120
CHEPAIKIN et al.
Table 3. Influence of the triphenylphosphine to p-toluenesulfonic acid ratio on isobutylene hydroethoxycarbonylation: pCO
2.0 MPa, T = 100°C, τ = 4 h, [Pd] = 0.000115 mol/l, [Pd] : [C2H5OH] : [iso-C4H8] = 1 : 435 : 550. Solvent-free conditions
=
Component ratio of catalyst system
Ethyl isovalerate yield*,
%
Set no.
Catalyst system
[PPh3]
[TsOH]
1
2
3
4
5
6
PdCl2(PPh3)2
–
–
–
–
4
7
–
10.0
85.0
–
PdCl2(PPh3)2–TsOH
Pd(PPh3)4
12
–
Pd(PPh3)4–TsOH
12
12
12
95.4
92.5
96.0
PdCl2(PPh3)2–PPh3–TsOH
Pd(PPh3)4–PPh3–TsOH
* The yields are given in terms of the product isolated by fractional distillation.
ternary systems (Table 3, entries 2, 4–6) examined ear- anism of ethylene hydrocarboxylation on binuclear Pd
lier [6, 12, 13].
complex I in acetic or propionic acid solution [5].
The “alkoxide” [20] and “hydride” [21, 22] mecha-
nisms are more broadly known. The alkoxide mecha-
nism of ethylene carbonylation is confirmed by indirect
data obtained in the alternating copolymerization of
carbon monoxide with ethylene [3, 5, 20]. On the basis
of reactions of isolated intermediates, Cavinato and
Toniolo [22] give preference to the hydride mechanism.
Petrov and Noskov surveyed in [23] both their
detailed kinetic studies and in situ spectral investigation
of several catalyst systems. They believe that the multi-
route hydride mechanism is realized in this case. Con-
siderable attention was given to the problem of regiose-
lectivity in the hydrocarboxylation of α-olefins. Regi-
oselectivity depends on many factors, such as the CO
pressure, the water concentration, and the nature of the
anionic ligand. Note that the regioselectivity was not
more than 90% when ClO4– and CF3SO3– counterions
were used in cationic palladium complexes for styrene
hydrocarboxylation.
Therefore, a practically quantitative yield of ethyl
isovalerate is attained under the optimal conditions (a
temperature of 100°C, a CO pressure of 2.0 MPa, and a
molar ratio [Pd] : [TsOH] : [i-C4H8] : [C2H5OH] =
1 : 12 : 550 : 435).
High regioselectivity (100%) in isobutylene
hydroalkoxycarbonylation in the presence of ethanol,
isopropanol, and butanol is not surprising and seems to
be characteristic of isobutylene. The regioselectivities
of 1-hexene and 1-heptene hydroethoxycarbonylation
in the presence of system I were 88.2 and 83.0%,
respectively, with the ester yields being practically
quantitative (Table 4). Under similar conditions, the
regioselectivity of 1-nonene hydroethoxycarbonylation
in the presence of palladium chloride–phosphine sys-
tems was 68% [17]. A regioselectivity on the order of
64–69% was found in isopropanol and 88%, in butanol.
However, reaction rates in butanol were rather low, and
the total ester yield was only 48% for 6 h [18].
There are several schemes for the mechanism of
hydrocarboxylation and hydroalkoxycarbonylation of
olefins. A four-membered palladacyclic scheme was
proposed in [19]. A variant of this scheme is the mech-
Thus, elucidation of the high regioselecivity of these
catalyst systems as compared with published data [17,
18] calls for further, more detailed investigation of the
kinetics and mechanism of the process.
REFERENCES
Table 4. Hydroalkoxycarbonylation of olefins in the pres-
ence of the Pd(PPh3)4–TsOH system: [Pd] = 0.000115 mol/l,
[Pd] : [TsOH] : [hexane (heptene)] : [ethanol] = 1 : 12 : 550 :
435, pCO = 2 MPa, T = 100°C, and τ = 4
1. L. Falbe, Carbon Monoxide in Organic Synthesis
(Springer, New York, 1970).
2. Carbonylation of Unsaturated Hydrocarbons, Ed. by
D. N. Rudkovskii (Khimiya, Leningrad, 1968) [in Rus-
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Product yields, mol %
No.
Olefin
Alcohol
linear
product
branched
product
3. A. Sen, Adv. Polym. Sci. 73/74, 125 (1986).
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1
2
3
4
5
Isobutylene Ethanol
Isobutylene Isopropanol
Isobutylene Butanol
95.4
90.1
89.0
88.2
83.0
–
–
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–
shcheva, Kinet. Katal. 40, 348 (1999).
1-Hexene
1-Hexene
Ethanol
Ethanol
11.8
17.0
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PETROLEUM CHEMISTRY Vol. 46 No. 2 2006