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Organic Lab Reactions 234

Organic Lab Reactions 234 - tion usually takes place para...

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MECHANISMS OF THE REACTIONS 229 free aryl radicate are produced by decomposition of the diazo compounds and of the nitrosoacetylamines, and that the radicals react with the second component to give the biaryl. Thus, in benzene, nitroso-m- nitroacetanilide decomposes into wvnitrophenyl and acetate radicals with evolution of nitrogen; the m-nitrophenyl radical reacts with benzene with elimination of a hydrogen atom and the formation of 3-nitrobiphenyl. The reactions are indicated in the following formulation, which shows also the probable fate of the acetate radical. NO 2 CH«C0O- NO S CH 3 COO + H- CH3COO CH S H- CH 3 COOH CH 3 • + CO 2 CH 4 In support of the free radical mechanism is the observation that the usual directive influences are not operative in these reactions. Substitu-
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Unformatted text preview: tion usually takes place para and ortho to the substituent in the benzene ring, irrespective of the nature of the groups. Even with nitrobenzene, para and ortho derivatives are formed. Thus, N-nitrosoacetanilide and nitrobenzene give 2- and 4-nitrobiphenyl. / V-N(NO)COCH 3 NO 2 NOj Similarly, in the few reactions that have been carried out with benzalde-hyde and benzonitrile, only the para isomer has been isolated from the re-action mixtures; with ethyl benzoate alT three isomers were obtained. Another point of interest is that nitrobenzene is attacked more rapidly than toluene....
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