Pyrolysis mechanisms indole

FIGURE 8.18 Pyrolysis mechanism of indole proposed by Laskin and Lifshitz. 

In the pyrolysis of proteins, the dominant mechanism is the splitting-off of the amino acids rather than break-up of the backbone into smaller fragments which are characteristic of the original amino acids.Usually highly characteristic signals are found for the aromatic and sulphur containing amino acids, e.g., hydrogen sulphide from cystine and in combination with methionine pyrrole pyrrolidine and methylpyrrole for proline, phenyl, and cresol from tyrosine, toluene, styrene and phenylacetonitrile for phenylalanine indole, and methylindol from tryptophan. 

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)]. 

Rees and colleagues explored the mechanism of the pyrolysis of 1,2,3-triazoles and established in elegant fashion that 1/7-azirines are intermediates (Scheme 7) [42]. Thus, pyrolysis of triazoles 21 and 22 yields the same two 2/7-azirines 24 and 25 and subsequent products via the single intermediate l//-azirine 23. Pyrolysis of 24 affords N-vinylphthalimide (26) and benzonitrile, whereas azirine 25 gives indole 27, with no crossover. Moreover, there is no equilibration of the triazoles 21 and 22. 

---