Rongalite

Rongalite, also called Rongalit (registered trademark of BASF) is sodium hydroxymethylsulfinate, or Na⁺HOCH₂SO₂^-. The salt has many names, including also sodium formaldehyde sulfoxylate and Bruggolite. It is water-soluble and generally sold as the dihydrate.

Reactions

This salt is prepared from sodium dithionite:

Na₂S₂O₄ + 2 CH₂O + H₂O → NaHOCH₂SO₃ + NaHOCH₂SO₂

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.

NaHOCH₂SO₂ can essentially be considered to be a source of SO₂^2-. 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 sulfones.

NaHOCH₂SO₂ + 2 C₆H₅CH₂Br → [C₆H₅CH₂]₂SO₂ + NaBr + CH₂O + HBr

Occasionally, alkylation will occur also at oxygen, thus α,α' dibromoxylene gives both the sulfone and the isomeric sulfinate ester.

Use

The original use of the compound was as industrial bleaching agent and in textile dying. The other dominating use today is the application as reducing agent in redox-initiator systems for emulsion polymerization.

Zinc formaldehyde sulfoxylate

The zinc complex Zn(HOCH₂SO₂]₂ is marketed under the trademarks Decroline, Decolin, and Safolin. This compound is an additive in polymers and textiles.

References

• Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
• L. Tschugaeff und W. Chlopin: Beiträge zur Kenntnis des Reduktionsvermögens der schwefligen Säure. I. Einwirkung von Natriumhydrosulfit auf Tellur und Selen" Chemische Berichte 1914, volume 47, pages 1269-1275.
• R. Steudel, V. Munchow "Determination of dithionite (S₂O₂^2- and Hydroxymethanesulphinate (HOCH₂SO₂^-; Rongalite) by Ion-Pair Chromatography" Journal of Chromatography, (1992) volume 623 174-I 77.