Sulfinic acid

Sulfinic acids are

Sulfinic acids RSO₂H are about 1000x more acidic than the corresponding carboxylic acid RCO₂H. Sulfur is pyramidal, consequently sulfinic acids are chiral.

Preparation

They are often prepared in situ by acidification of the corresponding sulfinate salts, which are typically more robust than the acid. These salts are generated by reduction of sulfonyl chlorides.^[2] An alternative route is the reaction of Grignard reagents with sulfur dioxide. Transition metal sulfinates are also generated by insertion of sulfur dioxide into metal alkyls, a reaction that may proceed via a metal sulfur dioxide complex. Unsubstituted sulfinic acid, when R is the hydrogen atom, is a higher energy isomer of sulfoxylic acid, both of which are unstable.

Examples

An example of a simple, well-studied sulfinic acid is

Another commercially important sulfinic acid is hydroxymethyl sulfinic acid, which is usually employed as its sodium salt (HOCH₂SO₂Na). Called Rongalite, this anion is also commercially useful as a reducing agent.

Sulfinates

The