Rhodium TPPTS

Keywords hydrotalcites, heterogeneization, rhodium, TPPTS, y-lactone. 

The third generation process concerns the Ruhrchemie/Rhone-Poulenc process utilizing a two-phase system containing water-soluble rhodium-tppts in one phase and the product butanal in the organic phase. The process has been in operation since 1984 by Ruhrchemie (or Celanese, nowadays). The system will be discussed in section 8.2.5. Since 1995 this process is also used for the hydroformylation of 1-butene. 

In 1976, water-soluble triarylphosphine, TPPTS (43, Figure 15), was synthesized and used for two-phase hydroformylation system. Here the rhodium catalyst is soluble in water, whereas the substrate and the product remain in organic solvents. The catalytic performance of the rhodium-TPPTS complexes is similar to the ordinary... 

Hydroformylation of Mid Range Olefins - Rhodium/tppts catalysts exhibit low catalytic activity in the hydroformylation of mid range olefins (C5-Cg) in a two phase system due to the much lower solubility of such olefins in water. In the Rh/tppts catalysed biphasic hydroformylation of 1-hexene, for example the conversion is only 11-22% with a n/i ratio of aldehydes of 98/2.353,373 The rate of 1-hexene hydroformylation catalysed by Rh/tppts increased by a factor 2.3 when subjected to ultrasound (35 kHz) and high stirring rates.360,361... 

Homologous w-alkenecarboxylic acid methyl esters were hydroformyl-ated with the water-soluble rhodium/tppts catalyst in an aqueous-organic two-phase system (75). By addition of surfactants a micellar system was created. Cationic surfactants are better than anionic or nonionic surfactants for this hydroformylation. 

Another novel technique for separation of the TPPTS-based catalyst is by immobilizing it on a solid support. This catalyst consists of a thin film of an aqueous solution of rhodium-TPPTS complex supported on high-surface-area... 

Catalyst decomposition is, overall, receiving little attention in academic work on homogeneous catalysis, and only in recent years has research on decomposition and stabilization of organometallic catalysts started to expand (116), with emphasis on reactions of significant commercial interest such as hydroformylation (117), metathesis 118), crosscoupling, and polymerization 119). Ligand decomposition seems to be a key issue for industrial application, because it affects the total number of turnovers, TON. Phosphine decomposition is an unavoidable side reaction in metal-phosphine complex-catalyzed reactions and the main barrier for commercial application of homogeneous catalysts. There are a few exceptions to this statement for example, the rhodium tppts-catalyzed hydroformylation of propene, a process developed by Ruhrchemie-Rhone Poulenc (now Celanese). 

Some of the examples presented in Section 4.2.2 are, however, not only restricted to the two liquid phases discussed, but contain in addition a further gas phase [89]. For instance, in hydroformylation a water-gas phase exists, in oligomerizations an ethylene phase and in telomerizations a butadiene phase. For these gas-liquid-liquid systems there is so far only a limited amount of published information on the reaction engineering aspects [90]. One exception is the study of 1-oc-tene hydrogenation using a rhodium/TPPTS catalyst [91], in which both thermodynamics and kinetics have been investigated in some detail. The same group also studied the hydroformylation of 1-octene [92]. 

During the hydroformylation of higher alkenes under the Ruhrchemie/Rhone-Poulenc conditions the pH value is controlled and adjusted between 5.5 and 6.2 [26], In discontinuous operation it drops by almost one pH unit from approximately 6.5 at the beginning of the reaction to pH 5.5-6 at the end of the reaction. According to our investigations the pH shift is due to the formation of carbon dioxide, formed via the water-gas shift reaction (WGSR), which is also promoted by rhodium TPPTS complexes but to a lower extent [27]. 

Figure 7.6 Rate of the hydroformylation (indicated by decrease of syngas pressure) in the hydroformylation of 1-olefins with a rhodium TPPTS catalyst effected by adding [OMIMJBr (0.5 mol dm" ). (Derived from Ref. [24].)...

TUloy and Monflier [39] hydroformylated higher olefins (1-decene, 1-tetracene, 1-hexadecene) in a biphasic medium with the assistance of commercially available RAME (Figure 7.5, Scheme 7.8). For example, 1-decene was converted with a rhodium-TPPTS catalyst in water in the presence of RAME-P-cyclodextrine with high yield and moderate regioselectivity. Noteworthy, almost no rhodium leaching into the organic phase was observed. 

The most used ionic liquids in the hydroformylation are those based on the 1-n-butyl-3-methylimidazolium cation, in particular, associated with hexafluorophosphate anion (BMI PF, see Table 6.1). However, the activity and selectivity in the hydro-formylation of 1-hexene catalyzed by rhodium-TPPTS complexes in BMI BF4 were much higher than those reported in other ionic liquids. Under optimum conditions, the TOF of 1 -hexene and selectivity for aldehyde were 1508 h and 92%, respectively. The high activity of the catalyst was ascribed to the much higher solubility of hydrogen [27] and rhodium-TPPTS complexes in BMI BF4 than in BMI PF ]28]. Other ionic liquids have also been used, such as those containing polyether chains attached to ammonium salts 2 (entries 7 and 8, Table 6.1) ]14], phosphonium salts (entry 3, Table 6.1) [11], tris[oxoethyl(trimethyl)ammonium]triazine derivatives... 

Hydroformylation of 1-dodecene using a rhodium-TPPTS catalyst in a microemulsion has been described. High activities and good selectivities toward the n-aldehyde were achieved at 80 °C and 80 bar CO H2 = 1 1. The reaction rates were higher than those in a two-phase system. Technical-grade polyglycolether type surfactants were used for the preparation of the microemulsions [95]. 

The rhodium/TPPTS-catalyzed hydroformylation of 1-octene and other higher olefins in an aqueous biphasic system was studied at pressures from 40 to 90 bar and temperatures of up to 120 °C. Nonionic amphiphiles of the alkoxyethylene type were applied to promote the contact between the reacting species by enlargement of the interfacial area. The highest reaction rates were obtained at a surfactant concentration of about 1 wt% [109]. 

The rhodium/TPPTS-catalyzed hydroformylation of higher olefins in organic/ aqueous biphasic system in the presence of double long-chain cationic surfactants (37) was studied at 100 °C and 20 bar CO H2 = 1 1 pressure. The reaction rate was comparable with that in homogeneous catalysis system [111]. 

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