Photolysis Kinetics And Mechanism Of Anthraquinones

Anthraquinones are a group of important intermediate of dye and medicament. Because of widely applying, they would enter into the environment during producing and consuming. Note that the photolysis is one of important transformations of these chemicals in the environment, it is necessary to investigate the photolysis of anthraquinones.The study determined the photolysis rate constants of 15 anthraquinones irradiated by high-pressure mercury lamp and discussed the effects of the position, number and species of substituted group on photolysis rates. Also, the effect of solvents, dimethyl sulfoxide (DMSO) and DMSO containing water, on photolysis rate was investigated. To study the photolysis mechanism of the anthraquinones, 9 aminoanthraquinones were selected to establish the quantity structure-properties relationship (QSPR) using partial least square (PLS). The results indicated that the factors affecting the photolysis rate were the heat of formation, the most positive net atomic charges on a hydrogen atom, the largest negative atomic charge on a carbon atom, and the energy gap between the lowest unoccupied molecular orbital and the highest occupied molecular orbital.On the other hand, the effect of solvents on the photolysis of 1-amino-4-hydroxyanthraquinone was discussed and it can be concluded that the polarity and nonprotonic solvent can accelerate the photolysis rate. Under the condition of light irradiation, 1-amino-4-hydroxyanthraquinone can generate O₂^·- and ¹O₂. In the course of its photolysis, direct photolysis and indirect photolysis occupied 43.0% and 57.0% respectively. In view of indirect photolysis, ¹O₂ and O₂^·- contributed 26.1% and 30.9% respectively. The results obtained from the frontier electron density calculation and GC/MS further proved that 1,4-dihydroxyanthraquinone was the primary photoproduct of 1-amino-4-hydroxyanthraquinone. Based on the currently experimental results, theoretical analysis and availably previous studies, three pathways of 1-amino-4-hydroxyanthraquinone photodegradation were proposed: direct photolysis pathway, ¹O₂ attack pathway and O₂^·- attack pathway. It confirmed that the photoinduced toxicity of 1-amino-4-hydroxyanthraquinone maybe induced by photosensitization mechanism. Moreover, the phototransformation from 1-amino-4-hydroxyanthraquinone to 1,4-dihydroxyanthraquinone was a process of environmentally acceptable.