The reaction of thiols on a model gold catalyst leads to the formation of thiolates capable of self-coupling and of displacing carboxylic acids

Abstract

The pathways of heterogeneous catalytic reactions depend on the adequate stability of reagents and intermediates on the catalyst. The development of efficient, selective catalysts require an understanding of such stability and it may differ from the one observed in the gas phase. Herein, we report the enhanced acidity of ethanethiol and benzenethiol (with respect to the gas-phase acidity) on an oxygen-covered gold surface as a model catalyst. This increased acidity is caused by the strong affinity of sulfur towards gold and leads to a facile dehydrogenation, even on a clean gold surface. The resulting thiolate species undergo further reactions through β-H elimination in ethanethiol and to coupling products for both thiols. Remarkably, this acidity is sufficient to displace formic acid and trifluoroacetic acid, confirming the increased surface stability of thiolates on gold. Nevertheless, the displacement of ethanethiol by benzenethiol shows that other effects, such as the van der Waals interactions, can add to the stability of intermediates. This study contributes to the understanding of the affinity of sulfur with gold and its impact on its catalytic activity.