Eriochrome Black T

Chemical properties

black powder

The Uses of Eriochrome Black T

Eriochrome black T is used as an indicator in analytical chemistry. It is also used in the detection of rare earth metals. It finds application in dyeing and printing of wool fabric, dyeing of silk and nylon as well as in leather dyeing. It can be used in the spectrophotometric determination of diphenhydramine hydrochloride in pharmaceutical preparations. As a complexometric indicator, it is useful in the determination of hardness of water.

The Uses of Eriochrome Black T

Eriochrome black T has been used to determine the concentration of Ca²⁺ using complexometric titration method.

Preparation

4-Amino-3-hydroxy-7-nitronaphthalene-1-sulfonic acid diazotization, and Naphthalen-1-ol?coupling.

General Description

Eriochrome black T is used as an indicator for complexometric titrations. It functions as an acid-base indicator. Eriochrome^? Black T forms complex with Ca²⁺ and Mg²⁺, but it binds more strongly to Mg²⁺ ions.

Color change

The indicator Eriochrome Black T is bright blue in the absence of alkaline earths, but with them forms a deep-red complex that has a higher ionization constant than that of the Na2EDTA complex. Hence, with Eriochrome Black T as an indicator, the alkaline earth can be titrated with Na2EDTA.

Hazards

Eriochrome Black T causes serious eye irritation, it is Toxic to aquatic life with long lasting effects.

Purification Methods

The sodium salt (200g) is converted to the free acid by stirring with 500mL of 1.5M HCl, and, after several minutes, the slurry is filtered on a sintered-glass funnel. The process is repeated and the material is air dried after washing with acid. It is then extracted with *benzene for 12hours in a Soxhlet extractor, the *benzene solution is evaporated and the residue is air dried. A further desalting with 1.5M HCl (1L) is followed by crystallisation from dimethylformamide (in which it is very soluble) by forming a saturated solution at the boiling point, and allowing to cool slowly. The crystalline dimethylammonium salt so obtained is washed with *benzene and treated repeatedly with dilute HCl to give the insoluble free acid which, after air drying, is dissolved in alcohol, filtered and evaporated. The final material is air dried, then dried in a vacuum desiccator over Mg(ClO4)2. The purified acid is converted to the dimethylammonium salt with Me2NH. [Diehl & Lindstrom, Anal Chem 31 414 1959]. It is an indicator in the complexometry of alkaline earth metals. [Beilstein 16 IV 429.]

Properties and Applications

blue black. Dark brown powder. Soluble in water for bordeaux red to jam red, moderate soluble in ethanol for brown light magenta, slightly soluble in Acetone. Dye in concentrated sulfuric acid for skipper, dilution to pale red light brown; In concentrated nitric acid to orange. Dye aqueous solution to join concentrated hydrochloric acid for sauce red; Join strong caustic into brown light magenta. Mainly used for all kinds of wool fabric dyeing, also used for silk, nylon and wool and a variety of fiber blended fabric dyeing, can be in chrome pretreatment of wool fabric direct printing. Is tasted can be used for indicator, also can be used for biological and fur dyeing.