Combining advantages of homogeneous organocatalysis and heterogeneous catalysis with thermosensitive single-chain nanoparticles in a representative tetrahydropyranilation of alcohols

Publication date: 31 January 2018
Source:Polymer, Volume 136
Author(s): Misha Rumyantsev, Sergey Rumyantsev
A significant scientific problem solved in this work is the development of effective polymer catalysts that allow carrying out organic reactions under homogeneous conditions with high rates and to remove catalyst from the system as a heterophase without the use of special treatment, thus combining the advantages of both homogeneous and heterogeneous catalysis. Kinetic experiments show high catalytic activity of the synthesized catalyst in homogeneous regime even at low dosage of the catalyst. Thus, it was demonstrated that tetrahydropyranilation of methanol was completed in nearly quantitative yield of the corresponding ether in 80 min at 60 °C with a dosage of the polymeric catalyst as low as 0.2 mol%. On the other hand anomalous decrease in the values of the effective rate constant was observed when the reaction was run at temperatures below the phase transition temperature. Kinetic data were used along with thermodynamic calculations to discuss the effect of the synthesized polymeric catalyst on the stabilization of the transition state. The high activity of the catalyst is complemented by its high sedimentation ability; thus, it usually takes a few minutes for the polymer to precipitate from the alcohol solution when cooled below the phase-transition temperature after the completion of the reaction. It was also revealed via dynamic light scattering that catalytic polymers adopt a thermodynamically stable conformation of the single-chain nanoparticles with average hydrodynamic radius in the range 2–2.5 nm.

Graphical abstract

http://ift.tt/2CqbcRK