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Organic Lab Reactions 243

Organic Lab Reactions 243 - particular instance at least...

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238 THE PREPARATION OF UNSYMMETRICAL BIARYLS which appeared to be a di-p-tolylbenzene. 4 It is of interest that the decomposition of benzenediazonium formate in acetic acid in the pres- ence of copper yields quinquiphenyl (XVII) and sexiphenyl (XVIII) in addition to biphenyl, p-terphenyl, and quaterphenyl. 21 XVII XVIII Another side reaction which occurs is reduction; in the reaction the —N 2 C1 or —N(NO)COCH 3 group is replaced by hydrogen. m-Bromo- toluene was isolated in 6% yield from the reaction between the sodium diazotate from 2-bromo-4-methylaniline and benzene, and in 10% yield in a similar reaction from 2-methyl-4-bromoaniline. 4 Some nitrobenzene is obtained in the preparation of 3-nitrobiphenyl from nitroso-m-nitro- acetanilide (p. 250). The source of the hydrogen effecting the reduction has not been determined. ' Azo compounds are formed to some extent in the biaryl reactions. From the reaction between diazotized p-toluidine and benzene, azo-p- toluene, CH3C6H 4 N=NC 6 H4CH3, was isolated, indicating that, in this
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Unformatted text preview: particular instance at least, the azo compound was derived entirely from the diazonium compound. In addition Do these types^of compounds, a considerable amount of high-boiling material is usually formed in the reactions. The disadvantages of the methods are the low yields in many of the reactions, the limitations to coupling with liquid aromatic compounds, the difficulty in some instances of getting the product out of-the mixture containing the high-boiling by-products, and the difficulty of separating isomers when more than one compound is formed. Related Reactions Employment of Dry Diazonjum Salts. Of interest is the reaction between dry diazonium salts and aromatic compounds in the presence of anhydrous aluminum chloride. 18-22 The reaction resembles a Friedel and Crafts reaction; nitrogen is evolved in addition to hydrogen chloride. 11 Gerngross and Dunkel, Ber., 57, 739 (1924). 2a Mohlau and Berger, Ber., 26, 1198 (1893)....
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