Production of pyridinecarboxy aldehydes, nicotinic and isonicotinic and picolinic acids by TiO2-sacrificial photocatalysis at ambient conditions and in aqueous solution through artificial solar radiation

The conversion of pyridinemethanol isomers into their respective aldehydes and carboxylic acids has been attempted in aqueous solution through sacrificial TiO2 photocatalysis in the presence of cupric ions, at ambient temperature, under acidic and deaerated conditions, using artificial sunlight. The presence of a nitrogen atom in the aromatic ring, with respect to benzylic alcohol and its derivatives, affects the photocatalytic behavior of the substrate. The influence of both pH and temperature has also been investigated. The position of the methanolic group on the aromatic ring leads to slight changes in the selectivities, yields and the oxidation rates. Under the adopted conditions, the yields and selectivities to aldehydes are always higher than those of the respective carboxylic acids. The photocatalytic process can be carried out in consecutive copper reduction/oxidation steps in order to reuse the catalyst. In this way greater yields and selectivities to the desired product than 60% can be achieved. The process can be considered interesting as it concerns the eco-green production of valuable fine chemicals, using water as a solvent at ambient conditions, a cheap heterogeneous catalyst and solar radiation.