The present invention relates to a process of cleaving lactones optionally having functional groups to give carboxylic acids, where the corresponding lactone is reacted with hydrogen with catalysis by a compound of a metal of group VIII of the Periodic Table of the Elements which has been modified with organophosphines. The process is preferably carried out in a two-phase system using catalysts which have water-soluble phosphine ligands.
The reaction is particularly suitable for cleavage 2-ethylidene-6-hepten-5-olide to give ethylidene-6-heptenecarboxylic acid or isomers thereof. This carboxylic acid can be hydrogenated in a manner known per se to give 2-ethylheptanoic acid.