Aromatic nucleophilic substitution of hydrogen: mechanism of reaction of 6-nitroquinoline with cyanide ions, with and without participation of methyl cyanoacetate

Abstract

The mechanism of nucleophilic substitution of hydrogen (S_NAr^H) in 6-nitroquinoline 1 by action of cyanide ion in the presence or in the absence of methyl cyanoacetate in dimethyl sulfoxide has been studied by means of ¹H NMR. The main reaction products and some side products have been identified and their time–concentration dependences have been determined. An experiment with ¹³C enriched potassium cyanide proved that the cyano group replaces hydrogen at the 5-position of the starting compound 1. The two main products obtained from the reaction mixture of 6-nitroquinoline 1 and potassium cyanide are 6-hydroxyquinoline-5-carbonitrile 11 and 6,6′-azoquinoline-5,5′-dicarbonitrile 13. On the basis of the data obtained, a mechanism has been suggested for aromatic nucleophilic substitution of hydrogen by cyanide ion in 6-nitroquinoline 1 involving a Meisenheimer adduct of 6-nitroquinoline 1 with cyanide ion and 6-nitrosoquinoline-5-carbonitrile 14 as unstable intermediates.