Aerobic Oxidation of Diverse Primary Alcohols to Carboxylic Acids with

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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 Downloaded from http://pubs.acs.org on July 6, 2017

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Aerobic Oxidation of Diverse Primary Alcohols to Carboxylic Acids with a Heterogeneous Pd-Bi-Te/C (PBT/C) Catalyst Maaz S. Ahmeda, David S. Mannelb, Thatcher W. Rootb, Shannon S. Stahla,* a

Department of Chemistry and bDepartment 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.

Introduction Heterogeneous catalysts for selective, liquid-phase aerobic oxidation of organic molecules could have widespread utility in organic chemical synthesis,1 particularly within the fine and specialty chemical industries where the complexity and molecular weight of the molecules prevents gas-phase processes. Carboxylic acids are prevalent in valuable organic chemicals, such as pharmaceuticals and agrochemicals, and the development of new catalysts for the aerobic oxidation of primary alcohols to carboxylic acids (eq 1) would provide appealing sustainable alternatives to many existing oxidation methods.2 In many cases, methods for this transformation still rely on the use of undesirable stoichiometric oxidants.

groups. Building on relevant precedents, our initial studies identified a new class of heterogeneous Pd-based catalysts, modified with main-group promoters.12 Bi and Te promoters were found to exhibit synergistic behavior in the oxidative methyl esterification of primary alcohols (Scheme 1).13,14 The Bi and Te promoters significantly improve the activity and selectivity of the catalyst (Scheme 1A), and they contribute to broader substrate scope and functional-group compatibility (Scheme 1B). Another noteworthy outcome of these studies Scheme 1. Oxidative Methyl Esterification of Primary Alcohols with Pd-Bi-Te/C Catalysts.

3

O R

OH + O 2

cat.

R

1M OH + H 2O

(1)

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 biomassderived 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 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

O

1 mol% [Pd] OH

100

B. Other Representative Products OMe

68%

60

OMe

98 % O

99 % O 20%

OMe S

0

F

F 3C

40 20

O

O

93%

80

OMe

3

60 °C, 1 bar O 2, MeOH 25 mol % K 2CO3, 8 h

A. Octanol oxidation

Ester Yield (%)

1 2 3 4 5 6 7 8 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 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Organic Process Research & Development

Pd

Pd/Bi Pd/Bi/Te

92 %

OMe N 93 %

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

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aerobic oxidation of a wide range of primary alcohols to the corresponding carboxylic acids.

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Table 1. Optimization of Reaction Conditions with PBT/C for Carboxylic Acid with 1-Octanol.a O

Results and Discussion 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 4methoxybenzyl 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. 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.

3

1 mol% [Pd], 5 mol% additive Solvent, KOH O 2, 50 oC

OH

1a

3

OH

2a

Entry Catalyst/Additive Solvent Yield b 1 Pd/char (5 wt %) H2 O 0 2 Pd/char (5 wt %) 99:1 H2O:MeOH 33 3 Pd/char (5 wt %) 9:1 H2O:MeOH 61 4 Pd/C (1 wt %) " 22 5 Pd/C (5 wt %) " 19 6 Pd/BaSO4 (5 wt %) " 0 7 Pd/Al2O3 (1 wt %) " 1 8 Pd/TiO2 " 0 9 Pd/CeO2 " 0 10 Pd/char, BiCl3 " 89 11 Pd/char, Te " 73 12 Pd/char, TeO2 " 85 13 Pd/char, Bi(NO3)3 " 96 14 Pd/char, Bi2Te3 " 96 15 Pd/char, Bi(NO3)3, Tec, d " >99 16 PdBi0.35/Cd,e " 76 17 PdTe0.23/Cd,e " 51 18 PdBi0.35Te0.23/C (PBT/C)d,e " 98 19 PtBi/Cd " 63 a Reaction conditions: 1a (1.0 mmol, 1 M), solvent (1 mL), 1.0 mol% [Pd cat], 0.84 equiv KOH, 1 atm O2, orbital mixing, 50 °C, 16 h. b% 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 d 3.4 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 (1 mmol, 1 M) Entry

KOH, MeOH:H 2O, O 2, 50 oC

Substrate

1b

3

OH

1a

R

OH

PtBi/C

Pd-Bi-Te admixture

PBT/C

PBT/C (1.0 mol%)

53%

12%

67%

95%

86%

29%

75%

85%

70%

53%

97%

97%

96%

58%

96%

>99%

58%

1%

31%

95%

OH 2c 1b OH 3d

MeO

1c OH

4d 1d OH 5d

F 3C

1e

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 a Conditions: Substrate (1.0 mmol, 1 M), 9:1 H2O:MeOH (1 mL), 1.0 mol% [cat], 3.4 equiv KOH, 1 atm O2, 50 °C. Yields based on 1H NMR spectroscopy; int. std. = PhSiMe3. b8 h. c16 h. d4 h.


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Subsequent catalyst deactivation, however, led to only 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.

which underwent efficient oxidation in excellent yield (>90%). 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%). Table 3. Substrate Scope for Aerobic Alcohol Oxidation with PBT/C Catalyst Systema R

3

Pd catalyst

OH

3


1a

A. Pd/char

KOH, MeOH:H 2O O 2, 50 oC, 4 h

1a-1z

OH

OH R

2a

B. PBT/C MeO

OMe

O OH 2o, 80%

MeO 1c

C. Pd/char

Pd catalyst


2p, 93%b

2c

OH 2t, 64%b

O

Cl 2u, >99% b

2v, 93%b O O

2y, 64%b

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.

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

2a, 96%b, (95%)

OH

O OH

N 2w, 83%c O

OH

OH 2b, 85%d

O

3 OH

OH

O

3 OH

O

O

2r, 92%b

O

S

2s, 77%b

D. PBT/C

2q, 95%b

O

O

OH N

N

OH

MeO

O OH

OH

O OH

2k, R1 = -F, 93% OH 2l, R1 = -Cl, 98% 2m, R1 = -Br, 4% 2n, R1 = -I, 0%

O

N

O

OH

R1

O

OH Me 2g, 96%

O

F 2j, 99%

2i, 85%

O

O Me

OH

OH

OH 2a-2z

O

O

O

R

2c, R = -OMe, 97%, (93%) 2d, R = -H, >99%, (95%) 2e, R = -CF3, 95% 2f, R = -Me, 93%, (91%) 2h, R = -SMe, 43%b

O

O

O

PBT/C (1 mol%)

OH

2x, 99%d O

OH

2z, >99% b (94%)

OH

2aa, 53%e

a

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, 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 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,


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as the enol form of the intermediate aldehyde is susceptible to 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 1 H 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. 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 O

O

OH

1ab (2 mmol, 1.5 M)

PBT/C (1 mol%) KOH, MeOH:H 2O O 2, 50 oC, 6 h

O

Page 4 of 7 O

PBT/C (1 mol %)

OH

O

KOH, MeOH:H 2O O 2, 50 oC, 4 h

O

OH

O

1o

2o 100

2h 4h

80

60

40

20

0

1

2

Cycle

3

4

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. A. Schematic Diagram of the Flow Reactor.

O O

O

OH

HO 2ab 95%

(2)

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. In order to determine the best conditions, the reaction was tested with different residence times in the reactor, and an

B. Benzyl Alcohol Oxidation Under Continuous Flow Conditions

a

O PBT/C

OH

KOH, MeOH:H 2O 9 % O 2/N2, 50 oC, WHSV= 620 h -1

1d

OH

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. = 1,3,5trimethoxybenzene.

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


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inductively coupled plasma atomic emission spectroscopy after completion of the experiment showed that small amounts 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.

Summary and Conclusion 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: [email protected]

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-9304546mass 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-

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.; WileyVCH 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.; Milstein, D. A. Nat. Chem. 2013, 5, 122. (c) L. Han, P. Xing, B. Jiang, Org. Lett., 2014, 16, 3428. (d) Jiang, X.; Zhang, J.; Ma. S. J. 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. (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. (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. (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, S.; Veith, G. M.; Prati, L. ChemSusChem 2013, 6, 609. (f) Rass, H. A.; Essayem, N.; Besson, M. Green Chem. 2013, 15, 2240. (22) Weight hourly space velocity (WHSV) = (Mass of substrate/time) / (mass of Pd)


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TOC Graphic R

OH

O

O

1 mol% Pd-Bi-Te/C KOH, MeOH: H 2O O 2 (1 atm)

O

HO

R

OH

− 28 examples − Up to 99% yield − Continuous flow operation (> 30,000 Turnovers)

O

O OH

O

O

OH

O

O

O

Cl 3

O OH

OH

OH

OH Cl

N F


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Aerobic Oxidation of Diverse Primary Alcohols to Carboxylic Acids with

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