Catalytic Activity of the Water-soluble Organometallic Complex
[Rh(µ-Pz)(CO)(TPPTS)]2 in the Hydroformylation of Short-chain Olefins in a Venezuelan Refinery’s Naphtha Cut
a report by Luis G Melean,1 Sheyla Rivera,1 Victor J Guanipa,1
Maria Modroño Alonso,1 Merlin Rosales2
Angel Gonzalez,2 and Pablo J Baricelli1
1. Center for Chemical Research, Faculty of Engineering, University of Carabobo, Valencia, Venezuela; 2. University of Zulia, Faculty of Experimental Sciences, Department of Chemistry, Inorganic Chemistry Laboratory, Maracaibo, Venezuela
The amount of olefins present in naphtha is higher than required for gasoline formulation and might produce a very viscous polymer or solids capable of blocking the carburetors and injectors of the vehicle. Currently, this excess of olefins is lowered by a hydrogenation-over-solids catalyst that is costly and results in a marked decrease in the octane rating of the fuel, which must be corrected by the addition of oxygenated products. A very interesting alternative, which takes advantage of the chemical potential of the olefins, is to hydroformylate them to directly obtain functionalised, oxygenated products.
Hydroformylation cannot be performed with homogeneous catalysts due to the well-known drawbacks of product separation and purification, yet heterogeneous catalysts lack the activity and selectivity required for optimal performance. Thus, this hydroformylation alternative is perfectly suited to a biphasic system that would allow the easy separation of products and recycling of the catalyst, while maintaining the activity and selectivity characteristic of homogeneous complexes.
The biphasic oxo process was introduced by Ruhrchemie/Rhone-Poulenc (R/RP) in 1984 for the hydroformylation of propene to butaldehyde.1 Since this time, there has been a continuous search in academia and the industry for conditions, additives, ligands and catalytic precursors that could enable the methodology to be run with more elaborate substrates, such as longer chain alkenes, which react unacceptably slowly under the standard R/RP process conditions.
Binuclear rhodium complexes are a good alternative since their reactivity has been known for a number of years. Surprisingly, their use has not been explored in many reactions. Few reports deal with rhodium in binuclear systems; one of them is by Kostas and co-workers,2
studied the [Rh2(µ-StBu)2(CO)2(TPPTS)2]2 complex in the biphasic hydroformylation of 1-octene under low pressure. They obtained a
and 1-octene. They obtained good selectivity towards the branched aldehydes in the first case and lineal aldehydes in the second. Kalck et al.3
good selectivity towards the linear aldehyde and observed a dramatic increase in conversion with the addition of methanol as the co-solvent. Duran et al.4
The amount of olefins present in naphtha is higher than required for gasoline formulation and might produce a very viscous polymer or solids capable of blocking the carburetors and injectors of the vehicle.
phosphine obtained from menthone in the hydroformylation of styrene. They obtained a significant selectivity towards the branched aldehydes. Uson et al.5
reported the catalytic activity of the binuclear rhodium
complex with a pyrazolate bridge ligand, [Rh(µ-Pz)(CO)(PPh3)]2, in the hydroformylation reaction of 1-heptene showing a moderate activity.
Baricelli et al. recently reported on the synthesis and catalytic activity of two rhodium binuclear water soluble complexes – [Rh(µ-Pz)(CO)
(TPPMS)]2 and the dimer complex dicarbonylbis(µ-pyrazolate) bis[tris(sodium-m-trisulphonated-triphenylphosphine)]-dirhodium(I)
who
synthesised binuclear aryloxide- and carboxylate-bridged rhodium complexes and evaluated them in the hydroformylation of styrene
Pablo J Baricelli is Director of the Centro de Investigaciones Químicas (CIQ) of the Universidad de Carabobo in Valencia in Venezuela, and leads the Homogeneous and Biphasic Catalysis Laboratory of the CIQ. His areas of research interest are the hydrogenation and hydroformylation reactions of naturally occurring olefins and petroleoum naphthas with transition metal complexes and he has authored over 80 papers.
E:
pbaricel@uc.edu.ve
Merlin Rosales is a Titular-Full Professor in the Chemistry Department at the Universidad del Zulia (LUZ), where he leads a research group working in organometallic chemistry and homogeneous catalysis. He has authored over 40 papers. Professor Rosales received his PhD in Chemistry from the Instituto Venezolano de Investigaciuones Científicas (IVIC) in Caracas in Venezuela, in 2000.
([Rh(µ-Pz)(CO)(TPPTS)]2) – in the biphasic hydroformylation and hydrogenation of a variety of olefins and their mixtures.6,7
These
complexes showed high catalytic activity and were recycled several times without any significant drop in performance.
In this article, the activity of [Rh(µ-Pz)(CO)(TPPTS)]2 was analysed in the biphasic hydroformylation of the olefins present in a real life naphtha
cut from the El Palito refinery in Venezuela. Experiment
General Procedures
All manipulations were carried out under nitrogen using standard Schlenck techniques. Organic solvents and 1-hexene were dried
and purified by distillation over standard agents under N2 prior to use. RhCl3*3H2O was purchased from Pressure Chemicals, 1-hexene
12 © TOUCH BRIEFINGS 2011 used a binuclear rhodium complex with a hydroxylated
Catalysts
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