Reactivity of some products formed by the reaction of sorbic acid with sodium nitrite: decomposition of 1,4-dinitro-2-methylpyrrole and ethylnitrolic acid.

Sorbic acid reacts with nitrite to yield mutagenic products such as 1,4-dinitro-2-methylpyrrole (NMP) and ethylnitrolic acid (ENA). In order to know the stability of these compounds, a kinetic study of their decomposition reactions was performed in the 6.0-9.5 pH range. The conclusions drawn are as follows: (i) The decomposition of NMP occurs through a nucleophilic attack by OH- ions, with the rate equation as follows: r = k(dec)NMP[OH-][NMP] with k(dec)NMP (37.5 degrees C) = 42 +/- 1 M(-1) s(-1). (ii) The rate law for the decomposition of ENA is as follows: r = k(dec)ENA[ENA]K(a)/(K(a) + [H+]), with K(a) being the ENA dissociation constant and k(dec)ENA (37.5 degrees C) = (7.11 +/- 0.04) x 10(-5) s(-1). (iii) The activation energies for NMP and ENA decomposition reactions are, respectively, E(a) = 94 +/- 3 and 94 +/- 1 kJ mol(-1). (iv) The observed values for the decomposition rate constants of NMP and ENA in the pH range of the stomach lining cells, into which these species can diffuse, are so slow that they could be the slow determining step of the alkylation mechanisms by some of the products resulting from NMP and ENA decomposition. Thus, the current kinetic results are consistent with the low mutagenicity of these species.