Photocatalytic organic synthesis in an NMR tube: C-C coupling of phenoxyacetic acid and acrylamide

NMR was used to study the semiconductor photocatalytic (SPC) C C coupling of phenoxyacetic acid (PAA) with acrylamide (ACM) in an NMR tube photoreactor. Using an NMR tube with a sol-gel titania inner coating as a photoreactor, this reaction is relatively clean, forming only 1 product, 4-phenoxybutanamide (4-PB), in yields up to 78%. This SPC reaction is used to assess the activity of the sol-gel titania coating as a function of their annealing temperature, which alters the surface area and phase of the titania, and the general reusability of the TiO2 coated NMR tubes. The optimum temperature range for annealing the sol-gel titania films is between 450 degrees C and 800 degrees C, with the maximum yield and rate attained at 450 C. Despite a decrease in the initial rates of formation of 4-PB above an annealing temperature of 450 degrees C, the final product yields remained similar, giving maximum yields within 60 min of irradiation. The reusability study reveals that the activity of the sol-gel titania can quickly deteriorate with repeated use due to the adsorption of yellow/brown coloured, insoluble, most likely organic polymeric, material and its screening effect on the underlying photocatalyst. The titania can, however, be restored to its original activity by a simple heat treatment at 450 degrees C for 30 min. (C) 2013 Elsevier B.V. All rights reserved.