Process for hydrolysing cyclopropanecarboxylic esters to the free acid

Process for preparing cyclopropanecarboxylic acid (5), characterized in that methyl or ethyl cyclopropanecarboxylate (1), if appropriate in admixture with one or more alcohols (2), and also with water (4) and, if appropriate, hydrochloric acid (3), is hydrolysed, in which

• a) methyl or ethyl cyclopropanecarboxylate (1), if appropriate in admixture with one or more alcohols (2), and also with water (4) and, if appropriate, hydrochloric acid (3), are fed, either separately or together, into an apparatus comprising a vessel (D) which may be equipped with an automatic stirrer and is connected to a 1 st column (A) provided with a condenser, with the alcohol or alcohols (2) being taken off via the top of the column (A) and either:
• 1) methyl or ethyl cyclopropanecarboxylate (1), if appropriate in admixture with one or more alcohols (2), and also with water (4) and, if appropriate, hydrochloric acid (3), being introduced either separately or together into a 1 st column (A) provided with a condenser, or
• 2) methyl or ethyl cyclopropanecarboxylate (1), if appropriate in admixture with one or more alcohols (2), and also with water (4) and, if appropriate, hydrochloric acid (3), being fed either separately or together into the vessel (D), or
• 3) methyl or ethyl cyclopropanecarboxylate (1), if appropriate in admixture with one or more alcohols (2), being introduced into the 1st column (A) provided with a condenser while water (4) and, if appropriate, hydrochloric acid (3) are fed either separately or together into the vessel (D),
• b) the reaction mixture which goes either directly or in cases a)l) and a)3) either in its entirety or partly via the 1st column (A) into the vessel (D) is subsequently fed to a 2nd column (B) provided with a condenser, with the cyclopropanecarboxylic acid (5) being taken off in the bottoms from the column (B) while the remaining reaction mixture is recirculated to the vessel (D) and, if no hydrochloric acid (3) is used, at least one acidic solid (9) being placed initially in the vessel (D).