2,4,6-Trimethylpyridine (2,4,6-collidine) is an organic compound which belongs to the heterocycles (more precisely, heteroaromatics). It consists of a pyridine ring substituted with three methyl groups. It belongs to the substance group of the collidines, a group of six constitutional isomers. 2,4,6-trimethylpyridine is the most well-known isomer of this group.
Properties The compound has a refractive index of 1.4959 (25 °C).
Preparation 2,4,6-Trimethylpyridine was isolated from Dippel's oil in 1854.Collidin. In: Heinrich August Pierer, Julius Löbe (Hrsg.): Universal-Lexikon der Gegenwart und Vergangenheit. 4. Auflage. Band 4. Altenburg 1858, S. 262 (zeno.org).Friedrich Auerbach: „Ueber ein neues Collidin“, in: Berichte der deutschen chemischen Gesellschaft, 1892, 25 (2), S. 3485–3490 (). A synthesis can be carried out analogously to the Hantzsch's dihydropyridine synthesis from ethyl acetoacetate (as β-ketocarbonyl compound), acetaldehyde and ammonia in the ratio 2: 1: 1.T. Laue, A. Plagens: Namen- und Schlagwort-Reaktionen der Organischen Chemie, 5. Auflage, Teubner Verlag, Wiesbaden 2006, , S. 172.
Use By oxidation of the methyl groups with potassium permanganate collidinic acid is obtained.
2,4,6-Trimethylpyridine is used in organic syntheses (for example, for dehydrohalogenation), by binding the formed hydrogen halides.
As a member of the pyridines, it can be used as a basic probe for Bronsted and Lewis acidity quantification on solid acids (such as zeolites, aluminas, metal oxides, etc.) with FTIR analysis. Its size difference with pyridine is advantageous for location-specific (external vs internal) acidity probing. Both for Lewis and Bronsted acidity probing, the nitrogen atom is the source of the basicity.
See also 2,6-Dimethylpyridine (lutidine)
References