What does dithionite mean?
Dithionite is the name given both to the chemical anion S₂O₄²⁻ — built from two sulfur atoms joined directly to each other and four oxygens — and to any salt that contains it. Its best-known representative, sodium dithionite (Na₂S₂O₄), is a powerful and fast-acting reducing agent: it eagerly takes up oxygen, which makes it invaluable for stripping unwanted color from textiles, bleaching pulp and clay, treating water, and keeping dye vats free of oxygen so natural indigo stays soluble enough to bond with cloth. The compound is chemically fragile, breaking down in the presence of air and moisture, so it must be stored and handled carefully. The name derives from Greek roots meaning 'two sulfurs,' reflecting its pair of linked sulfur atoms, and belongs to a family of sulfur-oxygen chemistry terms such as dithionate. Outside laboratories and factories, the word rarely surfaces, but within them it denotes one of the workhorse reagents of modern industry.
nounThe divalent anion S₂O₄²⁻, derived from dithionous acid, and any salt containing this anion; sodium dithionite is a widely used industrial reducing agent.
- The divalent anion S₂O₄²⁻, formally derived from dithionous acid, in which two sulfur atoms are bonded directly to each other.
- Any salt containing this anion, especially sodium dithionite (Na₂S₂O₄), used industrially as a strong reducing agent in dyeing, bleaching, and water treatment.
"The dyer added sodium dithionite to the vat to strip the oxygen and keep the indigo in its soluble form."
"Sodium dithionite was added to the vat to remove dissolved oxygen before the fabric was dipped."
"Because dithionite decomposes readily in air, the stock solution must be prepared fresh under an inert atmosphere."
Pluralized when referring collectively to different salts containing the S₂O₄²⁻ anion; uncountable when referring to the substance generically.
"Several metal dithionites have been studied for their unusual magnetic properties."
Sodium dithionite can pull the color out of indigo-dyed fabric and put it back again — it's the chemical heart of the classic denim vat.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of dithionite
Dithionite derives from 'dithionic acid' combined with the suffix '-ite', which in chemical nomenclature denotes salts of acids ending in '-ous'. The 'di-' prefix and the root come from the Greek 'theion' (θείον), meaning sulfur, giving the sense of 'two sulfurs' — fittingly, since the anion contains two directly bonded sulfur atoms. It thus shares its origin with related terms such as dithionic and dithionate, all part of the systematic nomenclature for sulfur oxoanions that developed alongside nineteenth-century analytical chemistry.
Related word forms
How dithionite is actually used
A technical term confined mainly to chemistry, textile processing, papermaking, and related industries. In older industrial usage the name 'hydrosulphite' (British spelling) was common for sodium dithionite but has largely fallen out of favor. The word is countable when referring to individual salts ('a dithionite') but more often appears uncountably as a substance name.
Easily confused with dithionite
Dithionate (S₂O₆²⁻) is the anion of dithionic acid with sulfur in a higher oxidation state, whereas dithionite (S₂O₄²⁻) comes from dithionous acid and is a much stronger reducing agent.
Thiosulfate (S₂O₃²⁻) contains sulfur atoms in different oxidation states and is used chiefly as a fixer in photography, while dithionite is a powerful oxygen-scavenging reductant used in bleaching and dyeing.