4,4′-Biphenol is an organic compound with the formula / It is 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, and PPSU-type polysulfone (also called polyphenylenesulfone, or Radel R).
Synthesis The industrial synthesis of 4,4′-biphenol was developed in the 1960s by Allan Hay, while working at the historic General Electric Research Laboratory. The reaction is driven by the formation and dimerisation of phenol radicals. As the direct oxidative coupling of phenols gives a mixture of isomers, 4,4′-biphenol is instead prepared from 2,6-di-tert-butylphenol, where para-coupling is the only possibility. A reaction with oxygen produces phenol-radicals which undergo rapid dimerisation, ultimately forming a diphenoquinone.
This intermediate is reduced to the tetra-butyl-biphenyl derivative by a reaction with two equivalents of 2,6-di-tert-butylphenol, in an oxygen-free environment (with the radicals generated dimerising to form additional tetra-butyl-biphenyl). 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 exhibits estrogenic SAR.
See also 2,2'-Biphenol Bisphenol
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