A kinetic study of the base catalyzed ring opening of 9-methylcaffeine halide and its homologs
This study provides information about the kinetics of the hydrolytic ring cleavage of imidazolium compounds and the catalytic effect of micelles in this ring cleavage. 9-Methylcaffeine iodide was synthesized and its base catalyzed ring cleavage was studied. The ring cleavage, via alkaline hydrolysis of the imidazole moiety, showed pseudo-first order kinetics over the pH range of 7.28 to 10.81. Activation parameters were found to be: Ea = 29.4 Kcal mole-1, △H+ = 28.8 Kcal mole-1 , and △S+ = 27.4 cal mole-l deg -1 The kinetics were studied in the presence of micelles and no rate enhancement was observed. The mechanism for ring cleavage was also investigated. 9-Ethylcaffeine iodide was synthesized and its base catalyzed ring cleavage, at 30°C and a pH of 9.42, showed pseudo first order kinetics. 6 -3 -1 The kobs was found to be 1. 5 x 10-3 sec-1. The oxidation kinetics of 8 ,8-dihydro-9-methylcaffeine to 9-methylcaffeinE:· iodide were also examined.
Halides, Micelles, Methylation, Physical Sciences and Mathematics
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