Kinetics and mechanism of alkaline hydrolysis of aryl carbazates

Hydrolysis of aryl carbazates (H2NNHCO2Ar with Ar = phenyl, 3- or 4-chlorophenyl, 3- or 4-nitrophenyl, 1-methylphenyl and 4-methoxyphenyl) and/or their 2- or 3-methyl derivatives in aqueous buffers or sodium hydroxide solutions gives phenolate and sodium carbazate. The kinetics and acidity constants and thermodynamic parameters are given. By analysing the pH profiles, the activation entropy, and effects of the substituent on the aromatic ring it was found that aryl carbazates containing a methyl group in the 2 position are hydrolysed by a B(Ac)2 mechanism and the others by an E1cB mechanism. The pH profiles of nitrophenyl carbazates show a maximum. The rate of decarboxylation of carbazic acid decreases with increasing pH value.