Comparison between phosphine and NHC-modified Pd catalysts in the telomerization of butadiene with methanol – A kinetic study combined with model-based experimental analysis

Abstract

Comparison between phosphine and NHC-modified Pd catalysts in the telomerization of butadiene with methanol ndash a kinetic study combined with model-based experimental analysis, Chemical Engineering and Processing http://dx.doi.org/10. 1016/j.cep.2015.07.007 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.Comparison between phosphine and NHC-modified Pd catalysts in the telomerization of butadiene with methanol -a kinetic study combined with model-based experimental analysis The telomerization of butadiene with methanol was investigated in the presence of different palladium catalysts modified either with triphenylphosphine (TPP) or 1,3-dimesityl-imidazol-2-ylidene (IMes) ligand. When pure butadiene was used as substrate, a moderate selectivity for the Pd-TPP catalyst toward the desired product 1-methoxy-2,7-octadiene (1-Mode) of around 87 % was obtained, while the IMes carbene ligand almost exclusively formed 1-Mode with 97.5 % selectivity. The selectivity remained unchanged when the pure butadiene feed was replaced by synthetic crack-C 4 (sCC 4 ), a technical feed of 45 mol % butadiene and 55 mol % inerts (butenes and butanes). The TPP-modified catalyst showed a lower reaction rate, which was attributed to the expected dilution effect caused by the inerts. Surprisingly, the IMes-modified catalyst showed a higher rate with sCC 4 compared to the pure feed. By means of a model-based experimental analysis, kinetic rate equations could be derived. The kinetic modeling supports the assumption that the two catalyst systems follow different kinetic rate equations. For the Pd-TPP catalyst, the reaction kinetics were related to the Jolly mechanism. In contrast, the Jolly mechanism had to be adapted for the Pd-IMes catalyst as the impact of the base seems to differ strongly from that for the Pd-TPP catalyst. The Pd-IMes system was found to be zero order in butadiene at moderate to high butadiene concentrations and first order in base while the nucleophilicity of the base is influenced by the methanol amount resulting in a negative reaction order for methanol.

The Telomerization of 1,3‐Dienes – A Reaction Grows Up

“…Using kinetic experiments, Haumann et al could identify a slightly different catalytic mechanism for Pd/NHC catalysts, involving an alcoholate‐mediated step ( IV in Scheme ). This probably accounts for the different reaction patterns in telomerization and dimerization . This also leads to the necessity of using bases with Pd/NHC catalysts as opposed to Pd/PR 3 catalytic systems.…”

Systematic Design of a Butadiene Telomerization Process: The Catalyst Makes the Difference

“…This monocarbene‐palladium complex is more selective than the standard Pd/TPP catalyst and can, in principle, be continuously separated and recycled, since it remains active at the end of the reaction . Based on literature data , , the key variables for catalyst selection proposed by Hintermair et al were analyzed as presented in Tab. .…”

“…In general, it is known that Pd/TPP and Pd/IMes can be applied successfully to this reaction in liquid phase , , , but there are no existing reports on the use of solid‐phase catalysts. Despite a recent assessment of the mechanism of butadiene telomerization , there seems to be no intrinsic barrier to use a solid‐phase supported analogue of either Pd/TPP or Pd/IMes. The impact of different approaches to the immobilization of homogeneous catalysts on the butadiene telomerization process has been assessed against the existing experimental data from literature , , with the results presented in Tab.…”

“…Völkl et al recently published a kinetic study for the Pd/TPP and Pd/IMes systems where they compared the systems' activity with a synthetic crude C 4 feed to pure 1,3‐butadiene feed and derived kinetic models for both reaction systems. For the Pd/TPP system, the initial reaction rate was higher for pure 1,3‐butadiene compared to C 4 (Fig.…”

“…Experimental conditions: 70 °C, 15 bar, butadiene/methanol = 0.5, butadiene/Pd = 40 000, ligand/Pd = 4, butadiene/base = 400. Experimental data are taken from Völkl et al .…”