Abstract
Four kinds of functional ionic liquids (ILs) ([C3SO3Hnmp]HSO4), 1-(3-sulfopropyl)-1-methylpyrrolidone phosphate ([C3SO3Hnmp]H2PO4), 1-(3-sulfopropyl)-1-methylpyrrolidone p-toluene sulfonate ([C3SO3Hnmp]CH3SO3H) and 1-(3-sulfopropyl)-1-methylpyrrolidone methyl sulfonate ([C3SO3Hnmp]C6H6SO3H)) were prepared and the catalytic activity of these ILs during esterification of carboxylic acids (formic acid, acetic acid, propionic acid, butyric acid) with alcohols was investigated. The results indicated that the IL ([C3SO3Hnmp]HSO4) exhibited an optimal catalytic performance. And then the IL ([C3SO3Hnmp]HSO4) was immobilized to the silica gel. The immobilized IL performed more excellent catalytic activity than the unsupported [C3SO3Hnmp]HSO4. The effects of reaction temperature, reaction time, molar ratio of acid to alcohol and catalyst dosage were investigated. The response surface methodology based on the Box–Behnken design (BBD) was used to explore the best reaction condition of different experimental variables. Accordingly, a high n-butyl butyrate yield of 97.10% under the deduced optimal reaction conditions was obtained, in good agreement with experimental results and that predicted by the BBD model. The immobilized IL [C3SO3Hnmp]HSO4 maintained high catalytic activity after five cycles.
Highlights
As an important fine organic chemicals product, carboxylic esters have been widely used in perfume, coating, pharmaceutical royalsocietypublishing.org/journal/rsos R
The supported Ionic liquids (ILs) [C3SO3Hnmp]HSO4 was synthesized according to previous studies [21,22]
The supported ILs [C3SO3Hnmp]HSO4 were insoluble in all reactants and products
Summary
As an important fine organic chemicals product, carboxylic esters have been widely used in perfume, coating, pharmaceutical royalsocietypublishing.org/journal/rsos R. The main methods to obtain carboxylic esters are 2 extraction of natural substances and chemical synthesis [2,3]. The method of extracting carboxylic ester from natural substance has the disadvantages of complex process, low purity and high production cost. The esterification of alcohols and carboxylic acids became fundamental and important reactions in chemical synthesis. Chemical syntheses of carboxylic esters mostly invoke homogeneous catalysts, such as sulfuric acid, p-toluene sulfonic acid, and phosphoric acid, etc. Using these highly concentrated strong acids as catalyst leads to several problems such as equipment corrosion, environmental pollution, undesirable side reactions and catalyst unrecyclable [4,5]. Acid catalysts have some problems such as low selectivity and catalytic activity, easy deactivation, formidable separation and unrecyclable and so on [10,11]
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