Rongalite is a chemical compound with the molecular formula Na
+HOCH
2SO
2−. 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 quantitie ...
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
The derivative of a function is the rate of change of the function's output relative to its input value.
Derivative may also refer to:
In mathematics and economics
* Brzozowski derivative in the theory of formal languages
* Formal derivative, an ...
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 F ...
:
:Na
2S
2O
4 + 2 CH
2O + H
2O → HO-CH
2-SO
3Na + HO-CH
2-SO
2Na
This reaction proceeds quantitatively, such that dithionite can be determined by its conversion to Rongalite, which is far less O
2-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.
NaHOCH
2SO
2 can essentially be considered to be a source of SO
22−. As such it is used both as a reducing agent and as a reagent to introduce SO
2 groups into organic molecules. Treatment of elemental Se and Te with NaHOCH
2SO
2 gives solutions containing the corresponding Na
2Se
x and Na
2Te
x, where x is approximately 2. As a nucleophile, NaHOCH
2SO
2 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-CH
2-SO
2Na + 2 C
6H
5CH
2Br →
6H5CH2">6H5CH2sub>2SO
2 + NaBr + CH
2O + HBr
Occasionally, alkylation will occur also at oxygen, thus
xylylene dibromide
Xylylene dibromide is an organic compound with the formula C6H4(CH2Br)2. It is an off-white solid that, like other benzyl halides, a strong lachrymator. It is a useful reagent owing to the convenient reactivity of the two C-Br bonds. Two other ...
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 p ...
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
Water conditioners are formulations designed to be added to tap water before its use in an aquarium. If the tap water is chlorinated then a simple conditioner containing a dechlorinator may be used. These products contain sodium thiosulfate which ...
for aquaria as it rapidly reduces chlorine
Chlorine is a chemical element with the Symbol (chemistry), 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 betwee ...
and chloramine
Chloramines refer to derivatives of ammonia and organic amines wherein one or more N-H bonds have been replaced by N-Cl bonds. Two classes of compounds are considered: inorganic chloramines and organic chloramines.
Inorganic chloramines
Inorgan ...
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 was ...
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 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 F ...
, 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 substan ...
.
It has a variety of specialized applications in organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...
.
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.
References
Further reading
*
*
*{{ cite journal , author1=Steudel, R. , author2=Münchow, V. , title = Sulphur compounds: CLIX. Determination of Dithionite (S2O42−) and Hydroxymethanesulphinate (HOCH2SO2−; Rongalite) by Ion-Pair Chromatography , journal = Journal of Chromatography A
The ''Journal of Chromatography A'' is a peer-reviewed scientific journal publishing research papers in analytical chemistry, with a focus on techniques and methods used for the separation and identification of mixtures.
Indexed by ISI the jour ...
, year = 1992 , volume = 623 , issue = 1 , pages = 174–177 , doi = 10.1016/0021-9673(92)85314-J
Organic sodium salts
Sulfinates
Reducing agents