Typical Reactions 1 Hydroformylation

The automatic procedure for time-series reference spectra generation was first demonstrated for the homogeneous catalyzed rhodium hydroformylation of cyclo-octene using Rh4(CO)i2 as precursor, n-hexane as solvent and FTIR as the in situ spectroscopy at 298 K [64]. Upon addition of hydrogen to the system, hydroformylation is initiated. A typical reaction spectrum (k=7) and the pre-conditioned... 

When triglycerides are used as the substrate, the final product is a triglyceride functionalized with hydroxymethyl groups. One hydroformylation process uses the less expensive cobalt catalyst, requires more harsh process conditions, and generally results in lower yields of the aldehyde products. This approach was investigated by Petrovic et al. at the Pittsburg State University [141]. The typical reaction scheme is outlined in Fig. 20. 

With regard to the structure of the olefins, tetrasubstituted olefins do not undergo hydroformylation reaction under typical reaction conditions, and olefinic substrates containing functional groups sometimes give poor yields and unexpected products. If there is no plane of symmetry in the substrate across the double bond, at least two isomeric aldehydes are obtained. Although methods for shifting the... 

Kuntz subsequently showed that the RhCl (tppts) 3 catalyzed the hydroformylation of propylene in an aqueous biphasic system [29]. These results were further developed, in collaboration with Ruhrchemie, to become what is known as the Ruhrchemie/Rhone-Poulenc two-phase process for the hydroformylation of propylene to n-butanal [18, 19, 22, 30]. Ruhrchemie developed a method for the large scale production of tppts by sulfonation of triphenylphosphine with 30% oleum at 20 °C for 24 h. The product is obtained in 95% purity by dilution with water, extraction with a water insoluble amine, such as tri(isooctylamine), and pH-controlled re-extraction of the sodium salt of tppts into water with a 5% aqueous solution of NaOH. The first commercial plant came on stream in 1984, with a capacity of 100000 tons per annum of butanal. Today the capacity is ca. 400000 tpa and a cumulative production of millions of tons. Typical reaction conditions are T=120°C, P=50bar, CO/H2 = 1.01, tppts/Rh = 50-100, [Rh] = 10-1000 ppm. The RhH(CO) (tppts)3 catalyst is prepared in situ from e.g. rhodium 2-ethylhexanoate and tppts in water. 

Along with studies of the catalyst solution and stoichiometric reaction mixtures, the hydroformylation reaction was studied online under typical reaction conditions by connecting a pressurized autoclave (20 bar) directly to the mass spectrometer via a splitter. While this allowed them to identify new reaction intermediates they did not extract any kinetic data from the observed intermediates over time. Nevertheless, a new hydroformylation reaction mechanism for self-assembling ligands (in which the ligands play an active role in H2 activation) was considered based on... 

Adsorption of a high-boiling solvent onto a high-surface-area microporous solid yields a supported liquid phase that can be removed from the sohd only by extraction with a second solvent or by distillation at high temperature under vacuum. Under typical reaction conditions, a solid that contains a supported liquid phase looks and behaves as a solid, yet it can dissolve small quantities of a metal complex into the supported phase. One of the first examples of this arrangement was achieved with the immobilization of Rh(CO)(PPh3)2Cl in benzyl butyl phthalate on silica. The supported complex was successfiilly used to effect the gas-phase hydroformylation of propene. 

Hydroformylation reactions have been one of the most well researched areas of CO2 reaction chemistry. Hydroformylation reactions are necessary for the formulation of complex chemicals. The first complete kinetic study of a hydroformylation reaction was in CO2 and was first published in 1999. Prior to this, most studies had considered the effect of dense CO2 on linear branch ratios or other forms of selectivity. Carbon dioxide has an effect on the selectivity of a variety of hydroformylation reactions and can enhance the rate of reaction Hydroformylation is by its nature regioselective and typically the linear branch or n iso ratio is used as the measure of selectivity. The use of asymmetric catalysts to achieve chiral products has introduced a second degree of selectivity to catalyst design. Advancements in catalyst design, together with solvent selection, are expected to make... 

The most typical examples in oleochemistry are the hydrogenation, the carbon monoxide reactions hydroformylation and hydrocarboxylation, and the oxidation reaction. 

Wachsen et al. [13] presented a chemical engineering analysis of typical biphasic hydroformylation, the RCH/RP process using propylene, to demonstrate that the reaction occurred at the gas-Hquid interface. With the comparison of the model of bulk liquid-phase reaction and that of reaction in the interphase region with experimental data, it was found that only the latter model elucidated the experimental measurements on the gas-phase pressure and the flux of reaction heat This model is instructive in further efforts to improve the biphasic hydroformylation performance. 

There are numerous examples where the concept of supported ILs has been applied to specific chemical reactions. Examples include hydrogenation [57, 61, 62], hydroamination [24, 43, 63], aUyUc substitution [47], hydroformylation [64], carbonylation [64, 65], and carboxylation [66] reactions as well as partial oxidation of alcohols [67], the Claisen-Schmidt reaction [68], Mukaiyama aldol reaction [69], Michael reaction [70], and many more [71]. The concept is readily applied to reactions in which the bulk fluid is a gas, a Hquid, or a two-phase mixture of gas and liquid. Organometallic complexes, metal clusters, and supported functional groups have been employed as the catalyticaUy active function F. Characteristic features of some selected reaction systems are summarized in the following, focusing on two typical reaction systems involving liquid bulk fluids. 

Scheme 5.144 Hydroformylation-decarboxylative Knoevenagel (Doebner-Knoevenagel) reaction and typical reaction products.

Examples of applying biphasic system to catalyzed reactions, such as phase-transfer catalysis, show the efficiency over stoichiometric reactions. In a typical catalytic biphasic system, one phase contains the catalyst while the substrate is in the second phase. In some systems, the catalyst and substrates are in the same phase while the product produced is transferred to the second phase. In a typical reaction, the two phases are mixed during the reaction and after completion, the catalyst remains in one phase ready for recycling while the product can be isolated from the second phase. The most common solvent combination consists of an organic solvent combined with another immiscible solvent, which, in most applications, is water. However, there are few examples of suitable water-soluble and stable catalysts, therefore various applications are limited to some extent [4]. Immiscible solvents other than water are recently becoming more applicable in biphasic catalysis due to the better solubility and stability of various catalysts in such solvents. For example, ionic liquids and fluorous solvents have many successful applications in liquid-liquid biphasic syntheses such as Heck reactions and hydroformylations using ionic liquid media, or Baeyer-Villiger reactions... 

In a Lewis-acid catalysed Diels-Alder reaction, the first step is coordination of the catalyst to a Lewis-basic site of the reactant. In a typical catalysed Diels-Alder reaction, the carbonyl oxygen of the dienophile coordinates to the Lewis acid. The most common solvents for these processes are inert apolar liquids such as dichloromethane or benzene. Protic solvents, and water in particular, are avoided because of their strong interactions wifti the catalyst and the reacting system. Interestingly, for other catalysed reactions such as hydroformylations the same solvents do not give problems. This paradox is a result of the difference in hardness of the reactants and the catalyst involved... 

Butylene isomers also can be expected to show significant differences in reaction rates for metaHation reactions such as hydroboration and hydroformylation (addition of HCo(CO). For example, the rate of addition of di(j -isoamyl)borane to cis-2-huX.en.e is about six times that for addition to trans-2-huX.en.e (15). For hydroformylation of typical 1-olefins, 2-olefins, and 2-methyl-l-olefins, specific rate constants are in the ratio 100 31 1, respectively. 

The catalysts used in hydroformylation are typically organometallic complexes. Cobalt-based catalysts dominated hydroformylation until 1970s thereafter rhodium-based catalysts were commerciahzed. Synthesized aldehydes are typical intermediates for chemical industry [5]. A typical hydroformylation catalyst is modified with a ligand, e.g., tiiphenylphoshine. In recent years, a lot of effort has been put on the ligand chemistry in order to find new ligands for tailored processes [7-9]. In the present study, phosphine-based rhodium catalysts were used for hydroformylation of 1-butene. Despite intensive research on hydroformylation in the last 50 years, both the reaction mechanisms and kinetics are not in the most cases clear. Both associative and dissociative mechanisms have been proposed [5-6]. The discrepancies in mechanistic speculations have also led to a variety of rate equations for hydroformylation processes. 

In a similar way, carbocycles having a quaternary center could be obtained from acyclic unsaturated 1,3-dicarbonyl compounds [206]. Other combinations are the domino hydroformylation/Wittig olefmation/hydrogenation described by Breit and coworkers [207]. The same group also developed the useful domino hydroformyla-tion/Knoevenagel/hydrogenation/decarboxylation process (Scheme 6/2.14) [208] a typical example is the reaction of 6/2-66 in the presence of a monoester of malonic acid to give 6/2-67 in 41 % yield in a syn anti-ratio of 96 4. Compounds 6/2-68 and 6/2-69 can be assumed as intermediates. 

Today, iridium compounds find so many varied applications in contemporary homogeneous catalysis it is difficult to recall that, until the late 1970s, rhodium was one of only two metals considered likely to serve as useful catalysts, at that time typically for hydrogenation or hydroformylation. Indeed, catalyst/solvent combinations such as [IrCl(PPh3)3]/MeOH, which were modeled directly on what was previously successful for rhodium, failed for iridium. Although iridium was still considered potentially to be useful, this was only for the demonstration of stoichiometric reactions related to proposed catalytic cycles. Iridium tends to form stronger metal-ligand bonds (e.g., Cp(CO)Rh-CO, 46 kcal mol-1 Cp(CO)Ir-CO, 57 kcal mol ), and consequently compounds which act as reactive intermediates for rhodium can sometimes be isolated in the case of iridium. 

Pettit and coworkers—metal hydride intermediates by weak base attack over Fe carbonyl catalysts. Pettit et al.ls approached the use of metal carbonyl catalysts for the homogeneous water-gas shift reaction from the standpoint of hydroformyla-tion by the Reppe modification.7 In the typical hydroformylation reaction, an alkene is converted to the next higher aldehyde or alcohol through reaction of CO and H2 with the use of a cobalt or rhodium carbonyl catalyst. However, in the Reppe modification, the reduction is carried out with CO and H20 in lieu of H2 (Scheme 6) ... 

All metals in the neighborhood of rhodium on the periodic table are known to be active in hydroformylation. Rhodium is by far the most active metal being used in concentrations of 10-100 mg/kg, usually at temperatures below 140 °C. Typical concentrations of cobalt-based catalysts are in the range of 1 -10 g/kg at temperatures up to 190 °C to get sufficient space-time yield. Apart from some specialized applications, other metals are only of scientific interest because of their low activity. A proper comparison of metal activity is difficult because of the different requirements on the reaction conditions. A generally accepted rough order of activity is given in Table 1. 

In the following sections a few typical processes will be described. An example of a cobalt catalysed hydroformylation reaction for higher alkenes is the Kuhlmann process (now Exxon process), for which the flow-scheme -a liquid/liquid separation- is shown in Figure 7.4. In this process the hydroformylation is done in one, organic phase consisting of alkene and aldehyde. The reactor is often a loop reactor or a reactor with an external loop to facilitate heat transfer. 

Rhodium-phosphine catalysts are unable to hydroformylate internal olefins, so much that in a mixture of butenes only the terminal isomer is transformed into valeraldehydes (see 4.1.1.2). This is a field still for using cobalt-based catalysts. Indeed, [Co2(CO)6(TPPTS)2] -i-lO TPPTS catalyzed the hydroformylation of 2-pentenes in a two-phase reaction with good yields (up to 70%, but typically between 10 and 20 %). The major products were 1-hexanal and 2-methylpentanal, and n/i selectivity up to 75/25 was observed (Scheme 4.12). The catalyst was recycled in four mns with an increase in activity (from 13 to 19 %), while the selectivity remained constant (n/i = 64/36). 

The hydroformylation reaction, also known as the oxo reaction, is used extensively in commercial processes for the preparation of aldehydes by the reaction of one mole of an olefin with one mole each of hydrogen and carbon monoxide. The most extensive use of the reaction is in the preparation of normal- and iso-butyraldehyde from propylene. The ratio of the amount of the normal aldehyde product to the amount of the iso aldehyde product typically is referred to as the normal to iso (N I) or the normal to branched (N B) ratio. In the case of propylene, the normal- and iso-butyraldehydes obtained from propylene are in turn converted into many commercially-valuable chemical products such as n-butanol, 2-ethyl-hexanol, trimethylol propane, polyvinylbutyral, n-butyric acid, iso-butanol, neo-pentyl glycol,... 

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