Phenylsulfinic acid

There is a large range of pKa values in the literature, with most authors giving a value of around 1.30. This inconsistency can be explained by differences in ionic strength between quoted values. By measuring the pKa at various ionic strengths and extrapolating to zero ionic strength, the pKa of phenylsulfinic acid was determined to be 2.76. ==Preparation==

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. :2 C6H5SO2Cl + 2 Zn → (C6H5SO2)2Zn + ZnCl2 :(C6H5SO2)2Zn + Na2CO3 → 2 C6H5SO2Na + ZnCO3 A convenient method is the reduction of the sulfonyl chloride or sulfonyl fluoride with sodium sulfite, producing the acid instead of a salt: :C6H5SO2Cl + Na2SO3 + H2O → C6H5SO2H + NaCl + NaHSO4 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. ==Properties==

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. ==Use==

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. == References ==