Carboxylic anhydride cpds. continuous prodn. - from corresp. acid and acetic anhydride in adiabatic reaction distn. column with short dwell time

摘要

Continuous prodn. of carboxylic anhydrides (I) of the formula R-CO-O-CO-R (in which R is t-Bu, cyclohexyl or (substd.) phenyl) from the corresp. carboxylic acid, RCOOH (II), and acetic anhydride (III) at elevated temp. is carried out adiabatically at normal or reduced pressure only with a reaction-distn. column with sump and feed heating. This operates with average dwell times of 1-15 min, with simultaneous sepn. of (I) and acetic acid (IV). A stoichiometric molar ratio is maintained in the supply of (II) and (III). A packed column is used. The reaction is carried out at 1000-10 (800-20)mbar. (II) is pivalic, cyclohexanecarboxylic or benzoic acid. (I) are valuable intermediates in numerous organic syntheses. The process uses extremely short dwell times and gives practically quantitative yield and high purity without using excess (III).