39456-05-8Relevant academic research and scientific papers
Studies of Amine-Induced Ring Opening of Some Mesoionic Xanthines
Mbagwu, Godwin O.,Bass, R. Gerald,Glennon, Richard A.
, p. 465 - 474 (2007/10/02)
The ring-opening reactions of seven mesoionic thiazolopyrimidine-5,7-diones by a series of primary and secondary amines have been investigated.The rates of the ring fission of five N(8)-substituted mesoionic xanthines with benzylamine were measured and found to follow second order kinetics.The Hammett relationship is followed with ρ value of +0.48 in p-dioxane as solvent.The dependence of rates on temperatures has been studied for the N(8)-ethyl derivative; the energy of activation (ΔE*) is 25.3 kcals mol-1, the enthalpy of activation (ΔH*) is 24.7 kcals mo l -1 and the entropy of activation (ΔS*) is -4.9 e.u.A slight increase in rate of reaction was observed when the solvent was changed from p-dioxane to dimethyl sulfoxide.In p-dioxane at constant mesoionic xanthine concentration, the rate constant for ring opening decreased with increasing benzylamine concentration.These results are consistent with a bimolecular nucleophilic mechanism proceeding by the rate-determining formation of a charged tetrahedral transition state.
