Kinetics of a Sequential Phosphazene Reaction in a Multi-phase System

• Main Authors: Meng, Shang-Shin, 蒙上欣
• Other Authors: Ho-Shing Wu
• Format: Others
• Language: zh-TW
• Online Access: http://ndltd.ncl.edu.tw/handle/73764745728579582599

碩士 === 元智工學院 === 化學工程學系 === 85 === Organophosphazenes can be used as pressuried working fluids, flame retardants and lubricant. Phase-transfer catalysis (PTC) is considered a useful tool insynthesizing organic chemicals from two immiscrible reaction. In the study ,phase-transfer catalysis was carried out for the substitution reaction of hexachlorocyclotriphosphazene ((NPCl2)3) and phenol in a mulitphase system tosynthesize the partial (phenoxy) chlorocyclotriphosphazene. The consumption of reactant and the production of products is observed and studied during thecourse of the reaction. There are three main topics which need to be understood in studying the phase-transfer catalytic reaction, including (i) the reactionrate in the organic phase, (ii)the mass-transfer steps between the organic andaqueous phase , (iii) the partition equilibrium of the catalysts between thetwo phase. So the kinetics, mass-transfer effect and effect of concentrationin each phase are discussed. Several rigid conclusions were obtained:(1) Thereaction rate was dramatically increasing by adding a small quantity ofphase-transfer catalyst. The products of the partial (phenoxy) chlorocyclotriphosphazene was separated by pressured column chromatograph and cooling crystallization. On the basis of 31P NMR spectra ,the reaction type belonging to a transion-nongeminal path. According to the experimental data , the electronic effect and the steric effect were empolyed to explain the reaction of an SN2 type of mechanism. (2) Changing the initial concentration ofhexachlorocyclotriphosphazene affected the value of pseudo- first-orderreaction-rate constant. Hence, the reaction system was controlled by both chemical-kinetics and mass-transfer effects. The mass transfer of the catalyst between two phases was investigated by a psedo-steady-state LLPTC model. Also, the intrinsic reaction-rate constants of the series substitution and the overall mass transfer coefficient of the catalyst from organic phase to aqueous phase were determined by a combined model. In addition, the corresponding energies,enthalpies and entropies of activtion of the series substritution werealso estimated.(3) Base on the experimental result, the relationship between the functions of NaOH in a PTC reaction such as (i) salting out the intermediateproduct of catalyst QY to the organic phase and (ii)reducing the solvation between the catalyst and water to improve the reactivity of active catalyst in the organic phase,and the mass-transfer capability of the catalyst between bothphases was clarified. (4) In order to overcome the separating problem of the catalyst from the final product ,the catalyst was immobilized on a polymer support,i.e., triphase catalyst .The polymer support is a copolymer of styrene andchloromethylstyrene , using divinylbenzene as a crosslinking agent. The masstransfer limitation influences the triphase reaction rate. The particle diffusion and intrinsic reactivity limit the displacement reaction in the organic phase. The film diffusion of the aqueous phase limits in the ion-exchange step. (5)In the present study, the NMR chemical shifts and coupingconstant of cyclotriphosphazenes have been analyzed. I found that chemical shift of cyclotriphosphazenes can be calculated and predicted from partial chemical shift of cyclotriphosphazenes.The coupling constant of cyclotriphosphazenes are not regular than chemical shift. Therefore, coupling constant difficult to be analysized in synthesizing cyclotriphosphazenecompound.