Thionyl chloride is an inorganic compound with the chemical formulaSOCl2. It is a moderately volatile, colourless liquid with an unpleasant acrid odour. Thionyl chloride is primarily used as a chlorinating reagent, with approximately 45,000 tonnes (50,000 short tons) per year being produced during the early 1990s,[5] but is occasionally also used as a solvent.[6][7][8] It is toxic, reacts with water, and is also listed under the Chemical Weapons Convention as it may be used for the production of chemical weapons.
Except where otherwise noted, 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 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.
Productionedit
The major industrial synthesis involves the reaction of sulfur trioxide and sulfur dichloride:[9] This synthesis can be adapted to the laboratory by heating oleum to slowly distill the sulfur trioxide into a cooled flask of sulfur dichloride.[10]
The second of the above four reactions also affords phosphorus oxychloride (phosphoryl chloride), which resembles thionyl chloride in many of its reactions.
Thionyl chloride has a long shelf life, however "aged" samples develop a yellow hue, possibly due to the formation of disulfur dichloride. It slowly decomposes to S2Cl2, SO2 and Cl2 at just above the boiling point.[9][12] Thionyl chloride is susceptible to photolysis, which primarily proceeds via a radical mechanism.[13] Samples showing signs of ageing can be purified by distillation under reduced pressure, to give a colourless liquid.[14]
Reactionsedit
Thionyl chloride is mainly used in the industrial production of organochlorine compounds, which are often intermediates in pharmaceuticals and agrichemicals. 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.
Many of the products of thionyl chloride are themselves highly reactive and as such it is involved in a wide range of reactions.
By a similar process it also reacts with alcohols to form alkyl chlorides. If the alcohol is chiral the reaction generally proceeds via an SNi mechanism with retention of stereochemistry;[15] however, depending on the exact conditions employed, stereo-inversion can also be achieved. Historically the use of SOCl2 with pyridine was called the Darzens halogenation, but this name is rarely used by modern chemists.
Sulfonic acids react with thionyl chloride to produce sulfonyl chlorides.[28][29] Sulfonyl chlorides have also been prepared from the direct reaction of the corresponding diazonium salt with thionyl chloride.[30]
As SOCl2 reacts with water it can be used to dehydrate various metal chloride hydrates, such magnesium chloride (MgCl2·6H2O), aluminium chloride (AlCl3·6H2O), and iron(III) chloride (FeCl3·6H2O).[9] This conversion involves treatment with refluxing thionyl chloride and follows the following general equation:[31]
Other reactionsedit
Thionyl chloride can engage in a range of different electrophilic addition reactions. It adds to alkenes in the presence of AlCl3 to form an aluminium complex which can be hydrolysed to form a sulfinic acid. Both aryl sulfinyl chlorides and diaryl sulfoxides can be prepared from arenes through reaction with thionyl chloride in triflic acid[32] or the presence of catalysts such as BiCl3, Bi(OTf)3, LiClO4 or NaClO4.[33][34]
In the laboratory, a reaction between thionyl chloride and an excess of anhydrous alcohol can be used to produce anhydrous alcoholic solutions of HCl.
Thionyl chloride undergoes halogen exchange reactions to give other thionyl species.
Thionyl iodide can likewise be prepared by a reaction with potassium iodide, but is reported to be highly unstable.[35][36]
Batteriesedit
Thionyl chloride is a component of lithium–thionyl chloride batteries,[37] where it acts as the positive electrode (in batteries: cathode) with lithium forming the negative electrode (anode); the electrolyte is typically lithium tetrachloroaluminate. The overall discharge reaction is as follows:
These non-rechargeable batteries had many advantages over other forms of lithium batteries such as a high energy density, a wide operational temperature range, and long storage and operational lifespans. However, their high cost, non-rechargeability, and safety concerns have limited their use. The contents of the batteries are highly toxic and require special disposal procedures; additionally, they may explode if shorted. The technology was used on the Sojourner Mars rover.
Safetyedit
SOCl2 is highly reactive and can violently release hydrochloric acid upon contact with water and alcohols. It is also a controlled substance under the Chemical Weapons Convention, where it is listed as a Schedule 3 substance, since it is used in the manufacture of G-series nerve agents[citation needed] and the Meyer and Meyer–Clarke methods of producing sulfur-based mustard gases.[38]
Historyedit
In 1849, the French chemists Jean-François Persoz and Bloch, and the German chemist Peter Kremers (1827-?), independently first synthesized thionyl chloride by reacting phosphorus pentachloride with sulfur dioxide.[39][40] However, their products were impure: both Persoz and Kremers claimed that thionyl chloride contained phosphorus,[41] and Kremers recorded its boiling point as 100 °C (instead of 74.6 °C). In 1857, the German-Italian chemist Hugo Schiff subjected crude thionyl chloride to repeated fractional distillations and obtained a liquid which boiled at 82 °C and which he called Thionylchlorid.[42] In 1859, the German chemist Georg Ludwig Carius noted that thionyl chloride could be used to make acid anhydrides and acyl chlorides from carboxylic acids and to make alkyl chlorides from alcohols.[43]
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^Arrieta, A.; Aizpurua, J. M.; Palomo, C. (1984). "N,N-Dimethylchlorosulfitemethaniminium chloride (SOCl2-DMF) a versatile dehydrating reagent". Tetrahedron Letters. 25 (31): 3365–3368. doi:10.1016/S0040-4039(01)81386-1.
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^Weinreb, S. M.; Chase, C. E.; Wipf, P.; Venkatraman, S. (2004). "2-Trimethylsilylethanesulfonyl chloride (SES-Cl)". Organic Syntheses; Collected Volumes, vol. 10, p. 707.
^Hazen, G. G.; Bollinger, F. W.; Roberts, F. E.; Russ, W. K.; Seman, J. J.; Staskiewicz, S. (1998). "4-Dodecylbenzenesulfonyl azides". Organic Syntheses; Collected Volumes, vol. 9, p. 400.
^Hogan, P. J.; Cox, B. G. (2009). "Aqueous Process Chemistry: The Preparation of Aryl Sulfonyl Chlorides". Organic Process Research & Development. 13 (5): 875–879. doi:10.1021/op9000862.
^Pray, A. R.; Heitmiller, R. F.; Strycker, S.; Aftandilian, V. D.; Muniyappan, T.; Choudhury, D.; Tamres, M. (1990). "Anhydrous Metal Chlorides". Inorganic Syntheses. Vol. 28. pp. 321–323. doi:10.1002/9780470132593.ch80. ISBN 978-0-470-13259-3.
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^Peyronneau, M.; Roques, N.; Mazières, S.; Le Roux, C. (2003). "Catalytic Lewis Acid Activation of Thionyl Chloride: Application to the Synthesis of Aryl Sulfinyl Chlorides Catalyzed by Bismuth(III) Salts". Synlett (5): 0631–0634. doi:10.1055/s-2003-38358.
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^Rao, M. R. Aswathanarayana (March 1940). "Thionyl iodide: Part I. Formation of thionyl iodide". Proceedings of the Indian Academy of Sciences - Section A. 11 (3): 185–200. doi:10.1007/BF03046547. S2CID 104552644.
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^Institute of Medicine (1993). Chapter 5: Chemistry of Sulfur Mustard and Lewisite. The National Academies Press. ISBN 0-309-04832-X. {{cite book}}: |work= ignored (help)
Persoz; Bloch (1849). "Des composés binaires formés par les métalloïdes, et, en particulier, de l'action du chloride phosphorique sur les acides sulfureux, sulfurique, phosphorique, chromique, etc" [Binary compounds formed by metalloids and in particular the action of phosphorus pentachloride on sulfurous acid, sulfuric acid, phosphoric acid, chromic acid, etc.]. Comptes rendus (in French). 28: 86–88.
Persoz; Bloch (1849). "Addition à une Note précédente concernant les combinaisons du chloride phosphorique avec les acides phosphorique, sulfurique et sulfureux" [Addition to a preceding note concerning compounds of phosphorus pentachloride with phosphoric acid, sulfuric acid, and sulfurous acid]. Comptes rendus (in French). 28: 389.
^Kremers, P. (1849). "Ueber schwefligsaures Phosphorchlorid" [On sulfurous phosphorus pentachloride]. Annalen der Chemie und Pharmacie (in German). 70 (3): 297–300. doi:10.1002/jlac.18490700311.
^The German chemist Georg Ludwig Carius noted that, when the reaction mixture that produced thionyl chloride was distilled, the crude mixture initially released substantial quantities of gas, so that phosphoryl chloride (POCl3) was carried into the receiver. Carius, L. (1859). "Ueber die Chloride des Schwefels und deren Derivate" [On sulfur chloride and its derivatives]. Annalen der Chemie und Pharmacie (in German). 111: 93–113. doi:10.1002/jlac.18591110111. From p. 94: " … dabei ist jedoch die Vorsicht zu gebrauchen, … und nie reines Chlorthionyl erhalten wird." ( … however, during that [i.e., the fractional distillation], caution must be used, [so] that one carefully avoids a concentration of hydrogen chloride or excess sulfurous acid in the liquid that is to be distilled, as otherwise, by the evolution of gas that occurs at the start of the distillation, much phosphoryl chloride is transferred and pure thionyl chloride is never obtained.)
^Schiff, Hugo (1857). "Ueber die Einwirkung des Phosphorsuperchlorids auf einige anorganische Säuren" [On the reaction of phosphorus pentachloride with some inorganic acids]. Annalen der Chemie und Pharmacie (in German). 102: 111–118. doi:10.1002/jlac.18571020116. The boiling point of thionyl chloride which Schiff observed, appears on p. 112. The name Thionylchlorid is coined on p. 113.
^Carius, L. (1859). "Ueber die Chloride des Schwefels und deren Derivate" [On sulfur chloride and its derivatives]. Annalen der Chemie und Pharmacie (in German). 111: 93–113. doi:10.1002/jlac.18591110111.
On p. 94, Carius notes that thionyl chloride can be " … mit Vortheil zur Darstellung wasserfreier Säuren verwenden." ( … used advantageously for the preparation of acid anhydrides.) Also on p. 94, Carius shows chemical equations in which thionyl chloride is used to transform benzoic acid (OC7H5OH) into benzoyl chloride (ClC7H5O) and to transform sodium benzoate into benzoic anhydride. On p. 96, he mentions that thionyl chloride will transform methanol into methyl chloride (Chlormethyl). Thionyl chloride behaves like phosphoryl chloride: from pp. 94-95: "Die Einwirkung des Chlorthionyls … die Reaction des Chlorthionyls weit heftiger statt." (The reaction of thionyl chloride with [organic] substances containing oxygen proceeds in general parallel to that of phosphoryl chloride; where the latter exerts an effect, thionyl chloride usually does so also, only in nearly all cases the reaction occurs far more vigorously.)