瞬态吸收光谱研究苯与H_2O_2水溶液的反应机理

Reaction Mechanism of Aqueous Benzene with Hydrogen Peroxide by Transient Absorbance Spectra

利用瞬态吸收光谱技术研究了不同条件下苯与H2O2水溶液复相体系的激光闪光光解情况,考察了其瞬态物种的生长和衰减等行为.研究表明,OH自由基和苯反应生成C6H6-OH加合物,其反应速率常数在近中性和酸性条件下分别为(8.0～8.1)×109L·mol-1·s-1和7.7×109L·mol-1·s-1,而在碱性时则为(6.7～6.9)×109L·mol-1·s-1,在有氧条件下C6H6-OH加合物被氧化为C6H6-OHO2后,进一步分解成对苯醌;C6H6-OH加合物和激发态的苯也可直接与H2O2反应生成对苯醌,三种反应途径同时存在.

The cross-reaction microscopic mechanism of aqueous benzene with hydrogen peroxide under different conditions was studied by laser flash photolysis. The main characteristic peaks in these transient absorbance spectra were assigned and the build-up/decay trends of several transient species were investigated. (OH)-O-. radical can be produced in aqueous solution of hydrogen peroxide exposed to 266 nm laser beam. The reaction of (OH)-O-. radical and benzene produces C6H6-OH adduct with a rate constant of (8.0 similar to 8.1) x 10(9) L (.) mol(-1) (.) s(-1) in the approximately neutral (PH approximate to 6) and 7.7 x 10(9) L (.) mol(-1) (.) s(-1) in acid (PH = 1.5) solution, while the rate constant is about (6.7 similar to 6.9) x 10(9) L (.) mol(-1) (.) s(-1) in the basic (pH = 9) solution. The C6H6-OH adduct will be able to react with O-2 to form C6H6-OHO2, then decompose into p-benzoquinone. In the meantime, C6H6-OH adduct and excited state of benzene may also react with H2O2 to form p-benzoquinone. The three reaction pathways were concurrently happened.