Polymeric Reagents Based on Poly(vinylpyridine)

As stated in Chapter 2 , polymer-supported reagents have become regularly used species in various fields because the attaching of reagents to the polymer matrix can eliminate the complications of product separation, instability, toxicity, or limited recovery and reusability usually associated with their unsupported counterparts [ 1–11 ]. They may exhibit greater compliance with continuous flow methods compared to batch processes [ 12 ]. The growing interest in polymeric reagents is also attributed to their remarkable selectivity and versatility in various synthetic transformations. They are often used in stoichiometric quantities or more to drive chemical transformation to complete conversion. However, the most important shortcomings of polymeric reagents may be reduced reactivity because of diffusional constraints, steric hindrance, site isolation effects, and challenges associated with their structural characterization. Furthermore, sometimes they are expensive and somewhat difficult to prepare. For example, Scheme 4.1 shows a typical polymeric reagent used in chemical reactions. The active functional group of the support would lead to the required chemical modification of the substrate. Such groups may be attached to the polymeric carriers by chemical bonding or by physical adsorption. Usually, physically adsorbed species are unsatisfactory due to leaching of active groups in the reaction mixture, and they are therefore unreusable and also inadequate for column applications.