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Author: Subject: About some details of the Birkeland-Eyde nitric acid synthesis
Arcaeca
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[*] posted on 5-4-2020 at 01:17
About some details of the Birkeland-Eyde nitric acid synthesis


So I've been thinking about making indigo via the old Baeyer-Dewerson synthesis that involves an aldol condensation of ortho-nitrobenzaldehyde and acetone; the reason this method appeals to me is it seems the reactants are relatively easy to get your hands on - if I understand, you could just grab some toluene from the hardware store, perform a mononitration, oxidize the methyl group up to an aldehyde (apparently MnO2 is the oxidant to use?), and presto, there's your ortho-nitrobenzaldehyde. Of course, hardware stores don't sell nitric acid, so I was expecting to have to grab that from a chemical supplier, until I saw an old CodysLab video where he made nitric acid from NO produced by an electrical arc between two copper pipes. Since I'm all for not having to buy chemicals from special suppliers, this interests me. I think what he was doing is the Birkeland-Eyde synthesis, or some variation of it.

There are a couple details I'd like to clear up before trying it... many of them related to the fact that I have a very limited understanding of how electricity works.


  • Although the copper tube must necessarily be cut in two (unless you can somehow make an arc inside the tubing, which I assume is more trouble than it's worth), I guess you'd want to minimize nitrogen oxide loss by putting the two openings of the tube as close together as possible and aligned as closely as possible? (bonus points for smaller gap = smaller voltage required to arc) Or does it not really matter if the reaction chamber is well sealed?
  • I assume the NO-producing reaction is more or less instantaneous? That is, all other things being equal, you can produce NO as quickly as you can pump air in?
  • Does the current affect the yield?
  • I assume you want to use the lowest possible voltage that will arc, or is an even higher voltage needed to oxidize nitrogen?
  • I assume the copper tubing should be a relatively small diameter?
  • Does AC vs DC matter at all? (I think he used a neon light transformer but I don't actually know what kind of current discharge tubes require)
  • What's the maximum concentration of nitric acid you can get from this, unconstrained by time? In other words, what is the limit of nitric acid concentration as t → ∞? (As I understand it's quite inefficient and often followed up with fractional distillation)
  • Since hose that will bubble the NO2 into the water can't be metal (lest it be dissolved by the nitric acid produced), what's the most acid-resistant tubing material I can easily get my hands on - is polyethylene fine? And what's the typical way to link it to the copper tube for minimal loss?
  • Anything else I'm overlooking


[Edited on 4-5-2020 by Arcaeca]
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[*] posted on 5-4-2020 at 02:33


In this proces, you need very high current to mentain the arc. Now, if you want to produce a usable yield , Cody's method won't do.
The easiest way would be a small jacob's ladder. Blow air from below, and you get your NO.
You have to understand: this process relies on the temperature of the arc. You won't do with a puny arc. You need hot arcs that can melt a copper wire in minutes.
So, use an AC flyback(if you can get one) and ZVS driver ,or a strong NST. Or, if you really like trouble, ballast an MOT very well, and use that.
You can get up to 1% NO as output.
I've seen a youtube video featuring that.
Link

I think it's too much trouble. Just buy the nitric.




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Metacelsus
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[*] posted on 5-4-2020 at 05:28


You can't buy nitric acid at a hardware store, but you can buy sulfuric acid. Add a nitrate salt (sometimes also found in hardware stores, or easily bought online) and distill, and there's your nitric acid.



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[*] posted on 5-4-2020 at 10:27


Oxidation of o nitro toluene to aldehyde is very hard.
I have tried it either with MnO2 and Manganese V suflate, none of them had actually worked.

I didn't manage to get the product. I did quite big research (in the internet of course as I don't have any better source) and all of syntheses were quite theoretical.
I abandoned the project after I realised that there's no point in doing this synthesis as I won't do it in normal amateur lab.

Then I was preparing to syntesise indigo by condensation of anthranillic acid with chloroacetic acid but I got bored of it and finally didn't do it.
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[*] posted on 5-4-2020 at 11:41


Quote: Originally posted by Arcaeca  
I have a very limited understanding of how electricity works


Then start by addressing that. You won't be able to produce usable quantities without a fairly decent understanding of the entire process. Wikipedia tends to be a good place to start:
https://en.wikipedia.org/wiki/Birkeland%E2%80%93Eyde_process




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clearly_not_atara
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[*] posted on 5-4-2020 at 13:02


The preparation of ortho-nitrobenzaldehyde is given on Orgsyn:
http://www.orgsyn.org/demo.aspx?prep=CV3P0641

Orgsyn uses CrO3/Ac2O, but I think that chromyl chloride could also work, since its reactivity is very similar. CrO2Cl2 is easier to prepare but it is a highly toxic volatile liquid. See:
https://en.wikipedia.org/wiki/%C3%89tard_reaction

Alternatively, as Orgsyn mentions, o-nitrotoluene may be deprotonated with NaOEt (or similar) and nitrosated with EtONO (or similar) to o-nitrobenzaldoxime, which can then be hydrolysed. This reaction is specific to nitrotoluenes.

Quote:
What's the maximum concentration of nitric acid you can get from this, unconstrained by time?

The Birkeland-Eyde process is not limited by the final concentration of nitric acid but it is limited in the concentration of nitrogen oxides in the product gas, which is thermodynamically limited to about 4% but practically lower. Most of the energy used to split N2 bonds is lost when nitrogen atoms recombine to dinitrogen, which is why the process is no longer used commercially.

However, the reaction is technically difficult, and I have trouble believing it wouldn't be easier to obtain nitric acid by literally any other method.




[Edited on 04-20-1969 by clearly_not_atara]
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Arcaeca
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[*] posted on 5-4-2020 at 13:15


Quote: Originally posted by anti  
In this proces, you need very high current to mentain the arc.

How high are we talking? As I understand it, most neon sign transformers' output is capped at 30 mA, and even high-end ones are usually capped at 60 mA, which is the output of... what, a handful of 9V batteries? (Except over 1,000x as many volts)

Quote: Originally posted by Metacelsus  
You can't buy nitric acid at a hardware store, but you can buy sulfuric acid. Add a nitrate salt (sometimes also found in hardware stores, or easily bought online) and distill, and there's your nitric acid.

Y'know, I'd never actually noticed, but I just checked and apparently both Ace and Home Depot carry pure potassium nitrate marketed as stump remover. And having worked at Ace in the past I know they carry sulfuric acid marketed as battery acid refill for backup batteries. So that's something useful to tuck away in the back of my mind in case the electrolytic method doesn't work, but still, Birkeland-Eyde still sounds more fun if I can make it work.

Quote: Originally posted by mackolol  
Oxidation of o nitro toluene to aldehyde is very hard.
I have tried it either with MnO2 and Manganese V suflate, none of them had actually worked.

I didn't manage to get the product. I did quite big research (in the internet of course as I don't have any better source) and all of syntheses were quite theoretical.
I abandoned the project after I realised that there's no point in doing this synthesis as I won't do it in normal amateur lab.

What do you mean it didn't work? How so? Just that the MnO2 won't dissolve in nitrotoluene, or it does but the mixture doesn't pass an aldehyde test (e.g. Tollens' test), or that it didn't turn blue after the condensation with acetone, or what?
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[*] posted on 6-4-2020 at 02:23


Quote: Originally posted by clearly_not_atara  
The preparation of ortho-nitrobenzaldehyde is given on Orgsyn:
http://www.orgsyn.org/demo.aspx?prep=CV3P0641

Orgsyn uses CrO3/Ac2O, but I think that chromyl chloride could also work, since its reactivity is very similar. CrO2Cl2 is easier to prepare but it is a highly toxic volatile liquid. See:
https://en.wikipedia.org/wiki/%C3%89tard_reaction

Alternatively, as Orgsyn mentions, o-nitrotoluene may be deprotonated with NaOEt (or similar) and nitrosated with EtONO (or similar) to o-nitrobenzaldoxime, which can then be hydrolysed. This reaction is specific to nitrotoluenes.


Oh yes I forgot about this synthesis, it seems quite expensive as it uses quite big quiantities of acetic anhydride and GAA and yield is pretty low.

Quote: Originally posted by Arcaeca  

What do you mean it didn't work? How so? Just that the MnO2 won't dissolve in nitrotoluene, or it does but the mixture doesn't pass an aldehyde test (e.g. Tollens' test), or that it didn't turn blue after the condensation with acetone, or what?


I just didn't manage to get any solid product. Maybe because I wanted to separate the aldehyde by forming bisulfite adduct, which now I know is not very efficient. But after all it didn't seem like the reaction is going.

Procedure of oxidation with MnO2 works well for unsubstituted toluene but rather doesn't work for nitro. I have tried as well with Mn V sulfate, but this didn't work either.
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[*] posted on 6-4-2020 at 13:25


Quote:
I have a very limited understanding of how electricity works.


Note that this is likely to involves seriously dangerous high voltages.
Things like microwave oven transformers or neon transformers are extremely dangerous unless you know exactly what you are doing. There is zero room for error.
There are many youtube videos were people seem to casually play with the sparks these make, but it is deceptively dangerous.

So, it can be done, and it can be done safely, and it is a very interesting project, but considering that you mention your limited understanding of electricity, I'd say It'd be better to find another route to nitric acid for now.




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[*] posted on 6-4-2020 at 14:51


If y'all want to amuse yourselves, check out some of the links in my signature. There are some links to high voltage processes there. I focused on making the design somewhat safe, so a high energy, low voltage arc was triggered by a low energy, high voltage initiator. The initiator would trigger the arc at some fixed rate (10-30Hz), and a neodynium magnet would blow out the arc almost as fast as it initiated. Average power was only about 5-7W, even though the instantaneous power in the arc was fairly high.



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[*] posted on 7-4-2020 at 06:12


The Jaccobsladder System works well too (System Pauling). Much more than Birkeland. The Chines sell cheap Ozon Generators with power suplies from 3000 to 6000 V with 100W.
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[*] posted on 8-4-2020 at 00:22


By the way, I was just thinking, the traditional reagent combo for the oxidation step in the Baeyer-Dewerson indigo synthesis is MnO2/H2SO4, but H2SO4 is pretty much always in aqueous solution, and don't aldehydes become hydrates in the presence of water, which is an intermediate in the oxidation of aldehydes to carboxylic acids? It seems like that would drastically reduce yields, so are you supposed to do it in the presence of a desiccant or something?

Also maybe when I'm actually in a position to make a Birkeland-Eyde generator I can grab someone from the EE department at my school and see if I can't get them to look over the plans, since I assume they know how to not electrocute themselves.

[Edited on 4-8-2020 by Arcaeca]
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[*] posted on 8-4-2020 at 13:17


Quote: Originally posted by Arcaeca  
Quote: Originally posted by anti  
In this proces, you need very high current to mentain the arc.

How high are we talking? As I understand it, most neon sign transformers' output is capped at 30 mA, and even high-end ones are usually capped at 60 mA, which is the output of... what, a handful of 9V batteries? (Except over 1,000x


Anti is wrong, you do not need a very high current to maintain the arc. You may use a high current to maintain the arc, or you may use a high voltage. What you must maintain is ionization. Voltage provides this directly, while a high current will provide it indirectly via heat. In this case heat is what you want, so high current may be the way to go.

Anyway, you can't really look only at voltage or current here. As long as you maintain an arc, it's all about power. I think for amateur/hobby amounts of HNO3, you'll want to have at least 200 watts, preferably 500 w. 200 watts is roughly 30 mA at 6000 V.

You might be able to get away with avoiding high voltages altogether. Just get a supply that can deliver at least 50 ish volts and 10 A, and hook up a biiiig inductor in series with your electrodes. Like, 500 mH big. Touch the electrodes together briefly to get the current flowing, and then pull them apart. The inductor will want to keep the current going and supply the voltage spike necessary to stabilize the arc.

[Edited on 8-4-2020 by Junk_Enginerd]
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[*] posted on 8-4-2020 at 16:01


Quote: Originally posted by Junk_Enginerd  
Anyway, you can't really look only at voltage or current here. As long as you maintain an arc, it's all about power. I think for amateur/hobby amounts of HNO3, you'll want to have at least 200 watts, preferably 500 w. 200 watts is roughly 30 mA at 6000 V.

Well, 180 W. I think the max voltage from most NSTs is 15 kV, which at 30 mA is still only 450 W. Although drawing a 450 W 24/7 is, what, 10.8 kWh per day? Over a third of a typical household's daily usage?

Quote:
You might be able to get away with avoiding high voltages altogether. Just get a supply that can deliver at least 50 ish volts and 10 A, and hook up a biiiig inductor in series with your electrodes. Like, 500 mH big. Touch the electrodes together briefly to get the current flowing, and then pull them apart. The inductor will want to keep the current going and supply the voltage spike necessary to stabilize the arc

If I'm anticpating having to unplug and move the setup around a lot, can it be made toggleable so I don't have to disassemble the reaction chamber to get to the electrodes and manually restart the arc every time?
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[*] posted on 9-4-2020 at 02:23


The old type iron cored NSTs (not electronic) are ballasted meaning they have an inductance in series with output to limit the output current. The current rating usually refers to the short circuit current and the voltage rating the open circuit voltage. Hence he output power is not simply the product of the two.

Assuming a simple resistive load, which sparks or arcs are not, from the maximum power transfer theorem the maximum output power would be half of the product of the open circuit voltage and short circuit current.

So a 15kV 30mA NST has a maximum output power of 225W with a resistive load of 500,000 ohms. Most sparks or arcs behavior more like a short circuit than 500,000 ohm resistor so the power will be much less.



[Edited on 4/9/2020 by wg48temp9]




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