Previous work has shown that thermomorphic systems that contain a phase isolated catalyst under biphasic conditions are useful in separating homogeneous polymer-supported catalysts from the products of a catalytic reaction. Such thermomorphic systems include two solvents, usually one polar and one nonpolar in nature, that are immiscible at room temperature but upon heating form a monophasic system in which the catalysis can take place. After the catalytic reaction is complete, the reaction solution can be cooled down to form a biphasic mixture. If the catalyst is designed so that it is phase selectively soluble in a phase opposite to that of the products, the catalyst and products can be effectively separated and a stable catalyst can be recycled. Two strategies have typically been used in such systems. The Bergbreiter group has primarily designed catalysts such that they are nonpolar phase selectively soluble, which allows for polar products of a catalytic reaction to be isolated in the polar phase. Others have used polar phase selectively soluble catalysts in which case products are isolated from the nonpolar phase. While both strategies are effective, in either case some leaching of the catalyst into the product phase can occur. Minimizing such leaching is a desirable goal as it avoids product contamination and increases catalyst recyclability. In this paper, we use polymer supported azo and dansyl dyes as surrogates of catalysts to test how additives can effectively reduce such leaching. Examples to be described will show how additives in a nonpolar phase can reduce leaching of nonpolar polymeric species into a polar phase and how additives in a polar phase can reduce leaching of polar polymer-bound catalysts into nonpolar phases. These studies suggest that with appropriate polymeric additives that such leaching can be significantly reduced. These studies also show that the amount of reduced leaching being dependent on the specific components of the thermomorphic system.

Strategies to reduce leaching of soluble polymer-supported catalysts in thermomorphic systems

251st National Meeting (2016)

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