Photocatalytic Hydroxylation of Phenol to Catechol and Hydroquinone by Using Organic Pigment as Selective Photocatalyst

The application of photocatalytic reactions in organic synthesis has attracted extensive attentions because of recent developments in environmentally benign synthetic processes. For the first time, an organic pigment (C. I. Pigment Green 8) was used as selective photocatalyst to accomplish the photocatalytic hydroxylation of phenol to catechol (CAT) and hydroquinone (HQ) with the assistance of UV irradiation at room temperature. The prepared photocatalysts were characterized by FT-IR spectrum and UV-visible diffuse reflectance spectroscopy (UV-vis DRS), and the result found that the photocatalyst exhibits excellent adsorption ability both in the ultraviolet and visible light region. The effects of various affecting-parameters, such as catalyst amount, H2O2 amount, co-solvents and reaction time, on the photocatalytic hydroxylation of phenol were studied to optimize the reaction conditions. The desired products (CAT and HQ) on the photocatalyst can be facilitated with an increase in the selectivity. In this study, the conversion efficiency of phenol could reach high up to 87.8% with a total selectivity of 73.0% as well as the yield of 37.0% and 27.4% for CAT and HQ, respectively. The reaction is a photo-Fenton like process, and the iron ions cycle between Fe2+ and Fe3+ occurs with the light irradiation. Keywords: Pigment photocatalyst, Selective photocatalysis, Hydroxylation, Phenol, Catechol, Hydroquinone