(365a) Carbon Dioxide Introduced for Green Synthesis of Thiuram Disulfides Vulcanization Accelerators Under Mild Conditions

Thiuram disulfides have been widely used in rubber industry as rubber vulcanization ultra-accelerators. The conventional industrial process for the production of thiuram disulfide included reacting a secondary amine with carbon disulfide in an aqueous solution of sodium hydroxide to form a sodium salt of dialkyldithiocarbamate acid, then adding the mixed solution of sulfuric acid and hydrogen peroxide to neutralize and oxidize sodium dialkyldithiocarbamate. The precipitate, thiuram disulfide, can be obtained by filtering, washing, drying. While this method uses the large quantities of sulfuric acid and generates huge amount of salt by-product, sodium sulfate. Thus, an eco-friendly method for oxidation of sodium dialkyl dithiocarbamate to the corresponding thiuram disulfides has been developed using carbon dioxide as neutralizing agent in the presence of H₂O₂ as the oxidant and water as the solvent. After optimizing the reaction conditions such as temperature, concentration of reactants, flow rate of carbon dioxide, dropping speed of hydrogen peroxide, aging time and so on, this method could provide green mild reaction conditions, reduce CO₂ emission and H₂SO₄ consumption remarkably, and reach the almost closely high yields and purity of products as traditional method. With the HPLC-MS analysis of mother liquor, it is proved that the main side reaction is the peroxidation of dialkyldithiocarbamate acid which produced corresponding sulfoxide and sulfone. By comparing the alkalinity of sodium carbonate, sodium bicarbonate and sodium dialkyldithiocarbamate, doing related experiments and reading relevant references, the reaction path has been proposed.