Eriochrome Черный T

Химические свойства

black powder

Использование

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.

Подготовка

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

Общее описание

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.

Методы очистки

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.]