Nucleophilic Addition to Diazaquinones. Formation and Breakdown of Tetrahedral Intermediates in Relation to Luminol Chemiluminescence

Article abstract of DOI:10.1021/ja00284a040

Nucleophilic addition to diazaquinones 2 was shown to occur at the carbonyl group.The rate constants and activation parameters for this process were determined with a large number of nucleophiles.The kinetics was rationalized in term of an equilibrium reaction between the reactants and a tetrahedral intermediate followed by the latter's breakdown.With some nucleophiles the enthalpy of activation for this process was found to be essentially zero.These cases were interpreted by assuming the formation of the tetrahedral intermediate to be the rate-determining step in the consumption of the diazaquinone.The complete mechanism of hydrolysis, azidolysis, and perhydrolysis were investigated.The stoichiometries were found to be 2a + H2O -> 2-formylbenzoic acid + N2 2a + HN3 -> phtalimide + 2N2 2a + H2O2 -> o-phthalic acid + N2 The breakdown kinetics of the tetrahedral intermediate of 2 with H2O2 was determined by chemiluminescence measurements while the lifetimes of the corresponding adducts of OH^- and N3^- were estimated from experiment.The initial additions of OH^- and N3^- were shown to generate acyldiazene species.The lattern were prone to further nucleophilic addition of OH^- or N3^- to the acyldiazene group.This second addition is also proposed to proceed via a tetrahedral intermediate the breakdown of which is exothermic involving the expulsion of N2.In the hydrolysis this step yields the end product (2-formyl benzoate) while in the azidolysis a second expulsion of N2 occurs which is followed by ring closure and tautomerization to yield the phthalimide.The neutral breakdown of the H2O2 adduct of 2 yields ground-state phthalate while its OH^--catalyzed rupture leads to chemiexcitation.The latter process is proposed to involve as an intermediate an acyldiazene peracid anion.This species is prone to intramolecular nucleophilic addition to yield the cyclic tetrahedral intermediate.The breakdown of the latter through the expulsion of N2 generates an antiaromatic endoperoxide which transforms into excited phthalate in a pericyclic process.