The chemistry of heteroarylphosphorus compounds. Part 7. Heteroaryl-, heteroarylmethyl-, and substituted aryl-phosphonate esters. Electronic effects of substituents at phosphorus on the rates of alkaline hydrolysis, and phosphorus-31 nuclear magnetic resonance and phosphoryl infrared stretching frequency studies

Abstract

The rates of alkaline hydrolysis of a series of ethyl and phenyl esters of heteroarylphosphonic acids derived from furan, thiophen, and 1-methylpyrrole have been determined, and the variation of the rate of hydrolysis with the nature of the heterocycle is discussed. It is concluded that the heteroaryl substituent interacts with the phosphorus atom mainly by a σ-electron-withdrawing effect. Mesomeric p_π→d_π electron donation from the ring systems to phosphorus seems to be of little importance. ³¹P N.m.r. and phosphoryl i.r. stretching frequencies are also presented and discussed in relation to the electronic effects of the heteroaryl substituents.

In addition a study has been made of the rates of alkaline hydrolysis of a related series of heteroarylmethylphosphonate esters, and also of a series of substituted phenylphosphonates. In the latter case, a good correlation between the rate data and the Hammett σ constants of the aromatic substituents has been obtained. For both series of esters ³¹P n.m.r. data are presented and discussed.