Thioacetic acid
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| Names | |||
|---|---|---|---|
| Preferred IUPAC name
Ethanethioic S-acid[1] | |||
| Other names
Thioacetic S-acid
Thiolacetic acid | |||
| Identifiers | |||
3D model (JSmol)
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| ChEBI | |||
| ChemSpider | |||
| ECHA InfoCard | 100.007.331 | ||
| KEGG | |||
PubChem CID
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| UNII | |||
CompTox Dashboard (EPA)
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| Properties | |||
| CH3C(O)SH | |||
| Molar mass | 76.11756 g/mol | ||
| Appearance | Transparent, colorless to light yellow liquid[2][3] | ||
| Odor | Unpleasant, strong thiol-like | ||
| Density | 1.08 g/mL | ||
| Melting point | −58 °C (−72 °F; 215 K) | ||
| Boiling point | 93 °C (199 °F; 366 K) | ||
| −38.4·10−6 cm3/mol | |||
Refractive index (nD)
|
1.465 | ||
| Hazards | |||
| Occupational safety and health (OHS/OSH): | |||
Main hazards
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May cause severe skin and eye burns. Highly flammable liquid. | ||
| GHS labelling: | |||
   
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| Danger | |||
| H225, H301, H302, H314, H317 | |||
| 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 | |||
| Lethal dose or concentration (LD, LC): | |||
LD50 (median dose)
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75 mg/kg (mouse, intraperitoneal) | ||
| Safety data sheet (SDS) | Fischer Scientific | ||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Thioacetic acid is an organosulfur compound with the molecular formula CH3C(O)SH. It is a thioic acid: the sulfur analogue of acetic acid (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 (−SH) in molecules.[4]
Synthesis and properties
[edit]Thioacetic acid is prepared by the reaction of acetic anhydride with hydrogen sulfide:[5]
- (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.[6]
- 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 C=O 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
[edit]Acidity
[edit]With a pKa near 3.4, thioacetic acid is about 15 times more acidic than acetic acid.[7] The conjugate base is thioacetate:
- CH3C(O)SH → CH3C(O)S− + H+
In neutral water, thioacetic acid is fully ionized.
Reactivity of thioacetate
[edit]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.[8] 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:
- CH3C(O)SH + NaOH → CH3C(O)SNa + H2O
- CH3C(O)SNa + RX → CH3C(O)SR + NaX, where X = Cl, Br, I
- CH3C(O)SR + 2 NaOH → CH3CO2Na + RSNa + H2O
- 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:[9]
thioacetic acid application
Reductive acetylation
[edit]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.[10]
References
[edit]- ^ International Union of Pure and Applied Chemistry (2014). Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013. The Royal Society of Chemistry. p. 97. doi:10.1039/9781849733069. ISBN 978-0-85404-182-4.
- ^ "Thioacetic acid".
- ^ "Identification of the substance/mixture and of the company/undertaking - Thioacetic acid". www.sigmaaldrich.com.
- ^ Jeannie R. Phillips "Thiolacetic Acid" Encyclopedia of Reagents for Organic Synthesis, 2001 John Wiley. doi:10.1002/047084289X.rt096
- ^ Ellingboe, E. K. (1951). "Thiolacetic acid". Organic Syntheses. 31: 105. doi:10.15227/orgsyn.031.0105.
- ^ Schiff, Robert (1895-08-09). "Preparation of Thioacetic Acid and its Importance for Chemical-Legal Investigations". Chemical News and Journal of Industrial Science. 72: 64. Retrieved 2016-11-02.
- ^ 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
- ^ Ervithayasuporn, V. (2011). "Synthesis and Characterization of Octakis(3-propyl ethanethioate)octasilsesquioxane". Organometallics. 30 (17): 4475–4478. doi:10.1021/om200477a.
- ^ 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 Link
- ^ Bhattacharya, Apurba; et al. (2006). "One-step reductive amidation of nitro arenes: application in the synthesis of Acetaminophen" (PDF). Tetrahedron Letters. 47: 1861–1864. doi:10.1016/j.tetlet.2005.09.196. Archived from the original (PDF) on 2016-11-04. Retrieved 2016-11-02.