3-Nitro-4-acyloxybenzoic acid substrates

Overberger and coworkers carried out an interesting study on the hydrolysis of various 3-nitro-4-acyloxybenzoic acid substrates (V) catalyzed by imidazole (VI) and poly[4(5)-vinylimidazole] (VII) in ethanol-water mixtures [Overberger et al., 1973]. 

The preparation of pol)rmeric catalysts and substrates containing imidazole groups and nitro-phenyl esters, respectively, grafted onto crosslinked polystyrene beads has been described and the effects of the acyl chain length in the substrate in the aqueous alcohol solvent systems on the rate of hydrolysis of 3-nitro-4-acyloxybenzoic acid substrates catalyzed by insoluble catalysts were determined. 

Poly(l-methyl-5-vinylimidazole) catalyzed hydrolysis of 3-nitro-4-acyloxybenzoic acid substrates (Sn") exhibit substantial rate... 

Copoly[1-methyl-4-vinylimidazole/4(5)-vinylimidazole], copoly-[l-methyl-5-vinylimidazole/4 (5)-vinylimidazole], copoly[l-ethyl-5-vinylimidazole/4(5)-vinylimidazole], were synthesized according to Scheme I and their catalytic activity towards 3-nitro-4-acyloxybenzoic acid substrates (Sn ) measured in 28.5% ethanol-water and in water (17,18). 

In this study, insoluble pol)rmers containing imidazole groups were tested for esterolytic activity with several substrates of differing hydrophobic chain lengths. The substrates used were 3-nitro-4-acyloxybenzoic acid (Sn ). The concentration of substrate used does not allow the formation of substrate micelles, the concentration being below the critical micelle concentration for these esters (28,29). 

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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See also in sourсe #XX -- [ ]

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