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Could you make nitroglycerin by eating large quantities of pure glycerine soap? A quick google search told me flatus are 59% nitrogen, but I couldn't find anyone else with my exact question (which makes sense). In short, is it possible to make nitroglycerin through some human digestive process by eating soap? If so, how much soap?

According to Wikipedia, in the lab nitroglycerin is prepared by nitration of glycerin:

Nitration of glycerine to trinitroglycerin using nitric acid and sulfuric acid

There also exists a mechanism for intergastric nitration through consumed nitrite [1].

Is it feasible for such reactions to result in nitration of glycerine to nitroglycerin within the human digestive tract? Are there other possible pathways for this reaction?

Reference

  1. Rocha, B. S.; Gago, B.; Barbosa, R. M.; Lundberg, J. O.; Radi, R.; Laranjinha, J. Intragastric Nitration by Dietary Nitrite: Implications for Modulation of Protein and Lipid Signaling. Free Radic. Biol. Med. 2012, 52 (3), 693–698. https://doi.org/10.1016/j.freeradbiomed.2011.11.011.
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    $\begingroup$ No, it is not possible. The fact farts contain nitrogen is not relevant. But reasons for eating soap make me curious. $\endgroup$
    – Poutnik
    Commented May 15 at 5:26
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    $\begingroup$ It would not work. Mainly because of digestion. Your body cannot break down soap and combine it with nitrogen to form nitroglycerin. Your digestive system is incapable of doing that in its current state. Also you would probably vomit most of the soap out anyways. $\endgroup$
    – Ronith
    Commented May 15 at 6:04
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    $\begingroup$ @Poutnik Pica is a medical condition in which people eat non-food things, like sand, clay, or soap $\endgroup$
    – Chris H
    Commented May 15 at 13:09

2 Answers 2

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According to the metabocard at HMDB — Nitroglycerin, nitroglycerin is only found in individuals that have used or taken this drug. No known metabolic pathways for glycerin lead to nitroglycerin either.

Even if nitroglycerin were synthesized, it would be swiftly absorbed and metabolized. From DrugBank — Nitroglycerin:

After a sublingual dose of 0.5 mg of nitroglycerin in patients with ischemic heart disease, the peak concentration $(C_\mathrm{max})$ was 2.56 ng/mL and the mean $T_\mathrm{max}$ was 4.4 minutes.

A simulation made with BioTransformer 3.0 [1] for human gut metabolism of glycerin with the command

java -jar BioTransformer30.jar -k pred -b hgut -ismi "C(C(CO)O)O" -osdf glycerin-metab.sdf -a

results in a single metabolite glyceraldehyde via aldo-keto reductase family 1 member B10 (AKR1B10). So, the pathway of making nitroglycerin from glycerine in vivo appears to be inaccessible, at least for the human/mammal biosystems.

Reference

  1. Djoumbou-Feunang, Y.; Fiamoncini, J.; Gil-de-la-Fuente, A.; Greiner, R.; Manach, C.; Wishart, D. S. BioTransformer: A Comprehensive Computational Tool for Small Molecule Metabolism Prediction and Metabolite Identification. J. Cheminf. 2019, 11 (1), 2. https://doi.org/10.1186/s13321-018-0324-5.
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First of all, you don't need to eat soap to get glycerin in your system. Fats are broken down by digestion into glycerin and fatty acids. Glycerin is also available commercially as a cough syrup and food additive/ingredient.

Secondly, nitric acid is a strong oxidising agent and is toxic in fairly low concentrations.

Thirdly, sulphuric acid serves two functions in the synthesis of nitroglycerin. The first is to act as an acid catalyst (and importantly, concentrated sulphuric acid is a stronger acid than nitric acid, which means it can activate nitric acid by protonating it.) The second is to act as a deydrating agent (the reaction produces not only 1 equivalent of nitroglycerin but also 3 equivalents of water, which are not shown in the reaction scheme in the question.) (Concentrated) sulphuric acid's affinity for water helps push the equilibrium towards the products. In the body the opposite conditions exist: a vast excess of water.

In summary, synthesis of nitroglycerin in the body from glycerin in detectable quantities (if at all) is very unlikely for the following reasons:

  • Nitric acid is toxic.
  • There is a great deal of water in the body which tends to push the equilibrium in the reverse direction.

The only point in favour is that stomach acid is fairly acidic and can catalyse esterification/de-esterification reactions, typically of organic acids (it also contains many enzymes that help catalyse de-esterification of specific biomolecules in the digestion of food.) Stomach acid, being an aqueous solution, is not strong enough to protonate nitric acid.

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  • $\begingroup$ Also the synthesis of nitroglycerin would require huge amounts of energy, so it's not going to happen without the body making even more energetic feedstock molecules or feeding in huge amounts of energy into enzymes. $\endgroup$
    – matt
    Commented May 16 at 11:21
  • $\begingroup$ @Matt synthetic nitroglycerin & similar compounds find use as heart medicine. They decompose enzymatically to nitric oxide, a vasodilator. But turning N2 gas into biologically usable NH3 is of course a complex process carried out by specialised organisms (such as microbes that inhabit the roots of certain plants) not something mammals are believed capable of. The mammal body carries out at least one process with strong oxidant: iodide for use in thyroid hormone is oxidised in extracellular follicles by H2O2 to a form that can oxidise tyrosine. H2O2 is presumably synthesised with atmospheric O2 $\endgroup$ Commented May 16 at 18:59
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    $\begingroup$ Note, synthesis of nitroglycerin from nitric acid and sulfuric acid does not require huge amounts of energy. And synthesis of nitric acid from ammonia does not require huge amounts of energy. It's all a bit of a red herring. $\endgroup$
    – david
    Commented May 17 at 6:51
  • $\begingroup$ @david agreed, ammonia > nitric acid and nitric acid > nitroglycerin don't need much energy - the energy use goes into making the glycerin and NH3, and if you can use atmospheric O2 it's all downhill from there. Strong oxidants are usually indiscriminate and toxic however (except O2 gas, whose weird electronic structure makes it kinetically rather unavailable) hence my example of extracellular synthesis of thyroid hormone (how did evolution come up with that??) It shows that strong oxidants can be used - but unless there's a biological need for nitroglycerin there would be no synthesis path. $\endgroup$ Commented May 17 at 9:21
  • $\begingroup$ @david, given nitroglycerine is quite an energy dense product, the energy for assembling it has to come from somewhere. Making strong enough nitric and sulphuric acid for the synthesis is energy expensive, admittedly there is energy released when Glycerine gets nitrated, but a lot of the energy trapped in the nitration is at the expense of diluting sulphuric acid in the reaction. $\endgroup$
    – matt
    Commented Jun 1 at 13:34

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