Non-metallic Aerobic Oxidation of Alcohols over Anthraquinone Based Compounds

Article abstract of DOI:10.1016/j.apcata.2019.117277

The catalytic performances of substituted anthraquinones were investigated in catalytic oxidation of alcohols like cyclohexanol, benzyl alcohol and 5-hydroxymethylfurfural (HMF) to carbonyl compounds (cyclohexanone, benzyl aldehyde and diformylfuran). The reduction potential of anthraquinone plays the key role in the oxidation reactions. TOF numbers and selectivities to carbonyl compounds pass through the maximum with increase of the reduction potential. The maximum activity and selectivity (>80 %) is observed for sulfonated and carboxylated anthraquinones having intermediate reduction potentials (≈ 0.1-0.2 V vs SHE). Grafted 2-carboxyanthraquinone catalyst has demonstrated comparable catalytic performance to the parent molecule and might be used as heterogeneous catalyst. The oxidation reaction was found to have radical character with transfer of hydrogen from alcohol to anthraquinone and subsequent oxidation of hydrogenated anthraquinone by oxygen.

Full text of DOI:10.1016/j.apcata.2019.117277

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Non-metallic Aerobic Oxidation of Alcohols over Anthraquinone Based
Compounds
´
Jingpeng Zhao, Dan Wu, Willinton Yesid Hernandez, Wen-Juan
Zhou, Mickael Capron, Vitaly V. Ordomsky
PII:
S0926-860X(19)30432-6
DOI:
https://doi.org/10.1016/j.apcata.2019.117277
APCATA 117277
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Applied Catalysis A, General
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Revised Date:
Accepted Date:
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20 September 2019
28 September 2019
´
Please cite this article as: Zhao J, Wu D, Hernandez WY, Zhou W-Juan, Capron M, Ordomsky
VV, Non-metallic Aerobic Oxidation of Alcohols over Anthraquinone Based Compounds,
Applied Catalysis A, General (2019), doi: https://doi.org/10.1016/j.apcata.2019.117277
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Non-metallic Aerobic Oxidation of Alcohols over Anthraquinone Based Compounds
Jingpeng Zhaoa,b, Dan Wua,b, Willinton Yesid Hernándeza, Wen-Juan Zhoua, Mickael Capronb* and
Vitaly V. Ordomskya*
a Univ. Lille, CNRS, Centrale Lille, ENSCL, Univ. Artois, UMR 8181 - UCCS - Unité de Catalyse et
Chimie du Solide, F-59000 Lille, France
b Eco-Efficient Products and Processes Laboratory (E2P2L), UMI 3464 CNRS-Solvay, 201108
Shanghai, People’s Republic of China
AUTHOR INFORMATION
*Corresponding author:
Dr Vitaly V. Ordomsky,
E-mail: vitaly.ordomsky-ext@solvay.com
Dr Mickael Capron
E-mail: mickael.capron@univ-lille.fr
Graphical Abstract
1

Highlights
 Substituted anthraquinones (AQ) were studied in non-metallic oxidation of alcohols
 The alcohols were converted to carbonyl compounds using oxygen as terminal oxidant
 Intermediate potentials of AQ (~0.2 V) provided highest activity and selectivity
 This effect is result of balance of hydrogen transfer to AQ and from AQ to oxygen
 Grafted AQ demonstrated comparable catalytic performance to the parent molecule
ABSTRACT:
The catalytic performances of substituted anthraquinones were investigated in catalytic oxidation of
alcohols like cyclohexanol, benzyl alcohol and 5-hydroxymethylfurfural (HMF) to carbonyl compounds
(cyclohexanone, benzyl aldehyde and diformylfuran). The reduction potential of anthraquinone plays the
key role in the oxidation reactions. TOF numbers and selectivities to carbonyl compounds pass through
the maximum with increase of the reduction potential. The maximum activity and selectivity (>80 %) is
observed for sulfonated and carboxylated anthraquinones having intermediate reduction potentials (≈
0.1-0.2 V vs SHE). Grafted 2-carboxyanthraquinone catalyst has demonstrated comparable catalytic
performance to the parent molecule and might be used as heterogeneous catalyst. The oxidation reaction
was found to have radical character with transfer of hydrogen from alcohol to anthraquinone and
subsequent oxidation of hydrogenated anthraquinone by oxygen.
KEYWORDS: Alcohols oxidation, substituted anthraquinone, reduction potential, carbonyl
compounds

1. Introduction
Green and selective oxidation techniques are highly important in the chemical industry, especially
in the transformation of alcohols to the carbonyl compounds which can sequentially constitute important
intermediates for the production of fine and bulk chemicals like amines, imines, acetals, polymers etc. A
large number of oxidants have been reported in the literature and most of them are based on transition
metal oxides, such as oxides of chromium and manganese[1] that incidentally creates issues related to
handling and disposal. For this purpose, many heterogeneous and homogenous catalysts have been
developed on the basis of noble metals such as Pt, Ru, Pd, Au, and Ag for oxidation of alcohols using
oxygen and hydrogen peroxide as terminal oxidant [2-6]. Utilization of metallic catalysts creates a serious
problems related to over oxidation of aldehydes to acids, high cost of the metal and its potential leaching
[7].
To achieve more productive processes, researchers have paid a lot of attention to non-metallic
systems, mainly including TEMPO and its derivative systems [8] that are efficiently used on industrial
scale for dehydrogenation of alcohols selectively to aldehydes and ketones [9]. In-situ regeneration of
nitroxyl radical is the main challenge for TEMPO application as a catalyst. For example, a system based
on TEMPO and Mn(NO3)2-Co(NO3)2 was reported [10] to provide oxidation of both aliphatic and
aromatic alcohols at mild reaction conditions, however, it requires very diluted alcohol solutions in acetic
acid and deactivates in time.
Similar to nitroxyl radicals, quinone molecules provide three readily accessible oxidation states
[11], namely, fully oxidized quinone, one-electron-reduced semiquinone, and two-electron-reduced
hydroquinone [Scheme 1]:
Scheme 1. Three accessible oxidation states of quinones molecules
3

Stoichiometric dehydrogenation of alcohols by electron deficient quinone molecules like DDQ
(i.e. 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone) has been studied in numerous works [12, 13]. However,
it leads to costly two-step process with necessary DDQ separation and regeneration. Several alternative
strategies have been proposed to avoid it using co-oxidants also known as electron transfer mediators like
FeCl3 and Mn(OAc)3 for re-oxidation of hydrogenated DDQ [14-16]. Thus, it solves the problem of
continuous utilization of DDQ as oxidant but produces large amount of waste. Several strategies have
been proposed to mediate oxidation of hydroquinones by using heterogeneous or homogeneous co-
catalysts such as metal nanoclusters or polyoxometalates [17-19]. The efficient oxidation of activated
alcohols has been reported over DDQ using NO and tBuNO2 to facilitate hydroquinone regeneration [20,
21]. However, all these routes involve presence of aggressive and non-environmentally friendly
compounds which restricts the wide application of these processes in industry. Recently they have been
used for photooxidation of alcohols to obtain carboxylic acids and aldehydes/ketones in an air atmosphere
[22]. However, the productivity of this system was low and accompanied by deactivation of the
anthraquinone catalyst.
The advantage of anthraquinones in comparison with DDQ is lower reduction potential which
could result in in-situ regeneration of these molecules during oxidation of alcohols. Although a lot of
research has been devoted to investigation of different anthraquinones as hydrogen acceptors in
electrochemistry [23] or intermediate molecule for hydrogen peroxide synthesis [24] there is no
information about anthraquinones as catalytic material in oxidation reactions.
Herein, we demonstrate efficient application of homogeneous and heterogenized non-metallic
substituted 9,10-anthraquinones catalyst for selective oxidation of alcohols (i.e., cyclohexanol, benzyl
alcohol and HMF). Oxygen is employed as terminal oxidant for oxidative regeneration of quinones, which
is cheap and eco-friendly solution for regeneration of catalyst during reaction. Anthraquinone supported
catalyst has demonstrated comparable activity and selectivity to the parent homogeneous molecule, which
is important for recycling of the material.
4

2. Experimental
2.1. Materials
The chemicals 2-ethylanraquinone (EQ), p-benzoquinone (BQ), 2,6-dihydroxyanthraquinone
(DAQ), disodium anthraquinone-2,6-disulfonate (SQ), aminopropyl-functionalized silica, anthraquinone-
2-carboxylic acid (CQ), biphenyl, benzyl alcohol, HMF, cyclohexanol, 1-octanol, toluene were purchased
from J&K Scientific Ltd. All commercially available alcohols and solvents used were purified by standard
procedures.
2.2. Synthesis of Supported Catalyst
The supported quinone catalyst (CQ/SiO2) was prepared by a grafting method. 1 g of commercially
available aminopropyl-functionalized silica having approximately 1 mmol/g amino groups was placed in
the vessel together with 50 mg of anthraquinone-2-carboxylic acid dissolved in 15 mL of toluene. The
mixture obtained was stirred overnight at ambient temperature. The catalyst has been separated by
centrifugation, washed with toluene and ethanol to remove traces of anthraquinone-2-carboxylic acid and
dried at 80 °C. The procedure is standard for the synthesis amide bond over silica surface [25].
2.3. Catalysis
Typically, CQ/SiO2 or organic quinone (EQ, BQ, DAQ, CQ or SQ) compound was added into 30
mL autoclave together with 2 g of alcohol and 1 g of toluene as a solvent or 1 g of DMSO with 0.3 g of
water have been used as a solvent for SQ. The reactor was sealed and pressurized with O2 and heated to
appropriate temperature for 1~24 h under continuous stirring. The products of reaction have been filtered
after reaction and analyzed by GC with HP-5 column using biphenyl as internal standard. The products
have been identified by comparison of their residence time with individual compounds and GC-MS
analysis.
The stability of the grafted catalyst has been tested for 3 times by filtering of the catalyst after each
cycle with subsequent addition to the fresh alcohol mixture for the next test as described in oxidation of
cyclohexanol. Reaction products after filtering were quantitatively analyzed by GC and GC-MS with
biphenyl as the internal standard.
5

2.4. Characterization
Thermogravimetric analysis (TG) measurements were performed using a SDT 2960 analyzer from
TA instrument under air flow (50 mL∙min-1) with a ramping rate of temperature of 10 °C·min-1. FTIR
spectra were recorded using a Thermo Fisher Scientific Nicolet 6700 FTIR (16 scans at a resolution of 4
cm−1) equipped with a MCT detector. The pellets have been prepared using KBr. The morphologies and
particle size distribution of the catalysts were measured with JEOL 2100 transmission electron microscope
(TEM) with an accelerating voltage of 200 kV. X-ray diffraction (XRD) was used to characterize the
lattice structure. XRD patterns were recorded on a Rigaku D/max-2200/PC diffractometer using Cu Kα
radiation (λ = 1.5418 Å) operating at 20 kV. Solid State MAS NMR were recorded on a Bruker Avance
400 spectrometer. For 1H NMR spectrum, one pulse sequence has been applied, for 13C, we used CP MAS
1
sequence. Chemical shifts are given in ppm with respect to TMS as external reference for H and 13 C
NMR.
3. Results and discussion
3.1. Oxidation of alcohols over EQ
2-ethylanraquinone (EQ) has been used as a model compound for oxidation of cyclohexanol.
Figure 1 shows the results of cyclohexanol oxidation over EQ with variation of the main reaction
parameters like catalyst amount, temperature, oxygen pressure and reaction time. The key role of
anthraquinone and oxygen for the cyclohexanol oxidation reaction has been verified by catalytic test with
and without EQ and/or oxygen (Table S1, SI). The reaction did not proceed without oxygen or EQ. GC
analysis of EQ after reactions has shown that it does not transform during reaction and might be
considered as a catalyst (Figure S1, SI). Hydrogen peroxide has not been identified in the products of the
reaction, which could be the result of its fast decomposition with formation of oxygen and water.
First of all, we have found that the reaction is highly sensitive to oxygen pressure. The catalytic
activity increases dramatically with increase of the oxygen pressure up to 10 bar with no changes
afterwards (Figure 1a). Necessity of high pressure of oxygen might be explained by difficulties in transfer
6

of hydrogen from alcohol to oxygen through EQ molecule. Low pressure of oxygen is not enough to shift
the equilibrium of the reaction toward formation of aldehyde and water.
The reaction starts to take place only at the temperatures higher than 100 °C with 67 % conversion
of cyclohexanol at 150 °C after 12 h of test (Figure 1b). The main reaction product was cyclohexanone
with selectivity close to 90 % at low conversions (Figure S2, SI). Increase of the conversion (Figure 1d)
by variation of the reaction time resulted in decrease of the selectivity due to side reactions as cycle
opening leading to formation of adipic and hexanoic acid and their esters with cyclohexanol due to
esterification reaction.
It is interesting to note that increase of the amount of catalyst leads to increase of the activity only
till 1 mol/mol % with no further increase of the conversion at higher loading (Figure 1c). The maximum
conversion about 30 % is similar for variation of oxygen pressure and catalyst loading, which can be
explained by poisoning effect of the product cyclohexanone as carbonyl compound on the catalytic
activity. Increase of the time of the test results in increase of the conversion but it is mainly due to
formation of the products of deeper oxidation. To verify this hypothesis, we have conducted an experiment
with addition of cyclohexanone as an example of carbonyl compound during oxidation of benzyl alcohol
(Table S2, SI). The result showed that benzaldehyde production reduced by half in the presence of 10
wt. % of cyclohexanone, which clearly indicates an inhibition of the alcohol oxidation reaction by other
carbonyl compounds. The possible explanation could be in the hindrance of hydrogen abstraction in the
presence of another carbonyl group except anthraquinone in the proximity to alcohol.
Reduction potential of quinone based molecules should play an important role for the reaction of
hydrogen transfer as has been demonstrated earlier [11]. The substituted derivatives of quinones with
electrophilic and nucleophilic groups with different reduction potentials have been tested in alcohols
oxidation hereafter.
3.2. Effect of electrochemical potential of quinones on alcohol oxidation
Several commercially available anthraquinones with different groups have been used in this work
(Table 1). 1,4-benzoquinone (BQ) is a simplest quinone containing two carbonyl groups in the ring.
7

Disodium anthraquinone-2,6-disulfonate (SQ) contains two sulfo groups attached to anthraquinone
molecules at 2 and 6 carbon atom positions. 2,6-dihydroxyanthraquinone (DAQ) contains hydroxyl
groups at the same positions. Anthraquinone-2-carboxylic acid (CQ) contains one carboxylic group at the
second position.
The reduction potentials of the molecules vs standard hydrogen electrode (SHE) have been
calculated on the basis of Gibbs energy of the reaction:
AQ + 2H+ + 2 e = AQH2,
and taking into account E0 = -dG/2·F – 4.42 V.
The results correlate well with experimentally determined numbers for the reduction potentials of
known quinones (Table 1) [26]. BQ has the highest potential (i.e. 0.65 V) with high stability of formed
para-hydroquinone. Presence of electron donating hydroxyl groups leads to decrease of the potential of
DAQ to -0.042 V. EQ provides similar reduction potential of 0.043 V. Presence of electrophilic groups for
SQ and CQ as expected leads to intermediate reduction potentials between BQ and EQ at 0.21 and 0.12
V, respectively.
Figure 2 demonstrates the correlation between TOF numbers in cyclohexanol oxidation to
cyclohexanone and reduction potentials of quinones (Table 2). The reaction has been performed in the
presence of small amount of toluene to dissolve anthraquinones. DMSO as a solvent has been used only
in the case of SQ due to low solubility of this anthraquinone in toluene. The solvents have to be aprotic
in order to avoid competition with alcohols for interaction with anthraquinones. As might be observed the
curve has volcano form with the highest activity over anthraquinones containing carboxy (CQ) and sulfo
(SQ) groups with intermediate values of reduction potentials around 0.1-0.2 V. Benzoquinone which has
the highest reduction potential and highest stability of hydrogenated form has the lowest activity in the
reaction of cyclohexanol oxidation. At the same time, hydrogenated form of EQ has significantly lower
stability and is easy to oxidize at room temperature with formation of hydrogen peroxide and initial form
of EQ. Efficient oxidation of alcohols according to proposed scheme of the reaction should involve
hydrogenation and oxidation of reduced anthraquinone. In this case high efficiency of intermediate
8

reduction potentials for SQ and CQ might be explained by the fact that both reduction and oxidation steps
proceed with high rates without limitations [27].
Figure S3, SI presents selectivity of cyclohexanol, benzyl alcohol and HMF oxidation to carbonyl
compounds versus conversion over EQ. The selectivity decreases with increase of alcohol conversion for
all alcohols. Depending on the type of alcohol the by-products of the reaction are different (Table 2). Thus,
cyclohexanol during oxidation is accompanied by cycle opening leading to formation of hexanoic acid
and adipic acid and subsequent esters formation. These products recall the process of radical synthesis of
adipic acid through cycle opening of cyclohexyl peroxide [28]. Besides it, 2-cyclohexenone has been
detected as a side product of the reaction with significant amount in the case of BQ as a catalyst. This
effect might be explained by deep dehydrogenation of cyclohexanone by BQ possessing high reduction
potential. In the case of benzyl alcohol the main side reaction is deep oxidation to benzoic acid and ester
formation. Formation of benzyl ether might be explained by coupling of benzyl alcohol radicals. HMF
oxidation resulted mainly in stepwise oxidation of carbonyl groups to 2,5-diformylfuran (DFF) and
formation of 2,5-furandicarboxylic acid as a final product of the reaction.
The selectivity trends for oxidation of alcohols over quinones are similar to those observed for
TOF numbers with decrease of the selectivity to carbonyl compounds for high and low reduction
potentials (Figure 2). Thus, selectivity to cyclohexanone, benzaldehyde and DFF reaches 85-90 % during
oxidation of corresponding alcohols over CQ and SQ at high conversions. The high selectivity might be
explained by high rate of hydrogen transfer from alcohol to anthraquinone and subsequent oxidation of
hydrogenated form of anthraquinone. Application of anthraquinones with low or high reduction potentials
should result in the higher residence time of radical form of alcohol or peroxo radical. It should induce
deeper oxidation of alcohols, cycle opening and coupling with formation of ether.
3.3. Supported anthraquinone for oxidation
The heterogeneous catalysts have significant advantages for catalytic application due to easy
separation and possibility to use it in continuous flow reactors, which significantly reduce the cost of the
process. In order to verify if quinone might be used as supported catalyst in the reaction, we have prepared
9

grafted CQ to amino functionalized silica and tested this catalyst in the reactions of alcohols oxidation.
The catalyst has been prepared by treatment of aminopropyl-functionalized silica containing 1 mmol/g of
amino groups by CQ to form amide group for grafting of anthraquinone species (Figure 3). The prepared
1
13
catalyst has been characterized by solid H and C NMR, FTIR spectroscopy and TG analysis. Taking
into account molecular weight of CQ, the catalyst should contain about 21 wt. % of organic species on
the surface (Figure 3). TG analysis shows several losses of weight at 265, 400 and 560 °C corresponding
to decomposition and burning of organic species with a total mass decrease of ~17 wt. % which
corresponds well to the theoretical content of organic phase.
Solid 1H NMR analysis demonstrates presence of a broad peak with several maximums at 7.6, 5.5,
3.7 and 1.1 ppm (Figure 4). The peaks at highest chemical shift at about 8 ppm can be assigned to protons
in aromatic ring of anthraquinone [29]. The strong peak at 5.5 ppm is usually result of the presence of
adsorbed water and silanol groups of silica [30]. The protons of aliphatic propyl group should provide
signals in the range from 0 to 3 ppm depending on the distance from Si. The 13C CPMAS NMR spectrum
(Figure 4) exhibits clearly resolved 3 group of peaks with high (182 and 168 ppm), medium (133 and 126
ppm) and low chemical shifts (9, 22 and 44 ppm). The first group can be assigned to carbon in carbonyl
group of anthraquinone and amide. The peaks at about 130 ppm can be attributed to carbon of aromatic
rings of anthraquinone. The carbon atoms of aliphatic linker should provide peaks at low chemical shift.
The initial CQ has FTIR spectrum (Figure 5) with the bands corresponding to C=O in carboxylic
group and anthraquinone at 1695 and 1675 cm-1, respectively, with OH deformation bending from
carboxylic group at 1432 cm-1 [31], while the one at 1590 cm-1 might be due to C = C stretching of a
quinone ring. The group of bands at 1325, 1273 and 1250 cm-1 can be attributed to C-O stretching and C-
H deformation vibrations [32-34]. The prepared material after CQ grafting besides bands related to Si-O
modes in silica at 1065 and 797 cm-1 have similar set of bands to CQ at 1675 and 1590 cm-1. The emerging
bands at 1540 and 1640 cm-1 might be attributed to C-N and C=O vibrations in the new amide group [35,
36]. The band related to O-H vibration in carboxylic group at 1432 cm-1 disappears after CQ deposition
10

which indicates on formation of amide bond and successful grafting of CQ over aminopropyl-
functionalized silica.
XRD analysis indicates on amorphous nature of prepared catalyst CQ/SiO2 with uniform
distribution of anthraquinone species on the surface of silica (Figure S4, SI) in comparison with CQ-SiO2
prepared by simple impregnation method. CQ-SiO2 exhibits diffraction peaks at 8.7 o, 11.9 o, 15.3 o, 26.8
o, 39.8 o assigned to CQ [37].
The catalyst with supported CQ demonstrates TOF numbers similar to those of the parent CQ
(Table 2). The calculated reduction potential of grafted CQ (0.087 V) is lower in comparison with parent
CQ molecule due to electron donating properties of NH2- group. The high activity of supported
anthraquinone molecules could be explained by decrease of the poisoning effect of carbonyl groups of
isolated anthraquinone molecules on each other over silica surface in comparison with homogeneous
counterpart. The increase of the conversion versus amount of the catalyst supports this assumption
(Figure 6). The selectivities in oxidation of alcohols over CQ/SiO2 are similar to those over CQ (Table
2).
The stability of the catalyst has been demonstrated by catalytic tests in 3 cycles with intermediate
separation of supported CQ/SiO2 (Figure 7). The catalyst shows comparable conversion and selectivity
in all cycles. These results demonstrate high potential of application of grafted quinones as selective
heterogeneous catalyst in alcohols oxidation.
3.4. Mechanism of the reaction
To support that the oxidation mechanism has radical character, a series of experiments were carried
out with cyclohexanol as the model compound. The well-known radical scavengers like phenol [38] have
been used as additives (Table S3, SI). The presence of these compounds resulted in almost total
suppression of catalytic activity of EQ in oxidation of cyclohexanol. Thus, these results show the key role
of radical species forming in the presence of anthraquinones in oxidation of alcohols to carbonyl
compounds.
11

The possible mechanism of the reaction could involve stepwise process with abstraction of
hydrogen to hydrogenated form of anthraquinone with subsequent regeneration of anthraquinone by
oxidation with formation of peroxy species decomposing to water and oxygen. In order to verify this
assumption we have conducted experiment by treatment of benzyl alcohol in the presence of high amount
of SQ in inert atmosphere (Table S4, SI). The aldehyde was the only product of the reaction and
conversion of benzyl alcohol was about 10 % of SQ amount. In comparison with DDQ the reduction
potential for anthraquinones is relatively low and hydrogenated form is less stable. In order to shift the
equilibrium of the reaction the hydrogenated form has to be continuously oxidized with formation of water.
It explains strong effect of oxygen pressure on the catalytic activity (Figure 1).
Based on the above experimental observations, we propose a radical mechanism for the quinone-
induced catalytic oxidation of alcohols to carbonyl compounds which is described on the Figure 8. The
mechanism might involve quinone-prompted electron-transfer reaction through activation of C-H and O-
H bond over electron-deficient carbonyl group of SQ with subsequent fast oxidation with formation of
peroxy-species by oxygen attack.
4. Conclusion
The substituted anthraquinone molecules have been studied in non-metallic oxidation of alcohols.
The oxidation of benzyl alcohol to benzaldehyde, cyclohexanol to cyclohexanone and HMF to DFF
proceed with the highest activity and selectivity (>80 %) over sulfonated and carboxylated anthraquinone
molecules. This effect has been explained by intermediate reduction potentials, which should provide a
well balance hydrogen rate transfer from alcohol to anthraquinone and from anthraquinone to oxygen.
The radical mechanism of oxidation over anthraquinones has been demonstrated in this work by addition
of radical scavengers. Finally, grafted anthraquinone has been used as efficient catalyst in oxidation of
alcohols.
12

ACKNOWLEDGMENT
The authors thank Solvay for financial support of this work. J.Z. is grateful to the CIFRE scholarship. The
authors thank Raphael Wischert for calculation of reduction potentials.
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15

Figure 1. Cyclohexanol oxidation over EQ with variation of oxygen pressure (T=130 °C, 1 mol/mol %,
12 h) (a), temperature (1 mol/mol %, 12 h, p(O2)=10 bar) (b), catalyst amount (T=130 °C, p(O2)=10 bar,
12 h) (c) and time (T=130 °C, 1 mol/mol %, p(O2)=10 bar) (d)
16

Figure 2. Correlation between reduction potentials of quinones and TOF numbers of alcohols oxidation
(a) and selectivities to carbonyl compounds at comparable conversion 60 % (b). Conditions: cyclohexanol
(T=130 °C, 1 mol/mol %, p(O2)=10 bar, 2h), benzyl alcohol (T=150 °C, 1 mol/mol %, p(O2)=10 bar, 2h)
and HMF (T=130 °C, 1 mol/mol %, p(O2)=10 bar, 2h)
17

Figure 3. Structure of grafted CQ (a) and TGA curves of supported CQ/SiO2 (b)
18

7
Figure 4. Solid 1H and 13C CPMAS NMR spectrum of CQ/SiO2
19

Figure 5. Scheme of CQ/SiO2 and FTIR spectroscopy of supported CQ/SiO2 and CQ
20

45
40
35
30
25
20
15
10
5
0
0.0
0.4
0.8
1.2
1.6
Catalyst amount, mol supported CQ, mol %
Figure 6. Cyclohexanol oxidation activity over supported CQ/SiO2 with variation of catalyst
amount (T=130 °C, p(O2)=10 bar, 12 h).
21

Conversion, %
Selectivity to cyclohexanone, %
80
70
60
50
40
30
20
10
0
1
2
3
Cycles
Figure 7. Catalytic results of cyclohexanol oxidation over CQ/SiO2 for several cycles with separation of
the catalyst by centrifugation (T=130 °C, 0.5 mol/mol %, p(O2)=10 bar, 12h)
22

Figure 8. Scheme of oxidation of alcohol by anthraquinone based compounds
23

Table 1. Reduction potential of used quinones
Entry
1
Quinones
Formula
Reduction
potentials /
V (vs SHE)
0.65
BQ
2
3
SQ
0.21
0.12
CQ
4
5
EQ
0.043
DAQ
-0.042
24

Table 2. The catalytic results of oxidation of cyclohexanol, benzyl alcohol and HMF over anthraquinone
based molecules at the conversion of substrate about 60 %
Substrate
Catalyst TOF, h-1
Selectivity, mol.%
O
HO
OH
O
and esters
and esters
a
BQ
SQb
CQ
0.6
8.5
5.7
2.9
2.2
6.0
32
75
74
44
43
76
57
6
4
6
33
5
8
0
7
2
11
25
1
3
2
3
5
3
EQ
DAQ
CQ/SiO2
c
BQ
SQd
CQ
2.1
9.5
13
2
2.2
16
28
65
52
43
32
57
25
2
8
18
11
3
31
3
13
18
15
16
16
25
23
6
26
11
EQ
DAQ
CQ/SiO2
a
BQ
SQb
CQ
0.15
2.5
2.9
0.16
0.11
3.4
28
76
83
27
42
88
31
12
29
15
4
23
56
4
6
10
28
0
0
0
2
0
0
EQ
DAQ
CQ/SiO2
7
a substrate 2 g, catalyst 50 mg and 1 g toluene as solvent, 130 °C, time 1-24 h
b substrate 2 g, catalyst 50 mg and 1 g DMSO and 0.3 g H2O as solvent, 130 °C, time 1-24 h
c substrate 2 g, catalyst 50 mg and 1 g toluene as solvent, 150 °C, time 1-24 h
d substrate 2 g, catalyst 50 mg and 1 g DMSO and 0.3 g H2O as solvent, 150 °C, time 1-24 h
25