Biphenyl

For the compound including hydroxyl groups, see Bisphenol.

"Lemonene" redirects here. For the monoterpene in citrus oil, see Limonene.

Biphenyl

Names
Preferred IUPAC name 1,1′-Biphenyl
Other names Biphenyl Phenylbenzene Xenene
Identifiers
CAS Number	92-52-4 Y
3D model (JSmol)	Interactive image
3DMet	B00985
Beilstein Reference	1634058
ChEBI	CHEBI:17097 Y
ChEMBL	ChEMBL14092 Y
ChemSpider	6828 Y
ECHA InfoCard	100.001.967
EC Number	202-163-5
E number	E230 (preservatives)
Gmelin Reference	3808
KEGG	C06588 Y
PubChem CID	7095
RTECS number	DU8050000
UNII	2L9GJK6MGN Y
UN number	3077
CompTox Dashboard (EPA)	DTXSID4020161
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 c1ccccc1-c2ccccc2
Properties
Chemical formula	C12H10
Molar mass	154.212 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)
Magnetic susceptibility (χ)	−103.25·10−6 cm3/mol
Hazards
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H315, H319, H335, H410
Precautionary statements	P261, P264, P271, P273, P280, P302+P352, P304+P340, P305+P351+P338, P312, P321, P332+P313, P337+P313, P362, P391, P403+P233, P405, P501
NFPA 704 (fire diamond)	1 1 0
Flash point	113 °C (235 °F; 386 K)
Autoignition temperature	540 °C (1,004 °F; 813 K)
Explosive limits	0.6–5.8%
Lethal dose or concentration (LD, LC):
LD50 (median dose)	2400 mg/kg (oral, rabbit) 3280 mg/kg (oral, rat) 1900 mg/kg (oral, mouse) 2400 mg/kg (oral, rat)
NIOSH (US health exposure limits):
PEL (Permissible)	TWA 1 mg/m3 (0.2 ppm)
REL (Recommended)	TWA 1 mg/m3 (0.2 ppm)
IDLH (Immediate danger)	100 mg/m3
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 (also known as diphenyl, phenylbenzene, 1,1′-biphenyl, lemonene or BP) is an organic compound that forms colorless crystals. Particularly in older literature, compounds containing the functional group consisting of biphenyl less one hydrogen (the site at which it is attached) may use the prefixes xenyl or diphenylyl.

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 a solid at room temperature, with a melting point of 69.2 °C (156.6 °F). In the gas phase the molecule exists in two enantiomorphic twisted forms with an angle between the planes of the two rings of 44.4°. In the room-temperature solid, biphenyl is crystalline with space group P2₁/c, which does not allow for chiral crystals. Rather than there being a double-well potential entailing the two twisted conformations, the potential energy is minimized at zero twist.

Biphenyl occurs naturally in coal tar, crude oil, and natural gas and can be isolated from these sources via distillation. It is produced industrially as a byproduct of the dealkylation of toluene to produce methane:

C₆H₅CH₃ + C₆H₆ → C₆H₅−C₆H₅ + CH₄

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

2 C₆H₆ + ½ O₂ → C₆H₅−C₆H₅ + H₂O

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

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

It can also be prepared using diazonium salts. When aniline is treated with NaNO₂+dilute HCl at 5°C, it yields benzene diazonium chloride. When this is further reacted with benzene, biphenyl is formed. This is known as the Gomberg–Bachmann reaction.

${\ce {Ph-NH2->[{\text{NaNO}}_{2}{\text{(aq), HCl}}][T{\text{=273-278K}}]Ph-N2+->[{\text{Ph-H, Δ}}]Ph-Ph}}$

Reactions and uses

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

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

Li biphenyl radical

Lithium biphenyl contains the radical anion, which is highly reducing (-3.1 V vs Fc^+/0). Several solvates of alkali metal salts of biphenyl anion have been characterized by X-ray crystallography. These salts, usually prepared in situ, are versatile reducing agents. Lithium biphenyl offers some advantages relative to the related lithium naphthene. Related to Li/biphenyl is the derivative with tert-butyl groups on the biphenyl.

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).

Biphenyl compounds

Substituted biphenyls have many uses. They are prepared by various coupling reactions including the Suzuki-Miyaura reaction and the Ullmann reaction. 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 (5CB, 7CB, 8OCB and 5CT). 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. It is part of the active group in the antibiotic oritavancin.

Safety and bioactivity

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.

Biphenyl 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).

See also

• Naphthalene, where the rings are fused
• Terphenyl, three ringed analog
• Bithiophene
• Polypyrrole
• OMRE, experimental organic nuclear reactor that tested biphenyl as reactor coolant

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