Diphenylmethane is an organic compound with the formula (C6H5)2CH2 (often abbreviated CH
2Ph
2). The compound consists of methane wherein two hydrogen atoms are replaced by two phenyl groups. It is a white solid.
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| Names | |
|---|---|
| Preferred IUPAC name
1,1′-Methylenedibenzene[1] | |
| Other names
Diphenylmethane
Benzylbenzene | |
| Identifiers | |
3D model (JSmol)
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| Abbreviations | BnPh, Ph2CH2 |
| ChEBI | |
| ChEMBL | |
| ChemSpider | |
| ECHA InfoCard | 100.002.708 |
| MeSH | Diphenylmethane |
PubChem CID
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| UNII | |
CompTox Dashboard (EPA)
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| Properties | |
| C13H12 | |
| Molar mass | 168.234 |
| Appearance | colourless oil |
| Density | 1.006 g/mL |
| Melting point | 22 to 24 °C (72 to 75 °F; 295 to 297 K) |
| Boiling point | 264 °C (507 °F; 537 K) |
| 14 mg/L | |
| Acidity (pKa) | 32.2 |
| -115.7·10−6 cm3/mol | |
| Hazards | |
| Occupational safety and health (OHS/OSH): | |
Main hazards
|
flammable |
| Flash point | > 110 °C; 230 °F; 383 K |
| Related compounds | |
Related compounds
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Diphenylmethanol |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Diphenylmethane is a common skeleton in organic chemistry. The diphenylmethyl group is also known as benzhydryl.
Synthesis
editIt is prepared by the Friedel–Crafts alkylation of benzyl chloride with benzene in the presence of a Lewis acid such as aluminium chloride:[2]
- C6H5CH2Cl + C6H6 → (C6H5)2CH2 + HCl
Reactivity of the C-H bond
editThe methylene group in diphenylmethane is mildly acidic with a pKa of 32.2, and so can be deprotonated with sodium amide.[3]
- (C6H5)2CH2 + NaNH2− → (C6H5)2CHNa + NH3
The resulting carbanion can be alkylated. For example, treatment with n-bromobutane produces 1,1-diphenylpentane in 92% yield.[4]
- (C6H5)2CH− + CH3CH2CH2CH2Br → (C6H5)2CHCH2CH2CH2CH3 + Br−
Alkylation of various benzhydryl compounds 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), in yields between 86 and 99%.[3][4]
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 of 82 kcal mol−1 (340 kJ mol−1).[5] This is well below the published bond dissociation energies for comparable C–H bonds in propane, where BDE((CH3)2CH–H)=98.6 kcal mol−1, and toluene, where BDE(C6H5CH2–H)=89.7 kcal mol−1.[6][7]
See also
edit- Benzhydryl compounds
- Toluene, a.k.a. methylbenzene, phenylmethane
- Triphenylmethane
- Tetraphenylmethane
References
edit- ^ International Union of Pure and Applied Chemistry (2014). Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013. The Royal Society of Chemistry. p. 452. doi:10.1039/9781849733069. ISBN 978-0-85404-182-4.
- ^ W. W. Hartman and Ross Phillips (1934). "Diphenylmethane". Organic Syntheses. 14: 34. doi:10.15227/orgsyn.014.0034.
- ^ a b Hauser, Charles R.; Hamrick, Phillip J. (1957). "Alkylation of Diphenylmethane with Alkyl Halides by Sodium Amide. Substitution versus β-Elimination. Relative Acidities of Diphenylmethane and Ammonia". J. Am. Chem. Soc. 79 (12): 3142–3145. doi:10.1021/ja01569a041.
- ^ a b Murphy, William S.; Hamrick, Phillip J.; Hauser, Charles R. (1968). "1,1-Diphenylpentane". Organic Syntheses. 48: 80. doi:10.15227/orgsyn.048.0080.
- ^ Zhang, Xian-Man; Bordwell, Frederick G. (1992). "Homolytic bond dissociation energies of the benzylic carbon-hydrogen bonds in radical anions and radical cations derived from fluorenes, triphenylmethanes, and related compounds". J. Am. Chem. Soc. 114 (25): 9787–9792. doi:10.1021/ja00051a010.
- ^ Blanksby, S. J.; Ellison, G. B. (2003). "Bond Dissociation Energies of Organic Molecules". Accounts of Chemical Research. 36 (4): 255–263. doi:10.1021/ar020230d. PMID 12693923.
- ^ Streitwieser, Andrew; Bergman, Robert G. (2018). "Table of Bond Dissociation Energies". University of California, Berkeley. Retrieved December 30, 2021.
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