Hydroformylation overview

Various other biphasic solutions to the separation problem are considered in other chapters of this book, but an especially attractive alternative was introduced by Horvath and co-workers in 1994.[1] He coined the term catalysis in the fluorous biphase and the process uses the temperature dependent miscibility of fluorinated solvents (organic solvents in which most or all of the hydrogen atoms have been replaced by fluorine atoms) with normal organic solvents, to provide a possible answer to the biphasic hydroformylation of long-chain alkenes. At temperatures close to the operating temperature of many catalytic reactions (60-120°C), the fluorous and organic solvents mix, but at temperatures near ambient they phase separate cleanly. Since that time, many other reactions have been demonstrated under fluorous biphasic conditions and these form the basis of this chapter. The subject has been comprehensively reviewed, [2-6] so this chapter gives an overview and finishes with some process considerations. 

This chapter aims to provide an overview of the current state of the art in homogeneous catalytic hydrogenation of C=0 and C=N bonds. Diastereoselec-tive or enantioselective processes are discussed elsewhere. The chapter is divided into sections detailing the hydrogenation of aldehydes, the hydrogenation of ketones, domino-hydroformylation-reduction, reductive amination, domino hydroformylation-reductive amination, and ester, acid and anhydride hydrogenation. 

This brief review can provide only a snapshot of the state of art. The older literature up to 1980 is covered by the still important review by Falbe [3]. A concise overview up to 2002 can be found in Cornils and Flerrmann [4]. Hy-droformylation with rhodium catalysts is covered by the book of van Leeuwen and Claver [5]. Ungvary reviews new developments in hydroformylation, mainly in scientific papers, every year [6-9]. 

Figure 7.3 gives an overview of the reactions involved in the hydroformylation of internal alkenes to linear products. It has been suggested that cobalt, once attached to an alkene, runs along the chain until an irreversible insertion of CO occurs. Thus, the alkene does not dissociate from the cobalt hydride during the isomerisation process. There is no experimental support for a clear-cut proof for this mechanism. In alkene polymerisation reactions this type of chain running has been actually observed. 

General articles concerning transition metal hydrides,366 their crystallography,368 and on the preparation and properties of borohydride complexes369 are available. An overview on the use of HCo(CO)4 and related cobalt hydrides as catalysts in the hydroformylation of alkenes is available.367... 

Silica-supported ionic liquid-phase (SILP) catalysis has been developed as an alternative approach to address the problem of product isolation, a methodology well known from aqueous catalysis, and an overview of SILP-hydroformylation reactions in ionic liquids is given in Table 4.4.[631... 

In this section, we will report on investigations in the two-phase hydroformylation of higher alkenes with aqueous Rh-TPPTS catalyst systems. The overview on the present state of the art in two-phase hydroformylation will be confined to those investigations which are not covered by the respective original authors in this book. 

G. G. Stanley (1994) Carbonylation processes by homogeneous catalysis in Encyclopedia of Inorganic Chemistry, ed. R.B. King, Wiley, Chichester, vol. 2, p. 575 - A well-referenced overview which includes hydroformylation, Monsanto and Tennessee-Eastman processes. 

The chemistry of hydroformylation has been thoroughly described by Dr. J. Falbe in New Synthesis with Carbon Monoxide. This presentation is merely a brief overview of the processes of commercial importance. 

Because of the immense importance of phosphites as ligands, not only in rhodium-catalyzed hydroformylation, several recent reviews have dealt with these compounds and provided quite complete collections of individuals [2, 15], In contrast to these overviews, in this chapter we will focus on some issues that are seldom in the focus. This concerns the synthesis of alcohols that are required as the alcohol component for the synthesis of phosphorous acid triesters. This has never been considered in detail. However, their availability is an important criterion for chemists dealing with large-scale applications and therefore has economic consequences. Some general synthesis protocols of phosphites together with some typical examples will also be considered. The complexation behavior of phosphites with rhodium will also be discussed briefly. Some remarks about the stability of ligands and Rh catalysts will close this chapter. 

Myrcene is a very abundant acyclic monoterpene available from the essential oils of various plants including wild thyme and hops. Recently, an excellent overview on the manufacture and transformation of this natural product was given by Behr and Johnen [125]. Commercially, myrcene is produced by the pyrolysis of pinenes [126]. The rhodium-catalyzed hydroformylation of myrcene gives usually a mixture of fragrance aldehydes in more than 90% combined yields (Scheme 6.37) [127, 128]. The main aldehyde, which accounted for 70 - 80% of the mass balance, results from the reaction with the less substituted C=C bond through the formation of a T) -allyl rhodium intermediate complex [127]. The reaction was also performed in a toluene/water biphasic system using the water-soluble TPPTS ligand and a cationic surfactant [84]. 

In the following, the most important catalyst and process technologies for industrial olefin hydroformylation are presented and their specific advantages and disadvantages are discussed. Table 6.14.1 gives an overview of the different processes described in more detail throughout this subchapter. 

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