Reactive trisazo dyes

Trisazo dye of the formula (I)

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• or an alkali metal salt thereof;
• wherein:
• Ar1 is an optionally substituted arylene group;
• Ar2 is an optionally substituted aryl group;
• each of R1, R2, R3 and R4, independently, is H, alkyl or phenyl;
• each of X1 and X2, independently, is a labile atom or group;
• and
• each of D1 and D2 independently, is a chromophore group of the formula
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• wherein:
• Ar3 is an aryl group;
• Y is a vinyl or allyl group or the group —CH2CH2V
• in which V is a leaving group;
• a is zero, 1, 2 or 3;
• b is zero, 1 or 2;
• at least one of a and b is at least 1;
• c is zero or 1 and when c is 1, the group SO3H on the naphthalene nucleus is substituted at the 5- or 6-position thereof;
• and
• the bond (1) is substituted at the 6-, 7- or 8-position of the naphthalene nucleus.