The chemistry of heteroarylphosphorus compounds. Part 10. Synthesis and kinetics of alkaline hydrolysis of heteroarylphosphinate esters and hydrolysis of heteroarylphosphine oxides

Abstract

The rates of alkaline hydrolysis in aqueous dioxan of the ethyl esters of di-(2-furyl)-, di-(2-thienyl)-, and diphenylphosphinic acids have been determined. At 30 °C, second-order rate constants are respectively 2.76 × 10^–2, 1.02 × 10–3, and 2.57 × 10^–4 I mol^–1 s^–1. The variation in rate with the nature of the P-substituent is discussed, and it is concluded that the heteroaryl substituents interact with phosphorus mainly by a σ-electron-withdrawing effect.

The alkaline hydrolysis of tri-(2-furyl)- and tri-(2-thienyl)-phosphine oxides affords a convenient route to the above phosphinic acids. The corresponding bis-(1-methylpyrrol-2-yl)phosphinic acid could not be prepared by this procedure: other routes to this compound have been explored, without success, owing to the capacity of the 1 -methylpyrrol-2-yl substituent to inhibit nucleophilic attack at phosphorus.