The zinc tetraphenylporphin-sensitized photoredox reaction between N-phenylglycine and p-benzoquinone in polar solvents

Abstract

The photoredox reaction between N-phenylglycine (NPG) and p-benzoquinone (BQ) sensitized by zinc tetraphenylporphin (ZnTPP) has been studied in various solvents under nitrogen at 25 °C. Decarboxylation of NPG and reduction of BQ occurred equimolecularly to give N-methylideneaniline (NMA), carbon dioxide, and hydroquinone (BQH₂) when an acetonitrile solution of NPG and BQ was irradiated at λ_ex. > 500 nm in the presence of a catalytic amount of ZnTPP. ZnTPP was recorvered almost quantitatively after the photoreaction. The conversion of NPG increased linearly with increasing the molar ratio of ZnTPP to NPG up to ca. 2 × 10^–3. The quantum yield for the ZnTPP-sensitized decarboxylation of NPG (Φ_CO2) in nitrogen-purged acetonitrile solution was evaluated as 0.20. The sensitizing activity of ZnTPP was remarkably enhanced upon increasing the solvent polarity.