C6767 Sigma-Aldrich

Congo Red

Dye content ≥35 %

Synonym: Congo Red 4B, Cosmos Red, Cotton Red B, Cotton Red C, Direct Red 28, Direct Red R, Direct Red Y

  • CAS Number 573-58-0

  • Empirical Formula (Hill Notation) C32H22N6Na2O6S2

  • Molecular Weight 696.66

  •  Colour Index Number 22120

  •  Beilstein/REAXYS Number 3894858

  •  EC Number 209-358-4

  •  MDL number MFCD00004028

  •  PubChem Substance ID 24892892

  •  NACRES NA.47



Related Categories Analytical Reagents, Analytical/Chromatography, C, Cell Biology, Hematology and Histology,
Quality Level   200
form   powder
composition   Dye content, ≥35%
application(s)   hematology: suitable
  histology: suitable
  titration: suitable
pH   6.7 (10 g/L)
mp   >360 °C (lit.)
solubility   H2O: 1 mg/mL
Featured Industry   Diagnostic Assay Manufacturing
storage temp.   room temp
SMILES string   [Na+].[Na+].Nc1c(cc(c2ccccc12)S([O-])(=O)=O)\N=N\c3ccc(cc3)-c4ccc(cc4)\N=N\c5cc(c6ccccc6c5N)S([O-])(=O)=O
InChI   1S/C32H24N6O6S2.2Na/c33-31-25-7-3-1-5-23(25)29(45(39,40)41)17-27(31)37-35-21-13-9-19(10-14-21)20-11-15-22(16-12-20)36-38-28-18-30(46(42,43)44)24-6-2-4-8-26(24)32(28)34;;/h1-18H,33-34H2,(H,39,40,41)(H,42,43,44);;/q;2*+1/p-2/b37-35+,38-36+;;



• Congo red has been used as a histochemical stain for the quantification of amyloid deposits in brain tissues.
• It has been used as a cell wall inhibiting agent in fungus Cryptococcus neoformans.
• It has also been used to study microstructural details in the cell walls of raw potato and fried potato using confocal microscopy.


25, 100 g in poly bottle

Biochem/physiol Actions

Congo red is a benzidine-based anionic diazo dye. It is a histological dye which binds to many amyloid proteins and is used for the quantification of amyloid β-peptide aggregation. Congo red also interacts with β-D-glucans, polysaccharides containing continuous β-(1→4)-linked D-glucopyranosyl units and some hemicellulosic galactoglucomannans.

Safety & Documentation

Safety Information

GHS08  GHS08
Signal word 
Hazard statements 
Precautionary statements 
NONH for all modes of transport
WGK Germany 
Flash Point(F) 
Not applicable
Flash Point(C) 
Not applicable


Certificate of Analysis (COA)

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Certificate of Origin (COO)

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Frequently Asked Questions

Which document(s) contains shelf-life or expiration date information for a given product?
If available for a given product, the recommended re-test date or the expiration date can be found on the Certificate of Analysis.
How do I get lot-specific information or a Certificate of Analysis?
The lot specific COA document can be found by entering the lot number above under the "Documents" section.
How do I find price and availability?
There are several ways to find pricing and availability for our products. Once you log onto our website, you will find the price and availability displayed on the product detail page. You can contact any of our Customer Sales and Service offices to receive a quote. USA customers: 1-800-325-3010 or view local office numbers.
What is the Department of Transportation shipping information for this product?
Transportation information can be found in Section 14 of the product's (M)SDS.To access the shipping information for this material, use the link on the product detail page for the product.
Why does the SDS for Congo Red list carcinogen as an OSHA hazard, (Section 2) but in Section 11 on carcinogenicity, it states that there is no component identified as a carcinogen?
The reason that there is not an OSHA listing for carcinogens on most of SDS that have a hazard of a carcinogen hazard is because that section of the SDS is specifically for the OSHA regulated carcinogens, also referred to as the OSHA 13.Congo red at this time is not specifically called out as a carcinogen by the other 3 Organizations listed (IARC, NTP, ACGIH) either.Congo red is listed by the European Classification Labeling & Packaging (CLP) Regulation (which is a pretty definitive guide for hazard classification), as a carcinogen. No other organizations have had the time to classify this material at this time. This is why it is only listed as a carcinogen in section 2 and in section 15.
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