Cyclic organophosphorus compounds. Part VI. The hydrolysis of some 1,3,2-dioxaphospholans and 1,3,2-dioxaphosphorinans in aqueous alkali–dioxan solution

Abstract

Stepwise replacement of the hydrogen atoms at positions 4 and 5 in the 2-thiono-1,3,2-dioxaphospholan ring system by methyl groups stabilises the ring by a constant factor of two (approximately) for solutions of the compounds in aqueous sodium hydroxide–dioxan. This effect is thought to be due to electronic rather than steric interactions, and is very much weaker than that produced by exocyclic groups attached to phosphorus. Under the conditions employed, 2-oxo-2-phenoxy- and 2-ethoxy-4,4,5,5-tetramethyl-2-thiono-1,3,2-dioxaphospholan yield ring-opened products predominantly.

In contrast, 2-chloro-5,5-dimethyl-2-thiono- and 5,5-dimethyl-2-S-(morpholinocarbonylmethyl)thio-2-thiono-1,3,2-dioxaphosphorinan hydrolyse at the exocyclic bonds attached to phosphorus, the rate of reaction being comparable with that of the analogous acyclic ester. In the six-membered-ring system, steric effects of alkyl substituents are probably also of importance.