H/D exchange of amines and acetonitrile over transition metal catalysts

H/D exchange of acetonitrile, mono-, di-, and triethylamine was carried out at 75 degrees C over zeolite supported transition metal catalysts in a fixed-bed microflow reactor. In order to identify the location of the D atoms, the product of this primary exchange was, subsequently, subjected to secondary exchange with liquid D2O, which affects exclusively the N-bonded hydrons. H-1-NMR and mass spectrometry were used for product analysis. The results reveal a rather dramatic difference in exchange behavior between ruthenium and the group of metals including Pt, Pd, and Ni, while Ph displays an intermediate behavior. Pt, Pd, and Ni show stepwise exchange starting with the N-bonded hydrons. In contrast, multiple exchange is found for Ru; this exchange leads to preferential formation of d(3) acetonitrile. With primary, secondary, and tertiary amines, the hydrons bonded to the methylene C atom are most rapidly exchanged over Ru, followed by the hydrons in methyl groups. Surprisingly, the N-bonded hydrons are only negligibly exchanged over Ru. For instance, the d(2) product of ethylamine has its two D atoms predominantly in the methylene, NOT the amine group. With diethylamine, products up to d(10) are abundant, but d(11) is negligible. The results are rationalized on the basis of the known high propensity of ruthenium to form C=Ru double bonds. In contrast, formation of N=Ru bonds appears negligible under the conditions used.