Síntese seletiva de tiocarbonatos cíclicos utilizando catalisadores básicos

Abstract

The search for new carbon sources for the production of plastic polymers, pharmaceuticals and agrochemicals, among others, is essential. The use of carbon disulfide (CS2) is a viable alternative and can be used as a raw material for the production of thiocarbonates and various other industrially relevant substances. The aim of this work is to develop a methodology that employs mild conditions to produce cyclic thiocarbonates from CS2 and epoxides, using basic catalysts such as metal hydrides and hydroxides. Experiments were carried out to evaluate the catalytic capacity of various hydrides and hydroxides, in which sodium hydride and sodium hydroxide stood out significantly, leading to quantitative and totally selective conversions of CS2 into the respective cyclic dithiocarbonates. It is believed that the nucleophilicity of the hydroxide anion and the solubility of these substances were decisive for these results. The reaction conditions of the catalytic system were optimized, with the best results obtained at a temperature of 50 °C, reaction time of 2 hours and catalytic load varying between 2 and 5 mol%, depending on the type of epoxide used. Finally, a variety of epoxides were tested to assess the replicability of the method. Evaluation of the results revealed that epoxides with electron-withdrawing substituents, capable of increasing the electrophilicity of the ring, showed higher conversion rates while maintaining high selectivity. On the other hand, epoxides without these groups or containing bulky groups close to the epoxide ring showed low conversion rates or were not converted at all. This work has shown that a simple, low-cost substance such as sodium hydroxide can be used as a highly efficient and selective catalyst for the production of cyclic dithiocarbonates from CS2 and epoxides.