Thioacetic acid

Thioacetic acid

Names
IUPAC name Ethanethioic S-acid
Other names Thioacetic S-acid Thiolacetic acid
Identifiers
CAS Number	507-09-5
ChEBI	CHEBI:46800
ChemSpider	10052
Jmol 3D image	Interactive graph
KEGG	C01857
PubChem	10484
UNII	PS92MLC0FQ
InChI InChI=1S/C2H4OS/c1-2(3)4/h1H3,(H,3,4) Key: DUYAAUVXQSMXQP-UHFFFAOYSA-N InChI=1/C2H4OS/c1-2(3)4/h1H3,(H,3,4) Key: DUYAAUVXQSMXQP-UHFFFAOYAO
SMILES O=C(S)C
Properties
Chemical 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)
Hazards
Safety data sheet	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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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

Thioacetic acid is prepared by the reaction of acetic anhydride with hydrogen sulfide:^[2]

(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.

Reactivity

The thioacetate anion and radical generated from thioacetic acid are used to generate thioacetate esters.^[3] 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:^[4]

References

1. Jeannie R. Phillips "Thiolacetic Acid" Encyclopedia of Reagents for Organic Synthesis, 2001 John Wiley. doi:10.1002/047084289X.rt096.
2. Ellingboe, E. K. (1951). "Thiolacetic acid". Organic Syntheses 31: 105. doi:10.15227/orgsyn.031.0105.
3. Ervithayasuporn, V. (2011). "Synthesis and Characterization of Octakis(3-propyl ethanethioate)octasilsesquioxane". Organometallics 30 (17): 4475–4478. doi:10.1021/om200477a.
4. 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