organic chemistry Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic matter, organic materials, i.e., matter in its various forms that contain ...

, a thioacyl chloride is an

organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...

containing the

functional group In organic chemistry, a functional group is any substituent or moiety (chemistry), moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions r ...

. Their formula is usually written , where R is a

side chain In organic chemistry and biochemistry, a side chain is a substituent, chemical group that is attached to a core part of the molecule called the "main chain" or backbone chain, backbone. The side chain is a hydrocarbon branching element of a mo ...

. Thioacyl chlorides are analogous to

acyl chloride In organic chemistry, an acyl chloride (or acid chloride) is an organic compound with the functional group . Their formula is usually written , where R is a side chain. They are reactive derivatives of carboxylic acids (). A specific example o ...

s, but much rarer and less robust. Indeed, one of the simplest, thioacetyl chloride (c.f.

acetyl chloride Acetyl chloride () is an acyl chloride derived from acetic acid (). It belongs to the class of organic compounds called acid halides. It is a colorless, corrosive, volatile liquid. Its formula is commonly abbreviated to AcCl. Synthesis On an ...

), remained unknown as of 1972. Most thioacyl halides are "highly coloured, labile oils with pronounced pungent odours". Simple alkyl derivatives are volatile. The best studied thioacyl chloride is thiobenzoyl chloride, a purple oil first prepared by chlorination of

dithiobenzoic acid Dithiobenzoic acid is the organosulfur compound with the formula C6H5CS2H. It is a dithiocarboxylic acid, an analogue of benzoic acid, but more acidic and deeply colored. Synthesis and reactions It can be prepared by sulfiding benzotrichloride ...

with a combination of chlorine and

thionyl chloride Thionyl chloride is an inorganic compound with the chemical formula . It is a moderately Volatility (chemistry), volatile, colourless liquid with an unpleasant acrid odour. Thionyl chloride is primarily used as a Halogenation, chlorinating reagen ...

. A more modern preparation employs

phosgene Phosgene is an organic chemical compound with the formula . It is a toxic, colorless gas; in low concentrations, its musty odor resembles that of freshly cut hay or grass. It can be thought of chemically as the double acyl chloride analog of ...

as the chlorinating agent, by-producing

carbonyl sulfide Carbonyl sulfide is the chemical compound with the linear formula . It is a colorless flammable gas with an unpleasant odor. It is a linear molecule consisting of a carbonyl double bonded to a sulfur atom. Carbonyl sulfide can be considered to ...

: :PhCS₂H + COCl₂ → PhC(S)Cl + HCl + COS One example of a thioacyl chloride has been crystallized. In general, thioacyl chlorides are produced from passing

halocarbon Halocarbon compounds are chemical compounds in which one or more carbon atoms are linked by covalent bonds with one or more halogen atoms (fluorine, chlorine, bromine or iodine – ) resulting in the formation of organofluorine compounds, or ...

s through

phosphorus pentasulfide Phosphorus pentasulfide is the inorganic compound with the formula (empirical) or ( molecular). This yellow solid is the one of two phosphorus sulfides of commercial value. Samples often appear greenish-gray due to impurities. It is soluble in ...

or boiling sulfur. Such is the case for the simplest thioacyl chloride,

thiophosgene Thiophosgene is a red liquid with the formula . It is a molecule with trigonal planar geometry. There are two reactive C–Cl bonds that allow it to be used in diverse organic syntheses. Preparation Typically, is prepared in a two-step process ...

. Thiocarbamyl and -carbonyl chlorides are prepared from the corresponding

amines In chemistry, amines (, ) are organic compounds that contain carbon-nitrogen bonds. Amines are formed when one or more hydrogen atoms in ammonia are replaced by alkyl or aryl groups. The nitrogen atom in an amine possesses a lone pair of elec ...

and

alcohols In chemistry, an alcohol (), is a type of organic compound that carries at least one hydroxyl () functional group bound to a Saturated and unsaturated compounds, saturated carbon atom. Alcohols range from the simple, like methanol and ethanol ...

by careful thiophosgenation.

Reactions

Thioacyl chlorides are

electrophilic In chemistry, an electrophile is a chemical species that forms bonds with nucleophiles by accepting an electron pair. Because electrophiles accept electrons, they are Lewis acids. Most electrophiles are positively charged, have an atom that carr ...

at the carbon atom. Amines, alcohols, and

thiol In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl grou ...

s displace the chloride to form (respectively)

thioamide A thioamide (rarely, thionamide, but also known as thiourylenes) is a functional group with the general structure , where are any groups (typically organyl groups or hydrogen). Analogous to amides, thioamides exhibit greater multiple bond charact ...

s, thionoesters, and dithioesters. Friedel-Crafts reaction thioacylate

arene Aromatic compounds or arenes are organic compounds "with a chemistry typified by benzene" and "cyclically conjugated." The word "aromatic" originates from the past grouping of molecules based on odor, before their general chemical properties were ...

Cyanide In chemistry, cyanide () is an inorganic chemical compound that contains a functional group. This group, known as the cyano group, consists of a carbon atom triple-bonded to a nitrogen atom. Ionic cyanides contain the cyanide anion . This a ...

reacts with thioacyl chlorides to form thioacyl cyanides. These thioacyl cyanides are known to dimerize to dicyanoalkenes, eliminating sulfur. Likewise thioacyl

azide In chemistry, azide (, ) is a linear, polyatomic anion with the formula and structure . It is the conjugate base of hydrazoic acid . Organic azides are organic compounds with the formula , containing the azide functional group. The dominant ...

cyclizes to a thiatriazole, and

diazo compound In organic chemistry, the diazo group is an organic moiety consisting of two linked nitrogen atoms at the terminal position. Overall charge-neutral organic compounds containing the diazo group bound to a carbon atom are called diazo compounds ...

s and

tetrazole A tetrazole is a chemical synthesis, synthetic organic heterocyclic compound, consisting of a 5-member ring of four nitrogen atoms and one carbon atom. The name tetrazole also refers to the parent compound - a whitish crystalline powder with the f ...

s react to

thiadiazole In chemistry, thiadiazoles are a sub-family of azole compounds, with the name ''thiadiazole'' originating from the Hantzsch–Widman nomenclature. Structurally, they are five-membered heterocyclic compounds containing one sulfur and two nitrogen ...

s. Like other unstabilized

thiocarbonyl In organic chemistry, thioketones (; also known as thiones or thiocarbonyls) are organosulfur compounds related to conventional ketones in which the oxygen has been replaced by a sulfur. Instead of a structure of , thioketones have the structure ...

s, thioacyl chlorides undergo a variety of dimerization and cycloaddition reactions. "Simple thiocarbonyl halides all show a tendency to dimerize to some degree, especially fluorothioacyl fluorides," the only exception being trifluorothioacetyl fluoride.

Carbene In organic chemistry, a carbene is a molecule containing a neutral carbon atom with a Valence (chemistry), valence of two and two unshared valence electrons. The general formula is or where the R represents substituents or hydrogen atoms. Th ...

s attack the double bond to form

episulfide In organic chemistry, an episulfide is an organic compound that contain a saturated, heterocyclic ring consisting of two carbon atoms and one sulfur atom. It is the sulfur analogue of an epoxide or aziridine. They are also known as thiiranes, ol ...

s, and the double-bond in general is an extremely active dienophile.

Safety

Thioacyl chlorides are toxic.{{Rp, 359

References

Functional groups Organosulfur compounds