Triphenylmethane, or triphenyl methane, is the
hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ex ...
with the
formula
In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwee ...
(C
6H
5)
3CH. This colorless solid is soluble in nonpolar organic solvents and not in water. Triphenylmethane is the basic skeleton of many synthetic
dyes called
triarylmethane dye
Triarylmethane dyes are synthetic organic compounds containing triphenylmethane backbones. As dyes, these compounds are intensely colored. They are produced industrially as dyes.
Families
Triarylmethane dyes can be grouped into families accordin ...
s, many of them are
pH indicator
A pH indicator is a halochromic chemical compound added in small amounts to a solution so the pH (acidity or basicity) of the solution can be determined visually or spectroscopically by changes in absorption and/or emission properties. Hence, ...
s, and some display
fluorescence
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, tha ...
. A trityl group in organic chemistry is a triphenylmethyl group Ph
3C, e.g.
triphenylmethyl chloride
Triphenylmethyl chloride or trityl chloride (TrCl) is a white solid with the chemical formula C19H15Cl. It is an alkyl halide, sometimes used to introduce the trityl protecting group.
Preparation
Triphenylmethyl chloride is commercially available. ...
(trityl chloride) and the
triphenylmethyl radical
The triphenylmethyl radical (often shorted to trityl radical) is an organic compound with the formula (C6H5)3C. It is a persistent radical. It was the first radical ever to be described in organic chemistry. Because of its accessibility, the trit ...
(trityl radical).
Preparation
Triphenylmethane was first synthesized in 1872 by the German chemist
August Kekulé
Friedrich August Kekulé, later Friedrich August Kekule von Stradonitz ( , ; 7 September 1829 – 13 July 1896), was a German organic chemist. From the 1850s until his death, Kekulé was one of the most prominent chemists in Europe, especially ...
and his Belgian student Antoine Paul Nicolas Franchimont (1844–1919) by heating
diphenylmercury
Diphenylmercury is the organomercury compound with the formula Hg(C6H5)2. It is a white solid. The compound is of historic interest as a particularly stable organometallic compound but it finds few uses because of its high toxicity.
Preparation
...
(Hg(C
6H
5)
2, ''Quecksilberdiphenyl'') with
benzal chloride
Benzal chloride is an organic compound with the formula C6H5CHCl2. This colourless liquid is a lachrymator and is used as a building block in organic synthesis.
Preparation and usage
Benzal chloride is produced by the free radical chlorination o ...
(C
6H
5CHCl
2, ''Benzylenchlorid'').
Triphenylmethane can be synthesized by
Friedel–Crafts reaction
The Friedel–Crafts reactions are a set of reactions developed by Charles Friedel and James Crafts in 1877 to attach substituents to an aromatic ring. Friedel–Crafts reactions are of two main types: alkylation reactions and acylation reacti ...
from
benzene
Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms, ...
and
chloroform
Chloroform, or trichloromethane, is an organic compound with chemical formula, formula Carbon, CHydrogen, HChlorine, Cl3 and a common organic solvent. It is a colorless, strong-smelling, dense liquid produced on a large scale as a precursor to ...
with
aluminium chloride
Aluminium chloride, also known as aluminium trichloride, is an inorganic compound with the formula . It forms hexahydrate with the formula , containing six water molecules of hydration. Both are colourless crystals, but samples are often contam ...
catalyst
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
:
:3 C
6H
6 + CHCl
3 → Ph
3CH + 3 HCl
Alternatively, benzene may react with
carbon tetrachloride
Carbon tetrachloride, also known by many other names (such as tetrachloromethane, also IUPAC nomenclature of inorganic chemistry, recognised by the IUPAC, carbon tet in the cleaning industry, Halon-104 in firefighting, and Refrigerant-10 in HVAC ...
using the same catalyst to obtain the
triphenylmethyl chloride
Triphenylmethyl chloride or trityl chloride (TrCl) is a white solid with the chemical formula C19H15Cl. It is an alkyl halide, sometimes used to introduce the trityl protecting group.
Preparation
Triphenylmethyl chloride is commercially available. ...
–
aluminium chloride
Aluminium chloride, also known as aluminium trichloride, is an inorganic compound with the formula . It forms hexahydrate with the formula , containing six water molecules of hydration. Both are colourless crystals, but samples are often contam ...
adduct, which is hydrolyzed with dilute acid:
:3 C
6H
6 + CCl
4 + AlCl
3 → Ph
3CCl·AlCl
3
:Ph
3CCl·AlCl
3 + HCl → Ph
3CH
Synthesis from
benzylidene chloride, prepared from
benzaldehyde and
phosphorus pentachloride
Phosphorus pentachloride is the chemical compound with the formula PCl5. It is one of the most important phosphorus chlorides, others being PCl3 and POCl3. PCl5 finds use as a chlorinating reagent. It is a colourless, water-sensitive and moist ...
, is used as well.
Reactions of C-H bond
The
p''K''a is 33.3. Triphenylmethane is significantly more acidic than most other hydrocarbons because the charge is
delocalized
In chemistry, delocalized electrons are electrons in a molecule, ion or solid metal that are not associated with a single atom or a covalent bond.IUPAC Gold Boo''delocalization''/ref>
The term delocalization is general and can have slightly dif ...
over three phenyl rings. Steric effects however prevent all three phenyl rings from achieving coplanarity simultaneously. Consequently
diphenylmethane
Diphenylmethane is an organic compound with the formula (C6H5)2CH2 (often abbreviated ). The compound consists of methane wherein two hydrogen atoms are replaced by two phenyl groups. It is a white solid.
Diphenylmethane is a common skeleton in or ...
is even more acidic, because in its anion the charge is spread over two phenyl rings at the same time. The
trityl anion is red. This colour can be used as an indicator in
acid–base titration
An acid–base titration is a method of quantitative analysis for determining the concentration of an acid or base by exactly neutralizing it with a standard solution of base or acid having known concentration. A pH indicator is used to monit ...
s.
The sodium salt can be prepared also from
the chloride:
:(C
6H
5)
3CCl + 2 Na → (C
6H
5)
3CNa + NaCl
The use of tritylsodium as a strong,
non-nucleophilic base
As the name suggests, a non-nucleophilic base is a sterically hindered organic base that is a poor nucleophile. Normal bases are also nucleophiles, but often chemists seek the proton-removing ability of a base without any other functions. Typical ...
has been eclipsed by the popularization of
butyllithium Butyllithium may refer to one of 5 isomeric organolithium reagents of which 3 are commonly used in chemical synthesis:
* ''n''-Butyllithium, abbreviated BuLi or nBuLi
* ''sec''-Butyllithium, abbreviated ''sec''-BuLi or sBuLi, has 2 stereoisomers, ...
and related strong bases.
The Ph
3C-H bond is relatively weak, with a
bond dissociation energy
The bond-dissociation energy (BDE, ''D''0, or ''DH°'') is one measure of the strength of a chemical bond . It can be defined as the standard enthalpy change when is cleaved by homolysis to give fragments A and B, which are usually radical s ...
(BDE) of 81 kcal/mol. By contrast, the BDE for methane is 105 kcal/mol.
Triarylmethane dyes
Examples of triarylmethane dyes are
bromocresol green
Bromocresol green (BCG) is a dye of the triphenylmethane family (triarylmethane dyes). It belongs to a class of dyes called sulfonephthaleins. It is used as a pH indicator in applications such as growth mediums for microorganisms and titrations. ...
:
:
And the
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
-bearing
malachite green
Malachite green is an organic compound that is used as a dyestuff and controversially as an antimicrobial in aquaculture. Malachite green is traditionally used as a dye for materials such as silk, leather, and paper. Despite its name the dye is ...
:
:
Trityl group
Protecting group
The triphenylmethyl substituent, also called trityl, is widely used in organic chemistry. Trityl serves as a
protecting group for alcohols.
: protection (requires proton acceptor): Ph
3CCl + ROH → Ph
3COR + HCl
: deprotection: Ph
3COR + HBr → ROH + Ph
3CBr
Platform for unusual functional groups
Trityl derivatives of reactive functional groups are often crystalline and in some cases sterically stabilized relative to less bulky derivatives. Three such derivatives are
''S''-nitrosotriphenylmethanethiol (Ph
3CSNO), tritylsulfenyl chloride (Ph
3CSCl), and trityl sulfenamide (Ph
3CSNH
2).
See also
*
Tetraphenylmethane
Tetraphenylmethane is an organic compound consisting of a methane core with four phenyl substituents. It was first synthesized by Moses Gomberg in 1898.
Synthesis
Gomberg's classical organic synthesis shown below starts by reacting triphenylm ...
*
Triphenylmethanol
Triphenylmethanol (also known as triphenylcarbinol, TrOH) is an organic compound. It is a white crystalline solid that is insoluble in water and petroleum ether, but well soluble in ethanol, diethyl ether, and benzene. In strongly acidic solutions ...
*
Triphenylmethyl chloride
Triphenylmethyl chloride or trityl chloride (TrCl) is a white solid with the chemical formula C19H15Cl. It is an alkyl halide, sometimes used to introduce the trityl protecting group.
Preparation
Triphenylmethyl chloride is commercially available. ...
*
Triphenylmethyl hexafluorophosphate
Triphenylmethyl (also triphenylcarbenium, trityl, or tritylium) hexafluorophosphate is an organic salt with the formula or , consisting of the triphenylmethyl cation and the hexafluorophosphate anion .
Triphenylmethyl hexafluorophosphate is a ...
*
Triphenylmethyl radical
The triphenylmethyl radical (often shorted to trityl radical) is an organic compound with the formula (C6H5)3C. It is a persistent radical. It was the first radical ever to be described in organic chemistry. Because of its accessibility, the trit ...
References
{{Reflist
Aromatic hydrocarbons
Phenyl compounds