Alkylating potential of potassium sorbate

Abstract

A kinetic study of the alkylating potential of potassium sorbate (S)a food preservative used worldwidein 7:3 water/dioxane medium was performed. The following conclusions were drawn: (i) Potassium sorbate shows alkylating activity on the nucleophile 4-(p-nitrobenzyl)pyridine (NBP), a trap for alkylating agents with nucleophilic characteristics similar to those of DNA bases, (ii) The NBP alkylation reaction complies with the rate equation r = kalk[H+][S][NBP]/(Ka + [H+]), Ka being the sorbic acid dissociation constant and kalk the rate constant of NBP alkylation by the undissociated acid. In the range of pH 5-6, the alkylation time ranges between 18 days (pH 5.2) and >1 month (pH 6). (iii) NBP alkylation occurs through a reaction with H# = 78 kJ mol-1, which is much higher than those of NBP alkylation by stronger alkylating agents. (iv) The absorption coefficient of the sorbate-NBP adduct was determined to be = 204 M-1 cm-1 ( = 580 nm), this value being rationalized in terms of the adduct structure. (v) The results can help to establish suitable expiration times for products preserved with potassium sorbate.