| Summary: | 博士 === 國立清華大學 === 化學工程學系 === 90 === The primary objective of this dissertation is to study the oxidation of organic compounds which include epoxidation of olefin and oxidation of alcohol by phase transfer catalyst. The phase transfer catalytic epoxidation of various olefins using the hydrogen peroxide as oxidant in an organic/aqueous two-phase medium was investigated. Epoxides are widely used in various industries, such as curing the ulcer, manufacturing of cleaning reagent, stabilizing polychloroethyl resin and monomer of the epoxy resins etc.. Using sodium hypochlorite as the oxidant, benzaldehyde which is widely used in the industries of medicine, dyestuff, perfume and resin was obtained as the main product from benzyl alcohol via oxidation.
The purpose of this study is to use the phase transfer catalytic technique to solve the problems of two-phase reactions. High yield and high selectivity were obtained even at moderate conditions both in epoxidations and oxidation. The reaction mechanism, kinetics and the operating factors which affect the reactions and yields were discussed. The conclusions were obtained :
Epoxidation reaction:
(1) In this work, sodium tungstate and phosphoric acid were used as the cocatalyst, and hydrogen peroxide was used as the oxidant agent. The phase transfer catalyst added was to improve the rate of reaction which directly takes place in the two immiscible solutions. The phase transfer catalytic technique exhibits the excellent epoxidation of the C = C double bonds on the ring (e.g., 5-vinyl-2-norbornene and dicyclopentadiene), but not promise epoxidation of the C = C double bond on the end-chain (1,7-octadiene). In order to elevate the epoxidation of the C = C double bond on 1,7-octadiene, the reaction is greatly improved by adding phosphotungstic acid by carrying more oxygen atoms from aqueous phase to organic phase.
(2) In carrying these epoxidations, the ion-exchange and the complex reaction take place in the aqueous phase. In general, both ion-exchange and complex reaction in the aqueous phase are all rapid. Therefore, the transfer rate of phase transfer catalyst between two phases keeps at a constant value when the agitation speed reaches an appropriate level. Under this circumstance, the organic-phase reaction is a rate-controlling step. Based on the experimental data, a pseudo first order rate law is sufficient to describe the kinetic behavior.
(3) The derivation kinetic model is dependent on the structure of the organic-phase reactants. Only one C = C double bond on 5-vinyl-2-norbornene is epoxided. Therefore, the kinetic model is relatively simple. The apparent activated energy of the epoxidation of 5-vinyl-2-norbornene in dichloroethane/water two phase system is 11.43 kcal/mole. Nevertheless, there are two C = C double bonds on dicyclopentadiene. These two C = C double bonds are epoxided through series and parallel reactions. The four apparent activated energies obtained are Ea,1 = 6.84 kcal/mol、Ea,2 = 6.87 kcal/mol、Ea,3 = 7.76 kcal/mol and Ea,4 = 6.53 kcal/mol, respectively. Further, there are two C = C double bonds on the 1,7-octadiene molecule. Therefore, a series reaction from which these two C = C double bonds are epoxided. The apparent activated energies are Ea,1 = 11.40 kcal/mol、Ea,2 = 12.17 kcal/mol, respectively.
Oxidation reaction :
(1) In this work, sodium hypochlorite was used as the oxidant agent. The reaction is usually low because it is difficult to proceed the ionic exchange between sodium hypochlorite and phase transfer catalyst under strong alkalinity. In this work, the reaction is greatly improved by carrying out the reaction in acidic solution with the addition of concentrated sulfuric acid, buffer solution or sodium bicarbonate.
(2) In kinetic study, it is found that a zeroth order is sufficient to describe the reaction behavior. The apparent activated energy is 13.06 kcal/mol.
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