Esters binary azeotropes with

Esters of low volatility are accesible via several types of esterification. In the case of esters of butyl and amyl alcohols, water is removed as a binary azeotropic mixture with the alcohol. To produce esters of the lower alcohols (methyl, ethyl, propyl), it may be necessary to add a hydrocarbon such as benzene or toluene to increase the amount of distilled water. With high boiling alcohols, ie, benzyl, furfuryl, and P-phenylethyl, an accessory azeotroping Hquid is useful to eliminate the water by distillation. 

These layers are separated continuously in an automatic separator the upper layer is returned to the still, while the lower is taken off and measured. As the reaction nears completion, the amount of water that separates diminishes until there is none the temperature in the still, after rising steadily, flattens out at the refluxing temperature of l e butyl acetate. The crude ester is cooled and neutralized with aqueous sodium hydroxide. After separation of the water layer, the ester is ready for refining by distillation. The first fraction is the ester-water binary azeotrope which is caught in an automatic separator, from which the ester layer is returned to the still. The next is a smtdl fraction that contains some water, as shown by turlndity when it is mixed with 10 vol. of benzene. This is added to the next batch. The rest of the distillate is finished ester and goes to storage. 

For other volatile esters, there are corresponding ternary and binaiy azeotropes. In general, the ternary azeotrope of an alcohol, its ester, and water boils slightly lower than the binary of the ester and water. The percentage of water in the ternary increases and that of the ester decreases with an increase in molecular weight of the alcohol, as can be seen from the data in Table 12r4, most of which are from Hannotte. ... 

The most common way to prepare esters (2) is the acid-catalyzed direct esterification of carboxylic acids (1) with alcohols (Scheme 1). The reaction is reversible, hence the alcohol should be applied in excess and/or the water formed should be removed by distillation, in most cases, in the form of binary or ternary azeotropes. 

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