Selective Reduction of Nitroarenes via Noncontact Hydrogenation
Hua An, Yani Ding, Philippe Sautet, Geng Sun, Ning Yan
Abstract
In traditional hydrogenation, where H 2 and substrates with unsaturated bonds are activated on the same catalyst (contact mode), competitive hydrogenation of multiple reducible groups often occurs. We employ an unbiased H-cell for selective hydrogenation of the nitro group when multiple reducible groups are present. The setup spatially separates H 2 and nitroarenes into two chambers connected by a proton-exchange membrane, thus adding barriers for a Langmuir–Hinshelwood-type mechanism that is common in thermocatalytic hydrogenation. Through a unique proton/electron transfer pathway that is specific to nitro functional group reduction to hydroxylamine, side reactions like C═C, C═O, and C≡C bond hydrogenation are fully avoided. Using Pd/C for H 2 activation, and CNT for selective proton/electron transfer to −NO 2 groups while being inert to C≡C, C═C, and C═O hydrogenation, the system effectively eliminates the competitive hydrogenation, achieving 100% nitro-group reduction selectivity in the hydrogenation of various nitroarenes, in sharp contrast to negligible selectivity over the same catalysts in a batch reactor under contact mode. This device enables selectivity control in hydrogenation reactions, moving beyond the traditional focus on catalyst active site engineering.