Chemical Studies on Tobacco Smoke. XIII. Inhibition of the Pyrosyntheses of Several Selective Smoke Constituents

Earlier studies demonstrated that polynuclear aromatic hydrocarbons (PAH) are selectively reduced in the smoke of alkali nitrate rich tobaccos. We hypothesized, therefore, that in the burning cone of a tobacco product, the non-volatilized organic compounds are partially pyrolyzed to C,H-radicals that may combine with each other and form, among others, the thermodynamically favoured PAH. Since we have in the burning cone of nitrate rich tobaccos an excess of thermically activated nitrogen oxides, we assumed that these may react as scavengers for C,H-radicals and, with it, partially inhibit the PAH pyrosynthesis. The present study was designed to challenge our working hypothesis. For the experiments we employed cigarettes to which we had added various amounts of KNO3 (0, 2.5, 5.0, 7.0 and 8.0 %). As expected, the yields of nitromethane, nitroethane, and nitrobenzene in the smoke increased with the increased of nitrate in the tobacco and the yields of phenanthrene, benz[a]anthracene, and benz[a]pyrene decreased. The concentration of naphthalene was only to a minor degree reduced with the increase of nitrates in the tobacco. One explanation for this observation could be that naphthalenes are primarily formed from specific tobacco terpenes, as suggested in the literature. As was expected, the smoke yields of N-unsubstituted and N-alkylated indoles was relatively little affected by the increase in the nitrate content, since these agents are predominantly formed from tryptophan. It was our objective to contribute to the understanding of the pyrosynthesis of carcinogenic PAH and the selective reduction of PAH in the smoke of nitrate rich tobacco. With the increase of our knowledge in this area we may also find an explanation for the reduced tumorigenicity of condensates from nitrate rich tobaccos