Sulfurous acid

Sulfurous acid
Names
	IUPAC name Sulfurous acid
	Other names Sulfuric(IV) acid; Thionic acid; Sulfinic acid
Identifiers
CAS Number	7782-99-2 ;
3D model (JSmol)	Interactive image; Tautomer: Interactive image;
ChEBI	CHEBI:48854 ;
ChEMBL	ChEMBL1161699 ;
ChemSpider	1069 ;
ECHA InfoCard	100.029.066
EC Number	231-973-1;
Gmelin Reference	1458
KEGG	C00094 ;
PubChem CID	1100;
UNII	J1P7893F4J ;
CompTox Dashboard (EPA)	DTXSID7042435 ;
	InChI InChI=1S/H2O3S/c1-4(2)3/h(H2,1,2,3) Key: LSNNMFCWUKXFEE-UHFFFAOYSA-N ; InChI=1/H2O3S/c1-4(2)3/h(H2,1,2,3) Key: LSNNMFCWUKXFEE-UHFFFAOYAJ;
	SMILES O[S](=O)O; Tautomer: O[S+](O)[O-];
Properties
Chemical formula	H2SO3
Molar mass	82.07 g/mol
Acidity (pKa)	1.857, 7.172
Conjugate base	Bisulfite
Hazards
	GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H314, H332
Precautionary statements	P260, P261, P264, P271, P280, P301+P330+P331, P303+P361+P353, P304+P312, P304+P340, P305+P351+P338, P310, P312, P321, P363, P405, P501
Flash point	Non-flammable
Safety data sheet (SDS)	ICSC 0074
Related compounds
Related compounds	Sulfur dioxide; Sulfuric acid; Selenous acid
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Sulfuric(IV) acid (United Kingdom spelling: sulphuric(IV) acid), also known as sulfurous (UK: sulphurous) acid and thionic acid,^{[citation needed]} is the chemical compound with the formula H₂SO₃.

Raman spectra of solutions of sulfur dioxide in water show only signals due to the SO₂ molecule and the bisulfite ion, HSO−3.^[2] The intensities of the signals are consistent with the following equilibrium:

SO₂ + H₂O ⇌ HSO−3 + H⁺ K_a = 1.54×10⁻²; pK_a = 1.81.

¹⁷O NMR spectroscopy provided evidence that solutions of sulfurous acid and protonated sulfites contain a mixture of isomers, which is in equilibrium:^[3]

[H−OSO₂]⁻ ⇌ [H−SO₃]⁻

Attempts to concentrate the solutions of sulfurous acid simply reverses the equilibrium, producing sulfur dioxide and water vapor. A clathrate with the formula 4SO₂·23H₂O has been crystallised. It decomposes above 7 °C.

History and production

Sulfurous acid is commonly known to not exist in its free state, and due to this, it is stated in textbooks that it cannot be isolated in the water-free form.^[4] However, the molecule has been detected in the gas phase in 1988 by the dissociative ionization of diethyl sulfite.^[5] The conjugate bases of this elusive acid are, however, common anions, bisulfite (or hydrogen sulfite) and sulfite. Sulfurous acid is an intermediate species in the formation of acid rain from sulfur dioxide.^[6]

Uses

Aqueous solutions of sulfur dioxide, which sometimes are referred to as sulfurous acid, are used as reducing agents and as disinfectants, as are solutions of bisulfite and sulfite salts. They are oxidised to sulfuric acid or sulfate by accepting another oxygen atom.^[7]

References

^ Perrin, D. D., ed. (1982) [1969]. Ionisation Constants of Inorganic Acids and Bases in Aqueous Solution. IUPAC Chemical Data (2nd ed.). Oxford: Pergamon (published 1984). Entry 217. ISBN 0-08-029214-3. LCCN 82-16524.
^ Jolly, William L. (1991), Modern Inorganic Chemistry (2nd ed.), New York: McGraw-Hill, ISBN 0-07-032768-8
^ Catherine E. Housecroft; Alan G. Sharpe (2008). "Chapter 16: The group 16 elements". Inorganic Chemistry, 3rd Edition. Pearson. p. 520. ISBN 978-0-13-175553-6.
^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 719. ISBN 978-0-08-037941-8.
^ D. Sülzle; M. Verhoeven; J. K. Terlouw; H. Schwarz (1988). "Generation and Characterization of Sulfurous Acid (H₂SO₃) and of Its Radical Cation as Stable Species in the Gas Phase". Angew. Chem. Int. Ed. Engl. 27 (11): 1533–4. doi:10.1002/anie.198815331.
^ McQuarrie; Rock (1987). General Chemistry (2nd ed.). New York: W.H. Freeman and Company. p. 243. ISBN 0-7167-1806-5.
^ L. Kolditz, Anorganische Chemie, VEB Deutscher Verlag der Wissenschaften, Berlin 1983, S. 476.

[P82db-1] Perrin, D. D., ed. (1982) [1969]. Ionisation Constants of Inorganic Acids and Bases in Aqueous Solution. IUPAC Chemical Data (2nd ed.). Oxford: Pergamon (published 1984). Entry 217. ISBN 0-08-029214-3. LCCN 82-16524.

[2] Jolly, William L. (1991), Modern Inorganic Chemistry (2nd ed.), New York: McGraw-Hill, ISBN 0-07-032768-8

[InorgChem-3] Catherine E. Housecroft; Alan G. Sharpe (2008). "Chapter 16: The group 16 elements". Inorganic Chemistry, 3rd Edition. Pearson. p. 520. ISBN 978-0-13-175553-6.

[4] Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 719. ISBN 978-0-08-037941-8.

[5] D. Sülzle; M. Verhoeven; J. K. Terlouw; H. Schwarz (1988). "Generation and Characterization of Sulfurous Acid (H₂SO₃) and of Its Radical Cation as Stable Species in the Gas Phase". Angew. Chem. Int. Ed. Engl. 27 (11): 1533–4. doi:10.1002/anie.198815331.

[6] McQuarrie; Rock (1987). General Chemistry (2nd ed.). New York: W.H. Freeman and Company. p. 243. ISBN 0-7167-1806-5.

[7] L. Kolditz, Anorganische Chemie, VEB Deutscher Verlag der Wissenschaften, Berlin 1983, S. 476.

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History and production

Uses

See also

References