Electron exchange polymers. XII. Potentiometric titration of dicyclopentadienyliron (“ferrocene”) and some derivatives

Polymers bearing the dicyclopentadienyliron (“ferrocene”) functional group fall into the class of electron exchange polymers. Polyvinyl dicyclopentadienyliron is insoluble in common polar solvents suitable for use in electrometric titration. When sulfonated in the ferrocene rings, the material becomes more unstable toward oxidation than alkylsubstituted dicyclopentadienyliron, and upon oxidation readily loses iron. The midpoint potential for dicyclopentadienyliron (in acid alcohol) is −0.5369 ± 0.0005 v.; for cyclopentadienyl(ethylcyclopentadienyl)iron (in acid alcohol) it is −0.5081 ± 0.0005 v.; for the ammonium salt of monosulfonated dicyclopentadienyliron (in 0.5 N aqueous sulfuric acid) it is −0.6143 ± 0.0007 v. on oxidation, and −0.6141 ± 0.0008 v. on reduction. The diammonium salts of disulfonated dicyclopentadienyliron and of cyclopentadienyl(ethylcyclopentadienyl)iron could not be titrated successfully. Sulfonated polyvinyldicyclopentadienyliron could not be titrated because of its easy decomposition at potentials in the neighborhood of −0.6 to −0.7 v.