1 research outputs found
Organocatalytic Imidazolium Ionic Liquids H/D Exchange Catalysts
Simple 1,2,3-trialkylimidazolium
cation associated with basic anions,
such as hydrogen carbonate, prolinate, and imidazolate, is an active
catalyst for the H/D exchange reaction of various substrates using
CDCl<sub>3</sub> as D source, without the addition of any extra bases
or metal. High deuterium incorporation (up to 49%) in acidic C–H
bonds of ketone and alkyne substrates (p<i>K</i><sub>a</sub> from 18.7 to 28.8) was found at room temperature. The reaction proceeds
through the fast and reversible deuteration of the 2-methyl H of the
imidazolium cation followed by D transfer to the substrate. The IL
acts as a neutral base catalyst in which the contact ion pair is maintained
in the course of the reaction. The basic active site is due to the
presence of a remote basic site in the anion namely, OH of bicarbonate,
NH of prolinate, and activated water in the imidazolate anion. Detailed
kinetic experiments demonstrate that the reaction is first order on
the substrate and pseudozero order relative to the ionic liquid, due
to the fast reversible reaction involving the deuteration of the ionic
liquid by the solvent