Thiophenol
Encyclopedia
Thiophenol is an organosulfur compound with the formula C6H6S, and sometimes abbreviated as PhSH. This foul-smelling colourless liquid is the simplest aromatic thiol
. The chemical structure
s of thiophenols are analogous to phenols
except the oxygen
atom
in the hydroxyl group (-OH) bonded to the aromatic ring is replaced by a sulfur
atom. The prefix thio- implies a sulfur-containing compound and when used before a root word name for a compound which would normally contain an oxygen atom, in the case of 'thiol' that the alcohol oxygen atom is replaced by a sulfur atom.
Thiophenols also describes a class of compounds formally derived from thiophenol itself. All have a sulfhydryl group (-SH) covalently bonded
to an aromatic ring. The organosulfur ligand in the medicine merthiolate is a thiophenol.
Methods are the reduction of benzenesulfonyl chloride with zinc
. and the action of elemental sulfur on phenyl magnesium halide or phenyllithium
followed by acidification.
Phenols can be converted to the thiophenols via rearrangement of their O-aryl dialkylthiocarbamates. In the Leuckart Thiophenol Reaction the starting material is an aniline
through the diazonium salt (ArN2X) and the xanthate
(ArS(C=S)OR)
ity than does phenol. Thiophenol has a pKa
of 6 vs 10 for phenol. A similar pattern is seen for H2S
vs. H2O and all thiol
s vs. the corresponding alcohol
s. Treatment of PhSH with strong base such as sodium hydroxide (NaOH) or sodium
metal affords the salt sodium thiophenolate (PhSNa).
. Such reactions are fairly irreversible. C6H5SH also adds to α,β-unsaturated carbonyls via Michael addition.
:
The disulfide can be reduced back the thiol using sodium borohydride
followed by acidification. This redox reaction is also exploited in the use of C6H5SH as a source of H atoms.
(Cl2).
with thiophenol.
Thiol
In organic chemistry, a thiol is an organosulfur compound that contains a carbon-bonded sulfhydryl group...
. The chemical structure
Chemical structure
A chemical structure includes molecular geometry, electronic structure and crystal structure of molecules. Molecular geometry refers to the spatial arrangement of atoms in a molecule and the chemical bonds that hold the atoms together. Molecular geometry can range from the very simple, such as...
s of thiophenols are analogous to phenols
Phenols
In organic chemistry, phenols, sometimes called phenolics, are a class of chemical compounds consisting of a hydroxyl group bonded directly to an aromatic hydrocarbon group...
except the oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
atom
Atom
The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons...
in the hydroxyl group (-OH) bonded to the aromatic ring is replaced by a sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
atom. The prefix thio- implies a sulfur-containing compound and when used before a root word name for a compound which would normally contain an oxygen atom, in the case of 'thiol' that the alcohol oxygen atom is replaced by a sulfur atom.
Thiophenols also describes a class of compounds formally derived from thiophenol itself. All have a sulfhydryl group (-SH) covalently bonded
Covalent bond
A covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms. The stable balance of attractive and repulsive forces between atoms when they share electrons is known as covalent bonding....
to an aromatic ring. The organosulfur ligand in the medicine merthiolate is a thiophenol.
Synthesis
There are several methods of synthesis for thiophenol and related compounds, although thiophenol itself is usually purchased for laboratory operations.Methods are the reduction of benzenesulfonyl chloride with zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
. and the action of elemental sulfur on phenyl magnesium halide or phenyllithium
Phenyllithium
Phenyllithium is an organometallic agent with the empirical formula C6H5Li. It is most commonly used as a metalating agent in organic syntheses and a substitute for Grignard reagents for introducing phenyl groups in organic syntheses...
followed by acidification.
Phenols can be converted to the thiophenols via rearrangement of their O-aryl dialkylthiocarbamates. In the Leuckart Thiophenol Reaction the starting material is an aniline
Aniline
Aniline, phenylamine or aminobenzene is an organic compound with the formula C6H5NH2. Consisting of a phenyl group attached to an amino group, aniline is the prototypical aromatic amine. Being a precursor to many industrial chemicals, its main use is in the manufacture of precursors to polyurethane...
through the diazonium salt (ArN2X) and the xanthate
Xanthate
Xanthate usually refers to a salt with the formula ROCS2-M+ . The name xanthates is derived from Greek ξανθός , meaning “yellowish, golden”, and indeed most xanthate salts are yellow...
(ArS(C=S)OR)
Acidity
Thiophenol has appreciably greater acidAcid
An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...
ity than does phenol. Thiophenol has a pKa
PKA
PKA, pKa, or other similar variations may stand for:* pKa, the symbol for the acid dissociation constant at logarithmic scale* Protein kinase A, a class of cAMP-dependent enzymes* Pi Kappa Alpha, the North-American social fraternity...
of 6 vs 10 for phenol. A similar pattern is seen for H2S
Hydrogen sulfide
Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...
vs. H2O and all thiol
Thiol
In organic chemistry, a thiol is an organosulfur compound that contains a carbon-bonded sulfhydryl group...
s vs. the corresponding alcohol
Alcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....
s. Treatment of PhSH with strong base such as sodium hydroxide (NaOH) or sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
metal affords the salt sodium thiophenolate (PhSNa).
Alkylation
The thiophenolate is highly nucleophilic, which translates to a high rate of alkylation. Thus, treatment of C6H5SH with methyl iodide in the presence of a base gives methyl phenyl sulfide, C6H5SCH3, a thioetherThioether
A thioether is a functional group in organosulfur chemistry with the connectivity C-S-C as shown on right. Like many other sulfur-containing compounds, volatile thioethers have foul odors. A thioether is similar to an ether except that it contains a sulfur atom in place of the oxygen...
. Such reactions are fairly irreversible. C6H5SH also adds to α,β-unsaturated carbonyls via Michael addition.
Oxidation
Thiophenols, especially in the presence of base is easily oxidized to diphenyl disulfideDiphenyl disulfide
Diphenyl disulfide is the chemical compound with the formula [C6H5S]2. This colorless crystalline material is often abbreviated Ph2S2. It is one of the most popular organic disulfides used in organic synthesis...
:
- 2 C6H5SH + 1/2 O2 → C6H5S-SC6H5 + H2O
The disulfide can be reduced back the thiol using sodium borohydride
Sodium borohydride
Sodium borohydride, also known as sodium tetrahydridoborate, is an inorganic compound with the formula NaBH4. This white solid, usually encountered as a powder, is a versatile reducing agent that finds wide application in chemistry, both in the laboratory and on a technical scale. Large amounts are...
followed by acidification. This redox reaction is also exploited in the use of C6H5SH as a source of H atoms.
Chlorination
Phenylsulfenyl chloride, a blood-red liquid (b.p. 41–42 °C), can be prepared by the reaction of thiophenol with chlorineChlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
(Cl2).
Coordination to metals
Metal cations form thiophenolates, some of which are polymeric. One example is "C6H5SCu," obtained by treating copper(I) chlorideCopper(I) chloride
Copper chloride, commonly called cuprous chloride, is the lower chloride of copper, with the formula CuCl. The substance is a white solid sparingly soluble in water, but very soluble in concentrated hydrochloric acid...
with thiophenol.