Thioacetic acid
Skeletal formula of thioacetic acid
Ball-and-stick model of the thioacetic acid molecule
Names
Preferred IUPAC name
Ethanethioic S-acid[1]
Other names
Thioacetic S-acid
Thiolacetic acid
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.007.331 Edit this at Wikidata
KEGG
UNII
  • InChI=1S/C2H4OS/c1-2(3)4/h1H3,(H,3,4) checkY
    Key: DUYAAUVXQSMXQP-UHFFFAOYSA-N checkY
  • InChI=1/C2H4OS/c1-2(3)4/h1H3,(H,3,4)
    Key: DUYAAUVXQSMXQP-UHFFFAOYAO
  • O=C(S)C
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
1.465
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 Severe skin burns and eye damage. Highly flammable.
GHS labelling:
GHS02: FlammableGHS05: CorrosiveGHS06: ToxicGHS07: Exclamation mark
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):
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).
checkY verify (what is checkY☒N ?)

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

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

Acidity

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

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
thioacetic acid application

Reductive acetylation

Salts of thioacetic acid such as 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.[10]

References

  1. ^ 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.
  2. ^ "Thioacetic acid".
  3. ^ https://www.sigmaaldrich.com/GB/en/sds/aldrich/t30805
  4. ^ Jeannie R. Phillips "Thiolacetic Acid" Encyclopedia of Reagents for Organic Synthesis, 2001 John Wiley. doi:10.1002/047084289X.rt096
  5. ^ Ellingboe, E. K. (1951). "Thiolacetic acid". Organic Syntheses. 31: 105. doi:10.15227/orgsyn.031.0105.
  6. ^ 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.
  7. ^ 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
  8. ^ Ervithayasuporn, V. (2011). "Synthesis and Characterization of Octakis(3-propyl ethanethioate)octasilsesquioxane". Organometallics. 30 (17): 4475–4478. doi:10.1021/om200477a.
  9. ^ 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
  10. ^ 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.
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