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|標題:||第三液相相間轉移觸媒合成鄰-羥基苯甲酸苯甲酯之反應動力學研究||作者:||李菁菁||關鍵字:||phase-transfer catalysic;相間轉移催化反應;Third-liquid phase;Catalytic intermediate;Interfacial tension;o-hydroxybenzoic acid benzyl ester;kinetics;esterification;第三液相;觸媒中間體;界面張力;鄰-羥基苯甲酸苯甲酯;動力學;酯化反應||出版社:||化學工程學系||摘要:||
在含有相間轉移觸媒的系統中，其界面張力能以Gibbs與Langmuir 等溫吸附方程式來描述，此外界面過量與分子界面積皆能被計算。當水溶液中含有相間轉移觸媒其界面張力會降低，在系統中第三液相與水相的界面張力值約為1.2~2.8 mN/m；遠小於第三液相與正庚烷的介面張力8~12 mN/m，表示有機相與第三液相之間存在著質傳阻力。吸附界面的分子界面積為0.17~0.19 Å2，觸媒吸附活性以四級鏻鹽大於四級銨鹽。
The kinetics of esterification of sodium salicylate with benzyl bromide to produce benzyl salicylate were investigated via third-liquid phase-transfer catalysis in a tri-liquid system. The conditions of forming the third-liquid phase were performed for different aqueous reactants, inorganic salts, organic solvents, and catalysts to find the dependence of the characteristics of the catalytic intermediate on producing the third-liquid phase. First, this work explores the formation of a third liquid in the organic phase/ tetrabutylphosphonium bromide (TBPB) /aqueous (sodium salicylate + NaBr) system. It is found that the minimum quantity of TBPB required to form the third-liquid is dependent on the amounts of NaBr added, but the variation of the third-phase by NaBr is insignificant with greater amount of TBPB used. The volume of third-liquid generated increases with increasing amounts of catalyst used. The regime of 20~70 mL- water in a 30mL-heptane favors forming third-liquid phase.
The interfacial tensions in a tri-liquid system were measured and could be well described by the Gibbs adsorption equation coupled with the Langmuir monolayer isotherm. In addition, the interfacial parameters such as surface excess and molecular area of the present liquid-liquid phase-transfer-catalyzed systems. It was found that the interfacial tensions was decreased with catalyst added. The interfical tension between water and third-liquid was 1.2~2.8 mN/m, much less than 8~12 mN/m for the third-liquid/heptane interface, exhibiting the dominating mass-transfer resistance to be in heptane side. The molecular area was estimated in the range of about 0.17~0.19 Å2. The surface activity of phosphonium salts is higher than ammonium salts.
The amount was agreed sodium salicylate, catalyst and catalytic intermediate in the third-liquid phase. The product is present in both organic phase and in the third but not in the aqueous phase due to its insolubility in the latter. The reaction mechanism and kinetic model is present and validated from the experimental results. When the agitation speed exceeds 350 rpm, the mass transfer resistance at the third-liquid phase interface can be ignored. Above 85﹪of product yield in the organic phase can be obtained for 0.006 moles of TBPB used to form the third-liquid phase, and the reactivity increase with increasing the amount of TBPB employed. The experimental data were well described by the pseudo-first-order kinetics .
The apparent activation energy in heptane was obtained 17.69 kcal/mol using tetrabutylphosphonium bromide as the catalyst. The most advantage of using third-liquid phase is the reuse of catalyst. After separating the third-liquid phase form the reaction mixture, the volume of the third-liquid phase was reduced to some extent, however, introducing additional amount of third-liquid phase, the reaction rate was still high enough as the fresh catalyst used.
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