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. The ...

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 ...

(C₆H₅)₂CH₂ (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 Eart ...

wherein two hydrogen atoms are replaced by two

phenyl group In organic chemistry, the phenyl group, or phenyl ring, is a cyclic group of atoms with the formula C6 H5, and is often represented by the symbol Ph. Phenyl group is closely related to benzene and can be viewed as a benzene ring, minus a hydrogen ...

s. It is a white solid. Diphenylmethane is a common

skeleton A skeleton is the structural frame that supports the body of an animal. There are several types of skeletons, including the exoskeleton, which is the stable outer shell of an organism, the endoskeleton, which forms the support structure inside ...

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 Benzyl chloride, or α-chlorotoluene, is an organic compound with the formula C6H5CH2Cl. This colorless liquid is a reactive organochlorine compound that is a widely used chemical building block. Preparation Benzyl chloride is prepared indust ...

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 A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any sp ...

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 ...

: :C₆H₅CH₂Cl + C₆H₆ → (C₆H₅)₂CH₂ + 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 ...

. :(C₆H₅)₂CH₂ + NH₂⁻ → (C₆H₅)₂CH⁻ + NH₃ The resulting

carbanion In organic chemistry, a carbanion is an anion in which carbon is trivalent (forms three bonds) and bears a formal negative charge (in at least one significant resonance form). Formally, a carbanion is the conjugate base of a carbon acid: :R3C ...

can be alkylated. For example, treatment with ''n''-bromobutane produces 1,1-diphenylpentane in 92% yield. :(C₆H₅)₂CH⁻ + CH₃CH₂CH₂CH₂Br → (C₆H₅)₂CHCH₂CH₂CH₂CH₃ + 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 effecting ...

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 (

, 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 (C₆H₅)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 s ...

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 Propane () is a three-carbon alkane with the molecular formula . It is a gas at standard temperature and pressure, but compressible to a transportable liquid. A by-product of natural gas processing and petroleum refining, it is commonly used a ...

, where BDE((CH₃)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) at ...

, where BDE(C₆H₅CH₂–H)=89.7 kcal mol⁻¹.

References

Benzyl compounds {{Hydrocarbon-stub

Synthesis

Reactivity of the C-H bond

See also

References