Abstract
Proton affinities of several efficient organocatalysts METHOX, QUINOX, ANETOX, KOTOX, FUREOX, and FUROOX bearing a pyridine N-oxide or 2,2'-bipyridyl N,N'-dioxide moiety were determined by using extended kinetic method and density functional theory calculations. Proton affinities are in the range of 1030 - 1060 kJ mol-1.
Using isodesmic reactions, the effect of combining two pyridine N-oxide units in the neutral and the protonated molecule was studied: The combination of an unfavorable interaction in the former case and a favorable interaction in the latter accounts for the superbasic properties of 2,2'-bipyridyl N,N'-dioxides. Last but not least, the theoretically predicted pKa in ethanol are 0.1, -2.7, 0.9, 1.8, 1.9, and 2.3 for the METHOX, QUINOX, ANETOX, FUROOX, FUREOX, and KOTOX, respectively.