Reaction of aliphatic amines with 49% formic acid. 1-hexylamine, di-1-hexylamine, N,N-dimethyl-1-hexylamine, 1-dodecylamine, N,N-dimethyl-1-dodecylamine and N,N-dimethyl-1-butylamine

Article abstract of DOI:10.1002/prac.19973390109

Two primary amines, 1-hexylamine 2, 1-dodecylamine 19, one secondary amine, di-1-hexylamine 18, and three tertiary amines, N,N-dimethyl-1-hexylamine 6, N,N-dimethyl-1-butylamine 3, and N,N-dimethyl-1-dodecylamine 22 were each heated at 150°C, 250°C or 350°C with 49% aqueous formic acid for varying periods of time. The aliphatic primary amines underwent easy N-formylation and subsequent reduction to give N-methyl- and N,N-dimethylalkylamines. Especially at higher temperatures, other reactions intervened including elimination of NH₃ to the corresponding alkenes followed by partial double bond isomerization. Tertiary amines were more reactive at higher temperatures undergoing hydrolysis and reductive cleavages to secondary and primary amines, which subsequently followed the reaction sequences seen for primary amines. This series of saturated amines showed none of the cleavage into smaller fragments that was observed in the reductive alkylation of pyridine and 4-methylpyridine to a series of N-alkylpiperdines. This result reinforces the bis-aza-retro-Aldol-fragmentation mechanism postulated for the formation of the N-alkylpiperidines. Johann Ambrosius Barth 1997.