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Direct dyes

Congo red

Also known as Direct red 28, C.I. Direct Red 28, Congazone sodium

CAS 573-58-0Formula C32H22N6Na2O6S2Molar mass 696.68 g/molEC 209-358-4
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Congo red chemical structure, C32H22N6Na2O6S2, CAS 573-58-0
2D chemical structure

Key facts

What buyers check first

All properties
CAS number
573-58-0
Formula
C32H22N6Na2O6S2
Molar mass
696.68 g/mol
EC number
209-358-4
HS code
320414
Category
Direct dyes

What is Congo red?

Plain description, key identifiers and synonyms

Congo Red is an indicator dye that is blue-violet at pH 3.0 and red at pH 5.0. It contains a 3,3'-(biphenyl-4,4'-diyldidiazene-2,1-diyl)bis(4-aminonaphthalene-1-sulfonate). It is functionally related to a 3,3'-(biphenyl-4,4'-diyldidiazene-2,1-diyl)bis(4-aminonaphthalene-1-sulfonic acid).

Identifiers

Registry numbers, names and line notations, tap to copy

IUPAC name
disodium, 4-amino-3-[[4-[4-[(1-amino-4-sulfonatonaphthalen-2-yl)diazenyl]phenyl]phenyl]diazenyl]naphthalene-1-sulfonate
CAS number
573-58-0 CAS number cross-checked
EC number
209-358-4
Molecular formula
C32H22N6Na2O6S2
UNII
3U05FHG59S
MDL number
MFCD00004028
InChIKey
IQFVPQOLBLOTPF-UHFFFAOYSA-L
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
SMILES (canonical and isomeric)
C1=CC=C2C(=C1)C(=CC(=C2N)N=NC3=CC=C(C=C3)C4=CC=C(C=C4)N=NC5=C(C6=CC=CC=C6C(=C5)S(=O)(=O)[O-])N)S(=O)(=O)[O-].[Na+].[Na+]

Synonyms

  • Direct red 28
  • C.I. Direct Red 28
  • Congazone sodium
  • Benzo Congo Red
  • Mitsui Congo Red
  • Cotton Red L
  • Haemomedical
  • Haemonorm
  • Hemorrhagyl
  • Hispamin Congo 4B
  • Solucongo
  • Brasilamina congo 4B
  • Sugai Congo Red
  • Atul Congo Red
  • Vondacel Red CL
  • Kayaku Congo Red
  • Direct Red K
  • Azocard Red Congo
  • Congo Red H
  • Congo Red L
  • Congo Red M
  • Congo Red N
  • Congo Red R
  • Congo Red W
  • Congo Red CR
Show all 39 synonyms
  • Congo Red WS
  • Atlantic Congo Red
  • Cotton Red 4BC
  • Cotton Red 5B
  • Erie Congo 4B
  • Tertrodirect Red C
  • Congo Red 4B
  • Congo Red 4BX
  • Red K
  • Diacotton Congo Red
  • Peeramine Congo Red
  • Trisulfon Congo Red
  • Direct Red DC-CF
  • Direct Red C

Physical and chemical properties

Measured values and descriptors computed from the structure

Physical and chemical properties

Measured values, check the supplier specification for your grade

No measured properties are recorded for this substance yet. Ask suppliers for a technical data sheet.

Values vary by grade. Ask suppliers for the COA or TDS of the batch you buy.

Computed descriptors

Calculated from the structure, useful for screening and formulation

Molecular weight
696.68 g/molcalc.
Exact mass
696.0838 Dacalc.
LogP (octanol/water)
1.47calc.
Topological polar surface area
215.9 Ųcalc.
Hydrogen bond donors
2calc.
Hydrogen bond acceptors
12calc.
Rotatable bonds
7calc.
Heavy atoms
48calc.
Rings
6calc.
Aromatic rings
6calc.
Fraction sp3 carbons
0calc.
Formal charge
0calc.
Stereocentres
0calc.
Components
3calc.
Lipinski rule of five
Fails (2 violations)calc.

Calculated for screening. Confirm critical figures with the supplier.

Murcko scaffold

The ring system that remains when every side chain is removed

Murcko scaffold of this chemical, c1ccc2cc(N=Nc3ccc(-c4ccc(N=Nc5ccc6ccccc6c5)cc4)cc3)ccc2c1

c1ccc2cc(N=Nc3ccc(-c4ccc(N=Nc5ccc6ccccc6c5)cc4)cc3)ccc2c1

6 rings, 36 atoms.

154 other chemicals share this scaffold

Safety and hazards

GHS classification summary, not a safety data sheet

No GHS hazard classification is recorded for this substance yet. That does not mean it is harmless.

GHS classification summary, not a safety data sheet (SDS). Classifications can differ by supplier, grade and concentration. Always check the supplier's SDS.

Congo red suppliers

Sponsored listings first, then the documented ranking: membership, verification, replies, completeness, freshness and ratings

All 42 suppliers
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Where suppliers are based

42 suppliers in 9 countries

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Congo red price

Indicative price range per kg from live supplier offers

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Uses and applications

What the substance is used for, by industry and function

Industries and functions

Regulatory status

Inventories, regulations and trade controls that list this substance

Health and food

  • EU Cosmetics Regulation Annex II, prohibited in cosmetics
    Name: Disodium 3,3'-[[1,1'-biphenyl]-4,4'-diylbis(azo)] bis(4-aminonaphthalene-1- sulphonate), Ref no: 986, Annex ref: II/986

United States

  • TSCA inventory (USA)
    Status: Active in US commerce, Regulatory flags: Significant new use rule

HS code and trade data

Customs classification and reported world trade statistics

Global trade

World import and export statistics for the HS code Congo red is traded under.

HS 3204.14Indicative HS code

Direct dyes and preparations based thereon

World exports in 2024
$328M
−1.5% vs 2023, imports $336M
2019 to 2024
Top exporters
  1. India * partner reported34.9%
  2. China11.3%
  3. Spain9.0%
Top importers
  1. Italy9.8%
  2. Germany8.7%
  3. Netherlands7.8%

* Partner reported figures, a lower bound.

Reported customs values in USD, not prices.Full trade data

The HS code shown for Congo red is indicative (it is known at chapter level only). Confirm the classification with your customs broker before shipping.

Frequently asked questions

Quick answers about Congo red, based on the data on this page

What is Congo red?

Congo Red is an indicator dye that is blue-violet at pH 3.0 and red at pH 5.0. It contains a 3,3'-(biphenyl-4,4'-diyldidiazene-2,1-diyl)bis(4-aminonaphthalene-1-sulfonate). It is functionally related to a 3,3'-(biphenyl-4,4'-diyldidiazene-2,1-diyl)bis(4-aminonaphthalene-1-sulfonic acid).

What is the CAS number of Congo red?

The CAS registry number of Congo red is 573-58-0.

What is the molecular formula and weight of Congo red?

The molecular formula of Congo red is C32H22N6Na2O6S2 and its molar mass is 696.68 g/mol.

What is Congo red used for?

Known uses and roles of Congo red include textile dyes in textiles and leather.

Is Congo red hazardous?

No GHS hazard classification for Congo red is recorded on CompoundList yet. That does not prove it is safe. Always read the supplier safety data sheet.

What is the HS code of Congo red?

Congo red is usually classified under HS code 320414 (Direct dyes and preparations based thereon). This is indicative, confirm it with your customs broker before shipping.

Where can I buy Congo red?

CompoundList lists 42 suppliers of Congo red in United States, China, India, Hong Kong and 5 more. Send one free request to get and compare quotes. Your contact details stay private until you accept a quote.

Where can I buy Congo red in India?

9 suppliers in India list Congo red on CompoundList. Filter the suppliers list by country and send a request to compare prices, grades and delivery times.

What is the price of Congo red?

Suppliers quote Congo red on request because prices depend on grade, purity, quantity and destination. A free request on CompoundList gets you several quotes to compare.

Guides for buyers

Practical guides that help when you source, ship or handle Congo red

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Data last updated 7 Oct 2026. Details may have changed, please confirm them with the supplier. Report an error on this page
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