Titanium(IV) oxide photocatalyst of ultra-high activity for selective N-cyclization of an amino acid in aqueous suspensions

Titanium(IV) oxide (TiO2) powder was prepared by the high-temperature hydrolysis of titanium(IV) tetrabutoxide in toluene as anatase crystallites of average diameter ≈ 15 nm. They were platinized by impregnation from aqueous chloroplatinic acid solution followed by hydrogen reduction. The catalyst was suspended in an aqueous L-lysine (Lys) solution and photoirradiated under argon at ambient temperature to obtain L-pipecolinic acid (PCA). Among several platinized commercial TiO2 powders, the present TiO2 showed the highest photocatalytic activity for both Lys consumption and PCA production. This result is attributed to both the higher activity owing to the larger surface area with lesser defects and the higher dispersion of platinum deposits acting as an efficient reduction site for a Schiff base intermediate into PCA.