Use of reactive cross-linking agents for protein-containing substrates and processes for tanning and dyeing of leather

A reactive colourless protein cross-linking agent for the cross-linking of protein-based substrates having amine and optionally OH functionality, said cross-linking agent comprising a compound according to formula [1]:

• wherein
• L1 and L5 are each independently from each other selected from H or C1-C4 alkyl, and
• L2, L3, L4, L6, L7 and L8 are each independently from each other selected from H, C1-C4 alkyl, SO3H, and OL22 wherein L22 is selected from H and C1-C4 alkyl, and
• X is selected from Cl, F and nicotinic acid, and
• K1, K2, K3 and K4 are each independently from each other selected from —H and protein reactive radicals, and
• wherein the protein-based substrates are selected from collagen containing fibrous material, gelatin, fibroin, elastin and soy (soyabean).