Sulfonic acid resin-catalyzed oxidation of aldehydes to carboxylic acids by hydrogen peroxide

Article abstract of DOI:10.1080/00397911.2011.617487

Oxidation of benzaldehyde to benzoic acid can be performed efficiently with 30% H2_O2 as the oxidant and sulfonic acid resin Amberlyst 15 as the catalyst. The reactivities of benzaldehyde derivatives are determined by both hindrance effect and electron effect of substituents, and benzaldehyde derivatives with electron-withdrawing group at the meta- or para-position are highly active and almost quantitatively converted into their corresponding acids. In addition, this method also works well for the oxidation of aliphatic aldehydes. The key characteristic of the procedure is that the catalyst is recyclable.

Full text of DOI:10.1080/00397911.2011.617487

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Sulfonic Acid Resin–Catalyzed Oxidation
of Aldehydes to Carboxylic Acids by
Hydrogen Peroxide
Xiaomei Yang a , Si Tang a , Tianliang Lu a , Chen Chen b , Lipeng
Zhou a , Yunlai Su a & Jie Xu b
a Department of Chemistry, Zhengzhou University, Zhengzhou, China
b State Key Laboratory of Catalysis, Dalian Institute of Chemical
Physics, Chinese Academy of Sciences, Dalian, China
Accepted author version posted online: 22 Feb 2012.Version of
record first published: 07 Jan 2013.
To cite this article: Xiaomei Yang , Si Tang , Tianliang Lu , Chen Chen , Lipeng Zhou , Yunlai Su &
Jie Xu (2013): Sulfonic Acid Resin–Catalyzed Oxidation of Aldehydes to Carboxylic Acids by Hydrogen
Peroxide, Synthetic Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 43:7, 979-985
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Synthetic Communications1, 43: 979–985, 2013
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2011.617487
SULFONIC ACID RESIN–CATALYZED OXIDATION
OF ALDEHYDES TO CARBOXYLIC ACIDS BY
HYDROGEN PEROXIDE
Xiaomei Yang,1 Si Tang,1 Tianliang Lu,1 Chen Chen,2
Lipeng Zhou,1 Yunlai Su,1 and Jie Xu2
1Department of Chemistry, Zhengzhou University, Zhengzhou, China
2State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics,
Chinese Academy of Sciences, Dalian, China
GRAPHICAL ABSTRACT
Abstract Oxidation of benzaldehyde to benzoic acid can be performed efficiently with 30%
H2O2 as the oxidant and sulfonic acid resin Amberlyst 15 as the catalyst. The reactivities of
benzaldehyde derivatives are determined by both hindrance effect and electron effect of
substituents, and benzaldehyde derivatives with electron-withdrawing group at the meta-
or para-position are highly active and almost quantitatively converted into their correspond-
ing acids. In addition, this method also works well for the oxidation of aliphatic aldehydes.
The key characteristic of the procedure is that the catalyst is recyclable.
Keywords Aldehydes; carboxylic acids; hydrogen peroxide; oxidation; sulfonic acid resin
INTRODUCTION
The transformation of aldehydes to carboxylic acids is an important reaction in
organic synthesis.[1] The conventional oxidants used for this transformation are
mainly Mn- and Cr-based reagents, which produce large amounts of undesirable
waste.[2] Other oxidants such as hydrogen peroxide,[3] tert-butyl hydroperoxide,[4]
oxone,[5] calcium hypochlorite,[6] 2-hydroperoxyhexafluoro-2-propanol,[7] and O2
[8]
are also used to oxidize aldehydes to carboxylic acids. Among these oxidants, hydro-
gen peroxide has gained considerable interest as it is safe and cheap and produces
only water as a by-product. In 1941, Spa¨th first reported the transformation of dode-
canal to dodecanoic acid by using hydrogen peroxide as the oxidant.[3a] Thereafter,
Received March 1, 2011.
Address correspondence to Lipeng Zhou, Department of Chemistry, Zhengzhou University, 100
Kexue Road, Zhengzhou 450001, China, or Jie Xu, State Key Laboratory of Catalysis, Dalian Institute
of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, China.
E-mail: zhoulipeng@zzu.edu.cn; xujie@dicp.ac.cn
979

980
X. YANG ET AL.
hydrogen peroxide has been used in basic conditions[9] or in combination with other
reagents such as formic acid,[10] N-methylpyrrolidin-2-one hydrotribromide,[3c] and
transition metals[3d,11] for the aldehyde oxidation. However, these systems are asso-
ciated with the drawbacks such as difficult regeneration and reuse of the catalyst and
the use of toxic and heavy metals. Therefore, catalytic, economical, and efficient
alternative methods are required.
Sulfonic acid resin as an recyclable catalyst can effectively catalyze various
kinds of reactions such as the isomerization of a-pinene, the benzylation of toluene
using benzyl alcohol,[12], Beckmann rearrangement of cyclohexanone oxime to
e-caprolactam,[13] the dihydroxylation of olefins,[14] and the selective oxidation of
sulfides to sulfoxides.[15] Herein, we report the oxidation of aldehydes to carboxylic
acids with H2O2 catalyzed by a solid acid, Amberlyst 15. The sulfonic acid resin is
found to be an efficient, recyclable, heterogeneous catalyst for the oxidation of alde-
hydes to carboxylic acids by hydrogen peroxide.
RESULTS AND DISCUSSION
Initial attempts to optimize the reaction conditions for the oxidation of alde-
hydes to the corresponding carboxylic acids were performed with benzaldehyde as
a substrate, and the conditions including the amount of the catalyst and the oxidant,
the reaction temperature, the reaction time, and the solvents were investigated
(Table 1). Without Amberlyst 15, only 25% benzoic acid was obtained with 30%
H2O2 as the oxidant at 90 ꢀC for 8 h. The yield of benzoic acid was drastically
increased to 72% in the presence of a small amount of Amberlyst 15 (0.5 wt%) at
the same reaction conditions. Subsequently, the yield of benzoic acid gradually
increased with increasing the amount of Amberlyst 15 (Table 1, entries 3–5), but
the tendency slowed down at the larger amount of Amberlyst 15. The yield of ben-
zoic acid also gradually increased with increasing the amount of H2O2. When
30 mmol H2O2 (1.5 equiv.) was used, 85% yield of benzoic acid was obtained
(Table 1, entry 4). By further increasing the amount of 30% H2O2 to 35 mmol
(1.75 equiv.), the yield of benzoic acid only slightly increased to 87% (Table 1, entry
8). For the oxidation of benzaldehyde to benzoic acid, the temperature could not be
lower than 90 ꢀC; otherwise the yield of acid was poor. The reaction time of 7 h was
appropriate for the reaction, where 85% yield of benzoic acid was obtained. Among
the different solvents used for optimization, only acetic acid brought out greater
yield of benzoic acid than under the solvent-free conditions, and the yield of benzoic
acid was 86%. For comparison, in the absence of Amberlyst 15, 72% yield of benzoic
acid was obtained using acetic acid as solvent (Table 1, entry 19). The greater reac-
tivity in acetic acid may be caused by the formation of peracid, which is a stronger
oxidant than H2O2.[16,17] Finally, we investigated the reusability of Amberlyst 15.
Under solvent-free conditions, the yield of benzoic acid decreased on the regenerated
catalyst, and 75% yield of benzoic acid was obtained in the third reaction runs
(Table 1, entry 21). The reusability of Amberlyst 15 was better in acetic acid than
under solvent-free conditions. The isolated yield of benzoic acid over the regenerated
catalyst was same with that over the fresh catalyst (Table 1, entries 22 and 23). The
results indicated that Amberlyst 15 was an efficient, recyclable heterogeneous
catalyst for the oxidation of benzaldehyde to benzoic acid by hydrogen peroxide.

OXIDATION OF ALDEHYDES TO ACIDS
981
Table 1. Oxidation of benzaldehyde to benzoic acid with 30% H2O2 catalyzed by
Amberlyst 15 under different conditionsa
H2O2
(mmol)
Amberlyst
15 (wt%)
Temperature
(ꢀC)
Time
(h)
Yield
(%)c
Entry
Solventb
1
2
30
30
30
30
30
20
25
35
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
0
0.5
2.5
5
–
90
90
90
90
90
90
90
90
80
100
110
90
90
90
90
90
90
90
90
90
90
90
90
8
8
8
8
8
8
8
8
8
8
8
4
6
7
7
7
7
7
7
7
7
7
7
25
–
72
77
3
–
4
–
85
87
5
10
5
–
6
–
53
61
7
5
–
8
5
–
87
49
9
5
–
10
11
12
13
14
15
16
17
18
19
20d
21e
22d
23e
5
–
87
87
5
–
5
–
–
56
72
5
5
–
85
45
5
Acetone
Acetonitrile
Ethanol
Acetic acid
Acetic acid
–
5
44
5
81
5
96 (86)f
72f
81
0
5
5
–
75
5
Acetic acid
Acetic acid
86f
86f
5
a20 mmol benzaldehyde was used.
b5 mL solvent was used.
cDetermined by GC analysis.
dThe regenerated catalyst reused once.
eThe regenerated catalyst reused twice.
fThe isolated yield.
To explore the range of suitable substrates for this new catalytic system, the
oxidation of various aldehydes catalyzed by Amberlyst 15 was investigated under the
optimized conditions (5wt% Amberlyst 15 and 1.5 equiv. 30% H2O2 in 5 mL acetic acid
at 90 ꢀC for 7 h), and the results are given in Table 2. It can be seen that benzaldehyde
derivatives with one electron-withdrawing group such as -Cl, -Br, and -NO2 (Table 2,
entries 1, 2, and 6–9) were more reactive than with one electron-donating group such as
-CH3, -OCH3, and -OH (Table 2, entries 10–12). The catalytic behavior of Amberlyst
15 was similar with that of the lipophilic, acidic quaternary ammonium salt, which also
exhibited greater activity for the oxidation of benzaldehyde derivatives with an
electron-withdrawing group.[3b] In addition, the position of the substituent also affec-
ted the reactivity of the benzaldehyde derivatives. For example, the reactivity of
2-chlorobenzaldehyde was less than that of 4-chlorobenzaldehyde, and the reactivity
of 2-nitrobenzaldehyde was much lower than 3-nitrobenzaldehyde or 4-nitrobenzalde-
hyde. For benzaldehyde derivatives with two substituents, a similar phenomenon was
observed. For example, the reactivity decreased in the following order: 3,4-dichloro-
benzaldehyde > 2,4-dichlorobenzaldehyde> 2,6-dichlorobenzaldehyde. These results

982
X. YANG ET AL.
Table 2. Sulfonic acid resin–catalyzed oxidation of various aldehydes to the corresponding acids with
a
H2O2
Entry
1
Aldehyde
Acid
Yield (%)b
98
2
3
4
73
99
79
5
39
6
7
96
98
8
9
96
69
(Continued )

OXIDATION OF ALDEHYDES TO ACIDS
983
Table 2. Continued
Entry
10
Aldehyde
Acid
Yield (%)b
58
11
12
13
18
48
51
14
15
14
23
16
17
CH3 (CH2)7CH2CHO
CH3 (CH2)2CH2CHO
CH3 (CH2)7CH2COOH
CH3 (CH2)2CH2COOH
97
98
aReaction conditions: substrate (10 mmol), Amberlyst 15 (5 wt.%), and 30% H2O2 (15 mmol) in acetic
acid (5 mL) at 90 ꢀC for 7 h.
bIsolated yield.
indicated that the substituent at the ortho-position of aldehyde group hindered the reac-
tivity considerably. A similar phenomenon was also observed in the oxidation of ben-
zaldehyde derivatives with hydrogen peroxide catalyzed by N-methylpyrrolidin-2-one
hydrotribromide.[3c] Our catalytic system was also very effective for the oxidation of
aliphatic aldehydes. For example, the yields of 97% and 98% were obtained for the oxi-
dation of decanal and valeraldehyde to their corresponding acids (Table 2, entries 16
and 17). The oxidation of picolinaldehyde produced picolinic acid with the isolated
yield of 51% (Table 2, entry 13), whereas the oxidation of furan-2-carbaldehyde only
gave 14% yield of the corresponding acids (Table 2, entry 14). Additionally, the oxi-
dation of allylic aldehydes such as cinnamaldehyde produced 23% yield of cinnamic
acid (Table 2, entry 15).
Based on the results, we proposed a possible reaction mechanism (Scheme 1). At
first step, H2O2 and resin-supported sulfonic acid formed the intermediate peroxy-
sulfuric acid,[18] which reacted with aldehyde to give the intermediate peroxyace-
tal. Finally, peroxyacetal decomposed to acid and supported sulfonic acid via a
six-member ring. According to the mechanism, if there had substituent at the

984
X. YANG ET AL.
Scheme 1. Reaction mechanism for the oxidation of aldehyde to acid with H2O2 catalyzed by Amberlyst 15.
ortho-position of aldehyde group, the steric hindrance would restrict the formation of
the intermediate peroxyacetal, and thus the reactivity of the ortho-position substi-
tuted benzaldehyde was lower. On the other hand, the electron-withdrawing group
on the benzene ring resulted in the electron deficiency on the carbon of aldehyde
group, which promoted the homolysis of O-O bond, so electron-withdrawing groups
favored the oxidation of benzaldehyde derivatives to the corresponding benzoic acids.
In conclusion, we have developed a simple and effective procedure for the oxi-
dation of aldehydes to the corresponding acids using solid acid Amberlyst 15 as the
catalyst and 30% H2O2 as the oxidant. The characteristic of the procedure is that the
catalyst is recyclable.
EXPERIMENTAL
The general experimental procedure was as follows: desired amount of alde-
hyde, solvent, 30% H2O2, and Amberlyst 15 were charged to the flask (the detailed
amount of reactant and reagent are listed as footnotes to tables). The mixture was
heated by oil bath to the desired temperature with stirring and then cooled to room
temperature. Subsequently, the mixture was filtered to separate the catalyst for
further study. The solvent was removed from the filtrate through rotary evaporation.
The pH of the residuel was adjusted to 8.0 with NaOH (2 mol=L), and then it was
extracted with ethyl acetate. The aqueous layer was acidified to pH 2.0 using HCl
(6 mol=L) and extracted with ethyl acetate. The ethyl acetate was removed from
the organic layer through rotary evaporation and then the carboxylic acid was
obtained. The separated catalyst was washed with acetone three times and then dried
at 120 ꢀC for 2 h. The regenerated catalyst was used for the recycling study.
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