Page 420 - Basic Principles of Textile Coloration

OTHER TYPES OF INGRAIN DYE 409

19.5.2 Other ingrain dyes
Condensation dyes are usually organic thiosulphate derivatives, absorbed by
cotton fibres and subsequently insolubilised by treatment with an alkaline solution
of sodium sulphide. The reactions involved are illustrated in Scheme 19.2.

2Dye S SO3– + S2– Dye S S S Dye + 2SO32–

Dye S S S Dye + SO32– Dye S S Dye + S2O32–
Dye SO3– + S2– or

Dye S– + S2O32–

2Dye S– + O2 + 2H+ Dye S S Dye + H2O2

Scheme 19.2

The former Alcian dyes (ICI) were water-soluble isothiourea derivatives of
copper phthalocyanine bearing chloromethyl substituents. They dyed cotton
directly and aftertreatment with an alkaline solution precipitated the final
insoluble pigment (Scheme 19.3).

NR2 NR2
CP CH2 Cl + S C CP CH2 S C + Cl–

NR2 NR2

NR2 NR2
CP CH2 S C + HO– CP CH2 OH + S C

NR2 NR2

CP = copper phthalocyanine

Scheme 19.3

The phthalogen dyes are precursors of copper phthalocyanine, which is
generated in the fibre by a complex chemical reaction (Figure 19.5). For example,
impregnation of cotton with di-imino-isoindoline in the presence of a special