Disproportionation and Isomerization in Dehydartion of Cyclohexanol over Trifluoroacetic Acid/Alumina Catalysts

Abstract

本研究使用環已醇於350℃所進行的脫水反應，以比較兩種氧化矽一氧化鋁及十三種氧化鋁觸媒的酸性程度。 酸性觸媒可使環已醇產生不均衡反應產物（甲基環戊烷及環己烷）及骨架異構化反應產物（三種甲基環戊烯異構物及亞甲基環戊烷）伴隨著初期脫水產物（環己烯）。酸性最低的氧化鋁觸媒只產生環己烯。 依不均衡反應及骨架異構化反應之產物的量，可把觸媒按照其酸性程度排列。此排列法作為評定任一特定氧化鋁觸媒的酸性程度，為既簡便又直接之方法。 乙酸對氧化鋁觸媒的酸性有毒害效應，致使環己醇只產生環己烯但三氟乙酸則可大為增強氧化鋁觸媒的酸性；其反應產生很多不均衡反應及骨架異構化反應之產物。此觸媒經過再生後仍能保持或增加其效果。

The acidities of two silica aluminas and thirteen aluminas were com-pared using the dehydration of cyclohexanol at 350°C. Acidic catalysts tend to give disproportionation products (methylcyclopentane and cyclohexane) and skeletal isomerization products (the three methycyclopentenes and methylenecyclo-pentane) with the initial dehydration product (cyclohexene). The least acidic aluminas give only cyclohexene. The catalysts are arranged in the order of their acidities as reflected in the amount of the disproportionation and skeletal isomerization products. This ranking method for alumina catalysts provides a convenient, direct way of evaluating the acidity level of a particular alumina catalyst. Acetic acid has a poison effect on acidity of alumina, the probe reaction giving only cyclohexene. Trifluroacetic acid, on the other hand, has a great enhancement effect on acidity of alumina, the probe reaction giving a great deal of disproportiona-tion and skeletal isomerization products. This effect persists or is further enhanced upon regenerations.