Communications
280 ꢀ 103 tones per year directly from non-edible biomass,
respectively, for performing the hydroalkylation/alkylation of
2MF with butanal. With 2.5 wt% of p-TosOH and a 2:1 molar
ratio (stoichiometric ratio) of 2MF and butanal, 85%
conversion with 91% selectivity was obtained (Supporting
Information, Table S1, entry 1). The values can be increased
to 93% conversion and 95% selectivity by working with a
small excess of 2MF (Supporting Information, Table S1,
entries 2 and 3). The procedure is very simple, and the
crude reaction mixture separates rapidly into two phases upon
standing. The lower aqueous phase containing the acid
catalyst (when soluble) was separated (see Supporting
Information). We have seen that under the same reaction
conditions it is also possible to use a solid catalyst in the
hydroxyalkylation/alkylation of 2MF, and the results are
given in the Supporting Information, Table S1.
The second step in the process, that is, the hydrodeoxy-
genation of the 1,1-bisylvylalkanes (1,1-bisylvylbutane) was
performed in a fixed-bed continuous reactor directly as a neat
liquid without solvent. Results in Figure 1 and the Supporting
Information, Table S2 show nonane, 4-propylnonane, 6-pro-
pylundecane, and C14H28 monocyclic alkanes as predominant
alkane products. Good results were obtained with platinum
on carbon and alumina. The carbon balance was 98%, being
almost 90% in the liquid organic phase; the rest of the
carbon-containing products were C4H10, CH4, CO, and CO2,
with very small amounts of C2/C3 (Supporting Information,
Figure S1). In the liquid organic phase, approximately 95% of
the products are alkanes, with 76%, 17% and 2% of C14, C9,
and C12, respectively. Although there is no doubt that the
process could be optimized to produce even a higher yield of
liquid alkanes, the results obtained herein are already a
significant benchmark. We have run the process in the
laboratory for more than 140 h with constant activity and
selectivity (Supporting Information, Figure S2), and the
future perspectives of the process are even more promising
if one considers the excellent pour point (À908C) and cetane
number (70.9) of the total organic fraction obtained. There-
fore, blending conventional carburants with the new second-
generation biocarburant based on 6-alkylun-
such as corncobs, oat hulls, almond husks, bagasse, sunflower
husks, residues of olive extraction, and many other biomasses
that are rich in pentose biopolymers.[11] 2MF is obtained from
FUR in the industrial production of furfuryl alcohol,[12] and its
concentration in the effluent can be increased up to 93%
selectivity simply by raising the reaction temperature from
1358C (for production of furfuryl alcohol) to 2508C.[12,13]
There are important advantages in using 2MF as a starting
material owing to its hydrophobic nature that allows separa-
tion from water at room temperature and the high reactivity
and selectivity for alkylation reactions.[14] Thus, we thought of
producing long chain alkanes within the kerosene-diesel
range by means of cascade hydroalkylation/alkylation reac-
tions of 2MF. The starting hypothesis is that with 2MF,
selective hydroalkylations could be carried out, and polymer
formation should be inhibited since one of the two reactive
a-positions is “protected” by the unreactive methyl group.
These hydroalkylations/alkylations can be performed in
presence of soluble or solid acids,[15,16] and when selective,
the only by-product is water.
The validity of the concept was shown by reacting 2MF
with butanal as a test reaction, and from the successful results,
we show the direct trimerization of 2MF (no any other
reactant added). During the test reaction it was found that
with acid catalysts bisylvylalkane molecules with fourteen
carbon atoms are formed but no polymeric structures with
more than two furan moieties. Then hydrodeoxygenation of
the bisylvylalkanes give linear alkanes with branching in the
middle of the chain (for example, an isomer of tetradecane;
see Scheme 2). More specifically, and after hydrodeoxygena-
tion of the intermediate bisylvylalkanes, product mixtures
were obtained in excellent yield that can be used for direct
blending for high-quality diesel.
Alkylation and hydroalkylation of 2MF can be performed
using liquid or solid acids. Here we worked under solvent-free
conditions using either para-toluenesulfonic acid (p-TosOH)
or the Amberlyst 15 resin, as soluble and solid acid catalyst
decanes will improve cetane number and their
flow properties at low temperature.
After the successful results obtained with
the test reaction, the synthesis of diesel was
attempted starting only from 2MF, that is, no
any other reactant added, by generating in situ
4-oxopentanal from 2MF (Scheme 3). The 4-
oxopentanal will react with two other mole-
cules of 2MF, and the hydrodeoxygenation of
the intermediate should give pentadecane
isomers as the main products.
Water is added to 2MF under acidic
conditions and furan ring-opening occurs,
giving 4-oxopentanal. The hydroxyalkylation/
alkylation reaction of 2MF with 4-oxopenta-
nal is so fast that the aldehyde can hardly be
detected in the reaction mixture. It appears
that this trimerization reaction of 2MF is a
very sustainable reaction, as no by-products
are obtained (see Scheme 3). The trimeriza-
Scheme 2. Formation of 1,1-bisylvylalkanes by hydroxyalkylation/alkylation from Sylvan
and an aldehyde with subsequent hydrodeoxygenation to 6-alkyl undecane.
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ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2011, 50, 2375 –2378