3.4. Pathways of BPA by permanganate oxidation
Although many studies have made efforts to explore the BPA
oxidation pathways in various processes [7,28,34], the mechanisms
of BPA degradation by permanganate were kept unknown.
Eleven reaction intermediates were detected besides BPA by LC–
MS/MS. Eight of the eleven intermediates had been observed in
other oxidation processes while the other three, with m/z 248,
246 and 196 were reported for the first time, as summarized in
Table S3 and Fig. S1. All the intermediates eluted earlier than
BPA, indicating that they were more polar than their parent
compound [28]. To elucidate the reaction pathways of BPA with
permanganate, the intermediates detected in various oxidation
processes were also compiled in Table S3. Relying on the intermediates
specified in this study, Adamezyk and Paneth’s theoretical
evaluation [35] and the reaction pathways of BPA with other
oxidants, the possible pathways of BPA with permanganate were
proposed and illustrated in Fig. 4. In the early stage of the reaction,
permanganate oxidized phenolic compounds through [3 + 2]
addition across the O–Mn–O, followed by a hydride abstraction
(rate-limiting step) from the substrate to permanganate oxo group
[36]. It could be speculated that hydrogen abstraction contributed
to the formation of mono-hydroxylated BPA (m/z 244), which was
further degraded to m/z 242, followed by the ring cleavage.
The 4-isopropenylphenol (m/z 134) was the smallest molecular
with benzoic ring detected in this study. Its concentration reached
the maximum in less than 30 min, while 99% of BPA was