Distillation of esters

In the purification of dialkyl esters of dicarboxylic acids by distillation, preferably under reduced pressure, the ester is distilled in the presence of activated alumina, whereby thermal degradation of the ester is obviated. The activated alumina may be employed alone or in conjunction with an inert solid, such as silica. The esters specified are those of phthalic, adipic, azelaic and sebacic acids with alcohols containing from 6 to 13 carbon atoms per molecule, including the "oxo" alcohols. In an example a mixture comprising dihexyl phthalate, hexyl decyl phthalate and didecyl phthalate having an acid number of zero, was fractionated in the presence of 0,2% of activated alumina using a ten-plate column maintained at a pressure of 4mm. After distilling over unreacted alcohol and hydrocarbon (from the synthesis of the ester mixture), the esters were distilled over at 185-250 DEG C. with no deposition of phthalic anhydride and/or phthalic acid on the equipment. The recovered ester had a neutralization number of zero.ALSO:In the purification of dialkyl esters of dicarboxylic acids by distillation, preferably under reduced pressure, the ester is distilled in the presence of activated alumina, whereby thermal degradation of the ester is obviated. The activated alumina may be employed alone or in conjunction with silica. In an example, a mixture comprising dihexyl phthalate, hexyl decyl phthalate and didecyl phthalate was fractionated in the presence of 0.2% of activated alumina using a ten-plate column maintained at a pressure of 4 mm. After distilling over unreacted alcohol and hydrocarbon (from the synthesis of the ester mixture), the esters were distilled over at 185-250 DEG C. with no deposition of phthalic anhydride and/or phthalic acid on the equipment.