Phase Transfer Catalyzed Synthesis of Organosulfur Fine Chemicals using Hydrogen Sulfide

Abstract

The focus of this study is to utilize hydrogen sulfide (H2S) in the synthesis of fine chemicals, such as, thioethers and organic disulfides. Two different aqueous alkanolamines, such as, Nmethyldiethanolamine (MDEA) and monoethanolamine (MEA) were used for the absorption H2S to make H2S-rich alkanolamine solution. Dibenzyl sulfide (DBS) and dibenzyl disulfide (DBDS) were synthesized from the reaction of H2S-rich alkanolamine with organic reactant,benzyl chloride (BC). To carry out this biphasic reaction, three different phase transfer catalysts (PTCs) were used, namely, tetrabutylphosphonium bromide (TBPB), trihexyl (tetradecyl) phosphonium chloride (THTDPC) an ionic liquid (ILs) and a solid catalyst, amberlite IR-400. The main objective of the present study is to utilize H2S in synthesizing value-added chemicals such as DBS and DBDS, along with maximization of the conversion of the organic reactant, and the selectivity of desired product. Three different reaction systems have been carried out for the present work. First system dealt with the synthesis of DBS from the reaction of H2S-rich MDEA and BC using TBPB as PTC under liquid-liquid (L-L) phase transfer catalysis (PTC). Parametric study, mechanistic investigation and kinetic modeling have been performed for this system. In the second system, DBS was synthesized using THTDPC as a PTC under L-L PTC condition with around 98% BC conversion and 100% DBS selectivity. Parametric study and mechanistic investigation was performed and a detailed kinetic model was developed and validated using experimental values. In the last system, an investigation has been done on the utilization of H2S for the synthesis of DBDS under liquid-liquid-solid (L-L-S) PTC using amberlite IR-400 as a solid PTC. The effect of different parameters on the BC conversion was studied and the selectivity of desired product DBDS was found to be 100% at some level of process parameters. A suitable reaction mechanism has been proposed and a mathematical model has been developed and validated to explain the kinetics of the reaction.