Acid hydrolysis of phenylurea, 4-fluorophenylurea, and 3-methylphenylurea

Abstract

The rate constants of hydrolysis of phenylurea and 4-fluorophenylurea have been measured over the acid range 2·5–60·1% and 2·5–70·0% w/w H₂SO₄ respectively at five temperatures in the range 70·0–110·4 °C; those of 3-methylphenylurea have been measured over the acid range 2·5–60·1% w/w H₂SO₄ at 100·1 °C. Attempts to correlate the rate data with Bunnett w and w*, Bunnett–Olsen linear free energy relationship, and Zucker–Hammett criteria of mechanism have proved unsatisfactory. Application of a two-term equation and high activation parameters provide evidence that these phenylureas hydrolyse by an A-1 mechanism. Rate constants of hydrolysis of the sulphonated derivatives of phenylurea and 3-methylphenylurea are reported over the range 70·0–95·0% w/w H₂SO₄ at 100·1 °C.