5-7 OCTOBERISFR2011

139

TOLEDO (SPAIN)

A MODIFIED WACKER SYSTEM FOR THE OXIDATION OF HEAVY 1-OLEFINS
J.M. Escola1, J.A. Botas1, C. Vargas2 and M. Bravo
1Chemical and Energy Technology Department, ESCET, Universidad Rey Juan Carlos. C/ Tulipán s/n, 28933, Móstoles,Madrid, Spain
2Chemical and Environmental Technology Department, ESCET, Universidad Rey Juan Carlos. C/ Tulipán s/n, 28933,Móstoles, Madrid, Spaine-mail: juanangel.botas@urjc.esAbstract
Heavy olefins were oxidated using a modified Wacker system with TBHP as oxidant and acetonitrile as solvent. Theoxidation of both pure heavy olefins (C12-C20) and equimolecular mixtures of them with or without their corresponding nparaffins, were carried out with the addition of β-cyclodextrins in some cases. In the oxidation of 1-octadecene a value of
90 % of conversion was achieved and the selectivity towards the product of interest, 2-octadecanone, after 2h of reaction
time was of 60 %. The addition of β-cyclodextrins did not increase the production of 2-octadecanone. Nevertheless, theselectivity towards the ketone in the oxidation of an equimolecular mixture of n-dodecane + 1-dodecene was a 29 %higher than the achieved in the absence of the n-paraffin, likely due to a dilution effect of the n-dodecane which reduces
the extent of the isomerization reactions. Moreover, the oxidation of an equimolecular mixture C=12+C=16+C=20 in thepresence of equimolecular amounts of their corresponding n-paraffins gave rise to practically complete conversion andselectivities towards 2-methylketones within 70-90 % enhancing with decreasing chain length due to their higher solubility
in the biphasic system. Finally the catalyst was not active after two reaction cycles by the palladium clusters formation.
However increasing the 1-dodecene/PdCl2 ratio to 100 comparable catalytic results were obtained, being expected toincrease the catalyst lifetime by decreasing the extent of palladium aggregation.

Keywords: heavy olefins, Wacker oxidation, acetonitrile, palladium chloride, tert-butylhydroperoxide

1. Introduction
Wacker oxidation of alkenes to ketones is a conventional
industrial process for the synthesis of organic chemicals
catalysed by palladium. In this reaction air is typicallyused as oxidant and CuCl2 as cocatalyst [1]. However,
Wacker oxidation involves several disadvantages suchus the appearance of palladium black leading towards
the deactivation of the palladium catalysts, the formationof unwanted chlorinated by-products and the occurrenceof a corrosive reaction medium due to the use of CuCl2and HCl. In addition, in the case of heavy olefins which
are important as their application in polar waxes,
fragances, cetane improvers or printer inks, the usage ofthe Wacker system is limited due to their low solubility inwater. Consequently, different attempts can be found inliterature modifying the original Wacker system in order
to eliminate the aforementioned drawbacks. Many ofthem are related to the heterogeneization of thepalladium catalyst system over different supports such us
zeolites, pore glass, montmorillonite [2] or polymers, inorder to avoid the catalyst deactivation. In addition,
mixtures of water and ionic liquids have been also
reported as solvents in Wacker oxidation as well as
inverse phase transfer catalysts such as cyclodextrins, toimprove the solubility of the higher alkenes. Ecyclodextrins are soluble in water and well known
molecular recognition between the host cavity ofcyclodextrins and organic compounds allowed for higher

interiores libro.indd 139

oxidation rate and ketone selectivity. In a previous work[3], the most adequate operation variables were
determined for a model higher 1-olefin (1-dodecene)oxidized to 2-dodecanone and other ketones in a
modified Wacker system without copper chloride andemploying tert-butylhydroperoxide (TBHP) as oxidant,
acetonitrile as solvent and palladium chloride as catalyst([CH3CN] / [1-dodecene] = 10, [TBHP] / [1-dodecene] =7). In the present work, the performance of the modified
Wacker system in the oxidation of the heavy 1-olefins
C12, C16, C18 and C20 is carried out. These olefins can beeasily obtained in the feedstock recycling of polyethylene
by thermal cracking at 350–400 ºC in an almost
equimolar mixture with the corresponding n-paraffin ofeach fraction [4]. Owing to this, the performance of themodified Wacker system was studied under the presenceof the corresponding n-paraffins, finding an increase in
the selectivity of the corresponding 2-methylketones.

2. Materials and Methods
In a typical experiment, 5.0 g of the 1-dodecene wasloaded inside a stirred glass batch reactor equipped witha reflux column and propeller stirrer, with 11.6 g ofacetonitrile. After, 21.6 g of TBHP and 0.1 g of palladium(II) chloride were also loaded and the reaction started.
The reaction temperature was controlled by athermostatic bath, where the reactor was placed. The
mixture was stirred at 300 rpm at the reaction
temperature (80 ºC) during 7 h. In reactions with β-26/9/11 13:13:13

140

6th International Symposium on Feedstock Recycling of Polymeric Materials

ciclodextrin, this was added with a molar ratio of [1olefin] / [β-ciclodextrin] = 40. If the experiment wascarried out in the presence of the corresponding nalkane, the mixture loaded was [1-alkene] / [n-alkane]
molar ratio = 1. Finally, 179.0 g of tetrahydrofurane wereadded to the mixture in order to homogenize the medium
and for the subsequent analysis of the obtained products
by gas chromatography using a Varian 3900GC provided
with a CP8907 methylsilicone column of 15 m length x0,25 μm width, using a flame ionization detector (FID).

3. Results and Discussion
3.1. Oxidation of 1-octadecene with/without βcyclodextrins. According to the previous research, thereactions taking place in the studied Wacker system arepresented in scheme 1.
)

2-METHYL KETONE(21-OLEFIN(1)
OLEFIN ISOMERS(3)OTHER KETONES

Scheme 1. Reactions in studied Wacker system
Oxidation is a slow reaction (pathway 2) which competes
with the fast isomerization of 1-olefin (pathway 1).
However, isomerization is also a reversible reaction
which leads towards the starting 1-olefin as it isconsumed in the oxidation reaction. The relative extent ofthese reactions might be related either to the biphasic
nature of the system or to the occurrence of a specificinteraction with the solvent, being acetonitrile the one
with best results was achieved. Once the reported
modified Wacker system was proved to be suitable forthe oxidation of 1-dodecene, it was applied to theoxidation of a higher olefin (1-octadecene). In addition,
besides the proposed modified Wacker system, anotheridentical one but incorporating β-cyclodextrin ([βcyclodextrin] / [1-octadecene] = 1 / 40) were also studied
in order to study the effect of this phase transfer catalyst.
Conversion and selectivity results obtained in themodified Wacker oxidation after 2 and 6 h respectively
with or without β-cyclodextrin are shown in Figure 1.
100

A80

without E -cyclodextrin
with E -cyclodextrin

604020%B

without E -cyclodextrin
with E -cyclodextrin

80

Wacker system without β-cyclodextrin leads toconversions around 90% after 2 and 6 h, with aselectivity towards 2-octadecanone above 60% for bothtimes (61 and 66%, respectively). In addition, theselectivity towards other ketones was around 6-10%.
These are remarkable results considering the highmolecular weight of 1-octadecene. In addition, at it isshown in Figure 1 the presence of the β-cyclodextrin isslightly detrimental for both the conversion and theselectivity
towards
oxygenatedproducts(2octadecanone + other ketones). Consequently, anotherway to prepare heavy ketones with higher selectivity isrequired.
3.2. Oxidation of 1-dodecene under the presence ofn-dodecane. The performance of the modified Wacker
system in the oxidation of a model equimolar mixture ofn-dodecane + 1-dodecene at 80ºC was initially studied inorder to ascertain the influence of the presence of the nparaffin. The results obtained were compared to those of
the oxidation of 1-dodecene without n-dodecane. Firstly,
the conversion is about 6% higher with n-dodecane in themixture (95% vs. 89%). In terms of selectivity, thepresence of n-dodecane enhances markedly theselectivity towards 2-dodecanone (63% after 2h insteadof 34% with no n-dodecane present). In addition, theselectivity towards other ketones remains similar in bothcases (around 20%). Thus, the total amount ofoxygenates after 2 h with n-dodecane adds up to 85 %while in its absence accounts for only 60%.
Consequently, the presence of n-dodecane increases
meaningfully the selectivity towards oxygenates, mostly
2-dodecanone.

4. Conclusions
The reported modified Wacker system with TBHP asoxidant and acetonitrile as solvent has been proved
useful in the oxidation at 80ºC of the heavy 1-olefins.
Initially, the system allowed the oxidation of 1octadecene with complete conversion and selectivity
close to 60% towards 2-octadecanone after 2 h ofreaction. In addition, the presence of β-cyclodextrins in
the reaction medium was not effective in improving theconversion and selectivity towards 2-octadecanone.
In contrast, the addition of an equimolar amount of ndodecane to the reaction medium allowed to increase theselectivity towards 2-dodecanone from 34 to 63% after 2h of reaction, which was ascribed to a dilution effect of
the n-paraffin, leading to a lower extent of theisomerisation reaction.

References

6040200Conversion S2-octadecanone Sother ketones Sisomers

Y2-octadecanone

Figure 1. Modified Wacker oxidation of 1-octadecene
with and without β-cyclodextrin after 2 (A) and 6 h (B) ofreaction (T = 80 ºC, N = 300 rpm, [C18H36] / [PdCl2] = 50,[solvent] / [C18H36] = 10, [TBHP] / [C18H36] = 6).

interiores libro.indd 140[1] G.V.M. Sharma, P.R. Krishna, Curr. Org. Chem. 8(2004) 1187.
[2] T. Mitsudome, T. Umetani, K. Mori, T. Mizugaki, K.
Ebitani, K. Kaneda, Tetrahedron Lett. 47 (2006) 1425.
[3] J.M. Escola, J.A. Botas, J. Aguado, D.P. Serrano, C.
Vargas, M. Bravo, Appl. Catal. A: Gen. 335 (2008) 137.
[4] J. Aguado, D. P. Serrano, J. M. Escola, Ind. Eng.
Chem. Res. 47 (2008) 7982.

26/9/11 13:13:13