Selectivity vs. conversion dependence

Figure 4.16. Selectivity vs. conversion dependence for parallel reactions.

Figure 4.19. Selectivity vs. conversion dependence in cinnamaldehyde hydrogenation. (COL - cinnamylalcohol, PPAL- phenylpropanal)...

Figure 3.38 Comparison of selectivity to acrolein vs conversion of propene depending on time on-stream. Pre-treated in CO (t,) pre-treated in propene/nitrogen (tj) [37].

Week [203] developed a monomer salen complex linked to a norbomene via a stable phenylene-acetylene linker and its subsequent polymerization by means of the controlled ROMP method using 3 generation Grubb s catalyst (Scheme 137). This polymerization methodology led to fully functionalized immobilized metal-salen catalyst. By this way, the supported catalyst showed catalytic activities and stereoselectivities similar to the nonsupported Jacobsen catalyst. Moreover, activities and selectivities seemed to depend on the density of the catalytic moieties homopolymer 324 were less selective than their copolymer analogs 325. For example, AE of 1,2-dihydronaphtalene led in both cases to total conversion and 76% ee for the homopolymer 324 vs 81% ee for copolymer 325a. Recycle was possible and after 3 recyles a drastic decrease in ee was observed. AE of dihydronaphtalene led to 81% ee for the first cycle vs 6% ee for the third one. 

The extent of branching, of whatever type, is dependent on the polymerization conditions and, in particular, on the solvent and temperature employed and the degree of conversion. Nozakura et at.1 1 found that, during bulk polymerization of VAc, the extent of transfer to polymer increased and the selectivity (for abstraction of a backbone vs an acetoxy hydrogen) decreases with increasing temperature. 

Equation (88) shows, for highly porous catalysts, how the conversion to B depends on the fraction of A reacted for various values of the intrinsic selectivity factor S = ki/ki. In Fig. 11, lower curve, we plot as vs. ttA for 5 = 4. Thus, Fig. 11 gives a direct comparison between the performance of porous and nonporous catalyst. For the porous catalyst (lower curve) the maximum conversion to B is only 33% (at about 75% conversion of. 4) with a yield of B of only 44%. This is to be compared with the 62% conversion to B with a yield of 78% obtained with nonporous catalyst of the same intrinsic selectivity. It thus appears that the pore structure can cut down on yields in Type III selectivity by a factor of about two. These conclusions apply for a selectivity factor of 4.0. Calculation with other values of the selectivity factor ranging from 1.0 to 10 show that in all cases the yield loss of B due to pore structure corresponds to a factor of about two. 

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