Lösungsmitteleinflüsse und Basenkatalyse bei der nucleophilen aromatischen Substitution

Abstract

The rate of the reaction of piperidine with y-nitrofluorobenzene is strongly dependent on the polarity of the solvent. Furthermore, the reaction is catalysed by piperidine or tertiary bases. The solvent-dependence differs for substitution and base catalysis.Unter einer nucleophilen aromatischen Substitution versteht man eine Reaktion, bei der eine nucleophile Substanz (Lewisbase) iiber ihr freies Elektronenpaar mit einem Substrat reagiert. Die Gruppe X verlaBt dabei das Molekul unter Mitnahme des Elektronenpaares der C-X-Bindung (1) :Man kann die Vielfalt der Kombinationsmoglichkeiten in verschiedene Gruppen einteilen, je nachdem, ob neutrale oder geladene Molekule miteinander reagieren. Fur diese Gruppen sollte man eine unterschiedliche Abhangigkeit der Reaktionsgeschwindigkeit vom Losungsmittel erwarten. Der EinfluR des Mediums auf die Reaktion von neutralen [l-51 und positiv [6] geladenen

Toward a More Holistic Framework for Solvent Selection

“…In the case of 4-fluoronitrobenzene, the reaction with azide anion displays rate accelerations of 5 to 7 orders of magnitude upon moving from methanol to HMPA (Figure ). Switching to a neutral nucleophile such as piperidine leads to a similar yet different pattern in the projection plots (Figure ), suggesting that the underlying mechanisms of the two reactions differ slightly …”

Rapid investigation of the effect of binary and ternary solvent gradient mixtures on reaction outcomes using a continuous flow system

“…To develop the method, we chose the well-studied nucleophilic displacement between 1-fluoro-4-nitrobenzene 1 and piperidine 2 (Scheme 1) since there is a known balance between reaction medium polarity and the presence of hydrogen-bond donors on the reaction rate. 1,25–30 A flow system consisting of two pumps delivering the reagents, 1-fluoro-4-nitrobenzene 1 and piperidine 2 , respectively, and two pumps delivering the studied solvents were used (Fig. 2).…”