Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
FULL PAPERS
Abeda S. Touchy et al.
Table 2. Reductive esterification of dodecanoic acid.[a]
properties of this new catalytic system. We also study
the structure-activity relationship to address the influ-
ences of the electronic structure of the supported
metals, Lewis acidic nature of the support oxides, size
and phase of Pt on the activity.
Entry
Solvent
Conv. [%]
Yield [%][b]
1
2
3
4
5
6
no solvent
o-xylene
diglyme
mesitylene
n-octane
H2O
95
93
91
94
92
41
90 (3)
88 (2)
84 (4)
83 (3)
79 (3)
27 (9)
Results and Discussion
[a]
Optimization of Catalysts and Conditions
1 mol% Pt/SnO2, 1 mmol dodecanoic acid, 0 or 1 g sol-
vent, 2008C, 24 h.
GC yields. Yields of 1-dodecanol are in the parentheses.
[b]
As summarized in Table 1, we screened 18 types of
the supported transition metal catalysts, pre-reduced
in H2 at 1008C for 0.5 h, for hydrogenation of dodeca-
noic acid in solvent-free conditions under 8 bar H2 at CeO2, HZSM5 zeolite, SiO2, C). Pt/SnO2 (entry 1)
2008C for 24 h. First, we tested various transition showed a higher yield of the ester (91%) than the
metal (Pt, Rh, Ru, Pd, Ir, Re, Ni, Cu, Co, Ag) cata- other Pt-loaded catalysts. Pt/ZrO2 and Pt/TiO2 (en-
lysts supported on SnO2 (entries 1–10). Among the tries 12 and 13) gave moderate yields (45–63%), and
catalysts tested, Pt/SnO2 showed the highest yield the Pt loaded on Al2O3, CeO2, HZSM5 zeolite and
(90%) of the corresponding ester, dodecyl dodeca- SiO2 (entries 14–17) showed low yields (1–17%). A
noate. 1-Dodecanol was observed as a by-product in commercially available carbon-supported Pt as a con-
3% yield. Rh/SnO2 also showed high yield (85%), and ventional Pt catalyst was inactive (entry18). From
Ru- and Re-loaded SnO2 showed moderate yields these results, Pt/SnO2 is found to be the most effective
(50–54%). Entries 12–18 show the results of Pt cata- catalyst among the catalysts tested in Table 1. Taking
lysts loaded on other supports (ZrO2, TiO2, Al2O3, into account that SnO2 (entry 11) and Pt nanoparti-
cles loaded on an inert support (Pt/C) are inactive for
the hydrogenation of dodecanoic acid to the ester, it
is suggested that the high activity of Pt/SnO2 is due to
a synergistic effect of SnO2 and Pt. It should be noted
that Pt/SnO2 is also effective for the acceptor-less de-
hydrogenative dimerization of two primary alcohols
to esters as reported in our previous study.[5a]
Table 1. Catalyst screening for reductive esterification of do-
decanoic acid.
Next, we optimized the reaction conditions for the
hydrogenation of dodecanoic acid to the ester by
1 mol% of Pt/SnO2. Table 2 shows the effect of sol-
vent on the yield of the ester and 1-dodecanol as
a by-product for the reaction under 8 bar H2 at
2008C. The reaction under the solvent-free conditions
gave the highest yield of the ester (90%). Reactions
in various organic solvent (entries 2–5) were also suc-
cessful, which gave 79–88% yield of the ester. The re-
action in water gave the lowest yield (27%). Under
the solvent-free conditions, the reaction at a lower
temperature (1808C) resulted in lower yield (84%)
than that at 2008C (91%). The reaction under lower
H2 pressure (5 bar) at 2008C resulted in lower yield
(80%) than that under standard H2 pressure (8 bar).
A decrease in the catalyst amount from 1 mol% to
0.5 mol% decreased the ester yield from 90% to 59%.
The time course of the reaction under the standard
conditions (Figure 1) shows that the reaction time of
24 h is enough to obtain a high yield of the ester. Fur-
ther reduction of the ester to ether was not observed.
An interesting feature in Figure 1 is the fact that the
carboxylic acid is more reactive than the ester (dode-
cyl dodecanoate), because normally esters are more
reactive than carboxylic acids in hydrogenation reac-
Entry
Catalyst
Conv. [%]
Yield [%][a]
1
2
3
4
5
6
7
8
Pt/SnO2
Rh/SnO2
Ru/SnO2
Re/SnO2
Pd/SnO2
Ir/SnO2
95
90
61
53
58
37
3
1
0
0
0
71
59
56
52
11
7
90 (3)[b]
85 (2)[b]
54
50
38
30
3
1
0
0
Ni/SnO2
Cu/SnO2
Co/SnO2
Ag/SnO2
9
10
11
12
13
14
15
16
17
18
19
[c]
SnO2
0
Pt/ZrO2
Pt/TiO2
Pt/Al2O3
Pt/CeO2
Pt/HZSM5
Pt/SiO2
Pt/C
63
45 (2)[d]
17
12 (1)[d]
3 (2)[d]
1
0
0
0
0
blank
[a]
GC yields.
[b]
[c]
[d]
Yield of 1-dodecanol.
Catalyst amount was 39 mg.
Yield of n-dodecane.
1500
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2015, 357, 1499 – 1506