CAS number：573-58-0
molecular formula：C32H22N6Na2O6S2
molecular weight：696.66
EINECS number：209-358-4

English synonyms

3,3'-[(1,1'-BIPHENYL)-4,4'-DIYLBIS(AZO)]BIS(4-AMINO-1-NAPHTHALENESULFONIC ACID) 2NA;S NO 360;CONGO RED (CERT);Congo Red (0.1% in Water) [for pH Determination];3,3'-[(Biphenyl-4,4'-diyl)bisazo]bis(4-amino-1-naphthalenesulfonic acid sodium) salt;3,3'-[[1,1'-Biphenyl]-4,4'-diylbis(azo)]bis[4-amino-1-naphthalenesulfonic acid sodium] salt;Congo Ared 4b;Congo Red K

Related categories

Food and Beverage Standards; Pigments and Dyes; Analytical Standards; Pigments; Titration; Other Biochemical Reagents; Various Chemical Reagents; Professional Reagents; Corrosive and Alkaline Reagents; Biochemical Reagents; Dyes and Pigments;Organics;Analytical Chemistry; Indicator (pH);pH Indicators;Azo;Biochemical Reagents-Pigments;Analytical Reagents-Color Developers;Industrial Dyes-Direct Dyes;Materials;Indicators;Dye Intermediates;Organic Chemical Materials;Organic Reagents;Chemical Materials-Dye. Pigment intermediates; chemical raw materials; general biochemical reagents - biological dyes and chemical indicators; industrialization; dyes

Introduction

Congo red (English Congo red) is an acid dye, in the form of purplish red powder, soluble in water and alcohol, and blue in the presence of acid. It can be used as a dye and also as an indicator. It is often used as a backing agent for hematoxylin or other cell dyes in plant preparations. When used to stain cytoplasm, it can stain gelatin or cellulose red. In animal tissue preparations, it is used to stain nerve shafts, elastic fibers, embryonic materials, etc. In addition, Congo red can be used for double dyeing with hematoxylin, and can also be used for starch-like dyeing. Because it is soluble in water and alcohol, washing and dehydration should be done quickly.

Chemical properties

Brown-red powder, easily soluble in hot water, dissolved in 10 parts of cold water, the solution is yellow-red; soluble in ethanol, orange; very slightly soluble in acetone, almost insoluble in ether. Soluble in ethanol, it is orange, slightly soluble in acetone. It turns dark blue in concentrated sulfuric acid, and it turns light blue after dilution with blue-point precipitation. Its aqueous solution is added with concentrated hydrochloric acid to form a bright blue precipitate; the addition of acetic acid produces a blue precipitate that turns from blue to reddish purple. Insoluble in concentrated caustic soda. Sensitive to acids and salts, even if it absorbs carbon dioxide from the air, it will make the color darker, but it can be restored to the original color when treated with dilute soda ash. 

Use

●  It has been widely used in the dyeing of cotton and viscose, because it is easy to turn into blue when encountering acid, and there is no appropriate treatment method to improve its wet fastness. Therefore, since the advent of insoluble azo dyes and direct acid-resistant red 4BS The use of this product in dyeing is decreasing, but it is used in a large amount in the paper industry. It can also be used as an acid-base indicator, namely Congo red test paper, pH3.0 (blue-violet)-5.0 (red). Also used for biological staining, analytical reagents.

●  Mainly used for dyeing cotton, linen, silk and other textile and paper products, and can also be used as an indicator

●  It is a commonly used indicator in the laboratory, and it is also a kind of carcinogenic disperse dye for standard detection.

●  Used as acid-base indicator, adsorption indicator and biological dye, etc.

●  Acid-base indicator, pH 3.0 (blue-violet) ~ 5.0 (red); detection of hydrochloric acid and paper acidity in gastric juice; detection of boric acid and cyanide; additives for biological culture medium; biological staining, such as embryo slices, plant mucins, fibers pigment, elastic tissue, etc.

●  Acid-base indicator [pH3.0 (blue-violet)-5.0 (red)], adsorption indicator, protein precipitation, detection of free hydrochloric acid in gastric juice, staining of embryo slices, plant mucin, cellulose, elastic tissue, etc., determination of boric acid , cyanide and hydrochloric acid.

Production method

●  After diazotization of aniline, it is coupled with sodium 1,4-aminonaphthalene sulfonate, and then it is prepared by salting out, filtering and drying. The specific operation is as follows: Dissolve 48.4g of benzidine in 300ml of hydrochloric acid (containing 20ml of concentrated hydrochloric acid), add ice-cooling to below 5°C, add 30ml of concentrated hydrochloric acid, and then add 14.4g of sodium nitrite. 10% aqueous solution. After the diazotization is over, slowly add the diazonium salt solution to the solution prepared by 150g of sodium p-aminonaphthalene sulfonate and a small amount of water. After standing for half an hour, slowly add 35g of sodium carbonate under full stirring to make the solution alkaline. After heating to about 80 ℃, cooling, filtering, washing with saturated brine, and drying to obtain the finished product. Consumption of raw materials for industrial preparation (kg/t) benzidine (100%) 200 sodium naphthalene sulfonate (100%) 520 sodium nitrite (industrial) 160 hydrochloric acid (31%) 330 soda ash (industrial) 340 refined salt 2500 Taikoo oil 9 ethanol 60 sodium acetate 35 yuan Ming powder 50