Method for producing 2-methylbutanal from the secondary flows arising in the production of mixtures of isomeric alpha, beta-unsaturated decenals

A process for preparing 2-methylbutanal from the secondary streams obtained in the preparation of mixtures of isomeric decanals, characterized in that

• a) a mixture comprising linear butenes is reacted in the presence of transition metal compounds of group VIII of the Periodic Table of the Elements with carbon monoxide and hydrogen at elevated temperature and elevated pressure to give a pentanal mixture;
• b) the pentanal mixture obtained in step a) is converted in the presence of basic compounds to a mixture of isomeric α,β-unsaturated decenals;
• c) the mixture obtained in step b) is selectively hydrogenated in the presence of a hydrogenation catalyst with hydrogen at elevated temperature and elevated pressure to give a mixture of isomeric decanals;
• and
• d) the mixture obtained in step c) is separated into a stream enriched with unconverted 2-methylbutanal and a stream enriched with a mixture of isomeric decanals;
• with the proviso that the stream which has been separated off in step d) and is enriched with unconverted 2-methylbutanal is reacted with formaldehyde.