Catalytic Carbonylations in Ionic Liquids

Multiphase organoraetallic catalysis, in particular, liquid-liquid biphasic catalysis involving two immiscible phases, may offer the possibility of circumventing the problems associated with the homogeneous process such as product separation, catalyst recycling, and the use of organic solvents. The concept of this system implies that the catalyst is soluble in only one phase, whereas the substrates/products remain in the other phase. The reaction can take place in one (or both) of the phases or at the interface. In most cases, the catalyst phase can be reused and the products/substrates are simply removed from the reaction mixture by decantation. 

Nowadays, there are several alternatives under investigation as fluid for multiphase catalysis, including the resurgence of water, perfluorinated hydrocarbons, and supercritical fluids, in particular CO2. Indeed, the advent of water-soluble organo-metallic complexes, especially those based on sulfonated phosphorus-containing ligands, has enabled various biphasic catalytic reactions to be conducted on an industrial scale, in particular, for the hydroformylation of olefins. 

In the 1990, Chauvin and coworkers have introduced ionic liquids (ILs) - especially those derived from the combination of quaternary ammonium salts and weakly coordinating anions - as immobilizing agents for various classical transition metal catalyst precursors in reactions [1]. In particular, these liquids provide more adequate and favorable environment for carbonylation reactions as compared to those performed in classical organic solvents or water. The vast majority of these compounds a) are effectively nonvolatile (most of them exhibit negligible vapor pressure)  

Modem Carbonylation Methods. Edited by Liszld Kollar 

Copyright 2008 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim 

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Zulfiqar, F. and Kitazume, T. (2000) Lewis acid-catalysed sequential reaction in ionic liquids. Green Chem., 2, 296-297. Kamal, A. and Chouhan, G. (2004) Investigations towards the chemoselective thioacetalization of carbonyl compounds by using ionic liquid [bmim]Br as a recyclable catalytic medium. Adv. Synth. Catal., 346 (5), 579-582. 

Aminoalkyl and Related Acids. - Further development of the classical three component approach to aminoalkylphosphonates (the Kabachnik-Fields reaction) has been reported. The reaction of aldehydes, hydroxylamines and dimethyltrimethylsilyl phosphite using lithium perchlorate/diethyl ether as a catalyst gives N-trimethylsilyloxy-a-aminophosphonate derivatives. The catalytic activities of various lanthanide triflates as well as indium trichloride have been examined for the Kabachnik-Fields type reactions of aldehydes, amines and the phosphorus nucleophiles HP(0)(0Et)2 and P(OEt)3 in ionic liquids. TaCb-Si02 has been utilized as an efficient Lewis acid catalyst for the coupling of carbonyl compounds, aromatic amines and diethyl phosphite to produce a-... 

Another successful application of [BMIMJIPFe] ionic liquid supported catalytic microflow reactions for Pd-catalyzed carbonylative Sonogasnira coupling of aryl iodides and phenylacetylene was reported by Rahman et al. (2006). Ionic liquid containing Pd catalysts, CO and the substrates were mixed successively, in different micromixers (channel diameter = 1 and 0.40 mm), and then pumped as a multiphase (ionic liquid-substrate-CO) into heated capillary tube reactor acting as a residence time unit (V=14.1 mL). It was found that Pd-catalyzed production of solely the acetylenic ketones in ionic liquids, when conducted in conjunction with a microreactor, preceded efficiently with superior selectivity and higher yields compared to the conventional batch system, even at low CO pressures. Authors suggested that this improvement in selectivity and yield was the result of a large interfacial... 

Abstract The principle of catalytic SILP materials involves surface modification of a porous solid material by an ionic liquid coating. Ionic liquids are salts with melting points below 100 °C, generally characterized by extremely low volatilities. In the examples described in this paper, the ionic liquid coating contains a homogeneously dissolved Rh-complex and constitutes a uniform, thin film, which itself displays the catalytic reactivity in the system. Continuous fixed-bed reactor technology has been applied successfully to demonstrate the feasibility of catalytic SILP materials for propene hydroformylation and methanol carbonylation. 

In SILP carbonylation we have introduced a new methanol carbonylation SILP Monsanto catalyst, which is different from present catalytic alcohol carbonylation technologies, by using an ionic liquid as reaction medium and by offering an efficient use of the dispersed ionic liquid-based rhodium-iodide complex catalyst phase. In perspective the introduced fixed-bed SILP carbonylation process design requires a smaller reactor size than existing technology in order to obtain the same productivity, which makes the SILP carbonylation concept potentially interesting for technical applications. 

A biphasic system consisting of the ionic liquid [BMIM]PF6 and water was used for the epoxidation reactions of a, 3-unsaturated carbonyl compounds with hydrogen peroxide as an oxidant at room temperature 202). This biphasic catalytic system compared favorably with the traditional phase transfer catalysts. For example, under similar conditions (15°C and a substrate/NaOH ratio of five), the [BMIM]PF6/H20 biphasic system showed a mesityl oxide conversion of 100% with 98% selectivity to oc, 3-epoxyketone, whereas the phase-transfer catalyst with tet-rabutylammonium bromide in a CH2CI2/H2O biphasic system gave a conversion of only 5% with 85% selectivity. 

On the basis of encouraging work in the development of L-proline-DMSO and L-proline-ionic liquid systems for practical asymmetric aldol reactions, an aldolase antibody 38C2 was evaluated in the ionic liquid [BMIM]PF6 as a reusable aldolase-ionic liquid catalytic system for the aldol synthesis of oc-chloro- 3-hydroxy compounds (288). The biocatalytic process was followed by chemical catalysis using Et3N in the ionic liquid [BMIM]TfO at room temperature, which transformed the oc-chloro-(3-hydroxy compounds to the optically active (70% ee) oc, (3-epoxy carbonyl compounds. The aldolase antibody 38C2-ionic liquid system was also shown to be reusable for Michael additions and the reaction of fluoromethylated imines. 

Wang et report the carbonylation of nitroaromatics with aromatic amines in a catalytic system containing elemental sulfur in an ionic liquid, Scheme 3. 

The synthesis of a-methylene-7-lactone 317 through carbonylation of but-3-yn-l-ol 316 catalyzed by Pd(ll)-PPh2(2-Py) has been carried out in l-butyl-3-methylimidazolium tetrafluoroborate 315 as reaction medium in high yield with excellent product selectivity (Equation (30))4 Although the ionic liquid containing the catalytic species was recovered, a significant decrease in yield occurred with the recycled catalyst, which appears to be attributed to the decomposition of the catalyst during the isolation procedure ... 

The ionic liquid based on the l- -butyl-3-methylimidazolium cation was also used as an efficient catalytic medium for the chemoselective dithioacetalization of carbonyl compounds. This reaction proceeded with both activated and weakly activated aromatic aldehydes in almost quantitative yields in short reaction times. In addition, an acid-sensitive substrate such as furfural also gave the corresponding 1,3-dithiolane without a formation of any side products (Table 8). Moreover, aromatic ketones did not produce dithioketals under the same reaction conditions (room temperature, 10-20 min) or even after a prolonged reaction time <2004ASC579>. 

In this study, at first a series of nickel(II)-triphenylphosphine complexes with derivatives of A-(2-pyridyl)-N -(salicylidene)hydrazine (NiLl-NiL5) were prepared and catalytic activity of complexes was studied in ethyl-methylimidazolium (emim) at room temperature. The results show that this method is very useful for the oxidation of aromatic, aliphatic, and allylic alcohols to their corresponding carbonyl compounds in a conversion range of 60-96%. The catalytic activity of complexes notably varies with the size of the substituents. It was observed that the activity decreases with increase in the bulkiness of the substituents. This may be due to steric hindrance causes by the substituent, which can affect the planarity of the ligand in the complexes. Further, ionic liquid ethyl-methylimidazolium (emim) was recycled up to 90% along with the catalyst. Both ionic liquid and catalyst could be reused at least for ten times. 

In a further variation, the PVP-supported rhodium catalyst was used for methanol carbonylation in supercritical carbon dioxide [100]. This reaction medium has complete miscibility with CO and dissolves high concentrations of methanol and methyl iodide, while being a poor solvent for ionic metal complexes. Catalytic reaction rates up to half of those obtained in conventional liquid-phase catalysis were achieved with minimal catalyst leaching. 

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