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Organic Lab Reactions 248

Organic Lab Reactions 248 - for the preparation of biaryls...

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CHOICE OF METHOD 243 DUmann Reaction. Although the .Ullmann reaction is considered usually, in connection with the preparation of symmetrical biaryls, it has been employed also to prepare unsymmetrical biaryls. Thus, o- terphenyl has been synthesized by heating a mixture of iodobenzene and 2-iodobiphenyl with copper; 44 biphenyl and 2,2'-diphenylbiphenyl were by-products of the reaction. The Ullmann reaction appeared to be the only satisfactory method for preparing certain highly substituted unsymmetrical biphenyl derivatives which were required by Adams and coworkers 45 in their study of the stereoisomerism of biphenyl compounds. SELECTION OF EXPERIMENTAL CONDITIONS Choice of Method. The particular method to be used depends to some extent on the compound to be prepared. On "the basis of yield, the N-nitrosoacetyl method is generally to be preferred. However, the diazo reaction has been employed frequently, probably because it is less trou- blesome to carry out. Gomberg and Pernert 4 recommended the use of the sodium diazotates
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Unformatted text preview: for the preparation of biaryls from aniline and from p-toluidine and the normal diazo method for negatively substituted amines such as the bromo- and nitro-anilines. Grieve and Hey 7 found little difference in the yields of biaryls obtained by the two procedures when they coupled diazotized aniline with six different components: benzene, toluene, m-xylene, chlorobenzene, nitrobenzene, and ethyl benzoate. Where it is applicable, this modification offers the advantage that the dropwise addition of alkali is eliminated. Some comparative studies have been made of the use of sodium acetate in place of sodium hydroxide in the diazo reaction. 6 In five out of twelve reactions, the yield -of the biaryl was improved by using sodium acetate. Better yields were obtained by this variation with the following 44 Baohmann and Clarke, J. Am. Chem. Soc, 49, 2089 (1927). 48 See Adams and Teeter, J. Am. Chem. Soc., 62, 2188 (1940), and previous papers of this series....
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