Author Topic: Repeated failure of nitromethane reduction (Read 443 times)

Douchermann · « **on:** June 21, 2009, 05:59:09 PM »

Hey guys, For the past couple weeks I've been attempting a reduction of nitromethane, using aluminum/Hg. I think I've done it around 9 times now. For a brief introduction, abacus (or something similar) developed a method on the hive, which reduces nitromethane into methylamine. The reaction is performed with a large amount of methanol as a solvent, so the methylamine gas stays solvated in the methanol, even post distilation. This results in a 6% solution of methylamine. While yes, this is a large amount of solvent, it's the trade-off for being able to produce methylamine easily, quickly, and cleanly.

The closest thing I've had to success was a runaway at the start, but I then terminated the reaction. The problem is, the reaction will go, but it will progress slowly, and eventually stop maybe 1/4 the way through. I usually end up with a 1-2% methylamine solution upon distillation. My nitromethane source is R/C fuel. I've tried to distill the nitromethane from it, and use the RC fuel directly, and neither have pleased me. The RC car fuel is getting expensive if it keeps failing. I've spend $80 on it so far.

Anyone have any idea what the problem is? I wish I had pure nitromethane and pure methanol so I could rule those out. However, I will say that the methanol I'm using now, has worked in the past for more than one reductive amination. The aluminum I'm using is uncoated aluminum flashing from home depot. I've tried this with foil, and the flask fills up with aluminum hydroxide sludge.

Full scale is as follows:
1500ml methanol
0.5g HgCl2
183g Nitromethane
54ml water
162g aluminum peices

Test 1: 1/3 scale, pure nitromethane - runaway, reaction terminated
Test 2: 1/3 scale, RC fuel - reaction slowed and stopped resulting in 1% methylamine solution
Test 3: 1/3 scale, RC fuel - " " 2% methylamine solution
Test 4: 1/3 scale, RC fuel no water added - " "
Test 5: 1/3 scale, Aluminum foil used, RC fuel - " "
Test 6: 1/3 scale, Different brand RC fuel - " "
Test 7: 1/3 scale, Pure nitromethane, aluminum cleaned with NaOH soln. beforehand - " "
Test 8: 2/3 scale, pure nitromethane - " "
Test 9: Full scale, New brand RC fuel - " "

I can't figure out what is causing the reduction to stop. If I apply heat, it only continues so much farther, and then just seems to stop. Even after 24 hours of refluxing, there is still plenty of aluminum flashing left in the flask. They are uncoated - I'm positive. I've read through that post at the hive, and plenty of people have had success. That's why this is so frustrating. Anyone have any ideas?

Sedit · « **Reply #1 on:** June 21, 2009, 06:23:05 PM »

I just performed the same reaction albeit with different intent. The solvent I used was a matter of convience, denatured EtOH.

The smell of methylamine was over powering and the only real difference I see is your addition of H2O and solvent.
Why are you adding H2O to the mixture?

Instead of diluting it so much perhaps attach a tube into an HCl wash bottle to generate MeNH2*HCl would allow it to perform better in more concentrated conditions.

Basicly the MeNH2 that I made(more then likely all I made

) was done by setting the Al+EtOH on the stirrer in an ice bath and adding HgCl2. Let it stir while and go smoke some weed. 5-10 minutes tops. Come back and the Al will have a slight dark grey tint to it. Stoped stirring and the little fine bubbles can be seen. Added Distilled nitro methane and the faster it was added the faster it reacted. Went very smooth so the only thing I can think is your reaction is way to dilute or the H2O is interfering with the reaction.

Enkidu · « **Reply #2 on:** June 21, 2009, 07:12:21 PM »

Why don't you just use Fe/HCl?

Douchermann · « **Reply #3 on:** June 21, 2009, 09:13:35 PM »

Well, I just did another test, no water added, but this time 1/10 the scale. I also cut the aluminum up even further into ~1cm squares. This one didn't stop boiling even after all the fuel was added, so it's looking better than the other reactions so far

. It did slow down, so I threw it on an oil bath, where it will sit till I get off work tonight.

Sedit: I can imagine the reaction you are performing, and I believe this one runs differently. The Al sludge that is produced is much more voluminous than what you are attempting. That's the reason for the exorbitant amount of solvent. If less solvent is used, the reaction pretty much stops as there is no way for the fluid to effectively distribute.

Enkidu: Can the clemmenson really reduce nitromethane? If it can, then... fuck, what am I wasting my time with this for bahahahaha.

Sedit · « **Reply #4 on:** June 21, 2009, 11:18:35 PM »

The reduction of nitro compounds using Fe/HCl or quite a few other Dissolving Metal Reductions is well documented. I do not believe this to be a clemmensen reduction which uses an amalgum of zinc . This is more then likely not needed because it will reduce nitromethane without the amalgum. When you are finished with the reduction by using dissolving metals you would be left with a solution of MeNH2*HCl I believe.

@Douchermann
"I believe this one runs differently"

The only difference is that right after the nitromethane is reduced it forms the imine with a cabonyl compound which is then also reduced all in one pot to the secondary amine or the starting carbonyl compound. In your case it is just reduced to Methylamine gas and either absorbed into the system or expelled as a gas. Since it is a gas you could with ease just apply slight heat to the mixture when your done and feed it either into HCl for the chloride salt or into ice cold (anhy)MeOH after drying the gas to form anydrous Methylamine solution.

v16 · « **Reply #5 on:** June 22, 2009, 04:24:59 AM »

the reaction should run the same, its just in a nitromethane based Al reduction of MDP2P (or any P2P for that matter). The amalgam is doing "double duty", so it tends to break down faster and to a more particulate residue. Of course there are alot of variables in these reactions, and is one ofthe reasons people have trouble with them.

Foil size and type is something that has been discussed alot...In the foil one you ran, did you ball it up or level in as flat pieces. It makes a big difference. The thicker flashing foil makes the reaction much slower, which is sometimes what you want. It all comes down to surface area, as the reaction can only occur at the surface of the foil. Most procedures you read about try to maximize surface area. But, some times you want a nice slow, but long release. Other times you want it to go fast and short.

The problem is if you don't have enough surface area to sustain the reaction, it will peter out...this sounds like what is happening to you. If you don't get what you want this time, try grinding up the foil into balls, or cutting the pieces much smaller.

poisoninthestain · « **Reply #6 on:** June 22, 2009, 05:48:08 AM »

@Douchermann, I agree with V16.

Run aluminum foil through a paper shredder for incredible surface area. Never had a single amalgam fail in my personal experience with either acid or basic reductions.

A friend of mine over at PN had the same problem with in situ methylamine same as you and it was corrected after shredded the foil to a more suitable surface area(i recommended him the paper shredder method

).

Vesp · « **Reply #7 on:** June 22, 2009, 05:58:30 AM »

A blender is always another method.

Douchermann · « **Reply #8 on:** June 22, 2009, 10:23:46 PM »

@V16, thats what I was talking about as far as the reaction running differently. There is much more material given off as far as the reaction is concerned. However, I've never run the reaction to produce MeNH2 in situ - I'm trying to avoid that, so I'm producing the MeNH2 before hand.

I've already stated that I've tried foil before, and it swelled up so much it absorbed all of the solvent I was using, and filled the entire flask. I might try foil again, but ball it up in the blender, as the smaller pieces of aluminum showed a much better reaction (thus better surface area helping the reaction greatly). I'm thinking perhaps my aluminum flashing is much thicker than that of which abacus used and posted about on the hive.

Sedit · « **Reply #9 on:** June 22, 2009, 10:35:52 PM »

I agree and even with a blender the foil swells to engulf the entire solvent mass. Still you should give the dissolving metals a chance because when all is said and done with those you will not have any Hg to contend with.

v16 · « **Reply #10 on:** June 22, 2009, 11:44:23 PM »

Hey D, in situ methyalmine formation is really no problem. Yields around 70-75% are obtainable with really good technique. 60-65% are more likely. But if you can't get methylamine through formaldahyde or hexamine, trying to get it through a Al reduction is really kind of like doubling your effort.

I posted a something at psyconaught a while ago on all the variables and the order of their importance. If this is review, or redundant, just ignore it. The sort story is

1) stiring: it has to be great, not good, great. If your set up is not good enough to keep the "milk shake" going get a better system. You have to have good mixing to get the higher yields.

2) rate of addition: I was a big proponent of slow and steady addition, but after a long talk with spice, and some careful experimenting, I am now of the mind faster is better. Downside is if your condenser is not big, or if you water source is not cold, or you can run a ice/or dry ice system through it you may get an eruption doing it this way.

3) adding a little water...I know everyone says you don't needed it, but it helps. 1-2% is the sweet spot, but this is workign from memory. OTC methanol usually is about 1%.

4) double distilling your ketone. purity here really helps get those higher yields. Plus makes purification of the product so much easier.

The procedures using methalyamine are easier to run, more forgiving, and give nicer yields...but you need to have methylamine around the lab....in excess. If you don't mind that then go for it.

I also think scale up of the nitromethane based ones are easier....

WE had a good discussion going at psyconaught on ways to increase the yields of the nirtomethane reduction. Alot of goof ideas being tossed around. But as usually no on wanted to try any experimentation. I am not doing them anymore, so its kind of a mute point for me.

But if we want to talk about them here I'm game.

Douchermann · « **Reply #11 on:** June 23, 2009, 05:40:52 AM »

I can get methylamine from hexamine, or from formaldehyde/ammonium chloride as I have both. The issue being that I don't want to. I've done the hexamine reaction so many times it's frustrating hahaha. Mercury is not a problem either, I have 100 grams, and is certainly not hard to get. The issue is time, and what interests me with this reaction is not only can it be done in 5 hours, but it can be scaled up well, the reagents aren't "watched" (Timothy McVeigh might tell a different story), and the reaction and work-up are quite simplistic. Refluxing, and distilling. No filtering, no washing organics that spontaneously turn into a goo-polymer, just heating up basically.

What caused me to post this, is the numerous claims of how successful this reaction is. They can be seen on the hive, on science madness, etc. 65 and even 75% yeilds are unacceptable to me as far as reductive aminations go, when I know they can be much higher. Especially considering from one 500ml bottle of root beer flavoring, the difference in yeild between methylamine and nitro can be 100g (for 75% yields with nitro) or 150g for 65% yeilds. That's the difference; how much you lose.

I'll play around with what I have some more, then I'll order some pure nitromethane and pure methanol and try it with that. Perhaps with foil, it will be easier (as in possible) to stir it. I've only been shaking it occasionally to redistribute, and I can clearly see some aluminum getting burried under the sludge.

v16 · « **Reply #12 on:** June 23, 2009, 05:56:40 AM »

all good points. I guess I'm not too worried about end to end yields, but then again I promote crazy things like starting with vanillin and eugenol. I agree making methylamine is a true PIA.

If you run large enough runs, or pool multiple runs, one could always save the results, distill it and isolate the left over ketone. There is a old hat that swears by this method, claims his losses where less than 5%.

Is a 6% solution (that is what your are supposed to get, right? ) a high enough concentration to get the higher methylamine yields? I haven't looked at the ratios in a long time.

if you have just been shaking, in my experience that is a big yield killer. Perhaps a overhead stirrer is in order? I have used ones kind of like vesp made in large 5L runs. (Do yourself a favor and order a teflon tip..like 25$) So much less frustrating then trying to keep a stir bar going.

Also, if you did it right (and was able to generate that 6% solution,) why not just add more foil and the ketone and keep the reaction going? This is what me a M. over at psyconaught where talking about trying. Saves on mess and processing.

Douchermann · « **Reply #13 on:** June 23, 2009, 05:23:39 PM »

From what abacus claims, 6% was plenty. He was the only person that directly posted about this, and then followed with how to do the reductive amination right after (it was the same, except just use this 6% solution as the solvent). Plenty others in that thread claimed success without disclosing any further information however.

@Vesp: Is there any way I can upload the .html page of the thread I'm talking about? I feel it will answer more questions than I can.

I will definitely start working on an overhead stirrer of sorts, since like I said, I can see aluminum getting buried under the sludge.

I like your idea, on keeping the reaction going with the ketone. The only real worry I'd have would be the excessive amounts of aluminum by-products affecting the absorption of the ketone. If mechanical stirring was employed, this most likely would not be an issue.

v16 · « **Reply #14 on:** June 23, 2009, 05:53:38 PM »

I think you will find with good stirring the sludge is not a thick. running just a nitromethane reduction would be a good way to get your stirrer and reaction vessel dialed in.

I would not do this in a RB flask. go for a different geometry w/ overhead stirrer.

Douchermann · « **Reply #15 on:** June 23, 2009, 09:08:37 PM »

That's what I was thinking, however I'll want to get my RB flask to work eventually. The biggest Erlenmeyer I have is 1000ml, with a 24/40 joint, where as my 5L RB flask with 45/50 would be looking lonely and quite empty if I stuck with the Erlenmeyer. Lol I'm going to have to think of something creative for this. Perhaps the stirrer will go down through the reflux column.

v16 · « **Reply #16 on:** June 23, 2009, 09:46:39 PM »

I wouldn't go that way. I tried to get one to work down the condenser and wasn't really happy with the results.

better to get some adapters. A simple Claisen is good enough if you design the mixer right. I ended up using a hand held electric screwdriver. harbor freight has very good ones for no money. They really dont need to good very fast.

I have had good luck using large rubber stoppers with holes drilled in them to mate smaller condensers to larger glass. Not the best technique, but it gets you there.

Douchermann · « **Reply #17 on:** June 24, 2009, 06:49:17 AM »

Yeah I was thinking of just the clasien, but then I have to figure out a way to get my addition funnel to still work. I only have one clasien, so a double stack is out of the question. The reflux condenser is also 400mm, so positioning the addition funnel above it would be hard. Hmmm, maybe I could use my vacuum adapter to angle a liebig, that way instead of sitting 400mm higher, it would only be 103.53mm higher... pay attention in trigonometry classes!

Douchermann · « **Reply #18 on:** June 24, 2009, 10:41:40 PM »

Hmmm, I recently came across a spent fire extinguisher. Fortunately, the top twisted off easily as they do on this size of extinguisher, so I might be able to test my theory for using fire extinguishers as catalytic hydrogenation vessels. This one looks to be aluminum, so I have to be considerate in what I load it with, and hope that the catalyst doesn't react with it.

I might ditch the aluminum amalgam in favor of catalytic hydrogenation of nitromethane. It's even cleaner than the aluminum amalgam reaction, and it eliminates the main unfavorable aspect - the excessive amount of solvent. I'm quite sure this tank could hold well over 100psi, and I'm sure it can be vacuumed without collapsing (but we'll see). Just need to find me a hydrogen tank!

Sedit · « **Reply #19 on:** June 25, 2009, 12:01:03 AM »

I have to admit Douchermann I am a little lost as to why you appear to be taking the hard/expensive route to this every way shape and form. Is it for academic reasons or what?

Here is an exert from on it Written by Eleusis a while back on the dissolving metal reduction but much more literature can be found on the subject. Eleusis just had a way with words that makes it easy for us kind of chemist to understand him easy, like saying things like, Youll blow your fucking head off if you screwed it up" or... "this is some nasty shit" lets see a science journal tell us how it is like that

Quote

Reduction of Nitromethane
The lower nitroalkanes (sometimes refered to as nitroparaffins) are easily reduced by a multitude of systems, but by far the easiest, and also the highest yielding, is the Iron/Hydrochloric acid system. The reaction is:

4 RNO2 + 9 Fe + 4 H2O =HCl=> 4 RNH2 + 3 Fe3O4
First, your Nitromethane *may* require purification, especially if it was for "fuel" use. In this case, it needs to be vacuum distilled at a vacuum of better than 100mm Hg. At that pressure, it will come off at ~47°C. Distillation at atmospheric pressure is possible, but I do not recommend it due to the highly flammable nature of the compound and because it's flash point is 42°C. It's your choice.

*CAUTION*
The lower nitroalkanes form shock and/or temperature sensitive EXPLOSIVE compounds with amines and hydroxides. BE CAREFUL, DAMNIT! You have been warned.

Assemble a 500mL RB flask with claisen adapter, thermometer down the center to read the liquid temperature, and reflux condenser with a cork and tube leading to a beaker of 1M Hydrochloric acid. Drop a stirrer magnet in, then add 105g of 40 Mesh Iron filings, 225mL of water and 1g of Ferric Chloride. Next, add 35mL of concentrated Hydrochloric Acid ("muriatic acid" is ok). When the bubbling ceases, add 31g of Nitromethane.

Heat the reaction mixture to 100°C and hold for 14 hours. A temperature regulator is necessary if using a heating mantle, else use a large boiling water bath (if you will be doing it overnight, so it doesn't run out).

At the end of this time, allow to cool then add enough 25% Sodium Hydroxide solution to to get the pH above 11. Heat on a water bath or with gentle electric heat to drive the Methylamine off as a gas into the same beaker of Hydrochloric acid used as a trap during the reaction.

Evaporate the beaker contents to dryness on a glass plate in the oven to collect the crystals of Methylamine HCl (hygroscopic!). The yield should be approximately 15g (95%).

*NOTE*
Alternately, you may want to try using a Tin/HCl system which will give an equivalent yield in a much shorter time with the disadvantage that Tin is a much more expensive metal. The balanced equation for the reduction follows:

2 CH3NO2 + 6 Sn + 12H+ 2 CH3NH2 + 3 Sn(IV) + 4 H2O
Cognate procedure: Setup a flask with reflux condenser in which .25 mol of nitromethane, .38 mol of granulated tin metal and a stirrer magnet have been added. Carefully pour 115mL of 31.45% hydrochloric acid (muriatic acid) down the reflux condenser in 10-15mL increments, waiting for the reaction to settle down before pouring the next aliquot. If the reaction seems to get out of hand (excessive frothing, vapor escaping the reflux condenser, etc...) then quickly slide an ice bath in place until it slackens back down. Once all the HCl has been added, heat the mixture to reflux with an electric mantle for 1hr. At the end of this time, allow to cool, preferably in an ice bath, then add, carefully, a chilled solution of 75g sodium hydroxide in 125mL of water. If the flask contents start to bubble violently you will watch your yield go out the window, so add slowly! Since methylamine readily dissolves in water, you will need to distill the reaction contents carefully to first liberate the 40% constant boiling solution (bp: 53°C) and then the gas itself. The product is best captured by bubbling the distillation vapor into a beaker of hydrochloric acid (use a slight molar excess of HCl to insure no loss). Proceed as above by evaporating the bubbler solution to yield the crystals (take care when evaporating HCl solutions, as the excess acid will vaporize into the air, corroding ovens, lungs, etc...). [Vogel's, pg 892]

Additional notes - Nitromethane is found in high performance RC model fuel, usually as a mixture with methanol and various strange lubricants. One particular brand, found at a local hobby shop, was 55% nitromethane.

Johnson & Degering, J. Am. Chem. Soc., v61, 1939, pp3194-3195

If im not mistaken this will leave you with MeNH2*HCl which would be ideal because you can concentrate and the evolve the gas into a MeOH solution to what ever concentration your heart desires.

Author Topic: Repeated failure of nitromethane reduction (Read 443 times)

Douchermann

Repeated failure of nitromethane reduction

Sedit

Re: Repeated failure of nitromethane reduction

Enkidu

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Douchermann

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Sedit

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v16

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poisoninthestain

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Vesp

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Douchermann

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Sedit

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v16

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Douchermann

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v16

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Douchermann

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v16

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Douchermann

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v16

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Douchermann

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Douchermann

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Sedit

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