Loss of isocyanic acid from the internal oxadiazole ring of protonated molecules of some 2,5‐diaryl‐1,3,4‐oxadiazoles

Abstract

The fragmentation pattern of some protonated 2,5-diaryl-1,3,4-oxadiazoles is discussed. An unusual decomposition consisting of elimination of the isocyanic acid molecule from the internal oxadiazole ring was found. This fragmentation pathway was deduced on the basis of B/E linked scan mass spectra of metastable ions with liquid secondary ion mass spectrometry as the ionization method and also of low-energy CID mass spectra where electrospray was used as the ionization technique. High resolution measurements were also performed.

Mass spectrometric study of some protonated and lithiated 2,5-disubstituted-1,3,4-oxadiazoles

“…The B/E mass spectra of protonated 1-6 molecules ([M ϩ H] ϩ ions) are shown in Figure 2. In the previous paper the fragmentation pathways of protonated molecules of 2,5-disubstituted-1,3,4-oxadiazoles were presented [17]. It was shown that these compounds lost the isocyanic acid molecule (HNCO, loss of mass 43) from the oxadiazole ring.…”

“…In the case of [M ϩ H] ϩ ions the loss of isocyanic acid was observed and for [M [17]. In this paper the mass spectrometric fragmentation pathways of protonated 1,3,4-oxadiazoles (1-6, Scheme 1) are analyzed in more detail and compared with the fragmentation pathways observed for lithiated derivatives.…”

“…Mass spectrometric fragmentation pathways of protonated 1,3,4-oxadiazoles ([M ϩ H] ϩ ions) have been recently studied by chemical ionization (CI) [16], electrospray ionization (ESI) and liquid secondary ion mass spectrometry (LSIMS) [17]. In this paper the mass spectrometric fragmentation pathways of protonated 1,3,4-oxadiazoles (1-6, Scheme 1) are analyzed in more detail and compared with the fragmentation pathways observed for lithiated derivatives.…”

Preparation and evaluation of sulfonated polyoxadiazole membrane containing phenol moiety for PEMFC application

“…Because of the high affinity to water absorption, the wide signal at 2000-3700 cm −1 became wider and more intensive than SPPOD and SCDPPOD. The branching and degradation of diphenyl ether C-O-C bond catalyzed by acid at high temperature which lead to the phenoxy terminated segment formation has been previously reported in literatures [57,[60][61][62]. Also, at high temperatures, protonated oxadiazole groups are degraded and suffer from cleavage, analogous to the mechanism proposed by Franski et al [61].…”

“…The branching and degradation of diphenyl ether C-O-C bond catalyzed by acid at high temperature which lead to the phenoxy terminated segment formation has been previously reported in literatures [57,[60][61][62]. Also, at high temperatures, protonated oxadiazole groups are degraded and suffer from cleavage, analogous to the mechanism proposed by Franski et al [61]. This degradation produces some active groups such as amine, amide, carbonyl and others that lead to branching and some partially crosslinking in polymer structure [43,51,57,62].…”