Aqueous Photocatalytic Glycerol Oxidation to Formic Acid Coupled to H2O2 Production with an Anthraquinone Dye

Abstract The photocatalytic oxidation of glycerol into formic acid (FA) is reported employing a 9,10‐anthraquinone‐2,6‐disulphonate disodium salt (AQDS) photocatalyst. The system operates in water, in the absence of additives, using O 2 as the oxidant and irradiating with blue light (λ = 415 nm). In 22 h, conversion of glycerol up to 79% leads to 30% yield of FA (turnover number of 15 for AQDS), with 79% selectivity among the products in solution and a quantum yield of 1.2%. The oxidation of glycerol is coupled to the reduction of oxygen to hydrogen peroxide (up to 16±5 m m ), a high‐added value photosynthetic product. A mechanistic investigation combining electron paramagnetic resonance (EPR) spectroscopy, transient absorption spectroscopy (TAS), and time‐dependent density‐functional theory (TD‐DFT) calculations reveals a photoinduced hydrogen atom abstraction involving the triplet excited state 3* AQDS and the glycerol substrate ( k = 1.02(±0.03)×10 7 m −1 ·s −1 , H/D kinetic isotope effect = 2.00±0.16). The resulting ketyl radical of AQDS follows fast deprotonation to the radical anion AQDS •– , that further reacts with oxygen ( k = 1.2×10 8 m −1 ·s −1 ), ultimately leading to the production of H 2 O 2 .