Process for the preparation of azomethines

A process for the preparation of an azomethine of the formula ##STR9## in which R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6, R.sup.7 and R.sup.8 independently of one another denote hydrogen, linear or branched C.sub.1 -C.sub.6 -alkyl, C.sub.3 -C.sub.6 -cycloalkyl, benzyl or aryl, and

• R.sup.5, R.sup.6, R.sup.7 and R.sup.8 independently of one another additionally denote halogen, linear or branched C.sub.1 -C.sub.6 -alkoxy, hydroxyl, amino, C.sub.1 -C.sub.6 -alkylamino, di-C.sub.1 -C.sub.6 -alkylamino, aryloxy or arylamino,
• aryl representing phenyl or 5-membered or 6-membered heteroaryl attached in the 2-, 3- or 4-position and having 1 or 2 hetero atoms belonging to the group N, O and S, and
• X denotes --CH.sub.4 -- or a direct bond between the adjacent C atoms,
• comprising the condensation of a cycloalkanone of the formula ##STR10## with an aniline of the formula ##STR11## in which R.sup.1 to R.sup.8 and X have the above meaning, in the presence of an acid heterogeneous catalyst with azeotropic removal of the water of reaction, wherein the condensation reaction is carried out at a molar ratio of cycloalkanone to analine of 2:1-1:2, a pressure of 0.5 mbar-3 bar and in a continuous reaction in a column-like reactor having an applied temperature profile, ranging from 10.degree. C. to 300.degree. C. the starting materials being fed in in the low-temperature zone and, of the reaction products, the water of reaction to be removed as an azeotrope also being removed in the low-temperature zone and the azomethine formed being removed in the high-temperature zone.