Aniline, formation Carbohydrates

Phenylhydrazine on exposure to light slowly darkens and eventually becomes deep red in colour salts of the base share this property but to a lesser degree, the sulphate and acetate (of the common salts) being most stable to light. Phenylhydrazine is largely used in organic chemistry to characterise aldehydes and ketones as their phenyl-hydrazones (pp. 342, 345), and carbohydrates as their osazones (pp. 136-140). It is readily reduced thus in the process of osazone formation some of the phenylhydrazine is reduced to aniline and ammonia. On the... 

Since alcohols and carbohydrates readily form equilibrium concentrations of alkyl nitrites which are themselves inactive as direct nitrosating agents (see below), it is to be expected that the addition of alcohols and carbohydrates will inhibit N-nitrosation of amines. This has been shown to be the case for aniline derivatives, and the reduction in the measured first order rate constants can be accounted for quantitatively by such equilibria (Aldred and Williams, 1982). But since alkyl nitrite formation is a rapid equilibrium process, it is not possible, at least for the aniline derivatives studied, to suppress N-nitrosation completely this way. This is in contrast to the effect of thiols discussed in Section 9. In another study (Kurechi et al., 1980), the same effect was observed at pH 3 for the nitrosation of dialkylamines, whereas at pH 5 there was claimed to be a rate enhancement on addition of alcohols, an effect which was not explained. 

Schiff, for example, had included carbohydrates in his studies on the formation of Schiff bases from aldehydes and amino compounds. He heated D-glucose with aniline or withp-toluidine in substantia [11], and described that these components, under loss of water, formed yellow glass-like condensation products. These supported his suggestions on the formation of Schiff bases from aldehydes and suitable aromatic amines [12]. 

---