4,4′-Biphenol is an aromatic organic compound, and one of three symmetrical isomers of biphenol. It is a colourless crystalline solid with a high melting point. It is primarily used in the production of polymers, particularly liquid crystals where it imparts high thermal stability.

Synthesis

The industrial synthesis of 4,4′-biphenol was developed by Allan Hay in the 1960s. As the direct oxidative coupling of phenol gives a mixture of isomers, 4,4′-biphenol is instead prepared from 2,6-di-tert-butylphenol, where para-coupling is the only possibility. The reaction with oxygen produces phenol-radicals which undergo rapid dimerisation, forming a diphenoquinone. This is reduced to the tetra-butyl-biphenyl derivative by a reaction with additional 2,6-di-tert-butylphenol, in an oxygen-free environment. In the final step, high temperature dealkylation is performed to remove the butyl groups, producing the desired 4,4′-biphenol product. If groups less bulky that t-butyl are used then polyphenylene ethers such as poly(p-phenylene oxide) can be produced.

Safety

4,4'-Biphenol had actually been elucidated to have an estrogenic SAR.