Quaternary Nitrogen Heterocycles. IV. The 1-Methyl-4-nitroquinolinium and 4,4-Diiodo-1,1-dimethy1-1,4-dihydroquinolinium Cations, Two Methylation Products of 4-Nitroquinoline and their Reactions in Aqueous Solutions

Abstract

Methylation of 4-nitroquinoline with methyl fluorosulfonate ("magic methyl") gives the expected 1-methyl-4-nitroquinolinium fluorosulfonate. However, methylation with methyl iodide gives an unexpected product (C11H12I3N) which is shown to be 4,4-diiodo-1,1-dimethyl-1,4-dihydroquinolinium iodide. This latter salt readily loses a molecule of methyl iodide in aqueous alkaline solution and forms 4-hydroxy-4-iodo-1-methyl-1,4-dihydroquinoline. This latter product reacts in aqueous solution with excess silver iodide or bromide in the presence of silver nitrate to give 3-iodo-1-methyl-4-quinolone or the corresponding 3-bromo derivative. The 1-methyl-4-nitroquinolinium cation readily forms a pseudobase in aqueous solution (pKROH = 5.31; pKRO− = 10.95 ). Kinetic and spectroscopic data are consistent with the predominant neutral pseudobase species being 4-hydroxy-1-methyl-4-nitro-1,4-dihydroquinoline, while the predominant pseudobase anion is the alkoxide ion of 2-hydroxy-1-methyl-4-nitro-1,2-dihydroquinoline.