The C.I. Acid Red 211, with the cas registry number 12239-05-3, has other names as Chromate (1-), bis[4-[4-[(5-chloro-2-hydroxyphenyl)azo]-4, 5-dihydro-3-methyl-5-oxo-1H-pyrazol-1-yl]benzenesulfonamidato(2-)], sodium. This is a kind of dark red well-distributed powder and is soluble in water, with the color in aqueous solution being glow orange. Besides, its products categories are including dye; acidic dye; neutral dye. 

The production method of this chemical is as follows: Firstly, prepare the material of 2-amino-4-chlorophenol and 1-(m-sulfonamidophenyl)-3-methyl-5-pyrazolone; Secondly, diazotize the 2-amino-4-chlorophenol, and then couple with the latter; Thirdly, complex with sodium chromium formate and then go through the process of filtering and drying to get the products.

As to its usage, it is widely applied in many ways. It could be used as the basic dyestuff for light and dark red; It could be used in dyeing of common wool, fined wool and wool top and also in adjusting the colored light for neutral dye and colourful dye; It could also be used in the printing dyeing of wilk, nylon, vinylon, wool, and other blend fabrics; It could then used directly in the same-bath dyeing of neutral dye.