Abstract
EMPO [5-(ethoxycarbonyl)-5-methyl-1-pyrroline N-oxide]
is a highly hydrophilic cyclic nitrone spin trap,
whose superoxide adduct is considerably more stable
(t1/2=8.6 min) than DMPO (5,5-dimethyl-1-pyrroline
Noxide, t1/2=45 s). EPR spectra of spin adducts of
EMPO and its derivatives are very similar to those of
the respective DMPO spin adducts, in contrast to the
rather complex spectra obtained using DEPMPO [5-
(diethoxyphosphoryl)-5-methyl-1-pyrroline Noxide].
Several EMPO derivatives, with both the ethoxycarbonyl
group and the methyl group at position 5 of the
pyrroline ring being replaced by other substituents,
were synthesized and characterized by 1H and 13C
NMR spectroscopy. Thus, a series of derivatives was
obtained that exhibit large differences in the stability
of their superoxide adducts, ranging from less than
one to more than 25 min. The stability of the superoxide
adducts was mainly determined by the steric environment
of the nitroxyl group: in compounds with
less bulky 5-alkoxycarbonyl substituents the nitroxyl
group is sterically less shielded, which resulted in a
lower stability of the superoxide adducts. The spin
density distribution, as obtained from DFT computations,
was found to be nearly identical for all compounds,
so that in contrast to the steric influences the
spin density did not seem to be a crucial factor for the
stability of the superoxide adducts.
Synthesis And Characterization Of CoMo/Mordenite Catalyst For Hydrotreatment Of Lignin Compound Models
