H/D Exchange of Amines and Acetonitrile over Transition Metal Catalysts

Abstract

H/D exchange of acetonitrile, mono-, di-, and triethylamine was carried out at 75 °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. 1H-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 Rh 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 d3 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 d2 product of ethylamine has its two D atoms predominantly in the methylene, NOT the amine group. With diethylamine, products up to d10 are abundant, but d11 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.

Nitrile Hydrogenation on Solid Catalysts – New Insights into the Reaction Mechanism

“…Thus, the formation of amine is not a simple addition of chemisorbed atoms of hydrogen/deuterium atoms to the nitrile group. On the basis of these results, as well as an experimental study of the H/D exchange between amines and acetonitrile on metal catalysts [79], Huang and Sachtler suggested a special mechanism for the deuteration of acetonitrile, the simplified scheme of which is presented in Scheme 11. As an example of the metal, they used Ru, the propensity of which to form strong M-N bonds can be deduced from its ability to catalyze the synthesis of ammonia from the elements (N 2 + H 2 ).…”

“…According to Chojecki et al [42], the strong bond via the N-atom may stimulate fast hydrogenation of the carbon atom in the nitrile group to the amine and thus prevent secondary condensation reactions. Some very important results relating to the chemistry of nitriles and amines on metal surfaces and the mechanisms of nitrile hydrogenation were described in experimental studies by Huang and Sachtler [46][47][48]79,80]. The results of these studies demonstrate that the hydrogen atom to be added to the unsaturated CN bond need not originate from the "atomic hydrogen layer" on the surface of the catalyst but can be provided by some surface complexes, acting as hydrogen donors.…”

“…Furthermore, the authors state that the selectivities can also be correlated to another catalytic parameter characterizing the transition metals, specifically to the behaviour (viz. "the multiplicity") in the H/D exchange of alkanes [79].…”

Photoconductivity of poly(N‐vinylcarbazole) (PVK) doped with the metallofullerene Dy@C82 and the fullerenes C84 and C60

“…High purity samples of Dy@C 82, C 60 , and C 84 were prepared by the standard DC arc-discharge method. [15][16][17] The raw soot was subjected to Soxhlet extraction using DMF as a solvent, followed by HPLC separation using a 5PYE column and a mobile phase of toluene. The collected fraction in toluene solution was concentrated and re-purified with the same HPLC column before use.…”

Suppressing the spin relaxation of electrons in silicon

“…Because of the so-called conductivity and spin lifetime mismatch problem, [69][70][71] electrical spin injection to semiconductors is largely limited to tunneling or ballistic injection of hot electrons. [72][73][74][75][76][77][78][79][80][81][82][83][84][85] In the former, electrons tunnel across the built-in potential barrier in the semiconductor side of the junction. The barrier is formed by the depletion region, existing both in direct metal-semiconductor Schottky contacts and metal-oxide-semiconductor structures with ultrathin oxide layers.…”