A new reaction of bisphenol A and preparation of polysubstituted 9,9-dimethylxanthenes

A new transformation of bisphenol A (1) to polymethylated 9,9-dimethylxanthenes 2-5 in the presence of an exogenous phenol is described. The reaction proceeds with concurrent liberation of phenol, is catalyzed by strong acid, and takes place at synthetically useful rates at temperatures above 100 degrees C. Materials chemically related to bisphenol A polycarbonate 10, chroman fl, and tars generated during the manufacture of 1, behave similarly. The product xanthenes are useful as precursors to novel xanthene polyesters such as 33 having high glass transition temperatures relative to analogous materials based on 12 or 13. Catalytic oxidation of xanthenes 2-4 affords highly insoluble diacids that are esterified to the esters 6-8. A mechanistic framework accounting for the appearance of chroman 23 and spiroketal 24 as intermediates is given. Overall, the reaction has the characteristics of a complex series of equilibria in which xanthenes such as 2 are strongly favored.