Electron-induced hydroamination of ethane as compared to ethene: implications for the reaction mechanism

The properties of carbonaceous materials with respect to various applications are enhanced by incorporation of nitrogen-containing moieties like, for instance, amino groups. Therefore, processes that allow the introduction of such functional groups into hydrocarbon compounds are of utmost interest. Previous studies have demonstrated that hydroamination reactions which couple amines to unsaturated sites within hydrocarbon molecules do not only proceed in the presence of suitably tailored catalysts but can also be induced and controlled by electron irradiation. However, studies on electron-induced hydroaminations so far were guided by the hypothesis that unsaturated hydrocarbons are required for the reaction while the reaction would be much less efficient in the case of saturated hydrocarbons. The present work evaluates the validity of this hypothesis by post-irradiation thermal desorption experiments that monitor the electron energy-dependent yield of ethylamine after electron irradiation of mixed C₂H₄:NH₃ and C₂H₆:NH₃ ices with the same composition and thickness. The results reveal that, in contrast to the initial assumption, ethylamine is formed with similar efficiency in both mixed ices. From the dependence of the product yields on the electron energy, we conclude that the reaction in both cases is predominantly driven by electron ionization of NH₃. Ethylamine is formed via alternative reaction mechanisms by which the resulting NH₂˙ radicals add to C₂H₄ and C₂H₆, respectively. The similar efficiency of amine formation in unsaturated and saturated hydrocarbons demonstrates that electron irradiation in the presence of NH₃ is a more versatile tool for introducing nitrogen into carbonaceous materials than previously anticipated.