Synthesis of substituted dibenzophospholes. Part 9.1 Preparation of two water-soluble phosphinic-polyphosphonic acids

Several improvements, including a generally applicable method for reduction of aromatic nitro compounds to amines, were made to the preparation from 2,2',4,4'-tetranitrobiphenyl of the meso atropisomer 1 of a bis-phosphonomethylated 4,6-diaryldibenzophosphole 5-oxide, previously obtained in impure form. A concomitant product 12 containing one phosphonomethyl group was formed by a novel intramolecular displacement. Both products were converted by a specially developed method into crystalline phosphinic-polyphosphonic acids, containing respectively four and three phosphonomethyl groups, which formed stable monodisperse solutions in water at pH 2–4. These solutions catalysed the hydration of 2-methylpropene to tert-butyl alcohol somewhat more efficiently than a toluene-4-sulfonic acid solution of equivalent acidity.