Rongalite is a chemical compound with the molecular formula Na⁺HOCH₂SO₂⁻. This

salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quant ...

has many additional names, including Rongalit, sodium hydroxymethylsulfinate, sodium formaldehyde sulfoxylate, and Bruggolite. It is listed in the European Cosmetics Directive as sodium oxymethylene sulfoxylate (

INCI The International Nomenclature of Cosmetic Ingredients, abbreviated INCI, are the unique identifiers for cosmetic ingredients such as waxes, oils, pigments, and other chemicals that are assigned in accordance with rules established by the Personal ...

). It is water-soluble and generally sold as the dihydrate. The compound and its derivatives are widely used in the dye industry.D. Schubart "Sulfinic Acids and Derivatives" in ''Ullmann's Encyclopedia of Industrial Chemistry'', 2012, Wiley-VCH, Weinheim. The structure of this salt has been confirmed by

X-ray crystallography X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...

Synthesis and reactions

Although available commercially, the salt can be prepared from

sodium dithionite Sodium dithionite (also known as sodium hydrosulfite) is a white crystalline powder with a sulfurous odor. Although it is stable in dry air, it decomposes in hot water and in acid solutions. Structure The structure has been examined by Raman s ...

and

formaldehyde Formaldehyde ( , ) (systematic name methanal) is a naturally occurring organic compound with the formula and structure . The pure compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde (refer to section ...

: :Na₂S₂O₄ + 2 CH₂O + H₂O → HO-CH₂-SO₃Na + HO-CH₂-SO₂Na This reaction proceeds quantitatively, such that dithionite can be determined by its conversion to Rongalite, which is far less O₂-sensitive and thus easier to handle. The hydroxymethanesulfinate ion is unstable in solution towards decomposition to formaldehyde and sulfite. Addition of at least one equivalent of formaldehyde pushes the equilibrium towards the side of the adduct and reacts further to give the ''bis''-(hydroxymethyl)sulfone. Such solutions are shelf-stable indefinitely. Sodium hydroxymethanesulfinate was originally developed in the early 20th century for the textile industry as a shelf-stable source of sulfoxylate ion, where the latter can be generated at will. In use, when sodium hydroxymethanesulfinate is made acidic, the reducing sulfoxylate ion and formaldehyde are released in equimolar amounts. For safety reasons the generation of formaldehyde must be taken into consideration when used industrially. NaHOCH₂SO₂ can essentially be considered to be a source of SO₂²⁻. As such it is used both as a reducing agent and as a reagent to introduce SO₂ groups into organic molecules. Treatment of elemental Se and Te with NaHOCH₂SO₂ gives solutions containing the corresponding Na₂Se_x and Na₂Te_x, where x is approximately 2. As a nucleophile, NaHOCH₂SO₂ reacts with alkylating agents to give

sulfone In organic chemistry, a sulfone is a organosulfur compound containing a sulfonyl () functional group attached to two carbon atoms. The central hexavalent sulfur atom is double-bonded to each of two oxygen atoms and has a single bond to each of ...

s. ::HO-CH₂-SO₂Na + 2 C₆H₅CH₂Br → ₆H₅CH₂sub>2SO₂ + NaBr + CH₂O + HBr Occasionally, alkylation will occur also at oxygen, thus xylylene dibromide gives both the sulfone and the isomeric sulfinate ester.

Use

The original use of the compound was as industrial bleaching agent and as a reducing agent for

vat dye Vat dyes are a class of dyes that are classified as such because of the method by which they are applied. Vat dyeing is a process that refers to dyeing that takes place in a bucket or vat. The original vat dye is indigo, once obtained only from pl ...

ing. Another large-scale use is as a reducing agent in redox-initiator systems for emulsion polymerization. One of the typical redox pair examples is t-butyl peroxide. A niche use is its use as water conditioner for aquaria as it rapidly reduces

chlorine Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine i ...

and chloramine and reacts with

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...

to form the innocuous aminomethylsulfinate ion. It is also used as an antioxidant in pharmaceutical formulation. The compound has been used increasingly in commercial cosmetic hair dye colour removers despite the generation of

, a known human

carcinogen A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive subs ...

. It has a variety of specialized applications in organic synthesis.

Related compounds

The zinc complex Zn(HOCH₂SO₂)₂ is marketed under the trademarks Decroline, Decolin, and Safolin. This compound is an additive in polymers and textiles. Sodium hydroxymethanesulfinate is called Rongalite C. Calcium hydroxymethanesulfinate is called Rongalite H.

Synthesis and reactions

Use

Related compounds

References

Further reading