Thionyl chloride

Thionyl chloride
Thionyl chloride
CAS number 7719-09-7 YesY
PubChem 24386
ChemSpider 22797 YesY
EC number 231-748-8
UN number 1836
ChEBI CHEBI:29290 YesY
RTECS number XM5150000
Jmol-3D images Image 1
Molecular formula SOCl2
Molar mass 118.97 g/mol
Appearance clear; colorless to yellow
odorous liquid
Density 1.638 g/cm3, liquid
Melting point

−104.5 °C

Boiling point

74.6 °C

Solubility in water reacts
Solubility soluble in benzene, chloroform, CCl4
Refractive index (nD) 1.517 (20 °C) [1]
Viscosity 0.6 cP
Molecular shape pyramidal
Dipole moment 1.4 D
MSDS External MSDS
EU Index 016-015-00-0
EU classification Corrosive (C)
R-phrases R14, R20/22, R29, R35
S-phrases (S1/2), S26, S36/37/39, S45
NFPA 704
NFPA 704.svg
Flash point Non-flammable
Related compounds
Related thionyl halides Thionyl fluoride
Thionyl bromide
Related compounds Sulfuryl chloride
Selenium oxydichloride
 YesY chloride (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Thionyl chloride is an inorganic compound with the formula SOCl2. It 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. Thionyl chloride is sometimes confused with sulfuryl chloride, SO2Cl2, but the properties of these compounds differ significantly. Approximately 45,000 tons per year of SOCl2 were produced in the early 1990s.[2]


Properties and structure

The molecule SOCl2 is pyramidal, indicating the presence of a lone pair of electrons on the sulfur(IV) center. In contrast, the stoichiometrically related species COCl2 is planar. SOCl2 reacts with water to release hydrogen chloride and sulfur dioxide.

SOCl2 + H2O → 2 HCl + SO2


The major industrial synthesis involves the reaction of sulfur trioxide and sulfur dichloride:[3]

SO3 + SCl2 → SOCl2 + SO2

Other methods include syntheses from phosphorus pentachloride, chlorine, or phosgene:

SO2 + PCl5 → SOCl2 + POCl3
SO2 + Cl2 + SCl2 → 2 SOCl2
SO3 + Cl2 + 2 SCl2 → 3 SOCl2
SO2 + COCl2 → SOCl2 + CO2

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


Thionyl chloride is mainly used in the industrial production of organochlorine compounds, which are often intermediates in pharmaceuticals and agrichemicals.

Organic chemistry

Thionyl chloride is widely used in organic synthesis. For some applications, it requires purification.[4] Classically, it converts carboxylic acids to acyl chlorides:[5]

Reaction of thionyl chloride with a carboxylic acid

Alcohols react with thionyl chloride to give the corresponding alkyl chlorides. This method is known as Darzan's process.[6] This reaction proceeds via an internal nucleophilic substitution.

Alcohol Thionyl Chloride Reaction
Bicifadine synthesis Xu 2007

It is preferred over other reagents such as phosphorus pentachloride because the products of the thionyl chloride reactions, HCl and SO2, are gaseous, which simplifies the purification of the product. Excess thionyl chloride can be readily removed by distillation.

Sulfonic acids react with thionyl chloride to produce sulfonyl chlorides.[7][8] Sulfonyl chlorides have also been prepared from the direct reaction of the corresponding diazonium salt with thionyl chloride.[9] Likewise, thionyl chloride will transform sulfinic acids into sulfinyl chlorides[10] and phosphonic acids into phosphoryl chlorides. Thionyl chloride will react with primary formamides to form isocyanides.[11] Amides will react with thionyl chloride to form imidoyl chlorides. However, primary amides under heating with thionyl chloride will continue on to form nitriles.[12]

Thionyl chloride can also produce nitriles from amides via E2 elimination.[13]

Inorganic chemistry

Anhydrous metal chlorides may be obtained from hydrated metal chlorides by refluxing in freshly distilled thionyl chloride:[14]

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

Other applications

Thionyl chloride is a component of lithium-thionyl chloride batteries, where it acts as the positive electrode (cathode) with lithium as the negative electrode (anode).


SOCl2 is a reactive compound that can explosively release dangerous gases upon contact with water and other reagents. Industrial production of thionyl chloride is controlled under the Chemical Weapons Convention, where it is listed in Schedule 3. Thionyl chloride is used in the "di-di" method of producing G-series nerve agents.


  1. ^ Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0070494398
  2. ^ Hans-Dietrich Lauss, Wilfried Steffens “Sulfur Halides” in Ullmann's Encyclopedia of Industrial Chemistry Wiley-VCH, Weinheim, 2005.doi:10.1002/14356007.a25_623
  3. ^ Greenwood, Norman N.; Earnshaw, A. (1984). Chemistry of the Elements. Oxford: Pergamon. p. 820. ISBN 0-08-022057-6. .
  4. ^ Friedman, L. and Wetter, W. P., "Purification of Thionyl Chloride", J. Chem. Soc. A, 1967, 36-8.doi:10.1039/J19670000036
  5. ^ Allen, C. F. H.; Byers, Jr., J. R.; Humphlett, W. J. (1963), "Oleoyl chloride", Org. Synth., ; Coll. Vol. 4: 739 ; Rutenberg, M. W.; Horning, E. C. (1963), "1-Methyl-3-ethyloxindole", Org. Synth., ; Coll. Vol. 4: 620 
  6. ^ Mondanaro, K. R.; Dailey, W. P. (2004), "3-Chloro-2-(chloromethyl)-1-propene", Org. Synth., ; Coll. Vol. 10: 212 ; 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 ; Feng Xu, Bryon Simmons, Robert A. Reamer, Edward Corley, Jerry Murry, and David Tschaen (2008). "Chlorination/Cyclodehydration of Amino Alcohols with SOCl2: An Old Reaction Revisited". J. Org. Chem. 73 (1): 312–5. doi:10.1021/jo701877h. PMID 18052293. 
  7. ^ Weinreb, S. M.; Chase, C. E.; Wipf, P.; Venkatraman, S. (2004), "2-Trimethylsilylethanesulfonyl chloride (SES-Cl)", Org. Synth., ; Coll. Vol. 10: 707 
  8. ^ 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 
  9. ^ Philip J. Hogan and Brian G. Cox (2009). "Aqueous Process Chemistry: The Preparation of Aryl Sulfonyl Chlorides". Org. Process Res. Dev. 13 (5): 875–879. doi:10.1021/op9000862. 
  10. ^ 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 ; Kurzer, F. (1963), "p-Toluenesulfinyl chloride", Org. Synth., ; Coll. Vol. 4: 937 
  11. ^ 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 
  12. ^ Krynitsky, J. A.; Carhart, H. W. (1963), "2-Ethylhexanonitrile", Org. Synth., ; Coll. Vol. 4: 436 
  13. ^ John E. McMurry (2010). Fundamentals of Organic Chemistry (7th ed.). Cengage Learning. p. 767. ISBN 1439049718. 
  14. ^ Alfred R. Pray, Richard F. Heitmiller, Stanley Strycker (1990). "Anhydrous Metal Chlorides". Inorganic Syntheses. Inorganic Syntheses 28: 321–323. doi:10.1002/9780470132593.ch80. ISBN 9780470132593. 

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