A Kinetic and Mechanistic Study on the Thermal Decomposition Reactions of cis- and trans- fused 1,2,4-Trioxanes

LÁZARO F. R. CAFFERATA; RENE JEANDUPEX; GUSTAVO P. ROMANELLI; CARMEN M. MATEO; CHARLES W. JEFFORD

AFINIDAD

ASOC QUIMICOS

Lugar: Barcelona; Año: 2003 vol. 60 p. 206 - 211

0001-9704

The kinetics of the thermal decomposition reactions of artemisinine (1), a cis-fused 1,2,4-trioxane, and trans-3,3dimethyl-1,2,4-trioxane (6) in solutions of benzene, toluene, and methanol in sealed tubes were compared at temperatures between 100.1° and 171.4 °C. Pseudo first-order rate constant values were determined for conversions of both cyclic peroxides up to ca. 60%. The activation parameters and the composition of the reaction products were indicative of homolytic cleavage of their O-O bonds as the rate-determining steps followed by stepwise fragmentation. The free energies of activation (ΔG#) for 1 and 6 reactions in the aromatic solvents were calculated at the middle of each temperature range, giving values of 30.7 and 35.1 kcal/mol, respectively, which are evaluated considering their different molecular configurations. Furthermore, the rates of the thermal decomposition reactions of those trioxanes were sensitive to solvent effects.