Process for the preparation of cationic methine dyestuffs

In the preparation of cationic methine dyestuffs of the general formula ##STR33## in which R represents an alkyl radical which has 1 to 4 C atoms and is optionally substituted by hydroxyl, alkoxy having 1 to 4 C atoms, acyloxy, halogen, cyano, carboxyl, C.sub.1 to C.sub.4 -carboalkoxy, carbon-amido or acetyl,

• R.sup.1 represents hydrogen, alkyl having 1 to 4 C atoms, halogen, alkoxy having 1 to 4 C atoms, hydroxyalkoxy having 2 to 4 C atoms, a phenoxy, benzyloxy or benzyl radical which is optionally substituted by halogen, C.sub.1 to C.sub.4 -alkyl or C.sub.1 to C.sub.4 -alkoxy, carboxyl, a carboxylic acid alkyl ester which has 1 to 4 C atoms, a carbon-amide group which is optionally substituted by 1 or 2 C.sub.1 to C.sub.4 -alkyl radicals, a sulphonamide group which is optionally substituted by 1 or 2 C.sub.1 to C.sub.4 -alkyl radicals, alkylsulphonyl having 1 to 4 C atoms, phenylsulphonyl or a cyano, trifluoromethyl, acetyl or benzoyl group,
• A represents a radical of the formula ##STR34## in which R.sup.2 and R.sup.3 independently of one another represent an alkyl radical which has 1 to 4 C atoms and is optionally substituted by hydroxyl, C.sub.1 to C.sub.4 -alkoxy, halogen, cyano, phenyl, carboalkoxy having 1 to 4 C atoms, carbon-amido, acyloxy, benzyloxy, sulphonamido or acylamino,
• R.sup.2 additionally represents a phenyl or benzyl radical which is optionally substituted by halogen, C.sub.1 to C.sub.4 -alkyl or C.sub.1 to C.sub.4 -alkoxy, or, together with the adjacent C atom of the benzene ring, can form a partially hydrogenated 5-membered or 6-membered ring which contains N and optionally contains O, and
• R.sup.4 denotes hydrogen, an alkyl radical having 1 to 4 C atoms, an alkoxy radical having 1 to 4 C atoms or halogen,
• or
• A represents a radical of the formula ##STR35## in which R.sup.5 represents an alkyl radical having 1 to 4 C atoms, a phenyl radical which is optionally substituted by halogen, C.sub.1 to C.sub.4 -alkyl or C.sub.1 to C.sub.4 -alkoxy, or a carboalkoxy radical having 1 to 4 C atoms,
• R.sup.6 represents hydrogen, an alkyl radical which has 1 to 4 C atoms and is optionally substituted by hydroxyl, halogen, alkoxy having 1 to 4 C atoms, cyano or acyloxy, and
• R.sup.7 represents hydrogen, halogen, C.sub.1 to C.sub.4 -alkyl, C.sub.1 to C.sub.4 -alkoxy, carboalkoxy having 1 to 4 C atoms, C.sub.1 to C.sub.4 -alkylsulphonyl, phenylsulphonyl, acetyl or benzoyl,
• or
• A represents a radical of the formula ##STR36## in which R.sup.8 and R.sup.9 independently of one another have the same meaning as R and R.sup.1,
• and in which
• X represents the radical of an inorganic acid and
• the indices m, n, o and p independently of one another denote 1 to 4,
• by subjecting a compound of the formula ##STR37## wherein R, R.sup.1 and m have the meaning indicated above, to a condensation reaction with a compound of the formula
• A--CHO
• in which A has the meaning indicated above,
• and with acids, the improvement which comprises carrying out the condensation reaction by homogeneously mixing the reactants as a viscous melt with 1 to 5 equivalents of a strong inorganic acid or acid salt thereof in the presence of up to 15% by weight of water based on the total weight of the organic starting components, and removing substantially all water present.