A second issue associated with tobacco smoking is its addictive nature, which is due to the presence of nicotine. Recent research from James F. Pankow and associates at the Department of Environmental Sciences and Engineering at the Oregon Graduate Institute (3) has shed more light on the availability of nicotine in cigarette smoke, and is a nice example of the practical implications of acid-base chemistry. The results of this work hinge, first, on the properties of nicotine as a base.

Nicotine has two nitrogens that can undergo protonation, but in the structure shown below, only the nitrogen in the nonaromatic 5-membered ring is significantly protonated under the pH conditions of tobacco smoke. (For more information on the chemistry of nicotine see reference 4.)

To understand the implications of this work, it is also useful to know that the free-base form of nicotine is more volatile–has a higher vapor pressure, and thus forms a gas more easily–than the protonated, charged forms. Furthermore, the free-base form of nicotine passes more readily through membranes, and is therefore more easily absorbed into the body, than the salt form. Pankow and his associates showed that the inclusion of ammonia in cigarette smoke significantly increases the proportion of the free-base form. This occurs because ammonia is more basic than nicotine, and therefore deprotonates it:

As noted above, the free-base form of nicotine is more volatile than the charged form and is more easily absorbed into the body. Because nicotine is addictive, the presence of more free-base nicotine in cigarette smoke would enhance addiction to smoking. The Oregon group sorted out all of the quantitative details associated with the partitioning of nicotine into the gas phase as a function of ammonia concentration. Although they noted that the relative concentration of ammonia in actual cigarette smoke is not known, they also pointed out that tobacco is currently blended with significant amounts of compounds that could readily liberate ammonia on heating. The Oregon group also noted that the FDA, in arguing its case that cigarettes are being manufactured as nicotine delivery devices, quoted a cigarette-industry “leaf blender’s manual.” This manual states that ammonia, when added to a tobacco blend, acts as an “impact booster.” The implication is that, in operational terms, cigarette manufacturers have long since reached the same conclusions that were reached as a result of this research study, and have allegedly used this knowledge to increase the addictive potential (”impact”) of their products.

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