Oxidation of Sodium Hypophosphite by Oxygen in Alcoholic Solutions of Ferrum (III)

G.S Polimbetova,A.K Borangazieva,M.M Aleshkova,G.O Bugubaeva,Zh.U Ibraimova

doi:10.18321/ectj410

Abstract

Hypophosphites are widely used as reducers in the metal protection coating, as reagents in the synthesis of various organophosphorus compounds, in analytical chemistry, and in many other fields. NaH2PO2 difficultly reacts with many oxidizers without catalysts despite of the significant reduction potential. The kinetics and the mechanism of hypophosphite oxidation in aqueous acid solution of the metal and nonmetal salts are studied in detail. The reactivity of hypophosphite in the organic solvents was not almost studied. In this work the basic possibility of synthesis dialkylphosphites from cheap, accessible and harmless NaH2PO2 and alcohols is shown. Sodium hypophosphite is oxidized by oxygen in alcoholic solutions of FeCl3 at 50-80 °С to dialkylphosphites. Kinetic and mechanism of the reaction are investigated by methods of volumetry, redox-potentiometry, GC, IR-, UV-, EPR-, Mössbauer- and NMR 31Р-spectroscopy and X-ray powder diffraction analysis, optimum conditions are found, kinetic and activation parameters of the reaction are calculated. It is shown, that the process follows redox-mechanism and consists of two key stages: reduction of Fe (III) by hypophosphite with formation of dialkylphosphite and reoxidation of Fe (II) by oxygen. The coordination mechanism of reduction reaction of Fe (III) by hypophosphite is proposed. According to this mechanism the dialkylphosphite forms through innersphere redox-decomposition of intermediate alcoxyhypophosphite complex of Fe (III). The coordination mechanism of the process is confirmed by low values of Е≠ and negative activation entropies ∆S≠. The availability in an inner sphere of Fe (III) bromide, low-molecular alcohols, water, characterized by high acidity, increases the reaction rate of oxidative alcoxylation of hypophosphite and promotes the further transformation of dialkylphosphite to di- and trialkylphosphate.

Highlights

The existent technology of phosphoric ether production is based on multistep processes of toxic, flammable and explosive white phosphorus oxidation by chlorine up to PCl3, POCl3 followed by the alcoxylation and is accompanied by formation of a considerable quantity of toxic hydrogen chloride
NaH2PO2 difficultly reacts with many oxidizers without presence of catalysts despite of the significant reduction potential [2,3,4,5]
In the present work kinetics and mechanism of sodium hypophosphite oxidation by oxygen in alcoholic solutions (ROH = PrOH, BuOH, i-AmOH) of iron (III) chloride are studied for the first time

Summary

Introduction

The existent technology of phosphoric ether production is based on multistep processes of toxic, flammable and explosive white phosphorus oxidation by chlorine up to PCl3, POCl3 followed by the alcoxylation and is accompanied by formation of a considerable quantity of toxic hydrogen chloride. In the present work kinetics and mechanism of sodium hypophosphite oxidation by oxygen in alcoholic solutions (ROH = PrOH, BuOH, i-AmOH) of iron (III) chloride are studied for the first time. The X-ray powder diffraction analysis showed that the main reflections correspond to NaCl. Influence of NaH2PO2 – Increasing concentration of hypophosphite from 0.06 up to 0.36 mol/l increases the reaction rate and the amount of absorbed oxygen.

Results

Conclusion