2498. Congo Red

Nomenclature

CAS number: 573-58-0
3,3′-[[1,1′-Biphenyl]-4,4′-diylbis(2,1-diazenediyl)]bis[4-amino-1-naphthalenesulfonic acid] sodium salt (1:2); C.I. Direct Red 28; 3,3′-[[1,1′-biphenyl]-4,4′-diylbis(azo)]bis[4-amino-1-naphthalenesulfonic acid] disodium salt; sodium diphenyldiazo-bis-α-naphthylaminesulfonate; C.I. 22120.
C32H22N6Na2O6S2; mol wt 696.66.
C 55.17%, H 3.18%, N 12.06%, Na 6.60%, O 13.78%, S 9.21%.

Description and references

Prepn: B"ottiger, DRP 28753 (1884); Frdl. 1, 470; Whitehead, Chem. Trade J. 77, 386 (1925); Kline, J. Chem. Educ. 15, 129 (1938). Purification: Bedaux et al., Pharm. Weekbl. 98, 189 (1963) PubMed. See also Colour Index vol. 4 (3rd ed., 1971) p 4166; H. J. Conn's Biological Stains, R. W. Horobin, J. A. Kiernan, Eds. (BIOS Scientific, Oxford, 10th ed., 2002) 132-134. Toxicity: Richardson, Dillon, Am. J. Med. Sci. 198, 73 (1939). Clinical evaluation as diagnostic aid: E. Ouchi et al., Tohoku J. Exp. Med. 118, Suppl., 191 (1976) PubMed. Use in combination with Sirius red as histological stain: I. R. Hinds, Lab. Med. 16, 366 (1985).

Chemical structure

Properties

Brownish-red powder. Absorption max (pH 7.3): 488 nm (E1%1cm 595). Sol in water (yellowish-red) and in ethanol (orange); very slightly sol in acetone. Practically insol in ether. LD50 i.v. in rats: 190 mg/kg (Richardson, Dillon).

Derivative

Congo Red Paper.

Nomenclature

Riegel's paper; Herzberg's paper.

Properties

Paper charged with a 0.1% aq soln of Congo Red.

Use

As indicator, usually in 0.1% aq soln for estimating free mineral acids, particularly in presence of organic acids. pH: 3.0 blue-violet, 5.0 red. Detecting and estimating free HCl in gastric contents; detecting acidity of papers. Reagent for bitter-almond water. Dye. As addition to culture media. Biological stain for cytoplasm, elastic fibers, axons, embryonic material, amyloid, cellulose, etc.

Therapeutic Category

Diagnostic aid (amyloidosis).

Keywords

Diagnostic Aid