Hydrolysis of phenylureas. Part III. Micellar effects on the solubilization and decomposition of 4-methyl- and 4-nitro-phenylurea

Abstract

Measurement of the critical micelle concentration of non-ionic nonylphenoxypoly(oxyethylene)-14-ethanol (A-730) and cationic hexadecyltrimethylammonium bromide (CTAB) by surface tension and u.v. spectroscopic methods shows large increases on addition of very small amounts of 4-methyl- and 4-nitro-phenylureas. Micellar A-730, CTAB, and anionic sodium dodecyl sulphate (NaLS) have little effect on the rate constants of hydrolysis of these ureas. Arrhenius parameters have been evaluated and the mechanisms of hydrolysis are discussed in terms of sites of solubilization. By contrast, dodecylammonium propionate (DAP) in benzene enhances the rate of decomposition of 4-nitrophenylureas 3 × 10³ fold. This observed catalysis is discussed in terms of solubilization of the substrate in the polar micellar cavity where it is held fairly rigidly, thus enhancing proton transfer. General-acid and -base catalysis is also observed in DAP.