thioacetic acid
{{Short description|Organosulfur compound (CH3C(O)SH)}}
{{chembox
| verifiedrevid = 470606827
| ImageFileL1= AcSH.svg
| ImageSizeL1=120
| ImageClassL1 = skin-invert
| ImageAltL1=Skeletal formula of thioacetic acid
| ImageFileR1= Thioacetic acid 3D ball.png
| ImageSizeR1=120
| ImageAltR1=Ball-and-stick model of the thioacetic acid molecule
| PIN=Ethanethioic S-acid{{cite book |author=International Union of Pure and Applied Chemistry |date=2014 |title=Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013 |publisher=The Royal Society of Chemistry |pages=97 |doi=10.1039/9781849733069 |isbn=978-0-85404-182-4}}
| OtherNames=Thioacetic S-acid
Thiolacetic acid
|Section1={{Chembox Identifiers
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 10052
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = PS92MLC0FQ
| KEGG_Ref = {{keggcite|correct|kegg}}
| KEGG = C01857
| InChI = 1/C2H4OS/c1-2(3)4/h1H3,(H,3,4)
| InChIKey = DUYAAUVXQSMXQP-UHFFFAOYAO
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/C2H4OS/c1-2(3)4/h1H3,(H,3,4)
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = DUYAAUVXQSMXQP-UHFFFAOYSA-N
| CASNo_Ref = {{cascite|correct|CAS}}
| CASNo=507-09-5
| PubChem=10484
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 46800
| SMILES = O=C(S)C
}}
|Section2={{Chembox Properties
| Formula={{chem2|CH3C(O)SH}}
| MolarMass=76.11756 g/mol
| Density=1.08 g/mL
| MeltingPtC=-58
| BoilingPtC=93
| Appearance = Transparent, colorless to light yellow liquid{{cite web | url=https://pubchem.ncbi.nlm.nih.gov/compound/Thioacetic-acid | title=Thioacetic acid }}{{Cite web | url=https://www.sigmaaldrich.com/GB/en/sds/aldrich/t30805 | title=Identification of the substance/mixture and of the company/undertaking - Thioacetic acid | website=www.sigmaaldrich.com}}
| Odor = Unpleasant, strong thiol-like
| RefractIndex = 1.465
| MagSus = −38.4·10−6 cm3/mol
}}
|Section7={{Chembox Hazards
| LD50 = 75 mg/kg (mouse, intraperitoneal)
| MainHazards = May cause severe skin and eye burns. Highly flammable liquid.
| GHSPictograms = {{GHS02}}{{GHS05}}{{GHS06}}{{GHS07}}
| GHSSignalWord = Danger
| HPhrases = {{H-phrases|H225|H301|H302|H314|H317}}
| PPhrases = {{P-phrases|P210|P233|P240|P241|P242|P243|P260|P261|P264|P264+P265|P270|P272|P280|P301+P316|P301+P317|P301+P330+P331|P302+P352|P302+P361+P354|P303+P361+P353|P304+P340|P305+P354+P338|P316|P317|P321|P330|P333+P317|P362+P364|P363|P370+P378|P403+P235|P405|P501}}
| ExternalSDS = [https://fscimage.fishersci.com/msds/39916.htm Fischer Scientific]
}}
}}
Thioacetic acid is an organosulfur compound with the molecular formula {{chem2|CH3C(O)SH}}. It is a thioic acid: the sulfur analogue of acetic acid ({{chem2|CH3C(O)OH}}), as implied by the thio- prefix. It is a yellow liquid with a strong thiol-like odor. It is used in organic synthesis for the introduction of thiol groups ({{chem2|\sSH}}) in molecules.Jeannie R. Phillips "Thiolacetic Acid" Encyclopedia of Reagents for Organic Synthesis, 2001 John Wiley. {{doi|10.1002/047084289X.rt096}}
Synthesis and properties
Thioacetic acid is prepared by the reaction of acetic anhydride with hydrogen sulfide:{{cite journal|last1=Ellingboe|first1=E. K.|title=Thiolacetic acid|journal=Organic Syntheses|date=1951|volume=31|page=105|doi=10.15227/orgsyn.031.0105}}
:{{chem2|(CH3C(O))2O + H2S → CH3C(O)SH + CH3C(O)OH}}
It has also been produced by the action of phosphorus pentasulfide on glacial acetic acid, followed by distillation.{{cite journal |last=Schiff |first=Robert |date=1895-08-09 |title=Preparation of Thioacetic Acid and its Importance for Chemical-Legal Investigations |url=https://books.google.com/books?id=lSLOAAAAMAAJ&pg=PA412 |journal=Chemical News and Journal of Industrial Science |volume=72 |pages=64 |access-date=2016-11-02}}
:{{chem2|CH3C(O)OH + P2S5 → CH3C(O)SH + P2OS4}}
Thioacetic acid is typically contaminated by acetic acid.
The compound exists exclusively as the thiol tautomer, consistent with the strength of the {{chem2|C\dO}} double bond. Reflecting the influence of hydrogen-bonding, the boiling point (93 °C) and melting points are 20 and 75 K lower than those for acetic acid.
Reactivity
=Acidity=
With a pKa near 3.4, thioacetic acid is about 15 times more acidic than acetic acid.Matthys J. Janssen "Carboxylic Acids and Esters" in PATAI'S Chemistry of Functional Groups: Carboxylic Acids and Esters, Saul Patai, Ed. pp. 705–764, 1969. {{doi|10.1002/9780470771099.ch15}} The conjugate base is thioacetate:
:{{chem2|CH3C(O)SH → CH3C(O)S− + H+}}
In neutral water, thioacetic acid is fully ionized.
=Reactivity of thioacetate=
Most of the reactivity of thioacetic acid arises from the conjugate base, thioacetate. Salts of this anion, e.g. potassium thioacetate, are used to generate thioacetate esters.{{cite journal | last = Ervithayasuporn | first = V. | year = 2011 | title = Synthesis and Characterization of Octakis(3-propyl ethanethioate)octasilsesquioxane | journal = Organometallics | volume = 30 | pages = 4475–4478 | doi = 10.1021/om200477a | issue = 17}} Thioacetate esters undergo hydrolysis to give thiols. A typical method for preparing a thiol from an alkyl halide using thioacetic acid proceeds in four discrete steps, some of which can be conducted sequentially in the same flask:
:{{chem2|CH3C(O)SH + NaOH → CH3C(O)SNa + H2O}}
:{{chem2|CH3C(O)SNa + RX → CH3C(O)SR + NaX}}, where X = Cl, Br, I
:{{chem2|CH3C(O)SR + 2 NaOH → CH3CO2Na + RSNa + H2O}}
:{{chem2|RSNa + HCl → RSH + NaCl}}
In an application that illustrates the use of its radical behavior, thioacetic acid is used with AIBN in a free radical mediated nucleophilic addition to an exocyclic alkene forming a thioester:Synthesis of methyl 6-deoxy-4-O-(sodium sulfonato)-α-L-talopyranoside, its C-4 epimer and both isosteric [4-C-(potassium sulfonatomethyl)] derivatives László Lázár, Magdolna Csávás, Anikó Borbás, Gyöngyi Gyémánt, and András Lipták Arkivoc 2004 (vii) 196-207 [http://www.arkat-usa.org/ARKIVOC/JOURNAL_CONTENT/manuscripts/2004/SA-1033BP%20as%20published%20mainmanuscript.pdf Link]
== Reductive acetylation ==
Potassium thioacetate can be used convert nitroarenes to aryl acetamides in one step. This is particularly useful in the preparation of pharmaceuticals, e.g., paracetamol from 4-nitrophenol or 4-nitroanisole.{{cite journal |last=Bhattacharya |first=Apurba |display-authors=etal |date=2006 |title=One-step reductive amidation of nitro arenes: application in the synthesis of Acetaminophen |url=http://www.cs.gordon.edu/~ijl/_lead_papers/One%20step%20reductive%20amidation%20of%20nitroarenes%20-%20Tylenol.pdf |journal=Tetrahedron Letters |volume=47 |pages=1861–1864 |doi=10.1016/j.tetlet.2005.09.196 |access-date=2016-11-02 |archive-date=2016-11-04 |archive-url=https://web.archive.org/web/20161104050626/http://www.cs.gordon.edu/~ijl/_lead_papers/One%20step%20reductive%20amidation%20of%20nitroarenes%20-%20Tylenol.pdf |url-status=dead }}