Thionyl chloride is an
inorganic compound with the
chemical formula
In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbol ...
. It is a moderately
volatile, colourless liquid with an unpleasant acrid odour. Thionyl chloride is primarily used as a
chlorinating reagent, with approximately per year being produced during the early 1990s, but is occasionally also used as a solvent. It is toxic, reacts with water, and is also
listed
Listed may refer to:
* Listed, Bornholm, a fishing village on the Danish island of Bornholm
* Listed (MMM program), a television show on MuchMoreMusic
* Endangered species in biology
* Listed building, in architecture, designation of a historicall ...
under the
Chemical Weapons Convention as it may be used for the production of
chemical weapons
A chemical weapon (CW) is a specialized munition that uses chemicals formulated to inflict death or harm on humans. According to the Organisation for the Prohibition of Chemical Weapons (OPCW), this can be any chemical compound intended as a ...
.
Thionyl chloride is sometimes confused with
sulfuryl chloride
Sulfuryl chloride is an inorganic compound with the formula SO2Cl2. At room temperature, it is a colorless liquid with a pungent odor. Sulfuryl chloride is not found in nature, as can be inferred from its rapid hydrolysis.
Sulfuryl chloride is ...
, , but the properties of these compounds differ significantly. Sulfuryl chloride is a source of
chlorine
Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine i ...
whereas thionyl chloride is a source of
chloride
The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride salts ...
ions.
Production
The major industrial synthesis involves the reaction of
sulfur trioxide and
sulfur dichloride:
This synthesis can be adapted to the laboratory by heating oleum to slowly distill the sulfur trioxide into a cooled flask of sulfur dichloride.
:
SO3 + SCl2 -> SOCl2 + SO2
Other methods include syntheses from:
*
Phosphorus pentachloride
Phosphorus pentachloride is the chemical compound with the formula PCl5. It is one of the most important phosphorus chlorides, others being PCl3 and POCl3. PCl5 finds use as a chlorinating reagent. It is a colourless, water-sensitive and moist ...
:
*:
SO2 + PCl5 -> SOCl2 + POCl3
*
Chlorine
Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine i ...
and
sulfur dichloride:
*:
SO2 + Cl2 + SCl2 -> 2 SOCl2
*:
SO3 + Cl2 + 2 SCl2 -> 3 SOCl2
*
Phosgene:
*:
SO2 + COCl2 -> SOCl2 + CO2
The first of the above four reactions also affords
phosphorus oxychloride
Phosphoryl chloride (commonly called phosphorus oxychloride) is a colourless liquid with the formula . It hydrolyses in moist air releasing phosphoric acid and fumes of hydrogen chloride. It is manufactured industrially on a large scale from pho ...
(phosphoryl chloride), which resembles thionyl chloride in many of its reactions.
Properties and structure
SOCl
2 adopts a
trigonal pyramidal molecular geometry
In chemistry, a trigonal pyramid is a molecular geometry with one atom at the apex and three atoms at the corners of a trigonal base, resembling a tetrahedron (not to be confused with the tetrahedral geometry). When all three atoms at the corne ...
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 SOCl
2 forms
monoclinic
In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in the orthorhombic s ...
crystals with the
space group
In mathematics, physics and chemistry, a space group is the symmetry group of an object in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of an object that leave it uncha ...
P2
1/c.
Stability
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.
Thionyl chloride is susceptible to
photolysis, which primarily proceeds via a radical mechanism. Samples showing signs of ageing can be purified by distillation under reduced pressure, to give a colourless liquid.
Reactions
Thionyl chloride is mainly used in the industrial production of
organochlorine compound
An organochloride, organochlorine compound, chlorocarbon, or chlorinated hydrocarbon is an organic compound containing at least one covalently bonded atom of chlorine. The chloroalkane class ( alkanes with one or more hydrogens substituted by chlo ...
s, which are often intermediates in pharmaceuticals and agrichemicals. It usually is preferred over other reagents, such as
phosphorus pentachloride
Phosphorus pentachloride is the chemical compound with the formula PCl5. It is one of the most important phosphorus chlorides, others being PCl3 and POCl3. PCl5 finds use as a chlorinating reagent. It is a colourless, water-sensitive and moist ...
, as its by-products (HCl and ) 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.
With water and alcohols
Thionyl chloride reacts exothermically with water to form
sulfur dioxide and
hydrochloric acid
Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid
Acid strength is the tendency of an acid, symbol ...
:
:
SOCl2 + H2O -> 2 HCl + SO2
By a similar process it also reacts with
alcohols to form
alkyl chlorides. If the alcohol is
chiral
Chirality is a property of asymmetry important in several branches of science. The word ''chirality'' is derived from the Greek (''kheir''), "hand", a familiar chiral object.
An object or a system is ''chiral'' if it is distinguishable from i ...
the reaction generally proceeds via an
SNi mechanism with retention of stereochemistry; however, depending on the exact conditions employed, stereo-inversion can also be achieved. Historically the use of with
pyridine
Pyridine is a basic heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom. It is a highly flammable, weakly alkaline, water-miscible liquid with a ...
was called the
Darzens halogenation
Darzens halogenation is the chemical synthesis of alkyl halides from alcohols via the treatment upon reflux of a large excess of thionyl chloride or thionyl bromide (SOX2) in the presence of a small amount of a nitrogen base, such as a tertiary ...
, but this name is rarely used by modern chemists.
![SNi reaction mechanism](https://upload.wikimedia.org/wikipedia/commons/f/fa/SNi_reaction_mechanism.svg)
Reactions with an excess of alcohol produce
sulfite esters, which can be powerful
methylation,
alkylation
Alkylation is the transfer of an alkyl group from one molecule to another. The alkyl group may be transferred as an alkyl carbocation, a free radical, a carbanion, or a carbene (or their equivalents). Alkylating agents are reagents for effecti ...
and hydroxyalkylation reagents.
:
SOCl2 + 2 R-OH -> (R-O)2SO + 2 HCl
For example, the addition of to
amino acid
Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha a ...
s in methanol selectively yields the corresponding methyl esters.
With carboxylic acids
Classically, it converts
carboxylic acids to
acyl chlorides:
:
SOCl2 + R-COOH -> R-COCl + SO2 + HCl
The reaction mechanism has been investigated:
:
With nitrogen species
With primary amines, thionyl chloride gives
sulfinylamine derivatives (RNSO), one example being ''N''-
sulfinylaniline. Thionyl chloride reacts with primary
formamide
Formamide is an amide derived from formic acid. It is a colorless liquid which is miscible with water and has an ammonia-like odor. It is chemical feedstock for the manufacture of sulfa drugs and other pharmaceuticals, herbicides and pesticides, a ...
s to form
isocyanide
An isocyanide (also called isonitrile or carbylamine) is an organic compound with the functional group –. It is the isomer of the related nitrile (–C≡N), hence the prefix is ''isocyano''.IUPAC Goldboo''isocyanides''/ref> The organic fragme ...
s and with secondary formamides to give chloro
iminium
In organic chemistry, an iminium cation is a polyatomic ion with the general structure . They are common in synthetic chemistry and biology.
Structure
Iminium cations adopt alkene-like geometries. The central C=N unit is nearly coplanar with al ...
ions; as such a reaction with
dimethylformamide
Dimethylformamide is an organic compound with the formula ( CH3)2NC(O)H. Commonly abbreviated as DMF (although this initialism is sometimes used for dimethylfuran, or dimethyl fumarate), this colourless liquid is miscible with water and the maj ...
will form the
Vilsmeier reagent
The Vilsmeier reagent is an organic compound with the formula CH3)2NCHCll. It is a salt consisting of the N,N-dimethyliminium cation ( CH3)2N=CHClsup>+) and chloride anion. Depending on the particular reaction, the anion can vary. In typical POC ...
.
By an analogous process primary
amide
In organic chemistry, an amide, also known as an organic amide or a carboxamide, is a compound with the general formula , where R, R', and R″ represent organic groups or hydrogen atoms. The amide group is called a peptide bond when it i ...
s will react with thionyl chloride to form
imidoyl chloride Imidoyl chlorides are organic compounds that contain the functional group RC(NR')Cl. A double bond exist between the R'N and the carbon centre. These compounds are analogues of acyl chloride. Imidoyl chlorides tend to be highly reactive and are m ...
s, with secondary amides also giving chloro
iminium
In organic chemistry, an iminium cation is a polyatomic ion with the general structure . They are common in synthetic chemistry and biology.
Structure
Iminium cations adopt alkene-like geometries. The central C=N unit is nearly coplanar with al ...
ions. These species are highly reactive and can be used to catalyse the conversion of carboxylic acids to acyl chlorides,
they are also exploited in the
Bischler–Napieralski reaction as a means of forming
isoquinoline
Isoquinoline is a heterocyclic aromatic organic compound. It is a structural isomer of quinoline. Isoquinoline and quinoline are benzopyridines, which are composed of a benzene ring fused to a pyridine ring. In a broader sense, the term isoqu ...
s.
![Acyl chloride via amide catalysis](https://upload.wikimedia.org/wikipedia/commons/9/9f/Acyl_chloride_via_amide_catalysis.png)
Primary amides will continue on to form
nitriles if heated (
Von Braun amide degradation
The von Braun amide degradation is the chemical reaction of a monosubstituted amide with phosphorus pentachloride or thionyl chloride to give a nitrile and an organohalide. It is named after Julius Jacob von Braun, who first reported the reaction. ...
).
Thionyl chloride has also been used to promote the
Beckmann rearrangement
The Beckmann rearrangement, named after the German chemist Ernst Otto Beckmann (1853–1923), is a rearrangement of an oxime functional group to substituted amides. The rearrangement has also been successfully performed on haloimines and nitrone ...
of
oxime
In organic chemistry, an oxime is a organic compound belonging to the imines, with the general formula , where R is an organic side-chain and R’ may be hydrogen, forming an aldoxime, or another organic group, forming a ketoxime. O-substituted ...
s.
With sulfur species
* Thionyl chloride will transform
sulfinic acids into
sulfinyl chlorides
*
Sulfonic acids react with thionyl chloride to produce
sulfonyl chloride
In inorganic chemistry, sulfonyl halide groups occur when a sulfonyl () functional group is singly bonded to a halogen atom. They have the general formula , where X is a halogen. The stability of sulfonyl halides decreases in the order fluorides ...
s. Sulfonyl chlorides have also been prepared from the direct reaction of the corresponding
diazonium
Diazonium compounds or diazonium salts are a group of organic compounds sharing a common functional group where R can be any organic group, such as an alkyl or an aryl, and X is an inorganic or organic anion, such as a halide.
General properti ...
salt with thionyl chloride.
* Thionyl chloride can be used in variations of the
Pummerer rearrangement
The Pummerer rearrangement is an organic reaction whereby an alkyl sulfoxide rearranges to an α- acyloxy–thioether (mono thioacetal-ester) in the presence of acetic anhydride.
The stoichiometry of the reaction is:
:RS(O)CHR'2 + Ac2O → ...
.
With phosphorus species
Thionyl chloride converts
phosphonic acids and
phosphonate
In organic chemistry, phosphonates or phosphonic acids are organophosphorus compounds containing groups (where R = alkyl, aryl, or just hydrogen). Phosphonic acids, typically handled as salts, are generally nonvolatile solids that are poorly ...
s into
phosphoryl chloride
Phosphoryl chloride (commonly called phosphorus oxychloride) is a colourless liquid with the formula . It hydrolyses in moist air releasing phosphoric acid and fumes of hydrogen chloride. It is manufactured industrially on a large scale from phos ...
s. 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 agent
Nerve agents, sometimes also called nerve gases, are a class of organic chemicals that disrupt the mechanisms by which nerves transfer messages to organs. The disruption is caused by the blocking of acetylcholinesterase (AChE), an enzyme that ...
s. For example, thionyl chloride converts
dimethyl methylphosphonate
Ethane ( , ) is an organic chemical compound with chemical formula . At standard temperature and pressure, ethane is a colorless, odorless gas. Like many hydrocarbons, ethane is isolated on an industrial scale from natural gas and as a petroc ...
into
methylphosphonic acid dichloride, which can be used in the production of
sarin and
soman
Soman (or GD, EA 1210, Zoman, PFMP, A-255, systematic name: ''O''-pinacolyl methylphosphonofluoridate) is an extremely toxic chemical substance. It is a nerve agent, interfering with normal functioning of the mammalian nervous system by inhibiti ...
.
With metals
As reacts with water it can be used to dehydrate various metal chloride hydrates, such
magnesium chloride
Magnesium chloride is the family of inorganic compounds with the formula , where x can range from 0 to 12. These salts are colorless or white solids that are highly soluble in water. These compounds and their solutions, both of which occur in natu ...
(),
aluminium chloride
Aluminium chloride, also known as aluminium trichloride, is an inorganic compound with the formula . It forms hexahydrate with the formula , containing six water molecules of hydration. Both are colourless crystals, but samples are often contam ...
(), and
iron(III) chloride ().
This conversion involves treatment with refluxing thionyl chloride and follows the following general equation:
:
MCl_\mathit\! .\! \mathit\ H2O + \mathit\ SOCl2 -> MCl_\mathit + \mathit\ SO2 + 2\! \mathit\ HCl
Other reactions
* Thionyl chloride can engage in a range of different electrophilic addition reactions. It adds to alkenes in the presence of 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
Triflic acid, the short name for trifluoromethanesulfonic acid, TFMS, TFSA, HOTf or TfOH, is a sulfonic acid with the chemical formula CF3SO3H. It is one of the strongest known acids. Triflic acid is mainly used in research as a catalyst for este ...
or the presence of catalysts such as , , or .
* In the laboratory, a reaction between thionyl chloride and an excess of
anhydrous alcohol can be used to produce anhydrous alcoholic solutions of
HCl HCL may refer to:
Science and medicine
* Hairy cell leukemia, an uncommon and slowly progressing B cell leukemia
* Harvard Cyclotron Laboratory, from 1961 to 2002, a proton accelerator used for research and development
* Hollow-cathode lamp, a spe ...
.
* Thionyl chloride undergoes halogen exchange reactions to give compounds such as
antimony trifluoride
Antimony trifluoride is the inorganic compound with the formula SbF3. Sometimes called Swarts' reagent, is one of two principal fluorides of antimony, the other being SbF5. It appears as a white solid. As well as some industrial applications, i ...
and
antimony trichloride
Antimony trichloride is the chemical compound with the formula SbCl3. It is a soft colorless solid with a pungent odor and was known to alchemists as butter of antimony.
Preparation
Antimony trichloride is prepared by reaction of chlorine with an ...
:
*:
3 SOCl2 + 2 SbF3 -> 3 SOF2 + 2 SbCl3
* or
hydrogen bromide
Hydrogen bromide is the inorganic compound with the formula . It is a hydrogen halide consisting of hydrogen and bromine. A colorless gas, it dissolves in water, forming hydrobromic acid, which is saturated at 68.85% HBr by weight at room tempe ...
and hydrogen chloride:
*:
SOCl2 + 2 HBr -> SOBr2 + 2 HCl
Batteries
![Lithium Thionyl Chloride Battery](https://upload.wikimedia.org/wikipedia/commons/2/2a/Lithium_Thionyl_Chloride_Battery.JPG)
Thionyl chloride is a component of lithium–thionyl chloride
batteries, where it acts as the positive electrode (in batteries:
cathode
A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. A conventional current describes the direction in wh ...
) with
lithium
Lithium (from el, λίθος, lithos, lit=stone) is a chemical element with the symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the least dense metal and the least dense solid ...
forming the negative electrode (
anode
An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. A common mnemonic ...
); the
electrolyte is typically
lithium tetrachloroaluminate
Lithium tetrachloroaluminate (LAC, lithium aluminium chloride) is an inorganic compound, a tetrachloroaluminate of lithium, with the formula LiAlCl4.
Solution of lithium tetrachloroaluminate in thionyl chloride is the liquid cathode and electroly ...
. The overall discharge reaction is as follows:
:
4 Li + 2 SOCl2 -> 4 LiCl + 1/8 S8 + SO2
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
A sojourner is a person who resides temporarily in a place.
Sojourner may also refer to:
* Sojourner Truth (1797–1883), abolitionist and women's rights activist
* Albert Sojourner (1872–1951), member of the Mississippi House of Representative ...
Mars rover.
Safety
SOCl
2 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 "di-di" method of producing G-series
nerve agent
Nerve agents, sometimes also called nerve gases, are a class of organic chemicals that disrupt the mechanisms by which nerves transfer messages to organs. The disruption is caused by the blocking of acetylcholinesterase (AChE), an enzyme that ...
s and the Meyer and Meyer–Clarke methods of producing
sulfur-based mustard gases.
History
In 1849, the French chemists
Jean-François Persoz
Jean-François Persoz (9 June 1805–September 1868) was a French chemist known for discovering the enzyme diastase and on the properties of dextrin. He also wrote a report that coined the name cellulose.
Born in Cortaillod, Persoz studied ph ...
and Bloch, and the German chemist Peter Kremers (1827-?), independently first synthesized thionyl chloride by reacting
phosphorus pentachloride
Phosphorus pentachloride is the chemical compound with the formula PCl5. It is one of the most important phosphorus chlorides, others being PCl3 and POCl3. PCl5 finds use as a chlorinating reagent. It is a colourless, water-sensitive and moist ...
with
sulfur dioxide. However, their products were impure: both Persoz and Kremers claimed that thionyl chloride contained phosphorus, and Kremers recorded its boiling point as 100 °C (instead of 74.6 °C). In 1857, the German-Italian chemist
Hugo Schiff
Hugo (Ugo) Schiff (26 April 1834 – 8 September 1915) was an Italian naturalized chemist. The son of a Jewish businessman and brother of the physiologist Moritz Schiff was German by nationality. He discovered Schiff bases and other imines, ...
subjected crude thionyl chloride to repeated fractional distillations and obtained a liquid which boiled at 82 °C and which he called ''Thionylchlorid''. In 1859, the German chemist
Georg Ludwig Carius
Georg Ludwig Carius (August 24, 1829 – April 24, 1875) was a German chemist born in Barbis, in the Kingdom of Hanover. He studied under Friedrich Wöhler and was assistant to Robert Bunsen for 6 years. He was Director of the Marburger Chemical ...
noted that thionyl chloride could be used to make
acid anhydrides
An organic acid anhydride is an acid anhydride that is an organic compound. An acid anhydride is a compound that has two acyl groups bonded to the same oxygen atom. A common type of organic acid anhydride is a carboxylic anhydride, where the pa ...
and
acyl chlorides from
carboxylic acids and to make
alkyl chlorides from
alcohols.
[
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
Benzoic acid is a white (or colorless) solid organic compound with the formula , whose structure consists of a benzene ring () with a carboxyl () substituent. It is the simplest aromatic carboxylic acid. The name is derived from gum benzoin, ...
(OC7H5OH) into benzoyl chloride
Benzoyl chloride, also known as benzenecarbonyl chloride, is an organochlorine compound with the formula . It is a colourless, fuming liquid with an irritating odour, and consists of a benzene ring () with an acyl chloride () substituent. It is ...
(ClC7H5O) and to transform sodium benzoate
Sodium benzoate is the sodium salt of benzoic acid, widely used as a food preservative (with an E number of E211) and a pickling agent. It appears as a white crystalline chemical with the formula C6H5COONa.
Production
Sodium benzoate is commo ...
into benzoic anhydride. On p. 96, he mentions that thionyl chloride will transform methanol into methyl chloride
Chloromethane, also called methyl chloride, Refrigerant-40, R-40 or HCC 40, is an organic compound with the chemical formula . One of the haloalkanes, it is a colorless, odorless, flammable gas. Methyl chloride is a crucial reagent in industria ...
(''Chlormethyl''). Thionyl chloride behaves like phosphoryl chloride
Phosphoryl chloride (commonly called phosphorus oxychloride) is a colourless liquid with the formula . It hydrolyses in moist air releasing phosphoric acid and fumes of hydrogen chloride. It is manufactured industrially on a large scale from phos ...
: from pp. 94-95: ''"Die Einwirkung des Chlorthionyls … die Reaction des Chlorthionyls weit heftiger statt."'' (The reaction of thionyl chloride with rganicsubstances 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.)
See also
*
Oxalyl chloride
Oxalyl chloride is an organic chemical compound with the formula (COCl)2. This colorless, sharp-smelling liquid, the diacyl chloride of oxalic acid, is a useful reagent in organic synthesis.
Preparation
Oxalyl chloride was first prepared in 1892 ...
*
Phosphorus pentachloride
Phosphorus pentachloride is the chemical compound with the formula PCl5. It is one of the most important phosphorus chlorides, others being PCl3 and POCl3. PCl5 finds use as a chlorinating reagent. It is a colourless, water-sensitive and moist ...
*
Phosgene
*
Sulfur dichloride
*
Thionyl bromide
References
{{DEFAULTSORT:Thionyl Chloride
Thionyl compounds
Sulfur(IV) compounds
Sulfur oxohalides
Oxychlorides
Reagents for organic chemistry
Lachrymatory agents
Foul-smelling chemicals
Inorganic solvents