Synthesis of vanillin in water by TiO2 photocatalysis

The photoproductionof vanillinis studied inaqueousmediumstarting fromtrans-ferulic acid, isoeugenol,eugenol or vanillyl alcohol by using both commercial and home prepared TiO2 samples as photocatalystsand batch Pyrex photoreactors. The photo-oxidation at room temperature of these compounds producesvanillin with a selectivity ranging from 1.4 to 21 mol% with respect to the converted substrate. An investigationon the intermediates was performed in the case of trans-ferulic acid; for this substrate the mostimportant intermediates were homovanillic acid, vanillyl mandelic acid, trans-caffeic acid, formic acid,acetic acid, and oxalic acid. The carbon mass balance, including CO2 derived from the mineralization, wasmade for all of the substrates at irradiation times corresponding to the highest selectivity to vanillin.High closure of the carbon balance was obtained with vanillyl alcohol (ca. 90%) and trans-ferulic acid (ca.80%).