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Elimination Reactions of ( E )‐2,4,6‐Trinitrobenzaldehyde O ‐Benzoyloximes Promoted by R 2 NH / R 2 NH 2 + in 70 mol% MeCN (aq). Effects of the β‐Aryl Group and Leaving Group on Nitrile‐Forming Transition States
Author(s) -
Pyun Sang Yong,
Paik Kyu Cheol,
Han Man So,
Cho Bong Rae
Publication year - 2016
Publication title -
bulletin of the korean chemical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.237
H-Index - 59
ISSN - 1229-5949
DOI - 10.1002/bkcs.10791
Subject(s) - chemistry , medicinal chemistry , leaving group , kinetics , nitrile , stereochemistry , elimination reaction , aryl , catalysis , organic chemistry , physics , quantum mechanics , alkyl
Elimination reactions of ( E )‐2,4,6‐( NO 2 ) 3 C 6 H 2 CH NOC (O) C 6 H 4 X ( 3 ) promoted by R 2 NH / R 2 NH 2 + in 70 mol% MeCN (aq) have been studied. The reactions produced elimination products and exhibited second‐order kinetics. The β and |β lg | values remained nearly the same for all leaving groups and bases. The results can be described by the negligible p xy interaction coefficient, p xy = ∂β/∂p K lg = ∂β lg /∂p K BH ≈ 0, which provides a strong support for the (E1cb) irr mechanism. For eliminations from ( E )‐ArCHNOC(O)C 6 H 4 X ( 1 , 3 ) and ( E )‐2,4,6‐(NO 2 ) 3 C 6 H 2 CHNOAr′ ( 2 , 3 ), the change of the β‐aryl group (Ar) from 2,4‐dinitrophenyl ( 1 ) to 2,4,6‐trinitrophenyl ( 3 ) increased the rate by 270‐fold without appreciable change in the transition state structure. On the other hand, the leaving group (OAr′) variation from benzoate ( 3 ) to 4‐nitrophenoxy ( 2 ) induced a change in reaction mechanism from (E1cb) irr to E2. These results have been attributed to the cyclic transition state for the nitrile‐forming eliminations involving the benzoate leaving group.