Deuterodesulfurization of thiophene: An investigation of the reaction mechanism

The deuterodesulfurization of thiophene was investigated using selected MoS₂ and reduced molybdenum sulfide (Chevrel phase) catalysts. The extent of deuterium incorporation into thiophene and into specific desulfurization products (hydrogen sulfide, butadiene, and butenes) was determined at 400 °C for thiophene conversions near 4%. Unpromoted MoS₂ introduced up to 10 times more deuterium into thiophene than did the promoted catalysts (including the Chevrel phase materials). For all catalysts, H₂S was formed almost exclusively (typically 90+%), with only small amounts of HDS and D₂S being detected. Except for the unpromoted MoS₂ catalyst, the deuterium distributions determined for the cis- and trans-2-butene products were nearly identical; the deuterium distribution found for 1-butene was distinct. A mechanism of thiophene hydrodesulfurization can be proposed in which butadiene is the initial desulfurized reaction product. The hydrogen available for hydrogen sulfide formation is derived via hydrogen exchange with thiophene.