Mass spectra of new heterocycles: XVI. Electron impact study of alkyl 5-aminothiophene-2-carboxylates

Abstract

Electron impact mass spectra of alkyl 4-alkoxy-5-amino-3-methylthiophene-2-carboxylates were studied for the first time. These compounds, except for 4-(1-ethoxyethoxy) and 4-(ferrocenylmethoxy) derivatives, give rise to a stable molecular ion whose decomposition follows three pathways. The main fragmentation pathway of the molecular ion is elimination of alkyl radical from the 4-alkoxy group, the second pathway involves expulsion of alkoxy group from the ester moiety, and the third pathway is decomposition of the thiophene ring. The molecular ions of 4-(1-ethoxyethoxy)thiophenes decompose mainly via elimination of ethyl vinyl ether molecule with formation of [M–VinOEt]+ · odd-electron ion, and fragmentation of the latter follows general pathways. In the mass spectra of 4-(ferrocenylmethoxy)thiophenes the most abundant are ferrocenylmethyl ion with m/z 199 (I rel 100%) and fragment ions derived therefrom.