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.The structure formula is incomplete because the complete composition and the structure of Sulpher dye is not known.

Chemical Nature of Sulpher Dye

 The manufacturing method of Sulpher dye may be shown as below:

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

The reaction is carried in a closed vessel in the presence or absence of solvents. For this (Thionation/Sulphorization) 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 dye are marketed in the forms of powder, paste or liquid solutions. The dye are amorphous colloidal materials of high molecular weight and variable composition. Their exact chemical composition is not yet published. However, they are complex in structure. Some amorphous present Sulpher dyes are as below:

 

Chemistry of dyeing with Sulpher dye

Sulpher dyes contain sulpher linkages within their molecules. They are insoluble in water but they can be made water soluble in water by treating them with reducing agents. This also makes them substantive towards cellulosic fibers. Na2S acts as reducing agents that break the sulpher linkages and break down the longer molecules into simple components which can penetrate the material surface easily.

                               Dye - S - S – Dye + 2[H] = Dye – SH + SH – Dye
                                   [Water insoluble]                  [Water soluble]

The thiols contain the –SH groups which are readily oxidized in the fiber to the original insoluble sulpher by oxidizing agent and gives a color with very good wet fastness property.

                              Dye – SH + SH – Dye + 2[o] = Dye - S - S – Dye + H2O
                                        [Water soluble]                        [Water insoluble]

Sulpher dyes are negatively ionized. No vander waals force effects on them. Addition of slat improves efficiency of dyeing by increasing physical force.