Kinetics and Mechanism of Styrene Epoxidation by Chlorite: Role of Chlorine Dioxide

Abstract

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.

Kinetics of the Benzaldehyde-Inhibited Oxidation of Sulfite by Chlorine Dioxide

“…33,34 We note that oxygen atom transfer from ClO , 35 and styrene. 36 It has also been proposed previously in the reaction of ClO 2…”

STM and DFT Study of Chlorine Adsorption on the Ag(111)-p(4 × 4)–O Surface

“…The indication of the formation of the species containing Cl–O bonds is of particular interest for the recognition of the role of chlorine in alkene epoxidation reactions. Indeed, it is known that sodium chlorite can be used for the production of styrene epoxide without any catalyst. − Therefore, the formation of the Cl–O species in our case can open an additional channel of the epoxidation. It is also noteworthy that this derivation is in line with a recent publication by Jones et al, in which authors postulated that the epoxidation can occur on the specific SO 4 complexes adsorbed on the silver surface.…”

Degradation of the cellulosic key chromophore 2,5-dihydroxy-[1,4]-benzoquinone (DHBQ) under conditions of chlorine dioxide pulp bleaching: formation of rhodizonate as secondary chromophore—a combined experimental and theoretical study

“…ClO 2 is a strong oxidant for many organic compound classes, such as phenols, aldehydes, unsaturated structures, or amines. There are three typical initial reactions of ClO 2 -hydrogen atom abstraction, one-electron transfer, and radical addition reactions to double bonds-which are typically followed by subsequent reactions of ClO 2 -derived chlorine species (Leigh et al 2014;Aguilar et al 2014;Lehtimaa et al 2010;Napolitano et al 2005;Hull et al 1967). Because of the different reaction modes and many side reactions, its application in synthetic organic chemistry is rather limited, but it is a favored oxidant in pulp bleaching because of its high selectivity: it mainly attacks residual lignin, with its aromatic and quinoid structures, while leaving the carbohydrate structures in cellulose and hemicelluloses largely unchanged.…”