461127 Hydroxycarbonylation Vs. Methoxycarbonylation - Palladium Catalyzed Reactions in Multiphase Systems
The carbonylation of olefins with carbon monoxide, also known as Reppe carbonylation , is an important reaction for the functionalization of olefins. The palladium catalyzed, homogeneous reaction offers an easy access to esters and acids which are widely used for textile, agriculture and fine chemistry. Furthermore the reaction is extremely atom economical, all reactants are completely incorporated in the final product and no side products are formed. Besides the development of new catalyst systems to further improve the overall reaction performance , the recycling of the precious, homogeneously dissolved catalyst complex is in the focus of current research due to economical reasons. Many different concepts to overcome this problem are investigated like the immobilisation at a heterogeneous support or the separation by a multiphase system . As a member of the collaborative research center "InPROMPT", which is mainly involved in the development of efficient production processes based on chemical reactions in liquid multiphase systems, we focus on liquid/liquid multiphase systems in order to recycle the catalyst complex and to separate the product after the reaction.
In this contribution we set our focus on the choice of an appropriate multiphase system for the hydroxycarbonylation and methoxycarbonylation of 1‑dodecene in order to get high reaction rates and quantitative recycling of the catalyst complex. Different factors are analyzed to improve the reaction and separation behavior in the multiphase system for these reactions, e. g. the type of cosolvent, the polarity of the polar phase by addition of water and the kind of surfactant. Moreover, for the formation of the acid, we compare the one step hydroxycarbonylation with the two step sequence consisting of a methoxycarbonylation with a following alkaline hydrolysis step in order to identify the better overall reaction performance.
Experimental section and results
The carbonylation experiments are performed in a 100 mL stainless steel autoclave with double jacket for adjusting the temperature and a gas dosage to perform the reactions under constant pressure. A typical reaction mixture consists of the nonpolar phase with the substrate 1‑dodecene (12 g), the polar phase (methanol or water) and the catalyst system, which is formed from a palladium precursor, SulfoXantPhos as ligand (the sulfonated analogous of XantPhos) and a acid promoter. The carbonylation reaction is investigated under constant pressure at 30 bar carbon monoxide and at a temperature range between 80 °C and 110 °C.
As a result the use of a two phase system is favourable for the methoxycarbonylation of 1-dodecene. In contrast the hydroxycarbonylation is not feasible in a simple two phase system, it requires a microemulsion system to increase the interfacial area and the reaction rate. For the hydroxycarbonylation the kind and the concentration of the surfactant is crucial for the reaction performance and the separation behavior. Conversions of 30 % can be obtained after 30 h reaction time. For the methoxycarbonylation conversions over 95 % can be achieved after 20 h reaction time. An increasing amount of water in the polar phase decreases the reaction rate of the reaction, but it leads to an improvement of the separation. After the reaction 99 % of the catalyst complex can be recycled in the polar phase and 95 % of the product is in the non-polar phase. Recycling experiments were done and the catalyst is stable at least for four runs.
This work is part of the Collaborative Research Center/ Transregio 63 "Integrated Chemical Processes in Liquid Multiphase Systems" (subproject A2). Financial support by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) is gratefully acknowledged (TRR 63).
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