ELECTROCHEMICAL SYNTHESIS OF METHANESULFONIC ACID FROM AQUEOUS SOLUTIONS OF DIMETHYL SULFONE

In recent years, methane sulfonic acid (MSA) is being increasingly used in various fields of electrochemical production such as electroplating, electrorefining and electrodeposition of metals etc. In this regard development of new methods for the synthesis of MSA from organic sulfur compounds is today an urgent task. In this paper we studied the electrochemical synthesis of methane sulfonic acid from aqueous solutions of dimethyl sulfone (DMS). The electrochemical behavior of DMS in an acidic environment on a smooth platinum electrode in a wide range of the anodic potentials was studied by cyclic voltammetry. It is shown that electrooxidation of DMS occurs at high anodic potentials of 1.8 - 2.15 V. Within of DMS concentration range of 0.05 - 0.15 M, and the anode current density of 0.01 - 0.03 A / cm(2) MSA is the main product the oxidation. It was also found that with increasing concentrations of DMS there is a significant suppression of process of oxygen evolution. At concentration of dimethyl sulfone more than 0.2M the yield of MSA falls, which is associated with a change in the electrochemical mechanism of DMS oxydation. By methods of Raman and IR spectroscopy it was revealed that at the electrochemical oxidation of aqueous solutions at the concentration of DMS more than 0.2M on a smooth platinum electrode in the anodic electrolysis compartment two stable products - methanesulfonic acid and dimethyl disulfon (DMDS) are formed. The initial concentration of dimethyl sulfone affects the product yield. It was shown that the change in preparative electrosynthesis product yields of MSA and DMDS is connected with the increase in the concentration of aqueous solutions of DMS and the anode current density. On basis of data of voltammetric measurements and analysis of preparative electrosynthesis products the mechanism of electrooxidation of dimethyl sulfone in an acidic environment on a smooth platinum electrode to form the MSA and DMDS was proposed. It was shown that DMDS at the room temperature may easily be separated from the anolyte solution in an acidic environment in the form of crystal material. It was also found that by heating to temperature 80-85 degrees C the anolyte solution containing DMDS, decomposes to methanesulfinic and methanesulfonic acids. It was shown that methanesulfinic acid is unstable acid which is readily oxidized with atmospheric oxygen, which makes it possible to obtaine MSA by electrosynthesis with a high quantitative yield. Thus, MSA is a final product of dimethyl sulfone electrooxidation in an acidic environment on smooth platinum with a quantitative yield on current.