Monoazo reactive dyes

A dyestuff according to formula (I) ##STR43## or a salt thereof, wherein the sulphonic acid group can be in 3- or 4- or 5-position of the phenyl ring, preferably in the 4-position, and RG, which is bonded in the 2- or 3-position of the naphthalene ring, signifies ##STR44## wherein X and Y, independently from each other are a substituent which is selected from Cl, F, an amino group of the formula --NR.sub.4 R.sub.5 wherein R.sub.4 and R.sub.5 are independently hydrogen or C.sub.1-4 alkyl, optionally substituted by OH, COOH or SO.sub.3 H or a group A--SO.sub.2 --B wherein A is a divalent group selected from C.sub.2-3 alkylene, C.sub.5-8 cycloalkylene or phenylene and B is a group selected from --CH.dbd.CH.sub.2, --CH.dbd.CH--Z, --CH.sub.2 CH.sub.2 --Z or --CH(CH.sub.2 Z)--CH.sub.2 Z wherein Z is a group removable by alkali or R.sub.4 and R.sub.5 together with the nitrogen atom to which they are connected are a heterocycle having 4 to 8 carbon atoms optionally containing another hetero-atom selected from O, N or S or X is Cl or F and Y signifies a radical of formula (la) ##STR45## wherein W is C.sub.1-6 alkylene and all the substituents have the same definition as defined above with the proviso that W connects two identical radicals.