Sulfur Black

Sulfur Black, also known as Sulfur Black T or Sulfur Navy Blue, is a commonly used sulfur dye. Its CAS number is 1326-82-5, chemical formula is C_6H_4N_2O_5, and molecular weight is 184.106. It usually appears as black scaly solid or uniform black powder. It is insoluble in water and ethanol, but soluble in sodium sulfide solution to form a dark green color. In hydrochloric acid, it turns into a greenish-black precipitate; in sodium hydroxide solution, it shows a blue color; in concentrated sulfuric acid, it is slightly soluble when cold, turns into a dark greenish-blue precipitate when heated, and further heating converts it into black-blue, which will produce a greenish-blue precipitate upon dilution.

The production process of Sulfur Black involves hydrolyzing 2,4-dinitrochlorobenzene into sodium 2,4-dinitrophenoxide, followed by sulfuration with sodium polysulfide and oxidation in air. It is mainly used for dyeing cotton textiles, and also applicable to hemp, viscose fiber and their fabrics, as well as leather and paper dyeing. It is suitable for dip dyeing, jig dyeing and pad dyeing processes, and can also be used for dyeing vinylon.

It should be noted that Sulfur Black contains unstable disulfide bonds and polysulfide bonds in its structure. Improper post-dyeing treatment may cause oxidation in the air to generate sulfuric acid, leading to fiber embrittlement. Therefore, full water washing after dyeing is required, and anti-embrittlement treatment with urea, soda ash and other agents should be carried out.