| 摘要 |
Azo dyestuffs contng. three different negative substituents such as nitro, nitrile or sulphonyl groups can only be obtd. directly with difficulty. A method of preparing such dyes is to react, pref. in the presence of cuprous cpds., a mono or bis azo dyestuff having halogen atoms bound to aryl or heterocyclic rings with alkali or alkali earth nitrites in an inert solvent. One equivalent of nitrite is used per reactable halogen group. Suitable solvents are dimethyl formamide, dimethyl sulphoxide, N-methyl pyrrolidone and suitable catalysts are cuprous halides or cuprous oxide. The products have superior light and thermal fixing fastness compared to the unreacted dyestuff and are esp. suitable for dyeing or printing polyethylene terephthalate fibres. |
