25238-52-2Relevant academic research and scientific papers
The "dimer nucleophile mechanism" for reactions with rate-determining first step: Derivation of the whole kinetic law and further treatment of kinetic results
Alvaro, Cecilia E. Silvana,Nudelman, Norma Sbarbati
scheme or table, p. 735 - 742 (2011/07/29)
Overwhelming evidence has been previously reported for the existence of the so-called "dimer nucleophile mechanism" in aromatic nucleophilic substitutions by amines in aprotic solvents, for which the most prominent feature is the fourth-order kinetics (third order in amine) that has been observed with many different substrate-nucleophile systems, especially those in which departure of the nucleofuge is the rate-determining step. The mechanism has been confirmed by several other features, although other alternative mechanisms were suggested to explain the fourth-order kinetics, no one has been able to explain the other above-mentioned features. The present paper affords additional experimental evidence and derivation of the kinetic expressions for reactions with good nucleofugues, where the first step is rate determining. The work involves studies of the reactions of 2,4-dinitrofluorobenzene and 2,4-dinitrochlorobenzene with aniline and with alkyldiamines in toluene. The novelty of this work lies in the selection of substrate-nucleophile systems exhibiting kinetic behavior that allows estimations of the different k's involved. The satisfactory agreement between the quotients of k's calculated from sets of data obtained under different reaction conditions hereby reported indicates that the assumptions made are correct and that the whole treatment applied to the kinetic data is justified. All together, the results fit well with the reaction scheme involving the dimer nucleophile mechanism, adding new evidence to this mechanism that it is well established in the current literature.
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
Alvaro, Cecilia E. Silvana,Nudelman, Norma Sbarbati
, p. 880 - 885 (2007/10/03)
The kinetics of the reactions between 1-halogeno-2,4-dinitrobenzene (halogen = F, C1) 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 C1 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 kA 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
