Vinylation of phenol by acetaldehyde: A new reaction for the synthesis of o-vinylphenol

Article abstract of DOI:10.1016/j.catcom.2016.08.006

A new catalytic reaction for the single-step synthesis of o-vinylphenol from phenol and acetaldehyde in the gas phase is investigated in this work. A search for an efficient catalyst was made. The best results were obtained with a modified Cr₂O₃ catalyst supported on γ-Al₂O₃. The effect of content of Cr₂O₃ and potassium as a modifying additive was studied. It was shown that the catalyst containing 13% Cr₂O₃ and 1% K makes it possible to obtain o-vinylphenol with a selectivity of 100% referred to phenol and up to 87% referred to acetaldehyde. The influence of reaction conditions on the activity, selectivity and stability of catalyst operation was elucidated.

Full text of DOI:10.1016/j.catcom.2016.08.006

Vinylation of phenol by acetaldehyde: ¡!–[INS][a]–¿A¡!–[/INS]–¿ new
reaction for the synthesis of o-vinylphenol
Mikhail V. Parfenov, Larisa V. Pirutko, Igor E.Soshnikov, Eugeny V.Starokon,
Alexander S. Kharitonov, Gennady I. Panov
PII:
DOI:
Reference:
S1566-7367(16)30264-3
doi: 10.1016/j.catcom.2016.08.006
CATCOM 4736
To appear in:
Catalysis Communications
Received date:
Revised date:
Accepted date:
17 June 2016
3 August 2016
4 August 2016
Please cite this article as: Mikhail V. Parfenov, Larisa V. Pirutko, Igor E.Soshnikov,
Eugeny V.Starokon, Alexander S. Kharitonov, Gennady I. Panov, Vinylation of phenol by
acetaldehyde: ¡!–[INS][a]–¿A¡!–[/INS]–¿ new reaction for the synthesis of o-vinylphenol,
Catalysis Communications (2016), doi: 10.1016/j.catcom.2016.08.006
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ACCEPTED MANUSCRIPT
Vinylation of phenol by acetaldehyde: a new reaction for the synthesis
of o-vinylphenol
Mikhail V. Parfenov*, Larisa V. Pirutko, Igor E. Soshnikov, Eugeny V. Starokon, Alexander
S. Kharitonov, Gennady I. Panov
Boreskov Institute of Catalysis, Novosibirsk 630090, Russia
*
Corresponding author. Address: Boreskov Institute of Catalysis, Prospect Akademika Lavrentieva, 5, Novosibirsk
30090, Russia. Fax: +73833269600/3308056. E-mail address: parfenov@catalysis.ru
6
Abstract
A new catalytic reaction for the single-step synthesis of o-vinylphenol from phenol and
acetaldehyde in the gas phase is investigated in this work. A search for an efficient catalyst was
made. The best results were obtained with a modified Cr O catalyst supported on γ-Al O . The
2
3
2
3
effect of content of Cr O and potassium as a modifying additive was studied. It was shown that
2
3
the catalyst containing 13% Cr O and 1% K makes it possible to obtain o-vinylphenol with a
2
3
selectivity of 100% referred to phenol and up to 87% referred to acetaldehyde. The influence of
reaction conditions on the activity, selectivity and stability of catalyst operation was elucidated.
Keywords: Vinylphenol; Phenol; Acetaldehyde; Monomer.
1
. Introduction
Incorporation of the vinyl CH =CH− group into the molecule of a substance allows
2
obtaining monomers for polymerization reactions and building blocks for fine chemistry. Long-
term studies have been performed to find the vinylation methods that are most topical for
aromatic compounds. Well arranged and efficient processes have been devised for the synthesis
of the simplest substances of this type, for example, styrene [1]. Methods for obtaining more
complicated compounds with heteroatoms are under development [2–5].
1
Of particular interest are vinylphenols (VPh) – the substances whose molecules include
two functional groups bound to the aromatic ring: hydroxyl and vinyl ones. Depending on
relative positions of these groups, three isomers of vinylphenol can exist: para-, meta- and ortho-.
1
Abbreviations: VPh – vinylphenol; p-VPh – p-vinylphenol; o-VPh – o-vinylphenol; m-VPh – m-vinylphenol; AA
–
acetaldehyde.
1

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Such a bifunctional structure determines wide possibilities in the application of these
compounds.
Vinylphenols are used as precursors in the production of medicinal substances and
materials for cosmetic and food industries. Polymers based on vinylphenols – polyvinylphenols –
are employed to obtain photosensitive materials, in the production of liquid crystals, antibacterial
polymers, etc. [6].
The available methods used for the synthesis of vinylphenols are quite complicated. Only
the synthesis of p-vinylphenol (p-VPh) is implemented on industrial scale. One of the early
methods of p-VPh production is based on decomposition of Bisphenol-E (1,1-bis(4-
hydroxyphenyl)ethane). This method gives a complex mixture of products with a significant
degree of resinification; the recovery of the target p-VPh from this mixture is quite difficult [7].
Another method is based on electrophilic acylation of phenol followed by the reduction of
ketone to alcohol and dehydration of the latter. Although this is a complex multi-step process,
the indicated method has been implemented by Maruzen Petrochemicals Co. [6,8].
Only the preparative methods are available for the production of other vinylphenol
isomers – o-VPh and m-VPh; this strongly limits the application of such substances. It seems
that the first method of o-vinylphenol synthesis was decarboxylation of 2-hydroxycinnamic acid
[
9]. Later, the reaction of phenol with ethylene oxide catalyzed by sulfuric acid [10] was
proposed as a method of o-vinylphenol synthesis. However, all attempts to reproduce results of
this work have failed [11–13]. A method of direct vinylation of phenol and its derivatives using
acetylene was also proposed. The reaction is performed in the liquid phase in organic solvents
(
acetonitrile, chlorobenzene) in the presence of SnCl and Bu N [6,14]. The reaction proceeds
4 3
with a yield up to 80%, probably referred to phenol. However, the use of explosive acetylene and
the necessity to run the reaction in the liquid phase may limit the application of this method.
In this work, we explored the reaction of catalytic gas-phase condensation of phenol with
acetaldehyde (AA) that was recently discovered by our research team. The main product of this
transformation is o-VPh (equation 1).
OH
OH
O
Catalyst
H O
(1)
-
2
H
2
. Experimental
γ-Al O (Sasol Germany GmbH) was used as a support for the catalysts. The catalysts
2
3
were prepared by incipient wetness impregnation of the support with aqueous solutions of
2

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appropriate salts or acids. Details of catalyst preparation and characterization (including
chemical composition, textural characteristics and XRD data) are summarized in Supporting
Information.
The catalytic experiments were carried out in a flow setup with on-line chromatographic
analysis of the gas phase. Gas lines of the setup were mounted in an oven heated to 200°C. A
3
preliminarily weighed 0.5 cm catalyst sample was placed in a tubular quartz reactor. The initial
reaction mixture contained 2 mol.% AA and 8 mol.% phenol. The total flow rate of the reaction
3
mixture through the reactor was 30 cm /min. For more details about catalysts pretreatment,
products identification, and calculation of reaction parameters, see Supporting Information.
3
. Results and Discussion
3
.1. Preliminary experiments
Table 1 lists data of preliminary experiments on the reaction of phenol with acetaldehyde.
In run 1, a mixture containing 2% AA and 8% phenol was fed to the 2%Pt/A O catalyst. A
2
3
consumption of AA and phenol was observed; their conversions were not higher than 10 and
0
3
.9%, respectively. o-VPh was detected in the reaction products, the selectivity for o-VPh was
4%. Other products of the reaction were represented by crotonal and a considerable amount of
other substances with a low concentration. According to the NMR and GC-MS data (see
Supporting Information), o-VPh is a single product of phenol conversion, while the other
products are formed due to side transformations of AA.
We suggested that o-VPh was formed due to a reaction between AA and phenol. To
verify this assumption, the following experiments were carried out. The initial mixture
containing 2% AA in helium and not containing phenol was fed to the same 2%Pt/A O catalyst.
2
3
As seen from Table 1, run 2, in this case the conversion of AA increased to 86%. A complex
mixture of products was formed. We did not made its detailed analysis; it should be noted only
that the mixture contained a significant amount of crotonal. In the next experiment (Table 1, run
3
), the initial mixture containing 8% phenol in helium and no AA was fed to the catalyst. One
can see that in this case the reaction did not proceed (neither the conversion of phenol, nor the
formation of any products were observed). These results indicate that o-VPh formation is a result
of the reaction between AA and phenol.
In order to elucidate whether the formation of o-VPh can occur in the gas phase without
catalyst, an appropriate experiment was performed. As seen from Table 1, run 4, in the absence
of catalyst neither the conversion of AA or phenol nor the formation of products take place.
3

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In run 5 (Table 1), the catalyst was represented by pristine Al O . It is seen that in this
2
3
case o-VPh is not formed, only a weak conversion of AA into by-products (essentially crotonal)
is observed. Hence, the deposition of active component is necessary to obtain o-VPh.
3
.2. Effect of the nature of the catalyst active component
We screened a series of catalysts represented by metals and metal oxides supported on
Al O . To compare the catalysts, a similar amount of the deposited component was used, 2 wt.%.
2
3
Since the first catalyst used in our work contained Pt, we primarily tested other noble
metals: Pd and Ru (see Table 2, runs 2 and 3). These samples did not show good results. On the
% Pd/Al O sample, both the conversion of AA and the selectivity for o-VPh were not high
2
2
3
(taking into account that selectivity for o-VPh referred to phenol was close to 100%, hereinafter
selectivity for o-VPh will imply the selectivity referred to AA). On 2% Ru/Al O , the AA
2
3
conversion reached 34% at a selectivity for o-VPh of 19%.
The screening was continued with a series of metal oxides (V, Mn, Co, Ni, Cr) supported
on A O . The results are listed in Table 2, runs 4-8. It is seen that o-VPh forms on all the
2
3
catalysts; however, the catalysts have radically different activity and selectivity. Samples
%V О /Al O and 2% NiО/Al O showed a moderate activity toward AA, but their selectivity
2
2
5
2
3
2
3
for o-VPh was very low. On the other hand, 2% MnО/Al O and 2% CoО/Al O were
2
3
2
3
characterized by a low activity, but selectivity for o-VPh on these samples was close to 50%.
Of particular interest are the results observed for the 2% Cr О /Al O sample. At the AA
2
3
2
3
conversion near 20% the selectivity for o-VPh exceeded 60%. This made the chromium catalyst
most promising for a further investigation.
3
.3.Optimization of chromium catalysts
Table 3 lists the results of experiments with the modified chromium catalysts.
The effect of chromium oxide content, which was varied from 2 to 17 wt.%, on the
reaction performance was studied. The results are listed in Table 3 (runs 1-5) and on Fig. 1a. One
can see that an increase in the chromium oxide content strongly enhanced the activity of the
sample. Thus, the conversion of AA increased from 21 to 49%. Therewith, a change in the
chromium oxide content from 13 to 17% increased the AA conversion only from 47 to 49%. The
selectivity for o-VPh also depended on the chromium oxide content. A change in the Cr O
2
3
content from 2 to 13% exerted virtually no effect on the selectivity, which remained at a level of
60%. Meanwhile, a further increase in the chromium oxide content produced a considerable
drop in selectivity, to 52%. Thus, for this catalyst the optimal content of chromium oxide was
~
4

ACCEPTED MANUSCRIPT
1
3 wt.%. Selectivity for crotonal somewhat decreased with increasing the amount of chromium
oxide.
Quite a low (ca. 60%) selectivity of the reaction on chromium catalysts is caused by side
reactions of AA on the catalyst surface. This may be related to some acidity of the catalyst
surface. We tried to improve the selectivity by modifying the catalyst via the deposition of
potassium. The 13% Cr О /Al O sample was chosen for the study. Results of these experiments
2
3
2
3
are presented in Table 3 (runs 6-8) and on Fig. 1b. It is seen that modification of the sample
substantially suppressed its activity (AA conversion decreased from 47% on non-modified
sample to 7.0% on the sample containing 1.5% K). Selectivity for o-VPh increased upon addition
of potassium and reached 83% at a K content of 1.0%. A further increase in the amount of the
modifier somewhat decreased the selectivity. Thus, the optimal content of potassium was 1.0%.
3
.4. Effect of temperature
The effect of temperature on the reaction of AA with phenol was studied on the
3%Cr O , 1%K/Al O sample in the temperature region from 300 to 400°C with a step of 25°C.
1
2
3
2
3
The results are presented in Table 4. One can see that raising the temperature strongly increased
the conversion of AA (from 14 to 41%) with a moderate decrease in the selectivity for o-VPh
from 87 to 81%. The main by-product was crotonal. Selectivity for this product slightly changed
in the course of reaction; hence, selectivity for o-VPh decreased due to formation of other by-
products. Data of Table 4 allow calculating the apparent activation energy of the reaction, which
was equal to 16.3 kcal/mol. For more details see Supporting Information.
3
.5. A study of catalyst stability
Taking into account high reactivity of both the reactants (AA) and products (o-VPh) as
well as their ability to polymerization and catalyst coking, it seemed interesting to estimate their
operational stability. Fig. 2 displays results of the experiment on stability of the 13%Cr O ,
2
3
1
%K/Al O catalyst. The reaction was conducted for 5 hours. In the first two hours, the catalyst
2 3
activity decreased (AA conversion dropped from 32 to 14%) and then remained virtually
constant. Selectivity for o-VPh showed a slight decrease in the experiment, from 84 to 78%.
It should be noted that high activity upon deactivation of the catalyst can be ensured by
raising the temperature, because on this catalyst the selectivity decreases slightly with
temperature elevation.
5

ACCEPTED MANUSCRIPT
Conclusion
In this work, the single-step gas-phase synthesis of o-VPh from phenol and acetaldehyde
has been discovered and studied for the first time. A wide-scope screening of the catalysts
supported on γ-Al O , including noble metals and metal oxides, was performed. The best results
2
3
were observed for the chromium oxide catalyst modified with potassium, which made it possible
to obtain o-VPh with a selectivity up to 100% for phenol and up to 87% for acetaldehyde.
However, it cannot be ruled out that optimization of the catalyst and reaction conditions could
give even more interesting practical results. In addition, crotonal, which is the main by-product
of the reaction, is also a valuable compound and can readily be recovered from the reaction
mixture.
It should be noted that the development of a simple and efficient method for the synthesis
of o-VPh could significantly reduce the cost of this substance and open new ways of its
application both in polymerization reactions and as an intermediate in the fine chemistry
reactions.
The nature of catalyst active sites and mechanism of the reaction are not discussed in this
work but could be found in further more detailed studies using a set of physicochemical methods
and quantum-chemical calculations.
Acknowledgments
We thank A. S. Noskov for useful discussion, M. V. Shashkov for GC-MS analysis, and T. Yu.
Kardash for XRD analysis. This work was supported by RAS and FASO (Project No. V.44.2.3).
6

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[
[
[
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[
[
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[
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[
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[
11] A.M. Bader, Unsaturated Phenols. II.1 Attempted Syntheses of o-Vinylphenol, J. Am.
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[
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7

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Figures
Fig. 1. The dependence of activity and selectivity of catalyst vs
a) the Cr O content
2
3
b) the K content
Fig. 2. The time dependence of o-VPh formation parameters at 375°C on the 13%Cr O ,
2
3
1
%K/Al O sample.
2 3
8

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Table 1. Preliminary experiments, 375°С, contact time 1 s, reaction time 30 min
Composition
No.
Sample
X(AA), %
10
X(PhOH), % S (o-VPh), %
34
of initial mixture
2% AA + 8%
phenol in He
2% AA in He
8% phenol in He
2% AA + 8%
phenol in He
2% AA + 8%
phenol in He
1
2
% Pt/Al O
2
3
0
.9
2
3
4
2% Pt/Al O
86
-
0.0
0.0
2
3
0
0
.0
.0
2% Pt/Al O
2
3
no catalyst
0.0
3.0
-
0
0
.0
.0
5
Al O
0.0
2
3
Table 2. Preliminary experiments, 375°С, contact time 1 s, reaction time 30 min. Composition of
the initial mixture 2% AA + 8% phenol in He
No.
1
Sample
X(AA), % X(PhOH), % S (o-VPh), %
2% Pt/Al O
10
14
34
11
7.0
2.0
20
21
34
5.0
19
2
3
0
0
1
0
0
0
0
3
.9
.2
.6
.1
.9
.3
.2
.2
2
2% Pd/Al O
2 3
3
2% Ru/Al O
2 3
4
2%V О /Al O
3
5.0
54
2
5
2
5
2% MnО/Al O
2
3
6
2% CoО/Al O
52
2
3
7
2% NiО/Al O
4.0
61
2
3
8
2% Cr О /Al O
2 3 2 3
9

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Table 3. Properties of Cr O samples, 2% AA + 8% phenol in He, 375°С, contact time 1s,
2
3
reaction time 30 min
No.
Sample
X(AA),
%
X(PhOH),
%
S (o-VPh), S (crotonal),
%
61
61
60
58
52
66
83
79
%
16
18
17
15
14
16
14
21
1
2
3
4
5
6
7
8
2% Cr О /Al O
2 3 2
3
3
3
2
3
4
4
1
5
4
7
3.2
5.3
6.6
6.8
5% Cr О /Al O
2
3
2
9% Cr О /Al O
2
3
2
13% Cr О /Al O
2
3
2
3
17% Cr О /Al O
49
39
28
7.0
2
3
2
3
6
6
5
1
.4
.4
.8
.4
13%Cr O , 0.5%K/Al O
2
3
2
3
13%Cr O , 1%K/Al O
3
2
3
2
13%Cr O , 1.5%K/Al O
2
3
2
3
Table 4. Effect of temperature on reaction performance. Sample 13%Cr O , 1%K/Al O , 2% AA
2
3
2
3
+
8% phenol in He, contact time 1s, reaction time 30 min
No. T, C X(AA), %
S (o-VPh), %
S (crotonal), %
X(PhOH), %
1
2
3
4
5
300
325
350
375
400
15
16
18
28
41
87
84
83
83
81
13
14
15
14
15
3
3
3
5
8
.3
.4
.7
.8
.3
1
0

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Graphical abstract
1
1

ACCEPTED MANUSCRIPT
Highlights
. The catalytic reaction of o-vinylphenol synthesis from phenol and acetaldehyde was
discovered
1
2
3
4
. A series of catalysts (metals and metal oxides) supported on alumina was screened
. The chromium catalyst modified with potassium was shown to be optimal
. Selectivity for o-VPh on the optimal catalyst was up to 87%
1
2