Selective photocatalytic oxidation of alcohols to corresponding aldehydes in solvent-free conditions using porphyrin sensitizers

In this work, selective and aerobic photooxidation of a range of aromatic, aliphatic and α,β-unsaturated alcohols to corresponding carbonyl compounds has been performed with tetraphenylporphyrin (H2TPP), ClFeTPP and ZnTPP as sensitizers using visible light and in the presence of molecular oxygen in solvent-free conditions. The conversion rates for alcohols oxidations were in the order of free-base porphyrin (H2TPP) > metalloporphyrin (ClFeTPP) and (ZnTPP). This method has a wide range of applications, remarkable conversion and product yield in reasonable time, does not include cumbersome work-up, exhibits chemoselectivity, and proceeds under mild reaction conditions. As the matter of oxidation of cycloheptanol and cyclooctanol using H2TPP as photosensitizer, the TON reached up to 1686 and 2464, respectively and selectivity more than 99 %.