Radicals from the oxidative pyrolysis of tobacco

The fractional, oxidative pyrolysis of Bright tobacco was performed in an oxygen/nitrogen atmosphere containing from 0 to 20.4% of O-2 over the temperature range of 200-510 degrees C in a specially constructed, high-temperature flow reactor system. The effect of the temperature and the concentration of oxygen in the reaction atmosphere on the generation of free radicals from Bright tobacco and two major components of Bright tobacco (polyphenols and cell wall biopolymers) were studied. Electron paramagnetic resonance (EPR) spectroscopy was used to analyze for free radicals in the initially produced total particular matter (TPM) and in the gas phase. Two types of radicals were observed in the initially produced TPM: type I radicals characterized by a five-line EPR spectrum with an apparent g-value of similar to 2.0064 that was tentatively assigned to a tyrosyl radical formed at lower temperatures from the cell wall biopolymer fraction of tobacco, and type 11 radicals characterized by a single-line EPR spectrum with g-factor of 2.0035 assigned as a surface-associated, carbon-centered radical that is vicinal to an oxygen-containing functional group or an unpaired electron in the bulk of an oxygen-containing polymeric matrix. The yields of both types of primary radicals decreased with increasing oxygen concentration. This decrease in TPM radicals was accompanied by a significant increase in the formation of the gas-phase, alkoxyl radicals. The type I and type 11 primary TPM radicals formed during the oxidative pyrolysis were the same as those observed from pyrolysis of Bright tobacco. The oxidative pyrolysis of chlorogenic acid (a major component of the polyphenol fraction) formed radicals characterized by a single-line EPR spectrum with g-factor of similar to 2.0053 and Delta Hp-p of 10-13 G. The structure of these radicals is assigned as oxygen-centered, semiquinone-type radicals that were formed from the thermal decomposition of chlorogenic acid. Their yield was not dependent on the oxygen concentration and appeared to be the same radicals previously reported in aged TPM.