SULPHUR DYES
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These dyes are generally produced by sulphurisation or thionation of aromatic hydrocarbons containing hydroxy, nitro and/ or amino groups. The reaction is carried out in closed vessels in the presence or absence of solvents. For carrying out sulphurisation sulphur or polysulphide is used. The different methods employed include sulphur bake, sodium, polysulphide bake, sodium polysulphide melt in aqueous or solvent medium. The properties of the products of sulphurisation are controlled by the intermediates selected, the conditions of reaction (time temperature etc.) and the conditions of isolation of the dye from the reaction mixture. In one method, after the reaction is over, the dye is precipitated by after the reaction is over, the dye is precipitated by acidification or by oxidation or by both. Sulphur dyes are marketed in the form of dry standardised powders.
