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Author: Subject: Rocket Fuel from UV Photolysis of Alcohol/Aqueous Nitrate?
AJKOER
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[*] posted on 19-9-2017 at 09:54
Rocket Fuel from UV Photolysis of Alcohol/Aqueous Nitrate?


Well, may be not so much as rocket fuel as a fuel spiker for testing on the old lawn mower!

Lets consider the hypothetical UV photolysis of a methanol (or ethanol) and water solution containing nitrate. First, I could expect some radical formation, which is reported to occur in the UV (defined bands, see https://en.m.wikipedia.org/wiki/Ultraviolet) photolysis of aqueous nitrates:

NO3- (aq) + hv → •OH + •NO2

Source: "Mechanism of Nitrite Formation by Nitrate Photolysis in Aqueous Solutions:  The Role of Peroxynitrite, Nitrogen Dioxide, and Hydroxyl Radical", by Sara Goldstein and Joseph Rabani, published in Journal of the American Chemical Society, Vol. 129: , Issue. 34, 2007, Pages. 10597-10601. To quote from the first page :

"Photolysis of aqueous NO3- with λ ≥ 195 nm is known to induce the formation of NO2- and O2 as the only stable products. The mechanism of NO3- photolysis, however, is complex, and there is still uncertainty about the primary photoprocesses and subsequent reactions. This is, in part, due to photoisomerization of NO3- to ONOO- at λ < 280 nm, followed by the formation of •OH and •NO2 through the decomposition of ONOOH (pKa = 6.5−6.8)."

Link: http://pubs.acs.org/doi/abs/10.1021/ja073609+

Further reactions in say a water methanol solution containing nitrate under UV photolysis could include:

CH3OH + •OH → •CH3 + H2O

NO3- + •OH → •NO3 + -OH

•CH3 + •NO2 → CH3NO2. (Caution, per Wikipedia on Methyl nitrite, it is a toxic asphyxiating gas and a potent cyanotic agent with exposure possibly resulting in methemoglobinemia, see https://en.m.wikipedia.org/wiki/Methyl_nitrite )

•CH3 + •NO3 → CH3NO3 (Caution, per Wikipedia on Methyl nitrate, it is a toxic, volatile, and a sensitive HE, see https://en.m.wikipedia.org/wiki/Methyl_nitrate )

•OH + •NO2 → HONO2

•OH + •NO3 → HONO3
......

With the possible indicated formation, in small amounts (maybe a good thing here) of some interesting energetic/toxic compounds.

Miscellaneous comments: CH3OH + CH3NO3 has been used as a rocket fuel (Wikipedia reference above), pure methyl nitrate is listed as a high explosive (see demo at https://www.google.com/url?sa=t&source=web&rct=j&url=https:/...). Also, the photolysis of any produced nitrite is said to be superior to aqueous nitrate, which could increase the rate of product formation. I would not advise heating the product brew as CH3NO2 is a heat sensitive explosive which could likely detonate any formed CH3NO3. Final comment, if you dismiss the feasibility of my chemistry above, please note this comment on Wikipedia on incidental methyl nitrite creation:

"Methyl nitrite is also present in aged cigarette smoke. Here it is presumably formed from nitrous oxide (itself formed by autoxidation of nitric oxide) and methanol.[5]"

which I would alternately explain as the result of thermally induced methyl radical creation reacting in the presence of NxOy.

[Edited on 19-9-2017 by AJKOER]
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[*] posted on 19-9-2017 at 11:09


How high does the alkyl nitrate concentration need to be before the rate of photolysis is as high as the rate of production?
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AJKOER
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[*] posted on 19-9-2017 at 11:48


Quote: Originally posted by unionised  
How high does the alkyl nitrate concentration need to be before the rate of photolysis is as high as the rate of production?


I would not claim to be much of an authority in this area. However, my general comment is that the rate of photolysis is generally low, and per my recollection depending on the reactants, may be further even subject to a threahold limitation (meaning, after a concentration point, the reaction rate may be independent of further increases/decreases in reactant concentration).

As here the rate of product production is due to fast reactions with short lived radicals, I would not expect any of these radical reactions to constitute a rate limiting step.

Here is a reference, for example https://www.google.com/url?sa=t&source=web&rct=j&url=http://...

Another source comments:

"For NO2 and O3, photodissociation quantum yields do not drop immediately to zero below the dissociation threshold. This effect is explained by channeling the internal energy of molecules into the dissociation process."

Link: https://www.google.com/url?sa=t&source=web&rct=j&url=http://...


[Edited on 19-9-2017 by AJKOER]
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[*] posted on 19-9-2017 at 11:58


"However, my general comment is that the rate of photolysis is generally low".
That's the problem.
You only photolyse nitrate slowly, so you only make alkyl nitrate slowly.
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AJKOER
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[*] posted on 19-9-2017 at 12:29


Quote: Originally posted by unionised  
"However, my general comment is that the rate of photolysis is generally low".
That's the problem.
You only photolyse nitrate slowly, so you only make alkyl nitrate slowly.


True, I did mention 'small quantities'.

Perhaps a list of favorable/unfavorables would help. My comments would be:

) Process is slow but yield increases with time.

) Total expected products, assuming using something other than a weather balloon, would still be small.

) No demand for strong acids or expensive reagents.

) Unconventional equipment required for the photolysis (UV lamp).

) Limited need for standard lab equipment.

I think whether the unfavorables out weigh the favorables may depend on personal preferences and restrictions. I cannot operate a legal lab and reagents/glassware purchases raise red flags. I even get questioned buying over the counter stuff (like, what are you doing?, what do you need it for?, ...)
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[*] posted on 19-9-2017 at 12:53


" Process is slow but yield increases with time."
Only until you start to destroy it as fast as it's made.
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[*] posted on 19-9-2017 at 13:24


Too slow for any practical use... also at a certain point CH3-ONO2 and CH3-ONO or CH3-NO2 also enter the photolysis process and are destroyed...

To speed things up... and circumvent those problems...
CH3-Cl (or even better CH3-I) + AgNO3 or AgNO2 would be more suitable...
CH3-I is a good source of CH3° and I° while AgNO3 and AgNO2 are good sources of Ag° and NO3° or NO2°...
Excluded the photochemical reaction; the reaction also occure into solution...because of the driving force of precipitation...
AgNO3 + CH3-Cl --> AgCl(s) + CH3-ONO2
AgNO2 + CH3-I --> AgI(s) + CH3-NO2 (66%) + CH3-ONO (34%)

The speed of that reaction is nearly instantaneous with primary alkyl halides... it is a known reaction to determine qualitatively the order of an alcohol function
==> primary, secondary or tertiary...
This by passing via its halide and reaction with aqueous AgNO3 solution ... immediate precipitate/trouble is a sign of primary... delayed means secondary and none means tertiary...

Another fuel than CH3OH would be aceton (propanone)... propanone has a very good quantum yield...
It is a way to obtain CH4 and CO from propanon

[Edited on 19-9-2017 by PHILOU Zrealone]




PH Z (PHILOU Zrealone)

"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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