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Role of hydrogen‐bonded nucleophiles in aromatic nucleophilic substitutions in aprotic solvents. reactions of halonitrobenzenes with ethylenediamine, 3‐dimethylamino‐1‐propylamine and histamine in toluene
Author(s) -
Alvaro Cecilia E. Silvana,
Nudelman Norma Sbarbati
Publication year - 2005
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.957
Subject(s) - chemistry , nucleophile , propylamine , ethylenediamine , hydrogen bond , medicinal chemistry , amine gas treating , dimer , toluene , morpholine , photochemistry , stereochemistry , organic chemistry , molecule , catalysis
The kinetics of the reactions between 1‐halogeno‐2,4‐dinitrobenzene (halogen = F, Cl) and the amines ethylenediamine (EDA) and 3‐dimethylamino‐1‐propylamine (DMPA) were studied in toluene at 25° ± 0.2C under pseudo‐first‐order conditions using varying amounts of amine. Even with Cl as the nucleofugue (where usually the first step is rate‐determining), a third‐order‐in‐amine kinetic law was observed: these results can be interpreted within the ‘dimer nucleophile’ mechanism where the amine homo‐aggregates are better nucleophiles than the amine monomers. To confirm this interpretation, the reaction of 2,4‐dinitrofluorobenzene with histamine was studied in the same solvent. Because of the rigid geometry, an intramolecular hydrogen bond is easily established, which prevents the formation of self‐aggregates. Consequently, the plot of k A vs. [histamine] is a straight line, as expected for a classical mechanism of base‐catalysed decomposition of the zwitterionic intermediate. All these results are well explained in the frame of the ‘dimer nucleophile’ mechanism. Copyright © 2005 John Wiley & Sons, Ltd.