Sulfur Exchange Reactions of Dialkyl Dithiophosphoric Acids and Their Derivatives with Elemental Sulfur

Abstract

Contrary to the Miklukhin's report that dialkyl dithiophosphoric acid and its salts do not have an exchange reaction with elemental sulfur, it was found that such exchange reaction did occur under our experimental conditions.The reaction was the second order for the concentration of dialkyl dithiophosphoric acid (or its derivatives) and the first order for sulfur concentration. The rate of reaction depended on the structure of the reactant compounds and the solvents. The rate was very small in the solvents containing ethanol. The eight-membered ring sulfur decreased in the system during the reaction, though the total amount of sulfur was constant.From the above experimental facts, it was concluded that an amphoteric polysulfide ion was produced by the reaction of elemental sulfur and dialkyl dithiophosphoric acid (or its derivatives). Therefore, it was proposed that the sulfur exchange does not occur by a bimolecular reaction between dialkyl dithio-phosphoric acid (or its derivatives) and elemental sulfur, but the exchange of sulfur is accomplished by the reaction of the amphoteric polysulfide ions formed and the other acid molecules (or the other derivative molecules).