Biphenyl

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Biphenyl
Skeletal formula
Space filling model showing its twisted conformation
Identifiers
CAS number92-52-4 YesY
PubChem7095
ChemSpider6828 YesY
UNII2L9GJK6MGN YesY
KEGGC06588 YesY
ChEBICHEBI:17097 YesY
ChEMBLCHEMBL14092 YesY
Jmol-3D imagesImage 1
Properties
Molecular formulaC12H10
Molar mass154.21 g mol−1
AppearanceColorless crystals
Density1.04 g/cm3[1]
Melting point69.2 °C; 156.6 °F; 342.3 K ([1])
Boiling point255 °C; 491 °F; 528 K ([1])
Solubility in water4.45 mg/L[1]
Hazards
EU Index601-042-00-8
EU classificationIrritant (Xi)
Dangerous for
the environment (N)
R-phrasesR36/37/38 R50/53
S-phrases(S2) S23 S60 S61
NFPA 704
NFPA 704.svg
1
1
0
Flash point113 °C (235 °F)[1]
Autoignition temperature540 °C (1,004 °F)[1]
 YesY (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references
 
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Biphenyl
Skeletal formula
Space filling model showing its twisted conformation
Identifiers
CAS number92-52-4 YesY
PubChem7095
ChemSpider6828 YesY
UNII2L9GJK6MGN YesY
KEGGC06588 YesY
ChEBICHEBI:17097 YesY
ChEMBLCHEMBL14092 YesY
Jmol-3D imagesImage 1
Properties
Molecular formulaC12H10
Molar mass154.21 g mol−1
AppearanceColorless crystals
Density1.04 g/cm3[1]
Melting point69.2 °C; 156.6 °F; 342.3 K ([1])
Boiling point255 °C; 491 °F; 528 K ([1])
Solubility in water4.45 mg/L[1]
Hazards
EU Index601-042-00-8
EU classificationIrritant (Xi)
Dangerous for
the environment (N)
R-phrasesR36/37/38 R50/53
S-phrases(S2) S23 S60 S61
NFPA 704
NFPA 704.svg
1
1
0
Flash point113 °C (235 °F)[1]
Autoignition temperature540 °C (1,004 °F)[1]
 YesY (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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[edit]

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.[2]

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

Natural occurrence[edit]

Biphenyl occurs naturally in coal tar, crude oil, and natural gas and can be isolated from these sources via distillation.[3]

Reactions and uses[edit]

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.[2]

Stereochemistry[edit]

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°.[4] 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).[5]

Biological aspects[edit]

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).[6]

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

Biphenyl compounds[edit]

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 valsartan 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[edit]

References[edit]

  1. ^ a b c d e f Record in the GESTIS Substance Database from the IFA
  2. ^ a b Karl Griesbaum, Arno Behr, Dieter Biedenkapp, Heinz-Werner Voges, Dorothea Garbe, Christian Paetz, Gerd Collin, Dieter Mayer, Hartmut Höke “Hydrocarbons” in Ullmann's Encyclopedia of Industrial Chemistry 2002 Wiley-VCH, Weinheim. doi:10.1002/14356007.a13_227
  3. ^ Adams, N. G., and D. M. Richardson.1953.Isolation and Identification of Biphenyls from West Edmond Crude Oil. Analytical Chemistry 25 (7): 1073-1074
  4. ^ Mikael P. Johansson and Jeppe Olsen (2008). "Torsional Barriers and Equilibrium Angle of Biphenyl: Reconciling Theory with Experiment". J. Chem. Theory Comput. 4 (9): 1460. doi:10.1021/ct800182e. 
  5. ^ B. Testa (1982). "The geometry of molecules: basic principles and nomenclatures". In Christoph Tamm. Stereochemistry. Elsevier. p. 18. 
  6. ^ Biphenyl degradation - Streptomyces coelicolor, at GenomeNet Database

External links[edit]