(E)-2,4-Dinitrobenzaldehyde O-aryloxime과 (E)-2,4,6-Trinitrobenzaldehyde O-benzoyloxime 유도체의 니트릴-형성 제거반응에 관한 연구

Abstract

In Chapter Ⅰ, nitrile-forming eliminations from (E)-2,4-(NO2)2C6H3CH=NOC6H3-2-X-4-NO2 (1a-e) promoted by R3N in MeCN have been studied kinetically. The reactions are second-order and exhibit Brönsted β = 0.83-1.0 and

βlg

= 0.41-0.46. The results have been interpreted in terms of highly E1cb-like transition state with extensive Cß-H bond cleavage and limited Nα-OAr bond cleavage. Comparison with exiting data reveals that the structure of the transition state changes from E2-central to highly E1cb-like either by the change of the β–aryl group from Ph to 2,4-dinitrophenyl under the same condition or by the base-solvent system variation from EtO--EtOH to Et3N-MeCN for a given substrate (1a-e). In Chapter Ⅱ, nitrile-forming eliminations from (E)-2,4,6-(NO2)3C6H2CH=NOC(O)C6H4X (1a-d) promoted by R2NH/R2NH2+ in 70 mol% MeCN(aq) have been studied kinetically. The reactions produced only elimination products and exhibited second-order kinetics. The β and

βlg

values remained nearly the same within experimental error regardless of the ability of the leaving groups and the base strength variation. The results can be described by a negligible pxy interaction coefficient, pxy = ∂β/∂pKlg = ∂βlg/∂pKBH ≈0, which describes the interaction between the base catalyst and the leaving group. The negligible pxy interaction coefficient are inconsistent with the E2 mechanism for which pxy > 0 is expected, but provide a strong evidence for the (E1cb)irr mechanism.