One-pot synthesis of secondary amines from aldehydes and primary amines over trifunctional Au-TiO2 as a water adsorbent, acid catalyst and photocatalyst without the use of hydrogen gas

Abstract

We succeeded in one-pot synthesis of N-phenylbenzylamine (PBA) from benzaldehyde (BAD) and aniline (AN) over titanium(IV) oxide having a gold (Au) cocatalyst (Au-TiO2) without the use of hydrogen gas. This process consists of two steps: 1) formation of benzylideneaniline (BAN) and water by condensation of AN and BAD, a step that is a thermal reaction and results in an equilibrium being reached, and 2) photocatalytic hydrogenation of BAN to PBA through a hydrogen transfer reaction from alcohol. Reactions under various conditions revealed that TiO2 showed bifunctionality in the condensation process as an acid catalyst and an adsorbent of water. Among the cocatalysts examined in this study, Au showed the highest performance for PBA production. Photoirradiation to the system in equilibrium containing Au-TiO2 produced PBA in a yield of about 92%. We found that TiO2 having a gold (Au) cocatalyst (Au-TiO2) works as a trifunctional catalytic material, i.e., an acid catalyst and water adsorbent for the first step and a photocatalyst for the second step. Expandability of this reaction system in production of halogen-substituted PBA and selection of alcohol was investigated.