Patent ID: 6890454

Claim:
An optical brightener (C) of formula (Ic): wherein R signifies hydrogen or methyl, R 1 signifies hydrogen, unsubstituted C 1-6 -alkyl, C 1-6 -alkyl substituted with carbamoyl or carboxy, C 2-6 -alkyl substituted with hydroxy or methoxy, hydroxy- or methoxy-(C 2-3 -alkoxy)-(C 2-3 -alkyl) R 2 signifies C 1-6 -alkyl substituted with carbamoyl or carboxy, or R 1 and R 2 together with the nitrogen to which they are linked form a carboxypyrrolidine ring, R 3 signifies hydrogen, unsubstituted C 1-6 -alkyl, C 2-6 -alkyl substituted with hydroxy or methoxy, or hydroxy- or methoxy-(C 2-3 -alkoxy)-(C 2-3 -alkyl), R 4 signifies hydrogen, unsubstituted C 1-8 -alkyl, C 2-6 -alkyl , substituted with hydroxy or methoxy, or hydroxy- or methoxy-(C 2-3 -alkoxy)-(C 2-3 -alkyl), or R 3 and R 4 together with the nitrogen to which they are linked form a morpholine ring, and M signifies an equivalent of a cation.