Hydroxy amines reaction with nitrous acid

The amino group present in these acids takes part in reactions characteristic of amines. When treated with nitrous acid, the amino-acids are converted into hydroxy-acids —... 

Good examples to start with are ammonia, the simplest amine, and its hydroxy derivative, hydroxylamine. Both react readily with nitrous acid in acidic aqueous solution, as shown in Schemes (3-1) and (3-2) ammonia yields molecular nitrogen. This method was used as a preparative process for N2 decades before fractionation of air became commercially available. The product of the corresponding reaction of hydroxylamine is dinitrogen oxide (originally called nitrous oxide). 

Traditional routes to phenoxazines (e.g., 72) include the thermolysis of 2-aminophenol 70 and catechol 71 (Scheme 40) or catechol and ammonia. Phenothiazines are prepared by heating diphenylamines with sulfur as exemplified in Scheme 41 < 1985AXC1062, CHEC-III(8.09.9.2)655>. 2-Hydroxy- (or mercapto-) 2,4-dinitrodiphenylamines 73 cyclize to phenoxazines (or phenothiazines) in the presence of base by elimination of nitrous acid. These reactions are complicated by Smiles-type rearrangements of the amines 73 so that mixtures of isomeric products 74 and 75 are obtained (Scheme 42). 

The kinetics of the diazotization of 4-aminopyridine in 0.0025-5.0 M perchloric acid were studied, and the reaction was believed to proceed by only one mechanism whose kinetic form is first order with respect to the amine as well as to nitrous acid. The rate of the reaction showed an exponential catalytic dependence on the concentration of added perchloric acid and sodium perchlorate. In solutions of constant ionic strength the rate was directly related to the acidity function Hq). The 4-diazonium ion was characterized as 4-(2-hydroxy-l-naphthylazo)pytidine. When 4-aminopyridine is diazotized and treated with Ar,7 A-dimethylaniline, 4-(p-dimethylaminophenylazo)pyridine (DC-95) is obtained. 2-(p-Dimethylaminophenyl)pyridine is isolated when 2-aminopyridine is used instead of 4-aminopyridine. ... 

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