Thioacetic acid

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Thioacetic acid
CAS number 507-09-5 YesY
PubChem 10484
ChemSpider 10052 YesY
KEGG C01857 YesY
ChEBI CHEBI:46800 YesY
Jmol-3D images Image 1
Molecular formula C2H4OS
Molar mass 76.11756
Density 1.08 g/mL
Melting point −58 °C (−72 °F; 215 K)
Boiling point 93 °C (199 °F; 366 K)
MSDS Fischer Scientific
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Thioacetic acid is an organosulfur compound with the molecular formula CH3COSH. It is a colourless liquid with a strong thiol-like odor. It is used in organic synthesis for the introduction of thiol groups in molecules[1]

Synthesis and properties[edit]

Thioacetic acid is prepared by the reaction of acetic anhydride with hydrogen sulfide:

(CH3C(O))2O + H2S → CH3C(O)SH + CH3CO2H

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 75K lower than those for acetic acid. It is also about 15x more acidic than acetic acid.


The thioacetate anion and radical generated from thioacetic acid are used to generate thioacetate esters.[2] 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 (X = Cl, Br, I, etc)
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:[3]

thioacetic acid application


  1. ^ Jeannie R. Phillips "Thiolacetic Acid" Encyclopedia of Reagents for Organic Synthesis, 2001 John Wiley. doi:10.1002/047084289X.rt096.
  2. ^ Ervithayasuporn, V. (2011). "Synthesis and Characterization of Octakis(3-propyl ethanethioate)octasilsesquioxane". Organometallics 30 (17): 4475–4478. doi:10.1021/om200477a. 
  3. ^ 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