Aerobic Oxidation of Diverse Primary Alcohols to Carboxylic Acids with a Heterogeneous Pd-Bi-Te/C (PBT/C) Catalyst

Article abstract of DOI:10.1021/acs.oprd.7b00223

Heterogeneous catalytic aerobic oxidation methods represent a near-ideal approach for the conversion of primary alcohols to carboxylic acids. Here, we report that a heterogeneous catalyst composed of Pd, Bi, and Te supported on activated carbon is highly effective for the oxidation of diverse benzylic and aliphatic primary alcohols, including 5-(hydroxymethyl)furfural (HMF) and substrates bearing heterocycles and other important functional groups. In many cases, the desired carboxylic acid product is obtained in >90% yield. Additionally, the catalyst has been demonstrated in a continuous-flow packed-bed reactor for the oxidation of benzyl alcohol, achieving near-quantitative yield while undergoing over 30 000 turnovers.

Full text of DOI:10.1021/acs.oprd.7b00223

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Full Paper
Aerobic Oxidation of Diverse Primary Alcohols to Carboxylic
Acids with a Heterogeneous Pd-Bi-Te/C (PBT/C) Catalyst
Maaz S. Ahmed, David S. Mannel, Thatcher W Root, and Shannon S. Stahl
Org. Process Res. Dev., Just Accepted Manuscript • DOI: 10.1021/acs.oprd.7b00223 • Publication Date (Web): 04 Jul 2017
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Aerobic Oxidation of Diverse Primary Alcohols to Carboxylic Acids
with a Heterogeneous Pd-Bi-Te/C (PBT/C) Catalyst
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Maaz S. Ahmeda, David S. Mannelb, Thatcher W. Rootb, Shannon S. Stahla,*
b
aDepartment of Chemistry and Department of Chemical and Biological Engineering, University of Wisconsin-Madison,
Madison, WI 53706, United States
KEYWORDS: alcohol oxidation, aerobic, heterogeneous catalysis, promoters, packed-bed reactor
Supporting Information Placeholder
ABSTRACT: Heterogeneous catalytic aerobic oxidation methods represent a near-ideal approach for the conversion of primary
alcohols to carboxylic acids. Here, we report that a heterogeneous catalyst composed of Pd, Bi, and Te supported on activated
carbon is highly effective for the oxidation of diverse benzylic and aliphatic primary alcohols, including 5-(hydroxymethyl)furfural
(HMF) and substrates bearing heterocycles and other important functional groups. In many cases, the desired carboxylic acid
product is obtained in >90% yield. Additionally, the catalyst has been demonstrated in a continuous-flow packed-bed reactor for the
oxidation of benzyl alcohol, achieving near-quantitative yield while undergoing over 30,000 turnovers.
groups. Building on relevant precedents, our initial studies
Introduction
identified a new class of heterogeneous Pd-based catalysts,
modified with main-group promoters.12 Bi and Te promoters
Heterogeneous catalysts for selective, liquid-phase aerobic
oxidation of organic molecules could have widespread utility
were found to exhibit synergistic behavior in the oxidative
in organic chemical synthesis,1 particularly within the fine and
methyl esterification of primary alcohols (Scheme 1).13,14 The
specialty chemical industries where the complexity and
Bi and Te promoters significantly improve the activity and
molecular weight of the molecules prevents gas-phase
selectivity of the catalyst (Scheme 1A), and they contribute to
processes. Carboxylic acids are prevalent in valuable organic
broader substrate scope and functional-group compatibility
chemicals, such as pharmaceuticals and agrochemicals, and
(Scheme 1B). Another noteworthy outcome of these studies
the development of new catalysts for the aerobic oxidation of
primary alcohols to carboxylic acids (eq 1) would provide
Scheme 1. Oxidative Methyl Esterification of Primary
Alcohols with Pd-Bi-Te/C Catalysts.
appealing sustainable alternatives to many existing oxidation
methods.2 In many cases, methods for this transformation still
O
rely on the use of undesirable stoichiometric oxidants.
1 mol% [Pd]
OMe
OH
3
3
60 °C, 1 bar O2, MeOH
25 mol % K2CO3, 8 h
O
1 M
cat.
R
OH + H2O
R
OH + O2
(1)
A. Octanol oxidation
B. Other Representative Products
O
O
100
Adam's catalyst (PtO2) represents an early example of a
heterogeneous catalyst for liquid-phase aerobic oxidation of
complex primary alcohols to carboxylic acids.3 High catalyst
loading is often required in these applications (e.g., 0.6 equiv
Pt3b), and organic chemists tend to favor other methods, such
as the use of Jones reagent (CrO3/H2SO4),4 bleach/TEMPO,5
among others.2 More recent work has led to numerous
improved catalysts for aerobic alcohol oxidation, including
many applications of liquid-phase oxidation of biomass-
derived feedstocks.1e Supported Pt/Bi1c,e and Au6 catalysts are
among the most effective examples. Homogeneous and
heterogeneous Pd catalysts have also been widely studied for
aerobic alcohol oxidation,7,8 although the majority of this work
has focused on the conversion of alcohols to aldehydes and
ketones. Homogeneous catalysts are often poisoned by
carboxylic acids,9,10 while heterogeneous catalysts tend to be
more tolerant of carboxylic acid functional groups.11
93%
F
OMe
OMe
OMe
80
68%
F3C
60
40
98 %
99 %
O
O
20%
OMe
20
N
S
0
93 %
92 %
Pd
Pd/Bi Pd/Bi/Te
was the observation that effective catalyst performance could
be achieved with simple "admixture" catalysts, prepared via
the in situ combination of Pd/charcoal, Bi(NO3)3, and Te.15
The results with these comparatively ill-defined catalyst
mixtures were validated by preparing specific PdBiTe/C
catalyst formulations via wet-impregnation methods. Response
surface methodology was used to identify optimal Pd-Bi-Te
catalyst stoichiometries14, including PdBi0.47Te0.09/C and
PdBi0.35Te0.23/C. Herein, we show that the latter oxidative
esterification catalyst, designated PBT/C, is very effective for
In this context, we have been pursuing the development of
heterogeneous catalysts for oxidation of primary alcohols to
carboxylic acids and esters that could be applied to complex
molecules containing heterocycles and other functional
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aerobic oxidation of a wide range of primary alcohols to the
corresponding carboxylic acids.
Table 1. Optimization of Reaction Conditions with PBT/C
for Carboxylic Acid with 1-Octanol.a
1
2
3
4
5
6
7
8
O
1 mol% [Pd], 5 mol% additive
OH
OH
Results and Discussion
3
3
Solvent, KOH
O2, 50 o
C
Catalyst Testing and Optimization of Reaction
Conditions. Aliphatic alcohols tend to be less reactive than
benzylic alcohols, so our catalyst development efforts focused
on the oxidation of 1-octanol (1a) to octanoic acid (2a) (see
Supporting Information for full screening data; Table S1).
Initial tests evaluated the performance of a commercial
Pd/charcoal (Pd/char) catalyst. No activity was observed when
water was the sole solvent (Table 1, entry 1), possibly
reflecting poor solubility of the substrate in this medium. In
light of the good oxidative esterification activity observed in
methanol,13,14 water/methanol solvent mixtures were
evaluated. Activity was observed in such mixtures (entries 2
and 3), and a moderate yield of octanoic acid (61%) was
observed in a 9:1 H2O:MeOH mixture. Different catalyst
supports did not exhibit better performance than charcoal
(entries 4–9), and oxide-supported catalysts showed negligible
product yield under these reaction conditions. Significant
improvements in the yield of octanoic acid were observed
upon addition of various sources of Bi and/or Te to the
reaction mixture (entries 10-15), and a nearly quantitative
yield was observed from an admixture catalyst composed of
Pd/char with Bi(NO3)3·5H2O and Te (entry 15). These results
closely resemble the Bi/Te promoter effects observed in the
oxidative esterification of alcohols (cf. Scheme 1).14
Consequently, we tested several of the more-precise catalyst
compositions that had been developed in the course of that
study, including PdBi0.35/C, PdTe0.23/C, PdBi0.35Te0.23/C
(PBT/C) (entries 16-18). The last of these catalysts achieved
nearly quantitative formation of octanoic acid, significantly
outperforming a PtBi/C catalyst, which has been used
previously for similar applications (entry 19).16
The results in Table 1 show that both the Pd-Bi-Te
admixture catalyst (entry 15) and the PdBi0.35Te0.23/C (PBT/C)
catalyst (entry 18) are very effective for aerobic oxidation of
octanol (1a) to octanoic acid (2a). To provide a more thorough
comparison among these two catalysts and a PtBi/C catalyst, a
series of additional substrates was evaluated at lower catalyst
loading in order to better discern the differences among the
catalysts (Table 2). The comparative effectiveness of PBT/C
was most evident in the oxidation of 1-octanol (1a) and 4-
methoxybenzyl alcohol (1c) (entries 1 and 3, Table 2), for
which PBT/C outperformed the Pd-Bi-Te admixture and
PtBi/C catalysts. With all substrates, use of 1 mol% PBT/C led
to excellent yields of the carboxylic acid product, showing that
this catalyst is a compelling complement or alternative to
PtBi/C.
1a
2a
Entry
1
2
3
4
5
6
7
8
Catalyst/Additive
Pd/char (5 wt %)
Pd/char (5 wt %)
Pd/char (5 wt %)
Pd/C (1 wt %)
Pd/C (5 wt %)
Pd/BaSO4 (5 wt %)
Pd/Al2O3 (1 wt %)
Pd/TiO2
Solvent
H2O
99:1 H2O:MeOH
Yield b
0
33
61
22
19
0
1
0
0
89
73
85
96
96
>99
76
51
98
63
9:1 H2O:MeOH
"
"
"
"
"
"
"
"
"
"
"
"
"
"
"
"
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
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47
48
49
50
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59
60
9
Pd/CeO2
Pd/char, BiCl3
Pd/char, Te
10
11
12
13
14
15
16
17
18
19
Pd/char, TeO2
Pd/char, Bi(NO3)3
Pd/char, Bi2Te3
Pd/char, Bi(NO3)3, Tec, d
PdBi0.35/Cd,e
PdTe0.23/Cd,e
PdBi0.35Te0.23/C (PBT/C)d,e
PtBi/Cd
a Reaction conditions: 1a (1.0 mmol, 1 M), solvent (1 mL), 1.0 mol% [Pd
b
cat], 0.84 equiv KOH, 1 atm O2, orbital mixing, 50 °C, 16 h. % Yields
determined by 1H NMR spectroscopy; int. std. = PhSiMe3. cAdmixture
catalyst: 1 mol% Pd/charcoal (5 wt%), 5 mol% Bi(NO3)3, 2.5 mol% Te.13
d3.4 equiv KOH eIndependently prepared catalyst.14
Table 2. Comparison of Different Catalysts for the Aerobic
Oxidation of Primary Alcohols.a
O
catalyst (0.5 mol%)
R
OH
KOH, MeOH:H2O,
O2, 50 o
R
OH
(1 mmol, 1 M)
C
Pd-Bi-Te
admixture
PBT/C
(1.0 mol%)
Entry
1b
Substrate
PtBi/C
PBT/C
67%
OH
3
53%
86%
12%
95%
85%
1a
OH
2c
3d
4d
29%
53%
58%
1%
75%
97%
96%
31%
1b
OH
70%
96%
58%
97%
>99%
95%
MeO
1c
1d
OH
OH
5d
F3C
1e
Time-Course Comparison for Oxidation of 1-Octanol
and 4-Methoxybenzyl Alcohol with Pd/char and PBT/C
Catalysts. In a preliminary effort to probe the effect of the
Bi/Te promoters, reaction time courses were monitored in the
oxidation of 1a and 1c with Pd/char and PBT/C catalysts
(Figure 1). In the oxidation of 1a with Pd/char, a rapid initial
rate was observed, generating a 41% yield of 2a after 2 h.
Catalysts:
• PtBi/C = 5 wt % Pt-1.5 wt % Bi/C, obtained from Alfa Aesar.
• Pd-Bi-Te = admixture catalyst: 0.5 mol% Pd/charcoal (5 wt %),
2.5 mol% Bi(NO3)3, and 1.25 mol% Te13
• PBT/C = PdBi0.35Te0.23/activated carbon14
aConditions: Substrate (1.0 mmol, 1 M), 9:1 H2O:MeOH (1 mL), 1.0
1
mol% [cat], 3.4 equiv KOH, 1 atm O2, 50 °C. Yields based on H NMR
spectroscopy; int. std. = PhSiMe3. b8 h. c16 h. d4 h.
2
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Subsequent catalyst deactivation, however, led to only which underwent efficient oxidation in excellent yield (>90%).
1
2
3
4
5
6
7
8
moderate overall yield and conversion (62% yield of 2a after
16 h, Figure 1A). In contrast, oxidation of 1a progressed
steadily to complete conversion to 2a over 12 h with PBT/C as
the catalyst (Figure 1B). In both cases, negligible aldehyde
intermediate was observed during the reaction.
Differences between the catalysts are also evident in the
oxidation of more reactive substrate 4-methoxybenzyl alcohol
(1c). With Pd/char as the catalyst (Figure 1C), nearly all of the
substrate was consumed within the first hour, during which
time significant aldehyde intermediate (44%) was observed
and along with nearly equal amount of product (49%). The
aldehyde then converted to the product, 4-methoxybenzoic
acid (2c), in quantitative yield within 8 h. With PBT/C as the
catalyst (Figure 1D), considerably less aldehyde was observed,
maximizing at 29%, and complete conversion to the
carboxylic acid product 2c occurred within 2 h.
Aromatic fluoride and chloride substituents (1j, 1k, 1l) are
well tolerated, while use of arylbromide and iodide substrates
(1m, 1n) led to hydrodehalogenation of 1m, resulting in
formation of benzoic acid for 2m (approx. 93% yield), and a
broad mixture of unidentified products for 2n. The heterocycle
tolerance of this catalyst is clearly evident in the oxidation of
the three isomers of hydroxymethylpyridine (1p-1r), each of
which underwent excellent conversion to the corresponding
pyridine carboxylic acid (>90%).
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Table 3. Substrate Scope for Aerobic Alcohol Oxidation
with PBT/C Catalyst Systema
O
PBT/C (1 mol%)
R
OH
KOH, MeOH:H2O
O2, 50 oC, 4 h
R
OH
1a-1z
2a-2z
O
2c, R = -OMe, 97%, (93%)
2d, R = -H, >99%, (95%)
2e, R = -CF3, 95%
O
O
Me
OH
Pd catalyst
OH
OH
OH
3
3
KOH, MeOH:H2O,
2f, R = -Me, 93%, (91%)
2h, R = -SMe, 43%b
R
O2, 50 o
C
1a
Me
2g, 96%
2a
A. Pd/char
B. PBT/C
O
O
O
2k, R1 = -F, 93%
2l, R1 = -Cl, 98%
2m, R1 = -Br, 4%
2n, R1 = -I, 0%
MeO
OH
OH
OH
OMe
R1
F
2i, 85%
2j, 99%
O
O
O
O
O
O
OH
OH
OH
OH
N
N
N
2p, 93%b
2q, 95%b
2r, 92%b
2o, 80%
O
O
O
O
OH
Pd catalyst
O
OH
OH
KOH, MeOH:H2O,
OH
OH
2t, 64%b
MeO
OH
3
O2, 50 o
C
MeO
O
S
1c
2c
2s, 77%b
2a, 96%b, (95%)
2b, 85%d
C. Pd/char
D. PBT/C
O
O
O
O
Cl
OH
O
OH
3
OH
OH
N
2u, >99%b
2v, 93%b
2w, 83%c
2x, 99%d
O
O
O
O
OH
OH
OH
2y, 64%b
2z, >99%b (94%)
2aa, 53%e
Figure 1. Time courses for the oxidation of 1-octanol (1a) using
Pd/char (A) and PBT/C (B) and for the oxidation of 4-methoxybenzyl
alcohol (1c) with Pd/char (C) and PBT/C (D). Reaction conditions:
Substrate (1.0 mmol, 1 M), 9:1 H2O:MeOH (1 mL), 1.0 mol% [cat],
3.4 equiv KOH, 1 atm O2, orbital mixing, 50 °C.
aReaction conditions: Substrate (1.0 mmol, 1 M), 9:1 H2O:MeOH (1 mL),
1.0 mol% [cat], 3.4 equiv KOH, 1 atm O2, orbital mixing, 50 °C, indicated
time. Yields determined by 1H NMR spectroscopy, int. std. = PhSiMe3;
isolated yields in parenthesis. b8 h. c12 h. d16 h. e8 h, 25 °C.
Aliphatic alcohols (1a, 1b, 1u-1z), which are typically less
reactive, were also effective substrates. The sterically more
hindered cyclohexyl methanol (1b) required a longer reaction
time relative to octanol (1a) (16 vs 8 h, respectively), but it
nonetheless proceeded in good yield to the corresponding
Evaluation of the Substrate Scope with the PBT/C
Catalyst. The broader utility of the PBT/C catalyst for
oxidation of primary alcohols to carboxylic acids was tested
with a wide range of substrates (Table 3). Various benzylic
and related heterocyclic alcohols (2c-2t), were subjected to the
reaction conditions. In most cases, a high yield of the
carboxylic acids was achieved. The scope included electron
rich and deficient benzyl alcohol derivatives (1c–1o), most of
carboxylic acid (2b, 85%). Substrates containing
a
tetrahydrofuran (1u), primary alkyl chloride (1v), and pyridine
(1w) afforded the acid in excellent yields. Homobenzylic
alcohols can be problematic substrates in oxidation reactions,
3
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O
as the enol form of the intermediate aldehyde is susceptible to
O
O
PBT/C (1 mol %)
OH
O
O
1
2
3
4
5
6
7
8
autoxidation at the benzylic position, which can lead to C–C
cleavage.17 The excellent yield in formation of phenylacetic
acid (2x) probably reflects the negligible build-up of the
aldehyde during the reaction (cf. Figure 1B). The benzylic
ether substrate (1y), which can undergo hydrogenolysis of
benzylic C–O bond afforded the acid 2y in only 64% yield.18
Similarly, oxidation of cinnamyl alcohol (1aa) generated the
carboxylic acid 2aa in only 53%, with considerable aldehyde
buildup and some alkene hydrogenation product evident in the
1H NMR spectrum of the crude reaction mixture. The
observations with these latter two substrates are consistent
with the transfer-dehydrogenation reactivity between alcohols
and alkenes observed with PdBi/Al2O3 catalysts by Baiker and
coworkers.19 Overall, the results in Table 3 demonstrate
excellent scope and functional group tolerance by the PBT/C
catalyst.
OH
KOH, MeOH:H2O
O2, 50 oC, 4 h
1o
2o
100
80
60
40
20
0
2 h
4 h
9
10
11
12
13
14
15
16
17
18
19
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50
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60
1
2
3
4
Cycle
Figure 2. Batch recycling of catalyst for the oxidation of primary
alcohol to the carboxylic acid using PBT/C to catalytically oxidize
piperonyl alcohol (1o). Reaction conditions: Substrate (1.0 mmol, 1
M), 9:1 H2O:MeOH (1 mL), 1.0 mol% [cat], 3.4 equiv KOH, 1 atm
O2, orbital mixing, 50 °C. Yields determined by 1H NMR
spectroscopy int. std. = PhSiMe3.
Oxidation of the biomass-derived compound 5-
(hydroxymethyl)furfural (HMF), to 2,5-furandicarboxylic acid
(FDCA) has been the focus of extensive recent attention with
both homogenous and heterogeneous catalysts.1e,20,21
A
number of precedents note the need to use dilute condition to
avoid polymerization or degradation of intermediates;
however, use of the PBT/C catalyst enabled efficient oxidation
of HMF in near quantitative yield with 1.5 M HMF (eq 2).
This concentration is nearly 15-fold more concentrated than
many of the previously reported conditions.21
A. Schematic Diagram of the Flow Reactor.
O
O
PBT/C (1 mol%)
O
O
O
OH
OH
KOH, MeOH:H2O
O2, 50 oC, 6 h
HO
2ab
95%
1ab
(2 mmol, 1.5 M)
(2)
B. Benzyl Alcohol Oxidation Under Continuous Flow Conditionsa
O
Testing of PBT/C Stability via Batch Recycling and
Operation in a Packed-Bed Flow Reactor. To assess the
long-term stability of the PBT/C catalyst, we conducted
catalyst-recycle tests and investigated the catalyst performance
during extended continuous-flow process conditions. In a
series of batch reactions with the benzylic alcohol 1o with 1
mol% PBT/C, we stopped the reaction at 2 h and 4 h, and then
repeated the reaction with the same catalyst, using fresh
solvent, base and substrate. Yields of carboxylic acid for the 2
h data points were very similar over a series of four sequential
experiments (red bars, Figure 2), while a decrease was evident
after the first experiment and then stabilized for the 4 h data
points (blue bars, Figure 2).
Possible complications associated with batch recycling
experiments (e.g., mechanical losses in catalyst recovery)
prompted us to conduct a more rigorous assessment of the
PBT/C catalyst stability under continuous process conditions
using a packed-bed reactor (Figure 3A). A 0.5 M solution of
benzyl alcohol in 9:1 H2O:MeOH was combined with a gas
stream composed of 9% O2 in N2 and fed together through a
packed bed reactor containing the catalyst. The gas and liquid
mixture was separated upon exiting the reactor, and the
product collected. Reaction progress was monitored by
obtaining aliquots from a sample-collection port and analyzing
the yields and conversions by 1H NMR spectroscopy.
PBT/C
OH
OH
KOH, MeOH:H2O
9 % O2/N2, 50 oC,
WHSV= 620 h-1
1d
2d
100
80
60
40
20
0
0
7,000 14,000 21,000 28,000 35,000
Turnovers
Figure 3. Slug-flow packed-bed reactor (A) used for extended
oxidation of 1d with PBT/C catalyst (B). aReaction conditions:
Substrate (0.50 M), PBT/C, 9:1 H2O:MeOH, 3.4 equiv KOH, 34 atm
9% O2/N2, WHSV = 620 h-1, 50 °C. Yields and conversions
determined by 1H NMR spectroscopy int. std.
trimethoxybenzene.
=
1,3,5-
optimal weight hourly space velocity (WHSV)22 of 620 h-1 was
identified at 50 °C (see Supporting Information, Figure S1).
Under these conditions, the catalyst achieved approximately
31,500 turnovers during a 51 h run, and analysis of the reactor
effluent during this period showed a sustained yield of >95%
to benzoic acid (Figure 3B). Analysis of the catalyst by
In order to determine the best conditions, the reaction was
tested with different residence times in the reactor, and an
4
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inductively coupled plasma atomic emission spectroscopy
after completion of the experiment showed that small amounts
1
2
3
4
5
6
7
8
of catalyst leaching occurs, corresponding to Pd/Bi/Te
quantities of 0.84/0.50/0.38 ppm in the final product solution
(see Supporting Information for details). In spite of the
changes to the catalyst under the reaction conditions, the data
in Figures 2 and 3 suggest that the PBT/C catalyst has
excellent prospects for utility batch and continuous process
conditions.
Sanchez, J. A.; Hutchings, G. J. Chem. Sci., 2012, 3, 20. (e) Besson,
M.; Gallezot, P.; Pinel, C. Chem. Rev., 2014, 114, 1827. (f)
Miyamura, H.; Kobayashi S. Acc. Chem. Res. 2014, 47, 1054. (g)
Pina, C. D.; Falletta, E.; Rossi, M. Oxidative Conversion of
Renewable Feedstock: Carbohydrate Oxidation. In Liquid Phase
Aerobic Oxidation Catalysis; Stahl, S. S., Alsters, P. L., Eds.; Wiley-
VCH Verlag GmbH & Co. KGaA: Weinheim, Germany, 2016, pp.
349.
(2) Tojo, G.; Fernández, M. Oxidation of Primary Alcohols to
Carboxylic Acids, Tojo, G., Ed.; Springer, New York, 2010.
(3) See, for example: (a) Heyns, K.; Blazejwicz, L. Tetrahedron 1960,
9, 67. (b) Maurer, P. J.; Takahata, H.; Rapoport, H. J. Am. Chem. Soc.
1984, 106, 1095.
(4) Harding; K. E.; May, L. M.; Dick, K. F. J. Org. Chem., 1975, 40,
1664. (b) Zhao, M.; Li, J.; Song, Z.; Desmond, R.; Tschaen, D. M.;
Grabowski, E. J. J.; Reider, P. J.; Tetrahedron Lett., 1998, 39, 5323.
(5) Zhao, M. M.; Li, J.; Mano, E.; Song, Z. J.; Tschaen, D. M. Org.
Synth. 2005, 81, 195.
(6) (a) Corma, A.; Garcia, H. Chem. Soc. Rev., 2008, 37, 2096. (b)
Della Pina, C.; Falletta, E.; Rossi, M. Chem. Soc Rev. 2012, 41, 350.
(7) For reviews, see: (a) Sheldon, R. A.; Arends, I. W. C. E.; ten
Brink, G.-J.; Dijksman, A. Acc. Chem. Res. 2002, 35, 774. (b) Zhan,
B.-Z.; Thompson, A. Tetrahedron 2004, 60, 2917. (c) Stahl, S. S.
Angew. Chem. Int. Ed. 2004, 43, 3400. (d) Sigman, M. S.; Jensen, D.
R. Acc. Chem. Res. 2006, 39, 221. (e) Schultz, M. J.; Sigman, M. S.
Tetrahedron 2006, 62, 8227. (f) Matsumoto, T.; Ueno, M.; Wang, N.;
Kobayashi, S. Chem. Asian J. 2008, 3, 196. (g) Parmeggiani, C.;
Cardona, F. Green Chem. 2012, 14, 547. (h) Davis, S. E.; Ide, M. S.;
Davis, R. J. Green Chem., 2013, 15, 17.
(8) For representative primary references: (a) Mallat, T.; Baiker, A.
Catal. Today, 1994, 19, 247. (b) Besson, M.; Gallezot, P. Catal.
Today, 2000, 57, 127. (c) Mori, K.; Yamaguchi, K.; Hara, T.;
Mizugaki, T.; Ebitani, K.; Kaneda, K. J. Am. Chem. Soc. 2002, 124,
11572. (d) Ng, Y. H.; Ikeda, S.; Harada, T.; Morita, Y.; Matsumura,
M. Chem. Commun., 2008, 27, 3181. (e) Zhang, P.; Gong, Y.;
Haoran, L.; Chen, Z.; Wang, Y. Nat. Commun., 2013, 4, 1593. (f)
Rass, H. A.; Essayem, N.; Besson, M. Green Chem., 2013, 15, 2240.
(9) For discussion, see: Steinhoff, B. A.; Guzei, I. A.; Stahl S. S. J.
Am. Chem. Soc. 2004, 126, 11268.
(10) For effective examples of homogeneous catalytic methods for
this transformation, see the following: (a) Zhao, M.; Li, J.; Mano, E.;
Song, Z.; Tschaen, D. M.; Grabowski, E. J. J.; Reider, P. J. J. Org.
Chem., 1999, 64, 2564. (b) Balaraman, E.; Khaskin, E.; Leitus, G.;
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Am. Chem. Soc., 2016, 138, 8344. (e) Wang, X.; Wang, C.; Liu, Y.;
Xiao, J. Green Chem., 2016, 18, 4605.
(11) Diverse heterogeneous catalysts have been employed for the
oxidation of primary alcohols to carboxylic acids, see refs. 1c, 1e, 6,
8, and the following: (a) Kimura, H.; Kimura, A.; Kokubo, I.;
Wakisaka. T.; Mitsuda, Y. Appl. Catal., A, 1993, 95, 143. (b) Mallat,
T.; Bodnar, Z.; Hug, P.; Baiker, A. J. Catal., 1995, 153, 131. (c)
Besson, M.; Lahmer, F.; Gallezot, P.; Fuertes, P.; Fleche, G. J. Catal.
1995, 152, 116. (d) Lee, A. F.; Gee, J. J.; Theyers, H. J. Green Chem,
2000, 2, 279. (e) Anderson, R.; Griffin, K.; Johnston, P.; Alsters, P. L.
Adv. Synth. Catal. 2003, 345, 517. (f) Benhmid, A.; Narayana, K. V.;
Martin, A.; Lücke, B.; Pohl, M. M. Chem. Commun., 2004, 21, 2416.
(g) Fan, A.; Jaenicke, S.; Chuah, G. K.; Biomol. Chem., 2011, 9,
7720. (h) Rass, H. A.; Essayem, N.; Besson, M. Green Chem., 2013,
15, 2240. (i) Zhou, C.; Gou, Z.; Dai, Y.; Jia, X.; Yu, H.; Yang, Y.
Appl. Catal., B, 2016, 181, 118.
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The results described herein show that a heterogeneous
PdBi0.35Te0.23/C (PBT/C) catalyst exhibits excellent activity
and selectivity for the aerobic oxidation of benzylic and
aliphatic primary alcohols to carboxylic acids. The catalyst
tolerates a broad range of functional groups that are commonly
encountered in agrochemicals and pharmaceuticals, and the
extended stability under continuous process conditions
suggests that it could have utility in large-scale applications.
The results described herein, together with the previous
oxidative methyl esterification results, suggests that PBT/C
could emerge as one of the most practical catalysts available
for the liquid-phase aerobic oxidation of primary alcohols. In
this context, ongoing work is focused on understanding the
mechanistic basis for the synergistic Bi/Te promoter effects,
and the results of these efforts will be reported in due course.
Supporting Information Available: Experimental details,
reaction optimization, bench top reaction conditions, HMF
reaction optimization, substrate characterization. This material
is available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: stahl@chem.wisc.edu
ACKNOWLEDGMENT
The authors thank Drs. Edward Calverley, Andre Argenton, Anna
Davis, and William J. Kruper (Dow Chemical) for useful
discussion and to Dow Chemical for financial support. The
authors would like to acknowledge the assistance provided by
Nicole Thomas in purification of 2,5-furandicarboxylic acid
(FDCA). The authors would like to acknowledge the assistance
provided by Dr. Alexander Kvit and Sarah Specht with assistance
in provided during acquisition of Transmission Electron
Microscopy images. Dr. Sourav Biswas in validation of
experimental robustness. Instrumentation was partially funded by
the NSF (CHE-1048642-NMR spectrometers and CHE-9304546-
mass spectrometers).
REFERENCES
(1) For representative reviews, see: (a) Sheldon, R. Catal. Today
1994, 19, 215. (b) Sheldon, R. Catal. Today 2000, 57, 157. (c) Mallat,
T.; Baiker, A. Chem. Rev. 2004 104, 3037. (d) Dimitratos, N.; Lopez-
(12) Each of the studies cited in ref. 11 utilize main-group promoters
in noble-metal catalyzed alcohol oxidation.
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(13) Powell, A. B.; Stahl, S. S. Org. Lett. 2013, 15, 5072.
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(14) (a) Mannel, D. S.; Ahmed, M. S.; Root, T. W.; Stahl, S. S. J. Am.
Chem. Soc. 2017, 139, 1690. (b) Stahl, S. S.; Powell, A. B.; Root, T.
W.; Mannel, D. S.; Ahmed, M. S., Conversion of Alcohols to Alkyl
Esters and Carboxylic Acids using Heterogenous Pd-based Catalyst.
U.S. Patent 9,593,064 B2, Mar 14, 2017.
(15) Important precedents for Pd/Bi and Pt/Bi admixture catalysts,
see: (a) Fiege H.; Wedemeyer K., Angew. Chem. Int. Ed., 1981, 20,
783. (b) Bai, X.-F.; Ye, F.; Zheng, L.-S.; Lai, G.-Q.; Xia, C.-G.; Xu,
L.-W. Chem. Commun. 2012, 48, 8592.
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(16) Heterogeneous PtBi/C catalysts have considerable precedent for
aerobic oxidation of alcohols. For leading references, see refs. 1e,
11d,e.
(17) See, for example: Hoover, J. M.; Stahl, S. S. J. Am. Chem. Soc.
2011, 133, 1690.
(18) See, for example: Wuts, P. G. M. Greene's Protective Groups in
Organic Synthesis: Fifth Edition; John Wiley & Sons, Inc.: Hoboken,
New Jersey, 2014, pp. 507-515.
(19) (a) Keresszegi, C.; Bürgi, T.; Mallat, T.; Baiker, A. J. Catal.
2002, 211, 244. (b) Keresszegi, C.; Mallat, T.; Grunwaldt, J. -D.;
Baiker, A. J. Catal. 2004, 225, 138.
(20) (a) Partenheimer, W.; Grushin, V. V. Adv. Synth. Catal. 2001,
343, 102. (b) Sanborn, A., Oxidation of Furfural Compounds. U.S.
Patent US 8,558,018, Oct 15, 2013.
(21) For representative primary references, see: (a) Casanova, O.;
Iborra, S.; Corma, A. ChemSusChem, 2009, 2, 1138. (b) Pasini, T.;
Piccinini, M.; Blosi, M.; Bonelli, R.; Albonetti, S.; Dimitratos, N.;
Lopez-Sanchez, J. A.; Sankar, M.; He, Q.; Kiely, C. J.; Hutchings, G.
J.; Cavani, F. Green Chem. 2011, 13, 2091. (c) Davis, S. E.; Houk, L.
R.; Tamargo, E. C.; Datye, A. K.; Davis, R. J. 2011, 160, 55. (d) Ta,
N.; Liu, J.; Chenna, S.; Crozier, P.; Li, Y.; Chen, A.; Shen, W. J. Am.
Chem. Soc. 2012, 134, 20585. (e) Vila, A.; Schiavoni, M.; Campisi,
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(22) Weight hourly space velocity (WHSV)
substrate/time) / (mass of Pd)
=
(Mass of
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− 28 examples
− Up to 99% yield
− Continuous flow operation
(> 30,000 Turnovers)
O
O
1 mol% Pd-Bi-Te/C
R
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KOH, MeOH: H2O
O2 (1 atm)
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O
Cl
OH
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OH
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