Streamlining Free Radical Green Chemistry

TAMARA V. PERCHYONOK*; IOANNIS LYKAKIS*; AL POSTIGO *

RSC Books Editorial-Royal Society of Chemistry-Thomas Graham House

Lugar: http://www.rsc.org/shop/books/2011/9781849733328.asp RSC Books Editorial-Royal Society of Chemistry-Thomas Graham House-Science Park-Cambridge, CB4 0WF, UK; Año: 2012 p. 780

978-1849733328

Solid-Phase Radical Reactions as Reactions in Alternative media: Introduction: A commonly used technique in high-throughput synthesis are termed ?solid phase? or ?solid supported? organic synthesis. This is the method whereby a reaction is run on an insoluble support. The fact that the support is insoluble to the reacting solvent does not negate the fact that reactions can still occur at the supports surface. The key steps in solid phase organic synthesis begin with the covalent attachment of an organic molecule or ?scaffold? to a linker molecule that is already attached to the surface of the insoluble support.(Scheme) This linker molecule should be cleaved under very selective conditions but also stable to the reaction conditions used to modify the scaffold. The scaffold is then exposed to reaction conditions that chemically modified it in some way, such as the covalent attachment of some molecule. After the reaction is complete, the support is washed and filtered to remove any un-reacted starting materials and/or excess of the reagent. The process can then be repeated to further modify the scaffold. After a series of reactions followed by washes and filtrations, the now modified scaffold can then be isolated by chemical cleavage from the linker. A simple filtration step removes the chemically cleaved scaffold from the insoluble support. From this process one can see that one advantage of using solid phase organic synthesis is in the reaction mixture by filtration. One can also use this rapid ability to separate the soluble components from the resin-bound components to drive reaction to completion. To fully understand how this can be done, let us first look at the hypothetical bimolecular solution phase reaction: A+B=C. The initial rate of formation of C can be described by the Eq (1) Initial Rate = d[C]/dt = k[A][B] Where the formation of C is dependent on both the concentration of A and B times some constant K (termed the reaction rate constant). If B is present in a large excess, its concentration of B will remain virtually unchanged throughout the initial stages of the reaction and therefore the initial reaction becomes pseudo first order reaction and therefore can be represented as Eq (2)