Biphenyl

Not to be confused with limonene or bisphenol.

"Ph-Ph" redirects here. For phph, see Phenolphthalein.

Biphenyl

Names
IUPAC name Biphenyl
Other names Phenyl benzene
Identifiers
CAS Number	92-52-4 Y
ChEBI	CHEBI:17097 Y
ChEMBL	ChEMBL14092 Y
ChemSpider	6828 Y
Jmol 3D model	Interactive image
KEGG	C06588 Y
PubChem	7095
UNII	2L9GJK6MGN Y
InChI InChI=1S/C12H10/c1-3-7-11(8-4-1)12-9-5-2-6-10-12/h1-10H Y Key: ZUOUZKKEUPVFJK-UHFFFAOYSA-N Y InChI=1/C12H10/c1-3-7-11(8-4-1)12-9-5-2-6-10-12/h1-10H Key: ZUOUZKKEUPVFJK-UHFFFAOYAV
SMILES c1ccc(cc1)c2ccccc2
Properties
Chemical formula	C12H10
Molar mass	154.21 g·mol−1
Appearance	Colorless to pale-yellow crystals
Odor	pleasant
Density	1.04 g/cm3
Melting point	69.2 °C (156.6 °F; 342.3 K)
Boiling point	255 °C (491 °F; 528 K)
Solubility in water	4.45 mg/L
Vapor pressure	0.005 mmHg (20°C)
Vapor pressure	{{{value}}}
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

Biphenyl (or diphenyl or phenylbenzene or 1,1'-biphenyl or lemonene) is an organic compound that forms colorless crystals.

It has a distinctively pleasant smell. Biphenyl is an aromatic hydrocarbon with a molecular formula (C₆H₅)₂. It is notable as a starting material for the production of polychlorinated biphenyls (PCBs), which were once widely used as dielectric fluids and heat transfer agents.

Biphenyl is also an intermediate for the production of a host of other organic compounds such as emulsifiers, optical brighteners, crop protection products, and plastics. Biphenyl is insoluble in water, but soluble in typical organic solvents. The biphenyl molecule consists of two connected phenyl rings.

Properties and occurrence

Biphenyl is produced industrially as a byproduct of the dealkylation of toluene to produce benzene:

C₆H₅CH₃ + C₆H₆ → C₆H₅-C₆H₅ + CH₄

The other principal route is by the oxidative dehydrogenation of benzene:

2 C₆H₆ + 1/2 O₂ → C₆H₅-C₆H₅ + H₂O

40,000,000 kg are produced annually by these routes.

In the laboratory, biphenyl can also be synthesized by treating phenylmagnesium bromide with copper salts.

Natural occurrence

Biphenyl occurs naturally in coal tar, crude oil, and natural gas and can be isolated from these sources via distillation.

Reactions and uses

Lacking functional groups, biphenyl is fairly non-reactive, which is the basis of its main application. Biphenyl is mainly used as a heat transfer agent as a eutectic mixture with diphenylether. This mixture is stable to 400 °C.

Biphenyl does undergo sulfonation followed by base hydrolysis produces p-hydroxybiphenyl and p,p'-dihydroxybiphenyl, which are useful fungicides. In another substitution reactions, it undergoes halogenation. Polychlorinated biphenyls were once popular pesticides.

Stereochemistry

Rotation about the single bond in biphenyl, and especially its ortho-substituted derivatives, is sterically hindered. For this reason, some substituted biphenyls show atropisomerism; that is, the individual C₂-symmetric-isomers are optically stable. Some derivatives, as well as related molecules such as BINAP, find application as ligands in asymmetric synthesis. In the case of unsubstituted biphenyl, the equilibrium torsional angle is 44.4° and the torsional barriers are quite small, 6.0 kJ/mol at 0° and 6.5 kJ/mol at 90°. Adding ortho substituents greatly increases the barrier: in the case of the 2,2'-dimethyl derivative, the barrier is 17.4 kcal/mol (72.8 kJ/mol).

Biological aspects

Biphenyl prevents the growth of molds and fungus, and is therefore used as a preservative (E230, in combination with E231, E232 and E233), particularly in the preservation of citrus fruits during transportation. It is no longer approved as a food additive in the European Union.

It is mildly toxic, but can be degraded biologically by conversion into nontoxic compounds. Some bacteria are able to hydroxylate biphenyl and its polychlorinated biphenyls (PCBs).

It is part of the active group in the antibiotic oritavancin.

Biphenyl compounds

Substituted biphenyls can be prepared synthetically by various coupling reactions including the Suzuki reaction and the Ullmann reaction and have many uses. Polychlorinated biphenyls were once used as cooling and insulating fluids and polybrominated biphenyls are flame retardants. The biphenyl motif also appears in drugs such as diflunisal and telmisartan. The abbreviation E7 stands for a liquid crystal mixture consisting of several cyanobiphenyls with long aliphatic tails used commercially in liquid crystal displays. A variety of benzidine derivatives are used in dyes and polymers. Research into biphenyl liquid crystal candidates mainly focuses on molecules with highly polar heads (for example cyano or halide groups) and aliphatic tails.

See also

• Naphthalene, where the rings are fused
• Terpyridine
• Terthiophene
• Tricyclobutabenzene, a unusual related molecule
• Terphenyl, three ringed analog

References

• Isolation and Identification of Biphenyls from West Edmond Crude Oil N. G. Adams and D. M. Richardson. Analytical Chemistry 1953 25 (7), 1073-1074
• Biphenyl (1,1- Biphenyl). Wiley/VCH, Weinheim (1991), ISBN 3-527-28277-7

External links

• International Chemical Safety Card 0106
• CDC - NIOSH Pocket Guide to Chemical Hazards
• National Pollutant Inventory - Biphenyl
• External MSDS