Process for preparing 3-hydroxyalkanals

A process for preparing 3-hydroxylalkanals having 3 to 12 carbon atoms, by hydration of a 2-alkenal with water in the presence of a catalyst in homogeneous phase at a reaction temperature of from 10 to 100.degree. C., at a pressure of from 1 to 20 bar, at an initial concentration of the 2-alkenal in the reaction mixture of from 3 to 30 wt. %, wherein the catalyst used is a compound corresponding to the formula:

• ##STR3## wherein Z denotes H, C.sub.1 - to C.sub.6 -alkyl, --CH.sub.2 --CH(CH.sub.3)--Y' or --(CH.sub.2).sub.o --Y';
• R denotes H;
• Y and Y' are identical or different and denote --COOH, --P(O)(OH).sub.2, --OH, pyridyl, or --P(O)(CH.sub.2 OH)OH, wherein the acid functional group may be present partly in the form of its alkali metal salt, alkaline-earth salt or ammonium salt;
• n denotes 1, 2, 3, 4, 5 or 6 where Y is --COOH, --P(O)(OH).sub.2, pyridyl or --P(O)(CH.sub.2 OH)OH;
• 2 or 3 where Y is --OH,
• o denotes 1, 2, 3, 4, 5 or 6 where Y' is --COOH, --P(O)(OH).sub.2, pyridyl or --P(O)(CH.sub.2 OH)OH;
• 0, 2 or 3 where Y' is --OH.