Megavat range of vat dyes are derived from anthraquinone. they are applied on cellulosic fibres to achieve overall high fastness. these products are marketed in the following physical forms.
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High conc.
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Powder
- Micro disperse
They are insoluble in water. however, when they are applied on cellulosic fibre they are converted into soluble "leuco" form by addition of sodium hydrosulphite in the presence of sodium hydroxide. here, sodium hydrosulphite is acting as reducing agent. insoluble form of dyestuff is regenerated by oxidation at the end of dyeing process.
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