Abstract: 1,3,4-Thiazole derivatives of the formula ##STR1## wherein R.sub.26 ' denotes a C.sub.1 -C.sub.8 -alkyl radical which is optionally substituted by hydroxyl, halogen, cyano, C.sub.1 -C.sub.4 -alkoxy, carboxyl, aminocarbonyl or C.sub.1 -C.sub.4 -alkoxycarbonyl, a C.sub.2 -C.sub.4 -alkenyl radical, a cyclohexyl radical which is optionally substituted by C.sub.1 -C.sub.4 -alkyl, a phenyl, benzyl or phenylethyl radical which is optionally substituted by halogen, C.sub.1 -C.sub.4 -alkyl or C.sub.1 -C.sub.4 -alkoxy, a C.sub.1 -C.sub.2 -alkylcarbonyl, C.sub.1 -C.sub.4 -alkoxycarbonyl, mono- or di-C.sub.1 -C.sub.4 -alkylaminocarbonyl, aminocarbonyl, mono- or di-C.sub.1 -C.sub.4 -alkylaminosulphonyl, 2-thienyl, 2-furyl, 2-tetrahydrofuryl, amino, C.sub.1 -C.sub.4 -alkylamino or di-(C.sub.1 -C.sub.4 -alkyl)-amino radical or a phenylamino or benzylamino radical which is optionally substituted by C.sub.1 -C.sub.4 -alkyl or C.sub.1 -C.sub.4 -alkoxy and R.sub.27 ' denotes a C.sub.1 -C.sub.

Abstract: Compounds of the general formula I ##STR1## where R is substituted alkyl and K is the radical of a coupling component free from unsaturated aliphatic radicals, are very useful for dyeing cellulose esters and synthetic polyesters.