The
separation of chiral compounds into their enantiomers is widely
used in the pharmaceutical industry. Two types of environmentally
benign tartaric acid derivatives, O,O′-dibenzoyl-(2S,3S)-tartaric
acid (d-DBTA) and O,O′-dibenzoyl-(2R,3R)-tartaric acid (l-DBTA),
were selected as efficient chiral selectors for the separation of
racemic ofloxacin by forming diastereomeric cocrystal pairs in the
aqueous phase. Effects of the type of chiral selectors, resolution
time, the amounts of racemic ofloxacin, and temperature on the resolution
performance of ofloxacin were investigated. The results indicated
that d-DBTA selectively cocrystallized with the R-enantiomer (R-OFLX), while l-DBTA selectively
cocrystallized with the S-enantiomer (S-OFLX) in the aqueous phase. Under the optimal conditions, the enantiomer
excesses (% ee) reached up to 81.8% ee and 82.3% ee for S-OFLX and R-OFLX at 278.2 K, respectively. The stoichiometric
ratio of d-DBTA or l-DBTA to R-ofloxacin
or S-ofloxacin in cocrystals was 1:1. Various characterization
and calculation methods, such as powder X-ray diffraction (PXRD),
Fourier transform infrared spectroscopy (FT-IR), differential scanning
calorimetry (DSC), thermogravimetric analysis (TGA), and density functional
theory (DFT), were performed for the study of the resolution mechanism,
the results of which demonstrated that the cocrystals were formed
by hydrogen bonding between d-DBTA or l-DBTA and
ofloxacin. Compared with previous studies, the proposed separation
process was not only environmentally benign but also beneficial to
increasing % ee. The proposed method has explored a new path for green
and efficient separation of racemic compounds that cannot form salts.
This
study reports highly efficient oxidative desulfurization (ODS)
of dibenzothiophene (DBT) over Na and Ce relatively modified MoO3/SBA-15 catalysts using H2O2 as an oxidant.
The relevant parameters, that is, temperature, reaction time, catalyst,
and oxidant dosage on oxidation performance were studied. Results
revealed that a remarkably high DBT conversion of 94% was obtained
within 60 min utilizing 10 mL of sample of 500 ppm, 0.02 g Na–MoO3/SBA-15 catalyst at 60 °C, and n(O)/n(S) value of 8. Under the same reaction condition, a DBT
conversion of 96% was achieved by using the Ce–MoO3/SBA-15 catalyst. Moreover, the stability of modified catalysts was
further improved compared with the MoO3/SBA-15 catalyst.
Catalysts were characterized by a series of tests such as scanning
electron microscopy, X-ray diffraction, Brunauer–Emmett–Teller,
and X-ray photoelectron spectroscopy, which helped in evaluating the
catalytic activity results. Corresponding results indicated that the
modification of Na or Ce can improve the dispersion of active Mo species.
The synergistic effect was observed between Na (or Ce) and Mo that
can further improve the activity and stability of the Mo-based catalyst,
which promotes the application of the molybdenum-based catalyst on
ODS.
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