2,4,6-Collidine: Pyridine, 2,4,6-trimethyl

This reaction consists of the condensation of two molecular equivalents of a 1,3 diketone (or a J3-keto-ester) with one equivalent of an aldehyde and one of ammonia. Thus the interaction of ethyl acetoacetate and acetaldehyde and ammonia affords the 1,4-dihy dro-pyridine derivative (1), which when boiled with dilute nitric acid readily undergoes dehydrogenation and aromatisation" to gb e the diethyl ester of collidine (or 2,4,6-trimethyl-pyridine-3,5 dicarboxylic acid (II)). For the initial condensation the solid aldehyde-ammonia can conveniently be used in place of the separate reagents. 

Preparation 181.—Potassium Collidine Dicarboxylate (Dipotassium-2 4 6-trimethyl-pyridine - 3 5-dicarboxylate). 

When more bulky base molecules(collidine 2,4,6-trimethyl-pyridine) were introduced on acid-type zeolites, only H-ZSM5 did not interact with collidine. The results suggest that all the acidic sites of H-ZSM5 are located in the channels but not on the outer surfaces. 

Homologues of Pyridine.—Many homologues of pyridine have been obtained from bone-oil and coal-tar or by syntheses from other compounds. The methyl derivatives of pyridine are called picoUneSy the dimethyl derivatives are called lutidines, and the trimethyl derivatives are called collidines. As in the case of toluene and the xylenes, the side-chains are converted into carboxyl groups by oxidation. The a, /S, and 7 mono-carboxylic acids of pyridine are called picolinic acid, nicotinic acid, and isonicotinic acid, respectively. 

Although they are not as widely used as pyridine, substituted pyridines have found their own place in the characterization of hydroxyl groups. It was proposed (470) that, for steric reasons, 2,6-dimethylpyridine (DMP, lutidine) does not interact with Lewis acid sites and is thus a proton-specific probe. Later, it was demonstrated that DMP (247,256,471-473) (as well as 2,4,6-trimethyl pyridine or collidine (474)) stiU forms coordination bonds with coordinatively unsaturated surface cations. This bond is only weakened by the steric interference of the methyl groups with the surface but not prevented. In any case, the steric hindrance leads to preferential interaction ofDMP with hydroxyl groups (471-473). DFT calculations suggest that the proton transfer is promoted by the stabilization of the lutidinium ion on the deprotonated site, rather than by the intrinsic acidity of the acid site itself (475). 

Trimethyl Pyridine (y Collidine) ((CH3)jC5H2N) —(mol weight 121.18), (Warning—See Note 8) conforming to the following requirements ... 

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