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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 34, Number 4
BKCSDE 34(4)
April 20, 2013 

Eliminations from (E)-2,4-Dinitrobenzaldehyde O-Aryloximes Promoted by R3N/R3NH+ in 70 mol% MeCN(aq). Effects of Leaving Group and Base-Solvent on the Nitrile-Forming Transition-State
Bong Rae Cho, Sang Yong Pyun*
Elimination, E1cb-like and (E1cb)irr, Leaving group and base-solvent effect
Elimination reactions of (E)-2,4-(NO2)2C6H2CH=NOC6H3-2-X-4-NO2 (1a-e) promoted by R3N/R3NH+ in 70 mol % MeCN(aq) have been studied kinetically. The reactions are second-order and exhibit Brönsted β = 0.80- 0.84 and |βlg| = 0.39-0.42, respectively. For all leaving groups and bases employed in this study, the β and |βlg| values remained almost the same. 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 is consistent with the (E1cb)irr mechanism. Change of the base-solvent system from R3N/MeCN to R3N/R3NH+-70 mol % MeCN(aq) changed the reaction mechanism from E2 to (E1cb)irr. Noteworthy was the relative insensitivity of the transition state structure to the reaction mechanism change.
1030 - 1034
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