Studies of the Formation of Smoke Phenols

Processes involving or forming phenols during combustion of tobacco were studied by differential scanning calorimetry (DSC), thermogravimetry (TG), mass-spectrometry (MS), X-band electron spin resonance (ESR), and thermocouple (TCT) and infrared thermography (IRT) methods. Thermochemical properties of polyhydroxybenzenes, polynuclear aromatic hydrocarbons (PAHs), and carbohydrates were investigated both individually and when the compounds were embedded in combustible or non-combustible matrices; the compounds were studied in an O₂/He atmosphere at temperatures up to 800 °C, with a heating rate up to 60 °C/min. ESR of the mainstream smoke ‘tar’ was performed at temperatures down to -253 °C. The radicals found differed in their magnetic behavior depending on the material studied; this difference was attributed to the presence of relatively unstable isolated semiquinone and/or PAH-type molecules and the more stable quinone-hydroquinone-semiquinone redox complex.

Phenols themselves were found to affect combustion by radical scavenging and initiation. Added carbohydrates introduced diffusion limitations to oxygen. They also affected the combustion temperatures and could intensify the formation of phenols via quinone. Oxidation of PAHs was investigated and enthalpies were determined. These enthalpies decreased from benzo[a]pyrene (BaP) to anthracene, naphthalene and phenanthrene.