In an effort to understand the effects of tobacco vs marijuana smoke on health, the chemistry of smoking plants, and remembering some of the chemistry I took in college, I came across a 2007 study comparing mainstream and sidestream marijuana and tobacco cigarette smoke, according to which:

a number of chemicals were present in marijuana smoke at levels that were substantially higher than in tobacco smoke. For example, NO, NO x , hydrogen cyanide, and aromatic amines were present in marijuana smoke at levels 3-5 times higher than in mainstream tobacco smoke, while ammonia was present at levels 20 times higher than tobacco. Conversely, some compounds such as PAHs, formaldehyde, and acetaldehyde were found at moderately higher levels in tobacco.

I have mostly understood the study but I do need some things clarified.

Question 1: Could the combustion of any plant material whether it is an edible herb or in my particular example, tobacco or marijuana, potentially produce similar products or by-products (e.g HCN, ammonia), because of the same functional groups present in the different compounds of the tobacco or marijuana plant?

Question 2: Would all of the molecules in the figure below which are found in the tobacco plant, be independently reacting with oxygen and what is the reaction of nicotine producing HCN and/or an aromatic amine which if I remember correctly is a cyclic molecule?

enter image description here Picture source


1 Answer 1


Question 1 is easy to answer: Yes.

The ‘burning’ of whichever plant you’re (or somebody else is) smoking is an incomplete combustion on the ember end of the cigarette/joint/whatever. In any incomplete combustion of nitrogen-containing organic compounds, $\ce{HCN}$ and ammonia can (and likely will) be a side product. Aromatic amines are probably also always generateable as are $\ce{NO_x}$. And PAHs, aldehydes etc. can also result from the incomplete combustion of practically all plant or animal material.

Question 2 is slightly harder. To the best of my knowledge, however, the answer is: We do not know.

While we may be able to say that all the molecules in your question would be independently reacting, the mechanisms are so many and so complex that I very much doubt they have been the target of investigations. I think I recall somebody once studying the reaction mechanism of the complete combustion of methane and coming up with tens if not hundreds of partial reactions and steps. That was complete combustion (i.e. enough oxygen present), so it all boiled down to:

$$\ce{CH4 + 2O2 -> CO2 + 2H2O}$$

In incomplete combustion, we cannot even be fully sure of the reaction equation (and the stoichiometries involved therein), let alone a mechanism.

Side note: the complete combustion of a cigarette in pure oxygen takes about seven seconds ($\pu{7s}$) and oxidises it entirely to $\ce{CO2}$ and $\ce{H2O}$ (plus something from the nitrogens and likely $\ce{SO3}$ from sulphur/$\ce{P4O10}$ from phosphorus)

  • $\begingroup$ How would one go about ensuring the complete combustion of Marijuana? Asking for a friend. $\endgroup$ Feb 3, 2019 at 18:12
  • $\begingroup$ @NonSecwitter Under high-oxygen conditions as shown in this video. Note: don’t try this at home. $\endgroup$
    – Jan
    Feb 4, 2019 at 3:16

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