Efficient and versatile synthesis of imines from alcohols and amines over CdS-SnS2 of heterostructure under visible-light irradiation

Abstract

Imines are important N-containing intermediates in organic synthesis. The photocatalytic production of specific imines through direct coupling of alcohols and amines under mild conditions has been widely explored. However, the reported processes are not practical due to negative factors such as low photocatalytic efficiency, involvement of non-stoichiometric raw materials, limited scope of substrates, and the need of additives that are not environmentally friendly. Herein, we report the synthesis of CdS-SnS2 photocatalysts with compact heterojunctions by a one-step hydrothermal method. Using air as oxidant and without the need of additive, the prepared CdS-SnS2 composites display good to excellent activity (conversion of amines up to 98% and selectivity to the corresponding imines 99.9%) for imines generation from primary amines and alcohols with different functional groups under visible light irradiation. Unlike most of the reported methods, equivalent amounts of alcohol and amine are involved in the present protocol. A reaction mechanism based on the quenching of active species is proposed. The present work offers an effective, versatile and atom-economic approach for the synthesis of imines by cross-coupling of alcohols and amines under mild conditions.