Effect of temperature and CO pressure on the rate of cyclohexene hydrocarbomethoxylation catalyzed by the Pd(OAc)2 - PPh3 - TsOH system

Article abstract of DOI:10.1007/s11172-014-0518-6

The quantitative regularities of the effect of CO pressure and temperature on the rate of cyclohexene hydrocarbomethoxylation catalyzed by the Pd(OAc)₂ - PPh₃ - TsOH system were defined. Extremal dependences of the reaction rate on the CO pressure were revealed in the temperature range from 353 to 383 K. To interpret the obtained results, the catalytic cycle was constructed which included the hydride, alkyl, and acyl palladium complexes of the cationic type as intermediates. It was proposed that the catalyst is partially converted into an inactive form due to the exchange between ligands. The experiments on the effect of the CO pressure on the reaction rate made it possible to estimate the apparent rate constants for the kinetic reaction equation obtained earlier.

Full text of DOI:10.1007/s11172-014-0518-6

Russian Chemical Bulletin, International Edition, Vol. 63, No. 4, pp. 837—842, April, 2014
837
Effect of temperature and CO pressure on the rate
of cyclohexene hydrocarbomethoxylation catalyzed
by the Pd(OAc)2—PPh3—TsOH system*
N. T. Sevostyanova, V. A. Averyanov, S. A. Batashev, A. S. Rodionova, and A. A. Vorob´ev
Tula State Lev Tolstoy Pedagogical University,
125 prosp. Lenina, 300026 Tula, Russian Federation.
Fax: +7 (487 2) 35 7807. Eꢀmail: piligrim.tula.ru@gmail.com
The quantitative regularities of the effect of CO pressure and temperature on the rate of
cyclohexene hydrocarbomethoxylation catalyzed by the Pd(OAc)2—PPh3—TsOH system
were defined. Extremal dependences of the reaction rate on the CO pressure were revealed in
the temperature range from 353 to 383 K. To interpret the obtained results, the catalytic cycle
was constructed which included the hydride, alkyl, and acyl palladium complexes of the cationꢀ
ic type as intermediates. It was proposed that the catalyst is partially converted into an inactive
form due to the exchange between ligands. The experiments on the effect of the CO pressure on
the reaction rate made it possible to estimate the apparent rate constants for the kinetic reaction
equation obtained earlier.
Key words: hydrocarbalkoxylation, palladium precursor, reaction rate, cyclohexene, methyl
cyclohexanecarboxylate.
Hydrocarbalkoxylation of alkenes is a promising method
for obtaining esters.1—3 The possibilities of the synthesis of
these products by the hydrocarbalkoxylation of linear alkꢀ
enes С6—С9, cyclohexene, and styrene were described. An
important information on the reaction mechanism can be
obtained from the kinetic data, in particular, from the
values of apparent activation energies. However, reports
about the effect of temperature on the kinetics of these
reactions are scarce and fragmentary. The hydrocarbꢀ
alkoxylation of propylene by primary, secondary, and terꢀ
tiary alcohols in the presence of the Pd(PPh3)Cl2 catalyst
at 363—403 K gave4 products in high yields with 40—50%
selectivity for butanoic acid esters. The study of the cataꢀ
lytic hydrocarbalkoxylation of steroid androsteneꢀ16 by
ethylene glycol and CO in the presence of Pd(PPh3)Cl2
showed5 that the conversion increases from 27 to 92%
with the temperature increase from 323 to 423 K. Analyzꢀ
ing values of apparent activation energy obtained for the
catalytic monoꢀ and polycarbonylation of ethylene to proꢀ
pionic acid derivatives and polyketones,6 interesting conꢀ
clusion about the reaction mechanism can be made. It
was concluded that at temperatures >363 K the rateꢀdeꢀ
termining step of the process is ethylene insertion at the
Pd—Ac bond rather than the coordination of ethylene to
the palladium center. The first attempts to study the temꢀ
perature effect on the direction of the reaction in detail
were made in works on the Pdꢀcatalyzed hydrocarbalkꢀ
oxylation of ethylene7 and cyclohexene.8 The study of the
catalytic hydrocarbalkoxylation of ethylene to methyl proꢀ
pionate7 in the presence of Pd(PPh3)2(TsO)2 established
that the turnover frequency of the catalyst (TOF) increasꢀ
es nonlinearly with increasing temperature iin the range
333—393 K. In addition, the palladium catalyst decomꢀ
poses at temperatures >373 K. The extremal dependences
of the TOF on the concentration of triphenylphosphine
and hydride sources (pꢀtoluenesulfonic acid (TsOH), waꢀ
ter, and hydrogen) were obtained in the range 353—373 K.
In all cases, the TOF increases with temperature; howevꢀ
er, the activation parameters were not determined. The
same groups of authors described the effect of the concenꢀ
tration of substances involved in cyclohexene hydrocarbꢀ
methoxylation8 on the reaction rate in the temperature
range 353—373 K.
Recently, we have conducted the study of the influꢀ
ence of the temperature, reagents (methanol, cyclohexꢀ
anol, and CO), and components of the Pd(PPh3)Cl2—
PPh3—TsOH catalytic system on the rate of cyclohexene
hydrocarbalkoxylation.9—11 Based on the results of this
study, we were able to estimate the apparent activation
energies and to use the relevant values to derive the series
of stability of the palladium complexes in the reacꢀ
tion medium.9—11 This report is a continuation of our
earlier works. We present herein the results of kinetic studꢀ
ies of the effect of the CO pressure and temperature on
* According to the materials of the International Symposium
"Modern Trends in Organometallic Chemistry and Catalysis"
(June 3—7, 2013, Moscow).
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 0837—0842, April, 2014.
1066ꢀ5285/14/6304ꢀ0837 © 2014 Springer Science+Business Media, Inc.

838
Russ.Chem.Bull., Int.Ed., Vol. 63, No. 4, April, 2014
Sevostyanova et al.
C•102/mol L–1
the rate of catalytic cyclohexene hydrocarbomethoxylaꢀ
tion in the presence of the Pd(OAc)2—PPh3—TsOH
system (Scheme 1).
10
1
8
6
4
2
Scheme 1
2
3
40
80
120
160 t/min
Cyclohexene was chosen as an alkene for hydroꢀ
carbalkoxylation because its reaction sites are chemically
equivalent and, hence, the hydrocarbomethoxylation of
cyclohexene is accompanied by the formation of a single
product, which makes it possible to use this reaction as
a model one.
Fig. 1. Typical kinetic curves of methyl cyclohexanecarboxylate
accumulation at PCO = 1.6 (1), 1.1 (2), and 3.1 MPa (3); Т = 373 K;
concentrations, mol L–1: [C6H10] = 0.10, [MeOH] = 0.45,
[Pd(OAc)2] = 2.0•10–3, [PPh3] = 1.2•10–2, [TsOH] = 2.4•10–2
,
and [оꢀxylene] = 5.0•10–2
.
r0•103/mol L–1 min–1
Experimental
1.4
5
4
The reaction was studied in a periodical reactor described
earlier.12. Each experiment was carried out at constant temperaꢀ
ture and CO pressure in toluene. Samples of the reaction mixꢀ
ture were analyzed by GLC. oꢀXylene was used as an internal
standard when determining the content of components. The proꢀ
cedures of kinetic experiments and analysis of the reaction mixꢀ
ture were described.13 The reagents (toluene, cyclohexene, methꢀ
anol, and oꢀxylene) were dried over calcium chloride and rectiꢀ
fied. All components of the catalytic system (Pd(OAc)2, PPh3,
and TsOH) were commercial grade materials (Sigma—Aldrich).
1.2
1.0
0.8
0.6
0.4
0.2
3
2
1
Results and Discussion
1
2
3
4
PCO/MPa
Fig. 2. Initial hydrocarbomethoxylation rate (r0) vs CO pressure
at 353 (1), 363 (2), 373 (3), 378 (4), and 383 (5) K; concentraꢀ
tions, mol L–1: [C6H10] = 0.10, [MeOH] = 0.45, [Pd(OAc)2] =
= 2.0•10–3, [PPh3] = 1.2•10–2, [TsOH] = 2.4•10–2, and
Five runs of experiments in the temperature range
353—383 K were carried out to study the effect of the CO
pressure and temperature on the rate of cyclohexene hydroꢀ
carbomethoxylation. The typical kinetic curves describing
the accumulation of the reaction product (methyl cycloꢀ
hexanecarboxylate) are shown in Fig. 1.
The initial reaction rates were determined using the
differentiation of the initial regions of the kinetic curves
describing ester accumulation in the reaction mixture. The
corresponding dependences of the initial reaction rate on
the CO pressure in the temperature range 353—383 K
are presented in Fig. 2. The dependences are described
by curves with maxima in the range of CO pressures
0.9—2.1 MPa. These results are consistent with the earlier
obtained data on the effect of the CO pressure on the
hydrocarbalkoxylation of cyclohexene by methanol9,10,14
and cyclohexanol.11,15
[оꢀxylene] = 5.0•10–2
.
16,17
to cyclohexene14—16 and Pd(OAc)2
and the deꢀ
pendences of the reaction rate on the concentration
of alcohols (methanol and cyclohexanol),10,11,14,15,18
PPh3,9,11,14—19 and TsOH16,18,19 are described by curves
with maxima. The following reaction mechanism can be
proposed on the basis of the results described above and
earlier obtained data (Scheme 2). Earlier the possibility of
reduction of the PdII precursors with methanol to form
zeroꢀvalence palladium complexes of the type Х1 was deꢀ
monstrated.7,8 Complex Х0 can add solvent (toluene) molꢀ
ecules: toluene is present in the reaction mixture in a sigꢀ
nificant excess over other components involved in the reꢀ
action (see Scheme 2, reaction (2)). At the same time, the
Earlier we found that, under the same conditions, hyꢀ
drocarbalkoxylation is the firstꢀorder reaction with respect

Hydrocarbomethoxylation: effect of CO
Russ.Chem.Bull., Int.Ed., Vol. 63, No. 4, April, 2014
839
Scheme 2
Sol are solvent (toluene) molecules.
reaction of the palladium complexes with pꢀtoluenesulfonꢀ
ic acid, which is a strong hydride source, affords the key
intermediate of the catalytic cycle Х2 (reaction (3)).1,7,8
The following arguments support the mechanism preꢀ
sented in Scheme 2. The types of intermediates shown in
Scheme 2 have earlier been isolated, spectrally characterꢀ
ized, and tested for participation in the catalytic cycle.20—24
The hydride intermediate HPd(PPh3)2Cl assigned to
the type Х2 and synthesized from Pd(PPh3)4 and НСl afꢀ
fords the corresponding carboxylic acids upon the adꢀ
dition of hexꢀ1ꢀene, HCl, CO, and water.20 In turn,
the hydride complex, which was isolated from the

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Sevostyanova et al.
Pd(OAc)2—P(C6H4SO3Naꢀm)3 system in a medium of
aqueous CF3COOH, in the presence of ethylene gives
alkylpalladium complexes of the type Х4 reacting with CO
to form acyl complex Х6. The hydrolysis of the latter afꢀ
fords propionic acid and regenerates complex Х2.21 At the
same time, for a series of Pdꢀcontaining catalytic systems,
including those based on Pd(PPh3)2Cl2, acyl complexes of
the type Х6 were isolated. The treatment of the complexes
with aqueous solutions of acids (for example, HCl) gives
the corresponding carboxylic acids, while the treatment
with alcohols affords esters.22—24
The extremal pattern of the dependences of the reacꢀ
tion rate on the CO pressure obtained in this work and the
earlier found dependences of the cyclohexene cyclocarbꢀ
alkoxylation rate on the concentration of alcohols (methꢀ
anol and cyclohexanol)10,11,14,15,18 is caused, in our opinꢀ
ion, by two factors. The increase in the reaction rate with
an increase in the alcohol concentration and CO pressure
in the region of their low values observed in several works
obeys the law of acting masses and, hence, an increase in
the reagent concentration leads to an increase in the reacꢀ
tion rate. At the same time, excessive amounts of these
reagents are involved in ligand exchange reactions (see
Scheme 2, reactions (9)—(12)) with intermediates of the
catalytic cycle. As a result, the formation of inactive pallaꢀ
dium forms and withdrawal of a portion of the catalyst
from the catalytic cycle are observed. Consequently, the
hydrocarbalkoxylation rate decreases in the region of high
alcohol concentrations and high CO pressures.
Thus, the water concentration increases with an inꢀ
crease in the concentration of pꢀtoluenesulfonic acid
monohydrate in the system, which induces an increase in
the rate of reaction (14) and, as a consequence, a decrease
in the hydrocarbalkoxylation rate observed in a series
of works.
It can be assumed that reaction (8) is the rateꢀdeterꢀ
mining step of the catalytic cycle. This assumption can be
supported by the following arguments. The sensitivity of
the reaction rate to the concentration and size of an alcoꢀ
hol molecule has earlier been established.8,22 In the chain
of reactions (1)—(8), alcohol participates in the first and
last steps only. If none of these two steps is rateꢀdeterminꢀ
ing, the rate of the whole process should be insensitive to
the alcohol concentration and the size of its molecule and
the reaction order with respect to alcohol should be zero.
However, the kinetic studies demonstrate the first order of
the hydrocarbalkoxylation reactions with respect to alcoꢀ
hol in the region of its low concentrations.10,11,14,15 In
addition, intermediates of the type Х6 were isolated from
the reaction systems of alkene hydrocarbalkoxylation conꢀ
taining all three reagents (alkene, CO, and alcohol),3,4,20,23
which indicates their higher concentration in the system
compared to preceding intermediates Х0—Х5. This sugꢀ
gests that reactions (1)—(7) are fast, whereas reaction (8)
is the slowest step of the process and, hence, intermediates
Х6 are accumulated in the system. Thus, all established
facts of sensitivity of the reaction rate to the concentration
and size of the alcohol molecule and the accumulation of
intermediates Х6 in the reaction mixture indicate the rateꢀ
determining character of step (8).
An explanation for the extremal pattern of the depenꢀ
dence of the hydrocarbalkoxylation rate on the PPh3 conꢀ
centration found earlier9,11,14—19 is that the rates of ligand
exchange reactions (11) and (12) and reaction (13) oppose
one another in influencing the rate of hydrocarboxylation.
The former two reactions are responsible for the generaꢀ
tion of the active Pd complexes, and the latter is responsiꢀ
ble for the withdrawal of a portion of the catalyst from the
catalytic cycle.
Earlier25 we obtained the kinetic equation for the
hydrocarbomethoxylation of cyclohexene catalyzed by the
Pd(OAc)2—PPh3—TsOH system. Under the conditions
of oneꢀfactor experiment on studying the effect of the CO
pressure, this equation takes the form
(I)
An extremal character of the dependences of the cyꢀ
clohexene hydrocarbalkoxylation rate on the concentraꢀ
tion of TsOH monohydrate is caused by several factors.16,18
An increase in the TsOH concentration in the system shifts
the equilibrium of reaction (3) toward hydride intermediꢀ
ate X2 and increases its concentration in the system. That,
in turn, results in an increase in the concentration of the
reaction products and the observed increase in the rate
because the catalytic cycle proceeds as a sequence of sevꢀ
eral steps (4)—(8). At the same time, the hydrocarbalkꢀ
oxylation rate can decrease in the region of high acid
concentration due to the decomposition of the Pd precurꢀ
sor to form palladium black (Pds) in the reaction with
water vapor1
where
СМ is the analytical concentration of all monomeric palꢀ
ladium forms, [С6H10] is the cyclohexene concentration,
HCO is Henry constant for CO, and [PPh3] is the concenꢀ
tration of free PPh3 determined by the difference of its
analytical concentration and the doubled concentration
Pd(OAc)2 + CO + H2O
Pds + CO2 + 2 AcOH.
(14)

Hydrocarbomethoxylation: effect of CO
Russ.Chem.Bull., Int.Ed., Vol. 63, No. 4, April, 2014
841
(PCO/r0)•10–3/MPa L min mol–1
of Pd(OAc)2 according to the stoichiometry of the Pd
phosphine complexes.
14
We obtained the kinetic equations similar to Eq. (I) for
the hydrocarbalkoxylation of cyclohexene by methanol and
cyclohexanol in a series of our earlier works.9—11,14,15 The
agreement of Eq. (I) with the experimental data can be
confirmed by the values of the initial reaction rate r0 as
a function of РСО. The transformation of Eq. (I) gives
12
1
2
3
10
8
6
PCO/r = A/kapp + (c/kapp)PCO + (b/kapp)P2
.
(II)
CO
4
4
The estimation by the leastꢀsquares method of the paraꢀ
meters of Eq. (II) gave the values presented in Table 1. It
is seen that parameter c/kapp is statistically insignificant in
the whole studied temperature range. Therefore, Eq. (II)
can be reduced to the following form:
5
2
5
10
15
25 P2CO/MPa2
Fig. 3. Fitting the kinetic equation to experimental data at temꢀ
peratures 353 (1), 363 (2), 373 (3), 378 (4), and 383 K (5).
PCO/r = A/kapp + (b/kapp)P2
.
(III)
CO
The dependences of PCO/r on P2 corresponding to
CO
rate on the CO pressure was established in the temperaꢀ
ture range studied. The data obtained were interpreted in
the framework of the hydride mechanism of hydrocarbꢀ
alkoxylation. The apparent constants of the earlier obꢀ
tained kinetic equation for the reaction were estimated by
varying the CO pressure.
Eq. (III) are shown in Fig. 3. The values of the parameters
of Eq. (III) obtained by the leastꢀsquares method are listꢀ
ed in Table 2. The values calculated by Eq. (III) taking
into account confidence intervals are close to the values
obtained using Eq. (II) and presented in Table 1. The
plots (see Fig. 3) constructed using Eq. (III) demonstrate
a good agreement between the experimental and calculatꢀ
ed data. This confirms the statistical insignificance of paꢀ
This work was financially supported by the Russian
Foundation for Basic Research (Project No. 14ꢀ08ꢀ00535).
rameter c/kapp
.
Thus, the kinetic regularities of the effect of the CO
pressure in the cyclohexene hydrocarbomethoxylation rate
catalyzed by the Pd(OAc)2—PPh3—TsOH system were
considered in the temperature range from 353 to 383 K.
An extremal pattern of the dependences of the reaction
References
1. G. Kiss, Chem. Rev., 2001, 101, 3435.
2. E. Drent, P. H. M. Buzelaar, Chem. Rev., 1996, 96, 663.
3. E. S. Petrov, Yu. G. Noskov, Ross. Khim. Zh., 1998, 42,
No. 4, 149 [Mendeleev Chem. J. (Engl. Transl.), 1998,
42, No. 4].
Table 1. Parameters in Eq. (II)
4. G. Cavinato, L. Toniolo, J. Mol. Catal. A: Chem., 1979, 6, 111.
5. E. Nagy, B. Heil, S. Törös, J. Mol. Catal. A: Chem., 1999,
143, 229.
6. E. G. Chepaikin, A. P. Bezruchenko, A. A. Leshcheva,
Kinet. Catal. (Engl. Transl.), 2006, 40, 313 [Kinet. Katal.,
1999, 40, 348].
7. A. Vavasori, G. Cavinato, L. Toniolo, J. Mol. Catal. A: Chem.,
2001, 176, 11.
8. A. Vavasori, L. Toniolo, G. Cavinato, J. Mol. Catal. A: Chem.,
2003, 191, 9.
Т/К
A/kapp•10–8
c/kapp•10–2
b/kapp•104
/Pa L min mol–1 /L min mol–1 /L min Pa–1 mol–1
353
363
373
378
383
10 7
7 2
6 2
6 2
5 2
3 10
–2 20
0 20
0 20
1 20
11 2.0
6.0 0.5
3.0 0.5
2.0 0.4
2.0 0.5
9. N. T. Sevost´yanova, S. A. Batashev, V. A. Aver´yanov, A. M.
Demerlii, Petroleum Chem. (Engl. Transl.), 2012, 52, 35
[Neftekhimiya, 2012, 52, 39].
Table 2. Parameters in Eq. (III)
10. V. A. Aver´yanov, N. T. Sevost´yanova, S. A. Batashev, A. M.
Demerlii, Petroleum Chem. (Engl. Transl.), 2013, 53, 39
[Neftekhimiya, 2013, 53, 43].
Т/К
A/kapp•10–8
b/kapp•104
/Pa L min mol–1 /L min Pa–1 mol–1
11. V. A. Aver´yanov, N. T. Sevost´yanova, S. A. Batashev,
Petroleum Chem. (Engl. Transl.), 2008, 48, 287 [Neftekhimiya,
2008, 48, 286].
12. A. R. El´man, V. A. Matveev, E. V. Slivinskii, S. M. Loktev,
Pharm. Chem. J. (Engl. Transl.), 1990, 24, No. 3, 217
[Khim.ꢀFarm. Zh., 1990, 24, No. 3, 47].
353
363
373
378
383
12 2.0
5 1.0
6.0 0.8
5.8 0.7
6 1.0
11.9 0.70
5.7 0.20
3.3 0.10
2.38 0.07
1.9 0.10

842
Russ.Chem.Bull., Int.Ed., Vol. 63, No. 4, April, 2014
Sevostyanova et al.
13. I. E. Nifant´ev, S. A. Batashev, S. A. Toloraya, A. N. Tavꢀ
torkin, N. T. Sevostyanova, A. A. Vorobiev, V. V. Bagrov,
V. A. Averyanov, J. Mol. Catal. A: Chem., 2011, 350, 64.
14. V. A. Aver´yanov, S. A. Batashev, N. T. Sevost´yanova,
N. M. Nosova, Kinet. Catal. (Engl. Transl.), 2006, 47, 375
[Kinet. Katal., 2006, 47, 381].
19. I. E. Nifant´ev, N. T. Sevostyanova, V. A. Averyanov, S. A.
Batashev, A. A. Vorobiev, S. A. Toloraya, V. V. Bagrov,
A. N. Tavtorkin, Appl. Catal. A: General, 2012, 449, 145.
20. M. I. Terekhova, A. B. Sigalov, N. E. Petrova, E. S. Petꢀ
rov, J. Gen. Chem. USSR (Engl. Transl.), 1985, 55, 944
[Zh. Obshch. Khim., 1985, 55, 944].
15. V. A. Aver´yanov, N. T. Sevost´yanova, S. A. Batashev, S. V.
Nesolenaya, Petroleum Chem. (Engl. Transl.), 2006, 46, 405
[Neftekhimiya, 2006, 46, 435].
16. N. T. Sevost´yanova, A. A. Vorob´ev, V. A. Aver´yanov,
S. A. Batashev, Tez. dokl. XIV Mezhdunar. nauchnoꢀtekhn.
konf. "Naukoemkie khimicheskie tekhnologiiꢀ2012" [Proc. XIV
Intern. Scientific Technical Conf. "Chemical High Technoloꢀ
gies"] (Tula, May 21—25, 2012), Izdꢀvo MITKhT, Moscow,
2012, 92 (in Russian).
21. G. Verspui, I. I. Moiseev, R. A. Sheldon, J. Organomet.
Chem., 1999, 586, 196.
22. R. Bardi, A. M. Piazzasi, G. Cavinato, L. Toniolo, Inorg.
Chim. Acta, 1985, 102, 99.
23. M. I. Terekhova, N. E. Petrova, R. R. Shifrina, E. S. Petꢀ
rov, J. Gen. Chem. USSR (Engl. Transl.)1988, 58, 581
[Zh. Obshch. Khim., 1988, 58, 658].
24. G. Cavinato, L. Toniolo, A. Vavasori, J. Mol. Catal. A: Chem.,
2004, 219, 233.
17. V. A. Aver´yanov, N. T. Sevost´yanova, S. A. Batashev, Izv.
Vuz. Khim. Khim. Tekhnol. [Bulletin of Higher Educational
Institutions. Chemistry and Chemical Technology], 2008, 55,
No. 4, 111 (in Russian).
25. V. A. Aver´yanov, N. T. Sevost´yanova, S. A. Batashev,
A. A. Vorob´ev, A. S. Rodionova, Russ. J. Phys. Chem. B
(Engl. Transl.), 2014, 8, No. 2, 140 [Khim. Fiz., 2014, 33,
No. 3, 19].
18. A. S. Rodionova, V. A. Averyanov, N. T. Sevostyanova, A. A.
Vorobiev, S. A. Batashev, Intern. Symp. "Modern Trends in
Organometallic Chemistry and Catalysis" dedicated to the 90th
anniversary of the Acad. M. E. Volpin (Moscow, June 3—7,
2013), Abstrs, Moscow, 2013, 147.
Received October 8, 2013;
in revised form February 24, 2014