Preparation and characterisation of 2-formyl-1,4,5,6-tetrahydropyridine,a compound with a cracker-like odour

2-Acetyltetrahydropyridine is an important flavour constituent that imparts roasty, popcorn-like, and cracker-like odours to foods, such as bread, rice, popcorn, taco shells and tortilla chips. We postulated that the homologue with a formyl group in the C-2 position, 2-formyltetrahydropyridine, might have similar desirable odour qualities. Synthesis of this compound was performed by oxidation of 2-piperidinemethanol with silver carbonate supported on Celite®. This reaction produced a major volatile (46.9% of the total volatiles) with a retention index of 1023 on DB-1. GC–O revealed that the unknown had a strong cracker-like odour. The electron impact mass spectrum of the unknown had the following major ions: m/z 82, 111, 54, 68, 28, 43. The m/z 53–54 ratio and m/z 82–83 ratio were consistent with a 1,4,5,6-tetrahydropyridine ring structure. GC-FTIR of the unknown revealed an N–H stretching band at 3435 cm⁻¹ and a Fermi doublet at 2827 and 2713 cm⁻¹ that indicated the presence of an aldehyde. A strong carbonyl absorption band was present at 1703 cm⁻¹. The unknown was tentatively identified as 2-formyl-1,4,5,6-tetrahydropyridine, based on its retention index, odour quality, mass spectrum, and vapour phase infrared spectrum.