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 listed in the European Cosmetics Directive as sodium oxymethylene sulfoxylate (INCI). It is water-soluble and generally sold as the dihydrate. The compound and its derivatives are widely used in the dye industry.

Although available commercially, the salt can be prepared from sodium dithionite and formaldehyde:

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 Na2Sex and Na2Tex, where x is approximately 2. As a nucleophile, NaHOCH2SO2 reacts with alkylating agents to give sulfones.

This page was last edited on 4 July 2017, at 18:38.
Reference: under CC BY-SA license.

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