Recycle experiments

After ten consecutive runs the overall turnover number reaches up to 3500 mol 1-octene converted per mol Rh-catalyst. In agreement with these recycling experiments, no Rh could be detected in the product layer by AAS or ICP, indicating leaching of less then 0.07 %. In all experiments, very good selectivities for the linear aldehyde were obtained, thus proving that the attachment of the guanidinium moiety onto the xanthene backbone had not influenced its known positive effect on... 

Figure 5.2-5 Recycling experiments - Rh-catalyzed, biphasic 1-octene hydroformylation in...

During the non-recycling experiment 40200 Kg of lemon fhiit were processed, with an average of 0.823% in weight of recoverable oil. Therefore, the total available oil in the lemons was 330.8 Kg. The oil finisher emulsion had an average of 0.995% (w/w) of recoverable oil. 

Another method for generating an epoxidation catalyst on a solid support is to simply absorb or non-covalendy attach the catalyst to the solid support <06MI493>. Epoxidation of olefin 6 with mCPBA and catalyst 8 provides 7 in quantitative yields and with 89% ee. The immobilization of 8 on silica gel improves the enantioselectivity of the reaction providing 7 with 95% ee. Recycling experiments with silica-8 show a decrease in both yield and the enantiomeric excess for each cycle (45% ee after 4 cycles). This is attributed to a leaching of the catalyst from the silica gel. Two other solid supports, a Mg-Al-Cl-LDH resin (LDH) and a quaternary ammonium resin (Q-resin) were also examined. It was expected that ionic attraction between 8 and the LDH or Q-resin would allow the catalyst to remain immobilized through multiple cycles better than with silica gel. Both of these resins showed improved catalytic properties upon reuse of the catalyst (92-95% ee after 4 cycles). 

A water-soluble chelating diphosphine ligand (9) based on the xanthene backbone was also studied as supported aqueous phase catalysts. It was shown that this ligand performed well as SAPC since it is much more selective than other SAPC systems reported in literature [68]. Recycling experiments showed that these catalysts retained their activity and selectivity for at least ten consecutive runs, whereas under similar conditions the TPPTS based catalyst showed a reduced performance in the fourth run. 

After a hydroformylation run, the reaction solution was subjected to ultrafiltration using an asymmetric polyethersulfone membrane (MWCO 50 kDa) supplied by Sartorius. A retention of 99.8% was found. When the catalyst solution was recycled, virtually the same catalytic activity was observed again (165 TO h 1). Repetitive recycling experiments resulted in 2-7% loss of rhodium, which was subscribed to partial oxidation of the phosphine ligand. 

The ionic catalyst solution was prepared by stirring [Rh(acac)(CO)2] with four equivalents of this ligand in an acctonitrile/[BMIM][PF6] mixture for 1 h followed by removal of the volatiles. The reaction conditions for the hydroformylation of 1-octene were similar to those used by Dupont et al. [58] (see earlier). The results of seven consecutive recycling experiments are shown in Table 7.3. 

Figure 5.19 Recycling experiments in the kinetic resolution of racemic amine using the sol-gel CaLB immobilizate prepared with 18-crown-6 as an additive. (Reproduced from ref. 30, with permission.)... 

First, suitable combinations of catalyst 13 and ILs were determined in batch experiments. Using [EMIM][BARF] as IL complete conversion was obtained with 89% ee of (R)-3-phenyl-l-butene. [EMIM][Tf2N] gave lower ee values in the range of 65%. Nevertheless, better availability and easier hand-hng made this the IL of choice for recychng and continuous-flow experiments. In batch-wise recycling experiments of catalyst 13 in ILs, it was found that the products could be readily isolated by extraction with SCCO2. However, the batch mode led to rapid deactivation of the catalyst within three to four cy-... 

Prior to the kinetic experiments, possible deactivation phenomena of the catalytic system were checked by recycling experiments with prenal and citral as substrates. These results provide not only important hints on the form of the rate equation, but also on which reaction is convenient for long-term investigations in the loop reactor. After the reaction, the aqueous and organic phases were separated and the catalyst phase was reused without further purification. Results on the hydrogenation of prenal are shown in Fig. 7. The reaction rate clearly decreases if the catalyst phase is reused. According to GC analysis and H-NMR studies, this can be attributed to the fact that the product of the reaction, prenol, is highly soluble in water. Consequently, a simple phase... 

Methylrheniumtrioxide (MTO) can straightforwardly be immobilized using copolymers consisting of polystyrene and polyvinyl pyridine. The authors proposed two possible structures 18 shown in Scheme 4.10. In the presence of H2O2 these catalysts are efficient and selective heterogeneous catalysts for the epoxidation of alkenes. It was shown that their activity is maintained for at least five recycling experiments [23 dj. In analogy to this work, bipyridyl-functionalized mesoporous silica can be employed for the immobilization of MTO [75]. 

Tab. 6.4 Recycling experiments Table 6.3, reaction time = 3 h). and subsequent reuse of the polymeric catalyst (macroligand 3,...

Borovik et al. [70] prepared a highly crosslinked polymeric porous material containing Co-salen units 38 (Figme 13) by template copolymerization method. The authors reported that as the cross-linking degree increases from 5 % to 50 %, the catalyst become more efficient in terms of reactivity, possibly due to the improved proximity of metal centers that work in cooperation. Unfortunately low enantioselectivity for the product epoxide was observed (<42 % ee) while the ee for concomitantly produced diol did not go above 86%. Reusability of the catalyst containing 50 mol% template showed consistent activity and enantioselectivity for three consecutive recycle experiments. 

Table 4 Recycling experiments with Cr(salen) 63-silica in the ARO reaction of...

Table 5 Catalytic results of the recycling experiments using the catalyst 56...

A chiral polymer-bound metathesis catalyst has been developed. The supported chiral complex 75d shows appreciable levels of reactivity and excellent enantios-electivity. " This complex 75d can be recycled and easily removed from unpurified mixtures. In the first and second cycles of the recycle experiment, almost the same reactivity has been shown. In the third cycle, high enantioselection and conversion are still obtained, but catalyst activity is notably diminished ... 

Recycling experiments were performed with the second- and third-generation dendrophites. Hydroformylation of propene was carried out in toluene, followed by... 

Arya et al. 50) immobilized similar dendrimers for the alkene hydroformylation on polystyrene (PS) beads, using solid-phase synthesis (58—60). The rhodium-catalyzed hydroformylation of styrene was investigated, and recycling experiments... 

We have observed with the above catalyst system that both butadiene conversion and methyl 2, 4-pentadienoate selectivity increase when the catalyst is recycled. Over a series of seven recycle experiments, conversion increases from the low 20 s to 32.2 mole % and selectivity increases from the low 70 s to 83.2 mole % (See Table III.). Conversion and selectivity reach steady state after the third catalyst recycle. 

Recycling experiments with MnClj2TMPS immobilized on methylated PVP, Recycling experiments were performed by re-using four times the same MnQi2TMPS catalyst supported on methylated PVP in the PhIO epoxidation of cyclooctene. For [MnCli2TMPS-PVPMe ][TsO"], it should be noted that the first two cycles are exactly the same, only a small activity decrease is observed for the third run. With 1 jimol of MnCli2TMPS immobilized on [PVPMe "][TsO ] the total epoxide production after 4 runs is 1970 jimol. The overall selectivity based on PhIO is 65%. ... 

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