Hydroformylation industrial relevance

Abstract This chapter presents the latest achievements reported in the asymmetric hydroformylation of olefins. It focuses on rhodium systems containing diphosphites and phosphine-phosphite ligands, because of their significance in the subject. Particular attention is paid to the mechanistic aspects and the characterization of intermediates in the hydroformylation of vinyl arenes because these are the most important breakthroughs in the area. The chapter also presents the application of this catalytic reaction to vinyl acetate, dihydrofurans and unsaturated nitriles because of its industrial relevance. 

In hydroformylation, several metals have high catalytic activity. Roelen discovered hydroformylation by using cobalt as the catalyst metal. Cobalt catalysts need relatively harsh conditions with high pressures and temperatures. A more active catalyst metal is rhodium, which enables working under milder conditions. Other metals which can be employed in hydroformylation are ruthenium, palladium, iridium, or platinum-tin catalysts however, only the most active rhodium and cobalt systems are industrially relevant. The development of hydroformylation catalysts in industry progressed through several steps. 

Besides the class of traditional phosphines ligands, the related class of phosphite ligands has been utilized as ancillary ligation in various industrially relevant processes such as the hydrocyanation see Hydrocyanation) of dienes or hydroformylation see Hydroformylation) or the copolymerization of CO and olefins.The thermochemistry of ligand substitution of a variety of phosphite ligands has... 

Double-bond isomerization has been exploited as a desired reaction in organic synthesis examples include the synthesis of steroids. It is also an undesired side reaction of industrially relevant reactions such as hydroformylation (cf. Section 2.1.1), hydrogenation (cf. Section 2.2), and hydrosilyation (cf. Section 2.6), it is a subject of current interest [34—36]. Two promising developments are worth mentioning here because they yielded highly selective catalysts which are, at the same time, easy to handle. 

Aliphatic amines are amongst the most important bulk and fine chemicals in the chemical and pharmaceutical industry [13]. Hydroaminomethylation of alkenes to amines presents an atom-economic, efficient and elegant synthetic pathway towards this class of compounds. In hydroaminomethylation a reaction sequence of hydroformylation of an alkene to an aldehyde with subsequent reductive amina-tion proceeds in a domino reaction (see Eq. 4) [14]. Recently, the highly selective hydroamination of alkenes with ammonia to form linear primary and secondary aliphatic amines with a new Rh/Ir catalytic system (] Rh(cod)Cl 2], ] Ir(cod)Cl 2], aqueous TPPTS solution) has been described (see Scheme 2) [15]. The method is of particular importance for the production of industrially relevant, low molecular weight amines. 

Transition metal catalysts encapsulated within the ligand-template nanoreactor G, P(Py)s [ZnJs, have been applied to catalyze industrially relevant processes such as hydroformylation and Heck reaction. Nanoreactor [G 3 Rh(CO)(acac)] encapsulates a Rh-species that contains only one tris(meta-pyridyl)phosphine ligand, P(m-Py)3, surrounded by three Zn-porphyrins or Zn-salphens. Under syngas pressure (H2/CO), rhodium species like Rh(CO)(acac)P(Py)3 transform into a complex of type HRh(CO)3P(Py)3, which is the active species for the hydroformylation reaction, hi this reaction terminal alkenes are converted into linear and/or branched aldehydes, and the ratio of these products strongly depends on the specific catalyst applied. Hydroformylation of 1-octene by encapsulated rhodium, [G 3 HRh(CO)3], resulted in a 10-fold rate enhancanent compared... 

Catalyst and olefin feed are the key to what type of alcohols are formed. The industrially relevant catalysts employed are cobalt carbonyP or cobalt carbonyl/tert-phosphine complexes. " In the hydroformylation of an olefin, linear terminal aldehydes are formed along with other isomeric 2-alkyl-branched aldehydes as noted in the structures in Figure 6.8. 

It is only relatively recently that data have started appearing on comprehensive studies of the use of intensified unit operations in industrially relevant reactions -particularly for bulk production. One such study involved a comparison between the stirred batch reactor process and a heat exchanger reactor (HEX-reactor). This was reported by a consortium involving Cardiff University, Givaudan, Johnson Matthey and Chart Energy and Chemicals (who supplied the HEX-reactor), and is presented in Enache et al. (2007). The hydroformylation reactions examined are used for the production of detergents, soap and surfactants - totalling millions of tonnes per annum. 

The hydroformylation of mixtures of Cg-olefins is a process with huge economic importance. A typical example is di-n-butene, consisting of isomeric -octenes, methylheptenes, and dimethylhexenes. The mixture is produced from Raffinate II, in which isomeric butenes are dimerized (e.g., by IFP Dimersol [47] or Octol process [48]). Hydroformylation of di- -butene produces linear and alkyl-branched Cg-aldehydes, which are converted to diisononyl phthalate (DINP), another additive for flexible PVC with immense industrial relevance. For this application, the use of terminal aldehydes is preferred. 

Cobalt carbonyls are the oldest catalysts for hydroformylation and they have been used in industry for many years. They are used either as unmodified carbonyls, or modified with alkylphosphines (Shell process). For propene hydroformylation, they have been replaced by rhodium (Union Carbide, Mitsubishi, Ruhrchemie-Rhone Poulenc). For higher alkenes, cobalt is still the catalyst of choice. Internal alkenes can be used as the substrate as cobalt has a propensity for causing isomerization under a pressure of CO and high preference for the formation of linear aldehydes. Recently a new process was introduced for the hydroformylation of ethene oxide using a cobalt catalyst modified with a diphosphine. In the following we will focus on relevant complexes that have been identified and recently reported reactions of interest. 

The lack of data is obvious and surprising at a time when the Ruhrchemie/ Rhone-Poulenc process has been in operation for more than 20 years. A rigid reaction rate model, established under idealized conditions, becomes complex and complicated when it is transferred to the hydroformylation of lower olefins under conditions relevant to the industrial practice, as the mass transfer phenomena involved in a triphasic system (gas-liquid-liquid) in large reactors have to be taken... 

Another catalytic cycle studied by Matsubara, Morokuma, and coworkers [77] is the hydroformylation of olefin by an Rh(I) complex. Hydroformylation of olefin by the rhodium complex [78-80] is one of the most well known homogeneous catalytic reactions. Despite extensive studies made for this industrially worthwhile reaction [81, 82], the mechanism is still a point of issue. The active catalyst is considered to be RhH(CO)(PPh3)2, 47, as presented in Fig. 25. The most probable reaction cycle undergoes CO addition and phosphine dissociation to generate an active intermediate 41. The intramolecular ethylene insertion, CO insertion, H2 oxidative addition, and aldehyde reductive elimination are followed as shown with the surrounding dashed line. Authors have optimized the structures of nearly all the relevant transition states as well as the intermediates to determine the full potential-... 

This chapter has presented a tabulation of transition-metal phosphine complexes bearing some relation to proposed intermediates in a number of catalytic reactions. It is an interesting commentary on structural inorganic chemistry that, despite the determination of approximately 2500 crystal structures of such complexes, there are so few structures of direct relevance to such processes. For example, there is but one direct structural analogue (compound 2) for any of the intermediates proposed in the hydroformyla-tion reaction, the most important and oldest industrial process based on a homogeneous transition-metal phosphine complex. Similarly, the structure of only one transition-metal allyl hydride is known,despite the fact that allyl hydrides are frequently proposed intermediates. This paucity of structural information does not necessarily result from the inherent reactivity of such intermediates—for example the synthesis of suitable analogues for the hydroformylation reaction would appear to be straightforward. There appear to be several potential routes to complexes of the type MH2(C0R)L3, and one would expect that complexes of the type A/(H)-(C0)L2 would be stable, especially for L, a bulky phosphine. 

Hydroformylation. Hydroformylation (homogeneous) and Hydroformyla-tion (industrial processes/engineering) constitute separate entries in this Encyclopedia, so there is no need for lengthy treatment of the general questions of this most important catalytic reaction in this section. Several aspects of the field are treated in recent reviews (1,3,5,28,145). Attention is paid only to those features that have direct relevance to the aqueous-organic biphasic nature of the process. With very few exceptions, the catalysts contain rhodium although attempts to use cobalt and platinum complexes have also been described in the literature for specific purposes. 

Especially in bulk chemistry, linear aldehydes are the favored products. To achieve this goal, a-olefins are ideal substrates, which can be converted with high -regioselectivity into the corresponding terminal aldehydes. Under appropriate reaction conditions, the formation of isomeric (preferably) 2-aldehydes is suppressed [2]. However, most technical feeds contain preferentially internal olefins, such as Raffinate I-III (all butene isomers) or di-w-butene (mixture of isomeric Cg olefins). Also, with this starting material the production of -aldehydes is the favored target. This can be achieved only by a shift of the olefinic double bond prior to hydroformylation. The whole approach is termed isomerization-hydroformylation (Scheme 5.1). Relevant industrial units operate in the 10 000-100 000 MT scale. 

An example with huge economic relevance is the manufacture of 2-propyl-heptanol (2-PH) as a component of plasticizer alcohols and, on a smaller scale, for use in cosmetics [9]. On an industrial scale, the transformation is commonly conducted as a three-step approach starting with the hydroformylation of isomeric butenes, subsequent aldol reaction of formed -valeraldehyde, and, finally, combined hydrogenation of the C-C double bond and aldehyde group [10]. In a similar process, the production of the plasticizer alcohol 2-ethyl-hexanol (2-EH) is carried out [11, 12]. 

In order to illustrate the potential of cluster chemistry in catalysis, the catalytic activity of cluster species in a number of selected processes will be described. The processes to be considered-hydrogenation and isomerization of unsaturated hydrocarbons, hydroformylation of alkenes, hydrogen reductions of carbon monoxide, and water-gas shift reaction-are interesting not only from the point of view of fundamental knowledge but also because of their great industrial and economical relevance. 

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