Deuterium exchange of benzo[b]thiophene: Model complex and heterogeneous reactor studies

Abstract

The complexes [CpRu(BT)] + and [CpRu(3-MeBT)] +, where BT is benzo[b]thiophene and 3-MeBT is its 3-methyl derivative, are models for π-coordination of BT to hydrodesulfurization (HDS) catalysts via the benzene ring. The BT in these complexes undergoes base-catalyzed deuterium exchange, at the 2 and 7 positions; in KOH CD 3OD solutions, the exchange follows the rate law: rate = k[Ru complex][OH −]. The mechanism is proposed to involve rate-determining proton abstraction by OH − from either [CpRu(BT)] + or [CpRu(3-MeBT)] + followed by transfer of D + from the CD 3OD solvent to give the deuterated BT complex. Heterogeneous reactor studies of deuterium exchange of BT with D 2 over several HDS catalysts (PbMo 6.2S 8, Co 0.25MoS, and 5% Re γ- Al 2O 3 ) and γ-Al 2O 3 indicate that BT is activated to exchange at the 2 and 3 positions over the catalysts. These results suggest that deuterium exchange of BT over HDS catalysts may occur through routes other than those involving BT π-bonding through its benzene ring to the catalyst surface.