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Is there a molecule with enough oxygen in it (for example, something like $\ce{HCOOOH}$) such that it can undergo complete combustion without requiring any additional oxygen? For example the above molecule could self-combust via:

$$\ce{HCO3H -> CO2 + H2O}$$

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    $\begingroup$ It depends on how narrowly you define "burn themselves". What you're describing is something that disproportionates into a more oxidized and a less oxidized molecules. Look up "monopropellant" rocket fuels for examples of this, but there isn't necessarily any "burning" going on in many cases. $\endgroup$
    – Andrew
    Commented Jan 8, 2022 at 16:47
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    $\begingroup$ Such compounds have usually explosive properties. $\endgroup$
    – Poutnik
    Commented Jan 8, 2022 at 17:17
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    $\begingroup$ Why, many. Also, many compounds contain even more oxygen than that. It is just that when they burn, this isn't called burning. $\endgroup$
    – Ivan Neretin
    Commented Jan 8, 2022 at 17:55
  • $\begingroup$ Peroxo compounds are super oxygen rich and serves better as explosives. Have a look: digitalcommons.wayne.edu/oa_dissertations/1372 $\endgroup$
    – Nilay Ghosh
    Commented Jan 9, 2022 at 3:39

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As shown in the question, to fully oxidize one carbon and two hydrogen atoms you need three oxygens. Such a molecule, $\ce{HCOOOH}$, exists and it's called performic acid. It is used as a bleach and disinfectant and is explosive in high concentrations.

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Ammonium dichromate $\ce{(NH4)2Cr2O7}$ is well known for being able to burn with its own oxygen. If you dip a match into a crucible containing about $10\text{–}\pu{15 g}$ of ammonium dichromate, it will start to burn softly and throw out sparks like an active volcano, according to the equation $$\ce{(NH4)2Cr2O7 -> N2 + Cr2O3 + 4 H2O}$$ This operation is picturesque and not dangerous. In the 20th century, it was shown in high school classrooms. But dichromates are presently forbidden in many countries.

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    $\begingroup$ I remember seeing this. A small orange pile magically turns into a big green mound! $\endgroup$
    – Oscar Lanzi
    Commented Jan 9, 2022 at 0:34
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    $\begingroup$ Then there is ammonium nitrate: Texas City, Oklahoma City and Beirut inter alia. $\endgroup$
    – user55119
    Commented Jan 9, 2022 at 3:27
  • $\begingroup$ @user55119 Of course ammonium nitrate reacts in a similar way. But it is an explosive. It is hard to state that you see it burning $\endgroup$
    – Maurice
    Commented Jan 9, 2022 at 18:16
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    $\begingroup$ I remember doing this myself. Also, I don't think it is considered not dangerous by the modern standards. Then again, of all self-oxidizing reactions, this one is probably the likeliest to count as burning, for it does not look like anything remotely resembling an explosion. $\endgroup$
    – Ivan Neretin
    Commented Jan 9, 2022 at 19:26
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One of the best known examples is nitroglycerin, $\ce{C3H5N3O9}$, which has $18$ oxygen atoms in two molecules whereas only $17$ are required to oxidize all the carbon and hydrogen in those molecules. Not surprisingly:

In its undiluted form, nitroglycerin is a contact explosive, with physical shock causing it to explode. If it has not been adequately purified during manufacture it can degrade over time to even more unstable forms. This makes nitroglycerin highly dangerous to transport or use. In its undiluted form, it is one of the world's most powerful explosives, comparable to the more recently developed RDX and PETN.

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