| 摘要: | 目前工業上製造酯類仍以羧酸在硫酸催化下與醇類直接進行酯化反應而得，但因反應系統容易發生逆反應，酯類產率不高，此外尚有反應條件嚴苛、反應速率慢等缺點。然而以現有的相間轉移催化方法合成酯類雖較傳統方法的反應條件溫和且成本低，但仍難以廣泛應用在酯類製程上，例如液-液相間轉移催化技術有羧酸根離子因水合作用降低其反應性的缺點、液-液與固-液兩種相間轉移催化技術皆有觸媒不易回收的困擾、而固-固-液相間轉移催化技術則有反應速率緩慢的缺陷。因此，發展出可解決上述缺點的合成酯類新相間轉移催化方法是當務之急。本計畫擬評估以一種新穎的相間轉移催化技術合成酯類化合物的可行性。即以具有富含觸媒(四級鹽類)之液相催化由醋酸鈉與正溴己烷轉化合成醋酸己酯的固-液反應，探討此固-液-液相系統在批式反應器與續流攪拌式反應器的反應情形。本計畫共為期三年(本年度為第二年)，第一年先將探討各變因對觸媒液相形成與組成的影響，並進行以此觸媒液相催化醋酸鈉與正溴己烷合成醋酸己酯的初步動力學實驗。第二年將深入探討各變因對批式系統轉化率與生成分率的影響，以找出最佳的反應條件。另外，也將評估觸媒重複使用的可行性。第三年將評估不使用有機溶劑之批式催化系統的效益。再根據最佳的批式反應條件進行續流攪拌式反應系統的效能評估，並以由批式反應系統所得之反應速率表示式模擬續流式反應系統，且與實驗結果互相比較。以上的技術若研發成功，將是相間轉移催化研究上的重大突破與創舉，勢必能提供給工業界另一重要的合成技術。This study, as the second part of a series of studies, aimed at evaluating the effect of synthesizing hexyl acetate (ROAc) from n-hexyl bromide (RBr) and sodium acetate (NaOAc) by a novel PTC technique. In this new technique, called as solid-liquid-liquid phase-transfer catalysis (SLL PTC), the factors influencing the reaction was investigated to find the optimal condition in a batch reactor, and the possibility of reusing the phase-transfer catalyst (tetra-n-butylammonium bromide, QBr) in SLL PTC system was also evaluated. Experimental results indicate that using n-heptane as an organic solvent, RBr and ROAc are almost partitioned in the organic phase, and the concentration of Q+ and OAc in the organic phase approaches to zero, so RBr mainly reacts in the catalyst-rich liquid phase. In this SLL PTC system, the optimal amounts of QBr and NaOAc are 0.03 mol and 0.04 mol respectively. Using the optimal amounts of QBr and NaOAc, both the volume and the concentration of Q+ in the catalyst-rich liquid phase are suitable, and the reaction rate constant is higher. Comparing the catalysts with same cation (Q+) but different ions, in the system used QBr as the catalyst, RBr can be completely converted to ROAc and the catalyst would not dissolve into the organic phase, although the reaction rate isn？？ t faster owing to the discrepancy in the type of the reaction system. High temperature obviously enhances the reaction rate, but the temperature must not be so high as to avoid vaporization of the organic solvent and thermal decomposition of the catalyst. The optimal temperature is about 90 oC. The overall reaction rate of catalyzing RBr can be expressed with a pseudo-first-order kinetic model ( rRBr=k[RBr]). In the case of reusing catalyst, the existence of byproduct (NaBr) causes the property of the catalyst-rich liquid phase to be changed, so the catalyzed efficiency of reusing the catalyst-rich phase is not good. However, adding an appropriate amount of water increases the feasibility of reusing catalyst. |
