Judit Frank

Tautomeric pyridines. Part XV. Pyridone–hydroxypyridine equilibria in solvents of differing polarity

Tautomeric equilibria of the hydroxypyridine–pyridone type are investigated for five compounds: the proportion of pyridone form, dominant for H2O solutions, falls roughly linearly with the solvent polarity as measured by Z. In cyclohexane solution, comparable amounts of both forms are present.

Alkylation of quinolines with trialkyl phosphates. Part 2. Mechanistic studies

The mechanism of alkylation of 4-quinolone (3) by trialkyl phosphates has been studied by preparative, kinetic, and isotopic methods, as well as by u.v. spectrophotometry. In a kinetically controlled process the transient initial formation of 4-methoxyquinoline (4a) was established; this was subsequently transformed by trimethyl phosphate to a quaternary N-methyl-4-methoxyquinolinium salt (6a). The latter catalyses the transformation of (4a) by intermolecular O→N methyl transfer to the more stable N-methyl-4-quinolone (5a). The end product is a mixture of (5a) and (6a). Their ratio is shifted at higher temperature in favour of (6a). This is due partly to differences in the temperature dependence of the individual reactions and partly to alkylation of (5a) by trimethyl phosphate at higher temperature. A mechanism for the alkylation reaction is proposed.

A novel mass-spectroscopic technique for the investigation of vapour-phase tautomeric equilibria

Comparison of collision-induced dissociation–mass analysed ion kinetic energy (CID–MIKE) spectra of cations found by chemical ionisation ethylation with those of chemical ionisation protonation of fixed ethyl derivatives, allows identification of predominant tautomers in vapour phase equilibria.

1,3-Dipolar character of six-membered aromatic rings. Part XXVI. 3-Hydroxypyridine and 1-benzyl-3-oxidopyridinium

3-Hydroxypyridine undergoes successive 1,3-dipolar and Michael addition of acrylonitrile or methyl acrylate in high yield. These additions are thermally reversed, and 4-bromo-3-hydroxypyridine was prepared by adduct bromination followed by retro-addition.1-Benzyl-3-oxidopyridinium undergoes various 1,3-dipolar additions.