kilomentor

My consideration here is the state of the art of these techniques in so far as they can be immediately used in scaled up processes. My interest is not to review what has been published as preparation to enter the research activity. I want to use the results not contribute to them!

A consideration, which is consistently repeated is the loading of the reagent or catalyst on the polymer. For practical purposes it seems that attaching reagents to polymers is for the purpose of purification rather than recycling because the reagents are not themselves particularly expensive and the expense of obtaining a COA of a recycled polymeric reagent and proving the reproducible production of a recycled reagent of predefined properties is too heavy a burden. A manufacturer prefers to transfer the problem of reproducible quality of the reagent to the reagent supplier.

For ease of purification attaching the reagent to a polymer does make some sense. With an expensive advanced intermediate a small improvement in the yield, which can arise from the use of such a reagent can pay a worthwhile dividend. It makes sense to invest a bit more money into a sophisticated reagent if it is going to be combined in reaction with an expensive advanced intermediate.

Modifying the reagent can be a cost effective alternative to an extensive optimization campaign using up the advanced, difficult to obtain, intermediate. Intuitively the recycling potential of the polymeric reagent is not as important as the improvement, most importantly in yield, and less importantly in process simplicity, that can be achieved.

The use of polymeric reagents would seem to be most likely to be cost effective towards the latter part of a complex reaction scheme where improvements in yield can have benefits through all the preceeding steps in terms of the number of repetitions. The increased reaction volume is often increased using polymeric reagents, because the loading is limited and a large amount of ballast arises from the bulk of the polymer backbone. This increased bulk can be most easily absorbed in the later reactions in a process scheme because the mass being processed in lower and the intermediates are often processes in several batches to avoid the risk of a single catastrophic failure losing everything.

In the latter reactions of a process the use of polymeric reagents does not seriously suffer from the higher dilutions, which may be required when these bulky reagents are used. When the step comes towards the end of the process scheme, there are not going to be as many repetitions of it so a larger volume at the point of maximum volume is better tolerated.

For ease of purification attaching the reagent to a polymer does make some sense. With an expensive advanced intermediate a small improvement in the yield, which can arise from the use of such a reagent can pay a worthwhile dividend. It makes sense to invest a bit more money into a sophisticated reagent if it is going to be combined in reaction with an expensive advanced intermediate.

Modifying the reagent can be a cost effective alternative to an extensive optimization campaign using up the advanced, difficult to obtain, intermediate. Intuitively the recycling potential of the polymeric reagent is not as important as the improvement, most importantly in yield, and less importantly in process simplicity, that can be achieved.

The use of polymeric reagents would seem to be most likely to be cost effective towards the latter part of a complex reaction scheme where improvements in yield can have benefits through all the preceeding steps in terms of the number of repetitions. The increased reaction volume is often increased using polymeric reagents, because the loading is limited and a large amount of ballast arises from the bulk of the polymer backbone. Yhis increased bulk can be most easily absorbed in the later reactions in a process scheme because the mass being processed in lower and the intermediates are often processes in several batches to avoid the risk of a single catostrophic failure losing everything.

In the latter reactions of a process the use of polymeric reagents does not seriously suffer from the higher dilutions, which may be required when these bulky reagents are used. When the step comes towards the end of the process scheme, there are not going to be as many repetitions of it so a larger volume at the point of maximum volume is better tolerated.

One situation where polymeric reagents would be useful in the initial steps of a synthesis is to reduce the point of maximum volume by simplifying the work-up by substituting for high dilution operations.

For polymer bound catalysts on the other hand, the isolation problem is usually not so significant an issue. This is not the case however where there is a tough specification set upon the limit of catalytic residue left in the product and the catalytic reaction occurs close to the final product.

Aside from the trace toxic residue situation, by their implied catalytic status, the mass of material to be removed is usually on the lower side. If the catalyst is used in small amounts and is cheap, there really is no driving force to experiment with polymer supported catalysts in the scale up. Only if the catalyst is expensive and complicated to prepare does it contribute substantially to the cost of the process and become a priority to be addressed in the scale up.

Here with catalysts where the motivation for recovery is expense; then recycling the recovered material becomes important.