Two Stage Synthesis of Aromatic Thioethers using Hydrogen Sulfide and Reusable Phase Transfer Catalyst

Abstract

This present investigation is based on the idea of using waste sulfur compound i.e. Hydrogen Sulfide (H2S) which is unutilized byproduct of industries like petroleum and natural gas processing industries. This proposed work comprises of two stages: firstly, conventional absorption of H2S in the absorbent alkanolamines like methyldiethanolamine (MDEA) which is selective towards hydrogen sulfide. This H2S-rich MDEA solution has been proposed to act as a sulfiding agent for aromatic halides to synthesize aromatic thioether which is a fine chemical used in photographic emulsions, high pressure lubricants and additive as anti-wear in motor oil and has application in various anticorrosive formulations. The objective is to synthesize the aromatic thioether like Bis-(p-chlorobenzyl) Sulfide) using reactant aromatic halides like (p-chlorobenzyl chloride) and H2S rich aqueous alkanolamines (e.g. MEA, MDEA etc.). For this double phasic reaction was carried out in presence or absence of solvent like toluene as well as insoluble phase transfer catalyst are being used. This present work is carried out using tributylmethylammonium chloride-polymer bound, tributylmethylphosphonium chloride-polymer bound and Amberlite IR-400 as the insoluble catalysts which were further reused for betterment of the economy of the project. So the study was carried out in three phases. The initial experiments shows encouraging results with 100% conversion of reactant p-chlorobenzylchloride in the solvent toluene, 100% selectivity of the desired product Bis-(p- chlorobenzyl) sulfide) and the catalyst was reused up to 3 times. A generalized empirical kinetic model was developed and successfully validated against the experimental results. In the second phase of study, Response surface methodology accompanied with Central composite design was used for the study of the reaction kinetics, model development and the optimization of the reaction conditions. In the third phase study, solvent free synthesis of Bis-(p-chlorobenzyl) Sulfide) was carried out. This whole investigation is oriented towards a green technology for utilizing toxic H2S under waste management approach.