Hydroformylation reaction types

Aliphatic Aldehyde Syntheses. Friedel-Crafts-type aUphatic aldehyde syntheses are considerably rarer than those of aromatic aldehydes. However, the hydroformylation reaction of olefins (185) and the related oxo synthesis are effected by strong acid catalysts, eg, tetracarbonylhydrocobalt, HCo(CO)4 (see Oxo process). 

In the aqueous biphasic hydroformylation reaction, the site of the reaction has been much discussed (and contested) and is dependent on reaction conditions (temperature, partial pressure of gas, stirring, use of additives) and reaction partners (type of alkene) [35, 36]. It has been suggested that the positive effects of cosolvents indicate that the bulk of the aqueous liquid phase is the reaction site. By contrast, the addition of surfactants or other surface- or micelle-active compounds accelerates the reaction, which apparently indicates that the reaction occurs at the interfacial layer. 

Scheme 9.1 General hydroformylation reaction showing all possible product types...

Betzemeier et al. (1998) have used f-BuOOH, in the presence of a Pd(II) catalyst bearing perfluorinated ligands using a biphasic system of benzene and bromo perfluoro octane to convert a variety of olefins, such as styrene, p-substituted styrenes, vinyl naphthalene, 1-decene etc. to the corresponding ketone via a Wacker type process. Xia and Fell (1997) have used the Li salt of triphenylphosphine monosulphonic acid, which can be solubilized with methanol. A hydroformylation reaction is conducted and catalyst recovery is facilitated by removal of methanol when filtration or extraction with water can be practised. The aqueous solution can be evaporated and the solid salt can be dissolved in methanol and recycled. 

The asymmetric reactions discussed in this chapter may be divided into three different types of reaction, as (1) hydrometallation of olefins followed by the C—C bond formation, (2) two C C bond formations on a formally divalent carbon atom, and (3) nucleophilic addition of cyanide or isocyanide anion to a carbonyl or its analogs (Scheme 4.1). For reaction type 1, here described are hydrocarbonyla-tion represented by hydroformylation and hydrocyanation. As for type 2, Pauson-Khand reaction and olefin/CO copolymerization are mentioned. Several nucleophilic additions to aldehydes and imines (or iminiums) are described as type 3. 

One may improve efficiency of an o-DPPB directed hydroformylation by incorporating this reaction into sequential transformations (domino reactions) [16]. The hydroformylation itself should be ideally suited for such a purpose, since this reaction provides under fairly mild reaction conditions access to the synthetically valuable aldehyde functionality. The aldehyde itself should be ideally suited to allow for further skeleton-constructing reactions. One type of sequential transformations employing the hydroformylation reaction as a key step is the hydroaminomethylation of olefins originally discovered by Reppe [17]. However, efficient control of diastereoselectivity in the course of this hydroaminomethylation reaction was unknown [18, 19]. 

The CO insertion mechanisms of the Pichlcr-SchuU type have been largely influenced by principles of homogeneous catalysis and are related to the mechanism proposed for the hydroformylation reaction (sec Mlydroformylation this volume. 

Surprisingly little information is available about the kinetics of hydroformylation reactions. For several decades Natta s equation served as a basic explanation however, in the last few years the application of reaction models of the Lang-muir-Hinshelwood type, even to biphasic systems, has been successfully demonstrated. This contribution (see Section 2.1.1) puts more emphasis on this area than has been usual in reviews on hydroformylation (see Section 2.1.1.3.2). In addition, the fundamentals of the oxo synthesis are discussed, along with the most important recent developments. The industrial processes in operation today are described as well. Due to its importance, the hydroformylation reaction has already been extensively reviewed elsewhere. For information beyond and in addition to this contribution, see [4, 7-12, 293]. 

Concerning the reactions of type 2, addition of CO across double bonds can be exemplified by the hydroformylation reaction ... 

For long-term stability, the SAPC must remain assembled. To test for this type of stability, it was investigated whether the components can self-assemble. The rhodium complex HRh(CO)(TPPTS)3, TPPTS and water were loaded into a reactor with cyclohexane and 1-heptene. The reactor was pressurized with approx. 70 bar H2 + CO (CO H2, 1 1) and heated with stirring to 100°C. A second experiment was carried out in a manner similar to the one previously described except that CPG-240 was added also. The components of the SAPC self-assemble to form an SAPC and carry out the hydroformylation reaction [13]. Upon termination of the reaction, the solid collected contained HRh(CO)(TPPTS)3 and TPPTS. This test indicates that, under the conditions of the experiment, the individual components of the SAPC are more stable assembled in an SAPC configuration than separated. Therefore, the reverse, i.e., the separation of the solution and complex from the support, is not likely to happen under reaction conditions. 

A highly fluorous C02-philic rhodium catalyst was effectively immobilized in an inverted H20/scC02 system for the prototypical hydroformylation reaction shown in Eq. (5) [57]. Emulsion-type mixtures are formed under the reaction conditions upon stirring, which separate rapidly when stirring is stopped. After removal of the aqueous phase from the bottom of the reactor, a clear supercritical catalyst phase remains in the reactor that can be re-used for subsequent reactions. Recycling is very efficient at moderate catalyst loadings, but noticeable deactivation occurs at very low rhodium concentrations, probably caused by the low pH of the aqueous solution in the presence of C02. 

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