Mechanism and proton activating factors in base-induced β-elimination reactions of 2-(2-chloroethyl)pyridine

摘要

The substrate 2-(2-chloroethyl)pyridine reacts in OHu0001/H2O, 50 u0002C, µ = 1 M KCl by an elimination reaction with thenformation of 2-vinylpyridine; the second order rate constant is kNnOH = 4.59 × 10u00014n dm3n molnu00011n snu00011n. In acetohydroxamate–nacetohydroxamic acid buffers, the elimination reaction competes with the SN2 reaction of the acetohydroxamatennucleophile. Studies of acid–base catalysis at pH values ranging from 8.42 to 9.42 are in agreement with an E1cbnirreversible mechanism, where carbon deprotonation occurs from the substrate protonated at the nitrogen of thenpyridine ring (NHu0001), even if it is present at very low concentrations with respect to the unprotonated substrate (N)nunder the reaction conditions. The value for the reactivity ratio between NHu0001 and N is of the order of 105n. The strongnreactivity of NHu0001 is attributed to the high stability of the carbanion intermediate formed; this intermediate has annenamine structure.