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Thionyl chloride

Thionyl chloride
Other names sulfurous oxychloride
sulfurous dichloride
sulfinyl chloride
sulfinyl dichloride
CAS number 7719-09-7
Molecular formula SOCl2
Molar mass 118.97 g/mol
Appearance clear to yellow
odorous liquid
Density 1.638 g ml−1, liquid
Melting point

−104.5 °C

Boiling point

76 °C

Solubility in water Reactive
Viscosity 0.6 cP at ? °C
Molecular shape pyramidal
Dipole moment 1.4 D
MSDS External MSDS
EU classification Corrosive (C)
NFPA 704
R-phrases R14, R20/22, R29, R35
S-phrases (S1/2), S26, S36/37/39, S45
Flash point non flammable
Related Compounds
Related compounds Sulfuryl chloride
Selenium oxydichloride
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)

Infobox disclaimer and references

Thionyl chloride (or thionyl dichloride) is an inorganic compound with the formula SOCl2. SOCl2 is a reactive chemical reagent used in chlorination reactions. It is a colorless, distillable liquid at room temperature and pressure that decomposes above 140 °C. SOCl2 is sometimes confused with sulfuryl chloride, SO2Cl2, but the chemical properties of these S(IV) and S(VI) compounds differ significantly.


Properties and structure

The molecule SOCl2 is pyramidal, indicating the presence of a lone pair of electrons on the S(IV) center. In contrast, COCl2 is planar.

SOCl2 reacts with water to release hydrogen chloride and sulfur dioxide.

H2O + O=SCl2SO2 + 2 HCl

Because of its high reactivity toward water, SOCl2 would not be expected to occur in nature.


The major industrial synthesis involves the reaction of sulfur trioxide and sulfur dichloride:[1]

SO3 + SCl2SOCl2 + SO2.

Other methods include

SO2 + PCl5SOCl2 + POCl3;
SO2 + Cl2 + SCl2 → 2 SOCl2;
SO3 + Cl2 + 2 SCl2 → 3 SOCl2.

The first of the above three reactions also affords phosphorus oxychloride (or phosphoryl chloride), which resembles thionyl chloride in many of its reactions.


Thionyl chloride is used inside lithium-thionyl chloride batteries as the positive active material with lithium as the negative active material. It is also used as a reagent for the production of other chemical compounds or materials.

In military usage, thionyl chloride is used in the "di-di" method of producing G-series nerve agents.

Organic chemistry

Thionyl chloride is widely used to convert carboxylic acids[2][3] and alcohols[4][5] to the corresponding acyl chlorides and alkyl chlorides respectively via an internal nucleophilic substitution. It is preferred over other reagents such as phosphorus pentachloride because the products of the thionyl chloride reactions, HCl and SO2 are gaseous, simplifying the purification of the product. Excess thionyl chloride may be removed by distillation.

RC(O)OH + O=SCl2RC(O)Cl + SO2 + HCl
R-OH + O=SCl2 → R-Cl + SO2 + HCl

Sulfonic acids react with thionyl chloride to produce sulfonyl chlorides.[6][7] Likewise, thionyl chloride will transform sulfinic acids into sulfinyl chlorides[8][9] and phosphonic acids into phosphoryl chlorides.

Thionyl chloride will react with primary formamides to form isocyanides.[10]

Amides will react with thionyl chloride to form imidoyl chlorides. However, primary amides under heating with thionyl chloride will continue on to form nitriles.[11]

Inorganic chemistry

Anhydrous metal chlorides may be obtained from hydrated metal chlorides by refluxing in freshly distilled thionyl chloride:[12]

MCln·xH2O + x SOCl2 → MCln + x SO2 + 2x HCl


SOCl2 is toxic, corrosive, and lachrymatory. It is a skin and inhalation hazard, as well as being odorous. It can react explosively when exposed to high concentrations of nucleophiles such as phosphites.

Industrial production of thionyl chloride is controlled under the Chemical Weapons Convention, where it is listed in schedule 3.


  1. ^ N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, Pergamon Press, 1984.
  2. ^ Allen, C. F. H.; Byers, Jr., J. R.; Humphlett, W. J. (1963). "Oleoyl chloride". Org. Synth.; Coll. Vol. 4: 739. 
  3. ^ Rutenberg, M. W.; Horning, E. C. (1963). "1-Methyl-3-ethyloxindole". Org. Synth.; Coll. Vol. 4: 620. 
  4. ^ Mondanaro, K. R.; Dailey, W. P. (2004). "3-Chloro-2-(chloromethyl)-1-propene". Org. Synth.; Coll. Vol. 10: 212. 
  5. ^ Krakowiak, K. E.; Bradshaw, J. S. (1998). "4-Benzyl-10,19-diethyl-4,10,19-triaza-1,7,13,16-tetraoxacycloheneicosane". Org. Synth.; Coll. Vol. 9: 34. 
  6. ^ Weinreb, S. M.; Chase, C. E.; Wipf, P.; Venkatraman, S. (2004). "2-Trimethylsilylethanesulfonyl chloride (SES-Cl)". Org. Synth.; Coll. Vol. 10: 707. 
  7. ^ Hazen, G. G.; Bollinger, F. W.; Roberts, F. E.; Russ, W. K.; Seman, J. J.; Staskiewicz, S. (1998). "4-Dodecylbenzenesulfonyl azides". Org. Synth.; Coll. Vol. 9: 400. 
  8. ^ Hulce, M.; Mallomo, J. P.; Frye, L. L.; Kogan, T. P.; Posner, G. H. (1990). "(S)-( + )-2-(p-toluenesulfinyl)-2-cyclopentenone: Precursor for enantioselective synthesis of 3-substituted cyclopentanones". Org. Synth.; Coll. Vol. 7: 495. 
  9. ^ Kurzer, F. (1963). "p-Toluenesulfinyl chloride". Org. Synth.; Coll. Vol. 4: 937. 
  10. ^ Niznik, G. E.; Morrison, III, W. H.; Walborsky, H. M. (1988). "1-d-Aldehydes from organometallic reagents: 2-methylbutanal-1-d". Org. Synth.; Coll. Vol. 6: 751. 
  11. ^ Krynitsky, J. A.; Carhart, H. W. (1963). "2-Ethylhexanonitrile". Org. Synth.; Coll. Vol. 4: 436. 
  12. ^ Alfred R. Pray, Richard F. Heitmiller, Stanley Strycker. "Anhydrous Metal Chlorides". Inorganic Syntheses 28: 321 - 323. doi:10.1002/9780470132593.ch80.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Thionyl_chloride". A list of authors is available in Wikipedia.
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