Solubilised Vat dyes
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Solubilised Vat dyes:-
As metioned earlier, these dyes are derived from vat dyes or their intermediates in which the two keto groups in the quinonoid systems —CO—CH=CH—CO— or similar systems —CO—(CH=CH)n —CO— as explained under vat dyes are convgerted to stable leuco sulphuric esters such as —C(OSO3Na) =CH —CH=C)OSO3Na). The synthesis of solubilised vat dyes from the corresponding vat dye or a vat dye intermediate is carried out by the treatment with sulphur trioxide in anhydrous pyridine containing a metal such as copper, iron or zinc, and subsequently converting it into the sodium salt of the leuco sulphuric ester. The solubilised vat dye is applied on cotton and the parent vat dye is regenerated on cotton by using an acid oxidising agent such as nitrous acid. For example, Indigosol Golden Yellow IGK is prepared from Indanthrene Golden Yellow GK, the indigosol is applied on cotton and then oxidised on cotton to the parent dye.
