The pyrolytic formation of formaldehyde from sugars and tobacco

Formaldehyde is a carcinogenic compound present in cigarette smoke. It is one of several constituents in cigarette smoke that is considered by health scientists and regulatory authorities to be relevant to the development of smoking-related diseases. In the present study, a thermogravimetric system connected to a Fourier-transform infrared spectrometer has been used to examine aspects of the pyrolytic generation of formaldehyde from sugars and tobacco samples in order to provide pyrolytic information to explain some of the diverse observations and mechanistic factors involved in the generation of formaldehyde during cigarette smoking. Samples of 10 sugars, sugar/amino compound mixtures and tobacco mixtures have been pyrolysed under non-isothermal conditions in an atmosphere of 10% oxygen in nitrogen. These conditions were chosen so as to approximately mimic the smouldering conditions inside a burning cigarette. The sugars pyrolysed were fructose, glucose, invert sugar, white sugar, brown sugar, sugar cane syrup, sugar cane molasses, corn syrup, honey and maple syrup. All of them are used as tobacco ingredients.Formaldehyde was formed from all of the sugars at temperatures between 220 and 550 °C, probably as a primary product of the pyrolysis of each sugar. Pyrolysis of the amino acid l-proline, which is present in honey and maple syrup, generated formaldehyde between 220 °C, its melting/sublimation point, and 500 °C, probably as a secondary product from gaseous l-proline. The addition of diammonium hydrogen phosphate suppressed the generation of formaldehyde from the pyrolysis of glucose and fructose. The addition of l-proline increased the generation of formaldehyde, and then decreased it as the level was increased. Pyrolysis of a US tobacco blend generated formaldehyde in one major temperature range, 200–400 °C, with small formation regions at about 400–550 °C and above 600 °C. The addition of 7% glucose or invert sugar to the tobacco left the formaldehyde formation below about 450 °C relatively unaffected but increased that formed in the 400–550 °C region. Pre-heating tobacco or tobacco with added sugars to 250 °C for 10 min resulted in the evolution of formaldehyde during this period and lower amounts generated during the major formation region. All of these pyrolytic results have been used to explain the known characteristics of the generation of formaldehyde during cigarette smoking.