Biphenyl, also known as phenylbenzene or biphenyl, is a compound formed by two phenyl groups connected together. The pure product is white or colorless to light yellow flaky crystals, while the industrial product is slightly yellow with a special aroma. Melting point 69.2℃, boiling point 255.2℃. It is insoluble in water but soluble in organic solvents. It is often used as a precursor for organic synthesis and is one of the main components of organic high-temperature heat carriers. Derivatives include benzidine, diphenyl ether, octabromobiphenyl ether, polychlorinated biphenyls, etc. Natural biphenyl exists in coal tar, crude oil and natural gas, and its mass fraction in coal tar is 0.20%-0.40%. The current chemical book preparation methods of biphenyl include coal tar extraction method and chemical synthesis method. The chemical bond in the middle of biphenyl can rotate freely, but if there are large groups at the four ortho positions, the rotation is hindered and atropisomers will be produced. This type of compound (such as BINAP) can be used as a chiral ligand. Substituted biphenyls can be prepared by coupling reactions such as Suzuki reaction and Ullmann reaction. Biphenyl is an important organic raw material, widely used in medicine, pesticides, dyes, liquid crystal materials, etc. It can be used to synthesize plasticizers and preservatives, and can also be used to manufacture fuels, engineering plastics and high-energy fuels.