Thioacetic acid

Last updated
Thioacetic acid
AcSH.svg
Thioacetic acid 3D ball.png
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 OOjs UI icon edit-ltr-progressive.svg
KEGG
PubChem CID
UNII
  • InChI=1S/C2H4OS/c1-2(3)4/h1H3,(H,3,4) Yes check.svgY
    Key: DUYAAUVXQSMXQP-UHFFFAOYSA-N Yes check.svgY
  • 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
AppearanceTransparent, 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:
GHS-pictogram-flamme.svg GHS-pictogram-acid.svg GHS-pictogram-skull.svg GHS-pictogram-exclam.svg
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).
Yes check.svgY  verify  (what is  Yes check.svgYX mark.svgN ?)

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]

Contents

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.svg
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]

Related Research Articles

<span class="mw-page-title-main">Acid</span> Chemical compound giving a proton or accepting an electron pair

An acid is a molecule or ion capable of either donating a proton (i.e. hydrogen ion, H+), known as a Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis acid.

<span class="mw-page-title-main">Carboxylic acid</span> Organic compound containing a –C(=O)OH group

In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group attached to an R-group. The general formula of a carboxylic acid is often written as R−COOH or R−CO2H, sometimes as R−C(O)OH with R referring to an organyl group, or hydrogen, or other groups. Carboxylic acids occur widely. Important examples include the amino acids and fatty acids. Deprotonation of a carboxylic acid gives a carboxylate anion.

<span class="mw-page-title-main">Ester</span> Compound derived from an acid

In chemistry, an ester is a functional group derived from an acid in which the hydrogen atom (H) of at least one acidic hydroxyl group of that acid is replaced by an organyl group. Analogues derived from oxygen replaced by other chalcogens belong to the ester category as well. According to some authors, organyl derivatives of acidic hydrogen of other acids are esters as well, but not according to the IUPAC.

Hydrolysis is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile.

<span class="mw-page-title-main">Ketone</span> Organic compounds of the form >C=O

In organic chemistry, a ketone is an organic compound with the structure R−C(=O)−R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group −C(=O)−. The simplest ketone is acetone, with the formula (CH3)2CO. Many ketones are of great importance in biology and industry. Examples include many sugars (ketoses), many steroids, and the solvent acetone.

<span class="mw-page-title-main">Thiol</span> Any organic compound having a sulfanyl group (–SH)

In organic chemistry, a thiol, or thiol derivative, is any organosulfur compound of the form R−SH, where R represents an alkyl or other organic substituent. The −SH functional group itself is referred to as either a thiol group or a sulfhydryl group, or a sulfanyl group. Thiols are the sulfur analogue of alcohols, and the word is a blend of "thio-" with "alcohol".

<span class="mw-page-title-main">Thioester</span> Organosulfur compounds of the form R–SC(=O)–R’

In organic chemistry, thioesters are organosulfur compounds with the molecular structure R−C(=O)−S−R’. They are analogous to carboxylate esters with the sulfur in the thioester replacing oxygen in the carboxylate ester, as implied by the thio- prefix. They are the product of esterification of a carboxylic acid with a thiol. In biochemistry, the best-known thioesters are derivatives of coenzyme A, e.g., acetyl-CoA. The R and R' represent organyl groups, or H in the case of R.

<span class="mw-page-title-main">Diethyl malonate</span> Chemical compound

Diethyl malonate, also known as DEM, is the diethyl ester of malonic acid. It occurs naturally in grapes and strawberries as a colourless liquid with an apple-like odour, and is used in perfumes. It is also used to synthesize other compounds such as barbiturates, artificial flavourings, vitamin B1, and vitamin B6.

<span class="mw-page-title-main">Acyl halide</span> Oxoacid compound with an –OH group replaced by a halogen

In organic chemistry, an acyl halide is a chemical compound derived from an oxoacid by replacing a hydroxyl group with a halide group.

<span class="mw-page-title-main">Sulfonic acid</span> Organic compounds with the structure R−S(=O)2−OH

In organic chemistry, sulfonic acid refers to a member of the class of organosulfur compounds with the general formula R−S(=O)2−OH, where R is an organic alkyl or aryl group and the S(=O)2(OH) group a sulfonyl hydroxide. As a substituent, it is known as a sulfo group. A sulfonic acid can be thought of as sulfuric acid with one hydroxyl group replaced by an organic substituent. The parent compound is the parent sulfonic acid, HS(=O)2(OH), a tautomer of sulfurous acid, S(=O)(OH)2. Salts or esters of sulfonic acids are called sulfonates.

<span class="mw-page-title-main">Organic acid anhydride</span> Any chemical compound having two acyl groups bonded to the same oxygen atom

An organic acid anhydride is an acid anhydride that is also an organic compound. An acid anhydride is a compound that has two acyl groups bonded to the same oxygen atom. A common type of organic acid anhydride is a carboxylic anhydride, where the parent acid is a carboxylic acid, the formula of the anhydride being (RC(O))2O. Symmetrical acid anhydrides of this type are named by replacing the word acid in the name of the parent carboxylic acid by the word anhydride. Thus, (CH3CO)2O is called acetic anhydride.Mixed (or unsymmetrical) acid anhydrides, such as acetic formic anhydride (see below), are known, whereby reaction occurs between two different carboxylic acids. Nomenclature of unsymmetrical acid anhydrides list the names of both of the reacted carboxylic acids before the word "anhydride" (for example, the dehydration reaction between benzoic acid and propanoic acid would yield "benzoic propanoic anhydride").

<span class="mw-page-title-main">Permanganate</span> Chemical compound

A permanganate is a chemical compound with the manganate(VII) ion, MnO
4
, the conjugate base of permanganic acid. Because the manganese atom has a +7 oxidation state, the permanganate(VII) ion is a strong oxidising agent. The ion is a transition metal ion with a tetrahedral structure. Permanganate solutions are purple in colour and are stable in neutral or slightly alkaline media. The exact chemical reaction depends on the carbon-containing reactants present and the oxidant used. For example, trichloroethane (C2H3Cl3) is oxidised by permanganate ions to form carbon dioxide (CO2), manganese dioxide (MnO2), hydrogen ions (H+), and chloride ions (Cl).

<span class="mw-page-title-main">Carboxylate</span> Chemical group (RCOO); conjugate base of a carboxylic acid

In organic chemistry, a carboxylate is the conjugate base of a carboxylic acid, RCOO. It is an anion, an ion with negative charge.

<span class="mw-page-title-main">Diazonium compound</span> Group of organonitrogen compounds

Diazonium compounds or diazonium salts are a group of organic compounds sharing a common functional group [R−N+≡N]X where R can be any organic group, such as an alkyl or an aryl, and X is an inorganic or organic anion, such as a halide. The parent compound where R is hydrogen, is diazenylium.

<span class="mw-page-title-main">Ortho ester</span> Chemical group with the structure RC(OR)3

In organic chemistry, an ortho ester is a functional group containing three alkoxy groups attached to one carbon atom, i.e. with the general formula RC(OR')3. Orthoesters may be considered as products of exhaustive alkylation of unstable orthocarboxylic acids and it is from these that the name 'ortho ester' is derived. An example is ethyl orthoacetate, CH3C(OCH2CH3)3, more correctly known as 1,1,1-triethoxyethane.

<span class="mw-page-title-main">Mercury(II) acetate</span> Chemical compound

Mercury(II) acetate, also known as mercuric acetate is a chemical compound, the mercury(II) salt of acetic acid, with the formula Hg(O2CCH3)2. Commonly abbreviated Hg(OAc)2, this compound is employed as a reagent to generate organomercury compounds from unsaturated organic precursors. It is a white, water-soluble solid, but some samples can appear yellowish with time owing to decomposition.

<span class="mw-page-title-main">Carbonyl reduction</span> Organic reduction of any carbonyl group by a reducing agent

In organic chemistry, carbonyl reduction is the conversion of any carbonyl group, usually to an alcohol. It is a common transformation that is practiced in many ways. Ketones, aldehydes, carboxylic acids, esters, amides, and acid halides - some of the most pervasive functional groups, -comprise carbonyl compounds. Carboxylic acids, esters, and acid halides can be reduced to either aldehydes or a step further to primary alcohols, depending on the strength of the reducing agent. Aldehydes and ketones can be reduced respectively to primary and secondary alcohols. In deoxygenation, the alcohol group can be further reduced and removed altogether by replacement with H.

In organic chemistry, thiocarboxylic acids or carbothioic acids are organosulfur compounds related to carboxylic acids by replacement of one of the oxygen atoms with a sulfur atom. Two tautomers are possible: a thione form and a thiol form. These are sometimes also referred to as "carbothioic O-acid" and "carbothioic S-acid" respectively. Of these the thiol form is most common.

<span class="mw-page-title-main">Thiobenzoic acid</span> Chemical compound

Thiobenzoic acid is an organosulfur compound with molecular formula C6H5COSH. It is the parent of aryl thiocarboxylic acids. It is a pale yellow liquid that freezes just below room temperature.

<span class="mw-page-title-main">Potassium thioacetate</span> Organosulfur compound (CH3COS- K+)

Potassium thioacetate is an organosulfur compound and a salt with the formula CH3COSK+. This white, water-soluble solid is used as a reagent for preparing thioacetate esters and other derivatives.

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. ": Identification of the substance/mixture and of the company/undertaking - Thioacetic acid". www.sigmaaldrich.com.
  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.