Phase Transfer Catalyzed Synthesis of BIS (4-Chlorobenzyl) Sulfide Using Hydrogen Sulfide

Abstract

The present research work is oriented towards a green technology that utilizes the environmentally hazardous chemicals like hydrogen sulfide (H2S) and to synthesize commercially important chemicals to overcome the disposal problems as well as to improve the economy of the process. This proposed work involves two stages: firstly, selective absorption of H2S in aqueous alkanolamine solution likes Methyl-diethanolamine (MDEA) and then the reaction of this H2S-rich MDEA with the organic compound. The overall objectives are to synthesize the aromatic thioether like bis(4-chlorobenzyl) sulfide using hydrogen sulfide rich aqueous MDEA solution and 4-chlorobenzyl chloride (CBC). 4-chlorobenzyl mercaptan (CBM) was identified from the reaction mixture as a secondary product. The biphasic reactions were performed in a batch reactor using a phosphonium based phase transfer catalyst, Ethyltriphenyl phosphonium bromide because of its thermal stability. In this system, we developed the alternative to the expensive Claus process for utilization of hydrogen sulfide to produce commercially significant value added chemicals. The role of various phases such as agitation speed, catalyst concentration, temperature variation, sulfide concentration, MDEA concentration and reactant concentration in enhancing the selectivity towards bis(4-chlorobenzyl) sulfide has been investigated. The apparent activation energy was found to be 11.28 kJ/mol that emphases the reaction to be a kinetically controlled reaction. The experiments show encouraging results with 87.57% conversion of reactant 4-chlorobenzyl chloride and 89.48% selectivity of the desired product bis(4-chlorobenzyl) sulfide.