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Sodium Dithionite CAS No: 7775-14-6, (also known as sodium hydrosulfite) is a white crystalline powder with a weak sulfurous odor. It is the sodium salt of dithionous acid. Although it is stable under most conditions, it will decompose in hot water and in acid solutions. It can be obtained from sodium bisulfite by the following reaction:

2 NaHSO3 + Zn → Na2S2O4 + Zn(OH)2

Specification

Appearance         White crystalline powder

Na2S2O4,%         ≥90.0

Na2S2O5,%         5.5-7.5

Na2CO3,%         ≤ 6

Na2S2O3 ,%         ≤ 1

Na2SO3,%         ≤ 1

Fe,ppm                 ≤ 20

Clarity                 Clear

Water insoluble,% ≤ 0.05

Uses

Industry

This compound is a water-soluble salt, and can be used as a reducing agent in aqueous solutions. It is used as such in some industrial dyeing processes, primarily those involving sulfur dyes and vat dyes, where an otherwise water-insoluble dye can be reduced into a water-soluble alkali metal salt (e.g. indigo dye). The reduction properties of sodium dithionite also eliminate excess dye, residual oxide, and unintended pigments, thereby improving overall colour quality.

Biological sciences

Sodium dithionite is often used in physiology experiments as a means of lowering solutions' redox potential (Eo' -0.66 V vs SHE at pH 7). Potassium ferricyanide is usually used as an oxidizing chemical in such experiments (Eo' ~ .436 V at pH 7). In addition, sodium dithionite is often used in soil chemistry experiments to determine the amount of iron that is not incorporated in primary silicate minerals. Hence, iron extracted by sodium dithionite is also referred to as "free iron." The strong affinity of the dithionite ion for bi- and trivalent metal cations (M2+, M3+) allows it to enhance the solubility of iron, and therefore dithionite is a useful chelating agent.

Geosciences

Sodium dithionite has been used in chemical enhanced oil recovery[citation needed] to stabilize polyacrylamide polymers against radical degradation in the presence of iron. It has also been used in environmental applications to propagate a low Eh front in the subsurface in order to reduce components such as chromium.

Photography

It can be used as a developer, but it is a very uncommon choice. It is prone to reduce film speed and, if improperly used, quickly fogs the image.

Laboratory

Aqueous solutions of sodium dithionite were once used to produce "Fieser's solution' for the removal of oxygen from a gas stream. Pyrithione can be prepared in a two-step synthesis from 2-bromopyridine by oxidation to the N-oxide with a suitable peracid by substitution using sodium dithionite to introduce the thiol functional group.

Packing & storage

50 kg/steel drum

Stored in dry and ventilation place, far from heat and water.