Thionyl chloride

The major industrial synthesis involves the reaction of sulfur trioxide and sulfur dichloride.{{Greenwood&Earnshaw2nd|page=694}} This synthesis can be adapted to the laboratory by heating oleum to slowly distill the sulfur trioxide into a cooled flask of sulfur dichloride.{{cite book|last=Brauer|first=George|date=1963|title=Handbook of Preparative Inorganic Chemistry|doi=10.1016/B978-0-12-395590-6.50015-6|pages=382–383}}

:{{chem2 | SO3 + SCl2 -> SOCl2 + SO2 }}

Other methods include syntheses from:

• Phosphorus pentachloride:

::{{chem2 | SO2 + PCl5 -> SOCl2 + POCl3 }}

• Chlorine and sulfur dichloride:

::{{chem2 | SO2 + Cl2 + SCl2 -> 2 SOCl2 }}

::{{chem2 | SO3 + Cl2 + 2SCl2 -> 3 SOCl2 }}

• Phosgene:

::{{chem2 | SO2 + COCl2 -> SOCl2 + CO2 }}

The second of the above five reactions also affords phosphorus oxychloride (phosphoryl chloride), which resembles thionyl chloride in many of its reactions. They may be separated by distillation, since thionyl chloride boils at a much lower temperature than phosphoryl chloride.{{cn|date=May 2024}}

SOCl₂ adopts a trigonal pyramidal molecular geometry with C_s molecular symmetry. This geometry is attributed to the effects of the lone pair on the central sulfur(IV) center.

In the solid state SOCl₂ forms monoclinic crystals with the space group P2₁/c.{{cite journal|last1=Mootz|first1=D.|last2=Merschenz-Quack|first2=A.|title=Structures of thionyl halides: SOCl₂ and SOBr₂|journal=Acta Crystallographica Section C|date=15 May 1988|volume=44|issue=5|pages=926–927|doi=10.1107/S010827018800085X|bibcode=1988AcCrC..44..926M |url=http://journals.iucr.org/c/issues/1988/05/00/bx0227/bx0227.pdf}}

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.{{cite book|editor-first=Georg|editor-last=Brauer|translator1=Scripta Technica|translator2-last=Reed|translator2-first=F.|title=Handbook of Preparative Inorganic Chemistry|volume=1|date=1963|publisher=Academic Press|location=New York, NY|isbn=978-0121266011|page=383|edition=2nd}} Thionyl chloride is susceptible to photolysis, which primarily proceeds via a radical mechanism.{{cite journal|last1=Donovan|first1=R. J.|last2=Husain|first2=D.|last3=Jackson|first3=P. T.|title=Spectroscopic and kinetic studies of the SO radical and the photolysis of thionyl chloride|journal=Transactions of the Faraday Society|volume=65|pages=2930|doi=10.1039/TF9696502930|year=1969}} Samples showing signs of ageing can be purified by distillation under reduced pressure, to give a colourless liquid.{{cite journal|last1=Friedman|first1=L.|last2=Wetter|first2=W. P.|title=Purification of thionyl chloride|journal=Journal of the Chemical Society A: Inorganic, Physical, Theoretical|date=1967|pages=36|doi=10.1039/J19670000036}}

File:Thionyl chloride 25ml.jpg

Thionyl chloride is mainly used in the industrial production of organochlorine compounds, which are often intermediates in pharmaceuticals and agrochemicals. It usually is preferred over other reagents, such as phosphorus pentachloride, as its by-products (HCl and {{chem2|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.

Thionyl chloride reacts exothermically with water to form sulfur dioxide and hydrochloric acid:

:{{chem2 | SOCl2 + H2O -> 2 HCl + SO2 }}

By a similar process it also reacts with alcohols to form alkyl chlorides. If the alcohol is chiral the reaction generally proceeds via an S_Ni mechanism with retention of stereochemistry;{{March6th|page=469}} however, depending on the exact conditions employed, stereo-inversion can also be achieved. Historically the use of {{chem2|SOCl2}} with pyridine was called the Darzens halogenation, but this name is rarely used by modern chemists.

File:SNi reaction mechanism.svg

Reactions with an excess of alcohol produce sulfite esters, which can be powerful methylation, alkylation and hydroxyalkylation reagents.{{cite journal|last1=Van Woerden|first1=H. F.|title=Organic Sulfites|journal=Chemical Reviews|volume=63|issue=6|pages=557–571|doi=10.1021/cr60226a001|year=1963}}

:{{chem2 | SOCl2 + 2 R\sOH -> (R\sO)2SO + 2 HCl }}

For example, the addition of {{chem2|SOCl2}} to amino acids in methanol selectively yields the corresponding methyl esters.{{cite journal|last1=Brenner|first1=M.|last2=Huber|first2=W.|title=Herstellung von α-Aminosäureestern durch Alkoholyse der Methylester|trans-title=Manufacture of α-amino acid esters by alcoholysis of methyl esters|journal=Helvetica Chimica Acta|volume=36|issue=5|pages=1109–1115|doi=10.1002/hlca.19530360522|language=de|year=1953}}

Classically, it converts carboxylic acids to acyl chlorides:{{Clayden|page=295}}{{OrgSynth | last1 = Allen | first1 = C. F. H. | last2 = Byers | first2 = J. R. Jr | last3 = Humphlett | first3 = W. J. | collvol = 4 | collvolpages = 739 | year = 1963 | title = Oleoyl chloride | prep = cv4p0739}}{{OrgSynth | last1 = Rutenberg | first1 = M. W. | last2 = Horning | first2 = E. C. | collvol = 4 | collvolpages = 620 | year = 1963 | title = 1-Methyl-3-ethyloxindole | prep = cv4p0620}}

:{{chem2 | SOCl2 + R\sCOOH -> R\sCOCl + SO2 + HCl }}

The reaction mechanism has been investigated:{{Clayden|page=}}

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With primary amines, thionyl chloride gives sulfinylamine derivatives (RNSO), one example being N-sulfinylaniline. Thionyl chloride reacts with primary formamides to form isocyanides{{OrgSynth | last1 = Niznik | first1 = G. E. | last2 = Morrison | first2 = W. H., III | last3 = Walborsky | first3 = H. M. | collvol = 6 | collvolpages = 751 | year = 1988 | title = 1-d-Aldehydes from organometallic reagents: 2-methylbutanal-1-d | prep = cv6p0751}} and with secondary formamides to give chloroiminium ions; as such a reaction with dimethylformamide will form the Vilsmeier reagent.{{cite journal|last1=Arrieta|first1=A.|last2=Aizpurua|first2=J. M.|last3=Palomo|first3=C.|title=N,N-Dimethylchlorosulfitemethaniminium chloride (SOCl2-DMF) a versatile dehydrating reagent|journal=Tetrahedron Letters|volume=25|issue=31|pages=3365–3368|doi=10.1016/S0040-4039(01)81386-1|year=1984}}

By an analogous process, primary amides will react with thionyl chloride to form imidoyl chlorides, with secondary amides also giving chloroiminium ions. These species are highly reactive and can be used to catalyse the conversion of carboxylic acids to acyl chlorides;{{cite book | author = Clayden, J. | title = Organic Chemistry | publisher = Oxford University Press | location = Oxford | year = 2001 | pages = [https://archive.org/details/organicchemistry00clay_0/page/276 276–296] | isbn = 0-19-850346-6 | url-access = registration | url = https://archive.org/details/organicchemistry00clay_0/page/276 }} they are also exploited in the Bischler–Napieralski reaction as a means of forming isoquinolines.

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Primary amides will continue on to form nitriles if heated (Von Braun amide degradation).{{OrgSynth | last1 = Krynitsky | first1 = J. A. | last2 = Carhart | first2 = H. W. | collvol = 4 | collvolpages = 436 | year = 1963 | title = 2-Ethylhexanonitrile | prep = cv4p0436}}

Thionyl chloride has also been used to promote the Beckmann rearrangement of oximes.

• Thionyl chloride will transform sulfinic acids into sulfinyl chlorides{{OrgSynth | last1 = Hulce | first1 = M. | last2 = Mallomo | first2 = J. P. | last3 = Frye | first3 = L. L. | last4 = Kogan | first4 = T. P. | last5 = Posner | first5 = G. H. | collvol = 7 | collvolpages = 495 | year = 1990 | title = (S)-(+)-2-(p-toluenesulfinyl)-2-cyclopentenone: Precursor for enantioselective synthesis of 3-substituted cyclopentanones | prep = cv7p0495}}{{OrgSynth | last = Kurzer | first= F. | collvol = 4 | collvolpages = 937 | year = 1963 | title = p-Toluenesulfinyl chloride | prep = cv4p0937}}
• Sulfonic acids react with thionyl chloride to produce sulfonyl chlorides.{{OrgSynth | last1 = Weinreb | first1 = S. M. | last2 = Chase | first2 = C. E. | last3 = Wipf | first3 = P. | last4 = Venkatraman | first4 = S. | collvol = 10 | collvolpages = 707 | year = 2004 | title = 2-Trimethylsilylethanesulfonyl chloride (SES-Cl) | prep = v75p0161}}{{OrgSynth | last1 = Hazen | first1 = G. G. | last2 = Bollinger | first2 = F. W. | last3 = Roberts | first3 = F. E. | last4 = Russ | first4 = W. K. | last5 = Seman | first5 = J. J. | last6 = Staskiewicz | first6 = S. | collvol = 9 | collvolpages = 400 | year = 1998 | title = 4-Dodecylbenzenesulfonyl azides | prep = cv9p0400}} Sulfonyl chlorides have also been prepared from the direct reaction of the corresponding diazonium salt with thionyl chloride.{{cite journal | title = Aqueous Process Chemistry: The Preparation of Aryl Sulfonyl Chlorides |first1=P. J. |last1=Hogan |first2=B. G. |last2=Cox | journal = Organic Process Research & Development | year = 2009 | volume = 13 | issue = 5 | pages = 875–879 | doi = 10.1021/op9000862}}
• Thionyl chloride can be used in variations of the Pummerer rearrangement.

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Thionyl chloride converts phosphonic acids and phosphonates into phosphoryl chlorides. It is for this type of reaction that thionyl chloride is listed as a Schedule 3 compound, as it can be used in the "di-di" method of producing G-series nerve agents. For example, thionyl chloride converts dimethyl methylphosphonate into methylphosphonic acid dichloride, which can be used in the production of sarin and soman.

As {{chem2|SOCl2}} reacts with water it can be used to dehydrate various metal chloride hydrates, such magnesium chloride ({{chem2|MgCl2*6H2O}}), aluminium chloride ({{chem2|AlCl3*6H2O}}), and iron(III) chloride ({{chem2|FeCl3*6H2O}}). This conversion involves treatment with refluxing thionyl chloride and follows the following general equation:{{cite book | first1 = A. R. | last1 =Pray | first2 = R. F. | last2 = Heitmiller | first3 = S. | first4 = V. D. | last4 = Aftandilian | first5 = T. | last5 = Muniyappan | first6 = D. | last6 = Choudhury | first7 = M. | last7 = Tamres | last3 = Strycker | title = Inorganic Syntheses | chapter = Anhydrous Metal Chlorides | volume = 28 | pages = 321–323 | doi = 10.1002/9780470132593.ch80 | year = 1990 | isbn = 978-0-470-13259-3 }}

:{{chem2 | MCl_{n}•xH2O + SOCl2 -> MCl_{n} + x SO2 + 2x HCl }}

If an excess of {{chem2|SOCl2}} is used to dehydrate aluminium trichloride, it will form an adduct (1 molecule of thionyl chloride for each molecule of the aluminium trichloride dimer).

• Thionyl chloride can engage in a range of different electrophilic addition reactions. It adds to alkenes in the presence of {{chem2|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{{March6th|page=697}} or the presence of catalysts such as {{chem2|BiCl3}}, {{chem2|Bi(OTf)3}}, {{chem2|LiClO4}} or {{chem2|NaClO4}}.{{cite journal|last1=Peyronneau|first1=M.|last2=Roques|first2=N.|last3=Mazières|first3=S.|last4=Le Roux|first4=C.|title=Catalytic Lewis Acid Activation of Thionyl Chloride: Application to the Synthesis of Aryl Sulfinyl Chlorides Catalyzed by Bismuth(III) Salts|journal=Synlett|date=2003|issue=5|pages=0631–0634|doi=10.1055/s-2003-38358}}{{cite journal |last1=Bandgar |first1= B. P. |last2=Makone|first2= S. S. | title = Lithium/Sodium Perchlorate Catalyzed Synthesis of Symmetrical Diaryl Sulfoxides| year = 2004 | journal = Synthetic Communications | volume = 34| pages = 743–750 | doi = 10.1081/SCC-120027723 | issue = 4 |s2cid= 96348273}}
• 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.

:Reactions with fluorinating agents such as antimony trifluoride give thionyl fluoride:

::{{chem2 | 3 SOCl2 + 2 SbF3 -> 3 SOF2 + 2 SbCl3 }}

: A reaction with hydrogen bromide gives thionyl bromide:

::{{chem2 | SOCl2 + 2 HBr -> SOBr2 + 2 HCl }}

:Thionyl iodide can likewise be prepared by a reaction with potassium iodide, but is reported to be highly unstable.{{cite journal |last1=Rao |first1=M. R. Aswathanarayana |title=Thionyl iodide: Part I. Formation of thionyl iodide |journal=Proceedings of the Indian Academy of Sciences - Section A |date=March 1940 |volume=11 |issue=3 |pages=185–200 |doi=10.1007/BF03046547|s2cid=104552644 }}{{cite journal |last1=Rao |first1=M. R. Aswathanarayana |title=Thionyl iodide: Part II. Rate of decomposition and spectroscopic |journal=Proceedings of the Indian Academy of Sciences - Section A |date=March 1940 |volume=11 |issue=3 |pages=201–205 |doi=10.1007/BF03046548|s2cid=104752226 }}

File:Lithium Thionyl Chloride Battery.JPG

Thionyl chloride is a component of lithium–thionyl chloride batteries,{{cite journal |last1=Gangadharan |first1=R. |last2=Namboodiri |first2=P.N.N. |last3=Prasad |first3=K.V. |last4=Viswanathan |first4=R. |title=The lithium—thionyl chloride battery — a review |journal=Journal of Power Sources |date=January 1979 |volume=4 |issue=1 |pages=1–9 |doi=10.1016/0378-7753(79)80032-4|bibcode=1979JPS.....4....1G }} 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:

:{{chem2 | 4 Li + 2 SOCl2 -> 4 LiCl +}} {{fraction|1|8}} {{chem2 | S8 + SO2 }}

These non-rechargeable batteries have 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 very corrosive, the {{chem2|SO2}} is toxic by inhalation, and the batteries therefore require special disposal procedures; additionally, they may explode if shorted. The technology was used on the 1997 Sojourner Mars rover.

{{chem2|SOCl2}} is highly reactive, releasing hydrochloric acid and sulfur dioxide 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|date=August 2018}} and the Meyer and Meyer–Clarke methods of producing sulfur-based mustard gases.{{cite book|url=http://books.nap.edu/openbook.php?record_id=2058&page=71|chapter=Chapter 5: Chemistry of Sulfur Mustard and Lewisite|author=Institute of Medicine |year=1993 |title=Veterans at Risk: The Health Effects of Mustard Gas and Lewisite |publisher=The National Academies Press |isbn=0-309-04832-X}}

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.See:

• {{cite journal |last1=Persoz |last2=Bloch |title=Des composés binaires formés par les métalloïdes, et, en particulier, de l'action du chloride phosphorique sur les acides sulfureux, sulfurique, phosphorique, chromique, etc. |journal=Comptes rendus |date=1849 |volume=28 |pages=86–88 |url=https://babel.hathitrust.org/cgi/pt?id=mdp.39015035450975;view=1up;seq=96 |trans-title=Binary compounds formed by metalloids and in particular the action of phosphorus pentachloride on sulfurous acid, sulfuric acid, phosphoric acid, chromic acid, etc. |language=fr}}
• {{cite journal |last1=Persoz |last2=Bloch |title=Addition à une Note précédente concernant les combinaisons du chloride phosphorique avec les acides phosphorique, sulfurique et sulfureux |journal=Comptes rendus |date=1849 |volume=28 |page=389 |url=https://babel.hathitrust.org/cgi/pt?id=mdp.39015035450975;view=1up;seq=401 |trans-title=Addition to a preceding note concerning compounds of phosphorus pentachloride with phosphoric acid, sulfuric acid, and sulfurous acid |language=fr}}{{cite journal |last1=Kremers |first1=P. |title=Ueber schwefligsaures Phosphorchlorid |journal=Annalen der Chemie und Pharmacie |date=1849 |volume=70 |issue=3 |pages=297–300 |url=https://babel.hathitrust.org/cgi/pt?id=hvd.hx3bh3;view=1up;seq=703 |trans-title=On sulfurous phosphorus pentachloride |language=de |doi=10.1002/jlac.18490700311}} However, their products were impure: both Persoz and Kremers claimed that thionyl chloride contained phosphorus,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. {{cite journal |last1=Carius |first1=L. |title=Ueber die Chloride des Schwefels und deren Derivate |journal=Annalen der Chemie und Pharmacie |date=1859 |volume=111 |pages=93–113 |url=https://babel.hathitrust.org/cgi/pt?id=hvd.hx3bhp;view=1up;seq=107 |trans-title=On sulfur chloride and its derivatives |language=de |doi=10.1002/jlac.18591110111|url-access=subscription }} 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.) 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.{{cite journal |last1=Schiff |first1=Hugo |title=Ueber die Einwirkung des Phosphorsuperchlorids auf einige anorganische Säuren |journal=Annalen der Chemie und Pharmacie |date=1857 |volume=102 |pages=111–118 |url=https://babel.hathitrust.org/cgi/pt?id=mdp.39015026321813;view=1up;seq=509 |trans-title=On the reaction of phosphorus pentachloride with some inorganic acids |language=de |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. 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.{{cite journal |last1=Carius |first1=L. |title=Ueber die Chloride des Schwefels und deren Derivate |journal=Annalen der Chemie und Pharmacie |date=1859 |volume=111 |pages=93–113 |url=https://babel.hathitrust.org/cgi/pt?id=hvd.hx3bhp;view=1up;seq=107 |trans-title=On sulfur chloride and its derivatives |language=de |doi=10.1002/jlac.18591110111|url-access=subscription }}

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.)

• Oxalyl chloride
• Phosphorus pentachloride
• Phosgene
• Sulfur dichloride
• Thionyl bromide

{{reflist|30em}}

{{Chemical agents}}

{{sulfur compounds}}

Category:Thionyl compounds

Category:Sulfur(IV) compounds

Category:Sulfur oxohalides

Category:Oxychlorides

Category:Reagents for organic chemistry

Category:Lachrymatory agents

Category:Foul-smelling chemicals

Category:Inorganic solvents