Catalytic methylation of phenol

Article abstract of DOI:10.1134/S1070427211010186

Attempt was made to methylate phenol with methyl formate in the presence of a zeolite-supported palladium and a ruthenium-titanium catalyst.

Full text of DOI:10.1134/S1070427211010186

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2011, Vol. 84, No. 1, pp. 107−110. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © A.A. Agaev, A.A. Bairamov, M.M. Muradov, 2011, published in Zhurnal Prikladnoi Khimii, 2011, Vol. 84, No. 1, pp. 107−110.
ORGANIC SYNTHESIS
AND INDUSTRIAL ORGANIC CHEMISTRY
Catalytic Methylation of Phenol
A. A. Agaev, A. A. Bairamov, and M. M. Muradov
Sumgait State University, Sumgait, Azerbaijan
Received March 11, 2011
Abstract—Attempt was made to methylate phenol with methyl formate in the presence of a zeolite-supported
palladium and a ruthenium-titanium catalyst.
DOI: 10.1134/S1070427211010186
Analysis of published data on methylation of phenols
shows that these processes are for the most part studied
in order to obtain methyl derivatives of phenol and,
in particular, anisole, xylenols, and trimethylphenols.
Representatives of various classes of organic compounds
have been examined as methylating agents: methyl
halides, methanol, formaldehyde, dimethyl ether, methyl
formate, and sulfonic acid salts having methylol groups
in their structure [1–4].
contained 0.04–0.08% sodium. H-forms of HSZs were
produced by calcination of the ammonium forms at
540°C for 6 h. A sample of the H-form was mixed with
a hydrogel of aluminum oxide in a 3 : 1 mass ratio,
thoroughly agitated, molded, granulated, dried at room
temperature, and calcined at 300 and 540°C for 3 h at
each temperature.
PalladiumwasdepositedontotheH-formsofHSZsby
their impregnation with a palladium tetraaminochloride
solution.
As catalysts have been used chlorides, oxides of
various metals and their combinations, natural and
synthetic aluminosilicates, zeolites and their modified
forms, acids, superacids, and supported heteropolyacids
[2, 5–8]. It is known [3] that, in the presence of ZnCl2
and ZnO, methyl formate methylates phenol to anisole
with good selectivity.
The ruthenium–titanium catalyst was fabricated by
a special procedure used in the electrochemical industry.
The catalyst was composed of ruthenium and titanium
oxides in a 0.43 : 1 mass ratio.
Experiments were carried out in an 60-cm3
electrically heated stainless steel autoclave with a reflux,
pressure gage, and sampling valve. The temperature in
the reaction zone was monitored with a thermocouple
connected to a potentiometer.
EXPERIMENTAL
We made an attempt to methylate phenol with
methyl formate in the presence of a Pd-zeolite and
a ruthenium-titanium catalyst (RTC). An H-form of
high-silica zeolites (HSZ) (zeolite family of the ZSM-
5 type) was obtained in several stages from the Na-
form by ion exchange, with the zeolite treated with
a 0.1 N ammonium chloride solution at 75°C. Before
the ion exchange, the zeolites were calcined at 540°C
for 12 h. After the ion exchange was complete, the
zeolite was washed and thermostated at 120°C for
4 h. The resulting ammonium form of the zeolite
The reaction products were analyzed with a Khrom-5
chromatograph with a heat-conductivity detector and
apackedcolumn(3.6m×4mm)withdimenthylphthalate
as the liquid phase supported in an amount of 18 wt %
by Chromosorb W.
Dimenthylphthalate was synthesized by an accelerat-
ed procedure, developed by the authors, from special-
purity menthol and phthalic anhydride.
An effective analysis of difficultly separable
methylphenols and, in particular, meta- and para-
107

108
AGAEV et al.
isomers can be made on dimenthylphthalate having
the liquid-crystalline structure (133–134°C). With
this temperature mode changed, the efficiency of the
chromatographic separation of isomeric methylphenols
is partly impaired. A chromatographic analysis of
gaseous products was made using 13X molecular sieves
and NaX zeolite.
methanol on this catalyst by a parallel scheme and is
a by-product of methanol conversion.
Before the reaction, formic acid methyl ester
produced from methanol was boiled over anhydrous
MgSO4 and distilled with a reflux condenser.
The interaction of phenol with methyl formate yields
catalyzates of various compositions. Anisole, isomeric
cresols, salicylic aldehyde, methanol, formic acid, and
carbon(II) oxide were found in the reaction products.
This gives reason to assume that the following reactions
occur under the process conditions:
Methyl formate was synthesized from methanol in
the presence of water and a cobalt-ferrite catalyst at
350–370°C [9]. It is known [10] that this compound is
formed in small amounts in alkylation of phenol with
OH
OCH3 + HCOOH
HCOOCH3, cat.
C6H4
o-, m-, p-HO
OH
CH3 + HCOOH
O
H
C
+ CH3OH
The results of the catalytic interaction of phenol
with methyl formate are listed in the table. Analysis
of the data obtained shows that salicylic aldehyde is
formed in small amounts over the catalysts under study,
especially in the presence of RTC. As temperature is
raised, its formation ceases. Thermodynamic factors
hinder formation of salicylic aldehyde under these
[11] take into account, occurrence of the reaction can
only be judged on the basis of additional experiments.
Low temperatures partly provide thermodynamically
favorable conditions for formylation; with increasing
temperature, the thermodynamic hindrance becomes
more pronounced.
The data in the table suggest that the formation of
anisole is the main process direction. The alkyl–O bond
conditions. With the fact that ΔG0 ≈ 0 and data of
298
Results of the reaction of methyl formate with phenol over Pd-HSZ and RTC catalysts. Reaction conditions: phenol : methyl
formate molar ratio 1 : 6, reaction duration 3 h
Reaction conditions
Selectivity, %
Phenol
conversion, %
cresol
Catalyst
Pd-HSZ
salicylic
aldehyde
T, °C
P, MPa
anisole
other products
ortho-
meta-
para-
240
280
320
340
240
280
320
0.8
0.8
1.0
1.0
0.8
0.8
1.0
10.2
25.1
30.2
43.5
8.3
90
–
–
–
9.5
5.6
–
–
–
55.0
50.0
30.0
96.0
79.0
62.0
20.5
20.0
25.0
2.5
4.6
14.6
20.0
–
12.0
15.0
18.0
–
–
–
6.0
–
RTC
1.2
–
20.0
22.5
13.0
18.0
–
6.5
–
5.0
11.0
–
2.0
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 1 2011

CATALYTIC METHYLATION OF PHENOL
109
in an ester is only ruptured in the case when the carbon
atom of the alkyl or aralkyl radical has groups that
can stabilize the intermediately formed carbonium ion
[12]. The observed alkylation can be accounted for by
hydrolysis of methyl formate with admixture of water
and by the interaction of phenol under acid catalysis
conditions with CH3OH being formed. However, it
is also probable that the mobility of the methyl group
increases upon adsorption of methyl formate on active
centers of the catalysts and its methylating capacity in
interaction with phenol from the bulk grows.
Under the conditions of alkylation with methanol,
phenol hardly forms any anisole, and meta- and para-
cresols, and the reaction mainly yields ortho-derivatives
of phenol (ortho-cresol and 2,6-xylenol). It can be seen
in the table that, in contrast to the aforesaid, mostly
anisole and a mixture of isomeric cresols are formed
from phenol and methyl formate over RTC at 320°C.
At the same time, similar effects are observed when
phenolisreactedwithmethanolandmethylformate.First,
the reaction selectivity with respect to anisole decreases
with increasing temperature and that with respect to
cresols grows. This relationship is less pronounced
in the case of methyl formate, compared with phenol
alkylation by methanol. Despite this circumstance, the
probability of isomerization of anisole produced in the
interaction of phenol with methyl formate into isomeric
cresols cannot be ruled out. However, a special study is
necessary for confirming this assumption.
It can be seen in the table that the highest activity in
the reaction of phenol with methyl formate is exhibited
by the Pd-HSZ at 320°C. The type of interaction of
phenol with methyl formate differs from that of the
reaction of phenol alkylation by methanol. Primarily,
a noticeable presence of anisole in catalyzates even at
320°C is observed. Under similar conditions, anisole is
formed on the given catalyst from phenol and methanol,
with a selectivity of 18.0%; mixture of isomeric cresols,
with selectivities with respect to ortho-, meta, and para-
isomers of 55.0, 1.0, and 20.0%, respectively; and di- and
trimethylphenols, with a selectivity of 23.0%. In the case
of methyl formate, there no di- and trimethylphenols,
and the isomeric composition of cresols strongly differs
from that specified above (see table).
The reaction duration affects the conversion of
phenol and yields of anisole and cresols similarly for
both the catalysts. Making the reaction longer raises
the conversion of phenol over Pd-HSZ and RTC and,
after 3–4 h, this parameter nearly stabilizes. A similar
behavior is observed in plots describing how the yield of
anisole and cresols depends on the process duration (see
figure). These yields grow as the reaction duration is
raised to 3 h and then, by the fourth hour of the reaction,
the yield of anisole somewhat decreases (by 2.5% in the
case of Pd-HSZ and by 1.5% over RTC), whereas the
yield of cresols remains nearly unchanged.
Comparison of the results obtained for the interaction
of phenol with methyl formate (see table) and methanol
[3] over RTC reveals their noticeable difference:
in alkylation of phenol with methanol at 320°C, its
conversion exceeds by 12.0% that in the interaction of
phenol with methyl formate.
Raising the temperature (>320°C) and the reaction
duration (>4 h) fails to improve the process parameters,
(a)
(b)
Q, %
Q, %
τ, h
τ, h
Effect of the reaction duration τ on (1) conversion of phenol and (2, 3) yields Q of (2) anisole and (3) cresols per reacted phenol.
Conditions: T = 320°C, P = 1.0 MPa. Catalyst: (a) Pd-HSZ and (b) RTC
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 1 2011

110
AGAEV et al.
prevrashcheniya alkilfenolov (Catalytic Transformations
of Alkylphenols), Moscow: Khimiya, 1973.
and, simultaneously, the decomposition of formic acid
to CO and H2O is enhanced and dimethylphenols and
condensation products are partly formed.
3. Nasadyuk, V.A., Fedovich, E.V., Pozderskii, Yu.A., and
Moiseev, I.I., Izv. Akad. Nauk SSSR, Ser. Khim., 1989,
no. 4, pp. 787–790.
CONCLUSIONS
4. Zhuravlev, V.A. and Murashkina, T.V., Vestn. Kuzbas.
Gos. Tekhn. Univ., 2005, no. 6, pp. 85–87.
(1) Methyl formate methylates phenol to anisole
with high selectivity in the presence of such catalysts as
palladium on high-silica zeolite and ruthenium-titanium
catalyst.
(2) As temperature is raised to above 320°C, the
reaction selectivity with respect to cresols grows, and
that with respect to anisole decreases when the reaction
is carried out in the presence of palladium on high-silica
zeolite and ruthenium-titanium catalyst by factors of 2
and 3, respectively.
5. FRG Patent 2756461.
6. GDR Patent 267034.
7. Tagiyev, D.B. and Agaev, A.A., Abstr. İnt. Conf.
Zeocat-90, Leipzig, 1990, p. 102.
8. Beklov, S.I., Tarasov, A.L., and Kustov, L.M., Kataliz
Prom–sti, 2004, no. 4, pp. 10–16.
9. Agaev, A.A., Kuliev, A.D., and Kasumova, D.G.,
Materialy Mezhdunarodnoi konferentsii “Tonkii
organicheskii sintez i kataliz” (Proc. Int. Conf. “Fine
Organic Synthesis and Catalysis”), Baku, 1999, p. 110.
10. Agaev, A.A., Akhundov, A.A., Indyukov, N.M., et al.,
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