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

摘要

A kinetic study of the decomposition reaction of 1,4-dinitro-2-methylpyrrole (NMP) and ethylnitrolic acid (ENA), both formed in the reaction between sorbic acid and sodium nitrite was performed in the 3.5-4.2 pH range in water/dioxane mixtures. Conclusions were drawn as follows: (i) The decomposition of NMP occurs through nucleophilic attack by OH- ions, the rate equation being: r = k(dec)(NMP) [OH-][NMP]. (ii) The rate law for the decomposition of ENA is: r=k(dec)(ENA) [ENA]K-a/(K-a + [H+]), K-a being the ENA dissociation constant. (iii) The value of K-a decreases when the water/dioxane ratio decreases, log K-a being proportional to the Onsager parameter (is an element of - 1)/(2 is an element of + 1). This permits the equilibrium between non-dissociated and the dissociated forms of ENA to be rationalized. (iv) No appreciable variation in the Delta H-# and Delta S-# values with composition of the medium was observed, either in the NMP decomposition reaction, or in the ENA decomposition reaction.