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

Abstract

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.

Reaction Pathway and Selectivity Control of Tetraethyl Thiuram Disulfide Synthesis with NaHCO3 as a pH Regulator

“…Compared with the NaHCO 3 method, the reaction rate of the CO 2 method is much faster and the yield is higher, while the selectivity is relatively lower. The organic side products of the CO 2 method are sulfonates and sodium diethylcarbamothionic S -acid as detected by HPLC–MS, which are consistent with the side products of TMTD (tetramethyl thiuram disulfide) synthesis previously reported …”

“…The organic side products of the CO 2 method are sulfonates and sodium diethylcarbamothionic S -acid as detected by HPLC–MS, which are consistent with the side products of TMTD (tetramethyl thiuram disulfide) synthesis previously reported. 28 …”

“…The related reaction mechanism has been discussed a lot while mainly in thiol chemistry for redox signaling. , As NaEt 2 DTC has an additional apparent carbon–sulfur double bond than regular thiols, and most of them are in the form of thiolate in a neutral or weakly alkaline environment because of their low pKa value (∼ 3.68), this substance has stronger nucleophilicity, − which makes it is easier to react with H 2 O 2.…”

“…Furthermore, experiments with CO 2 as the acid reagent were conducted as described in our previous work. 28 …”

“…Hence, in this study, we report a new method with NaHCO 3 as a pH regulator to synthesize TETD to improve the reaction selectivity. When the pH value of the reaction process ranges from 8 to 9.5, the selectivity could be around 100%, which is much higher than that using CO 2 as an acidifier . By deeply investigating the reaction process, we propose a reaction network to discuss the possible mechanism of reaction selectivity control.…”