diphenyl

Diphenyl, commonly referred to as biphenyl, is an aromatic hydrocarbon with the formula C12H10. It consists of two phenyl rings connected by a single carbon–carbon bond. The molecule is nonpolar, colorless, and typically exists as a white to off-white solid. It has a melting point around 70 °C and a boiling point near 255–260 °C. It is insoluble in water and soluble in many organic solvents such as ether, benzene, and chloroform.

Structure and properties are characterized by a twisted arrangement of the two phenyl rings due to steric interactions between adjacent ortho hydrogens. The rings are not coplanar, and rotation about the central bond is possible but hindered, contributing to its distinctive physical behavior compared with fully planar polycyclic systems.

Production and occurrence are mainly industrial. Diphenyl is typically prepared by copper- or palladium-catalyzed cross-coupling of appropriate phenyl partners (for example, chlorobenzene or iodobenzene) in Ullmann-type or modern cross-coupling reactions. It can also arise as a byproduct or intermediate in various aromatic syntheses and coupling processes.

Applications include use as a versatile building block in organic synthesis, where it serves as a precursor to dyes, pharmaceuticals, and other aromatic compounds. It has historically been employed as a heat-transfer medium in high-temperature oils and, in the past, as a dielectric fluid in some transformers and capacitors. It remains a reference material and solvent in certain analytical contexts.

Safety and handling follow general hydrocarbon guidelines: it is flammable and can irritate eyes and skin on contact or inhalation. It should be stored away from heat sources and oxidizers and handled with appropriate protective equipment.