Kemp elimination

28 May 2008 - Named reactions

Name : Kemp elimination
What : Ring-opening reaction of a benzisoxazole by a base. The reaction product is a alpha-cyanophenol (See benzonitrile, phenol)
Year: 1973
Literature: DOI DOI DOI.

Researchers before Kemp have noted decomposition of certain oxazoles substituted at position 3 but Kemp was the first to attach a mechanism to it.
Mechanism: E2 elimination. Main evidence: general base catalysis, large KIE for D/H at 3-position, large leaving group dependence.
Main characteristics: irreversible reaction, highly exothermic, reaction rate strongly depends on base strength and solvent type. Large rate-acceleration with a carboxylic acid as 3-substituent accompanied by loss of carboxylic acid.

The Kemp reaction is occasionally used as a probe for bases for example BSA (DOI) and most recently in 2008 (DOI) with a set of different amines and an ionic liquid solvent. Interestingly in this particular research not the base strength but the base shape carries weight. For example, the reactivity of dibutylamine (acyclic) is 5 times that of pyrrolidine (cyclic) even though their base strength is comparable. The researchers attribute this effect to a degree of pre-ordering for this particular solvent.