Green Synthesis of Thiuram Disulfides with CO₂ as an Acid Agent for Sustainable Development

A green synthesis method for the oxidation of sodium dialkyldithiocarbamate to the corresponding thiuram disulfides was developed in the presence of CO₂ as the neutralizing agent, H₂O₂ as the oxidant, and water as the solvent. The method could provide much greener reaction conditions, convert CO₂ to a relatively high-quality product without H₂SO₄ consumption, and obtain high yields and purity of products. The effects of CO₂ flow rate, reaction temperature, concentration, dropping speed, and excess degree of hydrogen peroxide, as well as the concentration of sodium dimethyldithiocarbamate, were investigated. By HPLC-MS detection of the mother liquor, it was found that the organic byproducts of this oxidation process were the hydrolysis product of TMTD (tetramethyl thiuram disulfide), sodium dimethylcarbamothioate, and the peroxidation product of sodium dimethyl­dithio­carbamate, sodium (dimethyl­amino)­(thioxo)­methane­sulfonate, which have been rarely proven experimentally by previous work. These byproducts were generated in the latter stage of the oxidation process. Therefore, possible chemical reactions of this synthesis process were proposed. On the basis of these reactions, a 0.6 stoichiometric hydrogen peroxide dosage was added, the mother liquor was recycled, and no organic byproduct was found after five stages of recycling. As a result, the discharge of wastewater was greatly reduced. Tetraethyl thiuram disulfide was also synthesized by this method to demonstrate its universality.