Highly efficient controllable oxidation of alcohols to aldehydes and acids with sodium periodate catalyzed by water-soluble metalloporphyrins as biomimetic catalyst

Article abstract of DOI:10.1016/j.bmc.2010.10.026

Highly efficient controllable oxidation of alcohols to aldehydes or acids by sodium periodate in the presence of water-soluble manganese porphyrins (meso-tetrakis(N-ethylpyridinium-4-yl)manganese porphyrin, MnTEPyP) with different reaction media has been reported. The manganese porphyrin showed excellent activity for the controllable oxidation of various alcohols under mild conditions. Moreover, different factors influencing alcohol oxidation, for example, oxidant, catalyst amount, temperature, and solvent, have been investigated. A plausible mechanism for the controllable oxidation of alcohol has been proposed.

Full text of DOI:10.1016/j.bmc.2010.10.026

Bioorganic & Medicinal Chemistry 18 (2010) 8144–8149
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Highly efficient controllable oxidation of alcohols to aldehydes and acids
with sodium periodate catalyzed by water-soluble metalloporphyrins as
biomimetic catalyst
⇑
Qing-Gang Ren, Shao-Yun Chen, Xian-Tai Zhou, Hong-Bing Ji
School of Chemistry and Chemical Engineering, The Key Laboratory of Low-carbon Chemistry & Energy Conservation of Guangdong Province, Sun Yat-sen University,
Guangzhou 510275, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Highly efficient controllable oxidation of alcohols to aldehydes or acids by sodium periodate in the pres-
ence of water-soluble manganese porphyrins (meso-tetrakis(N-ethylpyridinium-4-yl)manganese porphy-
rin, MnTEPyP) with different reaction media has been reported. The manganese porphyrin showed
excellent activity for the controllable oxidation of various alcohols under mild conditions. Moreover, dif-
ferent factors influencing alcohol oxidation, for example, oxidant, catalyst amount, temperature, and sol-
vent, have been investigated. A plausible mechanism for the controllable oxidation of alcohol has been
proposed.
Received 25 August 2010
Revised 8 October 2010
Accepted 9 October 2010
Available online 15 October 2010
Keywords:
Water-soluble metalloporphyrins
Controllable oxidation
Alcohols
Ó 2010 Elsevier Ltd. All rights reserved.
Aldehydes
1. Introduction
reported the oxidation of a broad range of alcohol substrates by
(TSPP)RhIII in water using molecular oxygen as the terminal oxi-
Selective catalytic oxidation of alcohols to corresponding alde-
hydes or acids is of great importance for both laboratory and
synthetic industrial applications.1 As model catalysts of cytochrome
P-450, metalloporphyrins could be used as intermediate of oxygen
carriers for biological systems. Metalloporphyrins have been widely
used as catalystsfor various biomimeticoxidationreactionsas well.2
Oxidation of alcohols catalyzed by metalloporphyrins has been well
investigated with PhIO,3 Cl2PyNO,4 t-BuOOH,5 and m-chloroperben-
zoic acid6 used as oxidants. In general, these oxidations were
performed with organic solvents as reaction media.7
The development of green chemical processes has become one
of the most important tasks for chemical researchers to date.8 To
reduce or eliminate emission of volatile organic compounds to
the environment, the possibility of using water as solvent for or-
ganic reactions has gathered much attention. Taking the form of
biomimetic compounds, water-soluble metalloporphyrins have
good solubility in water due to the presence of hydrophilic groups.
These compounds could be employed to simulate catalytic
performance of enzymes in water. Accordingly, water-soluble
metalloporphyrins-catalyzed oxidations have been developed in
water or mixtures of water with organic solvents.9 However, only
few investigations on water-soluble metalloporphyrins-catalyzed
oxidation of alcohols have been reported. Fu and co-workers
dant.10 Fabbri et al. reported the oxidation of a series of
a-alkyl-
substituted mono and dimethoxylated benzyl alcohols catalyzed
by FeTMPyPCl and FeTSPPCl with selectivity up to 49% in aqueous
solutions.11 Wietzerbin reported the catalytic oxidation of tertiary
alcohols in water-soluble Mn-TMPyP/KHSO5 systems, but many
products were obtained with poor selectivity.12
Subsequently, as a part of our studies on metalloporphyrins-
catalyzed oxidations,13 a controllable oxidation procedure for
alcohols for corresponding acids or aldehydes catalyzed by
water-soluble metalloporphyrins (MnTEPyP), has been developed
(Scheme 1). Various alcohols were oxidized readily and controlla-
bly to obtain the corresponding products under mild conditions.
Furthermore, high-valent oxo intermediate was verified by UV–
vis spectroscopy in the oxidation of benzyl alcohol. Finally, a plau-
sible mechanism was proposed.
2. Experimental
2.1. Materials and instruments
Alcohols were of analytical grade and purchased from Alfa Aesar
or Aldrich without further purification unless indicated. Other sol-
vents were all of analytical grade.
UV–vis spectra were recorded on a Shimadzu UV-2450 UV–vis
spectrophotometer. Mass spectra were obtained on a Shimadzu
LCMS-2010A.
⇑
Corresponding author. Tel.: +86 20 84113653; fax: +86 20 84113654.
E-mail address: jihb@mail.sysu.edu.cn (H.-B. Ji).
0968-0896/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2010.10.026

Q.-G. Ren et al. / Bioorg. Med. Chem. 18 (2010) 8144–8149
8145
O
MnTEPyP, NaIO4, H2O/Toluene=(5/1, v/v), 30ºC
MnTEPyP, NaIO4, H2O, 60ºC
OH
O
OH
N
MnTEPyP:
N
N
N
N
Mn
N
N
N
Scheme 1. Controllable oxidation of alcohols to acids or aldehydes catalyzed by MnTEPyP.
2.2. Synthesis of meso-tetrakis (N-ethylpyridinium-4-yl)
manganese porphyrin
3. Results and discussion
3.1. Effect of oxidant on the oxidation of alcohol to acid
meso-Tetrakis(4-pyridyl) porphyrin (TPyP) was prepared
according to reported works.14 MnTPyP (0.15 g, 0.221 mmol) and
fresh distilled iodoethane (0.62 mg, 4 mmol) were added to
20 mL dimethylformamide solution. The mixture was stirred for
4 h at 45 °C, and the solution was cooled to room temperature.
Next, 20 mL ethyl ether was added, and the mixture was kept over-
night. After filtration, the filter cake was washed thoroughly with
ethyl ether and recrystallized with water/acetone (1:2) to obtain
Various oxidants were tested as oxygen resource for the metal-
loporphyrins-catalyzed aqueous oxidation of benzyl alcohol. The
results are summarized in Table 1. Sodium periodate was more
effective compared with O2, t-BuOOH, H2O2, NaIO3, and NaClO
for the oxidation catalyzed by MnTEPyP in water. Although high
conversion for benzyl alcohol could be obtained by using NaClO
as oxidant, the oxidation system showed unsatisfactory selectivity
for benzoic acid (entry 4). Compared with sodium periodate,
sodium iodate presented poor activity (entry 5), indicating that
IOÀ4 ion is crucial for oxidation.15
The effects of sodium periodate contents on the catalytic oxida-
tion of benzyl alcohol were also examined. It seemed that the con-
version of benzyl alcohol and the selectivity of benzoic acid
increased with increase in sodium periodate contents (entries 6
and 7). However, no significant difference was observed when
the molar ratio of sodium periodate to substrate was over 4 for
the sodium periodate oxidation system (entries 6–8).
0.189 g (71.4%) [MnTEPyP]4+. EI-MS: m/z 787. UV–vis (H2O): kmax
,
nm (log e) 464 (2.48), 559 (1.25), 675 (0.87), 769 (0.54). Anal. calcd
for [MnTEPyP]4+: C, 44.50; H, 3.42; N, 8.65. Found: C, 44.67; H,
3.51; N, 8.49.
2.3. General procedures for oxidation of alcohol to acid
Water (5 mL), benzyl alcohol (0.5 mmol), MnTEPyP (0.5 Â 10À2
mmol), and NaIO4 (2 mmol) were mixed at 60 °C while stirring
for 4 h. Then, the aqueous solution was extracted with ethyl ace-
tate (3 Â 5 mL). Naphthalene (0.05 g) was added as internal stan-
dard. The consumption of alcohols and formation of oxidized
products were monitored by gas chromatography (GC) (Shimadzu
GC-14C) with a packed column and GC–mass spectrometry (MS)
(Shimadzu GCMS-QP2010 plus) equipped with Rtx-5MS capillary
column.
Table 1
Effect of oxidant on the aqueous oxidation of benzyl alcohol catalyzed
by MnTEPyPa
Entry
Oxidant
Conversion (%)
Yield (%)
1
2
O2
H2O2
1
6
1
6
2.4. General procedures for oxidation of alcohol to aldehyde
3
4
t-BuOOH
NaClO
NaIO3
NaIO4
NaIO4
NaIO4
47
90
16
84
100
100
38
75
16
55
94
95
Water (5 mL), toluene (1 mL), benzyl alcohol (0.5 mmol),
MnTEPyP (0.5 Â 10À2 mmol), and NaIO4 (2 mmol) were mixed at
30 °C while stirring for 1.5 h. Then, the aqueous solution was ex-
tracted with ethyl acetate (3 Â 5 mL). Naphthalene (0.05 g) was
added as internal standard. The consumption of alcohols and for-
mation of oxidized products were monitored by GC (Shimadzu
GC-14C) with a packed column and GC–MS (Shimadzu GCMS-
QP2010 plus) equipped with Rtx-5MS capillary column.
5
6b
7
8c
Benzyl alcohol (0.5 mmol), MnTEPyP (0.5 Â 10À2 mmol), oxidant
a
(2 mmol), H2O (5 mL), 4 h, 60 °C.
b
NaIO4 (1 mmol).
NaIO4 (3 mmol).
c

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Q.-G. Ren et al. / Bioorg. Med. Chem. 18 (2010) 8144–8149
Table 3
3.2. Effect of catalyst contents on the oxidation of alcohol to
acid
Effect of temperature on benzyl alcohol oxidation catalyzed by
MnTEPyPa
Entry
T (°C)
Conversion (%)
Yield (%)
The effects of MnTEPyP contents on the oxidation of benzyl
alcohol by sodium periodate were investigated. The results are
summarized in Table 2.
1
2
3
4
5
30
40
50
60
70
94
96
95
100
100
68
77
85
94
95
As shown in Table 2, the reaction cannot take place in the ab-
sence of a catalyst, indicating that MnTEPyP is crucial in oxidation
reaction (entry 1). When the molar ratio of catalyst to substrate
was 1/1000, only 33% of benzyl alcohol could be converted, as
the reaction continued for 4 h (entry 6). As depicted clearly in Table
2, the reaction rate and conversion increases with increasing cata-
lyst contents. Benzyl alcohol could be converted completely when
the molar ratio of the catalyst to substrate was 1/100 (entry 2), in
which the yield for benzoic acid could reach 94%. Therefore, the
optimal molar ratio of water-soluble metalloporphyrins to sub-
strate for the aqueous oxidation of benzyl alcohol to benzoic acid
was 1/100.
In addition, compared with other manganese cationic salts,
water-soluble metalloporphyrins were proven to have the signifi-
cant unique properties required in the selective oxidation of alco-
hols. Only 9% of benzyl alcohol could be converted when the
catalyst was replaced to manganese(II) acetate tetrahydrate with
the same catalytic amount as water-soluble metalloporphyrins,
and the product was benzaldehyde (entry 7).
Benzyl alcohol (0.5 mmol), MnTEPyP (0.5 Â 10À2 mmol),
a
NaIO4 (2 mmol), H2O (5 mL), 4 h.
Table 4
Effect of different axial ligands on the oxidation of benzyl alcohol catalyzed by
MnTEPyPa
Entry
Axial ligand
Conversion (%)
Yield (%)
1
2
3
4
5
NH4Ac
100
100
100
100
100
97
99
99
99
94
Imidazole
Pyridine
N-Methylimidazole
No axial base
Benzyl alcohol (0.5 mmol), MnTEPyP (0.5 Â 10À2 mmol), axial ligand
a
(0.03 mmol), NaIO4 (2 mmol), H2O (5 mL), 4 h, 60 °C.
without axial ligands. However, the presence of axial ligands
slightly and positively affected the selectivity of benzoic acid (en-
tries 1–4). Oxidations were carried out in the absence of axial
ligands in subsequent testing.
3.3. Effect of temperature on the oxidation of alcohol to acid
The effect of reaction temperature on the oxidation of benzyl
alcohol to benzoic acid catalyzed by MnTEPyP was also investi-
gated. Results are shown in Table 3.
3.5. Controllable oxidation of benzyl alcohol to benzyaldehyde
From Table 3, it seemed that the conversion of benzyl alcohol
was minimally influenced by reaction temperature. The conversion
increased slightly with rising temperature from 30 to 60 °C and re-
mained unchanged at temperature over 60 °C. Meanwhile, the
selectivity for benzoic acid was closely related to reaction temper-
ature. The selectivity for benzoic acid increased from 68% to 94%
while temperature rose from 30 to 60 °C, and no obvious increase
was observed at temperature over 60 °C. Therefore, the optimal
reaction temperature for the oxidation of benzyl alcohol to benzoic
acid was 60 °C.
The profiles for oxidation of benzyl alcohol by sodium periodate
in the presence of MnTEPyP are shown in Figure 1, demonstrating
that reaction proceeds via two steps: (1) oxidation of benzyl alco-
hol to benzyaldehyde and (2) oxidation of benzyaldehyde to ben-
zoic acid. Benzyaldehyde was used as the reaction intermediate.
Similar to the reaction intermediate during the oxidation pro-
cess, benzyaldehyde showed solubility that much lower than that
of benzyl alcohol in water. If organic solvents were added onto
the reaction mixture, benzyaldehyde might be enriched in the or-
ganic phase. If the reaction intermediate could be selectively dis-
tributed onto the reaction media, the reaction process would be
influenced to some extent, and the selectivity of product would
be adjusted. Based on these considerations, non-polar organic sol-
vents like toluene (1 mL) was chosen. The mixture was stirred at
3.4. Effect of axial ligands on the oxidation of alcohol to acid
The presence of axial ligands can improve the catalytic perfor-
mance of catalysts by facilitating the formation and stabilization
of the proposed high-valence metalloporphyrin intermediate.16
The effect of different axial ligands on the oxidation rate of benzyl
alcohol was investigated. As shown in Table 4, no significant differ-
ences for the conversion of benzyl alcohol can be found with or
100
80
Table 2
60
Conv. of benzyl alcohol
Effect of MnTEPyP contents on the oxidation of benzyl alcohola
Yield of benzalehyde
Entry
Catalyst/substrate
(molar ratio)
Conversion
(%)
Yield of benzoic
acid (%)
Yield benzoic acid
40
20
0
1
2
3
4
0
0
100
51
40
37
33
8
0
94
33
27
28
27
8
1:100
1:300
1:500
1:800
1:1000
1:100
5
6
0
1
2
3
4
5
6
7
7b
Time/h
a
Benzyl alcohol (0.5 mmol), NaIO4 (2 mmol), catalyst (MnTEPyP), H2O (5 mL),
4 h, 60 °C.
Figure 1. Reaction profile for the oxidation of benzyl alcohol by sodium periodate
in the presence of MnTEPyP. Benzyl alcohol (0.5 mmol), MnTEPyP
(0.5 Â 10À2 mmol), NaIO4 (2 mmol), H2O (5 mL), 60 °C.
b
The catalyst was manganese(II) acetate tetrahydrate. The product was
benzaldehyde.

Q.-G. Ren et al. / Bioorg. Med. Chem. 18 (2010) 8144–8149
8147
30 °C for 1.5 h. Surprisingly, the selectivity for benzaldehyde
soared to 97%.
Catalytic oxidations with the addition of different organic sol-
vents were well investigated. The solvents used included polar
and non-polar organic solvents with different dielectric constants.
The results are summarized in Table 5.
water was much lower compared with those in toluene. Therefore,
benzaldehyde could be removed easily from the aqueous system
and then protected from over-oxidation to benzoic acid when ben-
zyl alcohol was oxidized to benzaldehyde. The oxidant was also
dissolved in aqueous phase, and benzaldehyde could not be trans-
ferred to the benzoic acid in the organic phase due to the absence
of oxidant. From the viewpoint of mass transfer, the presence of
the organic solvent is favorable for benzaldehyde when diffusing
into the organic phase.18 The process for controllable oxidation of
benzyl alcohol to benzaldehyde or benzoic acid is shown in
Figure 2.
Results showed that the oxidation of benzyl alcohol in 1:5 (v/v)
mixture of C7H8/H2O resulted in benzaldehyde. The selectivity of
benzaldehyde also decreased with the increase in polarity of the
organic solvent. When the reaction was carried out in water, the
main product was benzoic acid and the yield for benzaldehyde
was only 33%. The increasing selectivity for benzaldehyde in non-
polar solvents attributable to the solubility of benzaldehyde in
non-polar solvent is much higher compared with those in polar
solvents. In addition, by adding non-polar solvent onto the system,
the formed benzaldehyde could be removed from the aqueous
phase, resulting in the increase in selectivity for benzaldehyde.
Benzaldehyde or benzyl alcohol could be obtained from the
oxidation of toluene by molecular oxygen in the presence of metal-
loporphyrin under high pressure.17 For the present system, no
benzaldehyde or benzyl alcohol could be detected by GC–MS (en-
try 8) in the absence of benzyl alcohol, indicating that toluene
could not be oxidized in the present work. Nevertheless, in the
present protocol, the oxidation of benzyl alcohol could be well con-
trolled to obtain benzaldehyde with excellent selectivity under
mild conditions.
Table 6
Controllable oxidation of alcohols to acids and aldehydes catalyzed by MnTEPyP
Entry Substrate
Product
Aldehydeb
Acida
O
OH
O
OH
1
(1.5h, 97%)
(4h, 98%)
(4 h, 98%)
(1.5 h, 97%)
O
OH
O
In the reaction system adopted in this study, two phases (aque-
ous and organic) were employed. The catalyst and NaIO4 were dis-
solved in the aqueous phase. The solubility of benzaldehyde in
OH
Cl
Cl
2
Cl
(2h, 94%)
(4h, 94%)
(4 h, 94%)
(2 h, 94%)
Table 5
O
OH
O
Effect of organic solvent on the selectivity of benzaldehyde in the oxidation of benzyl
alcohol catalyzed by MnTEPyPa
OH
O2N
O2N
3
Entry
Solvent
Conversion (%)
Yield (%)
Selectivity (%)
O2N
1
2
3
4
C7H8/H2O
98
64
98
92
79
99
—
97
63
89
41
34
33
—
99
98
91
45
43
33
—
(1h, 96%)
(1 h, 96%)
(4h, 50%)
(4 h, 50%)
CHCl3/H2O
CH2Cl2/H2O
(CH3)2CHOH/H2O
CH3CN/H2O
H2O
O
OH
O
5
OH
O
6
4
7b
C7H8/H2O
Benzyl alcohol (0.5 mmol), MnTEPyP (0.5 Â 10À2 mmol), NaIO4 (2 mmol), 1.5 h,
(2h, 93%)
(2 h, 93%)
a
(4h, 96%)
(4 h, 96%)
30 °C, solvent/H2O = 5/1 (v/v).
b
No substrate was added.
OH
O
OH
MeO
MeO
5
MeO
(2h, 84%)
(2 h, 84%)
(4h, 98%)
(4 h, 98%)
Water
O
OH
O
OH
N
N
6
O
Toluene
N
OH
(3h, 27%)
(4h, 50%)
(4 h, 50%)
(3 h, 27%)
O
OH
O
O
OH
OH
7
O
OH
(0.5h, 97%)
(4h, 96%)
(4 h, 96%)
(0.5 h, 97%)
a
Alcohol (0.5 mmol), MnTEPyP (0.5 Â 10À2 mmol), NaIO4 (2 mmol), H2O (5 mL),
60 °C. The values in parentheses are reaction time and yield.
b
Alcohol (0.5 mmol), MnTEPyP (0.5 Â 10À2 mmol), NaIO4 (2 mmol), H2O (5 mL),
Figure 2. The schematic of controllable oxidation of benzyl alcohol to benzalde-
hyde or benzoic acid catalyzed by MnTEPyP.
toluene (1 mL), 30 °C. The values in parentheses are reaction time and yield.

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Q.-G. Ren et al. / Bioorg. Med. Chem. 18 (2010) 8144–8149
3.6. Controllable oxidation of various alcohols to aldehydes and
acids
clearly suggest that manganese porphyrin is crucial for the oxida-
tion of benzyl alcohol. High-valent porphyrin intermediate is
generally accepted as the active species for metalloporphyrins-cat-
alyzed oxidations. The presence of manganese-oxo porphyrin was
confirmed by in situ UV–vis spectra for the oxidation of benzyl
alcohol (Fig. 3).
To evaluate the scope of the controllable oxidation, various aro-
matic alcohols were subjected to the reaction system catalyzed by
MnTEPyP. The results are summarized in Table 6.
As shown in Table 6, most aromatic alcohols can be smoothly
converted to the corresponding acids or aldehydes in high yields
except 4-pyridinemethanol (entry 6). It seemed that catalytic effi-
ciency was not affected by the electronic property of substrates
with electron-donating groups (entries 4 and 5). However, for the
substrate with strong electron-withdrawing group, such as 4-
nitrobenzyl alcohol, the catalytic system seemed favorable for oxi-
dation to aldehyde (entry 3). The catalytic system also exhibited
high activity for the oxidation of diols like 1-phenyl-1, 2-ethane-
diol (entry 7). The main products, benzaldehyde and benzoic acid,
were obtained from the oxidative cleavage of C–C bonds. Diols that
could be cleaved to the corresponding aldehydes were also re-
ported in previous works with ruthenium porphyrins used as
catalyst.7a
In Figure 3, the initial characteristic absorption peaks of MnTE-
PyP were at 464 and 562 nm. After adding sodium periodate and
benzyl alcohol onto the reaction system, in situ determination re-
vealed that the characteristic absorption peak of MnTEPyP weak-
ened gradually, suggesting the consumption of oxidant active
species (MnIV@O) by substrate.19 In addition, color changes of the
reaction mixture from dark green to tinge also indicate valence
change of manganese. GC analysis of these reaction products re-
vealed the formation of benzoic acid and benzyaldehyde, indicative
of the presence of active oxidation species.
Based on these presented observations, a plausible reaction
mechanism for the oxidation of benzyl alcohol using water-soluble
manganese porphyrin (MnTEPyP) as catalyst was proposed (Fig. 4).
The reaction mechanism could involve the use of oxo-manganese
intermediate generated from the reaction between manganese
porphyrin and sodium periodate. The formation of benzaldehyde
was attributed to the reaction of benzyl alcohol with Mn-oxo spe-
cies, followed by the b-hydride elimination.10 Benzoic acid was
generated by the further reaction of benzaldehyde to Mn-oxo
species.
3.7. Plausible mechanism for controllable oxidation of benzyl
alcohol
In the blank experiments without catalyst, no products could be
detected for the oxidation of benzyl alcohol even if they were con-
ducted in either water or 1:5 mixture of toluene/water. Results
4. Conclusion
2.0
1.6
A controllable procedure for selective oxidation of alcohols to
acids or aldehydes has been developed in the presence of water-
soluble manganese porphyrin and sodium periodate with different
reaction media. A plausible reaction mechanism involved the for-
mation of Mn-oxo species has been proposed.
464nm
1.2
Acknowledgments
0.8
The authors thank the National Natural Science Foundation of
China (21036009 and 20976203), Higher-level talent project for
Guangdong provincial Universities and the Fundamental Research
Funds for the Central Universities for providing financial support to
this project.
562nm
600
0.4
0.0
400
450
500
550
650
References and notes
Wavelength(nm)
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H
Ph
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Figure 4. Plausible reaction mechanism for the oxidation of benzyl alcohol by
sodium periodate in the presence of MnTEPyP.

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