Concerted mechanism of the reactions of 2,4-dinitrophenyl 4-cyanobenzoate with secondary alicyclic amines in aqueous ethanol

✍ Scribed by Enrique A. Castro; Andrea Hormazabal; Jose G. Santos

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 123 KB
• Volume: 30
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/(sici)1097-4601(1998)30:4<267::aid-kin4>3.0.co;2-q

✦ Synopsis

The title reactions are subjected to a kinetic analysis in ethanol-water, at 44 wt% ionic strength 0.2 (KCl). With a large excess of amine over the substrate, pseudo-first-25.0ЊC, order rate coefficients are obtained, which are linearly dependent on the amine concen-(k ) obs tration. The nucleophilic rate constants are determined from plots of vs. amine con-(k ) k N o b s centration. The Bro ¨nsted-type plot obtained with the values is linear, with slope k ␤ ϭ N

The magnitude of this slope suggests that the mechanism is concerted, as opposed to 0.63. a stepwise process with rate-determining breakdown of a zwitterionic tetrahedral intermediate in which the value of ␤ is usually 0.8-1.0. The pyridinolysis of the same substrate in the Ϯ (T ), same solvent is stepwise with the breakdown of as the rate-determining step. The change Ϯ T to a concerted mechanism for the title reactions is attributed to the superior nucleofugality of the alicyclic amines, compared to the isobasic pyridines, which destabilizes kinetically the "intermediate" in such a way that it does not exist, and the mechanism becomes enforced Ϯ