Abstract: There is disclosed a process for the preparation of 1,3-diketones of formula I ##STR1## wherein R.sub.1 and R.sub.2 are each independently of the other C.sub.1 -C.sub.20 alkyl, phenyl or phenyl which is substituted by halogen, hydroxy, NO.sub.2, C.sub.1 -C.sub.4 alkyl and/or C.sub.1 -C.sub.4 alkoxy, C.sub.7 -C.sub.9 phenylalkyl or a radical of formula II--A--X--R.sub.4 (II)whereinA is C.sub.1 -C.sub.12 alkylene, phenylene or phenylene which is substituted by halogen, hydroxy, NO.sub.2, C.sub.1 -C.sub.4 alkyl and/or C.sub.1 -C.sub.4 alkoxy, or is C.sub.1 -C.sub.12 alkylene which is substituted by hydroxy, halogen and/or alkoxy,X is oxygen or sulfur, andR.sub.4 is hydrogen, C.sub.1 -C.sub.18 alkyl, phenyl or phenyl which is substituted by halogen, hydroxy,C.sub.1 -C.sub.4 alkyl, NO.sub.2 and/or C.sub.1 -C.sub.4 alkoxy, or is C.sub.7 -C.sub.9 phenylalkyl, andR.sub.3 is hydrogen, C.sub.1 -C.sub.20 alkyl, phenyl or phenyl which is substituted by halogen, hydroxy, C.sub.1 -C.sub.4 alkyl, NO.sub.2 and/or C.sub.1 -C.