2,2′-Bipyridine and related N-chelants as very effective promoters for Cu catalysts in the decarboxylation

Effect of 2,2′-bipyridine (bipy) and analogous ligands on decarboxylation of 2,4-dimethylbenzoic (DMBA) and 4-hydroxybenzoic acids with Cu catalysts has been compared with that of quinoline. The chelating ligands were shown to exceed the traditional promoter in efficiency by two to three orders of magnitude per a mol basis. In combination with bipy-like promoters, Cu catalysts ensured complete conversion of even the low reactive DMBA for 15–30 min and gave expected product in >95% yield (S/C 40–100, Ph2O as solvent, 250 °C). In the decarboxylation of individual aromatic acids, the (Cu + bipy) system greatly surpassed carbon and Pd/C catalysts as well, but lost activity in solutions of natural acidic mixtures. The later was assigned to reduction of Cu ions by H-donor constituents of such mixtures.

Bipyridine-like chelating ligands accelerate decarboxylation of aromatic acids with copper catalysts much greater than the traditional monodentate promoters, and the reaction rapidly goes to completion when alternative catalysts show poor performance under the same conditions. Figure optionsDownload as PowerPoint slide