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The separation of the cis and trans isomers of decahydronapthalene by vacuum rectification Walker, Robert Duff 1937

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THE SEPARATION OF THE CIS AND TRANS ISOMERS OF DECAHYDRONAPHTHALENE BY VACUUM RECTIFICATION b y Robert Duff Walker A Thesis Submitted for the Degree of MASTER. OF APPLIED SCIENCE in the Department o f CHEMISTRY - The. University of B r i t i s h Columbia A p r i l 1937 TABLE OF CONTENTS. Page INTRO DUG TI ON A. Reasons for the research 1 B. 'Previous investigation "<• 2 G. Deductions from available data 2 BETAJLS OF APPARATUS A. The re c t i f y i n g apparatus and condensers 3 . • B. The receiving unit 4 C. The manometers 4 SEPARATION BY RECTIFICATION. A. Experimental procedure 5 " B. Experimental Results 6 C. Remarks 18 PURIFICATION OF SELECTED FRAGTIONS"BYFRAGTIONAL  GRYS TALLIZATION. A. Theory 19 B. Method ' 20 1. Preliminary Tests. :, . 2. Exact Tests. C. The purity of the f i n a l products. 23 1. The trans decalin 2. The cis decalin MEASUREMENT OF, PHYSICAL CONSTANTS A. Refractive Inde$ 24 B. Specific Gravity 25 G. Freezing Point 26 D. Conclusion 26 AN INVESTIGATION OF THE POSSIBILITY OF CONVERTING ONE ISOMERIC FORM OF DECALIN TO THE OTHER : Z§ge A. Previous Work 27 B. Experimental Procedure 28 C. Conclusion g]_ BIBLIOGRAPHY 3 2 DIAGRAMS Facing Page Graph 1. Volts across heating c o i l , small column 3 Graph 2* Volts across heating c o i l , large column 4 Graph 3. Refractive index vs. Composition 5 Figure 1.Receiving Unit & Figure 2... Eutectic Diagram 19 Figure 3. Freezing apparatus 20 Figure 4. Evacuating Apparatus 28 THE SEPARATION OF THE CIS AND TRANS ISOMERS OF DECAHYDRONAPHTHALEND BY VACUUM RECTIFICATION INTRODUCTION. A. Reasons for the research. Decahydronaphthalene (CioH]_g), or decalin, Is a hydrocarbon of the series CnHgn_2 and is usually prepared by the cata l y t i c hydrogenation of naphthalene. While decalin has only a limited commercial value, c h i e f l y as a fuel and as a solvent, i t i s of great theoretical interest.since two •isomeric forms exist.. The structure of these two isomers has, in recent years, provoked a great deal of controversy due almost entirely to the d i f f i c u l t y of preparing either of the two forms i n the pure state. The f i r s t object of this re-search was to devise a method for producing these two Isomers i n the pure form* The two isomers are designated by the terms cis and trans and the most generally accepted arrangement of the carbon atoms i n the two form i s that, shown i n sketches (a) and (b). If models of cis and trans decalin are constructed i t i s soon realised that one isomer cannot be converted to the other without disrupting "bonds. • T.0 - investigate the p o s s i b i l i t y of this conversion and the conditions under which i t takes place ' ( i f i t does take place) was the second object of this research. B. Previous Investigation. 1 In 1935 L. M. Kirk accomplished a p a r t i a l separation of decalin into i t s c i s and trans isomers by rect-i f i c a t i o n at 100 mm. pressure. The decalin used i n this p experiment was prepared by D. Manley by ,the reduction of t e t r a l i n . The results of Kirk's d i s t i l l a t i o n s were as follows: Fraction 1. 106*8 - 108.0° 0; L^©.8795; n^l.4737; .72.5$ trans. Fraction 4. 115.6 - 116.2° G; Djo.8944; n^l.4804; 18. Cf trans* Charging stock r£o.8888; n£>1.4756; 57.5$ trans. Gi Deductions from available data. •'"'».. From Kirk's data i t was thought that a d i s t -i l l a t i o n at a much lower pressure, say 10mm., would effect a greater separation since at t h i s pressure the difference between the boiling-points ,of the two isomers would be much increased. Available data Indicated that i t would not be practicable to work at an even lower pressure since then the bo i l i n g point would be i n the neighbourhood of room temperature • 1% L. M. Kirk, B.A.Se. Thesis, 1935. 2. D. Manley, B.A.Sc. Thesis, 1934.. and excessive evaporation would occur while the decalin was running from the condenser to the receiver. DETAILS Off APPARATUS. A* The apparatus i n which the vacuum r e c t i f i c a -tion was performed consists of three main parts, namelyj the r e c t i f y i n g column and the condensers, the receiving unit, and the manometers. A. The r e c t i f y i n g apparatus and condensers, „ Two r e c t i f y i n g columns are available. The f i r s t i s a glass tube, one inch i n diameter and 44 inches long. -It' i s packed with No. 18 galvanized iron jack chain. A 2000 cc. flask* provided with an i n l e t tube:, was blown on. the bottom of the column. The f l a s k and column are thorough-l y lagged and heat losses to the atmosphere compensated for by a heating c o i l of nichrome wire wound about the column next the glass. The heat losses, from the column for various tem.peratures.differences between the inside of the column" and the external a i r were calculated; knowing the resistance of. the heating c o i l , the volts required across the c o i l to balance the heat loss at various temperature differences were calculated and from t h i s data Graph 1 was constructed, A- reflex condenser i s blown i n the side of the column near the top and a thermometer Inserted down the column to the 'mouth of the condenser. There i s a c a p i l l a r y tube at the foot of the condenser through which the product is taken off. The seoond r e c t i f y i n g column was b u i l t to obtain a better separation i n one d i s t i l l a t i o n . It i s of the same construction as the previous column but i t s length i s 95 inches and the capacity of the d i s t i l l i n g bulb' Is 3000 cc. Graph 2 shows the volts required across the heating c o i l required to maintain adiabatic operation., instead of one condenser there are two condensers i n p a r a l l e l attached to •the side tube blown hear the top of the column. B. The receiving unit. The design of the•receiving unit and i t s operation, i s best understood by reference to Fig . 1. An electromagnet i s held outside the glass-casing, this magnet attracts the iron bars, and thus by moving the magnet, the discharge tube i s rotated from one receiving bulb to the next* When the discharge tube was set to take off a fraction a permanent magnet was strapped to the outside of the glass-casing to make sure- that during the d i s t i l l a t i o n the discharg tube would not wander out of position. C. . The manometers. The pressure measuring apparatus consists of a mercury manometer and a d i f f e r e n t i a l sulphuric acid mano-meter. The mercury manometer measures the absolute pressure i n the apparatus and the other i s used to detect any small fluctuations i n the pressure. This i s done by cutting off one arm of the sulphuric acid manometer when the desired *APH PAPER, C.P.C. pressure has been reached and then watching the change i n the level i n the other arm. Ti i s about 7.5 times as sensitive as the m e r o u r y manometer. SEPARATION BY RECTIFICATION. A. Experimental procedure. This part of the research consisted of r e c t i f y -ing under vacuum,.ten charges of decalin, collecting the d i s t i l l a t e from each i n five different fractions and measuring the refractive indem of each of these fractions. The refract-ive index with Graph 3 gives the composition of the fraction. The f i r s t f i v e r e c t i f i c a t i o n s were made with the 44 inch column and the l a s t five vri.th the. 95 inch column.airMositeof the r e c t i f i c a t i o n s were made i n one continuous run though two were carried out in three stages. The weak point of this apparatus l i e s in~ the fact that the reflux r a t i o cannot be measured but can be judged only by observation of the amount of vapour condensing.' With experience, however, i t can be kept very nearly constant. The water for the condensers was pumpfcd from a large bath which was maintained at a constant temperature by a thermostat, heaters and cooling c o i l . The variation i n room temperature has fortunately only a slight effect on the apparatur since the l i q u i d boils i n a range from 60O to 700 c (at 10 mm. pressure). . JMO d i f f i c u l t y was . experienced in maintaining a constant pressure, once the pressure had been set i t would stay steady for hours without adjustment. 33. Experimental results* For each of the f i v e fractions of every rect-i f i c a t i o n the following facts are given. 1 . The volume of each fraction i n cubic eentimeters. , 2 . The temperature of the condensing vapour at the start of the fraction and at the end. 3. The variation i n the temperature of the room. This item i s given so that i f any change i n the external temperature occurred the other items could be checked to see i f they had been affected. Actually during the r e c t i f i c a t i o n the temp-erature Of the Eondenslng vapour and the temperature of the room were noted every f i f t e e n minutes or oftener and the variation In room temperature did not appear to affect the readings, 4. The time i n which the fraction was collected. 5. The rate* In ccs. per hour at which the product was taken off. - . 6. The refractive index measured at 20° G. Later when accurate measurements of the refractive Index were being made the thermometer on which these readings were based was found to be inaccurate. The figures ,givenare r e a l l y for 20.2° G. These values are, however, important c M e f l y as a basis for noting the degree of separation accomplished by the r e c t i f i c a t i o n . 7\ The composition of each fraction i n percent of c i s and trans. These compositions were, determined.from Graph 3 which - 7 -i s based, for convenience, on the values given on the C r i t i c a l Tables for the refractive indices of the pure isomers, namely, ci s and trans . The values of the compositions w i l l be no more accurate than^the figures on which they are based but they v a i l be useful for comparing various fractions. In addition to this data for each fraction for each fraction general information on each r e c t i f i c a t i o n i s given such as the nature of the charge and to what use the various fractions were put. RECTIFICATION NO. 1 DATE. Feb. 21 to March 21. , CHARGE.. 1425 cc. of B r i t i s h Drug House decalin, 68$ c i s . PRESSURE IN APPARATUS.1 15 mm., of Hg. CONDENSER WATER, not regulated. RESULTS. Fraction 1 2 3 4 Residu< Volume (cc.) 133 550 310 120 300 Yap. Temp .*C •43.8-69.0° 69.1-73.8° 74,9-75.8° 75.5-76.7° Ext.Temp.°C 28.6-21.2° 28.9-23.2° 26.6-24.0° 25.6-22.6 Time (hrs.) 6.75 ' 27.25 16.50 6.50 Rate(cc/hr) 19.5 t 20.2 18.8 18.5 ' . • — 1.4603 1.4691 1.4717 1.4735 1.5071 Comp.$ ci s — 0 12.5' 27.0 fo, trans -- 100 ' 87.5 73.0 — . Total Tap. Temp Range. 45.8-76.7°C Total Time. 57.0 hrs. Total d i s t i l l a t e 1115.oc. Residue 300 GC . Loss 12 cc •This r e c t i f i c a t i o n was carried out in.a series of runs that lasted 6 to 12 hours each. Before further r e c t i f i c a t i o n s were made a new ca p i l l a r y tube was put i n to increase the rate at which the product was taken off Later r e c t i f i c a t i o n s with Eastman Kodak decalin indicated the decalin used i n this test to contain large amounts of impurities.; -- 8 -RECTIFICATION NO. 2 DATE. Oct. 22 - 23. 1936. CHARGE. 1450 cc. of Eastman Kodak Decalin, 45.5% c i s . PRESSURE IN APPARATUS. 10 mm.of Hg. CONDENSER WATER. 19° C. RESULTS. Fraction 1 2 3 4 5 Volume(cc) 143 665 233 250 100 Vap.TemptC 40.0-65.8° 65.8-66.9° 66.9-69.0° 69.0-69.4° 69.4-69.8° Ext.Temp °C.25.8-22.0° 23.5-22.2° 24.0-23.8° 23.0-25.7° 25.8-22.0° Time(hrs) 4.25 Rate(cc/hr) 34 1.47140 Comp.fo cis 10.0 ^trans. 90.0 Total- Vap.Temp.Range 40.0-69.8° , Total Time 19.91 hrs. Total d i s t i l l a t e 1391 cc. Residue 30cc. Loss 29 cc. Fractions 4 and 5 were r e d i s t i l l e d i n R e c t i f i c a t i o n No.5. 7.33 4.00 3.33 1.00 91 58 77 100 1.47423 1.47640 1.47911 1.48112 32.5 50.0 70.5 82.5 67.5 50.0 29.5 17.5 . RECTIFICATION NO. 5. -DATE. Nov. 5 - 6 , 1936. • CHARGE. 1500 cc. of Eastman Kodak Dec a l i n , 45.5% c i s . PRESSURE IN APPARATUS,. 10 mm. of f i g . CONDENSER WATER. 19° C. RESULTS. .Fraction 1 2 .3 4 5 Volume(oo) 120 325 470 295 250 Tap.Tempt 25.2-65.7° 65.7-67.1° 67.1-69.0° 69.0-70.6° 70.6-72.0° ~Ext.TemptC 22*4-21.0° 21.8-20.9° 22.1-20.9° 22.2-20.7° 22.0-21.0° .Time(hps) 1.17 2.50 • 3.75 2.50 2.50 Rate(cc/hr) 102 130 125 118 10Q (\%Q 1.47190 1.47280 1.47419 1.47728 1.48011 Comp. % c i s 14.0 21.0 32.0 56.0 79.0 'fo trans 86.0 79.0 68.0 44.0 21.0 To t a l Yap. Temp. Range 25.2 - 72.0° Total Time. 12*42 h i s . T o t a l D i s t i l l a t e 1460 cc. Residue 20 cc. Loss 20 cc. re Eractions 4 and 5 -w e r e / d i s t i l l e d i n R e c t i f i c a t i o n No.5. F r a c t i o n 2 was r e d i s t i l l e d i n R e c t i f i c a t i o n No.10. - 11 -RECTIFICATION No. 4 . DATE. Nov. 1 7 , 1 8 , 1 9 , 1 9 3 6 . -CHARGE. 1 5 0 0 oo. of Eastman Kodak Decalin, 4 5 . 5 $ e l s . PRESSURE IN APPARATUS. 10 mm of Hg. CONDENSER WATER. 190 Q . RESULTS. F r a c t i o n 1 2 3 4 5 Volume(cc) 157 3 2 5 :. 475 2 9 3 2 4 5 TempiTapfC 35 .0 -66 .5° 6 6 . 5 - 6 7 . 6 ° 6 7 . 6 - 6 8 . 8 ° 6 8 . 8 - 6 9 . 5 ° 6 9 . 8 - 7 0 . 1 ° Ext.Temp.°C 2 5 / 8 - 2 5 . 3 0 2 5 . 5 - 2 5 . 2 ° 2 6 . 6 - 2 2 . 8 ° 2 5 . 3 - 2 3 . 6 ° 2 5 . 3 - 2 4 . 0 ° Time(hrs.) 1 . 0 8 2 . 5 0 4 . 0 8 2 . 7 5 2 . 4 2 Rate(cc/hr) 127 130 116 107 1 0 1 Y L ^ o 1 . 4 7 2 1 0 1 . 4 7 3 4 1 1 . 4 7 4 8 7 1 . 4 7 7 4 0 1 . 4 8 0 1 1 Gbmp. % c i s 1 5 . 5 2 6 . 0 3 7 . 5 5 7 . 0 7 9 . 0 fo trans 8 4 . 5 7 4 . 0 6 2 . 5 4 5 . 0 2 1 . 0 TOTAL VAP. TEMP. RANGE. 3 3 . 0 - 7 0 . 1 ° C. TOTAL TIME 1 2 . 8 3 h r s . TOTAL DISTILLATE 1475 ce. 1ESIDH1 20 cc. LOSS 5 cc. F r a c t i o n 4 and S were r e d i s t i l l e d i n RECTIFICATION No. 5 . F r a c t i o n 2 w a s . r e d i s t i l l e d i n RECTIFICATION .NO. 1 0 . - 12 -RECTIFICATION No. 5. DATE. Nov. 27, 1936. CHARGE. 1421 cc. (for details see below) PRESSURE IN APPARATUS. 10 mm.. 'of Hg. CONDENSER WATER. 19° C. RESULTS. Frac t i on 1 2 3 4 5 Yolume(cc) 145 387 357 217 155 •Yap.Temp ?C 68.6-69.4° 69.4-70.2° 70.2-71.1° 71.1-72.0° 72*0-72.1 E?t.Temp.°C 24.8-24.0° 25.4-24.4° 24,5-23.8° 25.0-24.4° 24,4-24.3 Time(hrs) 2.25 3.25 3.25 2.00 1.50 Rate(cc/hr) 64 119 113 108 103 flto 1.47630 1.47732 1.47898 1.47988 1.48093 Comp.% cis 48.5 56.5 69.5 76.5 85.0 % trans 51.5 43.5 30.5 23.5. 15.0 Total Vap. Temp. Range. 68.6 - 72.1° C. Total Time. 12.25 hrs. Total d i s t i l l a t e 1394.cc. Residue 133 e.c. , 1.48262, % c i s 98.0. (the residue was a light-brown colour) Loss 27 cc. The charge consisted of Fractions 4 and 5 from Rectifications No. 2,3y and 4. Its composition was calculated to be 68.5% c i s . Fractions 2,3, and 4 were r e d i s t i l l e d in Rectification No.8* Fraction 5 and Residue were r e d i s t i l l e d i n Rectification No,9. - 15 -RECTIFICATION NO. 6 . DATE. . .Jan* 14, 1937* • CHARGE. 2000 cc. of B r i t i s h Drug House decalin ( PRESSURE IN APPARATUS. 10 mm. of Hg (at s t a r t ) . CONDENSER WATER. 19° C. h CIS. RESULTS. Fraction Volume (cc.) Vap.Temp.S Ext.Temp. . 1 270 2 605 3 540 4 280 5 200 2.00 Time (hrs) Rate(cc/hr) 135 o 2.33 260 1.83 295 .50 400 TV 20 1.46521 Comp.f? c i s . 0.0 fa trans. 100.0 Total Time 7.66 hrs Residue 75 ec. 1.00 280 1.46887 1.477280 1.47993 1.53528 0.0 21 77 100.0 100.0 79 23 0.0 Total D i s t i l l a t e 1895 cc Loss 30 cc. This was the f i r s t run made with the new column. Early in the run a slow leak developed; at the end of the run the pressure had risen to 2 4 mm., therefore no temperature, readings are given. The B r i t i s h Drug House decalin was used to check on suspected impurities; the refractive indices of the fractions sho?; that there are large amounts of impurities i n both the low and high boiMng fractions. For thi s reason this decalin was not used i n any further r e c t i f i c a t i o n s . - 14 -RECTIFICATIONNo. 7. DATE, dan. 28, 1937. , CHARGE. 2065 eo. of Eastman Kodak Decalin, 45.5f0 c i s . PRESSURE IN APPARATUS. 10 mm. of Hg. CONDENSER WATER. 20° 0 . RESULTS. Fraction 1 2 3 4 5 Volume(cc) 205 440 483 460 310 ' Vap.Temp'. 41.0-62.2° 62.2-63.7° 63.7-67.4° 67.4-69.2° 69.2-69,9° Ext.Temp. 22.-3-22.0P 24.6-22.2° 25.1-24*6° 25.1-24.1° 24.4-24.1° TimeChrs) 1.67 3.50 4.33 4.83 3*33 Rate(oc/hr) 123 126 1L2 .95 93 _ o y \ z o 1.47050 1.47093 L.47404 1.47892 1.48082 Comp. f0 c i s ":'3.2 6.5 3110 69.0 84.0 fo trans 96.8 93.5 69.0 31.0 16.0 Total 'Vap. Temp. Range. 41.0-69.9°C. Total Time.. 17.66 hrs. Total d i s t i l l a t e 1900 cc. Residue 120 cc. Loss 45 cc The new column has effected a marked improvement i n the separation. Fractions 4 and 5 were r e d i s t i l l e d i n RECTIFICATION No. 8. Fractions 1 and 2 were r e d i s t i l l e d in RECTIFICATION No. 10. RECTIFICATION No*. 8. . DATE.; Feb. 5, 1937. ' CHARGE. 1650 oo. (for details see below). PRESSURE IN APPARATUS. 6.mm. etf Hg. CONDENSER WATER. 20° G. RESULTS. Fraction 1 2 3 4 5 Volume(cc) 145 465 370 280 190 Yap.Temp. 56.0-5®.8° 59.8-60.5° 60.5-61.5° 61.5-62.1° 62.1-62.2° Ext.Temp. 25.9-24.0° 26.1-25.2° 26.2-25.8° 25.8-25.2° 25.4-25.2° Timellars) 1.33 4.50 4.25 5.25 2.00 Rate(cc/hr) 109 103 87 86 95 tv°0 1.47372 1.47680 1.47815 1.48094 1.48130 Corap. fo c i s . 28.5 52.5 63.0 85.0 87.5 fo trans. 71.5 47.5 37.0 15.0 - 12.5 Total Yap. Temp. Range. 56.0 - 62.2 C Total Time 15.55 Total D i s t i l l a t e 1450. Residue. 155 -co...; 90$ c i s , 1.48161 (light brown color) Loss. 45 cc. The charge consisted of Fractions 2, 5, 4, RECTIFICATION No.5 and Fractions 4 and 5, RECTIFICATION No. 7. .Composition was calculated to be 69.8$ c i s . Fractions 4 and 5 and Residue were r e d i s t i l l e d i n RECTIFICA-TION .No. 9. - 16 -RECTIFICATION NO. 9. DATE. Feb. 10, 1937. CHARGE. 1000 c c . (for d e t a i l s see below) PRESSURE IN APPARATUS. 10 mm. of Hg. CONDENSER WATER. 20° C. RESULTS. Fraction . 1 2 3 4 5 Volume(cc) 102 155 155 270 210 Vap.Temp. 68.5-68.9° 68.9-69.5° 69.5-69.5° 69.7-69.7° 69.7-69.7 Ext,Temp. 25.5-24,0° 25.8-25.5° 25.8-24.0° 24.1-23.8° 24.8-23.6 Time (hrs.$> 1.17 2,0 2.0 3.0 Rate(cc/hr) 87 78 78 90 84 . n& 1.48082 1.48101 1.48110 1.48122 1.48130 Comp. f0 c i s . 84.0 85 e 5 86.0 87.0 87.5 fo trans. 16.0 14.5 14.0 13.0 12.5 Total Vap.Temp Range . 68.5 - 69 .7° C. Total Time. 10.67 hrs. x o t a l d i s t i l l a t e 892 cc. Residue. 60 cc. (very dark) Loss 48 cc. The charge consisted of fraction 5 and lesidue, RECTIFICATION No, 5; Residue, RECTIFICATION No. 7; Fractions 4, 5 and Residue RECTIFICATION No. 8. - 17 -RECTIFICATION No. 10. DATE. Feb. 12, 1937. , CHARGE. 1275 co. (for details'see below). PRESSURE IN APPARATUS. 10 mm. of Hg. CONDENSER WATER. 20° C. RESULTS. Fraction. 1 2 3 4 5 Volume(cc) 130 255 265 150 75 Vap.Temp. 40.9-60.3° 60.3-62.7° 62.7-62.7° 62.7-24.5° 64.5-68.9° Ext. Temp. 26.1-25.1° 26.3-26.1° 26.1-24.6° 24.9-24.6° 24.6-24.2° Time (hrs) 1.53 .3.0 3.0 1.75 1.0 Rate (cc/hr) 82.6 85 88 86 75 n.£> 1.46877 1.46967 1.46967 1.47042 1.47528 Comp. fo c i s . 2.5 40.5 fo trans. 100 100 100 97.5 59,5 Total Vap. Temp. Range 40.9 - 68.9° Total Time 10.33 hrs. Total S l s t l l l a t e 1075 cc. Residue 140 cc., 84.0$ c i s , 1.48082. Loss 60 cc. The charge consisted of Fraction 2. RECTIFICATION No.3; Fraction 2, RECTIFICATION No. 4; Fraction 1 and 2, RECT.No.7. Composition was calculated to be 83.4$ trans. - i s -G. Eemarks. RectificationsNo. 8 and No. 9 .show that further d i s t -i l l a t i o n w i l l do l i t t l e to increase the cis content of the f i n a l fractions. i n both r e c t i f i c a t i o n s Fraction 5 had the same composition. This i s a constant b o i l i n g point fraction and should therefore be very pure. The fact that i t s refractive index (1.48130) does not agree with that i n the C r i t i c a l Tables for pure c i s (1.4828) i s not an indication of impurity. The value obtained by Jiuckel 3 for pure c i s i s 1.47950 which i s lower than that of the fractions obtained here. ' ^ efore making accurate measurements of the re f r a c t i v e index the fractions from Re c t i f i c a t i o n No.9 were put through a series of f r a c t i o n a l c r y s t a l l i z a t i o n s . This procedure should purify them and the freezing points w i l l give an indication of th e i r purity. ,In Fractions 2 and 3 from Re c t i f i c a t i o n No. 10 a very high trans content has apparently been reached. The refractive index i s 1.46967 for these fractions; for pure trans the C r i t i c a l Tables give 1.4701 and Huckel's value i s 1.46958. Fractions 2,5,and 4 were selected for treatment by f r a c t i o n a l c r y s t a l l i z a t i o n to see i f they could be p u r i f i e d further. Walter•, Hu'ofcel.,. Ann. 441,1,(1925) -3o°c + T 'a. U so/id. f l r u A S rn/xfurs Solid. CiS I solid. I Cixtecfic ' Sol'li. trans Solid. eutectic -f-SolicL CIS 0 % c'.s /OO'/. frans 'OO'/o c/'s 0% trans - 19 -PURIFICATION OF SELECTED FRACTIONS BY FRACTIONAL .CRYSTALLIZjl-ATI ON. A. Theory. This p u r i f i c a t i o n i s based on the formation of a eutec-t i c when a, mixture of cis and trans decalin is frozen. When a mixture that i s , say, A percent, trans (Fig.2) i s cooled crystals of solid trans start to separate out at Ta° and con-tinue forming u n t i l the temperature has dropped to Te° at which point the eutecimc mixture starts to c r y s t a l l i z e out and the temperature stays constant u n t i l a l l the mixture has frozen. Now i f the mixture is removed from the freezing bath before the temperature has dropped to Te° and the l i q u i d siphoned away from the cr y s t a l s , these crystals w i l l on meIt -ing give'a l i q u i d that i s higher i n trans than the l i q u i d . from which the crystals came* Some of the.cis decalin w i l l have been clinging to the crystals of trans as the mixture i s now, say, B percent trans (Fig. ). On cooling this mixture crystals of trans w i l l start to separate out at T^0 and the process of separation of crystals from l i q u i d i s repeated. This f r a c t i o n a l c r y s t a l l i z a t i o n i s continued u n t i l i t is found that the removal of a portion of l i q u i d from the crystals does not lower the temperature at which crystals f i r s t separate out. When th i s point has been reached the temperature should stay constant u n t i l a l l the l i q u i d has frozen. This result w i l l show that a pure l i q u i d has been prepared. In any mixture FREEZING APPARATUS of c i s ana trans cfeealin the higher the freezing point the higher the cis or trans content w i l l be, depending, of coursse, •on which side of the eutectie the mixture i s . B. Method. 1. Preliminary tests. A number of fractions of comp-aratively pure trans had been prepared i n R e c t i f i c a t i o n No.10. Fraction 1 was not considered since i t l i k e l y contains some low-boiling impurities. The. middle fractions 2,3, and 4 weee tested to f i n d the temperature at which crystals started to separate out. The apparatus i s shown i n Fig.3. The outer vessel i s a pla i n glass Dewai flask; the freezing mixture i s methyl alcohol colled by the addition of small pieces of so l i d carbon dioxide; three i s a glass s t i r r e r and a pentane thermometer i n the freezing mixture; the fraction being tested i s contained In a large glass tube provided with a glass s t i r r e r and a large pentane' thermometer. Some d i f f i c u l t y was experienced with super cooling, the fraction always 'supercooled and i t was d i f f i c u l t to keep the supercooling about the same for each test.. If the supercooling i s too great the true freezing point w i l l not be given and i f i t i s not about the same for each test the results cannot be compared. As already explained the fraction that has the highest freezing point w i l l have' the highest trans content. Fractions 2, 3, and 4 from Rectification No. 10 were tested with this apparatus to find which had the highesttrans content. Results. Fraction 2. Rectification No.10. Freezing point, -35.0° C. S 3, » " » » •« ' -30.2° C. n 4, tt tt „ it t. -31.8° C. These fractions were then put through two fr a c t i o n a l c r y s t a l -l i z a t i o n s , a portion of l i q u i d , about 30 cc. being siphoned away from each fraction each time. When a portion had been removed the temperature at which crystals came down in the part l e f t behind was again found. Due to d i f f i c u l t i e s with supercooling i t was not possible to say d e f i n i t e l y that the process was rai s i n g the temperature at which crystals f i r s t formed. I t was therefore decided that before making f u r t s r efforts at p u r i f i c a t i o n to construct a more accurate apparatus. • Re c t i f i c a t i o n No, 9 produced fractions with a high c i s content. Of these fractions 2, 3, 4 and 5 were tested by the same method as the high trans fractions. Results Fraction 2. Rectification No.9. Freezing point,-43.2° 0... Fraction 3, " " " 11 -42.6° C. » 4, " " "• " -42.2° G. : n 5 s » tt tt n -43*5° G. Two portions of l i q u i d were removed from each of these and the same d i f f i c u l t i e s were encountered^iith the trans fractions. 2. Exact Tests. Two modifications were made on the apparatus used"for the preliminary t e s t s . F i r s t , the tube holding the frac t i o n being frozen was placed inside a - a s -s l i g h t l y larger tube, this created an a i r space between the freezing mixture and decalin and therefore prevented the •decalin from cooling too rapidly and also neutralized sudden changes i n the temperature of the freezing mixture. In this way the effect of supercooling was reduced and st a b i l i z e d . Second, i n place of the large pentane thermometer a platinum resistance thermometer was used to read the temperature of the decalin. From the preliminary tests Fractions, Rect. Mo, 10, appeared to have the highest trans content. This fraction was carerully cooled u n t i l crystals started to form. The temperature stayed constant (showing high purity already) for nearly five minutes. The -resistance of the platinum was measured and from t h i s the temperature calculated. The i e c a l i n and was melted/again carefully cooled u n t i l crystals started to fomm and wtien about, f o u r - f i f t h s of the l i q u i d had frozen the remain-der, about 40 c c , was siphoned off. After melting the decalin crystals l e f t behind i t s freezing-point was found && previously. Results.« Before decanting - Resistance 2.2012, Freezing point, -30.50° G. After decanting - 2.2013, » -30.29° C. The rise i n the freezing point was so small that i t could have. very been an experimental error. This sample was apparently/pure and was therefore set aside for determination of the physical constants of titans decalin. - 23 -From the preliminary tests Fraction 4, Rect. NO. 9 appeared to have the highest cis content, -"-t was put through the same procedure as the high trans f r a c t i o n . Result s Before Decanting, Resistance 2.0811, Freezing point, -42.60° C After decanting, " . 2.0814, » .-42.57° c . Again the r i s e i n freezing point i s very sl i g h t . This fraction was therefore set aside for the -determination of the physical constants of cis decalin. 0. The purity of the f i n a l products. 1. The trans decalin. This material i s from the middle f r a c t i o n of five taken off from the r e c t i f i c a t i o n (Rect. No,10} of a sample of decalin whose composition had been raised to 83.4% trans by combining the high trans fractions from previous d i s t i l l a t i o n s . Thus there could be l i t t l e im-purity i n the sample to start with as a l l of i t has been d i s t i l l e d at least twice previously, i n addition the fraction used i s a middle fra c t i o n which i s least l i k e l y to contain any of the lovi or high b o i l i n g impurities. The fraction was collected over a period of three hours during which tjiime the temperature remained constant at 62.7° C. which Is another i n d i c a t i o n of high purity.., This fr a c t i o n has also been pu r i f i e d by th^ee f r a c t i o n a l c r y s t a l l i z a t i o n s u n t i l the freezing point remained constant. This freezing point, -30.30° G., i s higher than that given by Huckel for pur trans, -36° C , and assuming the formation of a eutectic (Fig. ), the higher - 24 -freezing point should indicate greater purity. 2. The-cis decalin. This material i s from the fourth of fi v e fractions taken off from the r e c t i f i c a t i o n -(Rect.No.9) of a sample of decalin whose composition had been raised to very nearly 90$ cis by combining high fractions from prevx&aus d i s t i l l a t i o n s . Most of these fractions had been d i s t i l l e d two or three times previously and should therefore contain very l i t t l e trans. Some high b o i l i n g impurities were introduced into the charge for .Sect. No. 9 due to the inclusion of residues. In no case, however, were the residues used more than just s l i g h t -l y discoloured. As the f i f t h fraction from this r e c t i f i c a t i o n was s t i l l perfectly colourless these impurities ?/ere certainly l e f t i n the f i n a l residue. This f r a c t i o n was collected .over a period of three hours, during which the temperature of the condensing vapour remained constant at 69.7° G. which i s an ind i c a t i o n of high purity. In addition the fraction has been further p u r i f i e d by three f r a c t i o n a l c r y s t a l l i z a t i o n s u n t i l the freezing point could not be lowered by further c r y s t a l l -i z a t i o n . This freezing point, -42.60^ G., i s higher than that given by Huckel for puis c i s , -51° G., and should mean that this f r a c t i o n i s more pure than that obtained by huckel. MEASUREMENT OF PHYSICAL CONSTANTS. A.Refractive index. = The measurements were made with a P u l f r i c h Refracto-1: - 25 -meter i n conjunction with a constant temperature water supply for the cooling jacket about the prism of the refTactometer. ,The temperature of the water i n the bath was maintained at exactly 20.0° G. as read by a thermometer that had been checked against a platinum resistance thermometer. The thermometer of the refractometer was checked against this one. Results. a. Erans decalin C r i t i c a l Tables Huckel Ts Value b. Gis decalin C r i t i c a l Tables Huckel's Yalue a 20 1 , 4 6 9 4 8 1.4701 1.46958 1.48084 1.4828 1.48054 Huckel's values are for c i s and trans decalin prepared by the synthesis starting with o c t a l i n . ^ B, Specific Gravity. These measurements were made with a calibrated vacuum spec i f i c gravity bottle and the weighings done on a chainomatic balance reading to 0.1 mg. Results. a. Trans decalin C r i t i c a l Tables Huckel's Yalue b. Cis decalin C r i t i c a l Tables Huckel's Value 4. Walter Hucke1, Ann. 441, 1, (1925) £>2'o 0.86887 0.872 0.8695 0.89145 0.898 0.8952 D zo C. Freezing point. These were determined with the platinum .resistance .thermometer during the last part 'of the fract i o n a l c r y s t a l l i -zation process. Resuits. a. Trans decalin -50.30° 0. G r i t i e a l Tables -125° C. Huckel's Value -36° C. b. Gis decalin -42.60° G C r i t i c a l Tables 6 •Huokei's Value -51° G. D. Conclusion. The physical constants of the trans and c i s decalin prepared during t h i s research are i h good agreement with values 5 reported by other experimenters. The differences from other experimenters values are, i n fact, of such a nature that i t may be claimed that the trans and c i s decalin prepared here are purer, than that used i n previous research work. In addition an apparatus has been constructed with which large amounts of either pure trans or cis can be obtained in a short time from technical decalin. 5. Walter Hucke,, Ann. 441,45,(1925) - 27 -AN INVESTIGATION OF THE POSSIBILITY OF CONVERTING- ONE ISOMERIC .FORM OF DECALIN TO THE OTHER. A. Previous work. The experiments . of N.O .Zellinsky and M.B.Turova-Pollok showed that ois decalin could be converted to trans* 'These investigators found that in the presence of A.lBr^ this conversion took place smoothly at temperatures below 100° C. Research work carried out i n this laboratory also appeared t o furnish evidence for the conversion of one form to the other, without the presence of a catalyst. W. F. Cornett carried o u t tests i n various mixtures of the c i s and t B a n s o 7 isomers over a period of several weeks at 20 e. and at 100°G. Compositions were determined a t different times by refractive index measurements. From his work Cornett concluded that cis was changed into trans and that the rate of change was much faster at 100° C. than at 20° C. but he could obtain no con-clusive evidence for the conversion of trans to c i s . Further evidence of conversion appeared to be found i n the results of R e c t i f i c a t i o n No. 1, The decalin r e c t i f i e d was a water-white B r i t i s h Drug house product, produced by the catalytic hydrogenatlon of naphthalene. Four fractions were collected and analyzed. This analysis indicated that these four fractions contained at least a 1000 c c . of the trans isomer while the o r i g i n a l charge had contained only 470 c c . of trans. This result appeared t o indicate: a large degree of conversion of the c i s Isomer to the- trans. 7 . hi. F, Cor-rxetfr . F . / / , S c T^es}& , 1935, T o «ftnos /p'i»r \ r ?\ ?\ To va.£uux.rf\ Fia.4-- 28 -B. Experimental Procedure. In an effort to explain or confirm the results of the above experiments a series of tests ?rere carried out. In de-t a i l i n g the results of these tests compositions w i l l be given in terms of the cis content of the fraction testedj compositions determined as usual by refractive index measurements. Glass tubes about 30 cms. long and 1.5 cms. diameter, with a small glass tube blown on one end were used. Twenty-f i v e to •thirty ccs. of decalin of known composition were placed i n each tube. To prevent oxidation of the decalin the a i r above the sample was pumped off and hydrogen allowed to enter. Before sealing the tube off the valve to the atmosphere(Fig.4) was opened momentarily so that the hydrogen over the sample would be at one atmosphere pressure. The sealed bulbs were then placed i n ovens and maintained at a constant temperature for a number of days. They were then removed and the re-fractive index of each -sample measured. Test 1. 480 hrs. at 86° G. ' Sample I n i t i a l Gomp. F i n a l Gomp. AA : 0 0 BB 26.0 26.0 ; • FF 84*5 ; 84.5 ^Sample BB contained several pieces of mossy zinc introduced to see i f the galvanized chain used to pack the r e c t i f y i n g column caused any conversion of the isomeric forms. From the results of this test i t appears that no conversion takes place at - 29 -this temperature and also that the zinc has no particular effect. Test 2. 453 hrs. at 108° G. Sample. I n i t i a l Comp. Final,Comp. M11X 21.0 . 26.0 M i l 21.0 26.0 -M28B'. 32.0 38.0 M33 76.5 77.5 Sample M i l contained some mossy zinc and zinc dust. Sample M22 after the heafiing had a cloudy, rather opalescent appear-ance. It was f i l t e r e d before measuring the refractive index. From the results there appears to be an increase in the arount of the c i s isomer which i s most marked, i n the. samples lowest In cis content. Test 5. 453 hrs. at 148° C. Sample I n i t i a l Comp. Final Comp. A l l 21.0 26.0 A22 23.0 59.0 A33 76.5 77.5 Sample A22 contained some zinc dust. Samples A l l and A35 ?;ere s l i g h t l y cloudy after heating. The portion used for measuring the refractive index was f i l t e r e d f i r s t . After these two samples had stood for a week the cloudiness had disappeared, This .cloudiness might have been due to slight dehydrogenation. The increase i n the c i s content of these samples i s very nearly the same as the increase In the samples used.for Test 2. The la t t e r was carried out at 108° C. compared to the 148° C. for - 30 -Test 3 but the higher temperature has apparently not inoreased the amount of conversion. On the other hand Test 1 at 86° C. 'showed p r a c t i c a l l y no change i n composition* A l l three tests lasted very nearly the same length of time. These results appear to show that some conversion w i l l take place when the temperature i s over perhaps 100° C. but they show l i t t l e else. A fourth test was carried out to see i f any further inform-ation could be obtained. o Test 4. 140 hrs. at 150 C.. Sample I n i t i a l Gomp. .final Gomp. AA \ 0 0 FF 84.5 85.0 M35s^ 77.5 77.5 M22 38.0 38.0 Samples AA and FF had previously been heated for 480 hrs. at 86° G. and samples M.33 and M22 had breviousley been heated 453 hrs. at 108° C. No conversion appeared to atke place i n t h i s test. The results of these four "tests were so contradictory that i t was decided to abandon this line of investigation.. One further test of a different type was carried ou:t i n which conditions existing i n the r e c t i f y i n g column were duplicated as nearly as possible. A glass tube 40 i n . long, 1 i n . : diameter,. was packed with wo. 18 galvanized iron jack chain; a round bottomed f l a s k was blown on to the bottoa and a reflux condenser to the top. A sample of decalin, 75 c c , of known composition was placed i n the bulb, the apparatuswas evacuated and then sealed o f f . This sample was refluxed for one week and then removed to be analyzed. It had become s l i g h t l y discoloured during the refluxing. Composition before refluxing 37.5% cis " after " 39.0% cis The apparent increase might be due to the effect of the d i s -colouration on the rafractive index reading. The sample used toi t h i s test was from the thi r d of five fractions obtained by a r e c t i f i c a t i o n of £000 cc. of Eastman Kodak decalin. It should have contained only cis and trans decalin and no impurities. Erom th i s test i t was concluded that the apparent large degree of conversion of trans isomer to c i s during the r e c t i f i c a t i o n of the B r i t i s h Drug House decalin ?/as not due to conversion at a l l but to the presence i n the o r i g i n a l decalin of large amounts, of impuritfes which during the r e c t i f i c a t i o n became concentrated i n different fractions. R e c t i f i c a t i o n No.6 of a sample of the same B r i t i s h Drug House decalin carried out with a more e f f i c i e n t r e c t i f y -ing columb confirmed the presence of large amounts of im-p u r i t i e s i n t h i s decalin. G. Conclusion. No definite evidence of conversion of either form to the other has been obtained, i f any conversion does take place the results indicate that the c i s form to the tnns i s more l i k e l y than the reverse reaction. - 32 -BIBLIOGRAPHY W. p. Cornett, B.A.Sc. Thesis, 1935. Walter Huckel, Annalen der Cheiaie; 441,1,1925. L. M. Kirk, B. A. Sc., Thesis, 1935. D. Manley, B. A. Sc. Thesis, 1934. N.O. Zellinsky and M. B. Turova-Pollak, Berichte, 58B., 1292-98, 1925. 

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