Thionyl chloride

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Thionyl chloride
Structure and dimensions of thionyl chloride
Ball-and-stick model of thionyl chloride Molecule arrangement in solid SOCl2
Thionyl chloride 25ml.jpg
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 liquid with unpleasant odor
Density 1.638 g/cm3, liquid
Melting point −104.5 °C (−156.1 °F; 168.7 K)
Boiling point 74.6 °C (166.3 °F; 347.8 K) 80 °C (176 °F; 353 K)
Solubility in water exothermic reaction
Solubility soluble in benzene, chloroform, CCl4
Vapor pressure 384 Pa (-40 °C)
4.7 kPa (0 °C)
15.7 kPa (25 °C)[1]
Refractive index (nD) 1.517 (20 °C) [2]
Viscosity 0.6 cP
Molecular shape pyramidal
Dipole moment 1.44 D
heat capacity
120.5 J/mol·K[3]
Std molar
278.6 J/mol·K[3]
Std enthalpy of
-247 kJ/mol[3]
MSDS External MSDS
GHS pictograms The corrosion pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)The exclamation-mark pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)The skull-and-crossbones pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)
GHS signal word Danger
GHS hazard statements H302, H314, H332
GHS precautionary statements P260, P264, P270, P271, P280, P301+330+331, P305+351+338, P304+340, P303+361+353, P363, P405, P501
EU Index 016-015-00-0
EU classification Corrosive C
R-phrases R14, R20/22, R29, R35
S-phrases (S1/2), S26, S30, S36/37/39, S45
Main hazards Water- and moisture- sensitive, reactive.
Never add water to this product as the hydrolysis reaction with water is violent.
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 4: Very short exposure could cause death or major residual injury. E.g., VX gas Reactivity code 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g., phosphorus Special hazard W: Reacts with water in an unusual or dangerous manner. E.g., cesium, sodiumNFPA 704 four-colored diamond
Flash point Non-flammable
Related compounds
Related thionyl halides Thionyl fluoride
Thionyl bromide
Thionyl iodide
Related compounds Sulfuryl chloride
Selenium oxydichloride
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Thionyl chloride is an inorganic compound with the formula SOCl2. It is a reactive chemical used as a reagent in chlorination reactions. It is a colorless, distillable liquid at room temperature and pressure with a nauseating pungent odor that decomposes above 140 °C.

Thionyl chloride is sometimes confused with sulfuryl chloride, SO2Cl2, but the properties of these compounds differ significantly. Sulfuryl chloride is a source of chlorine whereas thionyl chloride is a source of chloride ions.

Approximately 45,000 tons per year of SOCl2 were produced in the early 1990s.[4]

Properties and structure[edit]

The molecule SOCl2 is pyramidal, indicating the presence of a lone pair of electrons on the sulfur(IV) center. In contrast, the stoichiometrically related 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:[5]

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.


Organic chemistry[edit]

Thionyl chloride is mainly used in the industrial production of organochlorine compounds, which are often intermediates in pharmaceuticals and agrichemicals. In some cases it requires purification prior to use.[6]

Thionyl chloride is widely used in organic synthesis for the synthesis of organochlorides. It usually is preferred over other reagents, such as phosphorus pentachloride, as its by-products (HCl and SO2) are gaseous, which simplifies purification of the product. Classically, it converts carboxylic acids to acyl chlorides[7]

RCO2H + SOCl2 → RC(O)Cl + HCl + SO2

By a similar stoichiometry it also converts alcohols to alkyl chlorides.

RCH2OH + SOCl2 → RCH2Cl + HCl + SO2

These reactions proceed via ester intermediates of the type RCH2OS(O)Cl, which decompose via the SNi mechanism.[8]

Many of the products of thionyl chloride are themselves highly reactive, which in combination with its easily removed by-products makes thionyl chloride well suited to one pot synthesis. Examples include the synthesis of oxazoline rings and the Darzens reaction[9] (shown below) which proceeds via an internal nucleophilic substitution.

Bicifadine synthesis Xu 2007

Thionyl chloride can facilitate numerous chemical transformations, some of which are shown below. Going clockwise from the top: 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] and can also produce nitriles from amides via E2 elimination.[13] Thionyl chloride can be used in variations of the Pummerer rearrangement. Sulfonic acids react with thionyl chloride to produce sulfonyl chlorides.[14][15] Sulfonyl chlorides have also been prepared from the direct reaction of the corresponding diazonium salt with thionyl chloride.[16]

SOCl2 reactions.png

Inorganic chemistry[edit]

Anhydrous metal chlorides may be obtained from hydrated metal chlorides by refluxing in freshly distilled thionyl chloride:[17]

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

Other applications[edit]

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), see lithium battery.


SOCl2 is a reactive compound that can violently and/or 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.

See also[edit]


  1. ^ Thionyl chloride in Linstrom, P.J.; Mallard, W.G. (eds.) NIST Chemistry WebBook, NIST Standard Reference Database Number 69. National Institute of Standards and Technology, Gaithersburg MD. (retrieved 2014-05-11)
  2. ^ Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0-07-049439-8
  3. ^ a b c d
  4. ^ Hans-Dietrich Lauss, Wilfried Steffens “Sulfur Halides” in Ullmann's Encyclopedia of Industrial Chemistry Wiley-VCH, Weinheim, 2005.doi:10.1002/14356007.a25_623
  5. ^ Greenwood, Norman N.; Earnshaw, Alan (1984). Chemistry of the Elements. Oxford: Pergamon Press. p. 820. ISBN 0-08-022057-6. .
  6. ^ Friedman, L. and Wetter, W. P., "Purification of Thionyl Chloride", J. Chem. Soc. A, 1967, 36-8.doi:10.1039/J19670000036
  7. ^ 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 
  8. ^ Smith, Michael B.; March, Jerry (2007), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (6th ed.), New York: Wiley-Interscience, ISBN 0-471-72091-7 
  9. ^ 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. 
  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 1-4390-4971-8. 
  14. ^ Weinreb, S. M.; Chase, C. E.; Wipf, P.; Venkatraman, S. (2004), "2-Trimethylsilylethanesulfonyl chloride (SES-Cl)", Org. Synth. ; Coll. Vol. 10: 707 
  15. ^ 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 
  16. ^ 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. 
  17. ^ 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 978-0-470-13259-3. 

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