Double bond migration, cyclohexadiene disproportionation and alkyne hydration by Dowex ® 1-RhCl₃ ion pair catalysts

Polystyrene-supported ion pairs, generated from RhCl₃ and Dowex® 1 anion exchangers were shown to be efficient, leach-proof and recyclable catalysts for double bond migration in allylic compounds, disproportionation of 1,3-cyclohexadiene and hydration of aromatic acetylenes. At 50-70°C the isomerization of allylbenzene in aqueous EtOH was found to be first order in the substrate, and for catalyst:substrate ratio > 1:40, pseudo-zero order in the catalyst. The reaction rate proved to be effected by the electronic nature of the allylic compound and by the structural properties of the polymeric support. The disproportionation of the diene in aqueous THF was found to follow the Michaelis-Menten rate equation. Addition of water was shown to be specific for aromatic alkynes. Aliphatic acetylenes proved to undergo, under the same conditions, catalytic oligomerization. While the rate of allylbenzene isomerization is mainly chemically controlled the disproportionation of 1,3-cyclohexadiene is governed chiefly by mass transfer processes.