Phenylsulfinic acid is an
organosulfur compound
Organosulfur compounds are organic compounds that contain sulfur. They are often associated with foul odors, but many of the sweetest compounds known are organosulfur derivatives, e.g., saccharin. Nature abounds with organosulfur compounds—sulfu ...
with the formula C
6H
5SO
2H. 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.
Acidity
There is a large range of p''K''
a values in the literature, with most authors giving a value of around 1.30.
[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).] This inconsistency can be explained by differences in ionic strength between quoted values. By measuring the p''K''
a at various ionic strengths and extrapolating to zero ionic strength, the p''K''
a of phenylsulfinic acid was determined to be 2.76.
This makes phenylsulfinic acid a stronger acid than its corresponding carboxylic acid,
benzoic acid
Benzoic acid is a white (or colorless) solid organic compound with the formula , whose structure consists of a benzene ring () with a carboxyl () substituent. It is the simplest aromatic carboxylic acid. The name is derived from gum benzoin, wh ...
(pK
a = 4.2), but weaker than its corresponding sulfonic acid,
benzenesulfonic acid
Benzenesulfonic acid (conjugate base benzenesulfonate) is an organosulfur compound with the formula C6 H6 O3 S. It is the simplest aromatic sulfonic acid. It forms white deliquescent sheet crystals or a white waxy solid that is soluble in water ...
(p''K''
a = −6.5).
[E. P. Serjeant, B. Dempsey. "Ionization Constants of Organic Acids in Solution" IUPAC Data, Series No. 23 (Pergamon Press, Oxford)]
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 C
6H
5SO
2Cl + 2 Zn → (C
6H
5SO
2)
2Zn + ZnCl
2
:(C
6H
5SO
2)
2Zn + Na
2CO
3 → 2 C
6H
5SO
2Na + ZnCO
3
A convenient method is the reduction of the
sulfonyl chloride
In inorganic chemistry, sulfonyl halide groups occur when a sulfonyl () functional group is singly bonded to a halogen atom. They have the general formula , where X is a halogen. The stability of sulfonyl halides decreases in the order fluorides ...
or sulfonyl fluoride with
sodium sulfite
Sodium sulfite (sodium sulphite) is the inorganic compound with the chemical formula Na2 SO3. A white, water-soluble solid, it is used commercially as an antioxidant and preservative. A heptahydrate is also known but it is less useful because of ...
, producing the acid instead of a salt:
:C
6H
5SO
2Cl + Na
2SO
3 + H
2O → C
6H
5SO
2H + NaCl + NaHSO
4
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.acid
In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...
:
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
{{Reflist
Sulfinic acids
Phenyl compounds