Diphenylmethane is an
organic compound
In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. T ...
with the
formula (C
6H
5)
2CH
2 (often abbreviated ). The compound consists of
methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ea ...
wherein two hydrogen atoms are replaced by two
phenyl groups. It is a white solid.
Diphenylmethane is a common
skeleton in organic chemistry. The diphenylmethyl group is also known as ''
benzhydryl
The benzhydryl compounds are a group of organic compounds whose parent structures include diphenylmethane (which is two benzene rings connected by a single methane), with any number of attached substituents, including bridges. This group typic ...
''.
Synthesis
It is prepared by the
Friedel–Crafts alkylation of
benzyl chloride with
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 ...
in the presence of a
Lewis acid such as
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 ...
:
:C
6H
5CH
2Cl + C
6H
6 → (C
6H
5)
2CH
2 + HCl
Reactivity of the C-H bond
The methylene group in diphenylmethane is mildly acidic with a
p''K''a of 32.2, and so can be deprotonated with
sodium amide
Sodium amide, commonly called sodamide (systematic name sodium azanide), is the inorganic compound with the formula . It is a salt composed of the sodium cation and the azanide anion. This solid, which is dangerously reactive toward water, is white ...
.
:(C
6H
5)
2CH
2 + NH
2− → (C
6H
5)
2CH
− + NH
3
The resulting
carbanion can be alkylated. For example, treatment with
''n''-bromobutane produces
1,1-diphenylpentane in 92% yield.
:(C
6H
5)
2CH
− + CH
3CH
2CH
2CH
2Br → (C
6H
5)
2CHCH
2CH
2CH
2CH
3 + Br
−
Alkylation
Alkylation is the transfer of an alkyl group from one molecule to another. The alkyl group may be transferred as an alkyl carbocation, a free radical, a carbanion, or a carbene (or their equivalents). Alkylating agents are reagents for effecti ...
of various
benzhydryl compounds
The benzhydryl compounds are a group of organic compounds whose parent structures include diphenylmethane (which is two benzene rings connected by a single methane), with any number of attached substituents, including bridges. This group typicall ...
has been demonstrated using the corresponding alkyl halides, both primary (
benzyl chloride,
β-phenylethyl chloride, and
n-octyl bromide) and secondary (
benzhydryl chloride,
α-phenylethyl chloride, and
isopropyl chloride
Isopropyl chloride is an organic compound with the chemical formula (CH3)2CHCl. It is a colourless to slightly yellow, volatile, flammable liquid with a sweet, ether-like (almost like petroleum) odour. It is used industrially as a solvent. It ...
), in yields between 86 and 99%.
The acidity of the methylene group in diphenylmethane is due to the weakness of the (C
6H
5)
2CH–H bond, which has 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 ...
of 82 kcal mol
−1 (340 kJ mol
−1). This is well below the published bond dissociation energies for comparable C–H bonds in
propane, where BDE((CH
3)
2CH–H)=98.6 kcal mol
−1, and
toluene
Toluene (), also known as toluol (), is a substituted aromatic hydrocarbon. It is a colorless, water-insoluble liquid with the smell associated with paint thinners. It is a mono-substituted benzene derivative, consisting of a methyl group (CH3) a ...
, where BDE(C
6H
5CH
2–H)=89.7 kcal mol
−1.
See also
*
Benzhydryl compounds
The benzhydryl compounds are a group of organic compounds whose parent structures include diphenylmethane (which is two benzene rings connected by a single methane), with any number of attached substituents, including bridges. This group typicall ...
*
Toluene
Toluene (), also known as toluol (), is a substituted aromatic hydrocarbon. It is a colorless, water-insoluble liquid with the smell associated with paint thinners. It is a mono-substituted benzene derivative, consisting of a methyl group (CH3) a ...
, a.k.a. methylbenzene, phenylmethane
*
Triphenylmethane
Triphenylmethane, or triphenyl methane, is the hydrocarbon with the formula (C6H5)3CH. This colorless solid is soluble in nonpolar organic solvents and not in water. Triphenylmethane is the basic skeleton of many synthetic dyes called triarylmeth ...
*
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 ...
References
Benzyl compounds
{{Hydrocarbon-stub