Sulfinic acids are

oxoacid An oxyacid, oxoacid, or ternary acid is an acid that contains oxygen. Specifically, it is a compound that contains hydrogen, oxygen, and at least one other element, with at least one hydrogen atom bonded to oxygen that can dissociate to produce ...

s of sulfur with the structure RSO(OH). In these organosulfur compounds, sulfur is pyramidal.

Structure and properties

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. 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 In organometallic chemistry, metal sulfur dioxide complexes are complexes that contain sulfur dioxide, , bonded to a transition metal. Such compounds are common but are mainly of theoretical interest. Historically, the study of these compounds ...

. 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 phenylsulfinic acid. A commercially important sulfinic acid is

thiourea dioxide Thiourea dioxide or thiox is an organosulfur compound that is used in the textile industry. It functions as a reducing agent. It is a white solid, and exhibits tautomerism. Structure The structure of thiourea dioxide depends on its environment. C ...

, which is prepared by the oxidation of thiourea with hydrogen peroxide.D. Schubart "Sulfinic Acids and Derivatives" in Ullmann's Encyclopedia of Industrial Chemistry 2012, Wiley-VCH, Weinheim. :(NH₂)₂CS + 2H₂O₂ → (NH)(NH₂)CSO₂H + 2H₂O 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 conjugate base of a sulfinic acid is a sulfinate anion. The enzyme

cysteine dioxygenase Cysteine dioxygenase (CDO) is a non-heme iron enzyme that catalyzes the conversion of L-cysteine to cysteine sulfinic acid (cysteine sulfinate). CDO plays an important role in cysteine catabolism, regulating intracellular levels of cysteine and res ...

converts cysteine into the corresponding sulfinate. One product of this catabolic reaction is the sulfinic acid

hypotaurine Hypotaurine is a sulfinic acid that is an intermediate in the biosynthesis of taurine. Like taurine, it also acts as an endogenous neurotransmitter via action on the glycine receptors. It is an osmolyte with antioxidant properties. Hypotaurine is ...

. Sulfinite also describes esters of sulfinic acid. Cyclic sulfinite esters are called sultines.

References

External links

*
Diagram at ucalgary.ca

* Functional groups {{organic-chem-stub