Reduction of Viologen Bisphosphonate Dihalide with Aluminum Foil

Abstract

An elegant undergraduate experiment similar to the popular Iodine Clock Reaction employs the reduction of methyl viologen by hydroxide ion. A major problem with the hydroxide reduction demonstration is that the mechanism is complicated by the existence of competing reaction pathways. It has been suggested that layered metal viologen phosphonates could be used in the design and construction of molecular materials. The active unit in the reversible photocoloration of these layered materials is the viologen bisphosphonate dihalide (VPX).During our study of these phoshponate systems, we discovered the reduction of viologen bisphosphonate dihalide by aluminum foil, mossy zinc, or magnesium turnings in dilute aqueous hydrofluoric acid solution. When we demonstrated this phenomenon with aluminum foil and VPBr in the classroom, the response of our students was enthusiastic. This demonstration can be used as prelaboratory discussion for an undergraduate kinetic experiment based on the same phenomenon.