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Kinetics and mechanism of the reactions of aryl chlorodithioformates with pyridines and secondary alicyclic amines
Author(s) -
Castro Enrique A.,
Gazitúa Marcela,
Santos José G.
Publication year - 2009
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.1555
Subject(s) - chemistry , alicyclic compound , tetrahedral carbonyl addition compound , amine gas treating , aqueous solution , aryl , ionic strength , medicinal chemistry , ion , ionic bonding , kinetics , inorganic chemistry , catalysis , organic chemistry , alkyl , nucleophile , physics , quantum mechanics
The reactions of pyridines and secondary alicyclic (SA) amines with phenyl and 4‐nitrophenyl chlorodithioformates (PClDTF and NPClDTF, respectively) are subjected to a kinetic study in aqueous ethanol (44 wt% ethanol) solution, at 25.0 °C, and an ionic strength of 0.2 M (KCl). The reactions are studied spectrophotometrically. Under amine excess, pseudo‐first‐order rate coefficients ( k obs ) are found. Plots of k obs versus [amine] are linear and pH independent, with slope k N . The Brønsted‐type plots (log k N vs . p K a of aminium ions) are linear for the reactions of PClDTF with SA amines (slope β of 0.3) and pyridines ( β = 0.26) and those of NPClDTF with pyridines ( β = 0.30). For the reaction of NPClDTF with SA amines the Brønsted‐type plot is biphasic, with slopes β 1 = 0.2 (at high p K a) and β 2 = 1.1 (at low p K a). The p K a value at the center of curvature (p K a 0 ) is 7.7. The magnitude of the slopes indicates that the mechanisms of these reactions are stepwise, with the formation of a zwitterionic tetrahedral intermediate as the rate‐determining step, except for the reaction of NPClDTF with SA amines where there is a change in the rate‐determining step, from formation to breakdown of the tetrahedral intermediate, as the amine basicity decreases. Copyright © 2009 John Wiley & Sons, Ltd.