d e n s i t y of the molecular form measured at the anion wavelength. ^ i o n i s the maximum'optical d e n s i t y measureable at t h i s same wavelength when the species i s f u l l y i n the i o n i c form. D i s the o p t i c a l d e n s i t y at t h i s same wavelength measured i n some intermediate t e s t s o l u t i o n . 30 The f i r s t of these two methods may be expected to c o r r e c t somewhat f o r medium e f f e c t s on s p e c t r a p r o v i d e d the medium e f f e c t on the molecule s p e c t r a i s i n the same d i r e c t i o n as on the anion s p e c t r a . The second method was favoured i n t h i s work because of the time dependent a b s o r p t i o n In the blank and the r e s u l t i n g p o s s i b i l i t y of e r r o r s i n balancing» This e r r o r i s n e g l i g i b l e above lj_00mu and a l l anions employed absorbed above t h i s wavelength. Thus, wi t h the second method a l l measurements co u l d be made i n an und i s t u r b e d r e g i o n . Again, p r o v i d e d the Hammett p o s t u l a t e was c l o s e l y f o l l o w e d , that i s , t h a t d i f f e r e n t s o l u t i o n s gave the same pK a d i f f e r e n c e between two i n d i c a t o r s , i t was f e l t t h a t medium e f f e c t s c o u l d not be s e r i o u s . 31 E Probable E r r o r . I t i s d i f f i c u l t to estimate a p r e c i s e experimental e r r o r but where simple s p e c t r a and good p l o t s are obtained i t i s estimated to be about 0 . 0 5 u n i t s . In s e t t i n g up a s c a l e t h i s e r r o r may be cumulative. Considerable e f f o r t was expended to measure each pK a d i f f e r e n c e i n many d i f f e r e n t s o l u t i o n s and to o b t a i n c l o s e l y spaced i n d i c a t o r s so that many measurements could be made of H- f o r each t e s t s o l u t i o n used. The degree of p r e c i s i o n may be estimated by examination of the l i s t e d values i n appendix B . No obs e r v a t i o n s have been used to determine H- values where, [*•] l o o was grea t e r than 1 . 0 or l e s s than - 1 . 0 since the [AH] o b s e r v a t i o n a l experimental e r r o r begins to i n c r e a s e r a p i d l y o u t s i d e t h i s range. The b i g g e s t s i n g l e problem i n the way of h i g h accuracy was I n s u f f i c i e n t s o l u b i l i t y of the molecular form of the i n d i c a t o r . P a r t i c u l a r a t t e n t i o n was p a i d to t h i s problem i n aqueous s o l u t i o n s and i n the most d i l u t e of the mixed s o l v e n t systems. T h i s problem f o r c e d work at lower o p t i c a l d e n s i t i e s than was d e s i r e d . In each case c a r e f u l checks were made to ensure complete s o l u t i o n had occurred and to ensure that work was c a r r i e d out near the s o l u b i l i t y l i m i t so that o b s e r v a t i o n a l e r r o r was as small as p o s s i b l e . For the pH r e g i o n the bes t t e s t here i s that s e v e r a l s o l u t i o n s of d i f f e r e n t and known pH gave the same c a l c u l a t e d pK a v a l u e . No attempt was made to apply a thermodynamic c o r r e c t i o n . Such 32 c o r r e c t i o n s are g e n e r a l l y l e s s than 0.1 l o g u n i t s and are probably much l e s s than t h i s i n the present work s i n c e the i o n i c strengths of the b u f f e r s o l u t i o n s used were l i m i t e d to 0„1 . Gold (5) has presented evidence which i n d i c a t e s that the mean a c t i v i t y c o e f f i c -i e n t s of e l e c t r o l y t e s do not d i f f e r by more than 0.05 at t h i s i o n i c s t r e n g t h . Robinson (ii) has made c a r e f u l measurements on the pK a value of [(.-nitrophenol i n d i f f e r e n t b u f f e r s o l u t i o n s and has shown that below an i o n i c s t r e n g t h of 0.1 only very small e r r o r s are i n t r o d u c e d . Some e r r o r i s probably i n t r o d u c e d by s o l v e n t e f f e c t s on spectr but these are probably not l a r g e because of the good A pK a agreements among the c l o s e l y spaced i n d i c a t o r s . The s o l u b i l i t y problem became s e r i o u s f o r s o l u t i o n s of benzyltrimethylammonium hydroxide i n water but f o r t u n a t e l y s u f f i c i e n t s o l u b i l i t y to make re a s o n a b l y accurate measurements was r e t a i n e d . In l i t h i u m hydroxide even though 10cm. c e l l s were employed onl y small o p t i c a l d e n s i t i e s c o u l d be obtained and the r e s u l t s must be considered of m a r g i n a l accuracy. 33 V R e s u l t s and D i s c u s s i o n , A Establishment of the H_ F u n c t i o n and A c i d i t y Constants. The experimental data on the compounds used as i n d i c a t o r s may be found i n appendix A. T h i s appendix shows the wavelength of maximal a b s o r p t i o n and the e x t i n c t i o n c o e f f i c i e n t at that wavelength f o r each compound employed f o r both the molecular and a n i o n i c specie and f o r d i f f e r e n t s o l v e n t s . A l s o i n c l u d e d are data r e p o r t e d by other i n v e s t i g a t o r s f o r comparison. The values of l o g as c a l c u l a t e d by the procedures fAH] d e s c r i b e d i n the experimental s e c t i o n are a l s o l i s t e d . F i g u r e 3 was produced i n the f o l l o w i n g manner. The pK a value of 2,1)., 6 - t r i n i t r o a n i l i n e was determined i n aqueous b u f f e r s and sodium hydroxide to be 12.20 i n good agreement w i t h the work of Schaal (13) who r e p o r t e d 12.25, T h i s i n d i c a t o r was then used to determine the H» value f o r s e v e r a l d i f f e r e n t mixtures of p y r i d i n e i n water c o n t a i n i n g 0,011 molar benzyltrimethylammonium hydroxide. I t was then p o s s i b l e to determine i n the same s o l u t i o n s the f r a c t i o n i o n i z e d f o r 2,14., Ix' - t r i n i t r odiphenylamine . . A best f i t s t r a i g h t l i n e was then drawn through these measured p o i n t s to determine the pK a d i f f e r e n c e from 2,\\, 6 - t r i n i t r o a n i l i n e u s i n g the Hammett p o s t u l a t e . T h i s procedure c o u l d be a p p l i e d r e p e a t e d l y f o r s u c c e s s i v e i n d i c a t o r s Thus, 2,1+, 6-tr i n i t r o a n i l i n e i s the compound analogous to i i - n i t r o -a n i l i n e which was used i n b u i l d i n g the H 0 s c a l e i n a c i d s o l u t i o n s . Now pK a values were assigned to the i n d i c a t o r s . These i n d i v i d u a l pK a values were then used to c a l c u l a t e the H_ va-lue f o r each s o l u t i o n i n which the p o s i t i o n of i t s I o n i z a t i o n e q u i l i b r i u m was measureable. Th i s procedure r e s u l t e d i n s e v e r a l measured H- values f o r each s o l u t i o n which were averaged. The r e s u l t s of t h i s a veraging process are p l o t t e d i n F i g u r e 3 . The H_ values f o r the v a r i o u s c o n c e n t r a t i o n s of p y r i d i n e i n water were now c o n s i d e r e d known and F i g u r e h was produced by p l o t -t i n g the o r i g i n a l values of l o g a g a i n s t I-I_ [AH] H_ appears to be an a c c e p t a b l e f u n c t i o n f o r the system s i n c e the p l o t s a r e ' . p a r a l l e l s t r a i g h t l i n e s of u n i t s l o p e . Care was taken to employ i n d i c a t o r s which were as c l o s e l y s i m i l a r In molecular s t r u c t u r e as was p o s s i b l e . For t h i s system i t was not found p o s s i b l e to make de t e r m i n a t i o n s above ...60 mole p e r c e n t - p y r i d i n e . A f t e r t h i s , p o i n t the i n d i c a t o r p l o t s were found to be no longer p a r a l l e l , t h a t i s , the Hammett p o s t u l a t e f a i l e d . Values are l i s t e d i n the appendix f o r three i n d i c a t o r s whose e q u i l i b r i a were measured i n s o l u t i o n s c o n t a i n i n g more than 6 0 mole percent p y r i d i n e . I t can be seen that even the order of a c i d i t y , as measured, can be d i f f e r e n t i n ' d i f f e r e n t m i x t u r e s . No doubt these s o l u t i o n s do i n c r e a s e i n b a s i c i t y as the. p y r i d i n e c o n c e n t r a t i o n i s augmented. A s o l u t i o n of benzyltrimethylammonium hydroxide i n p y r i d i n e w i l l , at l e a s t p a r t i a l l y , i o n i z e f l u o r e n e ( 3 9 ) - 35--16 • -15 -14 x -13 r FIGURE 2 / H- ACIDITY FUNCTION FOR PYRIDINE-WATER MIXTURES CONTAINING 0.011 MOLAR TETRAMETHYLAMMONIUM HYDROXIDE -12 ^ 0 • M O L E 10 • PERCENT PYRIDINE IN WATER 20 30 4 0 5 0 6 0 -14 -12 •10 •8 •6 -4 h2 -0 -2 h-4 •6 -8 FIGURE 4 PYRfDINE-WATER SOLUTIONS CONTAINING 0.011 MOLAR TETRAMETHYL AMMONIUM HYDROXIDE O O -10 -12 -14 12 246-TRINITROANILINE (1220) 244/-TRINITRODIPHENYLAMINE (1233) 243-TRINITRODIPHENYLAMINE (12.65) 6-BROMO-2.4-DINITROANILINE (13&6) 2,4-DINITRODIPHENYLAMINE (13.83) 4,4-DINITRODIPHENYLAMlNE (14.09) 3-NtTROCARBAZOLE (14.16) 15 i •19 18 •17 16 ± FIGURE 5 -15 H- ACIDITY FUNCTION FOR SULFOLANE-WATER MIXTURES CONTAINING 0.011 MOLAR •14 TETRAMETHYL AMMONIUM HYDROXIDE •13 MOLE PERCENT SULFOLANE IN WATER 10 20 1 30 40 . L , 50 i 60 70 80 90 100 1 1 1 i i FIGURE 6 1 4 PART 1 SULFOLANE-WATER SOLUTIONS 1 2 CONTAINING 0.011 MOLAR TETRA METHYL-AMMONIUM HYDROXIDE •10 08 06 04 027 O 02 04 06 0.8 10 12 14 12 — i _ 'A 24,6-TRINITRQANILINE (1220) B 244-TRINITRODJPHENYLAMINE <1231) C 243-TRINITROD1PHENYLAMINE (1262) D 6-BROMO-2,4-DINITROANILINE ,(13.60) E 24-DINITRODIPHENYLAMINE (13B3) F 4,4-DINITRODIPHENYLAMINE (1400) G 3-NITROCARBAZOLE (14D6) H 2,4-DINITRO-4-AMiNODIPHENYLAMINE (14.64) 14 15 FIGURE 6" PART 31 -14 SULFOLANE-WATER SOLUTIONS CONTAINING 0O11 MOLAR TETRAMETHYL-AMMONIUM HYDROXIDE " * - 4 0 --16 -15 •14 ± / FIGURE 7 / H- ACIDITY FUNCTION r FOR AQUEOUS BENZYL-' TR1METHYL AMMONIUM / HYDROXIDE -13 / -12 o 0.0 02 • i MOLARITY 04 0.6 OS 1.0 1.2 1.4 1.6 18 20 22 24 • .. i — J 1 — i . . . i i i _ i i • hi whose pK a value Has been estimated to- be 21. ' • • Presumably t h i s f a i l u r e of the Hammett p o s t u l a t e i s due to d e c r e a s i n g d i e l e c t r i c c o n s t a n t . I f i t is'assumed that change i n • d i e l e c t r i c i s l i n e a r w i t h mole f r ' a c t i o n i n a mixture of two l i q u i d s the d i e l e c t r i c of 60'mole percent p y r i d i n e In water w i l l be l e s s than i|0. The e f f e c t s observed i n t h i s work seem g r e a t e r than the expected e f f e c t of d i e l e c t r i c on l o g ( l c ) ' \ f Al-and i t i s p o s s i b l e some e f f e c t s due to i o n p a i r i n g or molecular a s s o c i a t i o n are p r e s e n t . Hammelstedt and Hume (87 ) have concluded there i s no hope f o r s u c c e s s f u l pK a measurements In s o l v e n t s -such as benzene where a s s o c i a t i o n phenomena are very pronounced. . They f e e l such measure ments may be. p o s s i b l e , i n , f o r example, or t h o - d i c h l o r o b e n z e n e p r o v i d very d i l u t e s o l u t i o n s * of the s u b s t r a t e can be used.' For t h i s purpose s u f f i c i e n t l y s t r o n g l y b a s i c I n d i c a t o r s w i t h very i n t e n s e a b s o r p t i o n are needed. These o p e r a t i o n s were c a r r i e d out i n an e n t i r e l y s i m i l a r manner f o r 'varying c o n c e n t r a t i o n s of4»sulfdlane In water, u s i n g the same indicators.!,; The higher d i e l e c t r i c of s u l f o l a n e allowed continuance of- the measurement^ from 100% water to 9 5 mole percent sulfolane.^ T h i s upper l i m i t r e s u l t e d from the n e c e s s i t y , of adding the b a s e . i n aqueous s o l u t i o n . I t was necessary to add 5 mole percent water to the s u l f o l a n e to b r i n g the c o n c e n t r a t i o n of quaternary base to the d e s i r e d 0.011* Molar>s The r e s u l t s , analogous to those f o r . p y r i d i n e , are p l o t t e d i n F i g u r e s 5 , 6 and 6 A 0 The e n t i r e o p e r a t i o n was repeated u s i n g s o l u t i o n s of b e n z y l -trimethylammonium hydroxide i n water. T h i s quaternary base has h i g h water s o l u b i l i t y / a n d may be prepared i n s o l u t i o n of 2 . 3 8 molar. F i g u r e 7 shows the r e s u l t s obtained i n t h i s system. Table I I shows a cpmplete summary of the pK a values determined i n the present work and shows the average values obtained i n these b a s i c systems. I t may be noted that b e t t e r agreement i s a c t u a l l y found between determinations i n d i f f e r e n t s o l v e n t s than the v a r i a t i o n s i n l o g f o r an i n d i v i d u a l i n d i c a t o r would l e a d one to expect. [AH] k3 Table I I Summary of Determined pK a Values I n d i c a t o r Ave. Aq. Pyr. Benzyl S u l f o l a n e value b u f f e r water TMA water 2,1;, 6,2',l+<,6'-hexanitro-diphenylamine 2, 6-dichlorophenol 2,la, 6, 2 1 ,1+' - p e n t a n i t r o -diphenylamine 2,1)., 6,I|.' - t e t r a n i t r o -diphenylamine 2,1+, 6, 3' - t e t r a n i t r o -diphenylamlne 2,1+, 6 - t r i n i t r o -d iphenylamine 2,1+,2',!+' - t e t r a n i t r o -diphenylamine 2,J+, 6-tr i n i t r o -1+' -amino-d iphenylamlne 2,J+, 6 - t r i n i t r o a n i l i n e 2,1+,[|.' - t r i n i t r o -dIphenylamlne 2jl+> 3' - t r i n i t r o -diphenylamlne 6-br orao -2, l+-d i n i t r o -a n i l i n e 2,l+-dinitro-diphenylamlne 3 - n i t r o c a r b a z o l e ]+,)+' - d i n i t r o -d i phe ny1amIne 2.63 2.63 -3.1+8 3.1+8 6.72 6.72 -8.88 8.88 -9.15 9.15 -IO.38 IO.38 10.82 10.82 -10.82 10.82 -12.20 12.20 -12.35 12.31 12.33 12.1+li. 12.31 12.6.5 13.63 13«8U 1I+.10 11+.08 12.65 12.68 12.62 13-66 13.60 13083 13-85 13-83 1I+.16 - 1I+.03 1I+.09 1I+.15 ll+.OO kh Table I I (cont.) Ave. Aq. ' * Pyr.' Benzyl S u l f o l a n e I n d i c a t o r value b u f f e r water TMA .•' water 2,11-dinitro-I i . 1 -amino d ipheny lamine-II4-06J4. - 14.61J. 2 , I j.-dinItroaniline 15.00 •14.97 15.02 2, 6 - d i c h l o r o - L t . - n i t r o a n i l i n e 15.55 15.55 I4. - n i t r od iphenylamine 15 = 90 15.90 l | - n i t r o - 2 , 5 ~ d i c h l o r o a n i l i n e 16.05 16.05 ij.-chloro -2 - n i t r o a n i l i n e 17 .-22 17.22 2-nitrodiphenylamine 17.57 - ' 17.57 2 - n i t r o a n i l i n e 17.88 17.88 I4. - n i t r o a n i l i n e 18.37 18.37 where Ave. i s average Aq. i s aqueous Pyr., i s p y r i d i n e TMA Is trimethylammonium hydroxide B Use of A c i d i t y Constants to E s t a b l i s h H_ f o r other Solvent Systems Once an e s t a b l i s h e d l i s t of a c i d i t y constants, such as Table I I , i s a v a i l a b l e i t can be used to measure H_ values i n other s o l v e n t systems. An I n v e s t i g a t i o n was c a r r i e d out on the e f f e c t of i n c r e a s -i n g the base c o n c e n t r a t i o n i n w a t e r - p y r i d i n e m i xtures. B e n z y l -trimethylammonium hydroxide i s a v a i l a b l e as a 2,19 molar s o l u t i o n i n anhydrous p y r i d i n e . Thus, by mixing these two s o l u t i o n s i n c a l c u l a t e d p r o p o r t i o n s w i t h p y r i d i n e or water one can o b t a i n any d e s i r e d p r o p o r t i o n of p y r i d i n e - w a t e r c o n t a i n i n g up to 2 molar base. Measurements i n each s o l u t i o n were c a r r i e d out w i t h s e v e r a l i n d i c -a t o r s . The r e s u l t s are t a b u l a t e d i n the appendix and p l o t t e d on F i g u r e 8 . The i n d i c a t o r s were a l s o used i n t h i s manner to e s t a b l i s h the H_ f u n c t i o n f o r dimethyl s u l f o x i d e - w a t e r mixtures c o n t a i n i n g 0.011 molar tetramethylammonium hydroxide. The c a l c u l a t i o n s are shown i n appendix B and the r e s u l t s p l o t t e d on F i g u r e 9« The e x t i n c t i o n c o e f f i c i e n t s of maximal absorption*were determined i n s o l u t i o n s as c l o s e as p o s s i b l e i n composition to those i n which the measurements were c a r r i e d out. The i n d i c a t o r s employed i n t h i s work possess marginal s o l u b i l i t i e s i n aqueous l i t h i u m hydroxide. Measurements were made up to 5 molar (saturated) l i t h i u m hydroxide by use of 10cm. c e l l s . Even w i t h t h i s path l e n g t h o p t i c a l d e n s i t i e s were very low and the r e s u l t s are a c c o r d i n g l y not of h i g h accuracy but are b e l i e v e d to r e p r e s e n t at l e a s t r o u g h l y the H- f u n c t i o n i n these systems. Measurements were even more d i f f i c u l t i n aqueous sodium and U6 potassium hydroxides. For one molar sodium hydroxide the r e s u l t s agree w i t h those f o r l i t h i u m hydroxide, w i t h i n the experimental e r r o r , but attempts to make measurements i n more conc e n t r a t e d s o l u t i o n s had to be abandoned. The f o l l o w i n g experiment was c a r r i e d out on 6 molar sodium hyd-r o x i d e . T h i s m a t e r i a l was shaken f o r s e v e r a l minutes w i t h a sample of 2 , J + - d i n i t r o a n i l l n e - an i n d i c a t o r which showed good s o l u b i l i t y i n aqueous benzyltrimethylammonium h y d r o x i d e . The a l k a l i n e s o l u t i o n was f i l t e r e d through a coarse s i n t e r e d g l a s s f u n n e l and then e x t r a c t e d w i t h a l a r g e amount of d i e t h y l e t h e r . The ether was evaporated and the r e s i d u e ( i f any) was taken up i n p y r i d i n e , c o n t a i n i n g benzyltrimethylammonium hydroxide. T h i s s o l u t i o n was known to f u l l y Ionize 2 , ] + - d i n i t r o a n i l i n e . The spectrum of the p y r i d i n e s o l u t i o n was then obtained i n a 10cm. c e l l . No t r a c e of the spectrum"'of the anion of. 2 , l | . - d i n i t r o a r i i l i n e was d e t e c t e d . - 47-F1GURE 8 H- ACIDITY FUNCTION FOR PYRIDINE-WATER MIXTURES CONTAINING BENZYLTRIMETHYL-AMMONIUM HYDROXIDE H9 OO Q2 04 0.6 OS' 10 12 14 16 18 20 22 24 — L 1 1 1 1 1 1 . I I I I I L_ •18 t • • • •17 Cf - • . .'. .' ' ' ; . i " . •16 " * x •15 •14 . FIGURE 9 H-ACIDITY FUNCTION FOR WATER-. DIMETHYLSULFOXIDE MIXTURES CONTAINING 0011 MOLAR I L I RAMETHYLAMMONIUM . ; -HYDROXIDE . -13 ' #» * ' .' * * •12 0 * * MOLE 10 20 • i i i... _ PERCENT 30 • i t DIMETHYLSULFOXIDE IN WATER 40 50 .60 70 80 i • • i i i • i • 50 G C r i t i c a l D i s c u s s i o n of R e s u l t s . T h e ' f i r s t q u e s t i o n to be answered i s :-How can we be sure we are a c t u a l l y d e a l i n g w i t h a p r o t o n removal process producing an anion ? -At present no c r y o s c o p i c work has been done in- any of the s o l v e n t s so no d i r e c t statement of the number of p a r t i c l e s pressent i s p o s s i b l e . P a r t l y f o r these reasons an examination of several•compounds which c o u l d not l o s e a p r o t o n under the. r e a c t i o n c o n d i t i o n s was undertaken. . These were N, N-dimethylpicramide, t r i n i t r o b e r i z e n e , the p i c r a t e , anion and nitrobenzene.. Each of these showed, a s p e c t r a l change when d i s s o l v e d In a s o l u t i o n of s u f f i c i e n t l y h i g h b a s i c i t y . However, a l l of them r e a c t e d at a f i n i t e r a t e and f o r a l l of them the r e v e r s e r e a c t i o n was a l s o , slow when the' b a s i c i t y of the s o l u t i o n was reduced. T h i s then became our main c r i t e r i o n :-We accepted as simple p r o t o n removal a l l those r e a c t i o n s which were a p p a r e n t l y instantaneous, and which r e v e r s e d i n s t a n t a n e o u s l y . A l l compounds whose pK a value we have r e p o r t e d obey t h i s c r i t e r i o n . T h i s Is i l l u s t r a t e d f o r the case of 3 j . 5 - d i n i t r o a n i l i n e . T h i s compound r e a c t e d slowly i n our -most b a s i c s o l u t i o n s to produce a s t a b l e s p e c i e s . A l s o , the reverse, rea-ction was- slow. Because of these o b s e r v a t i o n s i t was decided that a pKa d e t e r m i n a t i o n would not be meaningful.. D i f f i c u l t i e s of a s i m i l a r nature were encountered f o r i | - n i t r o p h e n y l h y d r a z i n e , 2,lj r-dinitrophenylhydraz-in'e and •51 2,1}., 6 - t r i n i t r o p h e n y l h y d r a z i n e . These compounds, among o t h e r s , w i l l be d i s c u s s e d l a t e r o I t s h o u l d be mentioned here t h a t a l l a n i o n s showed a v e r y slow decay i n these b a s i c s o l u t i o n s . I n most cases s e v e r a l hours were r e q u i r e d . A comparison of the phenols w i t h the a n i l i n e s , l a t e r i n t h i s d i s s e r t a t i o n , o f f e r s c i r c u m s t a n t i a l p r o o f t h a t the p r o c e s s e s we are d e a l i n g w i t h here are the same as those t h a t occur when phenols a re I o n i z e d i n aqueous s o l u t i o n . More i n d i c a t o r s need t o be deve l o p e d f o r the d i m e t h y l s u l f o x i d e -water system. R e s u l t s are r e p o r t e d h e r e i n o n l y up t o the 70 mole p e r c e n t s o l u t i o n . 3 - n i t r o a n i l i n e i s not measureably i o n i z e d i n 95 mole p e r c e n t ( e s t i m a t e d pKa - l 9 -5 ) j d l p h e n y l a m l n e i s l e s s t h a n h a l f i o n i z e d .judged by comparison of the o p t i c a l d e n s i t y a t t a i n a b l e f o r i t s a n i o n w i t h t h a t a t t a i n e d i n anhydrous e t h y l e n e d i a m i n e c o n t a i n i n g b e nzyltrimethylammonium h y d r o x i d e . For t h e s e r e a s o n s ; i t i s b e l i e v e d t h a t the 95 mole p e r c e n t s o l u t i o n i s not much more b a s i c t h a n the 75 mole p e r c e n t . 52 D C o r r e l a t i o n of R e s u l t s w i t h those of o t h e r i n v e s t i g a t o r s . Much of the p a s t c o n f u s i o n r e g a r d i n g the H - " f u n c t i o n has c e n t e r e d around the use of the i n d i c a t o r i j . - n l t r o b e n z y l c y a n i d e . As p r o o f of t h i s statement we submit F i g u r e s 11 and 12 showing the l a r g e e f f e c t s of d i f f e r i n g b a s i c i t y - and s o l v e n t systems on t h i s i n d i c a t o r . The v a r i o u s s p e c t r a a re l a b e l l e d w i t h the H_ v a l u e s determined h e r e i n and I t i s suggested t h a t the s p e c t r a l changes of t h i s i n d i c a t o r are s u f f i c i e n t r e a s o n t o e l i m i n a t e i t from s e r i o u s c o n s i d e r a t i o n i n e s t a b l i s h i n g an H. ' s c a l e . E x a m i n a t i o n of F i g u r e 11 shows t h a t the a b s o r p t i o n maximum s h i f t s , w i t h i n c r e a s i n g b a s i c i t y from a p p r o x i m a t e l y Ji^Omu a t 0.05 molar b e n z y l t r ime thylammonium h y d r o x i d e t o i|.90mu at 0.8l molar b a s e . W i t h i n c r e a s i n g c o n c e n t r a t i o n a more p r o f o u n d change t a k e s p l a c e i n the spectrum- and a new maximum d e v e l o p s near 537'nu w i t h c o n t i n u a l l y i n c r e a s i n g e x t i n c t i o n c o e f f i c i e n t . There i s no r e a d i l y a v a i l a b l e , r e a s o n a b l e , e x p l a n a t i o n f o r these s p e c t r a l s h i f t s . F i g u r e 12 shows the e f f e c t of changing t h e , s o l v e n t . I l l u s t -r a t e d are ethanolamlne, two c o n c e n t r a t i o n s of h y d r a z i n e i n water, 1 molar phenyltrimethylammonium h y d r o x i d e i n methanol, 0.01 molar phenyltrimethylammonium h y d r o x i d e i n s u l f o l a n e as w e l l as 1 normal and 5 normal aqueous p o t a s s i u m h y d r o x i d e . A g a i n a l l t hese a b s o r p t i o n s p e c t r a have been l a b e l l e d w i t h d e t e r m i n e d H_ v a l u e s f o r t h a t p a r t i c u l a r s o l v e n t system. A f t e r g a t h e r i n g a l l t h i s e v i d e n c e i t can be seen t h a t t h e r e appears no r e a s o n a b l e way t o determine the F I G U R E II FIGURE 12 PARA-NITROBENZYLCYANIDE IN SOME BASIC 'SOLVENTS? ,(195) A SULFOLANE-W/ ' ~R • T E T R A M E T H Y L -AMMONIUM H'....cOXIDE B 3 0 MOLE PERCENT PYRIDINE IN , WATER +.1.19 MOLAR IN BENZYLTRI-METHYLAMMONIUM HYDROXfDE C 7 3 . 2 ° / 0 HYDRAZINE IN WATER D 45.3 °/o HYDRAZINE IN WATER E . 1.0 M O L A R PHENYLTRIMETHYL-AMMONIUM HYDROXIDE IN METHANOL F ANHYDROUS ETHANOLAMINE 10 NORMAL AQUEOUS SODIUM HYDROXICJE FIGURES IN BRACKETS A R E H-V A L U E S WAVELENGTH (MU.) '. ' 500 CC f r a c t i o n i o n i z e d f o r t h i s i n d i c a t o r <> There have been many approaches •to the use of t h i s i n d i c a t o r . F i r s t , Stearns and Wheland (6) made measurements at 1+2 Omu, and p r e d i c t e d an e x t i n c t i o n c o e f f i c i e n t of. 28,900 at t h i s wavelength. " T h e i r work was c a r r i e d out i n water, that i s , aqueous h y d r o x y l s o l u t i o n s . In these s o l u t i o n s no more than a very s l i g h t wavelength s h i f t i s n o t i c e a b l e . In 6 normal potassium hydroxide a d e f i n i t e s h i f t to longer wavelength i s n o t i c e a b l e y the maximum being near [4.7 5mu. The broad f l a t nature of t h i s peak precludes an accurate measurement of X m a x . I t i s n o t i c e d that the observed maximum i s near t h i s p o i n t f o r O.I4.8 molar aqueous benzyltrimethylammonium hydroxide. The measured e x t i n c t i o n c o e f f i c i e n t f o r 1 normal potassium hydroxide i s near 16,000 and thus, a c c o r d i n g to Stearns and Wheland, [(.-nitrobenzyl cyanide should have a f r a c t i o n i o n i z e d of about 0.^ 5 based on t h e i r e x t r a p o l a t e d e x t i n c t i o n c o e f f i c i e n t o However, as can be seen from the f i g u r e s , t h i s e x t i n c t i o n c o e f f i c i e n t cannot be reached at t h i s wavelength since i n c r e a s i n g the b a s i c i t y of the s o l u t i o n produces d r a s t i c changes i n the appearance of the spectrum. Stearns' and Wheland's estimate of the pK a value f o r t h i s compound (130I4.) i s i n rough agreement with the H_ values determined i n t h i s work, by use of other i i n d i c a t o r s , provided one concludes that 0.1+8 molar b e n z y l t r i m e t h y l -.ammonium hydroxide has j u s t more than h a l f i o n i z e d the compound. The determined H_ value f o r t h i s s o l u t i o n i s 13»65° I t must be po i n t e d out that Stearns and Wheland d i d not consid e r t h e i r d e t e r m i n a t i o n of h i g h accuracy. T h i s compound was subsequently used by Deno ( l l ) and by Schaal 56 and co-workers ( 1 3 - 1 8 ) t o e s t a b l i s h the H_ f u n c t i o n . ' T h e i r r e s p e c t i v e approaches t o i t s use were v e r y d i f f e r e n t . Deno made measurements at 535m u > the approximate p o s i t i o n of Xmax. shown on our f i g u r e s f o r many s t r o n g l y b a s i c s o l v e n t s . H i s d e t e r m i n a t i o n i s not a c c e p t a b l e because of the l a r g e changes i n the shape of the spectrum as the b a s i c i t y changes. Deno r e p o r t s 2 2 , 2 0 0 as the e x t i n c t i o n c o e f f i c i e n t f o r t h i s i n d i c a t o r . T h i s i s much l e s s t h a n can be o b t a i n e d i n more b a s i c s o l u t i o n s . A v a l u e of 33>700 was o b t a i n e d i n the most b a s i c s o l -u t i o n used i n t h i s work and t h e r e i s no p r o o f t h a t the maximum had been r e a c h e d . A c a l c u l a t i o n from S c h a a l ' s data show3 25,l | .00 i n 6 0 % e t h y l e n e d i a m i n e i n water, i n agreement w i t h the value measured i n t h i s work i n 7 3 . 2 % h y d r a z i n e i n w a t e r . Thus, we are f o r c e d t o conclude t h a t b e s i d e s b e i n g unable t o u n e q u i v o c a l l y i n t e r p r e t the b e h a v i o u r of t h i s i n d i c a t o r Deno d i d not work w i t h an e x t i n c t i o n c o e f f i c i e n t r e p r e s e n t a t i v e of f u l l i o n i z a t i o n . Thus, i t must be c o i n c i d e n c e t h a t Deno was a b l e t o anchor h i s p l o t of l o g a g a i n s t H_ i n measured pH v a l u e s . I n s p i t e of [ ; A H ] a l l t h i s Denoi's and S t e a r n s ' and Wheland's d e t e r m i n a t i o n s are a p p a r e n t l y a p p r o x i m a t e l y c o r r e c t a l t h o u g h i t cannot be demonstrated why t h i s i s so. S c h a a l ' s approach t o the use of t h i s compound was d i f f e r e n t . He p r e f e r r e d t o i n t e r p r e t the change I n spectrum as two s u c c e s s i v e i o n i z a t i o n p r o c e s s e s . S c h a a l ' s r e p o r t e d s p e c t r a i n v a r i o u s c o n c e n t r a t i o n s of e t h y l e n e d i a m i n e i n water ( 1 3 ) are very s i m i l a r 57 to those obtained i n t h i s work i n aqueous b e n z y l t r i m e t h y l -ammonium hyd r o x i d e . A c c o r d i n g to S c h a a l ' s i n t e r p r e t a t i o n the f i r s t i o n i z a t i o n process i s complete i n 25 percent ethylenediamine i n water. T h i s i s near the p o s i t i o n of h a l f i o n i z a t i o n a c c o r d i n g to the Stearns and Wheland treatment. The spectrum f o r 25% ethylenediamine i n water corresponds r o u g h l y to that shown i n F i g u r e 11 f o r O.J4.8 molar aqueous benzyltrimethylammonium hydroxide. The H- f o r t h i s s o l u t i o n as determined by other i n d i c a t o r s i s 1 3°o5. Schaal used the same pK a value as Stearns and Wheland and by t h i s d e c i s i o n he made h i s H_ s c a l e approximately 0 . 8 u n i t s too b a s i c . T h i s i s to say t h a t 25 percent ethylenediamine i n water i s I n t e r p r e t e d as having an H„, value i n excess of IJ4. Instead of approximately 13-5o No reasonable e x p l a n a t i o n of the s p e c t r a seems p o s s i b l e on chemical grounds. The removal of the .second p r o t o n seems most u n l i k e l y i n these systems. [(.-nitrobenzyl cyanide was a l s o used by Langford and Burwell (22) ( 2 3 ) . There i s no mention of an e x t i n c t i o n c o e f f i c i e n t i n these r e f e r e n c e s . I t i s f e l t t h a t t h i s d i s c u s s i o n f u l l y e l i m i n a t e s t h i s compound from c o n s i d e r a t i o n as a usable i n d i c a t o r . I t i s noted that i t s e x t i n c t i o n c o e f f i c i e n t i n c r e a s e s across the whole H_ s c a l e from 12 to 2 0 and may w e l l continue to i n c r e a s e a f t e r that-. 58 Schaal and F a v i e r ( r e f , 17 page 2 0 1 1 + ) p o i n t out another r e a s o n f o r the i n a c c u r a c y of Deno's work. He f a i l e d to f u l l y i o n i z e h i s i n d i c a t o r s . He worked w i t h the assumption t h a t the b a s i c i t y of v a r i o u s c o n c e n t r a t i o n s of hydrazine i n water would continue to i n c r e a s e as the c o n c e n t r a t i o n of hydrazine passed 6 1 + % - t h i s c o n c e n t r a t i o n corresponds to hydrazine" h y d r a t e . In f a c t there i s a r a p i d l e v e l l i n g o f f of the f u n c t i o n at t h i s p o i n t . Since t h i s s o l u t i o n was the most b a s i c a v a i l a b l e to Deno he took the e x t i n c t i o n c o e f f i c i e n t s i n t h i s medium to correspond to f u l l i o n i z a t i o n U n f o r t u n a t e l y Schaal's e x t i n c t i o n c o e f f i c i e n t s seem to be approximate. He does not r e p o r t these values as such and the values l i s t e d i n the appendix were obtained by c a l c u l a t i o n from h i s r e p o r t e d weighing and d i l u t i o n procedures. For the above reasons Deno's r e s u l t s have not been con s i d e r e d In making the f o l l o w i n g c o r r e l a t i o n s . To summarizes a l l p r e v i o u s H- determinations have been based ' d i r e c t l y on l+-nitrobenzyl c y a n i d e . I t has now been c o n c l u s i v e l y e s t a b l i s h e d that i t i s u n s u i t a b l e f o r t h i s purpose. The pr e v i o u s d i s c u s s i o n has shown t h a t • s u i t a b l e i n d i c a t o r s have been found to r e p l a c e i t . I t i s now p o s s i b l e to r e v a l u a t e Table I and c o r r e l a t e our r e s u l t s w i t h those of Schaal and B u r w e l l . To do t h i s we must d i s c a r d l+-nltrobenzyl cyanide and choose, new s t a r t i n p o i n t s f o r the work of these authors. A c c o r d i n g l y the value of 1 3 = 6 3 f o r 6 - b r o m o - 2 s l + ~ d I n i t r o a n i l i n e , as determined 6 l i n t h i s work, was,used as a s t a r t i n g p o i n t f o r Burwell's work i n s t e a d of 1 3 » ? 1 obtained by comparison w i t h l ^ - n i t r o -b e n z y l cyanide. The pK a d i f f e r e n c e s determined by Burwell were then used to b u i l d up Table I I I . Schaal's data f o r ethylenediamine were r e p l o t t e d a f t e r a s s i g n i n g the value of 13°8l4- to 2,[|_-dinitrodiphenylamine , T h i s i s shown i n F i g u r e 13 » An examination of Table I I I shows that disagreements i n pK a determinations are l a r g e l y removed by these procedures„ A l s o i n c l u d e d i n Table I I I are values Schaal obtained i n ethanolamine (l6) and t e r t i a r y amyl a l c o h o l (19)» These were determined by an e x t r a p o l a t i o n procedure s i n c e f u l l i o n i z a t i o n was not a t t a i n e d . I t i s s a t i s f y i n g t h a t these values are i n at least, rough agreement. These values have a l l been a d j u s t e d by 1.02 pK u n i t s s i n c e we have a d j u s t e d 2,J4.-dinitroanillne by that amount. F i g u r e ik 'shows a s i m i l a r r e c a l c u l a t i o n of Schaal's data (17) f o r the hydrazine system. The p l o t t e d H- values, F i g u r e s 15 and 16, have been obtained i n the same manner employed f o r the other systems i n t h i s work. Edward ( 9 8 ) has r e c e n t l y p u b l i s h e d values f o r concentrated s o l u t i o n s of sodium hydroxide up to 6 molar u s i n g thioacetamide as an acid-base i n d i c a t o r . 6 2 Table I I I C o r r e l a t i o n of pK a values from t h i s work w i t h those r e c a l -c u l a t e d from the work of other i n v e s t i g a t o r s . Schaal and Langford and co-workers ' Burwell T h i s Ind i c a t o r or i g . ad.i. or i g . ad,j 0 work 2,1}., 6 - t r i n i t r o -a n i l i n e 1 2 . 2 5 - - - 1 2 . 2 0 2»l4_,2+T - t r i n i t r o -diphenylamine - - - - 1 2 . 3 5 2,I|., 3 ' - t r i n i t r o -d iphenylamlne - - - - 1 2 . 6 5 6 - b r omo-2, [j.-d i n i t r o a n i l i n e - - 1 3 . 7 1 1 3 . 6 3 1 3 . 6 3 2 , 4 ~ d i n i t r o -diphenylamine 111. o 6 5 1 3 . 8 4 * - - 1 3 . 8 1 + 3 - n i t r o c a r b a z o l e 1 5 . 1 0 - 1 4 . 1 0 4 , 4 ' - d i n i t r o -d iphenylamine l l + o 9 7 l l | . . 1 3 b 14.08 2 , l | - d i n i t r o - 4 ' -aminodiphenylamine - - 14.64 2 , ) j . - d I n i t r o -a n l l i n e 1 5 . 8 0 Ii4--78b 1 5.31+ I 5 » 2 6 d 1 5 . 0 0 2, 6 - d i c h l o r o -4 ~ n i . t r o a n i l i n e _ _ =• - 1 5 . 5 5 JL).-nitro-dIphenylamine 1 6 . 9 5 15.93° 1 5 » 7 6 I 5 . 6 8 d 1 5 . 9 0 2 S 5 ~ d l e h l o r 0 -4 -n 1 t r oani 1 ine - _ - - 1 6 . 0 5 l4.-ch.l0r 0 - 2 -n i t r o a n i l i n e _ 1 7 . 2 1 1 7 . 1 3 d 1 7 . 2 2 6 3 Table I I I (cont.) I n d i c a t o r 2 - n i t r o -diphenylamine 2 - n i t r o a n i l i n e I j . - n i t r e - a n i l i n e Schaal and co-vorker s or l g o 1 8 . 8 5 ad j o 1 7 . 8 3 ° Langford and Burwell or l g . ad j . T h i s work 1 7 * 5 7 1 9 - U 0 1 8 . 3 8 ° - - 1 7 o 8 8 1 8 . 9 5 1 7 * 9 3 ° 1 8 . 1 4 - 7 l 8 , 3 9 d 1 8 . 3 7 a - assigned s t a r t i n g p o i n t b - from r e p l o t of o r i g i n a l data c - a d j u s t e d by 1.02 which i s the adjustment found f o r 2 j,l|_-d i n i t r o a n i l i n e d - a d j u s t e d by 0.08 l o g u n i t s o r i g . - o r i g i n a l a d j . - as a d j u s t e d i n t h i s work FIGURE 15 H- ACIDITY FUNCTION FOR ETHYLENEDIAMINE-WATER MIXTURES BY RECALCULATION OF SCHAAL?S DATA REFERENCE PERCENT ETHYLENEDIAMINE IN WATER 3 0 AO 5 0 6 0 7 0 8 0 9 0 j i i i i i i i i i i a i L . . . - FIGURE 16 ' H- ACIDITY FUNCTION FOR 5 ' HYDRAZINE-WATER MIXTURES BY RECALCULATION OF SCHAACS DATA ' -16 ' REFERENCE. -15 x 66 E C o r r e l a t i o n of Molecular S t r u c t u r e of I n d i c a t o r s w i t h pK a v a l u e s . A»limited amount of i n f o r m a t i o n has been obtained In t h i s work which permits c o r r e l a t i o n with Hammett sigma v a l u e s . F i g u r e 17 shows the pK a values f o r three s e r i e s of s u b s t i t u t e d diphenylamines p l o t t e d a g a i n s t sigma-minus v a l u e s . These were taken from the ....summary of J a f f e (111). The three s e r i e s are l ^ - n i t r odiphenylamine, 2-,lj_y-dini.trodiphenylamine and 2,1)., 6-tr i n i t r odiphenylamine . Each" compound i s ' s u b s t i t -uted i n t h e . r i n g which does not c a r r y the n i t r o groups. F i g u r e 1'8 shows the same data p l o t t e d "against the sigma-zero values developed by T a f t ([(.2). I t can be seen that an improved c o r r e l a t i o n i s achieved by use of the sigma-zero v a l u e s . The normal Hammett sigma constants gave a poor f i t . T h i s i s reasonable f o r the two s e r i e s where an o r t h o - n i t r o group i s pr e s e n t . T h i s group should prevent the r i n g b e a r i n g the s u b s t i t u e n t from . a t t a i n i n g c o p l a n a r i t y and. so prevent e f f e c t i v e resonance i i n t e r a c t i o n between the s u b s t i t u e n t and the c e n t r a l n i t r o g e n atom which l o s e s the pro t o n . It i s i n s t r u c t i v e to p l o t the pKa values determined(Figure 19) i n t h i s , work a g a i n s t the pKBH"^ * values f o r the same compounds as determined by Hammett i n developing the H Q s c a l e f o r s u l p h u r i c acid'. The best values of Paul and Long have been used w i t h the . e x c e p t i o n of I4.,I4.1 - d i n i t r o d i p h e n y l a m i n e and 67 3 - n i t r o c a r b a z o l e f o r w h i c h p K g j j + h a s b e e n d e t e r m i n e d i n t h i s l a b o r a t o r y (I4.3) • T h i s c o r r e l a t i o n may b e c o n s i d e r e d a s r e a s o n a b l e e v i d -e n c e t h a t b o t h s e t s o f d e t e r m i n a t i o n s a r e a p p r o x i m a t e l y c o r r e c t o I t i s w o r t h n o t i n g t h a t t h e a c i d i t y c o n s t a n t s f o r [ ( . - n i t r o a n i l l n i u m i o n a n d 2 » I 4 . , 6 - t r I n i t r o a n i l i n e h a v e b o t h b e e n d e t e r m i n e d w i t h r e s p e c t t o t h e p H s c a l e . A r n e t t h a s s t a t e d ( I 4 J 4 . ) t h a t d e t e r m i n a t i o n s o f H 0 w i t h H a m m e t t i n d i c a t o r s i n t h e r e g i o n a b o v e H Q = -I4..85 {10% s u l p h u r i c ) c a n l e a d t o d i s c r e p a n c i e s o f O.^O H 0 u n i t s , d e p e n d i n g o n • t h e i n d i c a t o r u s e d . W i t h t h i s i n m i n d w o r k i s u n d e r w a y i n t h i s l a b o r a t o r y u s i n g some o f t h e i n d i c a t o r s w h o s e a c i d i t y h a s b e e n d e t e r m i n e d i n t h i s w o r k i n a n a t t e m p t t o i m p r o v e t h e m o s t a c i d p a r t o f t h e H Q s c a l e t h a t i s a b o v e t h e p o i n t w h e r e c h e c k s a r e n o t a v a i l a b l e f r o m o t h e r a c i d systems-(I4 .3) « I t i s o f i n t e r e s t t h a t S t e w a r t a n d Y a t e s (I4.9) f o u n d a s l o p e o f 0.59 o n a p l o t o f t h i s t y p e f o r s u b s t i t u t e d b e n z o i c a c i d s w h i l e t h e p r e s e n t r e s u l t g i v e s a v a l u e o f 0.7 f o r a n i l i n e s . The' b a s e s w h i c h w e r e o r i g i n a l l y u s e d t o e s t a b l i s h t h e Ho s c a l e a r e c h a r a c t e r i z e d b y h y d r o g e n b o n d i n g b e t w e e n B H + a n d w a t e r m o l e c u l e s (62). A g r e e m e n t w i t h t h e Ho s c a l e d e p e n d s o n t h e h y d r o g e n b o n d i n g e n e r g y a n d t h e a c t i v i t y c o e f f i c i e n t o f t h e p p o t o n a t e d b a s e b e i n g i n s e n s i t i v e t o - 6 8 -1 Q • F I G U R E 17 .:?=,. C O R R E L A T I O N O F D I P H E N Y L A M I N E A C I D I T I E S WITH T H E H A M M E T T E Q U A T I O N A'} U S I N G S I G M A - M I N U S V A L U E S •17 ,:H • S I G M A - M I N U S O " " -CJB -0.6 -0.4 -02 0.0 +Q2 +04 +06 +08 +10 +12 +14 *1£ i • • i • I I : I I I I I I I I - 6 9 -i 1 8 - FIGURE 18 . CORRELATION OF DIPHENYLAMINE ACIDITIES WITH HAMMET EQUATION USING SIGMA ZERO VALUES H7 •13 •16 •15 •14 CT. Q. •12 -11 -10 -9 8 r ho =220 14-NITROD! PHENYLAMINE (24-DINITRO-4-AMINODIPHENYLAMINE rho=190 24-DINITRO-. DIPHENYLAMINE 44-DlNITRCT: DIPHENYLAMINE 24.3-TRINITRODIPHENYLAMI? 244-TRINITRODIPHENYLAMINE^ 246-TRINITRO-4-AMINODIPHENYL AMINE rho=175 L246-TRINITRODIPHENYLAMINE 24J&,3-TETRANITRODIPHENYLAMINET 24j6,4-TETRANITRODIPHENYLAMINEN SIGMA-ZERO -OA -03 -02 -0.1 0 +0.1 +02 +03 +04 +05 +05 +07 +08 __i i i i i 1 1 1 1 1 i i i • - 70-.-21 FIGURE 19 CORRELATION OF ACIDITY O F NITROGEN ACIDS WITH THE ACIDITY OF THEIR PROTONATED SPECIES -20 / / 11 p K B H + -10 - 9 - 8 -7 -6 -5 - 4 - 3 - 2 - 1 0 A *2 +3 i 1 1 1 1 1 1 i i i i i • • 71 changes i n the s t r u c t u r e of the base. For bases whose i o n i z a t i o n e q u i l i b r i a do not f o l i o ? , the H Q f u n c t i o n the d i s c r e p a n c i e s noted have been a s c r i b e d to v a r i a t i o n of the r a t e of change of the hydrogen bonding energy w i t h the composition of the aqueous a c i d , b e i n g dependent on the s t r u c t u r e of the protonated base (63)• I t i s t h e r e f o r e , perhaps, s i g n i f i c a n t t h a t the p o i n t s shown f o r diphenylamine seem to f o l l o w a s l i g h t l y d i f e r e n t a c i d i t y - b a s i c i t y c o r r e l a t i o n than those f o r a n i l i n e s . Work which i s underway i n t h i s l a b o r a t o r y (J4.3) i n v o l v i n g study of the p r o t o n a t i o n e q u i l i b r i a of other s u b s t i t u t e d a n i l i n e s and diphenylamines may supply f u r t h e r i n f o r m a t i o n on t h i s p o i n t . I t i s to be noted p a r t i c u l a r l y t h a t diphenylamine seems to be much weaker as an -acid than the c o r r e l a t i o n would p r e d i c t . I t s a c i d i t y has not been measured but i t i s c e r t a i n l y much weaker than p a r a - n i t r o a n i l i n e . T h i s could not have been p r e d i c t e d by examining the p r o t o n a t i o n e q u i l i b r i a of these compounds. Evidence of a d i f f e r e n t k i n d i s based on the work of Yates ( 6 l ) . . Yates used the pKa value of d i e t h y l m a l o n a t e as determined by Jacqulnot-Verme',*ss'e, Schaal and Rumpf ( 2 0 ) to determine a b s o l u t e values of the v e l o c i t y constant f o r the h a l o g e n a t i o n of d i e t h y l m a l o n a t e . Based on t h i s pK a value (15.19) Yates obtained v e l o c i t y constants a c t u a l l y g r e a t e r than the t h e o r e t i c a l l y c a l c u l a t e d encounter r a t e 72 of o p p o s i t e l y charged ions i n s o l u t i o n . T h i s value i s about l i t e r s 10 ( r e f . 1 chap. V I I I ) . Jacquinot-Vermesse,' mole sec. Schaal and Rumpf obtained t h i s value by comparison w i t h I4., I4.' - d l n i t r odiphenylamine . The adjustment of the pKa value of diphenylamine i n t h i s work from that r e p o r t e d by Schaal i s about 1.0 l o g u n i t . I f t h i s a d j u s t e d value i s used i n Yates' c a l c u l a t i o n s h i s v e l o c i t y constants drop by one power of t e n . A f t e r t h i s adjustment these c a l c u l a t e d r a t e s are l e s s than, but s t i l l c l o s e to, that c a l c u l a t e d from the t h e o r e t i c a l e x p r e s s i o n . " Yates ( 6 l a ) has s t a t e d that Schaal's values are probably out by a .factor of t e n or more i n reasonable agreement with-.the H_ s c a l e developed i n t h i s work. I t i s to be. noted t h a t t h i s adjustment of the pK a value of d i e t h y l m a l o n a t e produces more reasonable agreement w i t h the d e t e r m i n a t i o n of pearson and M i l l s (6I4.) who r e p o r t e d 13.7 f o r t h i s compound. The c o r r e l a t i o n of pK a and pKgjj+ i s a c t u a l l y the comparison of the f i r s t and second i o n i z a t i o n constants of d i b a s i c a c i d s . I t i s i n t e r e s t i n g to. see how the i n f o r m a t i o n gained i n t h i s work f i t s i n t o our g e n e r a l knowledge of f i r s t and second i o n i z a t i o n c o n s t a n t s . Much of the a v a i l a b l e i n f o r m a t i o n of t h i s k i n d i s c o l l e c t e d i n Table IV and shown g r a p h i c a l l y i n F i g u r e 20. 7 3 Information has been i n c l u d e d f o r d i b a s i c a c i d s of any charge type whose two protons are l o s t from the same atom or from e q u i v a l e n t atoms attached to the same c e n t e r . The .data are arr'ang'ed i n order of i n c r e a s i n g a c i d i t y upward along the o r d i n a t e and to the r i g h t along the a b s c i s s a . , The l i n e shown i n F i g u r e 2 0 s l a b e l l e d P a u l i n g c o r r e l a t i o n ()4-5)J shows the remarkable success of t h i s o b s e r v a t i o n r e g a r d l e s s of formal charge on the species i n v o l v e d . , The s m a l l amount of evidence O4.6) which e x i s t s i n d i c a t e s the c o r r e l a t i o n may vary s l i g h t l y depending on whether the c e n t r a l atom i s a -non—metal or a t r a n s i t i o n metal „ - 7 4 --2 r-22 -24 .26 FIGURE 2 0 RELATION BETWEEN pKi -28 AND pK2 FOR SOME DIBASIC ACIDS -30 h32 -34 ©AMMONIUM ION h36 pKi 12 10 8 6 4 2 0 -2 -4 -6 -8 -10 -12 -14 - J I I I I I I 1 1 1 1 1 L . I 7 5 T a b l e I V p K a V a l u e s f o r S o m e D i b a s i c A c i d s . D i b a s i c a c i d pK]_ pIO? A p K a R e f e r e n c e I P r o t o n s l o s t f r o m e q u i v a l e n t a t o m s . P r o t o n a t e d B e n z o i c ' a c i d - 7 - 2 6 1+.20 11.1+6 (Ii-9) (7i|.) S u l f u r i c a c i d - 3 . 0 2 . 0 5 . 0 (1+7) C h r o m i c a c i d - 0 . 9 8 6.14-9 7.14-7 (1+6) S u l f u r o u s a c i d 1 - 7 7 7 . 2 1 5.1+1+ (I4.8) P h o s p h o r i c a c i d 2 . 1 6 7 . 1 6 5 . 0 0 (1+8) C a r b o n i c a c i d 3 . 9 1 0 . 3 0 6.1+0 ( l c ) ( 7 3 ) D i h y d r o g e n p h o s p h a t e a n i o n 7 d 6 12,14. 5.21+ (I4.8) D i h y d r o g e n v a n a d a t e a n i o n 8 . 9 5 H4 . .I4. 5 4 5 (U6) I I P r o t o n s l o s t f r o m t h e s a m e a t o m . 2 s l + } 6 - t r i n i t r ' o - 9 . 5 1 2 . 2 0 2 1 . 7 0 ( 2 5 ) ( T h i s w o r k ) a n i l i n i u m i o n P h e n o x o n i u m i o n - 6 -7k 1 0 . 0 0 16.714. ( 2 6 ) ( 5 0 ) H y d r o x o n i u m i o n . 7 1 5 . 7 17.1+0 ( l c ) l + - n i t r o a n i l i n i u m i o n 0 . 9 9 1 8,37 17.38 ( 2 5 ) ( T h i s w o r k ) A n i l i n i u m i o n . 0 2 0 . 8 1 5 . 8 ( 5 D ( T h i s w o r k ) H y d r o g e n s u l f i d e 7 . 1 1 I 4 . . 7 7 . 6 ( l c ) A m m o n i u m i o n 9 . 5 3 5 . 0 . ( l c ) 76 I t may be noted that the R i c c i c o r r e l a t i o n (52) p r e d i c t s the same pK a d i f f e r e n c e f o r any two such s u c c e s s i v e p r o t o n -a t i o n steps . Comparison of S u b s t i t u t e d A n i l i n e A c i d i t i e s w i t h those of the Corresponding Phenols. Table V S u b s t i t u e n t A n i l i n e Phenol A p K a Reference 2 - n i t r o - 17.88 7.08 10.80 (53) 4 - n i t r o - 18O37 7.15 11.22 (54) ' . 2,[|_-dinitro- 15.00 4.07 10.93 (53) 2 - n i t r o -Ii. - c h l o r o - 17.22 6.36 10.86 (53) 2 , 6 - d i c h l o r o -4 - n i t r o -15.55 3.48 12.17 (This work) 2,lx, 6 - t r i n i t r o - 12.20 0.29 11.91 (55) I n s p e c t i o n of these data show that there i s a v i r t u a l l y constant d i f f e r e n c e between the pK a value of a s u b s t i t u t e d phenol and that of the corresponding a n i l i n e . T h i s i n d i c a t e s t h at the Haramett rho value f o r the two s e r i e s of compounds i s r o u g h l y the same. Many of the a v a i l a b l e data i n the l i t e r a t u r e f o r phenols have been p l o t t e d . i n F i g u r e 21 to t e s t the p r i n c i p l e of the a d d i t i v i t y r e l a t i o n s h i p f o r s u b s t i t u e n t s (57)(51) i n 77 the phenol s e r i e s . I t was found that to a good approximation such a r e l a t i o n s h i p e x i s t s . In p a r t i c u l a r the p l o t f o r p a r a - s u b s t i t u t e d o r t h o - n i t r o p h e n o l s p a r a l l e l s that f o r p a r a -s u b s t i t u t e d phenols. The data f o r t h i s p l o t have been taken from Robinson (50) Rapoport and co-workers (53) Kortum, Vogel and Andrussow(55) and Ogston (56). I t should be noted that t h i s a d d i t i v i t y r e l a t i o n s h i p does not seem to be f o l l o w e d w e l l f o r 2 , 6-dinitrophenol. 2,l\.t 6-tr i n i t r o p h e n o l i s a stronger a c i d than would be p r e d i c t e d . Robinson (5o) has shown that each d i n l t r o p h e n o l i s more acid, than an a d d i t i v i t y r e l a t i o n would p r e d i c t . T h i s d e v i a t i o n from a d d i t i v i t y seems l e s s s e r i o u s f o r a n i l i n e s w i t h the r e s u l t the a c i d i t y constant d i f f e r e n c e i s g r e a t e r between 2 , 6 - d i s u b s t i t u t e d phenols and the corresponding a n i l i n e s than i t i s f o r the other s e r i e s shown. Use has been made of an analogous a d d i t i v i t y r e l a t i o n -s h i p i n F i g u r e 22 to p r e d i c t the pK a of a n i l i n e . A good s t r a i g h t l i n e f i t was obtained when the data f o r p a r a - s u b s t i t u t e d o r t h o - n i t r o a n i l i n e s was p l o t t e d a g a i n s t the Hammett sigma-minus values (lj.1) . The determined rho value was 2„25> c l o s e to the value r e p o r t e d f o r phenols and o r t h o - c h l o r o p h e n o l s (53) (78). A p a r a l l e l s t r a i g h t l i n e was drawn through the p l o t t e d value f o r p a r a - n i t r o -a n i l i n e and the pK a value from a n i l i n e read o f f at the sigma value f o r para-hydrogen ( z e r o ) . T h i s procedure p r e d i c t s the pK a value of a n i l i n e as 21.2. T h i s value - 78 -Ho p9 r8 r5 CO 12/46-TRIMETHYL-126-DIMETHYL 2£-DIMETHYL-4-CYANq 4^SYANO-26-aMETHYL-1-NiTRO-NITRO->2j3-DiNITRO OS4-DINITRO-26-DICHLORO - 4-NITRO-FIGURE 2 1 HAMMETT CORRELATIONS 2 OF ACIDITY OF SUBSTITUTED PHENOLS ho 42 SIGMA-MINUS CT--10 -Q8 -Q6 -04 -02 0 02 0.4 0.6 08 1.0 • 1 • • l_ 2^46-TRINITRO-12 1.4 16 — J i i - 7 9 -•22 T2ANILINE •21 •20 13-NITR0ANILINE -19 \ l 4 -NJTR0-^\ANILINE -18 2-NITROANILINE 3£-DINITRO-Bl ANILINE 2-NITRO-4-CHLOROANILINE -17 rho=£25 -16 -15 CO Q. 0 26-DINITROANILINE >Q24-DINITRO-^\ANILINE -14 -13 FIGURE 22 PREDICTION OF pKa OF ANILINE USING HAMMETT CORRELATIONS •12 SIGMA-MINUS CT" ©24.S-TRI-NFTROANILINE -12 • -10 -08 -Q6 -04 -Q2 0 *Q2 +04 +06 • i i i 1 1 1 1 — •08 +10 *12 +14 +16 8 0 i s not d i r e c t l y measureable at present, but i t seems r e a s o n -able t h a t i t i s not g r e a t l y i n e r r o r . P r e d i c t e d values are a l s o shown on the p l o t f o r 3 » 5 - d i n i t r o a n i l i n e and 2, 6 - d i n i t r o a n i l i n e . These values were not experimentally, a t t a i n a b l e due to r a p i d r e a c t i o n of the i o n i c s p e c i e s . I t i s worth n o t i n g from Table V that the pK a d i f f e r e n c e between p a r a - n i t r o a n i l i n e and p a r a - n i t r o p h e n o l i s s l i g h t l y g r e a t e r than the corresponding d i f f e r e n c e f o r the three examples l i s t e d which have a s i n g l e o r t h o - n i t r o group. I n t e r m o l e c u l a r hydrogen bonding i n v o l v i n g t h i s group i s a p p a r e n t l y much more important i n the phenol s e r i e s than i n the a n i l i n e s e r i e s , i n l i n e w i t h the l a r g e a c i d i t y d i f f e r e n c e -Dearden and Forbes ( 5 8 ) were able to c o n f i r m the presence of an i n t e r m o l e c u l a r hydrogen bond i n o r t h o - n i t r o -phenol by i t s e f f e c t on the i n f r a r e d f r e q u e n c i e s of the n i t r o group but have s t a t e d that there i s no unambiguous evidence of such a bond i n o r t h o - n i t r o a n i l i n e . - ; C e r t a i n l y i t seems' j u s t i f i a b l e to conclude that the hydrogen bond i s -very much weaker i n the a n i l i n e s e r i e s . I t I s to be noted t h a t while o r t h o - n i t r o p h e n o l i s 0 . 0 7 l o g u n i t s stronger than p a r a - n i t r o p h e n o l , o r t h o - n i t r o a n i l i n e i s O0J4.9 u n i t s stronger that para - n i t r o a n i l i n e . Tables 6 and 7 present a summary of the a c i d i t y d i f f e r e n c e s brought about by s t r u c t u r a l changes i n n i t r o -s u b s t i t u t e d p h e n o l s s a n i l i n e s and diphenylamines. I t i s 81 very d i f f i c u l t at the present time to make a complete r a t i o n a l e of these d i f f e r e n c e s but c e r t a i n r e g u l a r i t i e s appear* The e f f e c t of a t h i r d n i t r o group e n t e r i n g a r i n g i n the 6 p o s i t i o n , which a l r e a d y i s 2 4 - d i n i t r o - s u b s t i t u t e d i s i n t e r e s t i n g . For phenol, t h i s e f f e c t on the a c i d i t y i s 3,82 l o g u n i t s while f o r a n i l i n e t h i s e f f e c t i s 2,82 l o g u n i t s . For diphenylamines an i n t e r m e d i a t e value i s obtained i n the three cases f o r which t h i s work could supply r e l i a b l e d a t a . The d i f f e r e n c e between 2 4 - d i n i " t r o -diphenylamine and 2,Jx, 6 - t r i n i t r odiphenylamine i s 3 4 5 ° T h i s same d i f f e r e n c e i s 3 4 3 between 2 4 4 ' " t r i n i t r o d i p h e n y l -amine . and 2,1|, 6 4 s - t e t r a n i t r o d i p h e n y l a m i n e . A d i f f e r e n c e of 3.1+7 was recorded between 2 4 » 3 1 - t r i n i t r odiphenylamine and 2 4 s 6, 3 ' - t e t r a n i t r o d i p h e n y l a m i n e . The work of Fernandez and .Hepler (59) shows that f o r n i t r o - and chlorophenols the enthalpy change decreases w i t h the standard f r e e energy change. Biggs (60) has determined that f o r phenol, ere s o l s and x v l e n o l s the enthalpy change i n c r e a s e s w i t h the f r e e energy change. T h i s l a t t e r s t a t e -ment a l s o a p p l i e s to protonated n i t r o a n i l i n e s , There i s as yet no such i n f o r m a t i o n on the a c i d e q u i l i b r i a of methyl s u b s t i t u t e d a n i l i n e s . From the above statements i t seems that s p e c i f i c s o l v a t i o n of anions and c a t i o n s w i l l p l a y a l a r g e p a r t i n determining the p o s i t i o n of t h e i r i o n i z a t i o n e q u i l i b r i a , 82 The l a r g e s t e f f e c t noted f o r the e n t r y of a t h i r d n i t r o group occurs i n those diphenylamines where an ortho p o s i t i o n of the second r i n g i s a l r e a d y occupied„ Presumably anion s t a b i l i z a t i o n by s o l v a t i o n i n these compounds i s f a v o r e d compared to s o l v a t i o n s t a b i l i z a t i o n of the molecule. T h i s work shows a d i f f e r e n c e of 1+.10 between 2,1+, 2 ' ,1+' -t e t r a n i t r o d i p h e n y l a m i n e and 2,1+, 6 , 2 ' ,1+' - p e n t a n i t r o -diphenylamine and a d i f f e r e n c e of 1+.09 between 2,1+, 6 , 2 ' ,1+1 -pentanitrodiphenylamine and 2,1+, 6 , 2 1 , 1 + ' , 6 ' - h e x a n i t r o -diphenylamine. 8 3 T a b l e V I E f f e c t o f a d d i t i o n a l s u b s t i t u e n t n i t r o g r o u p s o n a c i d i t i e s o f p h e n o l s , a n i l i n e s a n d d i p h e n y l a m i n e s i n l o g u n i t s . COMPOUND E f f e c t E f f e c t E f f e c t E f f e c t E f f e c t of 2- of 3- of 1+- of 2,14.- of 2,14., 6-n i t r o n i t r o n i t r o d i n i t r o t r i n i t r o A n i l i n e ( 2 . 3 7 ) D i p h e n y l a m i n e ( 1 . 1 3 ) P h e n o l 2 . 7 9 1 . 5 6 ( 2 . 8 8 ) ( 5 . 2 3 ) ( 8 . 0 5 ) ( 2 , 8 0 ) (I4.087) ( 6 . 5 0 ) 2 . 8 5 5 ° 8 9 9 * 7 1 1+ -n i t r o a n i l i n e 2 - n i t r o a n i l i n e 2 - n i t r o -d i p h e n y l a m i n e l l . - n i t r o -d i p h e n y l a m i n e 2 - n i t r o p h e n o l 1 + - n i t r o p h e n o l 3 * 3 7 2 . 0 7 2 . 7 9 2 . 2 5 3.0I+ 2 . 1 9 2 . 8 8 k>05 3 . 1 0 5 . 6 8 5 - 3 7 6 . 9 2 2 , 1 | - d i n i t r o - 2 . 8 2 a n i l i n e 2 , 1 + - d i n i t r o - 3 4 5 d i p h e n y l a m l n e 2 , l + - d i n i t r o p h e n o l 3 . 8 2 2 J + - d i n i t r o-.4.' - ( 3 . 8 2 ) a r n i h o d i p h e n y l a m l n e 2 4 , 3 ' - t r i n i t r 0 - 3 . 1 + 7 d i p h e n y l a m i n e 2 , 1 + 4 ' " t r i n i t r o - 3 4 3 d i p h e m / l a m i n e 84 COMPOUND 2,4,2«,4»-t e t r a n i t r o -diphenylamine 2 ,4 , 6 , 2 ' ,4'-p e n t a n i t r o -diphenylamine Note - compounds are arranged i n order of i n c r e a s i n g a c i d w i t h i n each subgroup. E f f e c t of n i t r o groups e n t e r i n g r i n g 2 of n i t r o - s u b s t i t u t diphenylamlnes. i j . - n i t r o - - - 1 .82 3-59 7-02 diphenylamine 2 , l j . - d i n i t r o - - 1 .21 1.50 3 . 0 1 7 .11 diphenylamine 2 , 4 , 6 - t r i n i t r o - - 1 . 2 3 1 . 5 0 3-66 7 . 7 5 d iphenylamine Table VI (cont.) E f f e c t E f f e c t E f f e c t E f f e c t E f f e c t of 2 - of 3 " of 1+- of 2,4- of 2,4,6-n i t r o n i t r o n i t r o d i n i t r o t r i n i t r o 4 . 10 4 . 0 9 85 Table VII E f f e c t of N - s u b s t i t u t i o n on a c i d i t y of a n i l i n e s S u b s t i t u t e d a n i l i n e N - s u b s t i t u e n t pK a Product diphenylamine pK a a phenyl phenyl phenyl phenyl phenyl p - n i t r o p h e n y l p - n i t r o p h e n y l p - n i t r o p h e n y l p - n i t r o p h e n y l 2 s[(.-dlnitr o-phenyl 2 , I i - d i n i t r o -phenvl 2,k-dinitro-phenyl a n i l i n e (21 . 2 5 ) [(.-nitr o a n i l i n e 18.37 2 - n i t r o a n i l i n e 17*88 2 s [ ( . - d i n l t r o a n i l i n e 15.00 2,1)., 6-tr I n i t r o a n i l i n e 12.20 a n i l i n e (21 . 2 5 ) I4. - n i t r o a n i l i n e 18.37 2 slx-di n i t r o a n i l i n e 15.00 6-tr i n i t r o -a n i l i n e 12.20 a n i l i n e (21 . 2 5 ) [ ( . - n i t r o a n i l i n e 18.37 2 s l x - d i n i t r o a n i l i n e 15.00 diphenylamine (18.25) (3.00) [(.-nitroDPA 15.90 2.1^7 2-nitroDPA 17.57 0.31 2 , 4-dinitroDPA 13.83 1.17 2,I(., 6-tr i n i t r o DPA IO.38 1.82 [4.-nitroDPA 15.90 (5.35) [(.,[).' -dinitroDPA (Iii..08) I4..29 2$[(.,[(.' - t r i n i t r o -DPA 12.33 2.67 2,4, 6,Ii-' - t e t r a n i t r o DPA 8.88 3.32 2 , 4-dinitroDPA 13.83 (7.1|2) 2,14.^14.' - t r i n i t r o -DPA 12.33 6.OJ4. 29[4., 2 ' , i i ' - t e t r a n i t r o DPA 10.82 I4..I8 86 Table VII (cont.) S u b s t i t u t e d Product a n i l i n e - diphenylamine N - s u b s t i t u e n t pK„ pK a pK 2, 1+-dinitro - 2,1+, 6-tr i n i t r o - 2,1+,6,21,1+' -penta-phenyl a n i l i n e nitroDPA 548 12,20. 6,72 2,1+,6-tri- a n i l i n e 2,1+, 6-tr i -n i t r o p h e n y l nitroDPA (10.87) (21,25) 10,38 2,1+, 6 - t r i - 1+ - n i t r o a n i l i n e 2,1+, 6,1+' - t e t r a -n i t r o p h e n y l nitroDPA 949 18.37 8.88 2,1+, 6 - t r i 2,l+-dinitro- 2,1+, 6, 2 ' ,1+' -penta-n i t r o p h e n y l a n i l i n e nitroDPA 15.00 6.72 8.28 2,1+, 6-tr 1- 2,14., 6-tr i n i t r o - 2,l+,6,2'4',6'-n i t r o p h e n y l a n i l i n e hexanitroDPA 12,20 2.63 9.57 where DPA - diphenylamine 87 F I n t e r p r e t a t i o n of S o l u t i o n B a s i c i t y . In t h i s s e c t i o n an attempt w i l l be made to g a i n some understanding of the f a c t o r s i n f l u e n c i n g the b a s i c i t y of the s o l u t i o n s employed i n t h i s work and those employed by other i n v e s t i g a t o r s . F i g u r e 2 3 i s presented as a summary of the p r e s e n t l y a v a i l a b l e H_ values f o r mixed s o l v e n t systems where water i s one of the components. These data are a r e p l o t of m a t e r i a l presented e a r l i e r but are p l a c e d on the same s c a l e f o r easy comparison. An argument w i l l be based l a r g e l y on analogy w i t h s o l u t i o n s of protons i n aqueous media which have been more thoroughly i n v e s t i g a t e d and are b e t t e r understood at t h i s time. The e n t i t y FgO)^ i s c o n s i d e r e d to be the c a t i o n present i n d i l u t e aqueous s o l u t i o n s of proton a c i d s , ( l c ) E i g e n and Maeyer ( 2 1 ) . In c o n c e n t r a t e d ' a c i d s o l u t i o n s i t i s b e l i e v e d that the h y d r a t i o n number of the p r o t o n decreases more or l e s s -r c o n t i n u a l l y u n t i l the bare hydronium i o n , H3O , e x i s t s i n 1 0 0 % s u l f u r i c a c i d s o l u t i o n s (65)« T h i s change a p p a r e n t l y accounts f o r the h i g h hydrogen i o n a c t i v i t y measured i n c o n c e n t r a t e d a c i d s o l u t i o n s . T h i s concept i s g i v e n much weight,by the work of Wyatt (as quoted by B e l l ( l c ) ) and that of Hoegfeldt (66), as w e l l as the Raman measurement's 88 of Young and Walrafen ( 6 7 ) . Hoegfeldt has p l o t t e d H 0 a g a i n s t the a c t i v i t y of water f o r s o l u t i o n s of n i t r i c , h y d r o c h l o r i c , s u l f u r i c , p e r c h l o r i c and hydrobroraic a c i d s of v a r y i n g c o n c e n t r a t i o n s and has found t h a t a l l p l o t s follow- the same curve. Hoegfeldt concludes that when compared at the same water a c t i v i t y the a c t i v i t y c o e f f i c i e n t r a t i o are the same i n a l l these a c i d s . E xperimental work of t h i s type on b a s i c s o l u t i o n s i s p r a c t i c a l l y n o n - e x i s t e n t . B u r w e l l (22) has concluded t h a t a l a r g e i n c r e a s e In the r a t e of change of b a s i c i t y i n s u l f o l a n e - w a t e r s o l u t i o n s c o n t a i n i n g phenyltrimethylammonium hydroxides occurs at the p o i n t where four molecules of water are present f o r each h y d r o x y l i o n . Some of t h i s water may be t i e d up f i r m l y as water of h y d r a t i o n of the s u l f o n e group so that h i s c o n c l u s i o n i m p l i e s that four or l e s s molecules of water are att a c h e d i n t i m a t e l y to each h y d r o x y l i o n . I n c r e a s i n g the s u l f o l a n e content past t h i s p o i n t decreases the water a v a i l a b l e to the h y d r o x y l i o n and r e s u l t s i n a r a p i d l y I n c r e a s i n g h y d r o x y l i o n a c t i v i t y . I t i s more d i f f i c u l t to p i c t u r e the s t o i c h i o m e t r i c h y d r a t i o n of the h y d r o x y l i o n than i t i s f o r the p r o t o n but there seems no doubt that strong hydrogen bonds c o u l d as w e l l as the h y d r a t i o n e q u i l i b r i a of the proton, •18 -17 -16 i x -15 r14 13 r12 FIGURE 23 H- ACIDITY FUNCTION FOR SOME AQUEOUS SOLVENT SYSTEMS • PYRIDINE-WATER X SULFOLANE-WATER • HYDRAZINE-WATER © ETHYLENEDIAMINE-WATER B DIMETHYLSULFOXIDE-WATER MOLE PERCENT SOLVENT IN WATER 20 30 40 50 60 70 100 -19 9 1 be formed to two or more water molecules. Bur w e l l ( 2 2 ) has a l s o measured the water a c t i v i t y i n these mixtures and f i n d s i t to approach one t e n t h of i t s value i n pure water, , I t seems c e r t a i n that t h i s decrease i n water a c t i v i t y e x p l a i n s the enhanced b a s i c i t y of the s o l u t i o n s . The r e s u l t s of the present work show a r a p i d l y I n c r e a s i n g b a s i c i t y a f t e r the p o i n t where the s u l f o l a n e to water mole r a t i o passes 2 : 1 , that i s near 67 p e r c e n t . T h i s p o i n t i s emphasized by p l o t t i n g the H- f u n c t i o n determined a g a i n s t the d e n s i t y of the w a t e r - s u l f o l a n e mixture (Figure 2I4.) . The densit?/ of 67 mole percent s u l f o l a n e i n water i s near I.2I4.. T h i s perhaps i m p l i e s t h a t the s u l f o l a n e I n t i m a t e l y s o l v a t e s two molecules of water and that a f t e r t h i s p o i n t the exce.ss s u l f o l a n e competes w i t h the h y d r o x y l i o n present f o r the a v a i l a b l e water mole c u l e s . Approximate Information on the water a c t i v i t y i n hydrazine-water and ethylenediamine-water mixtures i s a v a i l a b l e from the work of B u r t l e ( 6 8 ) „ T h i s author s t a t e s that the water a c t i v i t y i n these s o l u t i o n s i s approximately one f i f t h of i t s value i n pure water. T h i s i n f o r m a t i o n , coupled w i t h that provided by V i e l a n d and Seward ( 6 9 ) that the h y d r o x y l i o n c o n c e n t r a t i o n i n aqueous hydrazine and ethylenediamine i s probably l e s s than 0 . 0 1 molar, i n d i c a t e s that the f i v e systems under c o n s i d e r a t i o n here may indeed be very s i m i l a r . In the case of the 92 p y r i d i n e and s u l f o l a n e and dimethyl s u l f o x i d e systems i t was necessary to add the h y d r o x y l ion.but f o r hydrazine and ethylenediamine the h y d r o x y l Ion i s present due to the i n t r i n s i c b a s i c i t y of the s o l v e n t molecules themselves. I t Is i n t e r e s t i n g to remember, at t h i s p o i n t , that on a d d i t i o n of a c e t i c a c i d or s u l f o l a n e to aqueous s o l u t i o n s of strong a c i d s an i n c r e a s e d a c i d i t y i s noted. T h i s i s a p p a r e n t l y due to i n c r e a s e d hydroxonium i o n a c t i v i t y which i s i n t u r n due to decreased s o l v a t i o n of the p r o t o n . T h i s statement a p p l i e s a f o r t i o r i to a s o l u t i o n of hydrogen c h l o r i d e gas i n benzene which i s a much stronger a c i d than the same m o l a r i t y of hydrogen c h l o r i d e i n water ( 7 0 ) o U n f o r t u n a t e l y , the above p i c t u r e , though p l a u s i b l e , i s not based on e x t e n s i v e evidence. Much work Is needed on the p h y s i c a l p r o p e r t i e s of 'the s o l u t i o n s i n v o l v e d . From t h i s p i c t u r e the c o n c l u s i o n may be drawn that a d d i t i o n of a solvent to aqueous s o l u t i o n s of h y d r o x y l ions w i l l i n c r e a s e the b a s i c i t y of the mixture. The amount of t h i s i n c r e a s e w i l l depend on the e f f e c t i v e n e s s w i t h which the added so l v e n t can compete with h y d r o x y l ions Tor the a v a i l a b l e water mole c u l e s . I n t e r e s t i n g r e l a t e d o b s e r v a t i o n s have r e c e n t l y been medvj by Cram (71) (72) and Parker ( 7 3 ) . Cram measured the r a t e of base c a t a l y s e d ' r a c e r n i z a t i o n of (-¥) 2-nethyl-3~Phenylpropionitrile i n s o l u t i o n s of 9 3 dimethyl s u l f o x i d e of v a r y i n g c o n c e n t r a t i o n s i n methanol. He employed a l k a l i methoxides as bases i n t h i s system and found r a p i d l y i n c r e a s i n g r a t e s as the c o n c e n t r a t i o n of dimethyl s u l f o x i d e i n methanol was i n c r e a s e d . Cram s t a t e d i n e x p l a n a t i o n of the enhanced b a s i c i t y of h i s s o l u t i o n s "Thus dimethyl s u l f o x i d e competes wi t h methoxide anions f o r the remaining methanol molecules and i n e f f e c t decreases the c o n c e n t r a t i o n of methanol a v a i l a b l e to methoxide ion"„ T h i s statement i s seen to be an exact p a r a l l e l to our b a s i c i t y e x p l a n a t i o n . Parker ( 7 3 ) has found n u c l e o p h i l i c aromatic s u b s t i t u t i o n to be up to 1 0 ^ times as f a s t i n nine d i p o l a r a p r o t i c s o l v e n t s than i n three p r o t i c s o l v e n t s . He found that the r a t e constant i n c r e a s e d as the hydrogen bonding c a p a c i t y of the s o l v e n t decreased i n a s e r i e s from methanol to dimethyl acetamide. At present there i s a l a c k of k i n e t i c - a c i d i t y c o r r e l a t -ions but i t i s to be hoped t h i s i n f o r m a t i o n w i l l be f o r t h -coming In the near f u t u r e and l e a d to f u r t h e r understanding of the s u b j e c t . F l u o r n o y and Wilmarth (7^+) have i n v e s t i g a t e d the c a t a l y t i c e f f i c i e n c y of concentrated aqueous a l k a l i . They s t u d i e d the r a t e of ortho-para hydrogen c o n v e r s i o n i n concentrated aqueous a l k a l i and i n s i x t y weight percent aqueous s o l u t i o n s of hydrazine and ethylenediamine. For the l a t t e r s o l u t i o n s the r a t e was comparable to that measured i n 0.1 molar potassium hydroxide at the same r temperature. In c o n t r a s t , the r a t e of c o n v e r s i o n i n 18 m o l a l a l k a l i was found to be 5000 times that of a one mola s o l u t i o n i m p l y i n g an II_ value of 17 • 7 (assuming one molal equals 1I4.) . These r e s u l t s c o n t r a s t w i t h the comparison of 0,1 molar sodium hydroxide and hydrazine or ethylenediamine s o l u t i o n s by i n d i c a t o r methods. Furt h e r r a t e - e q u i l i b r i a c o r r e l a t i o n s are needed to provide more l i g h t on t h i s problem, Edward (98) has r e c e n t l y determined the H-f u n c t i o n f o r aqueous sodium hydroxide up to 5 molar. These determinations were based on the a c i d i o n i z a t i o n e q u i l i b r i a of thioacetami.de whose pK a value he determined to be 1 3 H i s values f o l l o w l o g [pH~] c l o s e l y to about 2 molar and then d e v i a t e i n the d i r e c t i o n of higher h y d r o x y l i o n a c t i v i t y r e a c h i n g approximately 15 i n 5 molar sodium h y d r o x i d e . I t i s i n t e r e s t i n g t h at these r e s u l t s are Intermediate between those r e p o r t e d i n t h i s work f o r aqueous l i t h i u m hydroxide and aqueous benzyltr.lmethylammonium hydroxide , 9 5 G Study of presumed K u c l e o p h i l i c A d d i t i o n . A p r e l i m i n a r y study was made on the r e a c t i o n of the f o l l o w i n g compounds i n b a s i c systems; t r i n i t r o b e n z e n e ; N,N-dimethylpicramide; p i c r a t e anion and ni t r o b e n z e n e . These compounds cannot l o s e a pro t o n under the c o n d i t i o n s used and t h e i r mode of r e a c t i o n may be c o n t r a s t e d w i t h these accepted as simple Bronsted a c i d s i n t h i s work. A l l of these compounds r e a c t i n s u f f i c i e n t l y b a s i c media as judged by the presence of a new a b s o r p t i o n band at longer wavelengths. No evidence i s presented which helps to i d e n t i f y the species produced but i t i s assumed that they r e s u l t from the a d d i t i o n of one or more h y d r o x y l ions or other n u c l e o p h i l i c species to the aromatic r i n g i n the manner of a Meisenheimer complex ( 7 5 ) ° These compounds w i l l be discussed, i n t u r n . P i c r i c a c i d i n methanol absorbs at 3 5 3 m u ( € = 1 7 > 6 0 0 ) and i n lfo aqueous hydrazine at 353^u (€ = 19s 2 0 0 ) . T h i s species i s presumably i n both cases the p i c r a t e anion since the spectrum i n 0 . 0 1 N sodium hydroxide i s very s imllar„ A species absorbing at 380mu ( € = l 6 5 7 0 0 ) i s obtained i n a system 9 5 mole percent s u l f o l a n e i n water c o n t a i n i n g 0.01 molar tetramethylammonium hy d r o x i d e . T h i s species forms at a f i n i t e r a t e and the r e a c t i o n may be r e v e r s e d by a d d i t i o n of water so that the spectrum approximates that 96 obtained i n 0 o 0 1 molar sodium h y d r o x i d e . T h i s 380mu s p e c i e s i s formed completely i n f i v e minutes and remains s t a b l e f o r at l e a s t twenty four hours. When methoxide io n was added to the system ( 9 5 mole percent s u l f o l a n e i n methanol c o n t a i n i n g 0 . 0 1 molar sodium methoxide) a new sp e c i e s absorbing at .4.7 8mu ( £ « 1 3 , 2 0 0 ) was produced. This s p e c i e s gave the 380mu species p r e v i o u s l y d e s c r i b e d when ' water was added to t h i s system. N,N-dimethylpicramlde absorbed at 370mu i n methanol (€. m a x p 1 1 , 5 0 0) . In one normal sodium hydroxide t h i s compound r e a c t e d to produce a s p e c i e s absorbing near l+lOmu (€. * 1 2 , 9 0 0 ) o T h i s r e a c t i o n was complete i n about 30 minutes. The " a b s o r p t i o n at t h i s wavelength then began to decrease and an i n c r e a s e i n a b s o r p t i o n at lower wavelengths was noted. In the s u l f o l a n e system ( 9 5 mole percent s u l f o l a n e i n water c o n t a i n i n g 0 . 0 1 molar tetramethylammonium hydroxide) a species was formed i n i t i a l l y absorbing near J+lOmu (£ = 1 9 , 3 0 0 ) . The maximum a b s o r p t i o n a t ' t h i s wavelength was a t t a i n e d a f t e r 6 minutes. A f t e r I4.5 minutes the p o s i t i o n of maximal a b s o r p t i o n had moved to lj.32mu and the e x t i n c t i o n c o e f f i c i e n t had dropped to ( 1 6 , 2 0 0 ) . T h i s s pecies continued to r e a c t and a f t e r 3 hours a broad f l a t maximum at s l i g h t l y s h o r t e r wavelength was observed-. A l l of-these s p e c t r a were r e v e r s i b l e by a d d i t i o n of water to d u p l i c a t e the spectrum found i n d i l u t e sodium hydroxide (l+OOmu). When methoxide was present i n the system ( 9 5 mole percent 97 s u l f o l a n e I n methanol c o n t a i n i n g 0 . 0 1 molar sodium methoxide) a s p e c i e s a b s o r b i n g at I4.28.mu- (£ = 2lj . j800) was formed r a p i d l y . T h i s a g a i n c o u l d be r e v e r s e d by ad'dition of water t o ap p r o x -imate the sodium h y d r o x i d e spectrum. .• S y m m e t r i c a l t r i n i t r o b e n z e n e was examined i n a v a r i e t y o f b a s i c s o l v e n t systems and a g r e a t v a r i e t y of s p e c i e s noted, depending on t i n e , i d e n t i t y of the base and the b a s i c i t y of the s o l u t i o n . I n one normal sodium h y d r o x i d e Xmax was I4.6l4.mu w i t h £ - 1 6 , 3 0 0 a f t e r f i f t e e n m i n u t e s . The spectrum was time dependent and the ^ m a x moved w i t h time to l o n g e r w a v e l e n g t h . The maximum a b s o r p t i o n was r e a c h e d a f t e r one hour a f t e r w h i c h p o i n t the a b s o r p t i o n began to s l o w l y d r o p . A f t e r twenty f o u r hours the p o s i t i o n of Xmax w a s l)-78mu. When the s u l f o l a n e system was used ( 9 5 mole p e r c e n t s u l f o l a n e i n water c o n t a i n i n g 0 o 0 1 molar tetramethylammonium h y d r o x i d e ) a peak at 5 l 7 m u (£.= 18,14.00) was produced r a p i d l y . The r e v e r s a l of t h i s s p e c i e s on a d d i t i o n of water was slow and was not i n v e s t i g a t e d c l o s e l y . When methoxide i o n was p r e s e n t the spectrum showed two d i s t i n c t sharp a b s o r p t i o n peaks near 5 l 3 m u and l(.37mu. These peaks were o b t a i n a b l e I n s u l f o l a n e - m e t h a n o l w i t h added sodium methoxide or p h e n y l -trimethylammonlum h y d r o x i d e . A l l these s p e c i e s changed on a d d i t i o n of water but the r e s u l t s a r e ' c o m p l i c a t e d and have not been i n v e s t i g a t e d c a r e f u l l y . When 2 5 - 7 5 v.v. methanol water made one normal i n sodium h y d r o x i d e was used as the s o l v e n t a time dependent 98 spectrum X m a x l|.87mu was o b s e r v e d . When the s o l v e n t was changed t o 7 5 - 2 5 methanol-water or 100% methanol s t i l l one normal i n sodium h y d r o x i d e two a b s o r p t i o n maxima a t J4.2J4.mu and [|.9l+mu. were o b s e r v e d . T h i 3 s p e c i e s r e v e r s e d s l o w l y when water was added. N i t r o b e n z e n e was not i n v e s t i g a t e d beyond n o t i c i n g t h a t a time dependent c o l o r a t i o n i s produced when i t i s a c t e d on by h i g h l y b a s i c systems. Brockman and Meyer ( 7 6 ) have c a r r i e d out p o t e n t i o m e t r i c t i t r a t i o n s of n i t r o b e n z e n e , ' t r i n i t r o b e n z e n e and p i c r i c a c i d . They .used the sodium s a l t of ethanolamine d i s s o l v e d i n e t h y l e n e d i a m i n e as the t i t r a n t . For t r i n i t r o b e n z e n e t h r e e e q u i v a l e n t s of base were used w i t h o u t any i n d i c a t i o n of an i n f l e c t i o n p o i n t when the observ e d E.M.F. was p l o t t e d a g a i n s t amount of base u s e d . T h i s i m p l i e s the c o e x i s t e n c e of t h r e e s p e c i e s r e s u l t i n g from a d d i t i o n o f one, two or t h r e e m o l e c u l e s of the n u c l e o p h i l e . A s i m i l a r s i t u a t i o n may e x i s t i n the systems d e s c r i b e d above. T h i s would l e a d t o a c o m p l i c a t e d system of o v e r l a p p i n g s p e c t r a . N i t r o b e n z e n e was i n e r t i n Brockman and Meyer's system. The i m p o r t a n t p o i n t a b o ut.the above o b s e r v a t i o n s i s t h a t a l l r e a c t i o n s r e q u i r e d a f i n i t e time i n c o n t r a s t t o the a p p a r e n t l y i n s t a n t a n e o u s r e a c t i o n of those compounds we have a c c e p t e d as B r o n s t e d a c i d s . 2,1.)., 6 - t r i n i t r o a n i l i n e : When d i s s o l v e d i n a h i g h l y b a s i c system ( 9 5 mole p e r c e n t s u l f o l a n e i n water c o n t a i n i n g 99 0.01 molar tetrame thylammonium hydroxide) 2,1)., 6-tr i n i t r o-a n i l i n e showed two peaks (I|.07mu and approximately ^OOmu) . Thi s species r e v e r s e d r a p i d l y on a d d i t i o n of s u f f i c i e n t water to adjust the Ii_ to approximately l 6 . T h i s spectrum was i d e n t i c a l w i t h that accepted i n t h i s work as the anion spectrum. T h i s spectrum remained constant when the H- was subsequently a d j u s t e d to approximately 1I4.. Then on a d d i t i o n of s u f f i c i e n t h y d r o c h l o r i c a c i d to n e u t r a l i z e the base present the spectrum reproduced c l o s e l y that measured i n water. The species accepted as anion was produced a p p a r e n t l y i n s t a n t a n e o u s l y and was s t a b l e and a l s o r e v e r s e d i n s t a n t a n e -o u s l y . T h i s i n t e r p r e t a t i o n i s e s s e n t i a l to the method used i n t h i s work to e s t a b l i s h the H_ f u n c t i o n . I t can be seen that the behaviour of 2,l\.} 6-tr i n i t r o a n i l i n e c o n t r a s t s s t r o n g l y w i t h that of t r i n i t r o b e n z e n e . ¥/hen 2 S LL.9 6-tr i n i t r o a n i l i n e was allowed to r e a c t i n s u l f o l a n e c o n t a i n i n g methoxide i o n a spe c i e s was produced w i t h Xmax ~ i-!-93mu and £. = 12 7100. T h i s c o u l d be r e v e r s e d by the a d d i t i o n of water to produce the anion spectrum and the molecule spectrum by the a d d i t i o n of h y d r o c h l o r i c a c i d . 2 BI4., 6-tr i n i t r otoluene : When t h i s compound i s d i s s o l v e d i n one normal sodium hydroxide i n water a species absorbing at [(.pOmu r e s u l t s . I t i s not c l e a r whether t h i s s p e c i e s i s the anion or i s the r e s u l t of n u c l e o p h i l i c a t t a c k . C a l d i n and Long (77) b e l i e v e t h a t t h i s s p e c i e s i s the anion 100 When s u l f o l a n e - c o n t a i n i n g h y d r o x i d e as a base i s used a s p e c i e s a b s o r b i n g a t 528mu i s ' f u l l y formed i n about two m i n u t e s . T h i s s p e c i e s decays v e r y s l o w l y and i s r e v e r s e d v e r y s l o w l y on a d d i t i o n of w a t e r . Even a t an H_ comparable t o t h a t o f one normal sodium h y d r o x i d e ( 1 3 - 5 ) the p o s i t i o n of maximal a b s o r p t i o n i s s t i l l 528mu i n 'contrast t o the Jx^Omu mentioned above. When methoxide i o n i s used as the base i n s u l f o l a n e the a b s o r p t i o n maximum i s now $-V8mu. T h i s s p e c i e s has a much g r e a t e r e x t i n c t i o n c o e f f i c i e n t t han the 528mu s p e c i e s and r e v e r t s t o the £28mu s p e c i e ^ r a p i d l y on a d d i t i o n of w a t e r . N - a l k y l - 2 , 1 ) . , 6 - t r i n i t r o a n i l i n e s : The s p e c t r a l d a t a f o r N-me t h y 1-2 ,1). , 6 - t r i n i t r o a n i l i n e are r e c o r d e d i n Ta b l e V I I I . Analogous b e h a v i o u r i s found f o r the N - e t h y l , N - b u t y l and N - t e r t i a r y b u t y l compounds. T h i s b e h a v i o u r i s e x a c t l y analogous t o t h a t f o r p i c r a m i d e . ?/hen the pK a d e t e r m i n a t i o n s f o r the s e compounds were c a r r i e d out i t was found t h a t a p l o t of [ A " ] l o g — a g a i n s t pH, w h i c h s h o u l d have a u n i t s l o p e , a c t u a l l y [AH] • -had"a s l o p e of l . k . For t h i s r e a s o n the pK a d e t e r m i n a t i o n s are not c o n s i d e r e d r e l i a b l e . A l l the v a l u e s o b t a i n e d ranged between 1 1 . 5 and 1 1 . 8 but the s e are p r o b a b l y low and the a c i d i t y of t h e s e compounds p r o b a b l y not- f a r from t h a t o f p i c r a m i d e . One would e x p e c t e l e c t r o n r e l e a s e by the a l k y l group t o be a c i d weakening. A l s o the pr e s e n c e 1 0 1 of the a l k y l group probably I n t e r f e r e s w i t h i o n s o l v a t i o n . T h i s spectrum was r e v e r s i b l e when composition was changed to 80 mole percent s u l f o l a n e at ij.30mu £ = 1 6 , 2 0 0 . When the base present was e x a c t l y n e u t r a l i z e d u s i n g . h y d r o c h l o r i c a c i d a species was produced. X m a x - 3 5 2 m u . £ ~ 1 2 , 2 0 0 In 95% s u l f o l a n e i n methanol c o n t a i n i n g 0 . 0 2 molar sodium methoxide X f f l a x ~ 503mu £ = 2l | . , 1 0 0 . On a d d i t i o n of water t h i s s p e c i e s r e v e r s e d to X m a x — l+17mu • 6 = 1 8 , 6 0 0 . Slough ( 8 l ) has r e c e n t l y a t t r i b u t e d the 370mu band of 2 , Ij., 6 - t r i n i t r qdiphenylamine to a t r a n s i t i o n of the lone p a i r on the n i t r o g e n to an oxygen atom of the n i t r o group. Many of the N - s u b s t i t u t e d 2,1]., 6 - t r i n i t r o a n i l i n e s show two separate peaks when t h e i r s p e c t r a are re c o r d e d i n methanol or e t h a n o l .• The .observed values In t h i s work are l i s t e d together w i t h some taken from Brownlie (82) f o r comparison. 102 Table VIII S p e c t r a l data f o r N-me thy 1-2, 1+, 6-tr i n i t r o a n i l i r i e . MOLECULE Solvent " -Methanol ' ; Water pH 7 . 6 B u f f e r pH 10.[(.2 ( l % h y drazine i n water) pH 11.1.5 B u f f e r ANIONS 5% h y d r a z i n e i n water - pH IT.10 22.6% hydrazine i n water 1 normal•aqueous sodium hydroxide 0.1 molar sodium methoxide i n methanol 1 molar phenyltrimethylammonium hydroxide i n methanol 95 mole percent s u l f o l a n e i n water 0.011 molar tetramethylammonium hydroxide max 337 1+08 .31+6 1+20 314-7 1+18 314-8 31+-9 14-13 398 3 9 9 3 9 5 1+20 1+16 513 tmax 1.3,900 5,100 1-3, 000 5,700 13,000 6,500 13,000 94oo 12,800 10,000 16,900 18,200 9,650 19,850 15,200 15,200 103 Table IX S p e c t r a l data f o r N-substituted -2 , ]+ , 6-tr i n i t r o a n i i i n e s i n methanol"or 95% ethanol-water. N - s u b s t i t u e n t T e r t i a r y b u t y l Dimethyl B u t y l E t h y l Methyl Hydrogen Amino' Phenyl N i t r o A max 31+90 3760 3360 3370 3370 3180 3560 t max 10,900 12,600 18,200 ll+,100 ll+, 000 11,000 10,000 max max J+100.(SH) 6950 l+ioo 5700 4080 60'30 3920 7000 I4.O8O 7050 1+100 (SH) 7000 3680 - 811+0 3520 8 0 0 0 Note SH - shoulder" 10^ VI Suggestions f o r Future Research. Work i s underway i n t h i s l a b o r a t o r y u s i n g some of the i n d i c a t o r s whose a c i d i t y has been determined i n t h i s work to attempt improvement i n the accuracy of the H Q s c a l e In s u l f u r i c a c i d more concentrated 1 than 70%. E x t e n s i o n of the pKa - PKBH"** c o r r e l a t i o n may y i e l d i n f o r m a t i o n u s e f u l i n understanding the a c i d c h a r a c t e r of these s o l u t i o n s . Work i s a l s o underway to i n v e s t i g a t e ' the dimethyl s u l f o x i d e - methanol system of Cram (7l)» R e s u l t s I n d i c a t e t h a t a s u c c e s s f u l r a t e - e q u i l i b r i u m c o r r e l a t i o n w i l l be made. U s e f u l i n f o r m a t i o n may be obtained by a- c a r e f u l study of those compounds which a p p a r e n t l y r e a c t by h y d r o x y l i o n a d d i t i o n . I t may be p o s s i b l e to develop an a c i d i t y f u n c t i o n which w i l l r e l e t s the e q u i l i b r i a of those compounds which r e a c t i n t h i s manner. Information i s needed on the p h y s i c a l p r o p e r t i e s of the s o l u t i o n s I n v e s t i g a t e d i n t h i s work. The v a r i a t i o n s of d i e l e c t r i c constant, water a c t i v i t y and heat of. mixing w i t h c o n c e n t r a t i o n seem p a r t i c u l a r l y important to an under-standing of the measured b a s i c i t i e s . Of p a r t i c u l a r importance Is the study of the n i t r a t e d hydrocarbons. Compounds such as 2,4> 6 , 2 ' ,14.' - p e n t a n i t r o-diplienylmethane and 2 ,4 , 2 ' ,}.\.' -t e t r a n i t r o d i p h e n y l m e t h a n e are a v a i l a b l e . I t Is probable t h a t these compounds are' a c i d s i n aqueous s o l u t i o n . Since carbon a c i d s i o n i z e at a 1 0 5 f i n i t e r a t e i t i s probable that d i r e c t measurement of the energy of a c t i v a t i o n of the i o n i z a t i o n process w i l l be p o s s i b l e f o r these compounds. A comparison of the r e l a t i v e a c i d i t i e s of these compounds wit h those of the corresponding diphenylamines should provide more u s e f u l i n f o r m a t i o n -Nuclear magnetic resonance s t u d i e s of the anions and n e u t r a l molecules s t u d i e d i n t h i s work should provide u s e f u l i n f o r m a t i o n . The p r o t o n s h i e l d i n g parameters should provide i n f o r m a t i o n about d e l o c a l i z a t i o n of charge i n the r i n g s f o l l o w i n g i o n i z a t i o n . T a f t ( 9 9 ) has - r e c e n t l y shown t h a t the f l u o r i n e resonance s i g n a l can be used to measure a c i d i t y constants of aromatic a c i d s when the f l u o r i n e atom i s a r i n g s u b s t i t u e n t . T h i s technique may p o s s i b l y be a p p l i e d to proton resonances. P r e l i m i n a r y experiments . show that measurements of t h i s type may be p o s s i b l e on the three mononitrophenols In deuterium oxide s o l u t i o n . An X - r a y study of the potassium s a l t of h e x a n i t r o -diphenylamine i s being c a r r i e d out i n t h i s department. T h i s study may provide i n f o r m a t i o n r e g a r d i n g the h y b r i d i z a t i o n of the c e n t r a l n i t r o g e n atom i n t h i s compound. I t i s worth n o t i n g t h a t the H~ value and the water a c t i v i t y may be v a r i e d independently i n the s o l v e n t systems under c o n s i d e r a t i o n . T h i s may be done by s u i t a b l e v a r i a t i o n of the added base c o n c e n t r a t i o n . T h i s f a c t may prove u s e f u l i n k i n e t i c s t u d i e s of r e a c t i o n s which are b e l i e v e d to have a"two stage mechanism i n v o l v i n g the above.two i o 6 q u a n t i t i e s . K i n e t i c c o r r e l a t i o n s w i t h the developed a c i d i t y f u n c t i o n are needed.. An immediate p o s s i b i l i t y i s the s e r i e s of s u b s t i t u t e d b e n z y l cyanides whose base c a t a l y z e d r a t e of condensation w i t h ketones has been measured ( 100) . I t -may be p o s s i b l e to measure the i o n i z a t i o n e q u i l i b r i a of these compounds and compare them w i t h the measured r a t e s . 107 VII Appendix. A Experimental Data on Compounds used as I n d i c a t o r s . 2,i|, 6, 2 ',[). 1, 61 -hexanitrodiphenylamine was prepared a c c o r d i n g to Hoffmann and Dame (90). M e l t i n g Point 2l4.5-7°dec. a f t e r r e c r y s t a l l l z a t i o n from' concentrated n i t r i c a c i d , A change i n c r y s t a l s t r u c t u r e near 180° was noted. L i t . M.P. 2I4.O-50 dec. (90). MOLECULAR FORM Solvent X max Benzene' - 382 Aqueous h y d r o c h l o r i c a c i d 390 pH -'0.7 \ E t h a n o l i c h y d r o c h l o r i c a c i d 377 €-max Reference 16,300 T h i s work 16,000 T h i s work 17,000 (83) A N I O N Water G l y c i n e b u f f e r pH 8 .I4.8 O o l N sodium hydroxide pH 12.88 50-50 p y r i d i n e - w a t e r a l k a l i n e e t h a n o l 14.25 22,900 T h i s work 14.26 25, 000. T h i s work 14-26 25,000 T h i s work 14.27 2l+,500 T h i s work I 4 . l l 29,000 (83) 108 There i s u n c e r t a i n t y r e g a r d i n g the pKa of t h i s a c i d . Kertes and Goldschmidt ( 8 8 ) obtained an apparent pK a of O . 3 5 i n 70% dioxane water by p o t e n t i o m e t r i c t i t r a t i o n of the molecular form w i t h a l k a l i . They r e p o r t e d a t y p i c a l s t r o n g base strong a c i d t i t r a t i o n curve. ' Treadwell and Hepenstrick ( 8 9 ) r e p o r t 8.1.5 which they obtained by t i t r a t i o n of the sodium s a l t of h e x a n i t r o d i p h e n y l -amine w i t h h y d r o c h l o r i c a c i d . In the present work the spectrum of the anion was measured c a r e f u l l y i n s o l u t i o n s whose pH ranged from i | to 11,. The spectrum was i d e n t i c a l w i t h i n experimental e r r o r i n a l l these s o l u t i o n s . No change was d e t e c t a b l e near 8 . l 5 » the r e p o r t e d pKa• I t i s p o s s i b l e t h at some' thermodyhamically u n s t a b l e s p e c i e s i s formed by r a p i d n e u t r a l i z a t i o n of the anion w i t h the strong a c i d i n analogy with-, n i t r ome thane , and t r i s p a r a n i t r ophenyl-methane. I t must be p o i n t e d out, however, that the i o n i z a t i o n of hexanitrodiphenylamine' i n water i s a p p a r e n t l y i n s t a n t a n e o u s . No examination of the phenomenon r e p o r t e d •by Treadwell and'Hepenstrick has been made i n t h i s work. The pKa of t h i s compound was determined i n d i l u t e h y d r o c h l o r i c a c i d and p h t h a l a t e 'buffers. 109 B u f f e r pH 2.32 ' 3.02 3.1+5 3.82 I+.79 l o g -0.550. 0.1+86 0.782 '1.236 [ A H ] pK a 2.87 2.53 2.67.. . 2.58 The pK a was determined to be 2 . 6 3 g r a p h i c a l l y . 2 , 6-dichloro-J+-nitrophenol; M.P., 1 2 5 - 6°after r e c r y s t a l l i z a t i o n from e t h a n o l . L i t . M.P., 1 2 5 ° ( 8 £ ) . X max f o r molecule was 3Hrou i n 0.005N h y d r o c h l o r i c a c i d w i t h 6. max - 1 . 5 , 0 0 0 . - . A max f o r anion i n 0.1N sodium hydroxide was 397mu with, G m a x = 2 9 , 3 0 0 . ' . B u f f e r pH' 2 . 3 2 3.O3 3.1+5 •• 3 . 9 0 I + . 3 9 [A " J log - — t - 1 . 0 3 -0,1+9 -0.05 0.5I+ 0 . 9 6 ~ [ A H ] P K a 3 . 3 5 3 . 5 2 3 . 5 0 3 . 3 6 3 4 3 The pKa was determined g r a p h i c a l l y to be 3.1+8-2,1)., 6 , 2 ' ,1+' -pentanitrodiphenylamine : Prepared accord i n g . t o Van Duin and Lennep ( 9 1 ) M.P., I 9 6 ~ 7°after r e c r y s t a l o l i z a t i o n from g l a c i a l a c e t i c a c i d . L i t . M.P., 1 9 6 - 7 ( 9 1 ) • 110 MOLECULAR FORM Solvent Benzene A c i d i c e t h a n o l A max £ max 395 378 17,500 18,900 Reference T h i s work, (83) ANION Aqueous g l y c ine b u f f e r I4.8O pH 12.5 • ; 50-50 pyr i d ine-water • 1x80 25,-600 25, 300 T h i s work T h i s work, B u f f e r pH •_ 6-02 6.1x1 6.80 7.00 7.19 7.61 l o g [AH] pK a -0.68 -0.27 -0.06 O.32 0.1x3 6.82 6.70 6.-68 6.74 6.68 6.76 6.79 The pK a determined g r a p h i c a l l y was 6.72. 2,lx, 6,1L 1 - t e t r a n i t r o d i p h e n y l a m i n e : Prepared a c c o r d i n g o to Van Duin and Van Lennep. (91). M.P., 221-2 a f t e r o r e c r y s t a l l i z a t i o n from ethanol.M.P., 223 (91). For the molecular form: Amax i n benzene = 377niu w i t h € max -•17, 500.- , ' _ . ' For the anion Amax — l\.6^mu i n g l y c i n e b u f f e r pH = 12.5 w i t h € =2 3,800. " ' " Amax i n p y r i d i n e - w a t e r . 50-50 made 0.01 molar i n I l l p h e n y l t r ime thylammonium hydroxide = l+80mu w i t h £ max - 2 9 , 2 0 0 . 8.1+8 8 . 8 2 9 . 2 9 1 0 . 0 8 1 0 . 3 7 -O .39 0 . 0 9 0 . 5 1 1 . 0 6 8 . 8 7 . 8 . 7 3 8 . 7 8 ' 9 . 0 2 The pK a determined g r a p h i c a l l y was 8 . 8 8 . 2 , Ix , 6 , 3 ' - t e t r a n i t r o d i p h e n y l a m i n e : Prepared a c c o r d i n g o to Van Duin and Van Lennep ( 9 1 ) ' . M.P. was 2 1 1 - 2 1 3 a f t e r 0 r e c r y s t a l l i z a t i o n from e t h a n o l . L i t . M.P., 2 1 3 ( 9 1 ) . X m a x f o r the molecular form was 337mu i n benzene w i t h £max = 2 0 , 7 0 0 . The a n i o n i n p y r i d i n e - w a t e r 5 0 - £ 0 made - 0 . 0 1 molar i n tetramethylammonium. hydroxide had A m a x = lilxlmu w i t h £ m a x = 2 6 , 0 0 0 . 9 . 7 0 1 0 . 0 8 IO . 3 7 1 0 . 8 3 0 . 6 7 1 . 1 8 1 . 3 2 9 . 0 3 8 . 9 0 9 . 0 5 The pKa determined g r a p h i c a l l y was 9 « l 5 « B u f f e r pH l o g 7 T [AH] pKa ' B u f f e r pH 7 . 0 0 ' 8.1+8 8 . 8 2 9 ' . 2 9 M l o g - — _ - 1 . 9 2 - 0 . 8 8 -O .38 0.11+ [AH] pK a 8 . 9 2 9 . 3 6 9 . 2 0 9 . 1 5 112 2,ii, 6-tr i n i t r od Iphenylamine : Prepared a c c o r d i n g ' the method of Hantzsch (92). M .P. was 179-l8 l°after r e c r y s t a l l i z a t i o n from ethano-l. L i t . M.P. 177°(92). MOLECULAR FORM Solvent A m a x £max Reference Benzene 36O 13,100 T h i s work Methanol 368 13,000 T h i s work Water • 372 . 13,100 T h i s work B u f f e r pH 9 365 13,650 (13) E t h a n o l 367 13,300 (83) ANION G l y c i n e b u f f e r p H 12*5 I4.50 19,000 T h i s work 0 . 1 N sodium hydroxide J4.I4.5 p H 12,88 19,000 T h i s work Pyr i d ine-water 50-.50 J4.5I4-0.01 molar i n t e t r a m e t h y l -ammoniumhy dr ox1de 19,650 T h i s work pH 12 b u f f e r - Itii.^ 20,600 (13) 113 B u f f e r pH 10.08 I O . 3 7 10.83 11.05 .11.58 [A-1 l o g -0.30 0.03 O . 3 9 0.62 1.09 [AH] pK a 10..38 '. IO . 3 I 1 10.1+1+ 10.1x3 10.1x9 The pKa determined g r a p h i c a l l y was 10 .3 8 . T h i s pK a was p r e v i o u s l y determined by Schaal (10) who found 10.20. 2,1+, 2 1 ,1+' - t e t r a n i t r o d i p h e n y l a m i n e : Prepared a c c o r d ! to Hoffmann and Dame (90). M.P., l96-8°after r e c r y s t a l -l i z a t i o n from e t h a n o l . L i t . M.P., 199° (90)'l MOLECULAR FORM Solvent Xmax €. max Reference Benzene 1+06 21,800 .This work Water 1+13 21,200 T h i s work 0.1N h y d r o c h l o r i c a c i d l a 3 •21, 000 T h i s work G l y c i n e b u f f e r pH 8.1+8 14.13 21,200 T h i s work Et h a n o l 1+01 22,700 (83) ANION 0.1N sodium hydroxide pH 12.88 510 29,000 T h i s work P y r i d i n e -water 50-50 O'.OIM t e t r a m e t h y l -525 30,500 T h i s work ammonium hydroxide' 111+ B u f f e r pH 9-29 10.08 10.37 10.83 11.05 11.58 12.20 (VI l o g ^ — - -1.72 -0.80 -0.43 • - o . o i 0.29 o.64 1.28 [ A H ] pK a 11.01 10.88 10.80 10.84 IO.76 10.94 10.92 The pK a determined g r a p h i c a l l y was 10.82. 2 , 4 , 6 - t r i n i t r o ~ 4 1 - a m l n o d l p h e n y l a m i n e : Prepared a c c o r d -.0 ing to H e r t e l and Romer (93).- M.P. was 188-189.5 a f t e r o r e c r y s t a l l i z a t i o n from aqueous e t h a n o l . L i t . M.P.,l89«5 (93) MOLECULAR FORM Solvent A max max r e f e r e n c e 10 mole % s u l f o l a n e i n 420 water pH 8.82 b u f f e r 4l0 11,800 T h i s work 10,500 (93) ANION 10 "mole t s u l f o l a n e i n -470 water and t e t r a m e t h y l -ammonium hydroxide 0.1N sodium hydroxide 450 1 9 , 3 0 0 T h i s work 18,000 T h i s work 115 B u f f e r pH - 8.82 10.37 10.89 12.52 l o g - 1 - -0.27 -0.11 [ A H ] " ' . pK a - 10.64 11.00 T h i s d e t e r m i n a t i o n can only be regarded as approximately c o r r e c t . The compound i s extremely i n s o l u b l e i n b u f f e r s o l u t i o n s and the molecule spectrum and the anion spectrum are both very broad and are c l o s e t o g e t h e r . Even though 10 cm. c e l l s were used a completely s a t i s f a c t o r y d e t e r m i n a t i o n c o u l d not be made by t h i s method. However, the pK a value i s c e r t a i n l y w i t h i n 0.5 u n i t of the value we have used. pK a = 10.82. 2,lij 6 - t r i n i t r o a n i l i n e : M.P., l92-3°after r e c r y s t a l l i z a t i o n from ethanol.' L i t . M.P., '192-195°(84) 0 MOLECULAR FORM Solvent Amax £ m a x r e f e r e n c e Methanol - 318 11,800 T h i s -work ii08 7,140 T h i s work 50-50 p y r i d i n e - w a t e r 330 • 11,900 T h i s work iil5 • 5,46o- T h i s work 50-50 s u l f o l a n e - w a t e r 328 11,000 T h i s work 417 . 6,000 T h i s 'work 116 ANION S o l v e n t /\ max c£ max "re f e r e n c e IN sodium h y d r o x i d e J4.I2 2 3 4 0 0 T h i s work 5 0 - ^ 0 p y r i d i n e - w a t e r 0.01M t e ' t r a m e t h y l -aramonium h y d r o x i d e 1+10 2 2 , 0 0 0 T h i s work 5 0 - 5 0 s u l f o l a n e - w a t e r OoOlM t e t r a m e t h y l -ammonium h y d r o x i d e 1+20 2 1 , 2 0 0 T h i s work 5 0 - 5 0 s u l f o l a n e - w a t e r 0.01M sodium methoxide 1+20 2 1 , 2 0 0 - T h i s work H y d r a z i n e 5 - 6 % i n water ^ 1 3 " 3l+,ooo T h i s work H y d r a z i n e 1 2 . 5 % i n water J+18 3 2 , 0 0 0 T h i s work H y d r a z i n e 2 2 . 6 % i n water 1+18 3l+, 0 0 0 T h i s work Hydrazine" 2 7 » 7 % i n water 1|19 3l+s 0 0 0 T h i s work H y d r a z i n e 6 0 . 6 % i n water ii .27 3 7 , 5 0 0 T h i s work H y d r a z i n e 9 3 - 9 % i n water 3 0 , 5 0 0 T h i s work Ammonia 2 0 % i n water 1+10 2 2 , 5 0 0 T h i s work U n i d e n t i f i e d s p e c i e s - the s e are presumably the r e s u l t of n u c l e o p h i l i c a t t a c k on the b e n z e n o i d r i n g i n the h i g h l y b a s i c s o l u t i o n s , t h a t i s , a Meisenheimer complex. S c h a a l ( 1 3 ) r e p o r t s a s p e c i e s a t l+70mu i n h i s more c o n c e n t r a t e d e t h y l e n e d i a m i n e s o l u t i o n s . S o l v e n t 117 *)\ max £ m a x r e f e r e n c e S u l f o l a n e 0.01M sodium "' methoxide and 5 mole % J+93 • 21,000 methanol 95 mole % s u l f o l a n e i n It08 l l i , 100 water 0.1 M t e t r a m e t h y l - , 500 9,050 ammonium h y d r o x i d e I t i s t o be n o t e d t h a t the presence of h y d r a z i n e i n b u f f e r s o l u t i o n s of p i c r a m i d e changes the spectrum. Even when a s o l u t i o n c o n t a i n i n g p i c r a m i d e and h y d r a z i n e i s brough t t o a pH of zero the m o l e c u l e s t i l l has the appear-ance of b e i n g p a r t l y i o n i z e d . B u f f e r nH 11.05 11.35 11.58 12.20 12.52 12.88 (13-38) 12.0li IN NaOH l o g °^ -1.21 -0.89 -0.62 0.03 O.38 0.69 1.16 -0.21 1-oC pK a 12.26 12.2li 12.20 12.17 12.lJx 12.19 (12.20) 12.25 The p K a d e t e r m i n e d g r a p h i c a l l y f o r t h i s compound was 12.20. S c h a a l (13) has o b t a i n e d 12.25 by an i d e n t i c a l method. Note t h a t pH f o r the g l y c i n e b u f f e r i n p a r e n t h e s e s c o u l d not be measured d i r e c t l y . I n s t e a d , the det e r m i n e d pKa was used t o determine H- f o r t h i s s o l u t i o n . Then t h i s s o l u t i o n was used i n d e t e r m i n i n g the pKa o f the next-I n d i c a t o r . ' . 118 2 ,li, 6-tr i n i t r o a n i l i n e i n Aqueous Benzyltrimethylammonium Hydroxide . 0.02M 0.01M O.O^M 0.29 0 ,1L8 pK a 12.20 12.20 12.20 12.20 1-2.20 H l o g J:—1 0.15 -0.22 0.1x7 l.oo [ A H ] H_ 12.35 11.98 12.67 13.20 C a l c u l a t e d pH 12 .30 12.00 12.70 13.1+6 13.68 f o r comparison 2,1+, 6-tr i n i t r o a n i l i n e i n pyr i d ine -water c o n t a i n i n g 0.011 , molar tetramethylammonium hy d r o x i d e . Mole % p y r i d i n e 1.0 5.3 10.2 1I4..3 20.0 [ A " ] l o g J: i 0.07 0.38 0.83 ' 1.23 [AH] C a l c u l a t e d H_ 12.27 12..58 13.03 - 13.1+3 2", l i , 6-tr i n i t r o a n i l i n e i n s u l f o l a n e - w a t e r c o n t a i n i n g 0.011 molar tetramethylammonium hydroxide. Mole %. 1.79 3.99 16.85 10.12 20.22 30.I s u l f o l a n e [ A " ] l o g J: i. 0.16 0.36 0.7I4. 0.60 0.93 M C a l c u l a t e d IT- 12.36 12.56 12.91+ 12.80 13.13 119 2 ,k,Jx 1-trinitrodIphenylamine : Prepared a c c o r d i n g to Weiland and Lecher ( 9 4 ) ' -M.P. was 183-4° a f t e r r e c r y s t a l l i z a t i o n from e t h a n o l . L i t . M.P. l8lj0 (94) • - ' MOLECULAR FORM Solvent A max . max r e f e r e n c e Benzene E t h a n o l 361 50-50 pyrIdine-water 385 366 23, 300 - T h i s work 21,900 T h i s work 21,600 (83) ANION 15 molar ammonia 510 J4.O mole % s u l f o l a n e -•water 0.01M t e t r a - 525 methylammonium hydroxide 50-50 pyr i d ine-water 0.01M t e t r a m e t h y l - 520 ammonium hydroxide 25,000 T h i s work 25,800 T h i s work 27,400 -This work 2 , 4 , 4 ' - t r i n i t r o d i p h e n y l a m i n e i n aqueous b u f f e r . B u f f e r pH 1 1 . 5 8 1 2 . 2 0 1 2 . 5 2 - 1 2 . 8 8 ( 1 3 . 3 5 ) 1 2 . 0 4 1M BTA l o g pK £ [AH] -0.72 -0.11 .0.18 0.50 0.96 0.26 * 12.30 12.31 12.34 12.38 12.39 12.30 note - BTA Is benzyltrimethylarnmonlum hydroxide 120 Note - f i g u r e in' parentheses i s a c t u a l l y * H _ as determined by 2, i i , 6-tr i n i t r o a n i l i n e . pK a determined g r a p h i c a l l y i s 12.3I1, 2,IL,'1I' - t r i n i t r odiphenylamine i n " p y r i d i n e -water c o n t a i n i n g 0.011M tetramethylammonium hydroxide. Mole % p y r i d i n e ' 1,0 ^.3 10.2 I4 . 3 20.0 l o g -0.05 0.30 0.70 1,10 [AH] A p K a from 2 , i i » 6 - t r i - 0,12 0.08 0 . 0 7 O . 1 3 n i t r o a n i l i n e pK a determined g r a p h i c a l l y was 12,33' 2,ii,li-' - t r i n i t r o d i p h e n y l a m i n e , i n s u l f olane-water c o n t a i n i n g 0.011M tetramethylammonium h y d r o x i d e . Mole % s u l f o l a n e 1,79 3-99 10.12 7.03 20.22 [A"] l o g i - 0,07 0,25 0.1+9 0.59 0.85 [AH] A p K a from 2 , i i , 6 - t r i - 0.09 0.11 0.11 - 0.08 n i t r o a n i l i n e pK a determined g r a p h i c a l l y was 12.31. 2, Ji, i i ' - t r i n i t r odiphenylamine in' aqueous b e n z y l t r i m c t h y l -ammonium hy d r o x i d e . • ' M o l a r i t y 0.02 0.0£ 0.29 0.1+8 2.00 [A"] , , lo g i - -0.08 0.22 0.92 1.28 [AH] A?K a from 2 j j , 6 - t r i ~ 0.23 0..2£ 0,08' n i l i ' o a n i l i n e pK a determined g r a p h i c a l l y was 12 .J4J4.. 121 o 2 , Ix, 3 ' - t r i n i t r odiphenylamine : M.P., 192-Ix a f t e r r e c r y s t a l l i z a t i o n from p y r i d i n e . Prepared a c c o r d i n g to Van der Kam ( 9 5 ) . L i t . M.P. 1 9 3 ° ( 9 5 ) . MOLECULAR FORM Solvent Amax £ m a x r e f e r e n c e 7 0 mole % s u l f o l a n e - 3 6 0 1 7 , 8 5 0 T h i s work water-Benzene 337 - 1 7 , 0 0 0 T h i s work ANION 1x0 mole % ' 1+50 1 8 , 7 0 0 T h i s work su l f o l a n e - w a t e r 2 , lx, 3 ' - t r i n i t r odiphenylamine i n aqueous b e n z y l t r i m e t h y l -ammonium hydroxide. M o l a r i t y 0 . 0 2 0 . 0 5 0 . 2 9 0.1x8 1 . 1 9 [ A - ] ... " • l o g - 0 . 2 3 0 . 0 7 0 . 6 5 1 . 10 [AH] £ p K a from 2 , lx,lx' - t r i - 0 . 1 5 0 . 2 9 O .37 0 . 1 8 n i t r o d i p h e n y l a m i n e The pK a determined g r a p h i c a l l y was 1 2 . 6 8 . 122 2,it, 3' - t r i n i t r o d i p h e n y l a m i n e i n py r i d i n e - w a t e r s o l u t i o n s c o n t a i n i n g 0.011 molar tetramethylammonium hydroxide.. A p K a from 2,lj.,l4.'- 0.31 O.37 0»32 O.36 t r i n i t r o d i p h e n y l a m i n e " The pK a determined g r a p h i c a l l y was 12.65' 2,4, 3' - t r . i n i t r odiphenylamine i n s u l f o l a n e -water s o l u t i o n s containing -0 .011 molar tetramethylammonium hy d r o x i d e . Mole % s u l f o l a n e 1.79 16.85 7«03 20.22 30.I Mole % p y r i d i n e 1.0 5.3 10.2 14.3 20.0 l o g -O.36 -0.07 O.38 0.74 [ A H } A p K a from 2,4,4'-t r I n i t r o d i p h e n y l a m i n e TO.25 0.18 0.27 0.52 1.00 0.32 0."32 O.33 The pK a measured g r a p h i c a l l y was 12.62. 123 6-bromo - 2 , 4-dinitroaniline : M.P., 154-0 •5 a f t e r r e c r y s t a l l i z a t i o n from e t h a n o l . L i t M . P ., 153-4°(84)-MOLECULAR FORM Solvent X max max r e f e r e n c e P y r i d i n e 347 12,100 This' work pH 7«6 phosphate b u f f e r 350 ' 12,000 T h i s work Methanol 333 12,600 T h i s work ANION P y r i d i n e 0.01M t e t r a -methylammonium hydroxide 395 527 21,400 12,700 T h i s work T h i s work 61i mole % s u l f o l a n e In water 0.011M t e t r a -methylammonlumhydroxide 395 527 23,200 13,900 T h i s work T h i s work 95% hydrazine i n water 495 . 7,600-:; T h i s work - T h i s may .be a r e a c t i o n product or molecular compound of 2 , 4 , 6 - t r i n i t r o a n i l i n e . T h i s species i s completely r e v e r s i b l e . 12li i • 6-bromo-2,li-dinitr o a n i l i n e i n pyr idine-water c o n t a i n i n g 0.011M tetramethylammonium hydroxide. Mole % p y r i d i n e 5 . 3 10 - 2 lix.3 20 . 0 2 9 . 7 ILO . 1 1I9.IL [ A - ] • l o g 1 — i ' -1.20 -0.6l -0 .27 0.06 O.7I1 l . O l i 1 . 5 9 [ A H ] A p K a from 2,IL,3«-t r i n i t r o 1 . 1 7 0 .99 1.01 -diphenylamine The pK a determined g r a p h i c a l l y was 13.66. 6 - b r o m o - 2 , l L - d i n i t r o a n i l i n e in- s u l f o l a n e - w a t e r c o n t a i n i n g 0.011M tetramethylammonium hy d r o x i d e . Mole % s u l f o l a n e 10.12 20 . 2 2 3 0.I 1+0.3 50 . 3 7O . 3 61;. 3 [ A " ] " l o g i — - - 1 . 0 . 9 - o.Jii 0.09 0.63 1 . 1 1 -0.66 [ A H ] A p K a from 2,1+, 3 « -t r i n i t r o - O . 9 3 ' 0 .91 - - O . 9 3 diphenylamine The pK a determined g r a p h i c a l l y was I3.6O. .Note' - 6 - b r o m o - 2 , l i - d i n i t r o a n i l i n e was found to be too i n s o l u b l e f o r use i n aqueous benzyltrimethylammonium hydroxide. 125 2 ,Ji-dinitrodiphenylamine : Prepared a c c o r d i n g to o Hoffmann and Dame (90). M.P., 155_6 a f t e r r e c r y s t a l l i z a t i o n o from e t h a n o l . L i t . M.P., 155 (90). MOLECULAR FORM Solvent max max r e f e r e n c e P y r i d i n e E t h a n o l 362 351 16,800 T h i s work 17,000 (83) ANION P y r i d i n e 0.011M t e t r a -methylammonium hydroxide 2 . 3 8 M aqueous b e n z y l -trimethylammonium hydroxide 60 mole % s u l f o l a n e i n water 0.011M tetramethyl-ammonium hydroxide 1+32 1;95 14-95 i+95 21,800 18,200 16,000 T h i s work T h i s work Th i s work 17,500 : T h i s work 126 2 , l x-dinitrod^j^^Tiylamine i n benzyltrimethylammonium hydroxide M o l a r i t y ' 0.0£ 0.29 0.1x8 0.81 1.19 1.76 l o g - — 4 - i . i o -o.^Jx -0.19 0.32 0.68 0.96 • • [ A H J ApKa"' 1.17 1.19 1.29 --* - A p K a i s from 2, Ix, 3' -tr i n i t r odiphenylamine . The pK a determined g r a p h i c a l l y was 13.85* 2 , l x-dinitrodiphenylamine i n p y r i d i n e - w a t e r c o n t a i n i n g 0.011 molar tetramethylammonium hy d r o x i d e . ILO.1 1L9.JX 59.7 0.9Jx 1.21 2.00 0.10 0.38 The pK a was determined g r a p h i c a l l y to be 13.83 2.00 2.38 1.36 Mole % p y r i d i n e 5»3 llx«3 • 20.0 29«7 l o g -1 .00 - 0 . 4 0 0 . 0 0 0.56 ApKa from 6-brbmo-2,li- • 0.20 0.13 0.06 0.18 d i n i t r o a n i l i n e 127 2, J x - d i n i t r o d i p h e n y l a m i n e i n s u l f o l a n e - w a t e r c o n t a i n i n g 0.011M t e t r a m e t h y l a m m o n i u m h y d r o x i d e . M o l e % s u l f o l a n e 10,12 20.22 30.1 1x0.3 <Q, 3 [ A - ] l o g i ± -1.00 -0.70 -0.21 0.35 " l . O l i [ A H ] A.pK a f r o m 6 - b r o m o - 0.09 0,29 0,12 0.28 0.07 2 , 4 - d i n i t r o a n i l i n e T h e p K a d e t e r m i n e d g r a p h i c a l l y was 13.83' 3 - n i t r o c a r b a z o l e • P r e p a r e d a c c o r d i n g t o S c h a a l (13)• M . P . was 2X1L -5° a f t e r . s e v e r a l r e c r y s t a l l i z a t i o n s f r o m a c e t i c a c i d . L i t , M . P , 218° (1x6). ,128 M O L E C U L A R F O R M S o l v e n t M e t h a n o l P y r i d i n e E t h a n o l f A N I O N X m a x 279 305 361+ 372 363 P y r i d i n e 0.011 m o l a r -t e t r a m e t h y l a m m o n i u m - 1x88 h y d r o x i d e 70 m o l e . % s u l f o l a n e i n w a t e r 0.011M t e t r a m e t h y l - , 1x88 a m m o n i u m h y d r o x i d e . imax 2 4 , 6 0 0 •Hi, 300 1 0 , 5 0 0 1 0 , 8 0 0 1 0 , 3 0 0 r e f e r e n c e T h i s w o r k . T h i s w o r k T h i s w o r k T h i s w o r k (83)-1 9 , 0 0 0 T h i s w o r k ' 1 8 , 7 0 0 T h i s w o r k (9) 129 3 - n i t r o c a r b a z o l e i n py r i d i n e - w a t e r c o n t a i n i n g t e t r a m e t h y l -ammonium hydroxide. Mole % p y r i d i n e 10.2 lit.3 20.0 29.7 1+0.1 1x9.1+ 59.7 - 61+.7 M l o g i — - -0.86 -0.71 - 0 . I 4 . 3 0-12 0 .69 O.93 1.13 1.27 [ A H ] ApKa'"' - 0.31 0.1+3 0.1+1+ 0.25 0.28 -ApKa i s from 2,l+-dinitrodiphenylamine. The pKa determined g r a p h i c a l l y was l l + . l 6 . 3 - n i t r o c a r b a z o l e i n su l f o l a n e - w a t e r c o n t a i n i n g t e t r a m e t h y l -ammonium hydr o x i d e . Mole % s u l f o l a n e 10.12 20.22 30.I 1+0.3 50.3 60.7 61+. 3 l o g i -0.80 -0.60 -O.37 0.27 0.83 O.97 1.06 fAH] A p K a from 2j+- -0.20 -0.10 • 0.16 0.08 0.21 d i n i t r o diphenylamine The pK a determined g r a p h i c a l l y was II+.03. 130 l x , l x ' - d i n i t r o d i p h e n y l a m i n e : P r e p a r e d a c c o r d i n g t o S c h r o e d e r a n d c o w o r k e r s ( 8 3 ) . •• M . P . , 2 1 3 - 2 l 6 ° * ~ a f t e r r e c r y s t a l l i z a t i o n f r o m d i o x a n e w a t e r . L i t . M . P . , 2 l 6 ° ( 8 3 ) . M O L E C U L A R F O R M S o l v e n t m a x m a x r e f e r e n c e P y r i d i n e E t h a n o l 1x16 k02 35,1x00 T h i s w o r k 37,600 - (83) A N I O N P y r i d i n e 0 . 0 1 1 M t e t r a -m e t h y l a m m o n i u m h y d r o x i d e , 5-98 S u l f o l a n e 0 . 0 1 1 M t e t r a -m e t h y l a m m o n i u m h y d r o x i d e 585 2.38 m o l a r b e n z y l t r i -m e t h y l a m m o n i u m h y d r o x i d e 580 1x6,000 T h i s w o r k 38,200 T h i s w o r k 37,000 T h i s w o r k Ix, Ix ' - d i n i t r o d i p h e n y l a m i n e i n a q u e o u s b e n z y l t r i m e t h y l a m m o n i u m h v d r o x i d e . M o l a r i t y 0.29 0.1x8 0 . 8 1 - 1 . 1 9 1.76 2.00 [ A - ] l o g i 1 -0 .92 -0 .51 0.02 O . 3 8 0.71 1.02 [ A H ] A p K a f r o m 2,1L- -d i n i t r o d i p h e n y l - O . 3 8 O . 3 2 0.30 0.30 0.25 0.3I+ a m i n e T h e p K a d e t e r m i n e d g r a p h i c a l l y w a s l l x . 1 5 . 131 !+,!+' - d i n i t r o d i p h e n y l a m i n e i n p y r i d i n e - w a t e r c o n t a i n i n g 0.011M t e t r a m e t h y l a m m o n i u m h y d r o x i d e . 2 9 . 7 14-0 . 1 1+9 -1+ 5 9 . 7 61+. 7 0 .19 0 . 7 0 O . 9 7 I . 3 1 O . 3 7 0.21+ O.2I4. 0 . 6 9 T h e p K a d e t e r m i n e d g r a p h i c a l l y w a s 1I4..O9. l i j l i ' - d i n i t r o d i p h e n y l a m i n e i n s u l f o l a n e - w a t e r c o n t a i n i n g 0.011M t e t r a m e t h y l a m m o n i u m h y d r o x i d e . 20.22 3 0 . 1 1+0.3 5 0 . 3 6 O . 7 - O . 7 3 -0 . 3 2 0.20 0 .91 - O 0 O 3 -0 .11 . 0 .15 0 .13 T h e p K a d e t e r m i n e d g r a p h i c a l l y w a s l l + . O O . M o l e % p y r i d i n e 1I4..3 2 0 . 0 F A - 1 l o g L-J. • • - 0 . 6 7 - 0 . 1 + J + A p K a f r o m 2,1+-d i n i t r o - ' 0 . 2 7 0.1+1+ d i p h e n y l a m i n e M o l e % s u l f o l a n e A p K a f r o m 2 , 1 + - d i n i t r o d i n h e n y l a m i n e 132 2 , l x - d i n i t r o - l x ' -aminodiphenylamine : M.P., 133~l4-° a f t e r r e c r y s t a l l i z a t i o n from e t h a n o l . L i t . M.P., I 3 6 0 ( 3 6 ) ' MOLECULAR FORM Solvent max max r e f e r e n c e 95 mole % s u l f o l a n e 375 i n water 1 8 , 3 0 0 T h i s work ANION 95 mole % s u l f o l a n e 1x95 i n water 0 . 0 1 1 M t e t r a -methylammonium hydroxide 1 8 , 3 0 0 T h i s work 2 , I x - d i n i t r o - i i ' -aminodiphenylamine i n s u l f olane-water 0 . 0 1 1 M i n tetramethylammonium hydroxide. Mole% 2 0 . 2 2 3 0.I 1x0.3 1x9.2 5 0 . 3 5 5 . 7 6 O . 7 61x.3 s u l f o l a n e [ A - ] l o g - ± - 0 . 9 7 - 0 . 7 0 -0.1x1 0 . 0 7 O . l l x O .37 ' 1 . 0 2 1 .2lx [AH] A p K a i A p K & 2 O.2I4. O . 3 8 0 . 6 1 - 0 . 2 7 0.1x9 0 . 7 6 0 . 7 7 0 . 8 6 A p K a ^ » i s from ix,lx' - d i n i t r o d i p h e n y l a m i n e A p K a 2 ~ i s from 2 , I x - d i n i t r odiphenylamine . The pK a determined g r a p h i c a l l y was llx.6I4. < 1 3 3 2 , l i - d i n i t r o a n i l i n e : M.P., 1 8 0 - 2 ° a f t e r r e c r y s t a l l i z a t i o n from e t h a n o l . Lit.M.P., 1 8 0 ° (81;). MOLECULAR FORM Solvent X m a x 6 max r e f e r e n c e P y r i d i n e 3J4.7 i i i , 850 • T h i s work Methanol " 336 i l l , 9 0 0 • T h i s work Et h a n o l 336 111, 800 • ( 8 3 ) ANION •Pyridine 0.OHM' i n t e t r a - 388 21 , 100 T h i s work methylammonium hydroxide • 5 3 5 15,300 T h i s work 2 . 3 8 M b e n z y l t r i m e t h y l - 3 8 8 . ' 1 7 , 3 0 0 T h i s work ammonium -hydroxide 5 3 0 1 2 , 2 0 0 T h i s work Note - not f u l l y i o n i z e d . 7 5 mole % s u l f o l a n e i n water 0.011M t e t r a - 5 3 0 1 6 ,000 T h i s work ' methylammonium hydroxide 9 5 mole % s u l f o l a n e i n water c o n t a i n i n g p h e n y l t r i -methylammonium hydroxide 5 2 5 i i i , 9 0 0 ( 2 3 ) 134 2 , 4 - d i n i t r o a n i l i n e i n aqueous benzyltrimethylammonium hydroxide. 30 mole % M o l a r i t y O.J4.8 0 . 8 1 1 . 1 9 1*76 2 . 0 0 2 . 3 8 p y r i d i n e r , ( 2 . 1 9 M) f A ~ 1 - l o g ± - - - 1 . 0 6 - 0 . 8 2 -O . 3 8 -0.10 0 . 2 2 1 . 2 3 [A H] A p K a ' 0 . 5 5 0.80 O . 7 6 0 . 8 6 0.80 ApK a i s from 4»4' - d i n i t r o d i p h e n y l a m i n e . The pK a determined g r a p h i c a l l y was li| .«97 • The maximum . . . o p t i c a l d e n s i t y used was obtained by adding p y r i d i n e to the most b a s i c s o l u t i o n above. 2 , 4 ~ d l n i t r o a n i l i n e i n pyr idine-water c o n t a i n i n g -0 . 0 1 1 M tetramethylammonium hy d r o x i d e . Mole % p y r i d i n e 2 0 . 0 2 9 . 7 LLO . 1 J4.9.I4. 5 9 . 7 f A -1 i'og 4—^ . -1.J4.6 -0.65 0.24 1 . 0 0 - • • [ A H ] A pK a 1 . 0 2 0.84 0.46 - 0 . 0 3 -A p K a Is from 4»4' - d i n i t r o d i p h e n y l a m i n e . I t was not p o s s i b l e to determine the pK a i n t h i s s o l v e n t 33? stem. 1 3 5 2 , l } . - d i n i t r o a n i l i n e i n su l f o l a n e - w a t e r c o n t a i n i n g 0.011M tetramethylammonium hy d r o x i d e . Mole % .. 30.1 J4.0.3 5 0 . 3 6 0 . 7 - 6I+.3 6 8 . 6 7 0 . 7 s u l f o l a n e [ A - l l o g ^ ^ -1 . 1 8 -O.75 -0 . 1 5 0 . 5 9 0 . 8 9 1 . 1 4 1 . 5 8 [AH] A p K a .; 0 . 8 6 -0 . 9 5 1 . 0 6 -A p K a i s from lx , lx' - d i n i t r o d iphenylamine . The pK a determined g r a p h i c a l l y was l 5 » 0 2 . 2, 6 - d i c h l o r o - l i - n i t r o a n i l i n e : r e c r y s t a l l i z a t i o n from e t h a n o l . • MOLECULAR FORM Solvent P y r i d i n e ANION P y r i d i n e 0.011M t e t r a - I167 38,000' T h i s work methylammonium hydroxide S u l f o l a n e 0.011K t e t r a - i+67 36,100 T h i s work methylammonium hydroxide M.P., I87 - 1 8 8 ° a f t e r L i t . M.P., 1 8 9 ° ( 8 5 ) . X max £.max r e f e r e n c e , 368 1 3 , 7 0 0 T h i s work 1 3 6 2 , 6 - d i c h l o r o-b r - n i t r o a n i l i n e i n p y r i d i n e - w a t e r c o n t a i n i n g 0 . O H M t e t r a m e t h y l a m m o n i u m - h y d r o x i d e . M o l e % p y r i d i n e ij.0 .1 l i 9 4 59-7 61}..7 6 9 4 71+-6 . [ A - ] l o g ±—=- - - i . I ] . 2 1.59 o.oo [ A H ] ApK a I t was n o t f o u n d p o s s i b l e t o d e t e r m i n e t h e p K a i n t h i s s o l v e n t s y s t e m . 2 , 6 - d i c h l o r o - l i - n i t r o a n i l i n e i n s u l f o l a n e - w a t e r c o n t a i n i n g 0 . 0 1 1 M t e t r a m e t h y l a m m o n i u m h y d r o x i d e . M o l e % s u l f o l a n e 1+0.3 ' 5 0 . 3 6 0 . 7 6I4.. 3 6.8.6 7O .7 • f A i l o g i i - 1 . 2 1 - 0 . 6 6 - 0 . 0 0 O . 3 9 0 . 5 9 0 . 8 7 [ A H ] A p K a f r o m 2 , i t - 0 4 6 0 . 5 1 0 . 5 9 0 . 5 0 0 . 5 5 0 . 7 1 d i n i t r o a n i l i n e The p K a d e t e r m i n e d g r a p h i c a l l y was 1 5 » 5 5 ° 137. l i - n i t r o d i p h e n y l a m l n e : -Prepared a c c o r d i n g to Goldberg (97) • M.P., 1 3 1 - 3 0 a f t e r r e c r y s t a l l i z a t i o n from a c e t i c a c i d . ' L i t . M.P., 1 3 3 ° (97)-. MOLECULAR FORM Solvent max •max r e f e r e n c e P y r i d i n e E t h a n o l 1+00 390 19,550 Th i s work "21.200 ' (83) -ANION P y r i d i n e 0.011M t e t r a - 508 methylammonium hydroxide S u l f o l a n e 0.011M t e t r a - 508 methylammonium hydroxide S u l f o l a n e c o n t a i n i n g p h e n y l t r I m e t h y l - 5P3 ammonium hydroxide 3l+,600 T h i s work 3J+, 200 :\' ' T h i s work 37,14-00 (23> T h i s compound decayed very slowly i n the b a s i c s o l u t i o n s to a new 'species. P y r i d i n e 0.011M t e t r a - "i+li_8 methylammonium hydroxide 8 8 , 0 0 0 T h i s work 138 Ix-nitr odiphenylamine i n pyr Idin'e-water 0.011M tetramethyl-ammoniumhydroxideo Mole' %_ p y r i d i n e 2 9 . 7 ' i i O . l IL 9 . 1 X 5 9 - 7 6Ix . 7 ' 6 9 -U-[ A - ] l o g i — L -1 . 3 1 - 0 . 6 6 0 . 0 6 0 . 7 2 1 . 1 2 1 . 3 6 -[AH] A p K a from ix,ix ' -d i n i t r o - l.£0 1.36 0.91 0 . 5 9 diphenylamine I t was not p o s s i b l e to determine t h i s pK a i n .this s o l v e n t -system.. Ix-nitr odiphenylamine i n su l f o l a n e - w a t e r 0.011M tetramethyl-ammonium hydroxide. Mole % s u l f o l a n e 50.3 6O.7 '61|..3 68.6 7O.7 7ix«9 "77.0 [ A - ] lOK i i f A H ] - 0 . 8 6 - 0 . 3 1 0 . 0 1 0 . 2 5 0 . 5 5 0 . 8 5 1 . 1 5 ApK a from 2 S 6 -d i c h l o r o - i x - 0 . 2 0 0 . 3 1 0 . 3 8 0 . 3ix 0 . 3 2 n i t r o a n i l i n e The pK a determined g r a p h i c a l l y was 1 5 » 9 0 . ' ; 1 3 9 I | . - n i t r o - 2 , 5 - d i c h l o r o a n i l i n e r e c r y s t a l l i z a t i o n f r o m e t h a n o l - . MOLECULAR FORM S o l v e n t P y r i d i n e A N I O N max 368 P y r i d i n e 0 . O H M - t e t r a - 1+58 m e t h y l a m m o n i u m h y d r o x i d e S u l f o l a n e . 0.011M t e t r a - 1+58 m e t h y l a m m o n i u m h y d r o x i d e M.P., 1 5 1 - 3 a f t e r L i t . M . P . , 1 5 2 - 3 0 ( 8 6 ) • £• may x r e f e r e n c e 1 1 , 8 0 0 T h i s w o r k 3 7 , 2 0 0 T h i s w o r k 30,1+00 T h i s w o r k I | . - n i t r 6 - 2 , 5 - d i c h l o r o a n i l i n e i n s u l f o l a n e - w a t e r 0 . 0 1 1 M t e t r a m e t h y l a m m o n i u m h y d r o x i d e . M o l e % s u l f o l a n e l o g i — -[ A H ] A p K a f r o m 1+ - n i t r o -di p h e h y l a m i n e 6 0 . 7 '. 61+.3 6 8 . 6 7 0 . 7 -0.1+0 - 0 . 1 0 0 . 0 7 0.1+9 0 . 0 9 0 . 0 9 0 * 1 8 0 . 0 6 The p K a d e t e r m i n e d g r a p h i c a l l y was 1 6 . 0 5 . ll+O 4 - c h l o r o - 2 - n i t r o a n i l i n e : M.P., IO7-8 0 a f t e r r e c r y s t a l l i z a t i o n from e t h a n o l . L i t . M.P., (108°) (84),. MOLECULAR FORM Solvent max max r e f e r e n c e Methanol' . . 65% ethylenediamine i n water 95% hydrazine i n water 95 mole % s u l f o l a n e i n water P y r i d i n e 1|.17 I4.25 1+37 430 J+22 3450 3,500 3,500 3,500 3,550 T h i s work This work T h i s work T h i s work T h i s work ANION Anhydrous ethylenediamine 5l6 95 mole % s u l f o l a n e i n water 0.011M t e t r a - £l6 me thylammonium hydr oxide 95 mole % s u l f o l a n e i n methanol 0„01M*sodium 5l6 methoxide S u l f o l a n e c o n t a i n i n g p h e n y l t r i m e t h y l - 5l6 ammonium hvdroxide 6,900 6,900 6,900 1/850 T h i s work T h i s work T h i s work" (23) l l i l L i - c h l o r o - 2 - n i t r o a n i l i n e i n s u l f o l a n e - w a t e r c o n t a i n i n g 0.011M tetramethylammonium hydroxide. 6 8 . 6 7 0 . 7 7 4 - 9 77.0 8 3 . 9 86.1 8 7 . 2 -0 . 8 6 - o . 6 i i - o . i i O -0 . 1 5 0.I4J4. 0.6I+ 0 . 9 1 1.11 1 . 1 9 1 . 2 5 -The pK a determined g r a p h i c a l l y was 1 7 . 2 2 . Mole % s u l f o l a n e A p K a from l i - n i t r o -d iphenylamine 11+2 2 - n i t r o d i p h e n y l a m i n e : M.P., 75_76° a f t e r r e c r y s t a l -l i z a t i o n from a c e t i c a c i d . L i t . M.P., 750. (97). MOLECULAR FORM Solvent max max r e f e r e n c e S u l f o l a n e E t h a n o l 1+35 1+23 6 , 3 6 0 6 , 6 0 0 T h i s work (83) ANION 95 mole % 51+! s u l f o l a n e i n water 0 . 0 1 1 M t e t r a -methylammonium hydroxide 9 , 1 7 0 T h i s work 2-nitrodiphenylamine i n sul f o l a n e - w a t e r c o n t a i n i n g tetramethylammonium hydroxide. Mole o i yo 6I+.3 7 0 . 7 71+.9 7 7 . 0 8 3 . 9 8 6 . 1 8 7 . 2 s u l f o l a n e [ A - ] .1+ 9 0 . 9 l o g p - 1 . 0 0 - 1 . 0 2 -O.77 - 0 . 5 1 -O .36 - 0 . 0 7 0 . 3 0 0 . 5 9 1 . 1 6 [ A H ] A p K , 0 . 3 8 0 . 3 7 0 . 3 6 0 . 7 0 0 . 5 7 0 . 6 1 A p K a i s from 2 - n i t r o - l + - c h l o r o a n i l i n e . The pK a determined g r a p h i c a l l y was 1 7 . 5 7 ° 11+3 2 - n i t r o a n i l i n e : M.P., 7 0 - 7 1 .5 ° a f t e r r e c r y s t a l l i z a t i o n f r o m e t h a n o l . L i t . M.P., 71.5° (8]+). MOLECULAR FORM S o l v e n t P y r i d i n e S u l f o l a n e E t h a n o l max 1+10 1+10 k-ok ^ max 14-490 1+450 5, 300 r e f e r e n c e T h i s work T h i s work ( 8 3 ) ANION P y r i d i n e 0.011M t e t r a - 515 methylammonium h y d r o x i d e S u l f o l a n e 0.011M t e t r a - 5l5 methylammonium h y d r o x i d e 8400 8,350 Mole 1o s u l f o l a n e 7 7 ° 0 8 7 . 2 8 9 4 9 0 . 9 9 2 . 0 93.I+ [A-] l o g i ± ) g i -O.72 - 0 . 2 6 0 . 0 3 0 . 2 0 0 . 5 3 1 . 3 8 [AH] A ^ K from [ [ - c h l o r o -2 - n i t r o a n i l i n e O . 5 7 0.80 0 . 6 l O . 71 A p K a from 2 - n i t r o -d i p h e n y l a m i n e 0 . 2 1 0 . ^ 6 0 . £ 6 O . 9 6 The pK a of 2 - n i t r o a n i l i n e d e t e r m i n e d g r a p h i c a l l y was I 7 . 8 8 . l + - n i t r o a n i l i n e : M.P., l l + 7 - 8 ° a f t e r r e c r y s t a l l i z a t i o n from aqueous e t h a n o l . L i t . M.P., ll+ 8 ° (81+) . MOLECULAR FORM Solvent X max €, max r e f e r e n c e P y r i d i n e Ethylenediamine Anhydrous e t h a n o l 378 392 372 1 6 , 9 0 0 1 8 , 2 0 0 1 5 , 2 0 0 T h i s work T h i s work ( 8 3 ) ANION Ethylenediamine 0 . 0 1 M tetramethylammonium 1+7 0 hydroxide S u l f o l a n e 0 . 0 1 M t e t r a - I+67 methylammonium hydroxide S u l f o l a n e c o n t a i n i n g p h e n y l t r ime t h y l - 1+70 ammonium hydroxide 32,1+00 T h i s work 3 2 , 3 0 0 T h i s work 32,1+00 ( 2 3 ) l i - n i t r o a n i l i n e i n su l f o l a n e - w a t e r c o n t a i n i n g 0.011M tetramethylammonium hy d r o x i d e . Mole % 7 7 . 0 8 3 . 9 8 7 . 2 8 9 . I L 9 0 . 9 9 2 . 0 9 3 . i i 9 5 . 0 s u l f o l a n e l o g ± — z [AH] -i „ 0 8 - 0 . 8 5 - 0 . 5 1 - 0 . 0 9 0 . 1 1 0 . 3 8 0 . 7 3 ApK a from [).-chloro-2 - n i t r o - - 0 . 9 3 1 . 2 9 1 . 6 2 a n i l i n e A p K a from 0 . 5 7 O.I4.9 0 . 2 1 0 . 6 8 1 . 0 5 2 - n i t r o -diphenylamine The pK a determined g r a p h i c a l l y was 1 8 . 3 7 1 11+6 B C a l c u l a t i o n of the H_ F u n c t i o n f o r the Solvent Systems us C a l c u l a t i o n of H_ Values f o r Aqueous S o l u t i o n s of Benzyltrimethylammoniun Hydroxide. INDICATOR PK a M 0 : L A R I T Y 0.1 Dl 0 . 02 0 . 0 5 0 . 2 9 0 . 4 8 2,\\, 6 - t r i n i t r o a n i l i n e 1 2 . 2 0 11 . 9 8 12 . 3 5 12 . 6 7 13 . 2 0 2,14.,]+' - t r i n itroDPA 12 .44 ; - 12 . 3 6 12 . 6 6 13 . 3 6 13 . 7 2 2 , i i , 3 ' - t r i n i t r o D P A 1 2 . 6 8 - 12 4 5 12 • 7 5 1 3 . 3 3 13 . 7 8 2,[|_-dinitroDPA 1 3 - 8 5 - - 12 . 7 5 13 . 3 1 13 . 6 6 4 , 4 ' -dinitroDPA 3 4 .15 - - - 1 3 . 2 3 1 3 • 7 4 2, ] + - d i n i t r o a n i l i n e 14.97 - - - 1 3 . 9 1 AVERAGE VALUE 11 . 9 8 12 • 39 12 . 7 1 13 . 2 9 1 3 . 7 6 M 0 L A R I T Y 0 . 8 1 1 •19 1 . 7 6 2 . 0 0 2 . 3 8 2 , i[-dinitroDPA 1 3 . 8 5 14 . 1 7 14 • *3 14 . 8 1 15 . 2 1 -k, [(.-dinitroDPA 111'. 1 5 ILL . 1 7 Hi • ?3 14 . 8 6 1 5 • 17 -2 , ) + - d i n i t r o a n i l i n e 4 . 9 7 14 ^15 14 . 5 9 14 . 8 7 1 5 . 1 9 16 . 2 0 AVERAGE- VALUE 14 . 1 6 14 • 5 5 14 . 8 5 1 5 . 1 9 16 . 2 0 These r e s u l t s are p l o t t e d i n F i g u r e 7. Note - DPA i s diphenylamine. 114-7 C a l c u l a t i o n of H_ Values f o r Pyridine-water S o l u t i o n s 0.011M i n Tetramethylammonium Hydroxide. INDICATOR PKa M O L E % P Y R I D I N E 1 . 0 5 . 3 1 0 . 2 14 • 3 2 0 . 0 2,li, 6 - t r i n i t r o a n i l i n e 1 2 . 2 0 1 2 . 2 7 12.58 1 3 . 0 3 1 3 . 4 3 -2 , J.L-, [|.' - t r I n i t r oDPA 1 2 . 3 3 12 . 2 0 1 2 . 6 3 1 3 . 0 3 1 3 . 4 3 -2,IL, 3 ' - t r i n i t r o D P A 1 2 . 6 5 12.25 1 2 . 5 8 1 3 . 0 3 1 3 . 3 9 -6 -br omo - 2, ix -d i n i t r oAn 1 3 . 6 6 - 12 . 4 6 1 3 . 0 5 1 3 . 3 9 1 3 . 7 2 2,ix-dinitroDPA 1 3 . 8 3 - 1 2 . 8 3 - 1 3 . 4 3 1 3 . 8 3 3 - n i t r o c a r b a z d l e II4..I6 - - _ 1 3 . 4 5 1 3 . 7 3 Ix,U' -dinitroDPA 11L . 15 - - - 1 3 . 4 8 1 3 . 7 1 AVERAGE VALUES 12 . 2 7 1 2 . 6 2 1 3 . 0 3 1 3 . 4 3 1 3 . 7 5 M 0 L' E % P Y R I D I N E 2 9 . 7 4 0 . 1 4 9 . 4 5 9 . 7 6 4 . 7 6 -br omo - 2, ix - d I n i t r oAn 1 3 . 6 6 14 .1x0 l i | . . 7 0 - - -2 , 1 ) .-dinitroDPA 1 3 . 8 3 1 4 . 3 9 1 4 - 7 7 1 5 . 0 4 -3 - n i t r o c a r b a z o l e 1 4 . 1 6 - 1 4 . 2 8 14.85 1 5 . 0 9 1 5 . 2 9 1 5 . 4 3 4 , 4 ' -dinitroDPA 1 4 . 0 9 1 4 . 2 8 1 4 . 7 9 1 5 . 0 6 1 .5 .40 AVERAGE VALUES 14 • 3.5 1 4 . 7 8 1 5 . 0 6 1 5 . 3 5 Note - DPA i s diphenylamine An i s a n i l i n e These r e s u l t s are p l o t t e d i n F i g u r e 2 . il+9 C a l c u l a t i o n of H_ Values f o r Sulfolane-water mixtures c o n t a i n i n g 0.011M Tetramethylammonium H7/droxide. INDICATOR pKa M 0 L E % S U L P 0 ' L A N E 1 . 7 9 3 . 9 9 1 0 . 1 2 1 6 . 8 5 2 0 . 2 2 2,l\., 6 - t r i n i t r o a n i l i n e 1 2 . 2 0 1 2 . 3 6 12 . 5 6 12.80 1 2 . 94 1 3 . 1 3 2,[(.,l+< - t r i n i t r o D P A 1 2 . 31 1 2 . 3 8 12 . 5 6 12.80 1 3 . 1 6 2,L+, 3 ' - t r i n i t r o D P A 1 2 . 68 12-43 - - 12 . 8 6 1 3 . 2 0 6 -br omo - 2 , hr -d i n i t r oAn 1 3 . 6 0 _ 1 2 . 5 1 1 3 . 1 9 2 , 4 - d i n i t r o D P A 1 3 . 8 3 - 12 . 8 3 1 3 . 1 3 3 - n l t r o c a r b a z o l e ll+. 0 3 - 1 3 . 2 3 1 3 . 4 3 4 , 4 ' -dinitroDPA i l l . . 1.5 - - 1 3 . 4 2 AVERAGE VALUES 1 2 . 3 9 12 . 5 6 1 2 . 6 3 12 . 9 0 1 3 . 2 4 M 0 L E % S U L F 0 L A N E 3 0 . 1 ko . 3 5 0 . 3 6 0 . 7 6 4 . 3 2 , 4 , - 3 ' - t r i n i t r o D P A 12 . 68 1 3 . 6 8 - -6 -br omo -2,1+ -d i n i t r oAn 1 3 . 6 0 1 3 . 6 9 Ik . 2 3 11+.71 -2 , l+~d i n i t r o D P A 1 3 . 8 3 1 3 . 6 2 11+- . 1 8 1 4 . 9 7 _ 3 - n i t r o c a r b a z o l e li+ 0 0 3 1 3 . 6 6 11+ . 3 0 11+.86 1 5 . 0 0 1 5 . 0 9 ]+,]+' -dinitroDPA l l | . . 0 0 1 3 . 6 8 11+ . 2 0 1 4 . 9 1 -2, J+ -d i n i t r o -1+' -aminoDPA 1J+ . . 6 4 13.91+ 1k . 2 3 1 4 . 7 8 1.5. 01 1 5 . 8 8 2, J+-dinitr o a n i l i n e 1 5 . 02 13-81+ Ik . 2 7 1 4 . 8 7 1 5 . 6 1 1 5 . 9 1 2 , 6 - d i c h l o r o - l + ~ n i t r oAn 1 5 . - Ik - 31+- 1 4 . 8 9 1 5 . 1 5 . 9 4 i|-nitroDPA 1 5 . 9 0 - - 1 5 . 0 4 15. 59 1 5 . 9 1 continued on page 150 150 T a b l e c o n t i n u e d from page llx9 • INDICATOR pK a L . - n i t r o - 2 , ^ - d i c h l o r o -a n i l i n e 1 6 . 0 5 i i - c h l o r o - 2 - n i t r o A n 1 7 . 2 2 2 - n i t r o D P A 1 7 - 5 7 AVERAGE VALUES 2 , l i - d i n i t r o a n i l i n e 1 5 . 0 2 2 , 6 - d i c h l o r o - i i - n l t r o A n 1 5 . 5 5 [(.-nitroDPA 1 .5 .90 I i . - n i t r o - 2 , 5 - d i c h l o r o -a n i l i n e 1 6 . 0 5 l x - c h l o r o - 2 - n i t r o A n 1 7 . 2 2 2 - n i t r o D P A 1 7 . 5 7 2 - n i t r o a n i l i n e 1 7 . 8 8 4 - n i t r o a n i l i n e 1 8 . 3 7 AVERAGE VALUES M O L E % S U L F O L A N E 3 0 . 1 I4.0.3 5 0 . 3 6 0 . 7 61+. 3 1 5 - 6 5 1 ^ . 9 5 1 6 . 5 7 1 3 . 7 3 1 4 . 2 5 1 4 . 8 8 1 5 . 6 0 1 5 . 9 2 M O L E % S U L F O L A N E 6 8 . 6 7 0 . 7 7 4 . 9 7 7 . 0 8 3 . 9 8 7 . 2 1 6 . 1 6 1 6 . 6 0 -1 6 . 1 4 1 6 . 4 2 -1 6 . 1 5 1 6 . 4 5 1 6 . 7 5 1 7 . 0 5 1 6 . 1 2 1 6 . 5 4 I 6 . 3 6 1 6 . 5 8 1 6 . 8 2 17 . 0 7 1 7 . 6 6 1 8 . 1 3 1 6 . 5 5 1 6 . 8 0 I7.O6 1 7 . 2 1 1 7 . 8 7 1 7 . 1 6 1 7 . 6 4 1 7 . 9 1 1 7 . 2 9 1 7 . 5 2 1 7 . 8 6 1 6 . 1 9 1 6 . 5 2 1 6 . 7 9 1 7 . 1 3 1 7 . 5 1 1 7 . 9 4 • • 151 Table continued -from page 150 INDICATOR pK a 2-nitroDPA 1 7 . 5 7 2 - n i t r o a n i l i n e 1 7 . 8 8 [(.-nitr o a n i l i n e 1 8 . 37 AVERAGE VALUES M O L E % S U L F O L A N 89-1+ 9 0 . 9 9 2 . 0 93.I4. 9 5 . 0 1 8 . 1 6 1 8 . 7 3 -1 7 . 9 1 18.08 1 8 . 1 9 . 2 6 1 8 . 2 6 1 8 . IL8 1 8 . 6 5 1 9 . 1 0 1 8 . 0 5 1 8 . 2 8 1 8 . 5 3 1 9 . 1 8 Note - DPA i s diphenylamine An i s a n i l i n e The r e s u l t s from t h i s t a b l e are p l o t t e d i n F i g u r e 4. 152 Use of averaged pK a values to c a l c u l a t e H- f o r v a r y i n g c o n c e n t r a t i o n s of benzyltrimethylammonium hydroxide i n a s o l u t i o n .50 mole % p y r i d i n e and 00 mole % water. 0.01M benzyltrimethylammonium hydroxide. INDICATOR PKa lo g i H _ ! average 2,4, 6 - t r i n i t r o a n i l i n e 12.20 f u l l y i o n i z e d 2,1+ - d i n i t r o a n i l i n e 1 5 . 0 0 I.2I4. I6.2J4. 4- n i t r o d i p h e n y l a m i n e 1 5 . 9 0 -0 . 1 6 15.74 2 , 6 - d i c h l o r o - 4 - n i t r o A n 15 . 5 5 0.20 1 5 . 7 5 I f . - n i t r o - 2 , 5 - d i c h l o r o A n 1 6 . 0 5 -0 .52- 1 5 . 5 3 1 5 . 6 7 0.0.5M b e n z y l t r ime thylammonium hydroxide. 2, 6 - d i c h l o r o - k - n i t r o A n 15.55 0 . 9 8 1 6 . 5 3 I ) . - n i t r o - 2 , 5 - d i c h l o r o A n 1 6 . 0 5 0 . 3 5 I6.4O 4 ~ c h l o r o - 2 - n i t r o a n i l i n e 1 7 . 2 2 -O.64 1 6 . 5 8 1-6.50 0.10M benzyltrImethylammonium hydroxide. 2 , 6 - d i c h l o r o - 4 - n i t r o A n 1 5 . 5 5 1 . 1 5 16.7O J4 - n i t r o - 2 , 5 - d i c h l o r o A n 1 6 . 0 5 0 . 7 0 1 6 . 7 5 4 - c h l o r 0 -2 - n i t r o a n i l i n e 17.22 -O .38 1 6 . 8 4 i+ - n i t r odiphenylamine 1 5 . 9 0 0 . 8 1 1 6 . 7 1 1 6 . 7 5 1 5 3 Table continued from page 1$2.-r "1 INDICATOR pK a l o g r 1 [AH] H. average 0.2lxM benzyltrimethylammonium hydroxide. 1 2 , 6 - d i c h l o r o - l i - n i t r o A n 1 5 . 5 5 1 . 5 1 1 7 . 0 6 l i - n i t r o d i p h e n y l a m l n e 1 5 . 9 0 1 . 0 3 1 6 . 9 3 I I - n i t r o - 2 , 5-dichloroAn 1 6 . 0 5 1 . 0 5 1 7 . 1 0 4 - c h l o r o - 2 - n i t r o a n i l i n e 1 7 . 2 2 0 . 1 1 1 7 . 3 3 2 - n i t r o d i p h e n y l a m i n e 1 7 * 5 7 - 0 . 5 3 1 7 . 0 1 L 1 7 . 0 9 0 . [ L 8 M benzyltrimethylammonium hydroxide 4 - c h l o r o - 2 - n i t r o a n i l i n e 1 7 . 2 2 0.1x8 1 7 . 7 0 2 - n i t r o d i p h e n y l a m i n e 1 7 * 5 7 0 . 2 8 17.85 4 - n i t r o a n i l i n e 1 8 . 3 7 -O.Olx 1 8 . 3 4 1 7 . 9 6 O . 9 6 M benzyltrimethylammonium hydroxide i t - c h l o r o - 2 - n i t r o a n i l i n e 1 7 . 2 2 0 . 5 2 1 7 . 7 4 2 - n i t r o d i p h e n y l a m i n e 1 7 . 5 7 0 . 6 9 1 8 . 2 6 I x - n i t r o a n i l i n e 1 8 . 3 7 - 0 . 0 7 I8.3O 1 8 . 1 0 2 . 1 2 M benzyltrimethylammonium hydroxide 2 - n i t r o d i p h e n y l a m i n e f u l l y i o n i z e d . IX-JI1 t r o a n i l i n e 1 8 . 3 7 0.5lx • 1 8 . 9 1 1 8 . 9 1 Mote - An i s a n i l i n e These r e s u l t s are p l o t t e d i n F i g u r e 8, 154 Use of averaged pK a values to c a l c u l a t e H_ values f o r v a r y i n g c o n c e n t r a t i o n s of benzyltrimethylammonium hydroxide i n a s o l u t i o n 30 mole % p y r i d i n e and 7 0 mole % water. INDICATOR pK a l o g H- average [AH] O.O3M benzyltrimethylammonium h y d r o x i d e . 6 -br omo -2,14. -d i n i t r oAn 1 3 « 6 3 0 . 3 9 1 4 . 0 2 2 , 4 - d i n i t r o d i p h e n y l a m i n e I 3 . 8 4 O . 2 4 I4.O8 2 , i + - d i n i t r o - l + ' -aminoDPA l u . 6 4 -O .52 l i | . 1 2 2 , 4 - d i n i t r o a n i l i n e 1 5 . 0 0 -O .98 1 4 . 0 2 1 4 . 0 6 0 . 1 5 M benzyltrImethylammonium hydroxide 2 , 4 - d i n i t r o d i p h e n y l a m i n e 1 3 . 8 4 0 . 7 9 I 4 . 6 3 6,-bromo - 2 , 4 - d i n i t r o A n 1 3 . 6 3 0 . 7 0 14 .33"" 2 , 4 - d i n i t r o - 4 ' -amincDPA 1[|.. 6 4 O . 3 4 1 4 . 9 8 2 , 4 - d i n i t r o a n i l i n e 1 5 . 0 0 - 0 . 1 5 1 4 . 8 5 2 , 6-d i c h l o r 0 - 4 - n i t r o A n 1 5 . 5 5 - 0 . 6 8 1 4 . 8 7 4 - n i t r o d i p h e n y l a m i n e 1 5 . 9 0 - 0 . 8 2 1 5 . 0 8 1 4 . 8 8 0 . 2 9 M benzyltrimethylammonium hydroxide. 2 S 6 - d i c h l o r 0 - 4 - n i t r o A n 0 . 0 7 1 5 . 6 2 2 - d i n i t r o a n i l i n e 1 5 . 0 0 O . 5 4 1 5 . 5 4 4 - n i t r odiphenylamine 1 5 . 9 0 - 0 . 1 2 1 5 . 7 8 4 - n i t r o - 2 , 5 - d i c h l o r o A n 1 6 . 0 5 - 0 . 3 5 1 5 . 7 0 1 5 . 6 6 Note - DPA i s diphenylamine and An i s a n i l i n e . 155 T a b l e c o n t i n u e d from page l5l+» M INDICATOR pK a l o g H_ average H_ [AH] O 0 8 3 M b e n z y l t r i m e t h y l a m m o n i u m h y d r o x i d e . 2 , 6 - d i c h l o r o ~ l + - n i t r o A n 15.55 0 . 1 6 1 5 . 7 1 1 +-nitr o d i p h e n y l a m i n e •15.90 - 0 . 0 8 1 5 . 8 2 l + - n i t r o - 2 , 5 - d i c h l o r o A n 1 6 . 0 5 - 0 . 2 8 1 5 . 7 7 2 - n i t r o - l + - c h l o r o a n i l i n e 1 7 . 2 2 -1.01 1 6 . 2 1 1 5 . 8 8 1.19M b e n z y l t r i m e t h y l a m m o n i u m h y d r o x i d e . 2, 6 - d i c h l o r o - I ) . - n i t r o An 1 5 . 5 5 O.8I4. 1 6 . 3 9 1+ - n i t r o d i p h e n y l a m i n e 1.5.90 0 . 9 0 1 6 . 8 0 [ [ . - n i t r o - 2 , 5 - d i c h l o r o A n 1 6 . 0 5 0 . 7 0 1 6 . 7 5 16 . 6 5 . 1.62M b e n z y l t r i m e t h y l a m m onium h y d r o x i d e . • 2 - n i t r o - [ [ - c h l o r o A n 17 . 2 2 0 . 1 8 17.1+0 2 - n i t r o d i p h e n y l a m i n e 1 7 . 5 7 , - 0 . 2 1 ' 1 7 . 3 6 [ [ . - n i t r o a n i l i n e 1 8 . 3 7 - 0 . 5 7 1 7 . 8 0 17 . 5 2 2 . 1 9 M b e n z y l t r i m e t h y l a m m o n i u m h y d r o x i d e . i + - c h l o r o - 2 - n i t r o A n 1 7 . 2 2 0 . 2 6 17.1+8 2 - n i t r o d i p h e n y l a m i n e 1 7 . 5 7 0 . 1 1 1 7 . 6 8 l i - n i t r o a n i l i n e 1 8 . 3 7 - 0 . 6 1 1 7 . 7 6 17 . 6 5 Note - An I s a n i l i n e . 156 H_ c a l c u l a t i o n f o r benzyltrimethylammonium hydroxide i n water (2.38 m o l a r ) . INDICATOR pK a l o g ± — - H_ average M 2 , I ] . - d i n i t r o a n l l i n e 15-00 1.15 16.15 2, 6 - d i c h l o r o - l i - n i t r o -a n i l i n e . 15.55 0.88 l6.Ij.3 4-nitrodiphenylamine 15.90 O.56 16.46 4~nitro - 2 , 5 - d i c h l o r o -a n i l i n e l 6 . 0 5 O.42 16.47 4~chloro -2 - n i t r o -a n i l i n e 17.22 -0.22 17.00 16.50 These r e s u l t s are p l o t t e d In F i g u r e 8• 157 Use of pK a values to c a l c u l a t e H_ values f o r aqueous s o l u t i o n s of L i t h i u m h y d r o x i d e . ( C a r r i e d out i n 10cm c e l l s ) . INDICATOR ' — ~ pK a l o g 1 - H_ average H_ [AH] 1 normal l i t h i u m h y d r o x i d e . 2,1+, 6 - t r i n i t r o a n i l i n e 1 2 . 2 0 f u l l y i o n i z e d . 2 , [ [ - d i n i t r o d i p h e n y l a m i n e 1 3 . 8 3 -O .36 1 3 . 4 7 3-nitrocartaazole l l j . , 1 0 -0.1+9 1 3 - 6 l 4 ,l+ !-dinitrodiphenylamine 11+.08 -O .73 1 3 - 3 5 1 3 - 4 3 2 normal l i t h i u m h y d r o x i d e . 2,l+-dinitrodiphenylamine 1 3 . 8 3 - 0 . 5 3 1 3 - 3 0 3 - n i t r o c a r b a z o l e ll+.lO -0.1+0 1 3 . 7 0 4 , 4 '-dinitrodiphenylamine l ) + . 0 8 -0.1+9 1 3 - 5 9 1 3 - 5 3 3 normal l i t h i u m hydroxide 3 - n i t r o c a r b a z o l e li+.lO - 0 . 1 9 1 3 - 9 1 !+»!+' - d i n i t r o d i p h e n y l a m i n e 11+.08 - 0 . 2 2 1 3 . 8 6 2 , 1 +-dinitro -1+ ' -amino-diphenylamine II+06I+ - 0 . 6 l 11+.03 1 3 - 9 3 1+ normal l i t h i u m hydroxide 3 - n i t r o c a r b a z o l e ll+.lO - 0 . l 6 1 3 - 9 4 1+J1L! - d i n i t r o d i p h e n y l a m i n e 11+.08 - 0 . 0 6 li+°02 2 ,i+-dinitro-l+' -amino-diphenylamine 1I+.6I+ -0.1+9 l l + . i 5 2 , i + - d i n l t r o a n i l i n e 1 5 . 0 0 -O .87 ll+ » 1 3 ll+. 0i+ 158 Table continued from page 157 [*'] INDICATOR pK a l o g -—T H_ average H. [ A H ] 5 normal l i t h i u m hydroxide 3 - n i t r o c a r b a z o l e . l J i . l O 0 = 3 3 111. .I4.3 [ L . I I 1 - d i n l t r o d i p h e n y l a m i n e 111.08 0 . 0 8 l l i . l 6 2 , L L - d i n i t r o - L L ' -amino -diphenylamine 1I4..6I4. -O.I18 l l i . 1 6 2 , l i - d . i n i t r o a n i l i n e 15.00 -O .53 ill.1x7 i l l . 3 1 These r e s u l t s are p l o t t e d i n F i g u r e 10. 159 H_ c a l c u l a t i o n s f o r d i m e t h y l s u l f o x i d e - w a t e r mixtures c o n t a i n i n g 0.011M tetramethylammonium h y d r o x i d e . INDICATOR pK a MOLE % DIMETHYLSULFOXIDE 5 10 20 30 1+0 2 , 1 + , 6 - t r i -n i t r o A n 12.20 12 . 2 6 1 2 . 9 6 2 , 1 + , ! + '-tri-nitroDPA 1 2 . 3 3 12 . 1 6 12 . 9 7 2,1+, 3 ' - t r i -nitroDPA 12 . 6 5 12 . 0 9 12.72 2 , [j.-d i n i t r o -DPA 13.81+ 13.10 11+.32 3 - n i t r o -c a r b a z o l e 1J+.10 li|.l+l 15.27 !+,!+' - d i n i t r o -DPA 11+.08 11+.15 II+.9I4. 2,1+ - d i n i t r o-l+'-aminoDPA 1 1 + . 6 1 + l l + « 2 5 1 5 * 3 3 2?1+ - d i n i t r o a n i l i n e 1 5 . 0 0 1I+.O7 15.1+0 1 6 . 3 7 2 , 6 - d i c h l o r o -4 - n i t r o A n 1 5 - 5 5 1 4 - 4 9 1 5 * 5 3 l 6 . £ 8 l+-nitroDPA 1 5 - 9 0 1 6 . 3 6 2S5-dichloro-4 - n i t r o A n 1 6 . 0 5 1 6 . 3 2 4 ~ c h l o r o -2 - n i t r o A n 17 . 2 2 1 6 . 6 2 AVERAGE VALUES 1 2 . 1 7 12.91+ 11+.28 1 5 . 2 9 1 6 . 4 5 1 6 0 Table continued from page 1 5 9 INDICATOR MOLE % DIMETHYLSULPOXIDE. 5 0 6 0 7 0 2 , 5 - d i c h l o r o -i i - n i t r o A n 1 7 . 2 7 l i - c h l o r o -2 - n i t r o A n 1 7 . 4 7 2-nitroDPA 1 7 . 0 5 1 7 . 9 3 i i - n i t r o a n i l i n e 1 7 . 7 6 18 . 6 1 AVERAGE VALUES 1 7 . 2 6 1 7 . 8 5 1 8 . 6 1 An i s a n i l i n e DPA i s diphenylamine Note - diphenylamine appears to be l e s s than h a l f i o n i z e d i n 95% d i m e t h y l s u l f o x i d e - w a t e r s i n c e the o p t i c a l d e n s i t y of the anion i s l e s s than h a l f that a t t a i n a b l e i n anhydrous ethylenediamine c o n t a i n i n g tetramethylammonium hydroxide. For t h i s reason the 95% s o l u t i o n may not be much more b a s i c than the 70% s o l u t i o n . These r e s u l t s are p l o t t e d i n F i g u r e 9- -i 6 l C a l c u l a t i o n of H_ f u n c t i o n i n ethylenediamine-water from the data of Schaal ( 1 3 ) ' INDICATOR 2 , Ii - d i n i t r o -DPA 1 3 . 8 l i 3 - n i t r o -carbazole l k . 2k 1L.1L' - d i n i t r o -DPA I I L . 1 3 2 , k - d i n i t r o -a n i l i n e l l x . 7 8 /[OLE % ETHYLENEDIAMINE IN WATER 9 . 2 1 1 .LL 1 2 . 0 1 3 . 8 1 IL .IL 1 6 . o 1 2 . 7 6 I3 .3I+ 13-74 H i - . 15 1 3 . 2 9 1 3 . 6 2 13.14-5 1 3 - 7 5 1 3 . 9 9 1 3 - 8 3 AVERAGE VALUE 1 2 . 7 6 13-li-O 1 3 . 2 9 1 3 . 7 5 1 3 . 6 2 1 3 . 9 9 2, ix-d I n i t r o -DPA 1 3 . 8 l x 3 - n i t r o -c a r b a z o l e ilx . 2 i x Jo.»ix.1 -d i n i t r o -.DPA 111. 13 ?,k~d i n i t r o o n i l i n e llx . 7 8 MOLE % ETHYLENEDIAMINE IN WATER 1 7 . 2 1 9 . 7 2 1 . 0 2 3 . 0 2 5 . 2 2 6 . 9 3 1 - 0 Hi- . .53 I k . 8 6 l i x . O i i 111. 6 5 1 5 - 1 9 l i x . 2 9 1 1 + . 3 3 I k . 60 H4-.75 I i i . 88 1 5 . 2 3 1 5 . 0 9 1 5 . 7 3 AVTRAGE VALUES I IL . O IL l i t . 38 l k . 6 5 ±4-74 1.5.19 I k - 9 9 1 5 4 8 D5 \r, diphenylamine. These r e s u l t s are p l o t t e d i n F i g u r e 1 5 . Note - anhydrous ethylenediamine apparently f u l l y Ionizes k - c h l o r o " 2 n i t r o a n i l i n e ( p K a = 1 7 . 2 2 ) so that i t s H. must approach 1 9 . 162 C a l c u l a t i o n of H_ f u n c t i o n i n H y d r a z i n e - w a t e r from the d a t a of S c h a a l and F a v i e r (17). INDICATOR PKa 3 - n i t r o -c a r b a z o l e 1J4..2J4. 4 , 4 ' - d i n i t r o -DPA 1 4 . 1 3 AVERAGE VALUES MOLE % HYDRAZINE 23.2 27.4 31.5 36.O 40.7 45.8 5 i.i 95.0 13.34 13.79 14-06 14.36 14.84 13.06 13.23 13.62 13.98 14.31 14.69 15.08 13.06 13.29 13.70 14.02 14.34 14.77 15.08(15.5) DPA i s d i p h e n y l a m i n e . Note - No i o n i z a t i o n of 4 - c h l o r o - 2 - n i t r o a n i l i n e i s d e t e c t a b l e i n 95 % h y d r a z i n e . The pK^ of t h i s compound i s 17.22. Thus 95 % h y d r a z i n e cannot be more b a s i c t h a n H _ = 15.5. Note - R e p e t i t i o n of t h i s work f o r 3 - n i t r o c a r b a z o l e r e s u l t e d i n good e x p e r i m e n t a l agreement. These r e s u l t s are p l o t t e d i n F i g u r e 16. 1 6 3 C Experimental Data on Compounds not used as I n d i c a t o r s . [(.-nitrobenzyl c yanide. Solvent max • max r e f e r e n c e MOLECULE Methanol 2 6 2 1% hydrazine i n water ' 2 6 7 pH 7 . 6 phosphate b u f f e r 2 7 0 1 0 , 3 5 0 1 0 . 0 0 0 9,800 T h i s work T h i s work T h i s work ANION IN aqueous potassium hydroxide - 1+50 6N aqueous potassium hydroxide 1+75 1+5.3% hydrazine i n water 5 3 5 7 3 » 2 % hydrazine i n water ^L\2 Anhydrous ethanolamine 51+0 B e n z y l t r imethylammonium hydroxide i n methanol (1M) 552 30 mole % p y r i d i n e i n water 1.19M b e n z y l t r i - 51+3 methylammonium hydroxide 9 5 mole % s u l f o l a n e i n water 0.011M t e t r a m e t h y l - 5 3 8 ammonium hydroxide 1 6 , 0 0 0 T h i s work 1 8 , 6 0 0 25,1+00 3 0 ,000 T h i s work Th i s work This work T h i s work 2 1 , 2 0 0 T h i s work 3 0 , 3 0 0 T h i s work 3 3 , 7 0 0 T h i s work 161+ Diphenylamine. Solvent MOLECULE S u l f o l a n e Ethylenediamine ANION 99% ethylenediamine i n water, 0.011M t e t r a - 370 16,200*"' methylammonium hydroxide -«- probably not f u l l y i o n i z e d . Note - T h i s molecule showed no I o n i z a t i o n i n s u l f o l a n e 0.011 molar base. max c-max r e f e r e n c e 2 8 8 2 9 1 1 8 , 6 0 0 T h i s work 1 8 , 0 0 0 T h i s work 165 Fluorene: T h i s compound showed a b s o r p t i o n at l+l8mu i n 99% ethylenediamine i n water with 0.011M tetramethylammonium hyd r o x i d e . T h i s was r e v e r s i b l e and the apparent e x t i n c t i o n c o e f f i c i e n t was 2 0 , 0 0 0 . No i o n i z a t i o n was d e t e c t a b l e i n s u l f o l a n e . 2 , 6 - d i n i t r o a n i l i n e : T h i s compound showed an immediate purple c o l o u r i n our h i g h l y b a s i c s o l u t i o n s which very q u i c k l y faded producing a ,i p e d e s absorbing at l+5lmu i n p y r i d i n e . We were unable to c a r r y out a pK a d e t e r m i n a t i o n . 2, 6, 2 ' -trinitro-l+-methoxydiphenylamine : T h i s compound showed a very broad anion peak wi t h Xmax near 5 , 5 0 0 . I t showed anomalous behaviour and was a r b i t r a r i l y d i s c a r d e d as an i n d i c a t o r . 3 - n i t r o a n i l i n e : T h i s compound showed no measureable I o n i z a t i o n i n our s u l f o l a n e or p y r i d i n e systems. 3 , S - d i n i t r o a n i l i n e ; T h i s compound r e a c t e d slowly i n our most b a s i c systems to produce a species absorbing at 50.5mu. T h i s species a l s o r e v e r s e d s l o w l y . 5 - n i t v o i n d o l e ; T h i s compound a p p a r e n t l y i o n i z e d to produce a species absorbing at l+05mu. No i n v e s t i g a t i o n was made of the p o s s i b i l i t y of measuring i t s pK a. 1 6 6 ; I x - n i t r o t o l u e n e : No i o n i z a t i o n was d e t e c t a b l e i n any of 'our systems. D i p h e n y l a c e t o n i t r H e : T h i s compound showed a momentary yellow c o l o u r i n our b a s i c s o l u t i o n s and r a p i d l y decayed to a species absorbing at 3 i 7 t f i u . 3 - n i t r o p h t h a l i m i d i n e : T h i s compound ap p a r e n t l y i o n i z e d i n s u l f o l a n e with a b s o r p t i o n at 3 0 0 m u . 1 - n i t r o c a r b a z o l e : T h i s compound decayed r a p i d l y from an o r i g i n a l r e d co l o u r to a sp e c i e s w i t h A max = Jx35mu i n p y r i d i n e . 2 - n i t r o -Jx, 5 - d i c h l o r o a n i l i n e : T h i s anion decayed r a p i d l y to produce a species absorbing near Jx65mu. 2 , 6 - d i n i t r o - Ix-chloroaniline : T h i s anion decayed r a p i d l y from an o r i g i n a l p u rple colour to a sp e c i e s of \ m a x = Ixlx^mu. 2,ix, 6 - t r i b r o m o a n i l i n e : T h i s compound r e a c t e d s l o w l y to produce a species which absorbed at Jx20mu. I t a l s o r e v e r s e d s l o w l y . I x-nitrophenylhydrazine ; T h i s compound produced a spectrum at 520mu i n the most b a s i c s o l u t i o n s . The sp e c i e s was only slowly r e v e r s i b l e . 167 2 ,[(.-dinitrophenylhydrazine : T h i s compound r e a c t e d to produce a slowly r e v e r s i b l e species whose Xmax w a s 5 6 0 m u . 2,1+, 6 - t r i n i t r o p h e n y l h y d r a z i n e : T h i s compound ap p a r e n t l y i o n i z e d i n the pH i n t e r v a l between 8 .and 1 2 . The apparent anion at 39lmu had a broad maximum c l o s e to that of the molecular species at 3£5mu. No attempt was made to measure t h i s pK a. In our s u l f o l a n e system t h i s s p e c i es changed slowly w i t h time. 168 B i b l i o g r a p h y . (I) R.P. B e l l . The P r o t o n i n ^ C h e m i s t r y . C o r n e l l U n i v e r s i t y P r e s s . ( 1959 ). ( l a ) Chap. I I ( l b ) Chap. VI ( l c ) Chap. IV. .(2) W.F. Luder and S. Z u f f a n t i . . 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