Difluoropyrimidine dyes

In contrast to cellulosic dyeing with reactive dyes, the fibroin-dye bonds are remarkably stable in aqueous media of pH 4 to 10 [117]. Since there exists only a negligible amount of bond hydrolysis even at high temperature and in a medium of pH 2, the cleavage of the fibroin-dye bond is not a problem in reactive-dyed silk. The stability of these bonds when dyeing with difluoropyrimidine dyes is the highest in both acidic and basic media [118]. 

Dyeable neutral without salt good results with some high-reactivity dyes (dichlorotriazine and difluoropyrimidine) but not with some other types (monochlorotriazine and dichloroquinoxaline). Washing fastness very good but light fastness lower... 

Typical examples of dyes belonging to this group are dichlorotriazine, dichloro-quinoxaline, difluoropyrimidine and vinylsulphone dyes. 

Silk can be readily dyed with conventional high-reactivity dyes of the dichlorotriazine, dichloroquinoxaline or difluoropyrimidine classes. Exhaust dyeing at 60-70 °C and pH 5-6 gives satisfactory results, especially if a mildly alkaline aftertreatment is given to enhance fixation. Dichlorotriazine dyes can also be applied by pad-batch dyeing with bicarbonate and a batching time of 4-6 hours. The relatively low reactivity of aminochlorotriazine dyes, however, results in moderate to poor build-up on silk. Tertiary amine catalysts such as DABCO (7.66) can be used to accelerate the dye-fibre reaction and increase the fixation substantially [116], but it is difficult to achieve satisfactory compatibility in mixture dyeings by this method (section 7.4.2). 

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