Eriochrome Black T (CAS 1787-61-7), a significant compound in analytical chemistry, is more than just a color-changing reagent; it's a product of specific chemical synthesis designed for precise metallochromic applications. Its effectiveness as a complexometric indicator, particularly in EDTA titrations, is deeply rooted in its molecular structure and chemical properties. As a dedicated manufacturer, understanding this chemistry is fundamental to producing high-quality Eriochrome Black T for global markets.

The scientific name of Eriochrome Black T is 1-(1-hydroxy-2-naphthylazo)-6-nitro-2-naphthol-4-sulfonic acid, sodium salt. Its synthesis typically involves a diazotization and coupling reaction. The process begins with the diazotization of 6-nitro-1,2,4-acid oxygen body (which is essentially 6-nitro-2-hydroxy-1-diazonaphthalene-4-sulfonic acid). This diazonium salt is then coupled with 1-naphthol. Following the coupling, the product is usually salted out, filtered, and dried, resulting in a flaky process. The final product is a sodium salt, hence the presence of 'Na' in its molecular formula (C20H12N3NaO7S).

The molecule possesses several key functional groups that contribute to its indicator properties. The azo group (-N=N-) and the hydroxyl (-OH) groups are crucial for forming complexes with metal ions. These complexes exhibit different colors compared to the free indicator. Specifically, in alkaline solutions, Eriochrome Black T exists in a state where it can coordinate with metal ions like calcium and magnesium, forming a wine-red colored complex. When EDTA is introduced and binds more strongly to these metal ions, the Eriochrome Black T is displaced, reverting to its blue free indicator form. This distinct color transition is the basis of its use as an indicator.

The stability of Eriochrome Black T is an important aspect for its application. It is generally stable under recommended storage conditions (room temperature), but it is incompatible with strong oxidizing agents and strong reducing agents. Its solubility in water is also noteworthy, with figures often cited around 50 g/L at 20°C, making it suitable for aqueous titration systems. As a reliable supplier of this chemical, NINGBO INNO PHARMCHEM CO.,LTD. ensures that our production methods yield a product that adheres to these chemical specifications, providing a consistent and dependable analytical reagent for your needs. If you are looking to buy Eriochrome Black T and require detailed technical information or a competitive price, please reach out to our team.