Organic Lab Reactions 242

Organic Lab Reactions 242 - the pyridyl group Thus the...

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SIDE REACTIONS derivative and pyridine. 19 The best procedure is to add an aqueous solu- tion of the diazonium salt to an excess of pyridine at temperatures rang- ing from 20° to 70°; the yields of products vary from 20 to 80%. 20 Apparently the pyridine plays the role of sodium hydroxide in liberating the reactive intermediate diazohydroxide, for, if the pyridine is added to the solution of the diazonium salt, no nitrogen is evolved until after one equivalent of pyridine has been introduced. A mixture of isomers results which can be separated either directly or through the picrates. From benzenediazonium chloride and pyridine a 40% yield of phenyl- pyridines is obtained from which a-phenylpyridine (9%), (3-phenylpyri- dine (4%), and 7-phenylpyridine (4%) can be isolated in pure form. N 2 +C1- N Excess N By this procedure a considerable number of arylpyridines have been pre- pared. Pyridine derivatives can be prepared also from amines containing the pyridyl group. Thus,
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Unformatted text preview: the pyridyl group. Thus, the nitrosoacetyl derivative of m-a-pyridyl-aniline can be coupled with benzene to yield 3-a-pyridylbiphenyl (XVI). •N(NO)COCH 3 + XVI Similarly, the 0-and -y-pyridyl derivatives of biphenytcan be prepared. Side Reactions One of the side reactions is the formation of linear polyaryls, which may be considered to be formed by further reaction of the biaryl initially produced. From the high-boiling residue remaining after the removal of the biphenyl, formed from diazotized aniline, benzene, and alkali, p-terphenyl * and quaterphenyl 16 have been isolated; and in the mixture formed in the" preparation of 4-methylbiphenyl a hydrocarbon was found 19 Haworth, Heilbron, and Hey, / . Chem. Soc, 1940, 373 20 Haworth, Heilbron, and Hey, J. Chem. Soc , 1940, 349....
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