N-substituted heterocyclic cations. Part VI. Reactions of the pseudo-base derived from the N-cyanoquinolinium ion in basic solutions. Nature of the anion in ring–chain prototropy

Abstract

The pseudo-base 1-cyano-1,2-dihydro-2-hydroxyquinoline, derived from the N-cyanoquinolinium ion, has an apparent pK_a of 11·2 ± 0·2. The equilibrium between the pseudo-base, its conjugate base, and the conjugate base of cis-N-cyano-o-aminocinnamaldehyde has been studied in aqueous basic solution, the amount of the open-chain tautomer being increased by the addition of organic solvents. This observation of two distinct classical anions, rather than of a common mesomeric anion, from the pseudo-base and its tautomer, may be indicative of a general distinction between ring–chain and triad prototropy.

The rearrangement of the conjugate base of cis- to that of trans-N-cyano-o-aminocinnamaldehyde is base-catalysed and the trans-isomer has been isolated and characterised. The formation of alkyl ethers from the pseudo-base is both acid- and base-catalysed, the latter reaction involving the formation and subsequent ring closure of the hemiacetal of the conjugate base of cis-N-cyano-o-aminocinnamaldehyde.