Gas-phase study of the stability of α-substituted cyclic amino nitriles under electron ionization and electrospray ionization and fragmentation peculiarities of cyclic ketimines.

Abstract

α-Substituted cyclic amino nitriles show different reactivity and stability in solution depending on their ring size. Mass-spectrometric modeling of the reactions, which normally take place in solution, may shed light on the nature of the studied compounds and explain some observations. The stability of the nitriles in an acidic solution was studied by adding glacial acetic acid. Gas-phase modelling was conducted by gas chromatography/mass spectrometry (GC/MS) with electron ionization mass spectrometry and direct inlet electrospray ionization. QqQ and Orbitrap analyzers were used to carry out tandem mass spectrometry (MS/MS) experiments. The obtained data show that the elimination of HCN from α-substituted cyclic amino nitriles occurs in the same way for an acidic solution, thermolysis and electrospray ionization. According to GC, the most stable were N-formylated nitriles compared with N-benzylated or N-unsubstituted ones. Electrospray ionization demonstrated its advantages for the routine identification of cyclic amino nitriles due to milder conditions than in electron ionization. Fragmentations of cyclic ketimines, formed from N-unsubstituted amino nitriles, are discussed in particular. Similarities in the behavior of the α-substituted cyclic amino nitriles under electron ionization, electrospray ionization, thermolysis and reaction in solution under acidic catalysis were discovered and confirmed by MS/MS experiments. Fragmentation schemes of the studied nitriles and corresponding imines are proposed.