Pyrolysis mechanisms pyridine

It is very likely that the pyrolysis of poly(2-vinylpyridine-co-styrene) takes place by a random scission mechanism characteristic for both styrene and poly(2-vinylpyridine). Both benzene and pyridine were detectable in the pyrogram, but their levels were extremely low and these compounds are not included in Table 6.2.8 (even as trace type compounds). The presence of benzene and pyridine may be the result of the elimination of these compounds at very low level from the polymer backbone, but more likely they are formed from the free radicals that are already generated from the backbone cleavage. 

A new preparative synthesis of 2-arylquinazolin-4(3//)-ones, which was reported recently, involved the pyrolysis of Schiff bases derived from 3-amino-l,2,3-benzotriazin-4-one in paraffin oil at 300 C, or in boiling 1-methylnaphthalene. The yields were as high as 86-100% but failed entirely when p-HO-, P-O2N-, and p-Me2N-benzaldehyde, furfural, and pyridine-2-aldehyde were used. The mechanism in Eq. (5) was proposed although the... 

In general, pyrolysis of monocyclic 1,2,3-triazines 1 leads to acetylenes, nitriles and nitrogen.46, 295 297 300 Heating simple 1,2,3-triazines in a sealed tube led to the isolation of pyridines, pyrimidines, pyrazoles, pyrroles, pyridazine, and indeno[3,2-/>]pyridine, depending on the substituents bound to the 1,2,3-triazine ring and the reaction conditions.46 A mechanism formulated for the formation of these products involves an azete as an intermediate. 

Pyridines can be formed by mechanisms other than pyrolysis. The reaction of aldehydes with amino acids has been shown to generate pyridines (50). When a glycine-propanal mixture was heated to 180°C, 3,5-dimethyl-2-ethylpyridine, 3,5-di-methyl-4-ethylpyridine, and 3,5-dimethylpyridine formed. Glycine-propanal mixtnres, also heated to 180°C, gave 2,5-dimethylpyridine and 3,4-dimethylpyridine. This is an example of a nonpyrolytic method of forming pyridines. As small-chain aldehydes reqnired for this reaction are abundant in smoke, this is a feasible ronte to pyridines. 

Since nicotine is the most abundant and best known tobacco alkaloid, its pyrolysis has been thoroughly studied [Woodward et al. (4275a), Jarboe and Rosene (1923a)]. More recent work [Kaburaki et al. (2006)] on the pyrolysis of nicotine and various alkyl-pyridines has resulted in a proposed mechanism for the thermal degradation of nicotine. .. Schmeltz [Schmeltz et al. (3499)] also studied nicotine and identified a number of previously unreported compounds in the nicotine pyrolysates. .. These included pyrrole, acenaphthene, indole, skatole, and anthracene and/or phenanthrene. However, the presence of dibenzacridines and dibenzcarbazole, previously reported in nicotine and pyridine pyrolysates, could not be confirmed [Van Duuren et al. (4027)]. 

Pyrolysis of 3-(o-azidophenyl)pyridine gives a- and y-carboline. Although the process does not formally involve a free radical ( N.GeH4. C5H4N), it is reminiscent of a radical substitution. The mechanism of the Graebe-Ullmann reaction, the formation of carbazoles by the pyrolysis of 3-arylbenzotriazoles, has not been elucidated, but some examples of it, notably the formation of carbolines from 3-pyridylbenzotriazoles, suggest the character of a radical substitution. 

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