Phenylsulfinic acid

Phenylsulfinic acid
Other names

phenyl sulfinic acid, benzene sulfinic acid, benzenesulfinic acid
Identifiers
CAS number 618-41-7
PubChem 12057
Properties
Molecular formula C6H6O2S
Molar mass 142.18 g mol−1
Appearance colorless prisms
Density 1.45 g/cm3
Melting point

83 – 84 ºC
Boiling point

339.4 ºC at 760 mmHg
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Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
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.

Contents

Acidity

Although many sources report the pka value as somewhere around 1.30[1][2][3] these results are inconsistent. However a reproducable method was developed by Filippo et al. in which the pka was determined to be 2.764.[4] This is a strong acid compared to its corresponding carboxylic acid, benzoic acid (pKa = 4.2), but weak when compared to its corresponding sulfonic acid (pKa = -6.5).[5]

Preparation

Phenylsulfinic acid can be prepared in several ways, most easily through reduction of sulfonyl chlorides with zinc dust or iron.[1][4]. 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 + NaCO3 +NaOH → 2 C6H5SO2Na + ZnCO3

A convienient method is the reduction of the sulfonyl chloride or sulfonyl fluoride with sodium sulfite, producing the acid instead of a salt:[2]

C6H5SO2Cl + NaSO3 + 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.[3]. 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. Thus, they are prone to oxidization to sulphonic acids as well as reduction via sulphenic acids (+2) to thiols.[1]

Sulphinic acid derivatives disproportionate in the presence of acid:[1]

2PhSO2H → PhSO2SOPh + H2O
PhSO2SOPh → PhSO2• + PhSO → PhSO3SPh
PhSO3SPh + PhSO2H → PhSO3H + PhSO2SPh

When phenylsulfinic acid reacts with sulfur to give thiosulfinates and thiosulfinic acids.[6]

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 have been components for electroplating of palladium alloys.[7]

References

  1. ^ a b c d S. Patiai “The Chemistry of Sulphinic Acids, Esters and Their Derivatives” J. Wiley and Sons, 1990: New York. ISBN 0-471-91918-7
  2. ^ a b a) A. T. Fuller, I. M. Tonkin and J. Walker, J. Chem. Soc., 1945, 636; b) S. Smiles and C. M. Bere, "Organic Syntheses," Coll. Vol. I, ed. by A. H. Blatt, John Wiley and Sons, Inc., New York, 1948, p. 7; c) E. Bader and H. D. Hermann, Chem. Ber., 88, 46 (1955); d) M. Kulka, Can. J. Chem., 32, 601 (1954).
  3. ^ a b R. J. Cremlyn “An Introduction to Organosulfur Chemistry” J. Wiley and Sons, 1996: New York. ISBN 0-471-95512-4
  4. ^ a b D. D. Filippo, F. Momicchioli. Tetrahedron., 25, 5733 – 5744 (1969) doi:10.1016/S0040-4020(01)83080
  5. ^ E. P. Serjeant, B. Dempsey. “Ionization Constants of Organic Acids in Solution” IUPAC Data, Series No. 23 (Pergamon Press, Oxford)
  6. ^ B. Zwanenburg, A.J. H. Klunder. “Perspectives in the Organic Chemistry of Sulfur” Elsevier, 1987: New York. ISBN 0-444-42739-2
  7. ^ Y. H. Chiang, J. S. Luloff, E. Schipper. J. Org. Chem., 1969, 34 (8) 2397-2401 DOI: 10.1021/jo01260a031