Simultaneous proton removal from open and closed forms of hydrogen-bonded phenylazoresorcinols by general bases
The kinetics of equilibration between the monoanions and dianions of substituted phenylazoresorcinols has been studied in buffered 70%(v/v) Me2SO–H2O. Kinetic terms arising from proton removal by buffer base and hydroxide ion from hydrogen-bonded and non-hydrogen-bonded forms of the monoanions have been observed. The rate coefficients (Bkc) for proton removal from the hydrogen-bonded forms are several orders of magnitude below those for reaction of the open forms and depend on the strength of the catalysing base; Bkc for hydroxide ion is ca. 70-fold higher than Bkc for indazole ion. For reaction of 2-methyl-4-(4-nitrophenylazo)resorcinol with indazole ion, the kinetic solvent isotope effect is negligibly small Bkc(H2O)/Bkc(D2O)ca. 1.2.