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Producing Hydrogen by partial oxidation

Anders Hoveland

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I am not sure I believe it!

Hydrogen gas can be liberated by partial oxidation of formaldehyde using either H2O2 or CuO under certain reaction conditions.


Formaldehyde, Action of Hydrogen Peroxide on. A Harden. Proc. Chem. Soc. 15, [212], 158-159


When solutions of hydrogen peroxide and formaldehyde are mixed, no reaction appears to take place, but when the liquid is made strongly alkaline with soda, hydrogen is evolved. The reaction occurs according to the equation

H2O2 + 2 CH2O + 2 NaOH = 2 HCO2Na + H2 + 2 H2O

Hydrogen peroxide, therefore, when treated with alkaline formaldehyde, gives a volume of hydrogen exactly equal to the volume of oxygen which it would give with potassium permanganate and sulphuric acid. The reaction proceeds slowly and incompletely unless a large excess of alkali be present. When hydrogen peroxide is treated with excess of formaldehyde, the reaction takes place rapidly and completely, and the hydrogen which is evolved is pure. When, on the other hand, formaldehyde is treated with excess of hydrogen peroxide, the reaction is incomplete and proceeds very slowly, whilst the gas evolved contains oxygen.


Cuprous oxide and soda give a somewhat similar reaction with formaldehyde. This reaction was described by Loew (Ber. 1887, 20, 145) as a catalytic reaction, but it appears in reality to be a quantitative one, expressed by the equation

Cu2O + 2 NaOH + 2 CH2O = Cu2 + H2 + 2 HCO2Na + H2O

Cupric oxide also gives a similar reaction, two atoms of hydrogen being liberated for each atom of oxygen in the oxide


When caustic soda and then formaldehyde are added to a solution of copper sulphate and the liquid gently warmed, the cupric hydroxide is reduced to cuprous oxide without evolution of hydrogen, and when the temperature is subsequently raised, the cuprous oxide reacts as described above. When, on the other hand, caustic soda is added to a boiling solution of copper sulphate, the liquid cooled, and formaldehyde then added, no reduction of cuprous oxide occurs on warming, but metallic copper is formed, and twice as much hydrogen is evolced as the previous case.

Manganese dioxide does not appear to be reduced by formaldehyde, whilst the oxides of mercury and bismuth are reduced without evolution of hydrogen.

Journal of the Society of Chemical Industry, Volume 18, p716-717. [July 31, 1839]


The fact that hydrogen and oxygen gas can be liberated together from the same solution simultaneously may also be of interest, for making gas explosions inside of closed plastic bottles.



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the formaldehyde reduces [cupric oxide] not only to cuprous oxide, but to metallic copper [in colloid form], but as this happens a second reaction ensues in which the metallic copper acts upon the formaldehyde and decomposes it with the liberation of hydrogen.


Potassium cyanide, when added [to the above reaction] will inhibit or stop further reduction and liberation of hydrogen.

[text describes potassium cyanide as an example of an 'enzymatic poison']

Science, Volume 45, American Association for the Advancement of Science, p507



Loew recorded the highly significant observation that the interaction of aqueous solutions of formaldehyde and sodium hydroxide yielded a very small amount of hydrogen, and that if cuprous oxide were added to the reaction mixture, it was reduced to metallic copper.


As expected, formaldehyde is directly oxidized [by H2O2] to formic acid, and the latter in turn to carbonic acid.


But hydrogen peroxide may, on the one hand, oxidize formaldehyde to formic acid with the liberation of hydrogen.

2HCHO + H2O2 --> 2HCOOH + H2


while on the other hand it will reduce carbonic acid to formic acid with the liberation of oxygen

H2CO3 + H2O2 --> HCOOH + H2O2 + O2


Since hydrogen peroxide may thus react either as an oxidizing agent or as a reducing agent, and in some instances in both capacities concurrently…

“The Action of Hydrogen Peroxide upon Simple Carbon Compounds

H. Shipley Fry and John H. Payne, Journal of the American Chemical Society (1931)


for more details about this reaction see Journal of the American Chemical Society, Volume 29, Issue 2, p1233,



which explains that the hydrogen is formed only as the formaldehyde is being oxidized to formic acid

2HCHO + H2O2 --> 2HCOOH + H2

but not when the formic acid is subsequently oxidized to carbon dioxide. And some of the formaldehyde is oxidized to formic acid without any matching formation of hydrogen. About twice as much carbon dioxide is evolved as hydrogen gas.


The reaction between formic acid and hydrogen peroxide must be more complicated. Simply mixing the two chemicals apparently results in "performic acid", HOOCH=O, in equilibrium. The oxidation of formic acid to carbon dioxide apparently requires alkaline conditions.


Other than the mention in the above source, I cannot find anything else about hydrogen peroxide being able to reduce carbonic acid to formic acid, and such a reaction is very doubtful. I assume that the author made a mistake. I also found mention in another source that "Reduction of carbon dioxide by hydrogen peroxide... in the production of oxygen and formic acid from carbonic acid and hydrogen peroxide", but this was in the context of hypothesized uptake of carbon dioxide by plants in the year 1919, before the complete modern understanding of photosynthesis, so I would be very hesitant to accept it as fact.

Chemical abstracts, Volume 13, Issue 2, American Chemical Society. p1483 subarticle by Carl L. Alsberg.




Other Reactions involving liberation of Hydrogen from Organic Compounds

Wurtz found that ethylene glycol fused with solid potassium hydroxide yielded mostly potassium oxalate and hydrogen gas. The yield of hydrogen was 58% of that required by the below proposed reaction

C2H6O2 + 2KOH --> K2C2O4 + 4H2


Rosorcinol (1,3-dihydroxy-benzene) is similarly converted to phloroglucinol (1,3,5-trihydroxy-bezene) by fusion with sodium hydroxide, with the evolution of hydrogen.


These are both unusual examples of disproportionation reactions, where a compound is simultaneously oxidized and reduced.




J. Am. Chem. Soc., 1924, 46 (10), pp 2268–2275



Reaction Mechanism

I have a theory about how the reaction might proceed.


I think the reaction mechanism might involve the formation of an

HO-O-O-CH=O intermediate, and cylization of this intermediate to an unstable square ring, which could then decompose into O2, CO2, and H2


The driving force for the typically unfavorable formation of H2 would be the simultaneous formation of O2 and CO2, which are highly favorable.


The transient square ring would contain 3 atoms of oxygen and 1 atom of carbon, with an additional fourth oxygen, with a negetive charge on it, bonded to the carbon. A single atom of hydrogen would also be bonded to the carbon. The hydrogen atom on this ring would encounter a positively charged hydrogen ion from outside, which would pull out the negetive charge on the oxygen atom through the molecule. I am mostly writing this paragraph in the event that the accompanying picture stops working at some time.


If this is in fact correct, it suggests that the formation of hydrogen may actually be due to the oxidation of formic acid to carbon dioxide, rather than the direct oxidation of formaldehyde to formic acid.


It is known, for example, that dihydrogen trioxide, H2O3, has a transient existence in alkaline solution of hydrogen peroxide, and this could potentially be the reason that alkaline H2O2 acts as a stronger oxidizing agent.

H2O2 <==> HOO[-] + H[+]

H2O2 + HOO[-] <==> H2O3 + OH[-]


I really do not know if this is the correct reaction mechanism, or whether there is some other more predominant mechanism, but for now it seems like the best explanation for the liberation of hydrogen gas.



For pictures of the proposed reaction mechanism, you can see:


(third post down)




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Must you really cross-post everything you post on sciencemadness here as well? Half of what you say is completely unsupported drivel, though you have gotten somewhat better following your ban on scimad.

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