Chemical Structure of Sulpher Dye | Chemical Nature of Sulpher Dyes | Chemistry of Dyeing with Sulpher Dye

Chemical Structure of Sulpher Dye :

Sulpher dye contain Sulpher atom in their molecule and is characterized by the thiozine ring.
Chemical Structure of Sulpher Dye

The structure formula is incomplete because the complete composition and structure of Sulpher dye is mot known.
 
Chemical Nature of Sulpher Dyes

The manufacturing method of Sulpher dyes may be shown as below:-

Thionation Sulphorization
Aromatic Hydro Carbon Containing Hydroxy amino or nitro group  =  Sulpher Dye

This reaction is carried outb in a closed vessel in the presence or absence of solvents. For this (Thionisation/Sulphorisation) purpose Sulpher or Na- polysulphide is used. The features of the products of thionation are controlled by organic compounds, conditions of reaction (time, temp etc). Condition of separating dyes from reaction mixture etc.

After the reaction is over the dye is precipitated acidification or oxidation or both. Generally Sulpher dyes are marketed in forms of powder pastes or liquid solutions. The dyes are amorphous colloidal materials of high molecular weight and variable composition. Their exact chemical composition is not yet established. However they are complex in structure. Some amorphous present in Sulpher dyes are as below:
Chemistry of dyeing with Sulpher Dye:

The Sulpher dyes contain Sulpher linkage within their molecules. They are insoluble in water but can be made soluble in water by treating them with reducing agents. This also makes them substantive towards cellulosic fibres. Na2S acts as reducing agent that breaks the Sulpher linkage and break down the longer molecules in to simple components which can penetrate the material (fiber/fabric) surface easily.
Dye-S-S-Dye +2[H] = Dye- SH + HS-Dye

This thios containing the –SH groups are readily oxidized by the action of atmospheric O2 or any other oxidizing agents. This reconverts the water soluble luco form of Sulpher dye in to previous water insoluble form which has a very good wash fastness property.
Dye- SH + HS-Dye +[O] = Dye-S-S-Dye +H2O

Sulpher dyes are negatively ionized. No Vander wall’s force effect on them is activated. Addition of salt improves efficiency of dyeing by increasing physical force.

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