Acid catalysed transesterification of benzyl acetate in glycerol
The acid catalysed alcoholysis of benzyl acetate was successfully performed in glycerol that was simultaneously used as a green solvent and as the acyl acceptor. Both soluble and solid acid were employed, and it was found that increasing either the reaction temperature and time or substrate concentration and catalyst loading increased the conversion of benzyl alcohol. Using glycerol as the solvent also enabled the separation of product by simple extraction with diethyl ether, catalyst recycling, and microwave-promoted reactions.
Benzyl alcohol, a valuable organic solvent and bacteriostatic preservative agent, is traditionally produced by the hydrolysis of benzyl chloride under alkali conditions (1, 2). As hydrolysis usually requires an excess amount of alkali base that produces a correspondingly large amount of waste, alternative benzyl alcohol production routes have been investigated. One such alternative is the oxyacetoxylation of toluene with acetic acid and oxygen that produces benzyl acetate (3, 4), which can then be hydrolyzed to benzyl alcohol in a more environmentally benign fashion by transesterification (alcoholysis) using homogeneous and heterogeneous catalysts (5-7). Traditionally, the reaction has been performed in an acidic or basic aqueous solution under mild conditions to yield the corresponding carboxylic acid and alcohol. But because of the low miscibility of most esters in water and equipment corrosion due to the acidic or basic conditions, catalytic transesterification of the ester in the presence of an alcohol, which removes the ester's carboxylic group and releases the corresponding alcohol, i.e., alcoholysis, was also reported (5-7).