41378-14-7Relevant academic research and scientific papers
Hydrogen-bonded nucleophile effects in ANS: The reactions of 1-chloro and 1-fluoro-2,4-dinitrobenzene with 2-guanidinobenzimidazole, 1-(2-aminoethyl) piperidine and N-(3-aminopropyl)morpholine in aprotic solvents
Alvaro, Cecilia E. Silvana,Ayala, Alicia D.,Nudelman, Norma S.
, p. 101 - 109 (2011)
The kinetics of the reactions of 2,4-dinitrofluorobenzene (DNFB) and 2,4-dinitrochlorobenzene (DNClB) with 2-guanidinobenzimidazole (2-GB) at 40±0.2°C in dimethylsulphoxide (DMSO), toluene, and in toluene-DMSO mixtures, and with 1-(2-aminoethyl)piperidine (2-AEPip) and N-(3-aminopropyl) morpholine (3-APMo) in toluene at 25±0.2°C were studied under pseudo first-order conditions. For the reactions of 2-GB carried out in pure DMSO, the second-order rate coefficients were independent of the amine concentration. In contrast, the reactions of 2-GB with DNFB in toluene, showed a kinetic behaviour consistent with a base-catalysed decomposition of the zwitterionic intermediate. These results suggest an intramolecular H-bonding of 2-GB in toluene, which is not present in DMSO. To confirm this interpretation the reactions were studied in DMSO-toluene mixtures. Small amounts of DMSO produce significant increase in rate that is not expected on the basis of the classical effect of a dipolar aprotic medium; the effect is consistent with the formation of a nucleophile/co-solvent mixed aggregate. For the reactions of 3-APMo with both substrates in toluene, the second-order rate coefficients, kA, show a linear dependence on the [amine]. 3-APMo is able to form a six-membered ring by an intramolecular H-bond which prevents the formation of self-aggregates. In contrast, a third order was observed in the reactions with 2-AEPip: these results can be interpreted as a H-bonded homo-aggregate of the amine acting as a better nucleophile than the monomer. Most of these results can be well explained within the frame of the 'dimer nucleophile' mechanism. The shown polyamines were selected to examine its ability to form inter- or intra-molecular hydrogen-bonds. The reactions of 2-AEPip with both halodinitro-benzenes in toluene are third order in amine, consistently with the dimer nucleophile mechanism. On the contrary, the intramolecularly hydrogen-bonded structures of 2-GB and 3-APMo prevent formation of dimeric aggregates, the reactions are 2nd.order in amine as expected for the classical base-catalysed ANS. Copyright
