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Organic Seminar Abstracts L I B RA FLY OF THE U N IVERSITY OF 1LLI NOIS Q.54-1 Ii£s 1964/65 ,t.l P Return this book on or before the Latest Date stamped below. Theft, mutilation, and underlining of books are reasons for disciplinary action and may result in dismissal from the University. University of Illinois Library OCfcfcsrm L161— O-1096 Digitized by the Internet Archive in 2012 with funding from University of Illinois Urbana-Champaign http://archive.org/details/organicsemi1964651univ s ORGANIC SEMINAR ABSTRACTS 196^-65 Semester I Department of Chemistry and Chemical Engineering University of Illinois ' / SEMINAR TOPICS I Semester I96U-I965 f"/ ( Orientation in Sodium and Potassium Metalations of Aromatic Compounds Earl G. Alley 1 Structure of Cyclopropane Virgil Weiss 9 Vinylidenes and Vinylidenecarbenes Joseph C. Catlin 17 Diazene Intermediates James A. Bonham 25 Perfluoroalkyl and Polyfluoroalkyl Carbanions J. David Angerer 3^ Free Radical Additions to Allenes Raymond Feldt 43 The Structure and Biosynthesis of Quassin Richard A. Larson 52 The Decomposition of Perester Compounds Thomas Sharpe 61 The Reaction of Di-t -Butyl Peroxide with Simple Alkyl, Benzyl and Cyclic Ethers R. L. Keener 70 Rearrangements and Solvolysis in Some Allylic Systems Jack Timberlake 79 Longifolene QQ Michael A. Lintner 00 Hydrogenation ! Homogeneous Catalytic Robert Y. Ning 9° c c Total Synthesis of ( -) -Emetime R. Lambert 1* Paracyclophanes Ping C. Huang 112 Mechanism of the Thermal Rearrangement of Cyclopropane George Su 121 Some Recent Studies of the Photochemistry of Cross -Conjugated Cyclohexadienones Elizabeth McLeister 130 The Hammett Acidity Function R. P. Quirk 139 Homoaromaticity Roger A. Smith 1^7 Mechanism of the Kolbe Reaction Jermey Klainer 13^ Protonated Cyclopropane Intermediates Nina Sussmann 1°3 . - 1 - ORIENTATION IN SODIUM AND POTASSIUM METALATIONS OF AROMATIC COMPOUNDS Reported by Earl G. Alley September 28, 196^ Metalations of aromatic compounds by sodium or potassium may be accomplished by several general reactions, as follows: i RM + ArH -> RH + ArM ii. ArH + M -> ArM + 1/2 H2 iii. ArX + 2M * ArM + MX iv. ArOR + 2M > ArM + ROM v. ArM ! + M -> ArM + M 1 Most of the mechanistic investigations have involved the first of these reactions, specifically with sodium or potassium a IkyIs as metalating agents. There are several general reviews in the literature (1, 2, 3, *0 dealing with organos odium and organo- potassium compounds,, The Nature of Organos odium and Organopotassium Compounds - The alkyl and aryl compounds of sodium potassium are nonvolatile, practically insoluble in hydrocarbons, and do not have sharp melting points. These facts have been cited (1) as evidence that the carbon-metal bond in these compounds is ionic. In contrast, organolithium compounds are volatile and soluble in hydrocarbons (3). It has been proposed (5*6) that the carbon -lithium bond has considerable ionic character. The difference in pro- perties may be due to the tendency (3) of alkyl lithium to be highly associated. Alkylsodium and alkylpotassium are highly reactive substances. Under conditions similar to those employed in the metalation reactions, they have been shown (7, 8) to undergo a number of decomposition reactions: RCH2CHaK * RCH = CH2 + KH RCH2CH2K + RK + CH2 = CH2 RCHaCHaCHaCH^C -> RCH2CH2CH = CH 2 •> RCH2CHCH = CH2 > RCH = CH - CH = CH2 K by such processes a great variety of organopotassium compounds may arise and thus the identity of the actual metalating agent may be unknown. Alkylsodium compounds are much less reactive (8) than the corresponding potassium derivatives and these decomposition reactions are of little importance under the conditions used in aro- matic metalations with alkylsodium. Finnegan (9) has observed that butyl- and amyl- potassium will metalate such hydrocarbons as pentane, hexane, and cyclohexane. Often these or similar substances are used as solvents in the preparation of organopotas- sium compounds to be used as metalating agents. Thus the actual alkyl group in the metalating agent in these cases may be derived from the solvent rather than from the expected source. Metalation of Aromatic Hydrocarbons - In all of the experiments the metalation products were identified by carbonation, followed by quantitative analysis of the mixture of acids thus obtained. Bryce-Smith separated these acid mixtures by the following methods: When benzene was metalated (10) , benzoic acid was isolated by extraction with benzene, and iso- phthalic and terephthalic acids were separated by crystallization of the methyl esters. When alkylbenzenes were studied (11, 12) the acids from the carbonation were first oxidized to benzoic and phthalic acids and then separated by means similar to those above. No satisfactory method for separating phthalic acid was found, so the amount of the acid mixture that was not isolated as benzoic, isophthalic or tere- phthalic acids was assumed to be phthalic acid. Benkeser and coworkers could find no indication (13, 1^, 15) of ortho substitution in similar experiments, in which they analyzed (13, 1^-, 15) the acid mixtures they obtained from carbonation by con- version to the corresponding methyl esters and vapor phase chromatography of these esters. Control experiments proved this method to be very reliable. In cases where Bryce-Smith's (12) and Benkeser's (15) data overlap there was good agreement between the two analytical methods. It is possible that the mixture of acids obtained from carbonation of the re- - p - action mixtures does not reflect the true ratios of organometallic isomers present. No controls were made to study this possibility by either Bryce -Smith or Benkeser. Russell has reported (l6) that a-cumylpotassium upon treatment with deuterium oxide yields a product which has deuterium only in the side chain. Ziegler and Schnell re- ported (17) that carbonation of 1,1-diphenylethylpotassium produces only 2,2-diphenyl- propionic acid in 80 to 90$ yield. Benkeser has shown (l^t-) that p_-chloroethylbenzene when treated with potassium in decane for one hour followed by carbonation yields only p-ethylbenzoic acid, 'These results indicate that the products of the carbonation do reflect the isomer distribution in the organ ometalii c mixtures. The metalation of benzene was first reported (18) by Schorigin. Ethyls odium was the metalating agent employed . Gilman and coworkers investigated (19) the reaction and reported that in addition to phenyls odium, small amounts of ortho and para di~ metalated benzene occurred . Morton and coworkers reported, (20, 21) that dimetalation of benzene with n-amyls odium yields QCffo or meta and 20$ or para isomers and they inter- preted (1) these results in terms of an electrophilic substitution mechanism for the reaction. Bryce-Smith and Turner (10) attempted to clarify the contradictory results of Gilman and Morton. They found that action of ethyls odium on benzene produces para and meta disubstitution in a ratio of about 7:3= in this same work potassium meta- lation was also investigated. The alkyl group of the metalating agent was varied, and although some changes in the para to meta ratio were noted, no logical relationship was obvious. In all cases, para and meta disubstitution predominated. The metalating agent was produced by reaction of an alkyllithium with potassium. The reagent thus formed is an alkyllithium-alkylpotassium complex. The reactivity of such complexes is intermediate between those of alkyllithium and alkylpotassium compounds, Morton and Claff have investigated (22) the effect of alkoxide ion on the dimetalation of benzene. The alkoxide is thought (22) to form an ionic aggregate with the metalating agent. The effect of alkoxide was to increase the ratio of meta to para dimetalation from 3:1 in the absence of alkoxide to values that ranged from 3° 3:1 for sodium cyclopentoxide to 50:1 for lithium t-pentoxide. Morton and Lanpher assigned (23) the reaction product of benzene with phenyl potassium structure I. Evidence for this structure was absorption at II65 cm," in the infrared spectrum, which is also observed (2^-) in the spectra of benzyl, a-methylbenzyl, a,a-dimethylbenzyl anions. No assignment Oandof these bands was made so this evidence may not I be valid support for structure I. Pyrolysis of I yielded biphenyl, and carbonation of I gave a diacid, which upon pyrolysis yielded p-phenyl- benzoic acid. The behavior of I upon pyrolysis provides evidence against metalation mechanism D, page 5 . Orientation in the metalation of alkylbenzenes has been surrounded by consider- able confusion. Schorigin (25) studied the metalation of toluene, ethylbenzene , and cumene. He reported that metalation with ethylsodium occurred in the a-position of the side chain. Morton and coworkers reported (26) that n-amyls odium attacked cumene para and ortho to the isopropyl group. This result was interpreted (1, 26) as evi- dence for an electrophilic substitution mechanism for the reaction. Bryce-Smith has made a detailed study (11) of the metalation of alkylbenzenes including the effects of changes in temperature and reagent on the reaction. Ethylpotassium, the metalating agent in this study, was prepared from alkyiiithium and potassium and therefore the actual reagent is an alkyllithium-alkylpotassium complex (11). It was found that a- attack decreased in the order toluene ^> ethylbenzene )> isopropylbenzene. For toluene attack in the a-position was 100$, for ethylbenzene 50$, and for isopropylbenzene Ijfo of the total substitution. This order of reactivity parallels the stability
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