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Thionyl chloride

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Thionyl chloride
Structure of thionyl chloride3D model of thionyl chloride
General
Systematic name thionyl dichloride
Other names sulfurous oxychloride
sulfurous dichloride
sulfinyl chloride
sulfinyl dichloride
dichlorosulfoxide
Molecular formula SOCl2
Molar mass 118.97 g/mol
Appearance clear to yellow
odorous liquid
CAS number 7719-09-7
Properties
Density 1.638 g ml−1, liquid
Solubility in water Reactive
Melting point −104.5 °C
Boiling point 76 °C
Viscosity 0.6 cP at ? °C
Structure
Molecular shape pyramidal
Dipole moment 1.4 D
Hazards
MSDS External MSDS
EU classification Corrosive (C)
NFPA 704
NFPA 704
safety square
NFPA 704 four-colored diamondHealth 4: Very short exposure could cause death or major residual injury. E.g. VX gasFlammability (red): no hazard codeInstability 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g. white phosphorusSpecial hazards (white): no code
4
2
R-phrases Template:R14, Template:R20/22, Template:R29, Template:R35
S-phrases Template:S1/2, Template:S26, Template:S36/37/39, Template:S45
Flash point non flammable
Supplementary data page
Structure and
properties 		n, εr, etc.
Thermodynamic
data 		Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
Related compounds
Other anions 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, 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=SCl2 → SO2 + 2 HCl

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

Industrial usage

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.

Use in organic chemistry

Thionyl chloride is widely used to convert carboxylic acids[1][2] and alcohols[3][4] to the corresponding acyl chlorides and alkyl chlorides respectively. 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=SCl2 → RC(O)Cl + SO2 + HCl
R-OH + O=SCl2 → R-Cl + SO2 + HCl

Sulfonic acids react with thionyl chloride to produce sulfonyl chlorides.[5][6] Likewise, thionyl chloride will transform sulfinic acids into sulfinyl chlorides[7][8] and phosphonic acids into phosphoryl chlorides.

Miscellaneous reactions

Thionyl chloride will react with primary formamides to form isocyanides.[9]

Amides will react with thionyl chloride to form imidoyl chlorides. However, primary amides under heating with thionyl chloride will continue on to form nitriles.[10]

Synthesis of thionyl chloride

The major industrial synthesis involves the reaction of sulfur trioxide and sulfur dichloride:[11]

SO3 + SCl2 → SOCl2 + SO2

Other methods include:

SO2 + PCl5 → SOCl2 + 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.

Safety and toxicity considerations

SOCl2 is toxic, corrosive, and lachrymatory. It is a skin and inhalation hazard, as well as being odorous,

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

References

  1. ^ Allen, C. F. H.; Byers, Jr., J. R.; Humphlett, W. J. Org. Syn., Coll. Vol. 4, p.739 (1963); Vol. 37, p.66 (1957). (Article)
  2. ^ Rutenberg, M. W.; Horning, E. C. Org. Syn., Coll. Vol. 4, p.620 (1963); Vol. 30, p.62 (1950). (Article)
  3. ^ Weinreb, S. M.; Chase, C. E.; Wipf, P.; Venkatraman, S. Org. Syn., Coll. Vol. 10, p.707 (2004); Vol. 75, p.161 (1998). (Article)
  4. ^ Hazen, G. G.; Bollinger, F. W.; Roberts, F. E.; Russ, W. K.; Seman, J. J.; Staskiewicz, S. Org. Syn., Coll. Vol. 9, p.400 (1998); Vol. 73, p.144 (1996). (Article)
  5. ^ Hulce, M.; Mallomo, J. P.; Frye, L. L.; Kogan, T. P.; Posner, G. H. Org. Syn., Coll. Vol. 7, p.495 (1990); Vol. 64, p.196 (1986). (Article)
  6. ^ Kurzer, F. Org. Syn., Coll. Vol. 4, p.937 (1963); Vol. 34, p.93 (1954). (Article)
  7. ^ Mondanaro, K. R.; Dailey, W. P. Org. Syn., Coll. Vol. 10, p.212 (2004); Vol. 75, p.89 (1998). (Article)
  8. ^ Krakowiak, K. E.; Bradshaw, J. S. Org. Syn., Coll. Vol. 9, p.34 (1998); Vol. 70, p.129 (1992). (Article)
  9. ^ Niznik, G. E.; Morrison, III, W. H.; Walborsky, H. M. Org. Syn., Coll. Vol. 6, p.751 (1988); Vol. 51, p.31 (1971). (Article)
  10. ^ Krynitsky, J. A.; Carhart, H. W. Org. Syn., Coll. Vol. 4, p.436 (1963); Vol. 32, p.65 (1952). (Article)
  11. ^ N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, Pergamon Press, 1984.

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