Electrochemical Synthesis of Triethyl Phosphate From Red Phosphorus

This work is devoted to the electrochemical preparation of triethyl phosphate from red phosphorus in the presence of sodium bromide. This area of electroorganic synthesis has been studied most fully using white phosphorus and hydrogen chloride as an electrolytic additive, which significantly increases the ecological load on the environment. Replacement of highly toxic precursors with safer substances is an urgent task of modern chemistry and chemical technology. In the present work, the electrochemical synthesis was carried out in a diaphragmless electrolyzer at a constant current density of 0.075 A/cm2, with the electrolyte consisting of a suspension of red phosphorus in ethanol with the addition of water and sodium bromide. The influence of electrolysis parameters, such as the concentrations of water and sodium bromide in the electrolyte on the qualitative and quantitative composition of electrolysis products was investigated. It is shown that the concentration of sodium bromide in the range from 0.16 to 0.23 mol/L does not affect the composition of electrolysis products. The influence of water concentration in the electrolyte, in the range from 4 wt.% to 0.5 wt.%, was determined. Increase of water concentration has a negative effect on the electrolysis process, while the concentration of triethyl phosphate in the electrolysis product decreases from 90 wt % to 10 wt % and the concentration of by-products such as incomplete esters of phosphoric acid monoethyl phosphate and diethyl phosphate increases. The qualitative and quantitative composition of electrolysis products at different electrolysis parameters was studied by IR spectroscopy and gas chromatography. The electrolysis parameters were selected to achieve 90% triethyl phosphate yield and 50% phosphorus yield.