Effects of acetylacetone on the thermal and photochemical conversion of benzoquinone in aqueous solution

Quinones are components of electron transport chains in photosynthesis and respiration. Acetylacetone (AA), structurally similar to benzoquinone (BQ) for the presence of two identical carbonyl groups, has been reported as a quinone-like electron shuttle. Both BQ and AA are important chemicals in the aquatic environment. However, little information is known about their interactions if co-existed. We found here that AA significantly enhanced the conversion of BQ. By analyzing the evolution of chemical concentration, solution pH, dissolved oxygen, and the final products, the interactions between AA and BQ were elucidated. The reactions between BQ and AA generated oxygen but ultimately led to the reduction of solution pH and dissolved oxygen. The reactions proceeded faster under indoor lighting condition than in the dark. The formation of semiquinone radicals is believed as the primary step. The secondary AA-derived radicals might be strongly oxidative or reductive, depending on the concentration of dissolved oxygen. Insoluble humus was generated in the mixture of BQ and AA. These results suggest that the presence of AA might interfere with photosynthesis and respiration through the interactions with quinones.