The rate constants for the reactions of five-membered heteroaromatic aldehydes with aniline in acetonitrile (Schiff reaction) and with benzoylmethylenetriphenylphosphorane in methanol (Wittig reaction) were measured in order to attempt structure-reactivity correlations. The observed reactivity sequence (2-furyl > phenyl > 2-thienyl > 2-pyrrolyl) is the same as previously found in other substitutions at the carbonyl group. The electron-donating character of the heteroatoms in the Schiff reaction is proved by the Hammett treatment of the data. However, extension of this treatment to other reactions at the carbonyl group does not give constant σhet values. Application of the Taft-Pavelich eqation points out a dependence of the rate of reaction on polar and steric effects of heteroaromatic rings. Information from Hammett and Taft-Pavelich equations, however, is not unequivocal owing to inherent features of both free-energy relationships

Nucleophilic substitution in the side chain of five-membered heterocycles. 3. Reactions of heterocyclic aldehydes with aniline and with benzoylmethylenetriphenylphosphorane

TOMASELLI, Gaetano
1977

Abstract

The rate constants for the reactions of five-membered heteroaromatic aldehydes with aniline in acetonitrile (Schiff reaction) and with benzoylmethylenetriphenylphosphorane in methanol (Wittig reaction) were measured in order to attempt structure-reactivity correlations. The observed reactivity sequence (2-furyl > phenyl > 2-thienyl > 2-pyrrolyl) is the same as previously found in other substitutions at the carbonyl group. The electron-donating character of the heteroatoms in the Schiff reaction is proved by the Hammett treatment of the data. However, extension of this treatment to other reactions at the carbonyl group does not give constant σhet values. Application of the Taft-Pavelich eqation points out a dependence of the rate of reaction on polar and steric effects of heteroaromatic rings. Information from Hammett and Taft-Pavelich equations, however, is not unequivocal owing to inherent features of both free-energy relationships
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/20.500.11769/245184
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