2
ZHAO ET AL.
In the case of linear alcohol, with the increase of the car-
bon length, alkyl levulinates yield increased gradually.
(
Table 1, entries 1, 2, 3 and 5). This difference could be
attributable to the boiling point being the controlling fac-
tor. However, with the increase of the molecular volume,
the yield of alkyl levulinates significantly decreased from
SCHEME 1 Conversion of FA into alkyl levulinates over
5
-sulfosalicylic acid
96.2 to 43.8% with n-propanol and isopropanol, respec-
tively (Table 1, entries 3 and 4). In addition, the steric
effect was much more obvious when using n-butanol,
isobutanol, 2-butyl alcohol, or tert-butanol (Table 1,
[
13,14]
and furfuryl alcohol (FA).[15–21] Among
furfural,
them, FA is a preferred raw material due to its easy acces-
sibility from furfural and high reactivity for the alcoholysis
reaction to produce alkyl levulinate. Thus, the develop-
ment of a feasible and competitive pathway for FA
upgrading is strongly demanded.
It was found that FA alcoholysis with alcohol to pro-
duce alkyl levulinates is influenced by the acid site den-
sity, strength, and accessibility of active sites to
entries 5, 6, 7, and 8). This tendency is consistent with
[18]
[7,17,18]
the literature
and these results suggest that
5-sulfosalicylic acid as the catalyst with optimized condi-
tions was appropriate for the synthesis of linear-alkyl
levulinates by carrying out the alcoholysis of FA.
[19,22]
reactants.
Up to date, various homogenous or het-
2.2 | Effect of n-butanol volume on FA
alcoholysis
[
15]
erogeneous catalysts including ion-exchange resins,
[
16]
[18–20]
[21,23]
organosilica nanotubes,
salts,
oxides,
ionic
[
7,24]
[25,26]
liquids,
and zeolites
have been concretely inves-
The concentration of the starting material is a key factor
with great influence on most chemical reactions. Thus,
the effects of n-butanol volume were investigated in dif-
ferent reaction time, and the results are shown in
Figure 1. When n-butanol volume was 5 ml, the FA con-
version increased to 99.3% after 10 hr compared with that
obtained at low alcohol volume 3 ml. Consistent with the
literature reports, a lower mole ratio between FA to n-
butanol results in polymerization of FA in the presence
tigated. For example, Zhang et al. reported several
organic–inorganic hybrid solid acids for the alcoholysis of
FA and reached a high ethyl levulinate yield of 93%.
Shyam and coworkers studied
functionalized hafnium-based MOF, as an efficient solid
acid catalyst for the alcoholysis of FA and esterification
of LA affording alkyl levulinates. However, several
defects of these above-mentioned catalysts, such as the
complex preparation process, the cost, environmental
[
17]
a
sulfonic acid-
[]
[
27]
of strong acidic catalyst.
However, further increases in
[
3]
concerns, limited their applications to some extent.
the n-butanol volume led to a significant decrease in the
BL selectivity. The adverse effect of higher volume con-
centration of n-butanol may be caused by lowering the
Accordingly, the development of a more cheap, facile,
stable, and efficient catalyst system for the alcoholysis of
FA to produce alkyl levulinates is still a challenge.
[
12]
concentration of intermediates.
The intermediate
Herein, we wish to present a practical protocol, where
a simple aromatic acid, 5-sulfosalicylic acid was selected
as a sole catalytic component to promote alcoholysis of
FA to alkyl levulinates with excellent conversion and
decent selectivities (Scheme 1). The effects of multiple
process parameters, including catalyst amount, reaction
temperature, alcohol volume, and water content were
studied as a function of time to optimize the yield of alkyl
levulinates. 5-Sulfosalicylic acid is expected to be a poten-
tial candidate for alkyl levulinate production from
biomass-derived platform molecules.
2-butoxy methyl furan (BMF) is formed quickly by the
reaction of FA with n-butanol, but the rate of conversion
of the BMF to the product is very low. When the reaction
is carried out in 7 or 9 ml of n-butanol, the content of the
BMF is lower than that obtained in 5 ml of n-butanol.
2.3 | Effect of catalyst amount on FA
alcoholysis
The amount of catalyst definitely impacts the acidic con-
centration in the reaction solutions, and correspondingly
influences the product distribution. As shown in
Figure 2, the amount of 5-sulfosalicylic acid ranges from
2
2
| RESULTS AND DISCUSSION
.1 | Substrate screening
1
to 9 wt% based on FA, while the other conditions
remain constant. FA conversion increased with the
increase of catalyst amount from 1 to 5 wt%, which
should be attributable to an increase in the availability
and number of catalytically active sites. When the
Firstly, the alcoholysis of FA was carried out in a variety
of solvents in order to explore the scope of this method.