Hydroformylation heterogeneously catalyzed

Aldridge and Jonassen (7) have attempted to distinguish between the similar poisoning effects of thiophene and heavy metals on metal carbonyls and fresh metal surfaces. They concluded that Eq. (64) was heterogeneously catalyzed by cobalt metal. This is a point which is difficult to prove unequivocally, however. Attempts to vindicate the early assumption that the hydroformylation reaction is heterogeneously catalyzed (5, 6) have received no further support in recent years. 

The hydroformylation of alkenes is commonly run using soluble metal carbonyl complexes as catalysts but there are some reports of heterogeneously catalyzed reactions of olefins with hydrogen and carbon monoxide. Almost all of these are vapor phase reactions of ethylene or propylene with hydrogen and carbon monoxide catalyzed by rhodium, " 20 ruthenium,nickel, 22,123 cobalt, 23,124 and cobalt-molybdenum 23 catalysts as well as various sulfided metal catalysts. 23,125,126... 

The hydroformylation or oxo reaction has been chosen for particular study for several reasons (a) The reaction was discovered by Roelen 2) in the course of an investigation of the mechanism of the Fischer-Tropsch reaction, and a study of the hydroformylation reaction could furnish information on the course of this heterogeneously catalyzed synthetic fuel process (6) hydroformylation involves the activation of hydrogen by a molecularly dispersed catalyst (c) there are few side reactions (d) the catalyst for the reaction, Co2(CO)s, is easily prepared, is relatively nontoxic, and is consequently readily available for study and (e) the reaction is of great industrial importance. 

Pd-catalyzed allylic amination of crotyl acetate by piperidine, while exhibiting a reduced rate as is commonly observed for heterogenized systems (90% conversion achieved after 30 min compared with 5 min for the homogeneous system). Interestingly, the catalyst could be recycled three times via a simple filtration step. Subsequently, the catalyst was separated from the support and the support was uploaded with hydroformylation catalysts. 

This chapter has focused on heterogeneous catalysis in supercritical media, but the relationship between supercritical fluids and catalysis is much broader. There have been numerous studies of homogeneous catalysis in SCFs. Examples include hydroformylation via cobalt carbonyl complexes in supercritical CO2, oxidation via metal salts dissolved in supercritical water, and acid-catalyzed dehydration of alcohols in supercritical water. 

The hydroformylation of alkenes was accidentally discovered by Roelen [4] while he was studying the Fischer-Tropsch reaction (conversion of syn-gas to liquid fuels with a heterogeneous cobalt catalyst) in the late thirties. In what w s probably designed as a mechanistic experiment Roelen examined whether alkenes were intermediates in the Aufbau process for converting syn-gas (from coal, Germany 1938) to fuel. It took more than a decade before the reaction was taken further, but now it was the conversion of petrochemical hydrocarbons into oxygenates that was the driving force. It was discovered that the reaction was not catalyzed by the supported cobalt, but in fact by HCo(CO)4 which was formed in the liquid state. 

Two or three decades ago, no clear conceptual (mechanistic) or practical (experimental) bridge existed between homogeneous and heterogeneous catalysis. In some of his earliest work at Mobil, Werner demonstrated that hydroformylation, carbonylation, and other reactions catalyzed by transition metal complexes were accomphshed equally by heterogeneous catalysis when these complexes were anchored to solid organic resins. 

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