Aspirin proton transfer reaction

Like many drugs, aspirin is capable of undergoing a proton transfer reaction. Its most acidic proton is the H bonded to O, and in the presence of base, this H is readily removed. 

In aspirin, the acid catalysis is enhanced by the presence of an intra-molecular hydrogen bond. The H-bond in the salicylate anion is worth 17-21 kJ mol and raises the of the phenolic OH to 13. Other molecular models showed that EMs for intra-molecular general acid-base catalysis can be at least 10" M, if favourable intra-molecular H-bonds are formed [10]. This is also the factor that separates the typical pre-exponential factor of a bimolecular reaction in solution, 10 M sec from that of an intra-molecular reaction between the hydrogen-bonded reactants, 10 sec The basis for this change has been discussed in the context of the intersecting-state model (ISM) applications to proton transfers... 

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