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The study of highly strained cyclopropyl adamantane compounds with emphasis on their radical copolymerizations… Schmidt, Justin Orvel 1972

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THE STUDY OF HIGHLY STRAINED CYCLOPROPYL ADAHANTANE COMPOUNDS WITH EMPHASIS ON THEIR RADICAL COPOLYMERIZATIONS WITH OXYGEN BY JUSTIN ORVEL SCHMIDT B.S. Chemistry, Pennsylvania State U n i v e r s i t y , 1969 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the Department of CHEMISTRY We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA February, 1972 In presenting t h i s t h e s i s in p a r t i a l f u l f i l m e n t of the requirements f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r reference and study. I f u r t h e r agree t h a t permission f o r extensive copying o f t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s r e p r e s e n t a t i v e s . It i s understood that copying or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l gain s h a l l not be allowed without my w r i t t e n permission. Department of The U n i v e r s i t y of B r i t i s h Columbia Vancouver 8, Canada - i i -ABSTRACT The synthesis of a new type of h i g h l y strained cyclopropyl group between the two remaining bridgehead p o s i t i o n s i n 1,3-dimethyl-adamantane was accomplished by an i n t e r n a l coupling r e a c t i o n i n v o l v i n g the removal of two bromines with sodium-potassium a l l o y i n ether. 5 7 1 3 The product, 5 , 7 - d i m e t h y l t e t r a c y c l o [ 3 . 3 . 1 . 1 . 0 ' ]decane, commonly named 3,5-dimethyl-l,3-dehydroadamantane (DMDHA), formed a polymer on heating the pure material to a temperature above 90°C. The polymer's properties were studied by X-ray analysis and d i f f e r e n t i a l scanning calorimetry. The previously reported parent compound to DHDMA, t e t r a c y c l o -5 7 1 3 [ ' .Q. ' Jdecane, commonly named 1,3-dehydroadamantane (DHA), was synthesized and studied to determine the properties of the cyclopropyl bond between the bridgehead carbons. Reactions with sev e r a l stable free r a d i c a l s and other known reagents with a f f i n i t i e s f o r r a d i c a l s i n d i c a t e d a very high degree of r a d i c a l character present at the bridgehead p o s i t i o n s . From k i n e t i c studies of the reaction of DHA with molecular oxygen at approximately 1 atmosphere and 22°C, f i r s t order k i n e t i c p l o t s were obtained which y i e l d e d the -5 -1 -5 -1 rate constants of k = 15.0 x 10 sec i n octane and 32.8 x 10 sec i n xylene. Oxygen was absorbed to an extent s l i g h t l y greater than one mole per mole of DHA. The reaction was without ambiguity shown to be of r a d i c a l nature through the use of s e v e r a l free r a d i c a l i n h i b i t o r s to retard the reaction rate. The i n i t i a t i o n mechanism of the DHA-oxygen copolymerization c'puld not be determined with c e r t a i n t y . The spontaneous re a c t i o n was e i t h e r - i i i -i n i t i a t e d by oxygen r a d i c a l s a t t a c k i n g t h e h i g h l y s t r a i n e d , h i g h l y p - o r b i t a l - c h a r a c t e r e d carbon atom from i t s u n p r o t e c t e d back s i d e o r e l s e by the i n t e r n a l bond o f the c y c l o p r o p y l group s p o n t a n e o u s l y r i n g o p e n i n g t o form an adamantane d i r a d i c a l . I n the l a t t e r c ase the r a d i c a l formed would sometimes c a p t u r e an oxygen b e f o r e the e q u i l i b r i u m s h i f t e d back t o the c l o s e d form. A l l t h a t i s known f o r c e r t a i n t y i s t h a t the 1,3-carbon bond i n DHA i s v e r y h i g h l y s t r a i n e d and i s e i t h e r i n e q u i l i b r i u m between an open and a c l o s e d f orm o r e l s e i s a t l e a s t v e r y r a d i c a l - l i k e i n n a t u r e . - i v -TABLE OF CONTENTS Page INTRODUCTION 1 RESULTS 1 1 Synthesis ^ R a d i c a l Studies 1 5 Products of I n h i b i t e d Reaction !9 DISCUSSION 2 4 P r e p a r a t i v e Reactions 2 4 P o l y m e r i z a t i o n Reactions ^ R a d i c a l Studies 35 EXPERIMENTAL 51 Synthesis 52 59 R a d i c a l Studies . Product Studies 71 REFERENCES 7 7 APPENDIX 81 - v -LIST OF FIGURES F igure Page 1 C l a s s i c a l Synthesis of Cyc lopropy l Compounds 2 2a Walsh Model of Bonding i n Cyclopropane 3 2b Bent Bond Model of Bonding i n Cyclopropane 3 3 The DHDMA St ructure and i t s N.M.R. Absorpt ions 1 2 4a Poss ib l e Debromination Mechanisms Y i e l d i n g DHA from DBA 3 0 4b P o t e n t i a l Role of Na °-K ° A l l o y i n Formation of DHA . . 5 Two Poss ib l e Representat ions of the DHA Molecule . . . . 41 6 Mechanism of Rad i ca l I n h i b i t i o n of DBPC 44 7 DHA-O^ Reactions Occurr ing i n the Presence of DBPC . . 4 7 8 DHA-O^ Reactions Occurr ing i n the Presence of 1-Dodecane t h i o l and p-Quinone ^ 9 Poss ib le Explanat ion of DHA-02 and RSH React ion Products 49 10 DHA Subl imat ion Apparatus 64 11 Apparatus Used fo r K i n e t i c Studies 67 - v i -LIST OF TABLES Table Page I R e s u l t s of DHA-02 Reaction K i n e t i c s 16 I a Some Mean Values from Table I 17 I I Concentrations of Adamantane and I n h i b i t o r S o l u t i o n s . 63 I I I DHA Standardized S o l u t i o n s f o r K i n e t i c s 66 IV DHA-O^ Reaction: Experimental Q u a n t i t i e s 70 V Products of a 9:2 DHA:DBPC Reaction Mixture i n the Presence of 0_ 76 - v i i -ACKNOWLEDGEMENT I would l i k e t o e x t e n d my most s i n c e r e g r a t i t u d e t o Dr. R.E. P i n c o c k f o r h i s c o n c e r n and g u i d a n c e t h r o u g h o u t the d u r a t i o n o f t h i s p r o j e c t . H i s time and e f f o r t p r o v i d e d much encouragement. I a l s o w i s h t o thank the N a t i o n a l R e s e a r c h C o u n c i l o f Canada f o r f i n a n c i a l a i d d u r i n g t h i s t i m e . - 1 -INTRODUCTION The chemistry of adamantanes has been a f i e l d of i n t e n s i v e i n t e r e s t within the l a s t 15 years. Another f i e l d of great i n t e r e s t i s the study of cyclopropanes. To date the two studies have crossed paths very l i t t l e i n the l i t e r a t u r e ; those few times have usually involved studying the e f f e c t of various cyclopropyl substituents on adamantane r e a c t i v i t i e s . To study a system such as the dehydroadamantane (DHA) system which has properties of both molecules, a background study i n t o the two separate f i e l d s i s necessary. Cyclopropanes, due to t h e i r unusual geometry, bonding, and r e a c t i v i t y , have provided a basis f or vast numbers of both t h e o r e t i c a l and synthetic studies. Cyclopropanes themselves have been known and synthesized by numerous methods f o r many years. Reactions (1) through (6) i n Figure 1 are some of these syntheses. By making use of one of these methods or others unmentioned, a wide v a r i e t y of cyclopropyl compounds or compounds with cyclopropyl substituents have been made. Adamantane DHA - 2 -.CH2Br Na hydrocarbon (l)a ref. 1 X CH2Br Zn ethanol CH2Br (l)b ref. 2 -CH2-C-CH3 KOH CH2Br 0 II C-CH, (2) ref. 3 <C(COC H ) Na + _Na+ C(COC 2H 5) 2 (COC2R5)2 (COC 2H 5) 2 (3) ref. 4 »HCCOOC2H5 ^ HCCOOC2H5 4 W W (COC2H5) . (COC2H5) ,(COC2H5) (COC2H5) (4) ref. 5 :CH, (5) ref. 6 Br Br n-butyl L i . -30°,2.5 hr Br L i (6) ref. 7 minor major Figure 1. Classical Synthesis of Cyclopropyl Compounds. - 3 -The chemistry of cyclopropane reactions is in general similar to olefins. Cyclopropanes are unstable to acid, degradation occurring with ring opening, but are extremely stable to base. Radical attack i s generally a favourable reaction, excepting in the reactions of radical polymerizations, which are very d i f f i c u l t to induce, as w i l l be discussed later. The problem of bonding i n cyclopropane is as yet a very open discussion. In general, at least two models for bonding may be drawn with variations in these, depending on the type of calculations used. These are the Walsh model (Figure 2a) and the bent bond model 2 (Figure 2b). The Walsh model involves carbon sp hydridization with p 2 orbital overlap of the three carbons. One sp lobe from each carbon is directed toward the center with the other two bonded to hydrogens. The overlapping p orbitals contain four electrons while the central 2 sp orbitals contain two electrons. The bent bond model is described in different ways, but is generally thought to consist of approximately '5 2 8 sp C-C bonds and sp C-H bonds. Calculations concerning bent bond Figure 2a. Walsh Model Figure 2b. Bent Bond Model models have yielded degrees of p character (written i n the form sp n) varying from C-C sp , C-H sp (Clemente) and C-C sp , r „ 2.28 _ _ _ 4.91 _ „ 2.02 / c 1 _ . 10,9 .... „. ' , C-H sp to C-C sp , C-H sp (Slater). ' A l l these calcula-tions at least agree that carbon-carbon bonds have an unusually high - 4 -degree of p character for alkanes, whereas the carbon-hydrogen bonds have much more s character than usual. This bonding character, along with the strain energy of 27 K'cal mole \ is a strong factor i n cyclopropyl reactivity and in directing the types of reactions cyclo-propanes undergo. Adamantane, because of i t s r i g i d , almost strain-free t r i c y c l i c structure, has been subject to intensive study and several reviews 11-13 in the last 15 years. Due to the high degree of symmetry of the molecule, only two types of carbons are present: 6 secondary and 4 tertiary carbons. These two types of carbons react somewhat as expected to both carbonium ions and carbanions. Tertiary carbonium ions are stabilized to the order of 10 kcal more than secondary carbonium i o n s , ^ a sometimes complicating factor i n adamantane 14 reactions. Tertiary carbanions of adamantane have not been reported; however, recently a synthesis of secondary carbanions has appeared. Several other interesting properties of the adamantane structure are due to i t s symmetry and r i g i d i t y . Among these are i t s i n a b i l i t y to form olefins and the n.m.r. spectrum of the 1-adamantyl carbonium ion. The n.m.r. spectrum was studied by Olah and Schleyer and found to be of interest because the hydrogens g to the carbonium ion were shifted substantially downfield from the a hydrogens. The authors 3 explain the observations as resulting from back lobe sp stabilization of the carbonium ion. This stabilizing effect would draw electron density more from the tertiary B hydrogens than from the secondary a hydrogens, causing the three bridgehead hydrogens to be shifted further - 5 -downfield. The lack of a b i l i t y to form olefins within the adamantane structural body is due to the geometrical requirement of an olefin being located at a bridgehead position. This placement of a double bond at a bridgehead is a clear violation of Bredt's rule. Bredt's rule i n i t s modern form says that a double bond at a bridgehead position may only occur in an isolatable compound i f the ring containing the trans portion of the double bond is eight or more membered. Transitory species may occur with the trans portion of the 17 double bond in a seven membered ring. A double bond in adamantane by necessity must be placed trans in a six membered ring. This rule has been shown to hold i n the adamantane case despite several attempts * to disprove i t . With this brief background into cyclopropane and adamantane chemistry, attention may be directed toward the main aim of this thesis, namely the synthesis of a highly strained cyclopropyl adamantane compound and the study of i t s radical nature as determined by radical Two such attempts that failed involved either the elimination of HBr from l-bromoadamantanel8 o r the use of the photochemical Norrish Type II elimination using 1-adamantylacetone.^ - 6 -type reactions, in particular, i t s radical polymerizations. Previous work in this area has been quite limited; therefore, to study the radical properties of the system, both the properties of adamantyl radicals and the radical properties of cyclopropyl compounds should be investigated. Studies of adamantyl radicals, though not as numerous as carbonium ion studies, are quite common. Much of the information resulted from studies directed toward determining the geometry of alkyl radicals. The earliest of these was a study of the relative rates of decarbonyla-20 tions from t-butyl, adamantyl, and two b i c y c l i c aldehydes. The authors concluded that 1-adamantyl radical was just sl i g h t l y more stable than t-butyl radical, the relative rates being 2.5:1. Other similar studies were carried out on t-butyl and adamantyl peresters 22 23 of t-butyl carboxylates. ' A l l three studies indicated that 1-adamantyl radical i s just a normal tertiary radical with no unusual properties and reacts in a similar manner as t-butyl radical. More recent studies using carbochlorination in CCl^ led to f i n a l conclusions 24 concerning adamantane radicals. These were that 1-adamantyl radicals formed more readily than the secondary radical i n accord with normal tertiary versus secondary radical s t a b i l i t y , but that the secondary radical was more stable after formation due to i t s a b i l i t y to 2 rehydridize to sp . The tertiary radical would be less stable, and 2 hence more reactive, because the carbon cannot rehydridize to sp . Much information concerning the radical nature of cyclopropanes may be obtained from studies concerning their halo reactions, ring openings, and isomerizations. Halo reactions have been shown to proceed - 7 -by radical attack and ring opening as shown below. This .addition of two halo atoms instead of the exchange of a halogen for a hydrogen i s typical of olefins or other molecules which have carbon-carbon bonds with a high degree of p-character. Molecular isomerizations of cyclopropanes were studied extensively to determine whether the preferred mechanism was biradical or concerted ring opening and closing as seen in cases of conjugated olefins. The isomerizations of concern were only those resulting i n cyclopropane products and not the minor side reactions of hydrogen shifts to form propene. Bergman studied the isomerization of a single diastereomer of 1-ethy1-2-methyl 25 cyclopropane thermalized at 400°C. If isolation of only starting material, material with one center inverted, (the other retained), or material with both centers inverted occurred, then the concerted (con and/or disrotatory) mechanism would have been operating. When the reaction was complete only totally racemic material was obtained. Since this result could not have occurred by any process other than freely rotating biradicals, he concluded that the concerted mechanism was not operating and that biradicals were operating at least in this example. Benson has gone further to say that a l l cyclopropyl ring openings during isomerization are by the biradical mechanism with the 26 exception of cis-l,2-divinyl cycylopropanes. These observations of biradical ring openings indicate that formation of radicals in cyclopropane reactions is a reasonably favorable process, at least at high temperatures. As the temperature decreases,not enough energy i s tep 2 * C1CH2-CH2-CH2C1 + CI-- 8 -27 available to overcome the activation barrier of 27 Real/mole. Reactions to form polymeric material by radical ring openings are relatively rare in cyclopropane chemistry. In general, cyclo-propanes that are not either highly stabilized by groups such as vinyls or highly strained, are poor homopolymerization materials and form ' 28a b at best short chain polymers. ' Examples of highly strained cyclo-29 propane homo-polymerizations have been reported by Wiberg and by 28 Hall et a l . Wiberg found that 1-carbomethoxybicyclobutane polymerizes either readily when initia t e d or slowly when l e f t at room temperature (bicyclobutane i t s e l f would not polymerize). The polymer was that resulting from cleavage of the 1,3-carbon bond, making polycyclobutane, and not the one resulting from cleavage of the 1,2-carbon bond, as is the usually observed diradical cleavage pathway isomerizations of bicyclobutanes. Other properties of these strained (to the order of 64-67 kcal/mole) molecules include enough s t a b i l i t y to oxygen to allow their synthesis without excluding i t , and the lack of oxidation by m-chloro-perbenzoate. Hall's group also studied substituted bicyclobutanes and their polymerizations. They found bicyclobutanecarbon-n i t r i l e s to readily undergo radical i n i t i a t e d polymerizations to form high polymers. They concluded that the more radical stabilized the bridgehead positions were, the more facil e the polymerizations were. The strained cyclopropanes discussed above are in actuality structurally quite different from the cyclopropane in 1,3-dehydro-adamantane, which is the compound involved in the research of this thesis. Two compounds which may be considered structurally much more similar have been reported in the last five years. The f i r s t i s 2,4-dehydroadamantane, a compound which is thermally stable to at least 203°C (m.p. 202.5-203.5°) and does not seem to react with oxygen readily. 3^ a»^ This molecule w i l l , however, react readily with radical agents such as iodine or bromine. 2,4-Dehydroadamantane would not be expected to be as strained as 1,3-dehydroadamantane, however, because the bonding in the former is similar to that in 31 bicyclo[3.1.0]hexane,'a reasonably stable and normal cyclopropane, while the bonding i n the latter requires the inversion of two normally 3 tertiary sp centers. The other molecule similar to DHA i s t r i c y c l o -[^'^]octane. This molecule was found to have a strain energy of 1,3-Dehydroadamantane 2,4-Dehydroadamantane Tricyclo[^'octane 60 kcal/mole and spontaneously reacts with oxygen to form short chain 32 peroxypolymers. No mechanism was postulated or further information concerning the oxygen reaction mentioned. Another interesting property of this compound was that i t was extremely stable to thermal homo-polymerization ( t j y 2 < 20 hr at 190°C). It i s therefore evident that a cyclopropyl group formed across the 1 and 3 positions of adamantane is a unique structure within the groups of both cyclopropane and adamantane chemistry. Because this adamantane compound contains an extremely strained cyclopropyl group, - 10 -i t lends i t s e l f well to' a study'of the effects of strain on the properties and reactions of cyclopropanes. This study is aimed at determining these properties. RESULTS Synthesis Preparation of 5,7-Dimethyl-l,3-dehydroadamantane Bromination of 1,3-dimethyladamantane (Sunoco X-924-25) was done by the Friedel-Crafts reaction using aluminum bromide in bromine. The product was worked up by adding ice water and CCl^ and neutralizing the bromine with NaHSO^. The crude crystals obtained from evaporating the CCl^ fraction were recrystallized from hexane to give the pure l,3-dibromo-5,7-dimethyladamantane (DBDMA) which melted at 108.5-110°C and was identified by nmr and analysis. Synthesis of 1,3-dehydro-5,7-dimethyladamantane was accomplished through the reaction of DBDMA in ether with potassium-sodium alloy while under nitrogen. Additives such as triethylamine, t-butanol, and sometimes potassium bromide seemed to i n i t i a t e the reaction and improve the yield. Reaction progress was followed by vpc analysis. The product was unstable under prolonged reaction conditions and therefore must either be used immediately or stored in sealed degassed glass vessels. Several impurities including 1,3-dimethyladamantane (DMA) and l-hydroxy-3,5-dimethyladamantane were also formed during the reaction. The former was particularly troublesome because i t , as well as DHDMA, sublimed readily; thus precluding sublimation as a good - 12 -purification technique. DHDMA, purified by preparative vpc, was found to" have a melting point of 44-45.5°C and an IR spectrum containing absorptions (in cm"1) at 3030 (shoulder), 2900(s), 1445 (s), 1360 (s), 1280 (m), and 890 (m). The f i r s t and last absorptions are indicative 33 34 of cyclopropane groups. ' An nmr spectrum of DHDMA in degassed benzene showed absorptions at 6 .91 (s)(6H), 1.01 (d, 10 cps)(4H), 1.47 (broad)(2H), 1.60 (d, 10 cps)(4H), and 1.93 (s)(2H). These absorptions correspond in the li s t e d order to the methyl protons, H^, R^, ^ 4b' a n <^ E, as shown in Figure 3. Figure 3. The DHDMA Structure and i t s N.M.R. Absorptions DHDMA was found to react with many common laboratory reagents such as bromine, iodine, H^S, C^, and acids, to name a few. Attempts to determine by esr i f DHA were a diradical possibly in equilibrium with the ring closed system provided no evidence of radicals (this does not exclude that p o s s i b i l i t y ) . The major interests in this study were two reactions to form polymers, namely the thermal homopolymerization reaction and the spontaneous co-polymerization with oxygen. To make the thermal polymer, l,3-poly-5,7-dimethyladamantane, a capillary tube of DHDMA was collected - 13 -from the preparative vpc, sealed by flame, and heated i n an o i l bath to between 90 and 125°C. X-ray crystallography by powder method showed the material to be t o t a l l y lacking i n c r y s t a l structure. Further study using d i f f e r e n t i a l scanning calorimetry showed that on heating samples of polymer under nitrogen even to 500°C no phase changes occurred. However, i f the samples were run i n a i r , oxidative decomposition occurred at ca. 417°C. Analysis confirmed the composi-tion to be „H, „)- . These techniques a l l indicate the material i s 12 18 n ^ a true long chain amorphous polymer consisting of a chain of units of DMA joined through carbons 1 and 3. The other polymer studied, poly-1,3-peroxy-5,7-dimethyladamantane forms spontaneously at room temperature when DHDMA contacts a i r . When an ethereal solution of DHDMA had a i r passed through i t for several hours, the white co-polymer formed. Side products were mainly 1,3-dihydroxy-5,7-dimethyladamantane. The polymeric material was only s l i g h t l y soluble i n benzene and insoluble i n any other solvent t r i e d . Preparation of 1,3-Dehydroadamantane Several of the numerous l i t e r a t u r e descriptions of the bromination of adamantane using bromine and boron bromide with or without varying quantities of aluminum bromide, were previously t r i e d i n the labora-35-37 tory. A l l f a i l e d to give the results desired. The best bromina-tion technique of adamantane was f i n a l l y found to be the use of bromine 38 without boron bromide and with a trace of aluminum bromide. Twenty grams of adamantane (Aldrich 10,027-7) and 40 ml dried bromine when cooled on ice arid reacted with 100 mg of aluminum bromide formed - 14 -1-bromoadamantane. Repeat of the cooling process and addition of 200 mg of aluminum bromide followed by careful heating to 45-50°C gave 78.4% yield of 1,3-dibromoadamantane melting at 108.5-110°C. IR, nmr, and analysis agreed with literature values. 1,3-Dehydroadamantane was successfully synthesized by two methods. The f i r s t was by modification of the basic procedure previously 39 reported and consisted of reacting 2 g DBA and 2.5 g sodium-potassium alloy in ether while s t i r r i n g under nitrogen. A maximum purity of about 90% was possible with this method. The major impurities were adamantane, 1-bromoadamantane, and 1-hydroxyadamantane. The second and better synthesis was subsequently developed in the 38 lab. This synthesis consisted of reacting under nitrogen a precooled to -30 to -40°C reaction mixture containing 2 g DBA, 100 ml anhydrous ether, and 3.5 ml of hexamethylphosphoramide with n-butyl lithium. At the end of the dropwise addition of butyl lithium, the flask was warmed to room temperature and the solution washed with degassed water. The resulting solution contained about 95% DHA and very l i t t l e 1-bromoadamantane or 1-hydroxyadamantane. This method also v i r t u a l l y eliminated a l l adamantane, a previously very trouble-some impurity. Purification was accomplished by washing while under nitrogen with water and vacuum sublimation at -70°C. DHA was found to react with n i t r i c oxide radical at -78°C while under nitrogen. The products of the warmed system could not be purified or analyzed to any extent by vpc on Carbowax or SE-30 or eluted from a column of alumina or F l o r i s i l . The i r spectrum providing the only information concerning the few products that could - 15 -be obtained, indicated a possibility of nitrogen-oxygen bonding in the products ( (in cm"1): 1600 (s), 1500 (s), 1300 (s), 860 (s)). Radical Studies Galvinoxyl (Aldrich G30-7), a very dark bluish-purple stable free radical which does not react with oxygen in ai r , was thought to be a potential radical polymerization inhibitor. I t , however, reacted quickly with DHA i n heptane under nitrogen to produce a li g h t l y purple coloured solution. Controls without DHA remained unchanged. No product isolation was attempted. DHA reacted readily with atmospheric oxygen to form the peroxy co-polymer. Pure DHA is well stirred solutions in a 100% oxygen atmosphere were found to have half lives of reaction of 50 minutes in xylene and 125 minutes i n octane. In these reactions, a white cloudiness rapidly formed which turned to a white precipitate. When a radical inhibitor was added to the DHA solutions, the rate of reaction decreased and the white cloudiness and precipitate never formed, indicating that no polymer was produced. By measuring the rate of oxygen uptake with time and converting that value to the amount of DHA remaining, f i r s t order plots were possible. These standard plots of the logarithm of the i n i t i a l concentration of DHA divided by the concentration of DHA remaining at time t versus time, gave generally straight lines. These plots indicate that the rate for at least the major portion of the reaction i s f i r s t order with respect to DHA. Some deviations in the straight line plots were observed after 2 half lives, becoming more pronounced, especially after 4 half liv e s . - 16 -Table I. Results of DHA-C- Reaction Kinetics Solvent Inhibitor [DHA] Moles Inhibitor Moles DHA Moles 02 Moles DHA K sec"1 x 10 5 n-Heptane .086 - 1.38 11.3 " DBPC .056 .80 1.46 3.63 n-Octane - .231 - 1.17 15.0 DBPC .081 4.00 1.29 3.58 II II .158 1.00 1.22 4.22 II II .188 .50 1.19 4.10 II II .205 .25 1.26 3.98 II II .125 .159 1.24 3.98;22.4a II II .238 .139 1.21 3.38 II II .254 .086 1.32 3.10;18.7a II II .262 .042 1.35 2.75;18.2a " HMBP .174 .475 1.20 3.38 " DBHQ .174 .50 1.52 3.52 " 1-dodecane-th i o l .198 .50 1.25 6.68 Xylene - .484 - 1.20 32.8 " DBPC .185 .333 1.23 12.7 II II .278 .167 1.29 12.5 II II .345 .083 1.25 13.3;26.3a " HMBP .246 .80 1.24 13.8 II • II .326 .167 1.20 15.3 II II .345 .083 1.23 16.2 " p-quinone .088 .289 .96 209.3 II II .326 .307 .90 20.8 " 1-dodecane- .246 .504 1.11 16.5 M II .169 .980 .96 17.8 The f i r s t figure is the rate constant of the influence of inhibitor, the second figure i s reaction the rate while under the constant after a l l inhibitor i s consumed. DBPC = 2,6-di-t-butyl-p-cresol, HMBP = 4-hydroxymethyl-2,6-di-t-butyl phenol, DBHQ = 2,5-di-t-butyl-4-hydroquinone, p-quinone = 1,4-benzoquinone. - 17 -This deviation was, however, not surprising because i t was in the region where kinetic measurements are not nearly as accurate as the i n i t i a l measurements; therefore the deviations had no real significance. The i n i t i a l slopes of the plots, taken as soon as they got under way, were used to calculate the rate constants of reaction. Table I shows the values for each kinetic run of the experimental rate constant, the solvent i n which the run was made, the identity of the inhibitor used ( i f any was used), the molar ratio of inhibitor with DHA, and the molar ratio of oxygen absorbed with DHA. Table l a shows the mean values from Table I in the cases where several runs using the same solvent and inhibitor were made. Table l a . Some Mean Values from Table I. Solvent Inhibitor k x 10 5 Moles O2 Moles DHA Octane - .15.0 1.17 ti DBPC 3.67 ± .85 1.25 ± .1 Xylene - 32.8 1.20 II DBPC 12.8 ± .5 1.26 ± .03 II HMBP 15.2 ±1.4 1.22 ± .02 In general, rapid in xylene DHA polymerizations were found to as in octane. The inhibited rates be about twice as using DBPC dropped to 25% in octane and about 40% in xylene. The difference i n the two solvents may have been due to the greater stabilization of the - 18 -adamantyl radical by the aromatic system than by the saturated hydro-carbon system. The process of forming the more stabilized radical would require less energy than the corresponding process for the less stabilized radical; hence, the more stabilized radical would be formed more readily. If this formation were the rate controlling step of the reaction, that reaction would have a slig h t l y greater rate as a result. This stabilization would, of course, be expected to be small as was observed because radical reactions are affected only slightly by solvents. The explanation of the greater inhibiting effect of DBPC in octane than xylene can be explained in a similar manner. The aromatic solvent would tend to associate with the aromatic inhibitor slightly more than the saturated solvent w i l l . As a result the enhibitor w i l l be less "free" and less active for blocking radical reactions i n xylene. Perhaps another explanation of the differing degrees of inhibition by DBPC in the two solvents arises from the relative rates of reaction of the chain radical with the inhibitor versus with molecules of DHA. Since the DHA chain polymerization reaction i s slower in octane than xylene, the inhibitor would have more time in that solvent to trap the radical. If the trapping rate was somewhat comparable with the chain propagation rate, such a time factor could certainly account for the observed differences in the a b i l i t y of DBPC to inhibit the reaction in the two solvents. The molar ratio of oxygen to DHA consumed i n the reaction was approximately 1.25. If the reaction formed pure plymer of the type •fO-Ad-0}- the ratio would be 1; i f a l l of the reactions were stopped - 19 -immediately the product HOO-Ad-OOH would be formed and the ratio would be 2. A ratio of 1.25 indicates that some polymerization was occurring and that short oligomers were probably forming. If the oligomers were of the type H(KQ-Ad-OK>H, n would equal approximately 4. Two usual radical inhibitors, which when used were actually found to be " i n i t i a t o r s " and co-reactants, were p-benzoquinone and 1-dodecane-th i o l . When used as inhibitors,they actually increased the rate of reaction. Slight decreases in the amount of oxygen were noted in the case of the mercaptan while a drop in oxygen absorption to about 75% of normal was noted in the quinone case. When controlled experiments using identical conditions to the usual kinetic runs, excepting with total exclusion of oxygen, were run, i t was found that both reacted with DHA. The thi o l reacted quickly to form a single product with very long vpc retention time on Carbowax at 200°. Based on the lack of any detectable products from the DHA or the t h i o l (excluding the large single products) and from previous work with cyclopropyls and 40 thiols, i t was f e l t that the product was l-adamantyl-(l-dodecane)-sulfide. The quinone reacted to form an insoluble mud-like material which was not analyzed but which i s probably several products, possibly polymeric. Products of Inhibited Reaction The study of DHA reaction products when reacted with oxygen in the presence of a true inhibitor was accomplished by analyzing the products of the combined residues of a l l the kinetic runs using DBPC as the inhibitor'. The products were separated from the residue - 20 -f i r s t by column chromatography on F l o r i s i l and then by either recrystal-l i z a t i o n or preparative vpc on 3/8" x 10' Carbowax columns. Four products were obtained which could be seen on vpc; two of these being the products of the inhibitor and the other two the products of DHA. The two products of DBPC were identified as the dimers l,2-bis(3,5-di-t-butyl-4-hydroxyphenyl)ethane and 3,3',5,5'-tetra-t-butyl-stilbene-4,4'-quinone. Since these dimeric compounds have been reported i n the 1,2-bis-(3,5-di-t-butyl-4-hydroxy 3,3',5,5 1-tetra-t-butyl-stilbene-phenyl) ethane 4,4'-quinone literature as the products of reactions with DBPC, their identification was made with that knowledge and was based to a large extent on the 41-43 superimposability of their n.m.r. spectra with those reported. One of the adamantane products was easily confirmed as being 1,3-dihydroxyadamantane. This was accomplished by superimposing vpc recordings and i r spectra of the isolated uaterial and an authentic sample of 1,3-dihydroxyadamantane and noting their complete agreement. The other adamantane derivative was considerably smaller in quantity than the dihydroxide, a problem which hindered identification attempts. The purified material gave a melting point at 217-218°C with what appeared to be slight decomposition beginning at 210°C. N.m.r. gave a spectrum with approximately 14 protons, 8 between 6 1.85 and 2.0, - 21 -3 at 6 2.3, 2 at 6 3.6, one varying in location with solvent but centering around 6 2.8. This latter was removed with D^ O. IR absorptions at 3500 cm ''"(m), and 1145 cm ''"(s) indicated very strongly a tertiary hydroxyl group, at 1715 cm "*"(s) indicated a carbonyl, probably on a six membered ring, and at 900 cm 1 (m) and 885 cm ^(w) indicated possibly an exocyclic methylene group (literature for these * - l -1 groups: t-OH 1150 cm , 6 membered ring carbonyl 1715 cm , exocyclic methylene 890 cm Analysis of a sample of probably 99% purity (by vpc) gave values of C, 73.76; H, 8.36, as compared to the predicted C10 H14°2 v a l u e s o f : C> 72«265 H> 8.49. The mass spectrum of the material unfortunately provided l i t t l e information. A f i n a l piece of information concerning the compound's identity was a comparison of the IR of 7-methylene-bicyclo[3.3.l]nonan-3-one with the IR of the isolated material. The spectra were essentially identical except for the very strong hydroxylic absorptions at 3500 cm 1 and 1145 cm \ which were present in the isolated material. A speculative structure based on this data could be l-hydroxy-7-methylene-bicyclo-[3.3.l]nonan-3-one. l-Hydroxy-7-methylene-bicyclo[3.3.l]nonan-3-one - 22 -In order to help understand the reaction of DHA with oxygen, product studies on the reaction residues resulting from the reaction run with the addition of 1-dodecanethiol were made. Even though the t h i o l reacted with DHA as has been previously discussed, i t was not the exclusive reactant when oxygen was present. This was shown by the isolation and identification of 1-hydroxyadamantane and 7-methylene-bicyclo[3.3.l]nonan-3-one in addition to the thiol-DHA product. The DHA products were obtained from the residues in the benzene fraction from a F l o r i s i l column separation and were separated from each other and purified by use of preparative vpc on a 3/8" x 10' Carbowax column. The 1-adamantanol was identified by i t s i r , i t s n.m.r. (which was superimposible with Stadtler Standard Spectrum N.M.R. 4544 for the same compound), and by analysis. The methylene b i c y c l i c ketone melted at 163-163.5°C; literature: 1 6 0 - 1 6 4 ° C , 4 4 a n d gave correct analysis for C,_H.,.0o. It was further confirmed by the i r : 10 14 2 absorptions at 1710 cm 1 (s), indicating carbonyl, and 895 cm 1 (s) and 885 cm 1 (m), indicating exocyclic methylene; and by i t s n.m.r. which gave singlets of ratio 1:5:1 at 5 1.95, 2.40, 4.78. The relative ratios of the products of reaction were determined for one example using a 9:2 ratio of DHA to DBPC. This ratio was chosen to be as close as possible to the experimentally determined proportions of the two needed for complete inhibition. By doing this there would not be large excesses of either polymeric material or of unreacted DBPC. The product ratios were determined by vpc using the cut-out-and-weigh technique. Any products which were peroxides (i.e., polymeric material) or hydroperoxides would decompose - 23 -on the column and could not be detected. The remaining 27% of the products were determined to be 1,3-dihydroxyadamantane 63%, the s t i l l somewhat uncertain b i c y c l i c hydroxyketone 16%, and three minor peaks totalling 21%. Because 1-dodecanethiol was not a true inhibitor, no quantitative study was done on the reaction products obtained when i t was used. - 24 -DISCUSSION Preparative Reactions Previous authors have come to considerable disagreement as to the best method to selectively place two bromines on bridgehead positions of adamantane. Many of these same workers have also come into disagreement as to the correct melting point of 1,3-dibromoadamantane. 46 The f i r s t reported synthesis involved making the di- s i l v e r salt of 1,3-adamantane dicarboxylate and then adding bromine i n carbon tetrachloride and heating to 70°C. The product was purified by sublimation to give an 18% yield and found to have a melting point of 108°C.^ Stetter and co-workers reported selectively brominating by use of boron bromide and in refluxing bromine. The dibromide product obtained in 12.5% yield was also found to have a melting 47 point of 108°C. Later, using his same synthesis, Stetter reported 35 the melting point to be 112-3°C. Baughman later refuted Stetter's work, saying that when they tried his synthesis with bromine and boron bromide, no dibromide product was obtained, the major product 36 being the monobromide. He experimented with ratios of aluminum bromide and boron bromide in bromine and found the best results occurred with a 1000:1 molar ratio of catalysts. A yield of 74% with a melting point of 112-3°C was obtained. A f i n a l group of workers following Baughman's method found that they obtained only the mono-bromide when using the 1000:1 ratio of catalysts. They found 125:1 37 molar ratio to be the best, yielding 86% dibromide product. No melting point was reported. The last two authors could give no mechanism or explanation of the function of the co-catalysts in the reaction. This laboratory had followed previous suggestions on the synthesis of the dibromide without the best success in terms of yield or ease of purification. Therefore the method developed was to eliminate the boron bromide entirely and simply use small amounts of aluminum bromide under very carefully controlled conditions. By this method a yield of 78.4% was obtained with a melting point of 108.5-110.0°C. It is f e l t that this synthesis may not be the best possible synthesis, but to date i t appears to be the most convenient in terms of experimental ease and yield. The mechanism of the reaction appears not to involve any complicated undetermined co-catalysis schemes, but rather the ordinary accepted Friedel-Crafts mechanism. It probably involves formation of bromine cations and aluminum tetrabromide anions, the former abstracts a tertiary hydrogen from adamantane to form the 1-adamantane carbonium ion. The carbonium ion would then abstract a bromide from bromine and generate another bromine cation as shown below. Br-Br + AlBr. > B r + A l B r ~ + Br + + HBr + Br 2 > + Br + Br + Br r Br — > — ^ Br Br The process would be repeated to place a second bromine on the molecul A possible explanation for the need for aluminum bromide instead of boron in the placement of the second bromine may be found in the relative strength of the two as Lewis acids. Aluminum bromide, being more acidic than boron bromide, w i l l form the more stable tetra-bromide anionic complex, and therefore, allow the bromine cation to be "freer". A freer bromine cation would be a stronger acid for the removal of a hydride from the adamantane. The previously shown experimental fact that the addition of subsequent bromines to adamantane becomes progressively more d i f f i c u l t as more bromines are 35 added is reasonable on the basis of the stability of the resulting - 27 -carbonium ion as each'hydride is abstracted by a bromine cation. Olah and Schleyer have shown through acid media n.Tn.r. studies that 1-adamantane carbonium ion i s stabilized by the back lobes, of the 3 16 three tertiary sp hydrogens in adamantane. Since an electron withdrawing bromine on a tertiary position decreases the electron 3 density of the back lobe of one of the sp orbitals, the carbonium ion would not be as stabilized. Further addition of bromines successively decreases the back lobe stabilization, accounting for the experimental observations. Bromination of 1,3-dimethyladamantane was straightforward since excess bromination was impossible, baring extreme conditions which may have caused some secondary position bromination or decomposition. Syntheses of 1,3-dehydro-5,7-dimethyladamantane and 1,3-dehydro-adamantane by the a l k a l i metal technique proceeded with a great deal of hit or miss results. In general, the total synthetic method was not reproducible in any of the variations tried in hopes of improving the yield. It was found that lithium metal instead of sodium or potassium was not a strong enough reagent to abstract the bromines. Therefore, neither zinc or magnesium, other common metals used for Wurtz couplings and similar reactions, were tried. Another method hoped to work was the use of phenyl lithium. With the knowledge that 1-adamantene is a violation of Bredt's rule, i t was hoped that the phenyl lithium might react in a concerted mechanism to abstract both bromines, forming DHA, LiBr, and bromobenzene. The results i n fact, appeared to te the synthesis of phenyl adamantane, a novel but not practicable synthesis. - 28 -Since only a l k a l i metals seemed to work for the reaction, i t was f e l t that the reaction was in some respect similar to the Wurtz coupling. It could not have been the ordinary Wurtz reaction, for i f i t was the reaction would have proceeded by the following mechanism, polymer Rhinehard, in fact, reacted DBA with sodium at elevated temperatures and 48 obtained polymeric material. Since the results from this lab confirmed the existence of DHA and since this study confirmed the thermal polymerization of DHA, i t was f e l t that Rhinehard's reaction was also not a simple Wurtz coupling but instead was the same reaction as ours. It was f e l t that perhaps the reaction was a modified Wurtz mechanism which coupled the alkyl sodium and the alkyl bromide together by an internal Sn2 type of mechanism. Assuming this mechanism and knowing 49 that alkyl sodium compounds readily attack diethyl ether, i t was f e l t that hydrocarbon solvents such as heptane, hexane, pentane, and toluene would be necessary for the reaction. Using these solvents, the reaction would indeed produce DHA or DMDHA; however, i t was very slow and gave very poor yields, rarely over 70% DHA. The product also seemed to rapidly decompose into adamantane. Therefore despite the poss i b i l i t y of solvent decomposition, the solvent was changed to ether. It was found that the reaction went much smoother, more rapidly, - 29 -and in better yield than in hydrocarbons. The ether also did not decompose and was easier to remove. The lack of solvent decomposition indicated that either no 1-adamantanyl sodium was formed or else that i f i t was formed, i t was so transitory that i t did not get a chance to react with solvent. In other words, the reaction was essentially concerted. The ether may have improved the reaction by helping to solvate the sodium. In pure ether solvent i t was found that the reaction was often very slow to start. Once started i t would react very rapidly u n t i l completion. Although the reason for this was not understood, i t was fe l t that i f perhaps a catalyst could be found, the time to i n i t i a t e the reaction could be shortened and the yield could be improved. "Initiators" used for this purpose included trace quantities of methyl iodide or n-butyl iodide (in hopes of cleaning the alloy surface to expose reactive metal surfaces), potassium bromide and copper bromide (to help expose surfaces by breaking up the metal under s t i r r i n g , as well as to provide positive metal ions which may f a c i l i t a t e the elimination of bromide), and t-butanol and DBPC (in hopes of cleaning the surface of the alloy). No improvement was found by use of methyl iodide, butyl iodide, copper bromide, or DBPC. However, potassium bromide did in several reactions drastically improve the reaction time and yield. The effect was not reproducible and was f e l t to be caused in some systems because these systems were too "clean". The addition added impurities, perhaps oxygen, which appeared necessary to i n i t i a t e reaction. t-Butanol had the same effect as KBr had of improving many reactions, and was generally used in reactions to give better success. - 30 -These r e s u l t s were a l s o n o n - r e p r o d u c i b l e , the r e a s o n f o r improvement was n o t u n d e r s t o o d , though perhaps a g a i n the a d d i t i o n of i m p u r i t i e s may have been the r e a s o n . A f i n a l , e x p e r i m e n t a l m o d i f i c a t i o n which improved the r e a c t i o n was the a d d i t i o n o f anhydrous t r i e t h y l a m i n e to the s o l v e n t . The improvement which r e s u l t e d may p o s s i b l y be e x p l a i n e d by b e t t e r s o l v a t i o n o f the m e t a l by the amine than by e t h e r o r h y d r o c a r b o n s . The e x a c t mechanism o f the e l i m i n a t i o n i s n o t known. However, two p o s s i b l e mechanisms a r e i l l u s t r a t e d i n F i g u r e 4a. F i g u r e 4a. P o s s i b l e D e b r o m i n a t i o n Mechanisms Y i e l d i n g DHA from DBA. - 31 -The ionic mechanism is appealing in light of the precedence of the Wurtz reaction. However, i t has the disadvantage that a l k a l i metals have never been known to exist at bridgehead positions on adamantane. The second reaction i s radical in nature and may either involve a two step reaction or else be the concerted abstraction of both bromines by two sodium atoms. Another way to consider the reaction i s shown in Figure 4b. If the alloy emcompasses the molecule and by concerted Figure 4b. Potential Role of Na°-K° Alloy i n Formation of DHA. mechanism joins one electron from the metal electron cloud with an electron from each C-Br bond to make NaBr, the two remaining electrons from the C-Br bonds w i l l join to form a molecule of DHA. A similar ionic mechanism could perhaps also be drawn using electrons from the metal electron cloud. Whether the mechanism i s ionic or radical i s not known, but i t is f e l t that the lack of coupling reactions to form biadamantane or polyadamantane indicates that the reaction is concerted. The reaction of DBA with n-butyl lithium in ether to produce DHA is a much better synthesis. It reacts more rapidly, eliminates the hazards of alloy, reduces adamantane as a side product, gives a better yield, and is much easier to handle. - 32 -Mechanisms of organo lithium reactions are not well understood at present. It has been suggested that a mechanism consistent with the experimental results of lithium couplings could be the following slow 52 2-step process. This mechanism could not be the major pathway R' + R-Li fast R'-R + L i R1 -X + Li-R slow X:Li:R operating in the case of DBA because, i f i t was, one would expect the major product to be the product of electrophilic attack of the 1-adamantyl carbonium ion on butyl lithium. This would give l-bromo-3-(n-butyl)-adamantane and 1,3-di-(n-butyl)-adamantane as the products. These are not observed as major products. Synthesis of 1-adamantyl-lithium has not been accomplished due to i t s i n s t a b i l i t y . 1 ^ This report, along with the fact that the carbon on butyl lithium i s primary as opposed to being tertiary on adamantane, tends to make direct metal-halo exchange seem improbable. Yet this type of mechanism seems to be operating. The addition of HMPA to the reactants holds some key to the mechanism, although i t s exact function is not known. Previous published work on 2,4-dibromopentane indicated that the major product was 2-lithium-4-bromo-pentane (in this case direct metal-halo substitution) with some 1,2-dimethyl cyclopropane.^ This reaction was run without HMPA and had a very long reaction time in comparison. The authors formulate that the metal-halo replacement is with retention and the intramolecular displacement i s most probably - 33 -with inversion of both centres. The elimination of bromine from DBA may be somewhat similar to elimination reported from 2,4-dibromopentane. However, the lack of st a b i l i t y of 1-adamantyl lithium and the necessity of HMPA indicate that the mechanism i s somewhat more complicated. Polymerization Reactions Thermal polymerization of DHDMA was a simple process once the monomer was sealed in a tube. Since the capillary tube only had a small amount of DHDMA, small traces of oxygen which may have been sealed inside would be expected to form peroxypolymer. Since the peroxypolymer would be at most just a few percent of the product, i t could possibly explain the fact that the total C-H analysis only added up to 99% despite the fact that the carbon:hydrogen ratio was almost exact. Oxygen radicals would co-polymerize with DHDMA but, due to the low polymeric reactivity of the monomer to self-polymeriza-tion at room temperature, the presence of traces of oxygen could not i n i t i a t e self-polymerization. Self-polymerization at above 90°C may be due to spontaneous cleavage of the carbon 1,3 bond. Once initiat e d by this cleavage the temperature is high enough to make the energetics of propagation feasible. The lack of an esr spectrum at low temperature does not exclude the pos s i b i l i t y of ring opening to form biradicals. Rather, i t indicates that the radicals, i f they exist, —8 must be in concentrations of less than 10 molar. If an equilibration of ring-open and ring-closed forms were occurring, the esr observations could be r e a l i s t i c i f the equilibrium strongly favoured the ring-closed form at room temperature. - 34 -The calorimetric s.tudies of the thermal polymer indicated the polymer was stable in air to a temperature above 400°C (in the absence of oxygen the polymer appeared completely stable to 500°C). Also during the heating process no phase changes were detected. Since the polymer was also found to be almost totally insoluble in organic solvents, this property combined with i t s thermal s t a b i l i t y could make the polymer potentially very useful for industrial applications. DHA seemed a useful intermediate in the synthesis of 1,3-nitrogen derivatives of adamantane. N i t r i c oxide was known to readily react with radicals or olefins forming nitroso compounds._ While the very reactive primary and secondary nitroso compounds often give rearranged 53 and degradation products, tertiary nitroso compounds are much more stable. A major problem of a l l nitroso compounds, including tertiary ones, is the side reaction i l l u s t r a t e d below. It was hoped that R-N=0 + 2N0 > R- + N 2 + NC>3' rate = K[RN0][N0]2 N03 + NO > 2N02 by exluding air and running at low temperature that this reaction as well as other side reactions could be prevented. The dinitroso could then be reduced under nitrogen at room temperature and the diamine formed. If this synthesis worked i t would, in addition to indicating the reactivity of DHA, be a new synthesis of the diamino compound. If NO^  was formed at any time and nitrato compounds resulted, the adamantane system would be open-ringed and numerous products could be - 35 -formed. When the reaction was run, decomposition did occur extensively, yielding at least four products. After attempts to isolate some of the products failed, the study was abandoned. Radical Studies Galvinoxyl free radical is extremely stable to oxygen (no decomposi-tion of crystals took place in air in three months or in benzene solution in three days)."^'"^ It i s , indeed, best known for this oxygen s t a b i l i t y plus the fact that i t is the only known case of a radical product of hindered phenols which is stable to o x y g e n . I t does not in general react readily with any heteroatomic radical, reacting much more slowly with t-butoxy radical than with any carbon radical. It does, however, react very rapidly with carbon radicals, reacting with them ten times more rapidly than does the iodine radical (iodine i s also a compound which is non-reactive to galvinoxyl)."^ Knowing these properties and assuming i t does not react with DHA, galvinoxyl would make an excellent trapping agent to study the oxygen-DHA reaction. By competing with oxygen for adamantane radicals, i t could perhaps be an effective inhibitor by stopping the radical propagation. Isolation of even very minor amounts of digalvinoxyl adamantane product would be convincing evidence that the reaction was caused by the spontaneous ring-opening of DHA to form a biradical. As the situation turned out, galvinoxyl was very reactive with DHA even while under nitrogen and therefore was of no use for that purpose. It does, however, indicate that DHA does either form radicals i t s e l f or is at least very radical-like in nature. - 36 -The measurements of the kinetics of the DHA reaction with oxygen was relatively routine once the bugs of the system were eliminated. The solvents chosen were generally high boiling, saturated, or aromatic compounds which did not either react with DHA or have the same retention time as DHA on the vpc. Olefins were spe c i f i c a l l y excluded by thoroughly purifying to prevent any p o s s i b i l i t i e s of o l e f i n i c co-polymerization or other complication of products. The solvents were chosen to be high boiling to insure low solvent vapour pressure i n the system, thus requiring no correction factor in case the temperature of the system were to fluctuate a small amount during the reaction. A l l solvents were shown by blank runs to be nonreactive with DHA. The actual volume measurements were exact to within about 0.1-0.2 ml, these being due to the human error of equilibrating the mercury levels in the manometer. Also most runs were continued for approximately 1400 minutes to make a l l the end points consistent. The uncertainty A V of the individual points in the f i r s t order plots of log f^y^-Ay ] T t versus time may be considered negligible when the concentration of DHA is s t i l l high. This i s apparent when the precision of the measurements and the scale of the graphs are noted. As the DHA concentration becomes more dilute, the precision of the points becomes less as is the usual case with kinetic plots. The real error in the graphics arose from the exact determination of the end point. If i t was off by as l i t t l e as 2% of the total volume, the later points would curve significantly off the line. The early points however should be reason-ably good up to at least the h a l f - l i f e of the reaction. As has been observed in numerous radical reactions, there is frequently an induction - 37 -period at the beginning of the run. Those points taken during this induction period were omitted from the determination of the slope of the plot. The slope, due to considerations above-mentioned, was taken simply from the more exact points of the i n i t i a l reaction. The accuracy of the slopes of the curves may be taken as within about 30%. This approximate value i s obtained by drawing the extremes of reasonable lines through the i n i t i a l points and noting their deviation from the drawn line. If the reaction of DHA and oxygen were entirely stopped by inhibition after the f i r s t step of the chain, one would expect to observe DHA + 20 2 S t £ P  1> .OO-Ad-00- l n h i b i t o r > HOOAdOOH a slow uptake of oxygen as seen on the graph by a straight line of low slope. When the inhibitor i s entirely consumed the reaction would become a chain propogation with a greatly increased reaction rate. A straight line of much great slope would result. The graph below shows a hypothetical idealized reaction which is inhibited i n i t i a l l y and then consumes the inhibitor to return to the polymerization reaction. time - 38 -Mechanisms of radical reactions, in general, must involve three separate types of reactions: i n i t i a t i o n , propagation, and termination. In this case the reaction is an autoxidation. Almost a l l autoxidations of hydrocarbons involve, at least during the propagation steps, the abstraction of a hydrogen radical. A typical autoxidation once ini t i a t e d has propagation and termination reactions as shown below. R- + 0=0 ) R-0-0- (1) R-0-0- + HR S l ° W ) R-0-0-H + R- (2) >. propagation » termination 2R-0-0* ) often non-radical products (3) R-0-0- + R' > non-radical products (4) 2R- > non-radical products (5) In this reaction scheme, reaction (1) is extremely fast, being i n the 6 —1 order of k ( f i r s t order) = 10 sec with an activation energy of 5 8 E ^2 kcal. Reaction (2) varies considerably in rate, depending 3C u on the structure of R and the strength of the R-H bond, but often has a E of 8-12 kcal. Step (2) is therefore the slow step. Termination act reactions depend on the exact system studied; however, the combination of any of the two radicals has a rate constant of approximately k = lO 1^ liter-mole "''sec 1 and usually forms non-radical products. The use of inhibitors or "retarders" i n autoxidation is based on the non-reactivity of the material with either of the reactants and the fact that i t can break either step (1) or step (2) of the chain and form stable non-reactive products. It breaks the chain by reacting - 39 -with a chain radical more quickly than the co-reactant. Since step (1) is so rapid, usual inhibitors such as quinones, tertiary amines, thiols, phenols, etc. are often used to block the second step. By blocking this step the rate i s decreased almost to zero u n t i l a l l the inhibitor i s consumed after which time the reaction resumes at normal rate. In the DHA-O2 reaction, i t is immediately apparent that the previous pathway cannot be operating. DHA contains no hydrogens to extract from the 1 and 3 carbons, and abstraction from the secondary position would involve a violation of Bredt's rule. The two remaining tertiary hydrogens could perhaps be removed, but at room temperature this certainly could not occur in a chain. It should also be noted that the reaction occurs without any radical i n i t i a t o r s added. This brings up the problem of the source of i n i t i a t i o n . Is the reaction initi a t e d spontaneously in the same manner as other oxidations, or is the mechanism different? The two postulations for the spontaneous i n i t i a t i o n of usual autoxidations are reactions (6) and (7). R-H + 0 9 > R. + -00H (6) 0 I > radical products (7) I I2. II - > Reaction (6) is the usually accepted mechanism at high temperatures and i s believed to occur heterogeneously, perhaps with assistance of the 1 wall of the container. Reaction (.7) has l i t t l e support but has been 59 mentioned several times as a potential i n i t i a t o r . - 40 -Clearly, at room temperature, reaction (6), the usual mode of i n i t i a t i n g , cannot be occurring. This leave two possible mechanisms of i n i t i a t i o n (I) and (II). Possibility I involves the oxygen radical directly attacking the back lobe of the C^-C^ bonds, bonding with one electron of the central bond and displacing the other to the remaining carbon. This mechanism essentially means that the DHA molecule remains in i t s original form throughout i t s existence un t i l i t s strain i s relieved by an attacking radical. Possibility II involves the DHA strain being great enough that the molecule spontaneously ring-opens to the biradical and then closes rapidly again. If, however, oxygen is present, the biradical w i l l at least sometimes successfully attack the oxygen before i t closes again. The two mechanisms I and II are' in some respects like the debate over cl a s s i c a l versus non-classical carbonium ions. DHA may be thought of as having two resonance forms or else as having an equilibrium. Both p o s s i b i l i t i e s are shown in Figure 5. The resonance forms in (A) indicate that DHA has substantial - .41 -Figure 5. Two Possible Respresentations of the DHA Molecule. radical nature but that i t i s not a biradical. Form (A) may be illustrated as the hybrid formed by carbon p orbitals overlapping endwise in the centre to form the structure shown above. Form (B) is an actual equilibrium in which two distinct species are present. In this case, DHA would be an outright biradical at times. The results of this study cannot determine which i s the true case. Once the reaction of DHA and oxygen i s ini t i a t e d , the propagation steps are: {O-Ad-O} O-Ad- + 0„ > 40-Ad-O)—— o- (8) n z n+1 {O-Ad-0} 0- + DHA n -» {O-Ad-0} 0-Ad- (9) n - 42 -In light of the fact that 1-adamantyl free radical has very similar s t a b i l i t y and reactivity as does t-butyl radical, i t would be expected that i t would react about equally well with oxygen. Assuming this, the rate constant k„ would equal approximately 10^ liter-mole "''sec 1 as o indicated earlier for radicals with oxygen. The slow step therefore must be step (9), the peroxy attack on DHA. Termination of the chain would probably occur by the usual mechanisms illustrated in reactions (3), (4), and (5) with R being adamantyl or polymer. It might be noted, however, that diradical chain propagations are in general very poor and i n e f f i c i e n t , due partly to the entropy effects of forcing two radicals to remain in the same 61 62 proximity. ' This would cause substantial chain self-termination. The addition of inhibitor to the reaction system should terminate the reaction by trapping the f i r s t radicals as they are produced. Due to the lifetimes of the hydroperoxy radicals, presumably the trapping in this system would involve blocking their propagation, usually by the radical abstracting a hydrogen. The various inhibitors tried i n the reaction were a l l known for inhibiting qualities in various radical reactions. The different types of inhibitors were chosen to prove that many common radical inhibitors inhibited the reaction and that the inhibition was not due to a specific interaction with the particular inhibitor. The results of changing inhibitors also proved interesting in light of indicating the reactivity of DHA. In octane solutions the inhibitors DBPC, HMBP, and DBHQ showed essentially the same inhibiting effectiveness. The last had plots which were somewhat irregular, particularly in i n i t i a l rates, and seemed to cause the reaction to absorb about ?5% more oxygen - 43 -than usual. 1-Dodecanethiol and p-quinone were not inhibitors, but instead initi a t o r s and co-reactants. In xylene solvent, DBPC and HMBP showed very similar inhibitory properties. Another interesting aspect of the inhibition concerns the number of radical chains inhibited per molecule DBPC. In the study of the rate of loss of DHA versus the rate of loss of DBPC using concentrations of .294 and .039 molar, respectively (see appendix for graph) i t was .. , t d[DHA] ..-3 ,„ . j d[DBPC] ... found that S—- = -966 x 10 mole/£ min and - — ^ = .244 x dt dt _3 10 moles/£ min. The inhibition, therefore, seems to be operating i n a consistent ratio of 4 moles of DHA consumed per mole of DBPC. The reactions of DBPC as an inhibitor have been studied previously i n detail to determine both the number of radical chains inhibited per molecule DBPC and the actual inhibition mechanism. Various workers making these studies have shown the reaction to be quite variable as well as 41 42 mechanistically interesting. ' Their work showed the reactions of the inhibitor to be those shown in Figure 6. The reactions in Figure 6 are self-explanatory. DBPC radicals react with each other forming the end products V and VI with regeneration of some DBPC. If DBPC i s i n excess, product V is formed in largest quantity. Formation of V involves the overall consumption of two DBPC with the liberation of two H'. If DBPC is not in great excess, more of product VI i s expected. The degree to which V may react with radicals and ultimately form VI was not discussed. It may be mentioned however, that for each molecule of VI formed, six hydrogens were liberated, meaning six radical chains terminated. The number of radicals captured by DBPC can therefore vary from one to three per molecule. Since at most three - 44 -chains are stopped per inhibitor molecule, the termination of a l l the radical chains produced by the four DHA molecules per molecule DBPC certainly cannot be due entirely to the inhibitor. The inherent d i f f i c u l t i e s in studying the products unfortunately led to less useful information concerning the nature of the reaction than desired. The major problem with the product studies x^ as the fact that the methods of purification and detection of the products caused product decomposition. These involved the passage of the crude material through a F l o r i s i l column during the purification. This step - 45 -probably did not cause any decomposition of peroxy material because F l o r i s i l has been shown to be mild and has been used before to separate t-butyl peresters from t-butyl hydroperoxide (fate of the 6 3 latter material not mentioned). Since peresters are less stable than peroxy compounds, the latter surely survived the process; however, hydroperoxy compounds are much less stable than either, and may have decomposed on the column. The c r i t i c a l factor concerning peroxy material came with the detection of the products. This involved passage through a v.p.c. Carbowax column at 200°C. Polyperoxyadamantane has been shown to explode at 160°C and surely could not have survived the high 39 temperature. Once hydroperoxy or peroxy material decomposes on the column i t was seen to be mainly absorbed irreversibly on to the column. Because of peroxy and hydroperoxy decomposition on the columns, the product study was less informative than desired. The few remaining products which were stable turned out to be the expected reaction products from DBPC plus some 1,3-dihydroxyadamantane and a small unidentified bi c y c l i c compound. The exact origin of the adamantane products cannot be known. The 1,3-dihydroxy compound may have been formed in the reaction flask by the reaction of two hydroperoxy radicals followed by hydrogen abstraction, or else by hydroperoxide decomposition on the F l o r i s i l column. A third p o s s i b i l i t y , the decomposition of hydroperoxide in the reaction flask i t s e l f can be pretty well ruled 64 out at room temperature as has been well confirmed several times. The f i r s t p o s s i b i l i t y , the reaction of hydroperoxy radicals, has been studied in detail by Ingold.^^ 3'^ He has shown the reaction to occur via the tetroxide and i t s decomposition to the two caged radicals. - 46 -2R0- + 0 2 ROO- + ROO- -—» ROOOOR =• [RO-02-OR] cage ROOR + 0 2 The radicals formed quite frequently escape the cage to become free alkoxy radicals. If adamantane alkoxy radicals were formed, they could abstract hydrogens from DBPC to form the dihydroxy product. The poss i b i l i t y of decomposition of 1,3-dihydroperoxyadamantane on F l o r i s i l could also be very l i k e l y in light of the fact that the very polar solvent acetone was required to elute the column. The evidence concerning the mechanism of DBPC inhibition of the DHA-02 reaction is not conclusive, but does allow some speculation. Figure 7 shows some possible explanations of the observations. If the inhibitor was actually inefficient and could not trap a l l of the peroxy radicals, then significant amounts of polymer would form despite the inhibitor. The polymeric chain would of course be smaller as expected and the rate would be decreased. The ratio of four DHA molecules reacted per DBPC would be a result of the incomplete inhibition. The observation of 1,3-dihydroxyadamantane as a product would arise from one or both of the pathways, shown with question marks. The observations of the reactions of DHA and oxygen in the presence of thiol or quinone may be part i a l l y explainable in light of the various reactions which occur subsequent to i n i t i a t i o n of the reaction. It was observed that in both cases the i n i t i a l rate of oxygen absorption shot up drastically and stayed at a rapid rate u n t i l - 47 -1. 2'OCR DHA ' 2 02 •00-Ad-OO-2. 2IH ? HOO-Ad-OOH +21-F l o r i s i l 9 -7?^—» OfO-Ad-O^O-0„ n polymer •OO-Ad-00-Ad-OOH + I-DHA,0, HO-Ad-OH HO-Ad-OH + 2R0- + 20 2 + 21-IH = DBPC, R = 1-adamantyl or polymer chain polymer Figure 7. DHA-C^  Reactions Occurring in the Presence of DBPC. the t h i o l or quinone was consumed. After that the reaction became more normal. This factor of up to six-fold rate increase (k^ = 32.8 x 10 ^, versus 209 x 10 \ ) in the case of quinone could be due to xylene xylene the quinone reacting with DHA to form radicals. These radicals in turn prefer reaction with oxygen over reaction with quinone. Due to this competition most of the i n i t i a t o r only reacts with one of the DHA radicals, the other radical absorbs oxygen to give the rapid rate observed. With this mechanism i t would be expected that somewhat less oxygen would be absorbed, as i s the observation. Figure 8 indicates qualitatively what may be occurring. The quinone reaction would most l i k e l y form R = 1-dodecane Figure 8. DHA-O^  Reactions in the Presence of 1-Dodecanethiol and p-Quinone. - 49 -the complex of adamantane bonding to the oxygen of quinone,^ leaving a molecule with two radical ends which can only react with further DHA. The th i o l reaction would probably occur by donation of a hydrogen to DHA and thereby i n i t i a t i n g one chain. The RS- would then attack another DHA, i n i t i a t i n g the second chain. This somewhat oversimplified argument shows how essentially the same end products result in a l l cases and that the major difference in the rate i s caused by the rapid i n i t i a l reaction of DHA with t h i o l or quinone rather than with oxygen. The product studies using t h i o l with DHA and oxygen also tend to support the pathway in Figure 8. The products (other than polymer or hydroperoxide) that were formed were 1-hydroxy adamantane, 7-methylene-bicyclo[3.3.l]nonan-3-one and the same product as that observed i n the reaction of DHA and thiol under nitrogen (or one very similar). The products would arise by the scheme in Figure 9. The major products R = adamantyl or polymer R' = 1-dodecanyl Figure 9. Possible Explanation of DHA-0 + RSH Reaction Products. - 50 -are underlined. As expected, because they follow secondary routes, the quantities of 1-hydroxyadamantane and the bicyclononane were small. Apparently the competition for hydrogen transfer from t h i o l to adamantyl radical versus oxygen addition is f a i r l y good because substantial quantities of the sulfide were found in addition to the major polymeric product. In analyzing the potential of the DHA system i t is seen that the material may be suited for several practical uses. F i r s t of a l l the thermal polymer could i f industrial techniques are perfected find wide use in the plastics f i e l d . Perhaps the l i q u i d material could be squeezed into a cold mould, then heated to 150° quickly and removed as an extremely hard and r i g i d , highly temperature stable, solvent resistant material. These properties would result from the inherent r i g i d i t y and s t a b i l i t y of the parent adamantane monomers in the polymer. The other potential of the system is for studying radical ring openings and closings in cyclopropane systems. If there is a true equilibration of two distinct species (ring opened biradical and ring closed) this would be unique among 3 membered rings. The system does, however,have numerous complicating factors i n studies of. this type which must be overcome f i r s t . - 51 -EXPERIMENTAL Infrared spectra were taken on a Perkin-Elmer 137 Sodium Chloride Spectrophotometer. Any special methods of sample preparation and solvents used w i l l be mentioned. Symbols referring to stretch intensity are (s), strong; (m), medium; and (w) , weak. Proton Nuclear Magnetic Resonance Spectra were obtained by a Varian A-60 spectrometer unless otherwise specified. Differential Scanning Calorimetry was carried out using a Perkin-Elmer model DSC-1B. Analytical vapour phase chromatography (vpc) was carried out on a Perkin-Elmer 900 Gas Chromatograph using either a 1/8" x 6' OV-17 8% AW-DMCS, Chromosorb W, 80/100 mesh column (abbreviated OV-17), a 1/8" x 6' K-20M 20% Carbowax, Chromosorb W 80/100 mesh column (abbreviated as Carbowax), or a SE-30 1/8" x 6' 8% AW-DMCS Chromosorb W 80/100 mesh column (abbreviated SE-30). A l l programs were run at a flow rate of approximately 50 ml/min. Vpc specification w i l l be written shorthand: an example is (80°/6 min 32 /mln^ 200°C), which means that the column is at an i n i t i a l temperature of 80°C for 6 minutes and then i s heated at a rate of 32° per minute u n t i l i t reaches 200°C, where the temperature is maintained. Preparative vpc was done on a Varian Aerograph, Model 90-P • using either a 1/4" x 5' 10% Carbowax 20M, Chromosorb W 80/100 column - 52 -or a 3/8" x 10' Carbowax 20M 60/80 Chromosorb W column. Synthesis * Synthesis of 1,3-Dibromo-5,7-dimethyladamantane Vpc analysis of the f i l t e r e d products gave a yield of 95% DBDMA, less than 2% monobromination product, and the rest as small impurities. Recrystallization from hexane yielded the white crystalline product in excellent purity. M.p. 115-116 °C. IR (in CCl^) (cm - 1); 2940 (s), 2880 (shoulder), 1450 (s), 1160 (s); (in nujol): 830 (s), 715 (s); n.m.r. (benzene): 0.65 (s)(6H), 0.77 (s)(2H), 1.75 (s)(8H), 2.70(s)(2H). Anal. Calcd. for C 1 0H 1 QBr_: C, 44.75%; H, 5.63%. Found: C, l z l o z 44.69%; H, 5.54%. Synthesis of 1,3-Dihydro-5,7-dimethyladamantane A 250 ml 4-neck flask was fi t t e d with a nitrogen i n l e t , a CaC^ drying tube, a mechanical s t i r r e r , and a dropping funnel for slow addition of liquids. The flask was then charged with 125 ml of untreated (Mallinckrodt) absolute diethyl ether, 3.2 g of 4:1 Na°-K° alloy, and 20 ml of dry triethylamine (dried over CaC^ and d i s t i l l e d from sodium pellets). 1.5 g of DBDMA in 10 ml ether were added dropwise over a period of 10 minutes. After s t i r r i n g for 2 1/2 , i . -i /nno ir . 32°/min^ hours, qualitative vpc analysis using carbowax (80 /6 mm > 200°) showed the reaction to be complete with a product distribution of * The preparation of the crude dibromide was done by K. Waldman, a summer undergraduate research assistant. For the basic procedure of synthesis see the section under Synthesis of DBA. - 53 -85% DHDMA, 5 to 10% DMA, and 5 to 10% for the combined minor impurities. No DBDMA was remaining. Characterization of DHDMA was accomplished via f i r s t purification on preparative vpc using the 1/4" Carbowax column and a temperature of 150°C. The center fraction coming off the column was trapped in a long open-ended capillary tube which was packed on the outside with dry ice. Immediately upon completion of collection, the ends of the tube were drawn out and sealed by flame. Corrected melting points of these samples ranged from 41° to 45.5°C, with the best melting at 44.0-45.5°C. Several samples were then collected, dissolved i n benzene, and placed in an n.m.r. tube. Successive freeze-thawing, followed by flame-sealing preserved the sample for analysis on the Varian HA-100_ N.M.R. The spectrum obtained gave: 6 0.91 (s)(6H), 1.01 (d, 10 cps). (4H), 1.47 (broad)(2H), 1.60 (d, 10 cps)(4H), 1.93 (s)(2H). Due to rapid reaction of DHDMA in solution the infrared spectrum was obtained by dissolving the material from the melting point capillaries i n CCl^ and immediately running one-quarter of the spectrum. The process was repeated three times to obtain an entire spectrum. Absorptions were (in cm - 1): 3030 (shoulder), 2900 (s), 1445 (s), 1360 (m), 1280 (m), 890 (m). The absorptions at 3030 cm - 1, 1280 cm - 1, and 890 cm 1 quickly disappear i f the material was allowed to s i t i n air or allowed to remain for several minutes in CCl^. A sample for mass spectral analysis was prepared by collecting a capillary from the vpc, checking i t s melting point, and then breaking off the capillary ends and placing i t in a special evacuated attachment for the mass spectrograph. The analysis showed peaks at m/e+ of 485 and 324, - 54 -indicating the presence of dimers and trimers. Other fragments f e l l at m/e+ of 164, 163, 162(parent), 149, 107, 93, and 44. Ultraviolet analysis was attempted in heptane on the Bausch & Lamb Spectronic 502, but showed no absorptions above 210 mp as expected. An electron spin resonance analysis was also performed on a sample of DHDMA in thoroughly degassed hexane. The e.s.r. (Varian E-3) f a i l e d , however, to show any signs of a radical. Thermal Polymer of 1,3-Dehydro-5,7-dimathyladamantane Sealed capillaries collected from the vpc and melting at above 41°C were thermally polymerized i n the o i l bath of a melting point apparatus. The liquid DHDMA would begin to irreversibly polymerize at 90°C as indicated by a whitening which could not be reversed by cooling. By 125°C (heating at a rate of approximately. 5°/min) the polymerization was essentially complete, yielding a hard white amorphous material. The polymer was extremely stable and insoluble in any solvent tried. Crystal and phase properties of the polymer were studied by X-ray analysis and differential scanning coulometry. The X-ray study was made on powdered samples in very finely drawn glass thin-walled capillary tubing and exposed for 21.5 h on a G.E. powder camera. The powder technique was used because no single crystals could be obtained. None of the numerous samples gave any sharp diffraction lines or patterns as would be expected from a structured material. Differential scanning was done both in air and under nitrogen and at heating rates of 40° per minute and 80° per minute on ranges of 16, 8, and 4. - 55 -Blank samples of lead were used for temperature calibration. On a l l the above settings, the polymer under nitrogen had no deviations in the baseline up to the temperature of 773°Kelvin (machine maximum) and recorded only a gradual,baseline d r i f t . During this entire time, the sample remained vi s i b l y the same, with no melting, change of colour, etc. The polymer, when analyzed in ai r , again had no baseline deviations u n t i l a temperature of approximately 690°K at which time the line gradually began to curve upward, the slope increasing u n t i l a maximum of 728-735°K, after which i t dropped off quickly. Visibly the samples maintained their whiteness up to 690°K where they started turning yellow, the colour deepening with heating u n t i l the material was entirely black at 750°K. In order to obtain a microanalysis, vpc-collected and sealed samples melting at 43° and above were polymerized for 24 hours at 160°C. The ends were then broken, the samples pumped under vacuum for several hours to remove potential impurities (adamantanes generally sublime readily), and the polymer removed with great d i f f i c u l t y from the tube by scraping i t out with s t i f f steel wire. Anal. Calcd. for (C 1 0H 1 0) : C, 88.82; H, 11.18. Found: (A) C, L2. lo n 85.98; H, 10.82, and normalized to 100%: C, 88.82; H, 11.18. (B) C, 87.94; H, 11.19; and normalized to 100%: C, 88.61; H, 11.39. Synthesis of Poly-1,3-peroxy-5,7-dimethyladamantane Co-polymerization with oxygen of an ethereal solution of DHDMA (prepared as previously described) was accomplished by bubbling air through the sample. Almost immediately a whitish material precipitated - 56 -After several hours of reaction the ether was driven off and the polymer's solubility checked. It proved insoluble in any ordinary solvent except benzene and other aromatics, where i t s s o l u b i l i t y was limited. The material was then washed several times with pentane and ether and dissolved in benzene for vpc analysis. The polymer could not be detected either on analytical or preparative columns (Carbowax, OV-17, SE-30). The washings of the polymer were analyzed on Carbowax and found to contain the same impurities as those in the starting solution of DHDMA, plus 1,3-dihydroxy-5,7-dimethyladamantane as identified by comparison of an authentic sample (Sunoco X924-47B) and one other small unknown impurity. Because of the polymeric nature of the material and i t s i n s o l u b i l i t y , no spectral data were obtained. Microanalysis was omitted because the analyst claimed previous samples of poly-1,3-peroxyadamantane were d i f f i c u l t to analyze due to peroxide explosions. Identity was mainly based on the similarities of the polymer to known properties of the peroxypolymer of DHA. Synthesis of 1,3-Dibrom6adamaritane A 200 ml 3-necked flask was assembled with a slow mechanical s t i r r e r , a large, e f f i c i e n t , water-cooled condenser, and an i n l e t for N^. The flask was dried by passing a cool flame over the glass surfaces while purging with nitrogen. The flask was then charged with 20 g adamantane and 40 ml of pre-dried (with 20 ml concentrated H^SO^) bromine and cooled on ice for 15 minutes. 100 mg of aluminum bromide (BDH 27071) were added, causing a violent reaction as evidenced by evolution of large quantities of white HBr vapours. After 30 seconds the reactions and evolution of vapour slowed, at which time the flask - 57 -was removed from the ice bath and was stirred for 2 hours. By this time a l l v i s i b le evolution of HBr had ceased. The flask was then again cooled on ice and another 200 mg of aluminum bromide added. When the reaction again slowed, the flask was placed in a 35° bath and very slowly heated to 45-50°C over a period of about 1 1/2 hours. The temperature was maintained there for 1/2 hour. To work up the reaction, the flask contents were poured into 100 ml of CCl^ and 200 ml of ice. With good s t i r r i n g , NaHSO^ and ice were added so as to keep the temperature at a l l times below 15°C. When a l l colouration disappeared, the CCl^ layer was taken off, neutralized, and dried over CaCO^. CCl^ was then removed by rotatory evaporation and the dibromide recrystal-lized from hexane. The product was analyzed by vpc on OV-17 at 210°C. Retention times were 2.2 minutes for 1-bromoadamantane, 3.3 minutes for DBA, and 7.8 minutes for 1,3,5-tribromoadamantane. Crude vpc analysis gave 95% DBA with very l i t t l e mono- or tri-substituted material. Recrystallization gave 33.9 g (78.4% yield) of very pure DBA with m.p.: 108.5-110°; literature: 1 0 8 ° , 4 6 , 4 7 112°. 3 5 IR in nujol gave absorptions at (in cm - 1): 1335 (m), 1315 (m), 1280 (s), 1020 (s), 820 (s), 692 (s) and in CC14, at: 2910 (s), 1445 (s). The n.m.r. in benzene gave absorptions at: 1.22 (t)(IH), 1.70 (broad(IH), 2.06(4H), 2.85 (IH); l i t e r a t u r e 6 7 (benzene): 1.24 (2H), 1.88 (2H), 2.09 (8H), 2.79 (2H). Synthesis of 1,3-Dihydroadamantane A. 2.0 g of DBA, 250 ml of anhydrous diethyl ether, 2 g of dried KBr (200° for two hours), and 2.5 g of liquid 4:1 sodium-potassium alloy were placed i n a pre-dr'ied and well nitrogen-purged 4-neck flask. The flask was fit t e d with a nitrogen in l e t , a drying tube, a high speed s t i r r e r (Lab Line Instruments, Inc., 1285 s t i r r e r ) , and a stoppered neck for addition or removal of samples. Care was taken to maintain an air-free system and to keep the alloy suspension well-stirred. The reaction proceeded slowly at f i r s t , but after 2 1/2 hours analytical vpc analysis on Carbowax (80°/6 min 32 /min^ 200°C) showed only DHA i n about 90% purity with no starting material (DBA). The impurities present were adamantane (5%), 1-hydroxyadamantane (trace), 1-bromo-adamantane (trace) and several small unidentified compounds. B. 2 g of DBA, 100 ml anhydrous ether, and 3.5 ml of hexamethyl-phosphoramide (Fisher H343), dried over 5A molecular sieves (BDH), were placed in a 200 ml 3-neck flask f i t t e d with a magnetic teflon-coated s t i r bar, a nitrogen i n l e t , a calcium chloride drying tube, and rubber septum-capped stopper. The reaction vessel and i t s contents were cooled in a bath to -30°C to -40°C, 10 ml of n-butyl lithium in hexane (Foote, 1.6 Molar) were then added over a period of 10 minutes via a syringe through the rubber septum. Upon completion of addition, the flask was removed from the cold bath, allowed to warm to room temperature (1/2 hour), and washed with three 10 ml aliquots of oxygen free d i s t i l l e d water (boiled two hours). The f i n a l ether solution was dried while s t i l l under nitrogen over MgSO^. Identity and purity were confirmed by analytical vpc retention time comparisons with results of known samples. The DHA purity by this analysis was greater than 95% with no DBA or adamantane present and only traces of 1-bromoadamantane - 59 -plus a few unknown impurities. Since DHA had been identified and well 39 characterized in the lab previously, no further identification was made. Radical Studies DHA Reaction with N i t r i c Oxide Radical A 250 ml 3-neck flask was f i t t e d with a rubber septum capped stopper, a gas outlet line leading to a mineral o i l bath (to prevent back entry of a i r ) , and a f r i t t e d gas dispersion tube inserted below the liquid level in the flask. The system was purged with nitrogen for 20 minutes, charged with a freshly prepared ethereal solution of DHA (from 1 g DBA in 50 ml ether), and placed in a dry ice-acetone cold bath. When the vessel was cold, n i t r i c oxide (Matheson), purified by passage through a dry-ice-acetone-cooled glass-bead-filled U tube, was passed slowly through the system for two hours. The solution rapidly became a bluish-yellow, a colour which disappeared as the flask was allowed to slowly warm to room temperature while being purged with nitrogen. Vpc on Carbowax showed no DHA remaining after the reaction; however, no useful information concerning the products could be obtained. Changing columns to SE-30 did not make an improvement. Thin layer chromatography (TLC) in chloroform showed four major products, the two largest of which, unfortunately, could not be separated on alumina (Merck 1090) or on F l o r i s i l (Floridin Co. F-3938). The quantities of the smaller elutable products were not enough to be analyzed and were impure, while the larger products were non-elutable, being irreversibly adsorbed on the column. I.r. spectra of these smaller - 60 -products did, however, indicate the potentiality of nitrogen-oxygen bonds: Absorptions at (cm"1) 1600(s), 1500(s), 1300(s), and 860(s). Several attempts to repeat the reaction by modifying i t , or by adding lithium aluminum hydride (and refluxing before exposing to air) failed to give any more determinable products. The new products gave similar d i f f i c u l t i e s in separation and identification. The study was therefore discontinued. DHA Reaction with Galvinoxyl Stable Free Radical _3 0.062 g of galvinoxyl stable radical (0.145 x 10 moles) were dissolved in 15 ml heptane and kept under nitrogen in.a flask. Its -3 reaction with DHA was followed by adding 0.36 x 10 moles of DHA i n 2 ml o-dichlorobenzene and observing the change in the deep purple colour of the solution. The colour began to fade very rapidly, becoming a faint brownish-yellow by 26 minutes. At this time more DHA was added, affecting no further colour change. A control run in air using the same solvents retained the i n i t i a l colour for the 12 hours observed. Purification of Solvents Benzene: Reagent benzene was shaken five times with H„S0,, once 2 4 with NaHCO^, once with water, and dried over MgSO^. Final purification was accomplished by d i s t i l l a t i o n and collection of the centre fraction. o_-Dichlorobenzene (Eastman 494): 2 l i t e r s of o_-dichlorobenzene were shaken five times with cone. H„S0., once with water, aid dried 2 4 overnight over CaSO. and MgO. The dried reagent was d i s t i l l e d , the - 61 -middle 1 l i t e r fraction-being kept and stored over 5A molecular sieves. n-Heptane (Eastman 2215): Purification consisted of shaking three times with cone. H^SO^, once with 10% NaHCO^, once with water, and drying over MgSO^. n-Octane (Phillips Petroleum 1454 Technical grade): Approximately 1 l i t e r of octane was shaken three times with cone. R^SO^, once with Na2C0.j, once with water, and dried over MgSO^. The middle fraction of the d i s t i l l a t e was collected for use. Xylene: A mixture of (approximately 90% para) xylenes was shaken three times with cone. H^ SO^ , once with ^200^, once with water, and dried. Purification of Inhibitors 2,6-Di-t-butyl-p-cresol (Eastman P5917): The crude yellow cresol was d i s t i l l e d at 100-105° under vacuum, removing i t from the coloured materials. The d i s t i l l e d material was then further purified by recrystallizing twice from methanol followed by drying for one-half 68 hour at 50° under vacuum (m.p. 69-70.5°C; literature: 70°). 2,5-Di-t-butyl hydroquinone ' > (Eastman P5681): The crude yellow hydroxyquinone was washed with a small quantity of methanol to remove most of the colour and then was recrystallized once from methanol. Final purification was accomplished by recrystallizing three times from f>Qa benzene (m.p. 214-215°; literature : 213-214°). 4-Hydroxymethyl-2,6-di-t-butyl-phenol (Ethyl Corporation 754): The free sample was considered pure as given. 1,4-Benzoquinone (Eastman P220): The quinone was purified by vacuum sublimation, followed by recrystallization twice from tetrachloro-- 62 -ethylene (m.p. 112-114°; literature : 115-116°). 1-Dodecanethiol (Aldrich D22,140): The bottled reagent was used directly. Preparation and Standardization of Solutions A l l the solutions of adamantane and of the inhibitors were made by placing a precise amount of material i n a volumetric flask, f i l l i n g to the line and shaking. Table II l i s t s the pertinent data and the f i n a l concentrations of these standard solutions. The preparation of DHA standard solutions involved f i r s t the preparation of the oxygen free solvents. These were prepared by taking a 50 ml, 2-neck, clean and dry flask and f i t t i n g i t with a stopcock on one joint and a stopper on the other. The flask was next f i l l e d to within 90% of the possible volume with the chosen purified solvent. With the joints well greased, the solvent was degassed (including any water present) by evacuating to just above the vapour pressure of the solvent and pumping for 1/2-3 hours. Preparation was then'complete after purging the system with nitrogen and sealing i t while s t i l l under nitrogen. The next step was to prepare the DHA. This was done by the n-butyl lithium process and using 2 g of DBA to 50 ml ether. The water washed ethereal solution from this reaction was cooled in a refridgerator before i t s f i n a l purification by sublimation. The sublimation was carried out under vacuum in the specially designed apparatus ill u s t r a t e d in Figure 10. The system (as drawn minus the flask and stirbar) was - 63 -Table II Concentrations of Adamantane and Inhibitor Solutions Solute (mole wt.) Wt. (g) Solvent Volume of Flask (ml) Molarity Adamantane (136.24 g/mole) 1.3616 .4390 .1364 .4420 .8840 benzene 100 10 .100 .030 .010 .324 .648 DBPC (220.34 g/mole) .5611 2.7657 1.0954 2.552 heptane n-octane xylene n-octane 25 it 50 25 .1037 .5015 .0981 .462 HMBP (236.3 g/mole) .2383 1.1750 xylene 100 50 .0101 .0994 DBHQ (222.32 g/mole) .1360 .304 p-Quinone (108.1 g/mole) .1340 1.0414 n-octane xylene 50 .0248 .1929 1-Dodecanethiol (220.4 g/mole) .5524 .5579 n-octane xylene 25 .2502 .2530 - 64 -vacuum Figure 10. DHA Sublimation Apparatus. operated by f i r s t f i l l i n g dewar II with liquid nitrogen, turning on the vacuum pump, closing stopcocks I and II, opening III, and by then placing the flask (with stirbar) containing the cold freshly decanted DHA solution on the apparatus. The magnetic s t i r r e r was then turned on and stopcock I quickly turned past the open position several times to draw out the ai r in the system, yet not to cause excessive bumping on the ether. Immediately after, with the stopcock closed, dry ice and acetone were placed in the cold finger and liquid nitrogen was placed in dewar I. Next the vacuum is controlled via stockcock I to draw, without bumping, the ether onto the cold finger from which i t flows into the flask i n dewar I and is frozen. When a l l the ether was frozen, about 15 minutes, the st i r r i n g was stopped, the system was opened, the collecting flask in the dewar was quickly replaced with a small flask (simply to maintain the closed system), and the system was sealed off by closing stopcock I and a hot water bath - 65 -was placed under the sublimation flask. The system was closed because sublimed DHA w i l l also sublime off the cold finger, even at -78°C, and into the trap, i f the vacuum is pumping. The water bath was heated to 70°C and maintained at that temperature u n t i l sublimation was complete (1 to 2 hours). The transfer of the DHA to the prepared and sealed storage vessel was done by f i r s t warming the cold finger to room temperature (to prevent water condensation) and then breaking the vacuum and removing the cold finger. The transfer of the DHA from the cold finger to the storage flask was accomplished by "washing" the DHA into the storage flask,by use of a pipette,and the solvent from the flask. A l l during this time nitrogen was purging the system. For a typical standard solution of DHA, anywhere from four to eight preparations of DHA were required. A l l DHA solution concentrations were determined by comparative vpc quantitative analysis. This was done by comparing the areas under the DHA peaks with the areas under peaks of standard adamantane solutions. For these comparisons a l l instrumental settings and sample injections were identical. The determination of area was done by the cut out-and-weigh method; making the assumption that 1 molecule of DHA would yield the same area under the curve as a molecule of adamantane. For each solution, anywhere from three to eight samples were compared, the number depending on the reproducibility of areas. The column was Carbowax at 80°C. Table HI gives the solution concen-trations of the various standard solutions obtained by this method. The error values are a reflection of the inherent non total reproducibility of the vpc technique. - 66 -Table III: DHA Standardized Solutions for Kinetics. Solvent Molarity Error Heptane .099 3% Octane .273 2.5% II .148 3% II .345 7% Xylene .475 5% DHA Reactions with Oxygen The apparatus used i s il l u s t r a t e d i n Figure 11. To prepare for operation, the large neck of a 50 ml 2-neck flask containing a magnetic stirbar was connected to the apparatus, and the smaller neck was stoppered with a rubber septum capped stopper. A magnetic s t i r r e r with a styrofoam pad holding a large beaker of ambient temperature water was then elevated from under the system. The system was then alternatively evacuated and f i l l e d with pure oxygen. An oxygen bleed off device was attached to the line to keep the system closed to a i r during this time. The mercury in the manometer was then leveled, the volume on the graduated column read, the desired quantity of inhibitor solution injected through the septum and the s t i r r e r turned on. After ten minutes were allowed for equilibration (though no further volume change in the system could be detected after 30 seconds) the mercury was leveled, the stopcock on the top of the manometer was closed, the temperature and pressure were recorded, and the reading on - 67 -Figure 11. Kinetic Apparatus. - 68 -the graduate was taken. At this point the system was ready for the DHA which was injected into the flask while the s t i r r i n g was stopped. Immediately upon removal of the syringe the timer was activated, the mercury leveled for the reading of the i n i t i a l volume of the system, and the s t i r r e r turned on. For the f i r s t half (approximately) of the reaction readings were taken every five minutes; after that, ten minutes or longer, as was necessary. Most runs lasted only 400 to 500 minutes, after which the system was l e f t overnight for the f i n a l reading - usually at about 1300 ninutes. The technique for analysis of the kinetic data was based on the assumptions that the internal pressure of the system is constant (because stopcock D maintains the pressure in that tube of the manometer the same as the i n i t i a l pressure), that the Ideal Gas Law was a • suitable approximation, and that the temperature stayed constant (experimentally the water bath temperature seldom varied more than 1 to at most 2 degrees during a run). The i n i t i a l reading of the volume (V ) of the system was taken as the standard for 100% pure, unreacted DHA and the total difference (AVm) between V and the f i n a l T o reading (V ) was taken to be the value for 100% reaction of DHA. CO Vpc analysis, furthermore, showed absolutely no detectable quantities of DHA remaining after 600-800 minutes, regardless of the particulars of the run. The difference (AVI between V and the volume at a t o give time (Vfc) when subtracted from the total volume change (AV ), gave the amount of unreacted DHA. Kinetic f i r s t order plots were obtained in the usual manner by plotting the logarithm of the i n i t i a l concentration of DHA over the concentration at time t versus time - 69 -(log vs t ) . The rate constant of reaction was obtained by multiplying the slope of the line by 2.303. A second method of determining the kinetic plots was the analysis of DHA present at time t versus the total amount of DHA i n i t i a l l y . Because of minor deviations in sample injection sizes and the inherent non-total reproducibility of the apparatus, this technique was somewhat less precise. It did, however, allow for co-measurement of the rates of loss of both inhibitor and DHA. A l l these vpc comparisons were done by the cut-out-and-weigh technique (simple measurement of the peak heights was too inaccurate to be valid). Table xv l i s t s the experimental quantities used i n the individual kinetic determination. DHA Reaction with 1,4-Benzoquinone under Nitrogen The same apparatus that was used to measure oxygen uptake with DHA was used to totally exclude oxygen from (he reaction of DHA with p-benzoquinone. The same 50 ml 2-neck flask with rubber-septum-capped stopper and containing a s t i r bar was again placed on the system. The system was then alternatively evacuated and f i l l e d with nitrogen for a total of eight repetitions. Ten ml of quinone in xylene -3 (1.929 x 10 moles) were injected into the system, the volume was _3 measured, and 3.1 ml of DHA i n xylene (1.5 x 10 moles) were injected. After b r i e f l y mixing, a sample was removed and analyzed on the vpc (Carbowax 80°/6 min 3 2 / m l " > 200°C). By this time both the DHA and the quinone peaks had already shrunk and a new peak had appeared. on the vpc (Carbowax 80°/6 min 32°/min •> 200°) of the relative amounts - 70 -Table IV. DHA-0 Reaction: Experimental Quantities Moles DHAxlO3 [DHA] Inhibitor added Moles inhibitor xlO 3 [I] Solvent °C ml 02 absorb (at ST .69 .086 - - - n-heptane 19 21.4 .64 .056 DBPC .52 .045 I I 19. 0 21.4 1.5 .231 - - - n-octane 20 39.5 I I .158 DBPC 1.50 .158 I I 20 41.2 I I .188 n .75 .084 I I 19. 5 40.1 I I .081 I I 6.00 .324 M 19 43.3 I I .205 ti .375 .051 I I 20 42.3 1.18 .125 I I .188 .020 it 20 32.9 1.46 .254 it .125 .022 I I 22 43.4 ti .238 ii .206 .035 I I 22 39.6 1.50 .262 n .0625 .011 I I 22 45.5 I I .174 HMBP .706 .092 I I 22 38.6 I I .061 p-quinone .50 .020 I I 22 43.5 I I .174 DBHQ .743 .086 n-octane 22 45.2 I I .484 - - - xylene 22 39.9 1.50 .185 DBPC .50 .062 I I 22 41.4 I I .278 I I .250 .045 I I 22 43.3 I I .345 I I .125 .029 I I 22 42.0 I I .326 HMBP .25 .054 ti 22. .5 40.2 I I .345 I I .125 .029 ii 22 41.4 ti .185 I I .50 .062 I I 21 43.8 I I .326 p-quinone .482 .105 I I 21 30.1 I I .294 DBHQ .611 .120 n 22 38.4 I I .294 DBPC .20 .039 it 23 42.4 1.00 .088 p-quinone 2.89 .169 I I 22 21.5 1.50 .246 HMBP 5.94 .195 it 22 41.6 2.14 .329 DBPC .60 .092 n-octane 22 58.3 1.50 .246 1-dodecane-thiol .76 .124 xylene 21 37.4 I I .406 I I .152 .041 I I 21 38.5 I I .169 H 1.47 .165 I I 22 32.0 1.50 .198 11 .75 .099 n-octane 22 4.1.1 - 71 -The reaction was extremely fast and by the time the vpc could be -3 reprogrammed, no quinone remained. A further addition of 2.4 x 10 moles of quinone only served to completely eliminate the DHA. During the reaction the volume of gas evolved was measured and found to be a net change of less than 1 ml. DHA Reaction with 1-Dodecanethiol under Nitrogen Using the same apparatus and technique used to exclude nitrogen -3 as described for the DHA-quinone reaction, 0.425 x 10 moles of _3 1-dodecanethiol and 0.275 x 10 moles of DHA were reacted i n octane. Vpc analysis on carbowax after 2 1/2 minutes showed no trace of DHA with only excess mercaptan remaining. The reaction analysis remained unchanged for 680 minutes; the only product was seen, as a large broad peak of retention time 55 minutes at 200"C. Product Studies The reaction residues from the kinetic runs using DBPC as inhibitor were combined and were shown by analytical vpc (Carbowax 80°/6 min > 200°C) to contain four major (and several very minor) compounds, a l l of which were not present before reaction. The four were separated from the mixture by column chromatography on F l o r i s i l (Floridin Co. F-3938) 100/200 mesh. Elution was carried out using solvents in the order of: 1. hexane, 2. 3:1 hexane-benzene, 3. benzene, 4. 9:1 benzene-acetone, 5. 3:1 benzene-actone, 6. acetone. Most of the impurities and the unreacted DBPC eluted off with the hexane, the f i r s t two of the four compounds came in the benzene fraction, - l i -the, third compound in 9:1 benzene-acetone, and the fourth compound i n 3:1 benzene-acetone. Compounds 1 and 2 were purified by allowing the crude yellow fraction to remain in the neat form for several days, during which time whitish-yellow crystals formed. When the flask was inverted and allowed to drain overnight into a dish, the crystals remained fixed to the bottom of the flask. Since these crystals themselves were almost as soluble in pentane (as well as other solvents) as were the impurities, they were washed several times quickly with cold pentane, the washing being just enough to remove the impurities with l i t t l e loss of material from the crystals themselves. The crystals were identified mainly from nmr as being 1,2-bis(3,5-di-t-butyl-4-hydroxyphenyl)ethane (I) and 3,3',5,5'-tetra-t-butylstilbene-4,4'-quinone (II). The results of the nmr run in CC1, are given below. I II Compound I: 6 1.39(s), 2.71(s)(2H), 4.8(broad)(IH), 6.83(s)(2H); Absorption at 4.8 disappears on addition of D„0. Compound II: <5 1.39(s), 6.91(d) (IH), 7.11(s)(lH), 7.43(s)(lH). 43 Literature values (in CCl^): Compound I: 6 1.36(s)(H), 2.71(s)(H), 4. 7 (broad) (Hd) , 6. 80(s) (r^) . Compound II: <S 1.30 and 1.33(Hd,Hd') , 7.12(Ha), 6.90 and 7.44(Hc and YL^) The compounds were also identified as definitely not DBPC by vpc comparison with DBPC at various temperatures on Carbowax. An IR absorption band (in CHCl^) at 1720 cm 1 also identified compound II. The fourth and largest of the products was purified as were the f i r s t 2 by crystallizing from the neat solution and rapidly washing with hexane and then acetone. Vpc (Carbowax) analysis of this compound when compared to a known sample of 1,3-dihydroxyadamantane showed the two to be identical in retention time, size, and shape. Both samples were compared as saturated solutions in acetone. The compound and the diol also appeared to have identical s o l u b i l i t y properties i n most organic solvents as well as yielding identical IR spectra (saturated solutions i n CHCl^). The third and smallest of the major peaks had been obtained in f a i r purity from the 9:1 benzene-acetone fraction from the column. It was obtained in the pure form by use of preparative vpc (3/8" x 10' Carbowax, 230°, 100 ml He flow, retention time of 15-20 minutes), melting point: 217-218°C ( i t turned yellow at 210° and above). N.m.r.: (> 99% purity in CDC13): 6 1.85 (shoulder) and 2.0 (8H), 2.3 (3H), 2.8 (IH), 3.6 (2H). The absorptions were a l l broad except a spike from the center of the 3.6 peak. Anal. Calcd. for C 1 0 H 1 4 ° 2 : c> 72.26; H, 8.49. Found: C, 73.76; H, 8.36. IR (CC1 4): 3500 cm"1 (m, sharp), 2930 cm _ 1(s) , 2850 cm'^m) , 1715 cm"1 (s), 1670 cm~1(m), 1145 cm - 1(s), 900 cm_1(m), 885 cm_1(m). The reaction residues from kinetics using 1-dedecanethiol as "inhibitor" when analyzed on vpc carbowax gave three new peaks and several very minor peaks. Because two of these peaks occurred in the - 74 -region where unidentified impurities resulting from DHA synthesis were concentrated, the task of isolation was made more d i f f i c u l t . Column chromatography using F l o r i s i l and eluting with f i r s t hexane, and then benzene gave these two in moderate purity in the benzene layer. Separation of the two from each other was accomplished using the preparative vpc (3/8" Carbowax 150°C, He flow: 100 ml/min). The f i r s t compound was completely purified by again using preparative vpc with the same column and flow rate, except at 125°C. Retention time was approximately three hours. The compound was identified as 1-adamantanol. M.p. (sealed tube): 265° (sublimes); literature: 70 71 79 (300° (sublimes)) , 288.5-290°. ' . N.m.r. (20% CDC13 and 80% CC1 4): 6 1.37 (s)(lH), 1.70 (multiple)(12H), 2.15 (broad)(3H); add D20 and 6 1.37 disappears. Literature (in CDC13): 6 1.70 (multiplet)(12H), 2.15 (broad)(3H). 7 0 IR (saturated CC1 4): 3560 cm"1 (w, sharp), 2920 cm"1 (s), 2850 cm"1 (m), 1450 cm"1 (m), 1110 cm"1 (s), 1085 cm"1 (s) . Literature (KBr): 7 3 3500 cm"1 (m), 2920 cm"1 (s), 1450 cm"1 (m), 1110 cm"1 (s), 1085 cm"1 (s). Anal. Calcd. for C^H^O: C, 78.90; H, 10.59. Found: C, 78.69; . H, 10.32. Vpc analysis of the compound when compared to a known sample of 1-adamantanol showed the two to have identical retention times, shapes, and sizes. After i t s separation from the f i r s t compound, the second compound was also purified by preparative vpc on Carbowax (125°, He flow rate 100 ml/min, retention time - approximately four hours). Its identity was shown to be 7-methylenebicyclo[3.3.l]nonan-3-one. M.p. 163.5°C; l i t e r a t u r e 4 4 ' 4 5 , 7 4 : 160-164°C. IR (CC1 4): 2930 cm - 1 (s), 1710 cm"1 (s), 1450 cm"1 (s), 1215 cm"1 (m), 895 cm"1 (s), 885 cm"1 (m). N.m.r. (CDC13): 6 1.95 (broad)(IH), 2.40 (sharp)(5H), 4.78 (s)(lH). Anal. Calcd. for C^H^O: C, 79.96; H, 9.39. Found: C, 79. 79; H, 9.18. The third peak was the very long retention time product which was seen in the reaction of DHA and 1-dodecanethiol under nitrogen. Its identity was simply confirmed by inspection to be the same, but was not further identified. A general idea of the ratios of the products of kinetic reactions was obtained by taking a selected run and determining the product ratios from that. The particular reaction taken was .24 molar DHA -3 -3 (0.27 x 10 moles) and .053 molar DBPC (0.06 x 10 moles) in octane solvent. The ratios of the products were determined by the cut-out-and-weigh vpc peaks method. To do this, f i r s t a sample of pure DHA solution was run, and, after the same DHA reacted to completion, another sample was run under identical conditions. In this analysis method only peaks which changed during the course of reaction were considered, and, i f they were present i n i t i a l l y , that weight was subtracted from the weight at the end of the experiment. A l l of the products resulting from DHA (or suspected as having DHA as their origin) were assumed to give the same relative areas under the curve. The total weights of a l l the peaks resulting from new compounds were .summed and.taken.to be the 100% value for the products detectable by _ In addition to the l i s t e d properties, both IR and n.m.r. spectra, as well as vpc retention times were compared with a sample of the same material synthesized by a different method. A l l comparisons were identical. - 76 -vpc. Each peak was then compared to this and i t s percentage composition calculated. The total of the detectable products, when compared with the i n i t i a l value for DHA, indicated that only 27% of the DHA was accounted for in this fraction. The remaining 63% was i n the form of larger molecules probably polymeric which weren't identified. Table V gives the data concerning the composition of the detectable fraction. No quantitative study of the products whose origin was DBPC was made. Table V. Products of a 9:2 DHA:DBPC Reaction Mixture in the Presence of 0^. Retention Time (min) Peak .. % •k-k Growth (mg) of Total Products Identity 12.6 52.6 15.9 uncertain 14.4 28.0 8.5 1 17.1 9.9 3.0 1 19.4 207.8 62.9 1,3-dihydroxy-adamantane 29.0 32.2 9.7 1 * Carbowax 80°/6 32°/min „..c^ £ 1 mm • 200 C, flow rate % 50 ml/min. A* Calculated by subtracting the i n i t i a l wt. from the fi n a l weight of the peak. - 77 -REFERENCES 1. 0. Freund, Monatsh., 3_, 626 (1881). 2. G. Gustavson et a l . , J. Pr. Chem., 36, 300 (1887). 3. J.B. Cloke, R. Anderson, J. Lackmann, G.E. Smith, J. Am. Chem. Soc., 53, 2791 (1931). 4. 0. Pressel, Ann., 256, 1717 (1890). 5. E. Buchner, Ber., 23, 703 (1890). 6. P.S. Skell, R.C.. Woodworth, J. Am. Chem. Soc, 713, 4496 (1956). 7. B.M. Frost, W.L. Schinski, F. Chen,.I.D. Mantz, J. Amer. Chem. Soc, 93_, 676 (1971). 8. W.A. Bernett, J. Chem. Educ., 44, 17 (1967). 9. L. Klasine, Z. Maksiu, M. Kander, J. Chem. Soc, A, 1966, 755. 10. L.L. 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Chem.,26, 2207 (1961). 72. P. Schleyer, R.D. Nicholas, J. Am. Chem. Soc., 83, 182 (1961). 73. Sadtler Spectra I.R. 32783, Sadtler Research Lab., Phila. U.S.A. 74. H. Stetter, P. Jacke, Angew. Chem., 73, 354 (1962). - 81 -DHA - 0 „ Reaction in Xylene 0 S O 1 0 0 1 5 0 2JOO 2?0 30O 350 *OQ <+S0 t (min.) DHA - CL Reaction in Xylene t (min.) DHA - 0 Reaction in Xylene DHA - 0. Reaction in Xylene 0 SO (DO ISO AOO JlSO 3 o o 3 5 0 • WO ^So t (min.) DHA - 0 0 Reaction in Xylene t (min.) DHA - p-Benzoquinone Reaction in Xylene t,SV t (min.) t (min.) O 5 0 100 ISO ZOO 250 300 350 HOQ J+SQ t (min.) DHA - 0 2 Reaction in Octane l.So, US-o 1.0C > < H > MS-00 o 0.SC4 O- .081 M DHA + .324 M DBPC 2SO t (min.) 3oo i 3 SO HOO 4-So DHA - 0 o Reaction in Octane t (min.) DHA - CL Reaction in Octane *fSO t (min.) DHA - 0 'Reaction in Octane DHA - 0 o Reaction i n Octane I.5& 0 - .238 M DHA + .035 M DBPC * - .174 M DHA + .082.M HMBP I.OO OS t (min.) DHA - 0„ Reaction in Octane t (min.) DHA - 0„ Reaction in Octane DHA - 1-Dodecanethiol Reaction in Xylene (.So-t (min.) t (min.) Concentration Changes of DHA and DBPC with Time (in Xylene) 


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