Thioacetic acid is an
organosulfur compound
Organosulfur compounds are organic compounds that contain sulfur. They are often associated with foul odors, but many of the sweetest compounds known are organosulfur derivatives, e.g., saccharin. Nature abounds with organosulfur compounds—sulfu ...
with the
molecular formula
In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, ...
. It is the sulfur
analogue of
acetic acid
Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main component ...
(), as implied by the ''
thio-
The prefix thio-, when applied to a chemical, such as an ion, means that an oxygen atom in the compound has been replaced by a sulfur atom. This term is often used in organic chemistry. For example, from the word ''ether,'' referring to an oxyg ...
'' prefix. It is a yellow liquid with a strong
thiol
In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl gro ...
-like odor. It is used in
organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...
for the introduction of thiol groups () in molecules.
Synthesis and properties
Thioacetic acid is prepared by the reaction of
acetic anhydride
Acetic anhydride, or ethanoic anhydride, is the chemical compound with the formula (CH3CO)2O. Commonly abbreviated Ac2O, it is the simplest isolable anhydride of a carboxylic acid and is widely used as a reagent in organic synthesis. It is a col ...
with
hydrogen sulfide
Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The unde ...
:
:
(CH3C(O))2O + H2S -> CH3C(O)SH + CH3C(O)OH
It has also been produced by the action of
phosphorus pentasulfide
Phosphorus pentasulfide is the inorganic compound with the formula (monomer) or (dimer). This yellow solid is the one of two phosphorus sulfides of commercial value. Samples often appear greenish-gray due to impurities. It is soluble in carbon d ...
on glacial
acetic acid
Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main component ...
, followed by distillation.
:
CH3C(O)OH + P2S5 -> CH3C(O)SH + P2OS4
Thioacetic acid is typically contaminated by acetic acid.
The compound exists exclusively as the thiol
tautomer
Tautomers () are structural isomers (constitutional isomers) of chemical compounds that readily interconvert.
The chemical reaction interconverting the two is called tautomerization. This conversion commonly results from the relocation of a hydr ...
, consistent with the strength of the double bond. Reflecting the influence of
hydrogen-bonding
In chemistry, a hydrogen bond (or H-bond) is a primarily electrostatic force of attraction between a hydrogen (H) atom which is covalently bound to a more electronegative "donor" atom or group (Dn), and another electronegative atom bearing a ...
, the
boiling point
The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor.
The boiling point of a liquid varies depending upon the surrounding envir ...
(93 °C) and melting points are 20 and 75 K lower than those for
acetic acid
Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main component ...
.
Reactivity
Acidity
With a p''K''
a near 3.4, thioacetic acid is about 15 times more acidic than acetic acid. 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
Potassium thioacetate is an organosulfur compound and a salt with the formula . This white, water-soluble solid is used as a reagent for preparing thioacetate esters and other derivatives.
Synthesis and reactions
Potassium thioacetate, which is ...
, are used to generate thioacetate esters. Thioacetate esters undergo hydrolysis to give thiols. A typical method for preparing a thiol from an
alkyl halide
The haloalkanes (also known as halogenoalkanes or alkyl halides) are alkanes containing one or more halogen substituents. They are a subset of the general class of halocarbons, although the distinction is not often made. Haloalkanes are widely ...
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 \qquad (X\ =\ Cl,\ Br,\ I,\ \dots)
:
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
A daughter category of ''Ageing'', this category deals only with the biological aspects of ageing.
Ageing
Ailments of unknown cause
Biogerontology
Biological processes
Causes of death
Cellular processes
Gerontology
Life extension
Metabo ...
mediated
nucleophilic addition
In organic chemistry, a nucleophilic addition reaction is an addition reaction where a chemical compound with an electrophilic double or triple bond reacts with a nucleophile, such that the double or triple bond is broken. Nucleophilic additions di ...
to an
exocyclic
In organic chemistry, an alicyclic compound contains one or more all-carbon rings which may be either saturated or unsaturated, but do not have aromatic character. Alicyclic compounds may have one or more aliphatic side chains attached.
The ...
alkene
In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond.
Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, an ...
forming a
thioester
In organic chemistry, thioesters are organosulfur compounds with the functional group . They are analogous to carboxylate esters () with the sulfur in the thioester playing the role of the linking oxygen in the carboxylate ester, as implied by t ...
:
:
Reductive acetylation
Salts of thioacetic acid such as potassium thioacetate can be used to do one-step conversion of nitroarenes to aryl acetamides. This is particularly useful in pharmaceutical preparations, e.g.
paracetamol
Paracetamol, also known as acetaminophen, is a medication used to treat fever and mild to moderate pain. Common brand names include Tylenol and Panadol.
At a standard dose, paracetamol only slightly decreases body temperature; it is inferior ...
.
References
{{reflist
Organic acids
Reagents for organic chemistry
Organosulfur compounds
Foul-smelling chemicals