Preparation of tert-butyl esters of aliphatic carboxylic acids

Abstract

A process for continuously preparing the tert-butyl ester of an aliphatic C-Ccarboxylic acid comprises: a) the reaction of an aliphatic C-Ccarboxylic acid with isobutene in the presence of an acidic catalyst to give an esterification mixture (G); b) the partial evaporation of the esterification mixture (G), giving a liquid first high boiler phase (SPh) comprising the acidic catalyst, and a first vapor (B) comprising tert-butyl ester; c) the fractional condensation of the first vapor (B) by partially condensing the first vapor (B) at a first pressure and a first temperature and obtaining a first condensate (K), partially condensing the uncondensed second vapor (B) at a second pressure and a second temperature and obtaining a second condensate (K), the first temperature being 0 to 45° C. below the condensation temperature of the tert-butyl ester at the first pressure and the second temperature being 45 to 80° C. below the condensation temperature of the tert-butyl ester at the second pressure, with the proviso that the second temperature is at least 5° C. below the first temperature; and d) the combination of the first condensate (K) and the second condensate (K) and the feeding to a combined workup, and recycling of the third vapor (B) not condensed at the second temperature into step a). The process allows the preparation of the tert-butyl ester of an aliphatic C-Ccarboxylic acid by reaction of the carboxylic acid with isobutene, with isolation of unconverted isobutene from the esterification mixture in an energetically favorable manner and with an improved degree of removal.