Hydroformylation kinetic studies

A lot of research has been published on hydroformylation of alkenes, but the vast majority of the effort has been focused on the chemistry of various metal-ligand systems. Quantitative kinetic studies including modeling of rates and selectivities are much more scarce. In this work, we present the approach to modeling of hydroformylation kinetics and gas-solubility. Hydroformylation of 1-butene with a rhodium-based catalyst was selected as a case study. 

The formation of multinuclear clusters is much more favorable for rhodium than for cobalt. Additional evidence was obtained in comparative hydroformylation rate studies of 1-heptene and of cyclohexene at 75°C and 150 atm 1/1 H2/CO (19). For the acyclic olefin the kinetics followed the kinetic expression (except at low olefin) ... 

As mentioned earlier, in the Ruhrchemie-Rhone Poulenc process for propene hydroformylation the pH of the aqueous phase is kept between 5 and 6. This seems to be an optimum in order to avoid acid- and base-catalyzed side reactions of aldehydes and degradation of TPPTS. Nevertheless, it has been observed in this [93] and in many other cases [38,94-96,104,128,131] that the [RhH(CO)(P)3] (P = water-soluble phosphine) catalysts work more actively at higher pH. This is unusual for a reaction in which (seemingly) no charged species are involved. For example, in 1-octene hydroformylation with [ RhCl(COD) 2] + TPPTS catalyst in a biphasic medium the rates increased by two- to five-fold when the pH was changed from 7 to 10 [93,96]. In the same detailed kinetic studies [93,96] it was also established that the rate of 1-octene hydroformylation was a significantly different function of reaction parameters such as catalyst concentration, CO and hydrogen pressure at pH 7 than at pH 10. 

Studies of stoichiometric hydroformylation, spectroscopic identification, isolation, and transformation of intermediates provided valuable information of the understanding of the catalytic reaction. Despite the complexity of the process, important conclusions were also drawn from kinetic studies. 

A kinetic study of the hydroformylation has been carried out306 and the mechanism proposed by Wilkinson (Scheme 16) was extended to express both the associative and dissociative modes of alkene coordination298 and the formation of n- and iso-butyraldehydes. High-pressure IR spectroscopy using CO and either H2 or D2 has confirmed the formation of [RhH(CO)2(PPh3)2] in these reactions.307... 

Ionic liquids (continued) for Heck coupling, 1, 870 for homogeneous-multi-phase catalysis, 1, 856 for hydroformylations, 11, 450 for hydrogenations, 1, 857 for kinetic study monitoring, 1, 517 metalloorganic ILs, 1, 853 and molten salts, 1, 848... 

A kinetic study of the hydroformylation of soybean oil was undertaken by Kandanarachchi [25] the pressure was varied between 40 and 110 bar, and the conversion rate increased with the pressure. The activation energy was calculated both for a rhodium system with (PhO)3P and with (Ph)3P showing that the phosphine species has a lower activation energy. Also, the temperature effect was studied, and it was found that the reaction rate increased until 100°C. Above that, the high temperature apparently inhibited the reaction due to phosphido-bridged clusters which are favored at higher temperatures. 

Benaissa M, Jauregui-Haza UJ, Nikov I, Wilhelm AM, Delmas H (2003) Hydroformylation of linalool in a supported aqueous phase catalyst by immobilized rhodium complex kinetic study. Catal Today 79-80 419-125. doi 10.1016/s0920-5861(03)00074-9... 

Kinetic studies are of limited value for elucidating the mechanism of the hydroformylation reaction. This is because the empirically derived rate expressions are valid only within a narrow range of experimental conditions. For the rhodium-catalyzed reaction, in the absence of phosphine, the following rate expression has been proposed ... 

The synergistic effect often observed in bimetallic systems was further explored by Garland and coworkers. The hydroformylation of 3,3-dimethylbut-l-ene to form 4,4-dimethylpentanal in >95% selectivity at room temperature with [Rli4(CO)i2]-[Mn2(CO)io/HMn(CO)5] as catalyst coprecursors was investigated using in situ PT-IR spectroscopic techniques and kinetic studies revealing evidence of a bimetallic catalytic binuclear elimination reaction (CBER). 

The most detailed and generally accepted kinetic study on triphenylphosphine-modified rhodium catalysts was published in 1980 [109]. It was concluded from the coefficients obtained (Table 2) that the fast alkene insertion is followed by the rate-determining step involving CO or TPP [110]. The apparent activation energy for propene hydroformylation was found to be 84 kJ/mol, very similar to the value obtained for unmodified cobalt catalysts. 

Only limited data are available for the kinetics of oxo synthesis with the water-soluble catalyst HRh(CO)(TPPTS)3. The hydroformylation of 1-octene was studied in a two-phase system in presence of ethanol as a co-solvent to enhance the solubility of the olefin in the aqueous phase [115]. A rate expression was developed which was nearly identical to that of the homogeneous system, the exception being a slight correction for low hydrogen partial pressures. The lack of data is obvious and surprising at this time, when the Ruhrchemie/ Rhone-Pou-lenc process has been in operation for more than ten years [116]. Other kinetic studies on rhodium-catalyzed hydroformylation have been published, too. They involve rhodium catalysts such as [Rh(nbd)Cl]2 (nbd = norbomadiene) [117] or [Rh(SBu )(CO)P(OMe)3]2 [118], or phosphites as ligands [119, 120]. 

In the presence of alkali metal halides or iodine as promoters for the hydroformylation of ethylene catalyzed by [HRu3(CO)n]-, however, kinetic studies indicate that mono- and dinuclear species are responsible for the catalytic activity under these conditions (236). This is in line with reactivity studies involving [HRu3(CO)u]-, [HRu(CO)4]-, [Ru(CO)3I], and Ru(CO)4I2 (237). 

For Rh4(CO)12 as hydroformylation catalyst, several mechanistic studies including isotope labeling and kinetics have been undertaken. Thus, the deuteroformylation of 2,3,3-trimethylbut-l-ene and of styrene in the presence of Rh4(CO),2 have been studied In the first case, the 3,4,4-trimethyl-pentanal formed was found to be deuterated exclusively in the formyl position (238). In the latter case, the aldehydes formed were deuterated in the formyl and in the corresponding a-position ( > and (Zy PhCH=CHD and PhCH=CD2 were also observed (239). The mechanistic implications of these findings are not entirely clear. However, a kinetic study of the Rh4(CO)12-catalyzed low-pressure cyclohexene hydroformylation provides some evidence in favor of intact cluster catalysis A mechanism proposed on the basis of these findings includes fission of one Rh-Rh bond, whereby the tetranuclear cluster framework remains intact (Scheme 12) (240). 

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 aim of this contribution is to present a review of the current status of the kinetics of hydroformylation of olefins using water-soluble catalysis. Kinetic studies for various reaction systems and the role of ligands, pH, co-solvents, and surfactants are discussed. 

Kinetics of hydroformylation of styrene using HRhCO(TPPTS)3 catalyst in a bi-phasic system with various co-solvents was investigated by Nair [25]. He reported that 50% aqueous (v/v) N-methyl pyrrolidone (NMP) solution showed much better performance in comparison to ethanol as a co-solvent due to its non-reactive nature towards the aldehyde products. The rate was found to increase by seven times compared to that in the absence of any co-solvent. Kinetic study at 373 K revealed that the rate was first order dependent with catalyst concentration, fractional order with CO and first order tending to zero order with styrene concentration. 

The effect of agitation speed indicated that beyond 16.7,Hz the rate of hydroformylation was independent of agitation speed. This suggests that gas-liquid and liquid-liquid mass transfer effects can be eliminated beyond an agitation speed of 16.7, Hz, indicating kinetic regime. All the experiments for the kinetic studies were carried out at 16.7, Hz and at catalyst phase hold up of 0.4. The rate data for the purpose of kinetics is discussed below. 

A kinetic study has been carried out for the SLPC hydroformylation of propene using [RhH(CO)(PPh3)3] in triphenylphosphine. The reaction orders were 1.0, 1.03, and 0.09 in Rh concentration, p(propylene) and pCHj). For p(CO) the reaction order was pressure dependent and at pressures above... 

Purwanto and Delmas [10] proposed the addition of co-solvent (ethanol) to enhance the solubility of 1-octene in the aqueous phase so that the overall reaction rate was increased, and their kinetic study led to a rate model similar to that in homogeneous liquid systems consistently from the point of view of bulk reaction mechanism. Chaudhari et al. [11] reported the improvement of the hydroformylation rate by addition of a small amount of PPhj to the biphasic system to enrich the effective catalyst species at the liquid-liquid interface. Kalck et al. [12] tested two more approaches to improve the mass transfer rate of biphasic hydroformylation of 1-octene and 1-decene with catalyst precursor [Rh2(/i-S Bu)2(CO)2(TPPTS)3j use the phase-transfer agent /i-cyclodextrin to transport the substrate into the aqueous phase to react there (see Section 2.2.3.2.2), and the supported aqueous-phase (SAP) catalyst to increase the reaction area due to the high specific surface area of porous silica (see Section 2.6). The improved conversion and TOF gave informative suggestions for the reaction mechanisms. 

Several chemical engineering factors affect the biphasic hydroformylation of 1-dodecene in a gas-hquid-Hquid three-phase reachon system. In previous research [1], effects of temperature, total pressure, H2/CO molar raho, catalyst and ligand concentration, olefin concentration, surfactant concentration, and organic/ aqueous-phase volume ratio on the hydroformylation kinetics were studied with... 

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