Molecule structure of Congo red (CAS NO.573-58-0):

IUPAC Name: Disodium 4-amino-3-[4-[4-(1-amino-4-sulfonatonaphthalen-2-yl)diazenylphenyl]phenyl]diazenylnaphthalene-1-sulfonate 
Molecular Weight: 696.66322 g/mol
Molecular Formula: C₃₂H₂₂N₆Na₂O₆S₂ 
Density: 0.995 g/mL at 25 °C
Melting Point: >360 °C(lit.)
Storage Temp.: flammables area
Water Solubility: soluble
H-Bond Donor: 2
H-Bond Acceptor: 12
Rotatable Bond Count: 5
Tautomer Count: 3
Exact Mass: 696.083763
MonoIsotopic Mass: 696.083763
Topological Polar Surface Area: 216
Heavy Atom Count: 48
Complexity: 1180
Canonical SMILES: C1=CC=C2C(=C1)C(=CC(=C2N)N=NC3=CC=C(C=C3)C4=CC=C(C=C4)N=NC5=CC6=CC=CC=C6C(=C5)S(=O)(=O)[O-])N)S(=O)(=O)[O-].[Na+].[Na+]
InChI: 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
InChIKey: IQFVPQOLBLOTPF-UHFFFAOYSA-L
EINECS: 209-358-4
Product Categories: Dyes and Pigments; Organics; Analytical Chemistry; Indicator (pH); pH Indicators

In 1883, Congo red was first synthesized by Paul Bottiger who was working then for the Friedrich Bayer Company in Elberfeld, Germany. He was looking for textile dyes that did not require a mordant step. The company was not interested in this bright red color, so he filed the patent under his name and sold it to the AGFA company of Berlin. AGFA marketed the dye under the name "Congo red", a catchy name in Germany at the time of the 1884 Berlin West Africa Conference, an important event in the Colonisation of Africa. The dye was a major commercial success for AGFA. In the following years, for the same reasons, other dyes were marketed using the "Congo" name: Congo rubine, Congo corinth, brilliant Congo, Congo orange, Congo brown, and Congo blue.

 Congo red (CAS NO.573-58-0) is mainly used to produce cotton, hemp, silk and other textile dyeing and paper. It is also serves as a pH indicator agent, pH 3.0 (blue-violet)-5.0 (red). And Congo red is also used as an analytical reagent for biological staining.

Reported in EPA TSCA Inventory.

Hazard Codes: T, Xi
Risk Statements: 45-63-36 
R45:May cause cancer. 
R63:Possible risk of harm to the unborn child. 
R36:Irritating to eyes.
Safety Statements: 53-45-37/39-26 
S53:Avoid exposure - obtain special instructions before use. 
S45:In case of accident or if you feel unwell, seek medical advice immediately (show the label whenever possible.) 
S37/39:Wear suitable gloves and eye/face protection. 
S26: In case of contact with eyes, rinse immediately with plenty of water and seek medical advice.
RIDADR: 2811
WGK Germany: 3
RTECS: QK1400000
Hazardous Substances Data: 573-58-0(Hazardous Substances Data)
Human poison by ingestion with cardiovascular effects. Experimental poison by intravenous route. An experimental teratogen. Experimental reproductive effects. An eye irritant. Mutation data reported. When heated to decomposition it emits very toxic fumes of NO_x, SO_x, and Na₂O.

For occupational chemical analysis use NIOSH: Dyes, 5013.

 Congo red (CAS NO.573-58-0) is also named as 1-Naphthalenesulfonic acid, 3,3'-((1,1'-biphenyl)-4,4'-diylbis(azo))bis(4-amino-, disodium salt ; AI3-63036 ; Atlantic Congo Red ; Atul Congo Red ; Azocard Red Congo ; Benzo Congo Red ; Brasilamina congo 4B ; C.I. 22120 ; C.I. Direct Red 28 ; C.I. Direct Red 28, disodium salt ; CCRIS 2277 ; Cerven kongo ;
Diacotton Congo Red ; Direct Red 28 ; Direct Red C ; Direct Red DC-CF ; Direct Red K ; Hispamin congo 4B ; Mitsui Congo Red ; NSC 56651 ; NSC 7232 ; Natrium-salz der diphenyl-bis-azo-bis-naphthylamin-4-sulfonsaeure ; Natrium-salz der diphenyl-bis-azo-bis-naphthylamin-4-sulfonsaeure [German] ; Peeramine Congo Red ; Red K ; Sodium diphenyldiazo-bis(alpha-naphthylaminesulfonate) ; Solucongo ; Sugai Congo Red ; Tertrodirect Red C ; Trisulfon Congo Red ; UNII-3U05FHG59S ; Vondacel Red CL . Congo red (CAS NO.573-58-0) is brown-red powder. It is soluble in hot water, the solution is yellowish red; soluble in ethanol, solution is orange; very slightly soluble in acetone, almost insoluble in ether.