Phenylsulfinic acid

Phenylsulfinic acid

Names
Other names phenyl sulfinic acid, benzene sulfinic acid, benzenesulfinic acid
Identifiers
CAS Number	618-41-7 Y
3D model (JSmol)	Interactive image
ChemSpider	11560 N
ECHA InfoCard	100.009.591
PubChem CID	12057
InChI InChI=1S/C6H6O2S/c7-9(8)6-4-2-1-3-5-6/h1-5H,(H,7,8) N Key: JEHKKBHWRAXMCH-UHFFFAOYSA-N N InChI=1/C6H6O2S/c7-9(8)6-4-2-1-3-5-6/h1-5H,(H,7,8) Key: JEHKKBHWRAXMCH-UHFFFAOYAY
SMILES C1=CC=C(C=C1)S(=O)O
Properties
Chemical formula	C6H6O2S
Molar mass	142.17 g·mol−1
Appearance	Colorless prisms
Density	1.45 g/cm3
Melting point	83 to 84 °C (181 to 183 °F; 356 to 357 K)
Acidity (pKa)	2.76
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YN ?)
Infobox references

Phenylsulfinic acid is an organosulfur compound with the formula C₆H₅SO₂H. It is a colorless or white crystalline solid that is usually stored in the form of its sodium salt. In aqueous solution it is strongly acidic and is easily oxidized in air. Phenylsulfinic acid and its esters are chiral.

Although many sources report the pK_a value as somewhere around 1.30, these results are inconsistent. However, a reproducible method was developed by Filippo et al. in which the pK_a was determined to be 2.764. This is a strong acid compared to its corresponding carboxylic acid, benzoic acid (pK_a = 4.2), but weak when compared to its corresponding sulfonic acid (pK_a = -6.5).

Phenylsulfinic acid can be prepared in several ways, most easily through reduction of sulfonyl chlorides with zinc dust or iron. However other starting materials can be used. Due to the air sensitivity of this compound it is often formed as a salt.

A convenient method is the reduction of the sulfonyl chloride or sulfonyl fluoride with sodium sulfite, producing the acid instead of a salt:

Many other methods have been reported for production of sulfinic acids such as the use tin(II) chloride, or the Grignard reagent with sulfur dioxide. The preparation of sulfinic acids by the oxidation of thiols is difficult due to overoxidation.

In sulfinic acids, sulfur has the +4 oxidation state. They are prone to oxidation to sulphonic acids as well as reduction via sulphenic acids (+2) to thiols.

Sulphinic acid derivatives disproportionate in the presence of acid:

When phenylsulfinic acid reacts with sulfur to give thiosulfinates and thiosulfinic acids.

The main use of phenylsulfinic acid is for the asymmetric synthesis of carbon-carbon bonds due to its ability to stabilize negative charges on an adjacent carbon atom. Phenylsulfinic acid has been a component for electroplating of palladium alloys.