Figure 11. Oligomerization and fragmentation reactions for
oxidized oleic acid consistent with observation of trimer T1 and
fragments F1, F2 by NMR spectroscopy. OA = oleic acid, R =
C17H34.
Reaction of D1 with oleic acid to give T1 (Figure 11 )
corresponds to the rapid reaction of an alcohol with a carboxylic acid
described by Ball et al. . The minor oxidized species contains F1, with
a methylene carbon attached to oxygen (CH2-O) gives13C and 1H signals at 68 and 4.0
ppm, respectively. A methylene bonded to oxygen (CH2-O)
does not exist in oleic acid. This paramount finding could be easily
missed starting with acylglycerols, since they have these carbon types.
Formation of such a chemical group, stemming from a primary alcohol, can
only result from cleavage.
Fragment F1 is rarely proposed in the literature (e.g. Figure
S20 ), which instead claims F2. Note that oxidative cleavage of epoxide
M2 to give a primary alcohol does not occur since it would exhibit a1H CH2-O signal at 3.5 ppm. Instead, a1H CH2-O signal was observed at 4.0
ppm (Figure 8 ).