Aminodiphenylamines (ADPAs) and their derivatives have been known to be used as dye intermediates and antioxidant of rubber. Due to its high demand in industrial production, the synthesis methods have been widely developed. In the present study, a photocatalytic synthesis route was examined, i.e., the photocatalytic C–N coupling of aniline in an alkaline solution with a Pt-loaded titanium oxide (Pt/TiO2) photocatalyst. Nearly 20% of yield and 77% of selectivity were achieved with the Pt/TiO2 photocatalyst for 30 min. It was found that this C–N bond formation showed a high dependence on the initial pH of solvent and irradiation light wavelength, i.e., the reaction can only proceed when pH > 11.79, and an incident light wavelength of 365 nm gave a high ADPAs selectivity. The mechanistic studies by using isotopic compounds suggested that the rate-determining step (RDS) for ADPAs production would be the formation of a transition complex with the rehybridization to sp3 on the aromatic ring of aniline. The UV-vis spectra analysis and Arrhenius plots further revealed the presence of three formation routes of ADPAs in the present system: The first one begins with the hole-oxidation of aniline by TiO2 photocatalyst excited by UV light, the second one starts with one electron transfer from N atom in aniline to Ti in TiO2, which only occurred with an incident light wavelength of 365 nm, and the last one is the oxidation of aniline molecules by hydroxyl radicals.
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