A process is disclosed for preparing carboxylic acid derivatives having the general formula (I), in which X stands for OR or NH2, R stands for C1-C20 alkyl, C1-C20 hydroxyalkyl, C3-C12-cycloalkyl, C4-C12 alkyl-cycloalkyl, C4-C12-cycloalkyl-alkyl, C5-C20 alkyl-cycloalkyl-alkyl, aryl, C7-C20 aralkyl, C7-C20 alkylaryl, an heteroaliphatic or heteroaromatic ring with 5 to 8 carbon atoms and R stands for C1-C20 alkyl, from carboxylic acid nitriles having the general formula (II) R -CN, in which R has the above-mentioned meanings, and from alcohols having the general formula (III) R -OH, in which R has the above-mentioned meanings. The reaction is carried out in the liquid phase at temperatures from 50 to 300 DEG C and pressures from 0.1 to 350 bars in the presence of an heterogeneous catalyst.