Aromatics
play essential and unique roles in the areas ranging
from synthetic chemistry to the manufacturing industry. Production
of aromatics from biomass is of great fundamental interest and practical
importance to ease the burden of fossil resources. This work delineates
a one-step route for the synthesis of renewable aromatics from various
biobased furanics and dienophiles by acidic ionic liquids at mild
conditions. [Bmim]HSO4 was used as a catalyst and solvent
for the direct conversion of 2,5-dimethylfuran and acrylic acid into p-xylene and 2,5-dimethylbenzoic acid; up to 89% aromatic
selectivity was achieved at 87% conversion of 2,5-dimethylfuran at
room temperature and atmospheric pressure, and totally 84% selectivity
of p-xylene can be obtained with a subsequent decarboxylation
reaction. The reaction mechanism study supplemented with isotopic
tracing and DFT calculations revealed the lowest-energy pathway for
the two main products. Various starting materials were studied for
further extensions of the method, and it turned out that electron-donating
methyl groups on the furan ring played crucial roles on the activation
of dehydration and decarboxylation processes. This work provided convenient
access to industrial commodity aromatics from fully biomass-derived
feedstocks and thus can be regarded more economically and environmentally
feasible.
In
recent years, ionic liquids (ILs) have become a promising solvent
for cellulose pretreatment in biorefinery. However, almost all the
ILs that can dissolve cellulose have an unsaturated heterocyclic cationic
structure, while the ILs with cations of a saturated ring can hardly
dissolve cellulose. To reveal the underlying mechanism, four kinds
of ILs composed of unsaturated and saturated cations (1-butyl-3-methylimidazolium,
1-butylpyridinium, 1-butyl-1-methylpyrrolidinium, and 1-butyl-1-methylpiperidinium)
and the acetate anion were explored as the solvents for a cellulose
bunch by molecular dynamics simulation. It was shown that the cellulose
bunch only dissolved in the ILs containing cations with an unsaturated
heterocyclic ring. The reason lies in two aspects. One is the structure
factor: the π electron delocalization of the unsaturated heterocyclic
ring makes the cation more active to interact with cellulose and provides
more space for acetate anions to form hydrogen bonds with cellulose.
The other is the dynamic effect: the larger volume of cations with
the saturated heterocyclic ring results in a slow transfer of both
cations and anions, which is not beneficial to the dissolution of
cellulose.
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