Acylimidazoles determination

Hydrolysis of 2,4,5-triphenyl-V-acylimidazoles, as followed by UV-Vis measurements, was found to proceed through a concerted pathway that was accelerated by steric crowding around the V-acyl bond <1997JOC2872>. The pXa values were determined based on the kinetic data of the hydrolysis of 5-methyl-3,5-diarylimidazolidine-2,4-dione 101 yielding 102 <2005JHC899> (Scheme 20). 

Non-ionic (hydrophobic) association of the polymeric catalyst-substrate has also been shown to increase the catalytic activity. Thus, the rate of hydrolysis of 3-nitro-4-acyloxybenzoic acid (6) by polyvinylimidazole, increases with increasing bulk of acyloxy group (Over-berger and Sannes, 1974). It was observed that the deacylation step of the intermediate polymeric acylimidazole is rate-determining. Since the acylated polymer becomes more hydrophobic, because of the extra group attached to the polymer, apolar associations increase with the chain length of the acyl group, and, hence increase the catalytic activity. 

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