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Structure‐reactivity correlation in the reactions of pyrrolidine with O‐ethyl S‐aryl dithiocarbonates in aqueous ethanol
Author(s) -
Castro Enrique A.,
Cabrera Mauricio,
Santos Jose G.
Publication year - 1997
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/(sici)1097-4601(1997)29:2<113::aid-kin4>3.0.co;2-x
Subject(s) - chemistry , pyrrolidine , piperidine , amine gas treating , nucleophile , medicinal chemistry , aqueous solution , morpholine , tetrahedral carbonyl addition compound , reactivity (psychology) , ethanol , reaction rate constant , kinetics , organic chemistry , catalysis , medicine , physics , alternative medicine , pathology , quantum mechanics
The reactions of pyrrolidine with O‐ethyl S‐(X‐phenyl) dithiocarbonates (X = 4‐methyl, 4‐methoxy, H, 4‐chloro, 4‐nitro, 2,4‐dinitro, and 2,4,6‐trinitro) are subjected to a kinetic study in 44 wt% aqueous ethanol, 25.0°C, and ionic strength 0.2 M (maintained with KCl). Pseudo‐first‐order kinetics are found under amine excess. Linear plots of the pseudo‐first‐order rate coefficient against concentration of free‐base pyrrolidine are obtained for all the reactions, the nucleophilic rate coefficient ( k N ) being the slope of such plots. The Bronsted‐type plot (log k N vs. pK a for the leaving group) is linear with slope β lg = − 0.2, which is consistent with a mechanism through a tetrahedral intermediate (T ± ) where its formation is rate determining. The β lg value is very similar to that found in the same reactions in water. There is a great difference in the mechanism of the reactions of O‐ethyl S‐phenyl dithiocarbonate with pyrrolidine (order one in amine) and piperidine (complex order in amine) in aqueous ethanol, and this is attributed to a greater nucleofugality from T ± of piperidine rather than pyrrolidine. © 1997 John Wiley & Sons, Inc.