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Product FOB Price Min.Order Supply Ability Supplier
Direct Red 28
Cas No: 573-58-0
USD $ 3.0-3.0 / Kilogram 1 Kilogram 1-100 Metric Ton/Month Hangzhou Dayangchem Co., Ltd. Contact Supplier
High quality Direct Red 28 120%  supplier in China
Cas No: 573-58-0
No Data No Data No Data Simagchem Corporation Contact Supplier
Direct red 28 (C.I. 22120)
Cas No: 573-58-0
No Data No Data No Data Chemwill Asia Co., Ltd. Contact Supplier
Congo red
Cas No: 573-58-0
No Data No Data Metric Ton/Day Chengdu Yanxi Import & Export Trading CO.,LTD Contact Supplier
Direct Red 28
Cas No: 573-58-0
USD $ 1.0-1.5 / Gram 1 Gram 1-100 Metric Ton/Month Baowei Technology Qinhuangdao Co., Ltd Contact Supplier
Congo Red
Cas No: 573-58-0
No Data 10 Gram Metric Ton/Day Jilin Tely Imp.& Exp.Co., Ltd. Contact Supplier
Congo red manufacturer
Cas No: 573-58-0
No Data No Data No Data Shaanxi Mingqi Chemical Co., Ltd Contact Supplier
Direct Red 28
Cas No: 573-58-0
USD $ 10.0-10.0 / Gram 1 Gram 10000 Kilogram/Day Zhejiang J&C Biological Technology Co.,Limited Contact Supplier
Direct Red 28
Cas No: 573-58-0
No Data 1 Kilogram 1-100 Kilogram/Month Afine Chemicals Limited Contact Supplier
Direct Red 28
Cas No: 573-58-0
No Data 1 Kilogram 1000 Metric Ton/Month Tangshan Moneide Trading Co., Ltd. Contact Supplier

573-58-0 Usage


1. It has been widely used in cotton, viscose dyeing. Because it can easily be transformed into blue when in acid, while there is no appropriate treatment to improve, the usage amount is gradually decreased since the advent of insoluble azo dyes and acid-resistant red 4BS, however, the amount used in the paper industry is quite large. It can also be used as indicators of acid-base, namely Congo red test paper. The measurable range pH is 3.0 (blue)-5.0 (red). It is also used for biological staining, analysis reagents.
2. An indicator frequently used in lab as well as a carcinogenic disperse dyes; used to standard test.
3. Used as an acid-base indicator, adsorption indicator and biological stain, etc.
4. Acid-base indicator, pH 3.0 (blue violet)~5.0 (red); detect the acidity of paper and hydrochloric acid in the gastric juice; test boric acid, cyanide; biological media additives; biological staining, such as embryo slices, plant mucin, cellulose, elastic tissue dyeing.
5. Mainly used for dyeing cotton, hemp, silk and other textile and paper products; it can also be used as an indicator.

Chemical Properties

brown-red powder


ChEBI: An indicator dye that is blue-violet at pH 3.0 and red at pH 5.0.

Purification Methods

Crystallise the dye from aqueous EtOH (1:3). Dry it in air. [Beilstein 6 I 342.]

Artificial dyes

Congo red is aniline dye or coal tar dyes, and it has many types with very wide application. Its drawback is easy to fade by sunlight; aniline blue, bright green, methyl green are more easily fade. Be careful to handle the pH, and avoid direct sunlight when flaking, thus it will keep a few years without fading.
Congo red is an acid dye, a purplish red powder. It is soluble in water and alcohol, turning blue when in acid. It can be used as a dye as well as an indicator. In the production of plant slide, it is often used as a liner agent for hematoxylin or other cell dyes. When used in cytoplasm dyes, it can dye the cytosol or fibrin red. In the process of tissue slicing, it is used to dye nerve axis, elastic fibers, embryonic materials, etc. In addition, Congo red can be used for double staining with hematoxylin; it can also be used for amyloid staining. For it is soluble in water and alcohol, so washing and dehydration treatment should be quick.

Chemical properties

Congo red is red-brown powder, soluble in hot water and the cold water 10 times of its weight; the color of the solution is yellow-red; soluble in ethanol and the solution is orange; slightly soluble in acetone, while almost insoluble in ether. The solution is dark blue when in sulfuric acid, turning to light blue accompanied with the appearance of blue precipitate when diluted.
Its aqueous solution will form a blue floc when in concentrated hydrochloric acid. When added with acetic acid, the precipitate turned blue with a little purple to a precipitate with some red color.  It is insoluble in the concentration of caustic soda solution; susceptible to acid and salt which means even if its absorption of carbon dioxide from the air will make the color blue and dark, while dilute soda solution can restore the original color.
Information on the chemical properties, uses and production methods of artificial dyes Congo Red is compiled and edited by Chemcialbook.

Production methods

It is obtained by the coupling with  sodium naphthionate after the diazotization with benzidine, and then by salting out, filtration and drying in the system. The details are as follows: add 48.4 benzidine into 300ml of hydrochloric acid take 48.4g benzidine dissolved in 300ml hydrochloric acid (including 20ml of concentrated hydrochloric acid 20ml), add ice into the solution until the temperature is below 5 ℃; add 10% aqueous solutions prepared by 14.4g sodium nitrite after adding 30ml of concentrated hydrochloric acid.Add the diazonium salt solution slowly into the solution prepared by 150g sodium naphthionate and a little water after diazotization. Add 35g sodium carbonate slowly under the sufficient mixing after 30 minutes' standing, thus appearing an alkaline solution. Heating to 80℃, cooling, filtering, washing with saturated brine and drying can obtain the product. The materials consumption (kg/t) in industrial production are as follows: benzidine (100%) 200, sodium naphthionate (100%) 520, sodium nitrite (industry) 160, hydrochloric acid (31%) 330, soda ash (industrial) 340, fine salt 2500, turkey red oil 9, ethanol 60, sodium acetate 35, sodium sulfate 50.

573-58-0 Well-known Company Product Price

Brand (Code)Product description CAS number Packaging Price Detail
Sigma (C6767)  CongoRed  Dye content ≥35 % 573-58-0 C6767-100G 538.20CNY Detail
Sigma (C6767)  CongoRed  Dye content ≥35 % 573-58-0 C6767-25G 197.73CNY Detail
Sigma-Aldrich (75768)  CongoRed  analytical standard 573-58-0 75768-25MG 845.91CNY Detail
Alfa Aesar (B24310)  Congo Red, indicator grade    573-58-0 500g 1245.0CNY Detail
Alfa Aesar (B24310)  Congo Red, indicator grade    573-58-0 100g 350.0CNY Detail
Alfa Aesar (B24310)  Congo Red, indicator grade    573-58-0 25g 200.0CNY Detail
Alfa Aesar (44566)  Congo Red, Dye content ≈80%    573-58-0 5g 353.0CNY Detail
TCI America (C0550)  Congo Red  >98.0%(HPLC) 573-58-0 25g 450.00CNY Detail



According to Globally Harmonized System of Classification and Labelling of Chemicals (GHS) - Sixth revised edition

Version: 1.0

Creation Date: Aug 12, 2017

Revision Date: Aug 12, 2017


1.1 GHS Product identifier

Product name Congo Red

1.2 Other means of identification

Product number -
Other names disodium 4-amino-3-[4-[4-(1-amino-4-sulfonato-naphthalen-2-yl)diazenylphenyl]phenyl]diazenyl-naphthalene-1-sulfonate

1.3 Recommended use of the chemical and restrictions on use

Identified uses For industry use only.
Uses advised against no data available

1.4 Supplier's details

1.5 Emergency phone number

Emergency phone number -
Service hours Monday to Friday, 9am-5pm (Standard time zone: UTC/GMT +8 hours).

More Details:573-58-0 SDS

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