Method for producing optionally substituted aliphatic, aromatic or heteroaromatic aldehydes

The invention relates to a method for producing optionally substituted aliphatic, aromatic or heteraromatic aldehydes of formula (I), whereby the R represents a C 1 -C 20 Alkyl radical, an aromatic or heteraromatic radical Ar which can optionally be substituted once or on a number of occasions by OH, C 1 -C 6 alkyl, C 1 -C 6 alkoxy, C 1 -C 6 carboxylic acids or ester containing 1-6 C atoms in the ester part, phenyl, halogen, SO 3 H, NO 2 , NR 1 R 2 or SR 1 whereby R 1 and R 2 can be independently H, phenyl or C 1 -C 6 alkyl. The invention is characterised by a compound of formula (II) wherein R has the above meaning, a) is diazotized in an acidic medium, at a temperature of between −10 −+100 ° C. by a diazoation reagent and is transformed into the corresponding hydroxy carboxy acid whereby b) is transformed, by means of oxygen, into the appropriate aldehyde of formula (I) in the presence of a metal, the salt thereof, oxide or hydroxide as a catalyst.