ChemInform Abstract: REACTIONS OF 4‐CHLORONITROBENZENE WITH ALKOXIDES IN THE PRESENCE OF CROWN ETHERS

Abstract

Untersucht wird die Kinetik der Reaktion von 4‐Chlor‐nitrobenzol mit Alkoxiden in den entsprechenden AIkoholen, die in Gegenwart von [ 8]Krone‐6 und O2 (als Radikalfänger) zur Substitution des Cl‐Atoms durch die Alkoxy‐ und die OH‐Gruppe führt (in Abwesenheit des Kronenethers und unter Luftabschluß werden stattdessen 4,4′‐Dichlor‐azoxy‐benzol und p‐Chloranilin gebildet).

From Tars to Products: How To Disentangle the Reactions of Nitrobenzenes with Nucleophiles

“…Following these observations, experimental conditions were optimized to obtain anilines in very good yield (80-98%). 10 With added enolate ion but in the absence of water, on the other hand, the γ-diketone 10 (Chart 1) is obtained with yields up to 80%, via oxidation of i to a nitrone (12) and further enolate addition (route b in Scheme 2). 11 Support for Scheme 2 came from studies of the reactivity of postulated key intermediates, the ketoimino (11) and the nitrone (12) derivatives.…”

“…It was found, indeed, that reaction of 4c with different alkoxides (ROK) in the parent alcohols (ROH) shows, upon complexation of K + by 18-crown-6, rate enhancements which parallel the trend of the RO -K + ion association constants in ROH. 12 Since these kinetic determinations were carried out in oxygen-free solutions, it was remarkable and unexpected to find 12 that the quantitative conversion of 4c into 4or (R ) 2-Pr) observed in the presence of 18-crown-6-complexed K + /2-propoxide proceeded at a rate which was lower (k ) 0.7 × 10 -3 s -1 ) than that of the reduction process (k ) 1.09 × 10 -3 s -1 ) taking place under exactly the same conditions but without 18crown-6. 4 The addition of crown ethers must, therefore, bring about not only an increase in the rate of substitution but also a decrease in that of reduction.…”