Energetic precipitate from the reaction of ascorbic acid/Cu(II) and sodium nitrite

First of all, I feel kind of stupid to return to SMDB, being 100% sure now that this board is monitored by law enforment. I quit making energetic materials and do not own any chemical compounds nor information anymore that are illegal to possess. There is however no law against posting a 100% legal reaction on this board, so I hope this will not spawn further intimidations.

For an experiment I needed some nitric oxide gas, so I made a nitric oxide generator from the reaction of a large excess of ascorbic acid with sodium nitrite. When the nitric oxide production was measured however, yields were lower than theoretical, so I decided to try and add some copper sulfate as a catalyst.

Experimental:

3 g of ascorbic acid was added to a 250 ml erlenmeyer together with 250 ml of distilled water and cooled to about 10 deg C. When the ascorbic has dissolved, 0.5 g of copper sulfate pentahydrate was added, forming a light green solution. In very small amounts at the time, 0.5 g of sodium nitrite was added over the course of about 30 minutes. The flask being lightly stoppered directly after the nitrite additions. During the additions some nitric oxide (NO) was formed that escaped the solution (Do this outside or in a good fumehood!!!). During the additions the reaction mixture went from light green to a distinct yellow colour. After nearly all of the sodium nitrite was added, quite suddenly large amounts of a chocolate-brown amorphous precipitate started to form. This was allowed to settle for 30 minutes, decanted, filtered off into a pre-weighed filterpaper, washed with water and finally 98% ethanol. The filter paper was allowed to dry fully and weighed, yielding 0.16-017 g of a dark brown compound. The filtrate was strongly basified using sodium carbonate, which precipitated no additional copper, suggesting all was sequestered in the reaction.

The dry precipitate is very energetic and detonates in sub-mg amounts when heated on a spatula. It seems to gradually lose its energetic properties when exposed to the air for several days, (more quickly so when wet) and transforms to a pitch black compound. A few mg of the dark brown precipitate was added to a beaker and some dilute HCl was added. At first a white precipitate is formed, that dissolves again when more HCl is added, suggesting the compound is some cuprous salt. A very acrid metallic smell was formed upon acidification, reminiscent of hydrazoic. Since all of the copper was removed from the reation mixture, it seems to follow that the molecular weight of whatever is attached to the copper(I) is around 15-20 g/mol.

My best guess would be something like a double salt of cuprous oxide with cuprous fulminate (Cu(I)2O * CuCNO). If this is true this might be the first reported direct synthesis of a copper fulminate. Not sure this is a fulminate though, any other ideas anyone about the product formed and reaction mechanisms?

This reaction seems very interesting, it seems amazing to me that oxidation and reduction reactions can seemingly coexist simultanously under these conditions, maybe the strong copper(I) ligand interactions are helping here. So many new reactions spring to mind here, maybe also relevant to diazenium diolate chemistry as well...

[edit] A further note if this does produce a fulminate: Fulminates and fulminic acid are INCREDIBLY toxic, about equal to cyanides. On acidification of this precipitate or even during the reaction itself, fulminic acid or hydrocyanic acid could be released in quite large amounts. Do not scale this up without adequate safety measures!!!!

[Edited on 13-11-2019 by nitro-genes]

Quote: Originally posted by nitro-genes

Since all of the copper was removed from the reaction mixture, it seems to follow that the molecular weight of whatever is attached to the copper(I) is around 15-20 g/mol. My best guess would be something like a double salt of cuprous oxide with cuprous fulminate (Cu(I)2O * CuCNO). If this is true this might be the first reported direct synthesis of a copper fulminate. Not sure this is a fulminate though, any other ideas anyone about the product formed and reaction mechanisms?

The affinity for copper(I) towards the formed NO as a ligand is probably helping here indeed. Even when quite a lot of nitrite is added at once, the formed NO that escapes the solution is very quickly absorbed back into the reaction mixture. Since the energetic precipitate formed is quickly destroyed under even mildly acidic condictions, I tried doing the reaction reverse, so slowly adding ascorbic acid to a Cu(II)-sodium nitrite solution, though this does not produce any of the brown precipitate at all, suggesting that a high concentration of Cu(I) is needed for the reaction itself. This would probably also mean that any other possible reducing agent instead of ascorbic would have to be capable of reducing copper(II) in solution, yet not to copper metal and also not directly react with nitrite istelf, (like sulfites for example). Ascorbic may be pretty unique in this regard. Since the precipitation of the compound may be pH determined (it precipitates at a pH around neutral), it might also be informative to find the minimal amount of ascorbic/nitrite combination to establish how many moles of nitrite relative to the copper are needed.

After some reading... this thread may not even belong to organic chemistry at all! Apparently, the presence of copper(I) in some instances may lead to dimerization and further reduction of the NO dimer produced, forming a hyponitrite (also see. J. Am. Chem. Soc. 2017, 139, 38, 13276-13279 and Journal of the Chemical Society (1928): 1449-1455.) Ascorbic is a very strong reducing agent, so this would definitely be possible. Supposedly, even boiling nitrate salts with ascorbic acid alone is able to produce nitrites almost quantitatively.

Hyponitrite istelf apparently is a very strong ligand towards copper (I) and forms a chocolate coloured and water-insoluble precipitate with a copper(I) salt, even in the presence of a large excess of chloride ("Some reactions of hyponitrites and the related substances - part II, J.Indian Chem.Soc" see atachment). On decomposition it may form nitrogen gas and copper(II)oxide --> Cu2N2O2 --> 2 CuO + N2 + a lot of energy (a nanothermite of cuprous hyponitrite with aluminium or magnesium powder ought the be interesting! ) . The latter reference also studied the thermal decomposition of cuprous hyponitrite and strangely though, they never mention strongly energetic properties for their compound, so maybe the precipitate obtained from ascorbic/Cu/nitrite is something entirely different after all...hmmm

As metacelsus says, analyzing the copper content of the brown precipitate would probably be more informative, though I don't see an easy way of doing so, except heating it for a long time far under it's explosion temperature (around 210 deg C) and finally higher temperatures, which may leave relatively pure copper(II)oxide...The precipitate also dissolves easily in dilute ammonia, so this may also be an option for some tests.





[Edited on 18-11-2019 by nitro-genes]

Attachment: Some reactions of hyponitrites and the related substances.pdf (1.8MB)
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The chemistry of NOx is pretty complicated with all the different dimers and disproportionations possible...OH-NO-NO chemistry seems fitting

Yes, the formation of nitric oxide from ascorbic and nitrite was published in some paper on diazenium diolate chemistry IIRC, I'll see if I can find it again. Ag+ does produce a yellow precipitate with hyponitrites, though in the presence of ascorbic it is instantly reduced to metallic silver.

The mercury in the sodium amalgam preparation of the stable cis-form of sodium hyponitrite might be a necessary component of the reaction and not only to moderate the reactivity of the sodium metal. An interesting question is also what the role of ascorbic is in the formation of the cuprous hyponitrite indeed. The initial reaction of nitrous/nitrite with ascorbic acid has been described in several articles and is thought to occur via mono and di O-nitroso intermediates (1: Wasserman et al, 1981), figure attachment). The authors from the latter paper also postulate direct formation of hyponitrous via 2,3-dinitrosoascorbic ***, which could be competing with nitric oxide formation itself. Maybe a cuprous complex of intermediate III or VIII is what is mainy responsible for the preferential formation of hyponitrite in the presence of copper? Though, could this also explain the observed very quick absorption of NO gas and the lack of any cuprous hyponitrite formation with competing ligand present? Would NO directly react with nano copper metal to produce cuprous hyponitrite? Would leading NO gas into a copper sulfate/ascorbic mixture also produce cuprous hyponitrite? Maybe the ascorbic is just a sufficiently weak copper ligand that it allows direct reduction of nitric oxide itself via a Cu(I) NO complex?



1. Fox Jr, Jay B., Rosemary N. Fiddler, and Aaron E. Wasserman. "Initial reaction intermediates in the oxidation of ascorbic acid by nitrous acid." Journal of food protection 44.1 (1981): 28-32.

*** Formation of an internal vicinal nitroso dimer from nitrosoacorbic acid would account for the absence of an ascorbyl radical during the reaction. We propose that the electron transfer reaction begins with the further nitrosation of the nitrosoascorbic acid intermediate to form the 2.3 dinitrosoascorbic acid, II ....... III. A two electron transfer then takes place to yield dehydroascorbic acid, IV, and N202. The electron transfer would be facilitated by formation of the dimer, a stable form of NO (26)."

[Edited on 2-12-2019 by nitro-genes]

Any references for the hydroxamic oximes? Seems like interesting reading material.

The O-nitroso ascorbic derivatives are probably like very unstable alkylnitrites indeed, the attached NO+ being very quickly reduced to NO (g), leaving dehydroascorbic. In contrary to my first post... with the large excess of ascorbic present and absence of oxygen (air lock) I don't see large amounts of these pseudonitrosites being produced anyway (also see: Williams, Daniel Lyn Howell. Nitrosation reactions and the chemistry of nitric oxide. Elsevier, 2004, .p112-p114) Going from ascorbic or the hydrolysis products it seems only oxidation to carboxylic acid and finally CO2 seems likely. The best argument against this would also be the observation that the pea-green salt formed after air oxidation of the presumed cuprous hyponitrite itself is not energetic at all and also matches descriptions of the Cu(II)(OH2)(N2O2) in literature.

Would be interesting to test whether leading NO (g) into some nano-copper metal + maybe a little NaCl would produce cuprous hyponitrite. Or maybe simply leading NO (g) into an aqueous solution of Cu(II) sulfate + 0.5 mole eqvt ascorbic would produce cuprous hyponitrite. If so, using these amounts of ascorbic acid, such a synthesis might be competitive with other synthesis routes for sodium hyponitrite, since IIRC having read that cuprous hyponitrite + 2 mole eqvt NaOH produces a precipitate of cuprous hydroxide and a solution of reasonably pure sodium hyponitrite. Even the synthesis routes going from the sodium mercury amalgam give like 18% yield IIRC. While most direct routes only produce the unstable cis-forms of sodium hyponitrite.

Seen the volume of gas produced upon introducing the nitrite during the reaction, I'd really guess the production of the presumed hyponitrite is originating from the NO (g) btw and not from some O-(di)nitrosoascorbic. This would need some further testing though...

[Edited on 5-12-2019 by nitro-genes]

Quote: Originally posted by nitro-genes

......... After some reading... this thread may not even belong to organic chemistry at all! Apparently, the presence of copper(I) in some instances may lead to dimerization and further reduction of the NO dimer produced, forming a hyponitrite (also see. J. Am. Chem. Soc. 2017, 139, 38, 13276-13279 and Journal of the Chemical Society (1928): 1449-1455.)

An alternate view would be there is only reductions going on, another likely reason this is some cuprous hyponitrite or complex thereof, since it is the simplest explanation. I've made a lot of suggestions about the mechanisms (out of interest) in this thread, though it is really surprising to see how seemingly simple reactions can be quite complicated mechanistically, or at least to really prove anything in this regard using experiments.

The more than 2 molar excess of ascorbic could maybe point towards a cuprous complex of compound VIII as the most likely precursor, or maybe the lower pH is a requisite for formation of the nitroso ascorbic intermediates in general or, or maybe there just needs to be a large excess of reductant present for other reasons. Then there is the observed absorption of NO (g) which still puzzles me somewhat...more questions than answers as usual...

[Edited on 10-12-2019 by nitro-genes]

Tested on a small scale if the presumed cuprous hyponitrite would react with excess NaOH to produce cuprous oxide and leave a very basic solution of sodium hyponitrite. About 0.2 g of cuprous hyponitrite was added to a 25 ml erlenmeyer together with 25 ml dH2O and 0.3 g NaOH was added. The flask was stoppered airtight and stirred for 3 hours at 15 C. The colour of the precipitate gradually changed to a bright orange. This was allowed to settle overnight at 4 C, and the clear supernatant pipetted off into a 50 ml erlenmeyer.

Silver hyponitrite was then prepared according to: "Partington, James R., and Chandulal C. Shah. "384. Hyponitrites. Part II: metallic salts. Part III: esters." Journal of the Chemical Society (Resumed) (1932): 2589-2597".

With strong stirring 0.25 g silver nitrate in 4 ml dH2O was added dropwise to the supernatant. A transient brownish coloured precipitate forms, that changes very quickly back to a yellow. The bright orange precipitate is not energetic and seems likely entirely composed of curpous oxide.

Seems that the hyponitrite content of the cuprous hyponitrite can perhaps be titrated using the silver salt (planning this on larger scale), since I wonder if the initial complex formed from ascorbic/Cu(II)SO4/sodium nitrite might not be something like Cu2N2O2 * H2N2O2.

In some patents on the synthesis of the organic esters of hyponitrites (or diazenium oxides due to ambident nucleophilicity) the use of silver hyponitrite in combination with alkylhalides seems preferable. Would cuprous hyponitrite similarly be able to react with alkyl halides directly? Alkyl halide + cuprous hyponitrite --> alkyl hyponitrite + cuprous halide. The latter would be insoluble and easily filtered off if this would work, though the copper might also form more complex products as opposed to silver salts? Any ideas?

[Edited on 20-12-2019 by nitro-genes]