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

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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.

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