Phenylureas. Part 1. Mechanism of the basic hydrolysis of phenylureas

The mechanism of the hydrolytic decomposition of phenylureas in basic media in the pH range 12 to 14 is investigated. In this pH range a levelling of the rate–pH curve is observed as well as a change of the substituent influence on the hydrolysis rate. These experimental findings suggest the formation of an unreactive side product of the phenylurea in a parasitic side equilibrium at sufficiently high pH. The urea dissociates at the aryl–NH group to give its conjugate base. For the hydrolytic decomposition of phenylureas an addition–elimination mechanism is proposed as has been established for the alkaline hydrolysis of carboxylic acid esters and amides.