Thiocarboxylic acid#Dithiocarboxylic acids

Thiocarboxylic acids are typically prepared by salt metathesis from the acid chloride, as in the following conversion of benzoyl chloride to thiobenzoic acid using potassium hydrosulfide according to the following idealized equation:{{cite journal | first1= Paul |last1= Noble, Jr. |first2= D. S. |last2= Tarbell | title = Thiobenzoic Acid |journal= Organic Syntheses | volume = 32 | page = 101 | year = 1952 | doi = 10.15227/orgsyn.032.0101}}

:{{chem2|C6H5C(O)Cl + KSH -> C6H5C(O)SH + KCl}}

Covalent sulfides, such as P₂S₅, generally give poor yields unless catalyzed with triphenylstibine oxide.{{Cite book |last=Collier |first=S. J. |title=Category 3, Compounds with Four and Three Carbon Heteroatom Bonds: Three Carbon—Heteroatom Bonds: Esters, and Lactones; Peroxy Acids and R(CO)OX Compounds; R(CO)X, X=S, Se, Te |date=2007 |publisher=Georg Thieme Verlag |isbn=978-3-13-144691-6 |editor-last=Panek |editor-first=J. S. |series=Science of Synthesis |location=Stuttgart |pages=1600 |language=en |chapter=Product class 8: Thiocarboxylic S-acids, selenocarboxylic Se-acids, tellurocarboxylic Te-acids, and derivatives |doi=10.1055/sos-sd-020-01480}}

2,6-Pyridinedicarbothioic acid is synthesized by treating the diacid dichloride with a solution of H₂S in pyridine:

:{{chem2|NC5H3(COCl)2 + 2 H2S + 2 C5H5N → [C5H5NH+][HNC5H3(COS)2-] + [C5H5NH]Cl}}

This reaction produces the orange pyridinium salt of pyridinium-2,6-dicarbothioate. Treatment of this salt with sulfuric acid gives colorless the bis(thiocarboxylic acid), which can then be extracted with dichloromethane.{{cite journal |doi=10.1080/03086648308080490 |title=Zur Struktur Eines 1:1-Adduktes von Pyridin-2,6-Dicarbothiosäure und Pyridin |date=1983 |last1=Hildebrand |first1=U. |last2=Ockels |first2=W. |last3=Lex |first3=J. |last4=Budzikiewicz |first4=H. |journal=Phosphorus and Sulfur and the Related Elements |volume=16 |issue=3 |pages=361–364 }}

At neutral pH, thiocarboxylic acids are fully ionized. Thiocarboxylic acids are about 100 times more acidic than the analogous carboxylic acids. Thiobenzoic acid has a pK_a of 2.48 compared with 4.20 for benzoic acid, and thioacetic acid has a pK_a near 3.4 compared with 4.72 for acetic acid.{{cite book|author=M. R. Crampton|page=402|chapter=Acidity and hydrogen-bonding|title=The Chemistry of the Thiol Group|editor= Saul Patai|year= 1974|publisher=John Wiley & Sons Ltd|place=Chichester}} Alkylation of the corresponding thioate ion gives a thioester.Matthys J. Janssen "Carboxylic Acids and Esters" in PATAI's Chemistry of Functional Groups: Carboxylic Acids and Esters, Saul Patai, Ed. John Wiley, 1969, New York: pp. 705–764. {{doi|10.1002/9780470771099.ch15}}

The conjugate base of thioacetic acid, thioacetate, is a reagent used for installing thiol groups via the displacement of alkyl halides by a two-step process. The halide is displaced to give a thioester intermediate, which is then hydrolyzed:

:{{chem2|R\sX + CH3COS- -> R\sSC(O)CH3 + X-}}

:{{chem2|R\sSC(O)CH3 + H2O -> R\sSH + CH3CO2H }}

Thiocarboxylic acids react with various nitrogen functional groups, such as organic azide, nitro, and isocyanate compounds, to give amides under mild conditions.{{cite book |section= 21.1.2.6.1: Variation 1: From Thiocarboxylic Acids |pages= 52–54 |title=Science of Synthesis: Houben–Weyl Methods of Molecular Transformations |volume= 21: Three Carbon-Heteroatom Bonds: Amides and Derivatives; Peptides; Lactams |publisher= Georg Thieme Verlag |year= 2005 |isbn= 978-3-13-171951-5}}{{cite journal |journal= Chem. Sci. |year= 2016 |volume= 7 |pages= 713–718 |title= Base-catalyzed synthesis of aryl amides from aryl azides and aldehydes |first1= Sheng |last1= Xie |first2= Yang |last2= Zhang |first3= Olof |last3= Ramström |first4= Mingdi |last4= Yan |issue= 1 |doi= 10.1039/C5SC03510D |pmid= 29896355 |pmc= 5952891}} This method avoids needing the amine to initiate an amide-forming acyl substitution but does requires synthesis and handling of the unstable thiocarboxylic acid. Unlike the Schmidt reaction or other nucleophilic-attack pathways, reaction with an aryl or alkyl azide begins with a [3+2] cycloaddition. The resulting heterocycle expels N₂ and the sulfur atom to give the monosubstituted amide.{{cite journal |doi=10.1021/ja0294919 |title=The Reaction of Thio Acids with Azides: A New Mechanism and New Synthetic Applications |date=2003 |last1=Shangguan |first1=Ning |last2=Katukojvala |first2=Sreenivas |last3=Greenberg |first3=Rachel |last4=Williams |first4=Lawrence J. |journal=Journal of the American Chemical Society |volume=125 |issue=26 |pages=7754–7755 |pmid=12822965 |bibcode=2003JAChS.125.7754S }}

Halogens or their equivalents (e.g. sulfuryl chloride) oxidize thiocarboxylic acids to acylsulfenyl halides. The latter are unstable, and decay over the course of several hours to the free halogen and the diacyl disulfide.{{cite book|title=Comprehensive Organic Functional Group Transformations|volume=5|editor-first1=Christopher J.|editor-last1=Moody|publisher=Pergamon|location=Oxford, UK|year=1995|lccn=95-31088|isbn=0-08-042326-4|chapter=Acylsulfur, -selenium, or -tellurium functions|author1=Ogawa Akiya|author2=Sonoda Noboru|pp=244-246}}

• Dithiocarboxylic acid
• Thiocarbamate
• Thiocarbonate
• Thiocarbonic acid
• Thioformic acid, the simplest thiocarboxylic acid

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Category:Functional groups