Phase transfer catalysts, laboratory experiments

The first experiments which were carried out in the author s laboratory on organometallic phase-transfer catalysis were concerned with the reduction of nitrobenzenes (4) to anilines (5) by triiron dodecacarbonyl. Such a conversion was reported to occur in benzene containing methanol at reflux for 10-17 h, with the hydridoundecacarbonyltriferrate anion as the likely key intermediate (16). It was our expectation that the trinuclear iron hydride should be generated by phase-transfer catalysis and if so, effect reduction of nitro compounds (4) under exceedingly mild conditions. Indeed this was the case, as illustrated by the results shown in Table I (17). Not only is the reaction complete in 2 h or less using sodium hydroxide as the aqueous phase, benzene as the organic phase, and benzyltrieth-ylammonium chloride as the phase-transfer catalyst, but it occurs at room temperature and requires less metal carbonyl than when the reaction was... 

One of the most important metal carbonyl anions, as far as catalytic processes are concerned, is the cobalt tetracarbonyl anion, Co(CO)4. Prior to attempting phase-transfer catalysis using Co(CO)4" as a catalyst, it was imperative to establish that the anion is actually formed under these conditions. Therefore, model experiments in the author s laboratory involved the initial use of dicobalt octacarbonyl in a stoichiometric role. 

In the Difasol technology, the catalyst is dissolved in IL reaction products are poorly soluble. The reactants miscibility remains adequate to ensure reaction. Batch laboratory experiments on butene dimerization demonstrated that no reaction occurs in the organic phase. This indicates that the reaction takes place at the interface or in the ionic liquid phase. Experiments also proved that rising the mixing efficiency increases the reaction rate but does not change the octene selectivity. So excellent mixing is necessary to ensure good conversion by rapid mass transfer and efficient interaction of the ionic catalyst with the substrate. 

Applications for OSN have been under pilot-plant trial or demonstrated in laboratory experiments in solvent deoiling, homogeneous catalyst recovery, separation of phase-transfer agents, and solvent exchange. "... 

The catalyst particle sizes and shapes (Figure 5.1) vary considerably depending on the reactor applications. In fixed beds, the particle size varies roughly between 1 mm and 1 cm, whereas for liquid-phase processes with suspended catalyst particles (slurry), finely dispersed particles (<100 xm) are used. Heterogeneous catalysis in catalytic reactors implies an interplay of chemical kinetics, thermodynamics, mass and heat transfer, and fluid dynamics. Laboratory experiments can often be carried out under conditions in which mass and heat transfer effects are suppressed. This is not typically the case with industrial catalysis. Thus, a large part of the discussion here is devoted to reaction-diffusion interaction in catalytic reactors. 

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