On the other hand, a process is described in the literature (K. S. Y. Lau et al., Journal of Polymer Science, Polymer Chemistry Edition, 20. 2381-2393 (1982)) which facilitates the preparation of an isomeric diamine to 2,2-bis-(4-aminophenyl) hexafluoropropane from, 2,2-bis-(3-aminophenyl)hexafluoropropane, in very high yields. For this, the process also starts out from 2,2-bis-(4-hydroxyphenyl)hexafluoropropane, the hydroxyl groups of which are converted into F3C-SO3 groups by reaction with trifluoromethanesulfonic anhydride. Trifluoromethanesulfonic acid is eliminated from this compound in a second step by catalytic hydrogenation with a palladium/charcoal catalyst which is suspended in triethylamine and 2,2-bisphenylhexafluoropropane is thus obtained. This compound is nitrated using nitric acid in concentrated sulfuric acid to give 2,2-bis-(3-nitrophenyl)hexafluoropropane in a third step which is then hydrogenated on a palladium/charcoal catalyst to give 2,2-bis-(3-aminophenyl)hexafluoropropane in a fourth step.
