Solvent Effects on Chemical Processes. 11. Solvent Effects on the Kinetics of Decarboxylative Dechlorination of N-Chloro Amino Acids in Binary Aqueous—Organic Solvents

Abstract

The phenomenological theory of solvent effects is extended to chemical reaction rates and is tested against experimental data on the decarboxylative dechlorination of N-chloroalanine and N-chloroleucine at 25 degrees C in binary aqueous-organic solvent mixtures. The organic cosolvents studied were methanol, ethanol, l-propanol, 2-propanol, ethylene glycol, propylene glycol, acetonitrile, and dioxane. Reaction rates increased in all cosolvent systems. The kinetic solvent effects could be quantitatively described by the theory, and the parameters of the theory (solvation exchange constants K1 and K2 and cavity surface area parameter delta g++) were found to possess magnitudes reasonable for the physical significance assigned to them. In particular, the delta g++ value is consistent with a recent measurement of the volume of activation delta V++ of the reaction.

Aqueous chemistry of N-halo-compounds

“…The simplicity of the mechanism involved in the decarboxylation of N-Cl-a-amino acids has been used to test the phenomenological theory of solvent effects on chemical reaction rates. 22 At lower pH values, N-halo-a-amino acids can also occur in three protonation states, other than the anionic. Grob fragmentation is observed for such species if they are derived from secondary amino acids, in which case the disproportionation (Section 2.2) becomes rather slow.…”