Phenylhydrazones defined

The addition reactions of hydrazinesprovide a number of useful solid derivatives of well-defined melting point, such as the phenylhydrazones, the 2,4-dinitrophenylhydrazones (Scheme 3.45a) and the semicarbazones (Scheme 3.45b). These are used to characterize aldehydes and ketones. In each case the reaction takes place at the most nucleophilic nitrogen. 

In addition to the acid-catalysed hydrolysis of oximes, a kinetic study has also been made of the addition of bromine to a number of substituted benzal-dehyde phenylhydrazones . The measurements were made in 70% acetic acid v/v, in the presence of 0.1 M potassium bromide. The attacking species was shown to be predominantly molecular halogen, and not the tribromide ion, since a graph of 2(1 -t- X[Br ]) against [Br ] was linear, and of zero intercept, k-2 being defined by the equation... 

Another method of establishing structures depends upon the well-defined reaction of benzenediazonium chloride with acyclic phenylhydrazones to form diphenylformazans (215) no well-defined product is obtained from cyclic isomers. This method has given the same results as the acetylation method, and, in addition, has shown that the third isomer of glucose phenylhydrazone is also cyclic. 

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