N-Doped Yellow TiO2 Hollow Sphere-Mediated Visible-Light-Driven Efficient Esterification of Alcohol and N-Hydroxyimides to Active Esters.

Herein we report a simple synthetic protocol for N-doped yellow TiO2 (N-TiO2 ) hollow spheres as an efficient visible-light-active photocatalyst using aqueous titanium peroxocarbonate complex (TPCC) solution as precursor and NH4 OH. In the developed strategy, the ammonium ion of TPCC and NH4 OH acts as nitrogen source and structure-directing agent. The synthesized N-TiO2 hollow spheres are capable of promoting the synthesis of active esters of N-hydroxyimide and alcohol through simultaneous selective oxidation of alcohol to aldehyde followed by cross-dehydrogenative coupling (CDC) under ambient conditions upon irradiation of visible light. It is possible to develop a novel and cost-effective one-pot strategy for the synthesis of important esters and amides on gram scale using the developed strategy. The catalytic activity of N-TiO2 hollow spheres is much superior to that of other reported N-TiO2 samples as well as TiO2 with varying morphology.