Leigh Jessica K, Rajput Jonathan, Richardson David E
Center for Catalysis, Department of Chemistry, University of Florida , Gainesville, Florida 32611, United States.
Inorg Chem. 2014 Jul 7;53(13):6715-27. doi: 10.1021/ic500512e. Epub 2014 Jun 13.
An investigation of the kinetics and mechanism for epoxidation of styrene and para-substituted styrenes by chlorite at 25 °C in the pH range of 5-6 is described. The proposed mechanism in water and water/acetonitrile includes seven oxidation states of chlorine (-I, 0, I, II, III, IV, and V) to account for the observed kinetics and product distributions. The model provides an unusually detailed quantitative mechanism for the complex reactions that occur in mixtures of chlorine species and organic substrates, particularly when the strong oxidant chlorite is employed. Kinetic control of the reaction is achieved by the addition of chlorine dioxide to the reaction mixture, thereby eliminating a substantial induction period observed when chlorite is used alone. The epoxidation agent is identified as chlorine dioxide, which is continually formed by the reaction of chlorite with hypochlorous acid that results from ClO produced by the epoxidation reaction. The overall stoichiometry is the result of two competing chain reactions in which the reactive intermediate ClO reacts with either chlorine dioxide or chlorite ion to produce hypochlorous acid and chlorate or chloride, respectively. At high chlorite ion concentrations, HOCl is rapidly eliminated by reaction with chlorite, minimizing side reactions between HOCl and Cl2 with the starting material. Epoxide selectivity (>90% under optimal conditions) is accurately predicted by the kinetic model. The model rate constant for direct reaction of styrene with ClO2(aq) to produce epoxide is (1.16 ± 0.07) × 10(-2) M(-1) s(-1) for 60:40 water/acetonitrile with 0.20 M acetate buffer. Rate constants for para substituted styrenes (R = -SO3(-), -OMe, -Me, -Cl, -H, and -NO2) with ClO2 were determined. The results support the radical addition/elimination mechanism originally proposed by Kolar and Lindgren to account for the formation of styrene oxide in the reaction of styrene with chlorine dioxide.
本文描述了在25℃、pH值为5 - 6的条件下，用亚氯酸盐对苯乙烯和对位取代苯乙烯进行环氧化反应的动力学及反应机理研究。在水和水/乙腈体系中提出的反应机理涉及氯的七种氧化态（-I、0、I、II、III、IV和V），以解释观察到的动力学和产物分布情况。该模型为氯物种与有机底物混合物中发生的复杂反应提供了异常详细的定量机理，特别是在使用强氧化剂亚氯酸盐时。通过向反应混合物中加入二氧化氯实现了对反应的动力学控制，从而消除了单独使用亚氯酸盐时观察到的显著诱导期。环氧化剂被确定为二氧化氯，它是由亚氯酸盐与次氯酸反应不断生成的，而次氯酸是由环氧化反应产生的ClO生成的。总的化学计量关系是两个竞争链反应的结果，其中活性中间体ClO分别与二氧化氯或亚氯酸根离子反应，分别生成次氯酸和氯酸盐或氯化物。在高亚氯酸根离子浓度下，HOCl通过与亚氯酸盐反应迅速被消除，从而使HOCl与起始原料Cl2之间的副反应最小化。动力学模型准确预测了环氧化物的选择性（在最佳条件下>90%）。在60:40的水/乙腈和0.20 M乙酸盐缓冲液中，苯乙烯与ClO2(aq)直接反应生成环氧化物的模型速率常数为(1.16 ± 0.07) × 10(-2) M(-1) s(-1)。测定了对位取代苯乙烯（R = -SO3(-)、-OMe、-Me、-Cl、-H和-NO2）与ClO2的速率常数。结果支持了Kolar和Lindgren最初提出的自由基加成/消除机理，以解释苯乙烯与二氧化氯反应中环氧化苯乙烯的形成。
