psychokitty (Member)
12-20-99 07:30
No 105380
      What about this variation of the nitro/Al reaction??  Bookmark   

What about this variation of the nitro/Al reaction?:

When conducting the nitro/Al reductive amination, use only half the aluminum, the same amount of solvent, NO ketone, half the HgCl2, and the usual amount of nitromethane.  Allow the reaction to proceed as per usual and once it has subsided, then add the other half of aluminum and HgCl2 and allow to amalgamate.  When ready, then add the ketone and continue the reaction unto completion.  The initial modification is to ensure that all of the nitromethane is reduced to the methylamine to allow for a plentiful supply to react      *immediately* with the ketone (as opposed to the simultaneous addition which might promote pinacol formation of the ketone, which for awhile is just floating around).

Comments?

--PK

 
 
 
 
    Osmium
(Moderator)
12-20-99 13:23
No 105381
      Re: What about this variation of the nitro/Al reaction??  Bookmark   

I had good results with slow, dropwise ketone addition to the slightly refluxing reaction (done with MeNH2 not MeNO2). That way a huge excess of amine reacted with a tiny bit of ketone. Needless to say, the yields were very good. That's how I usually conducted this reaction.
I don't think that adding only part of the Al is a good idea. Because when you add fresh Al and HgCl2, the MeNH2 will complex or even precipitate the HgCl2. I know it still works, because I once made this mistake, adding the Al and HgCl2 to a MeNH2/EtOH mixture and the Al still amalgamated after some time. But use slow reacting thick foil or even thin sheet. You can amalgamate it all at once. Since the unproductive H2 producing reaction is quite slow with thick Al, interrupting the reaction for a few hours can be done without all the Al dissolving.
The same applies to the MeNO2-powered Al/Hg. Prereduce at least part, if not all MeNO2, and only then the mdp2p is slowly added, at about the rate the Al is consumed, to make sure that the concentration of mdp2p will always be low (high amine/ketone ratio)
 
 
 
 
    Methyl Man
(Member)
12-21-99 00:57
No 105382
      Re: What about this variation of the nitro/Al reaction??  Bookmark   

Mr. Adigk is very excited to try this suggestion of yours, Osmium. He will do so within a couple of days and I'll report the results.

He would also like to try thicker aluminum (relatively thin pie plate), since even thick foil seems to just break down too quick to employ this "MeNO2-first" tactic, but wonders how long he should expect that kind of aluminum to take to amalgamate. Last time he tried using this thicker aluminum, he was confused by the total lack of any bubble action after what seemed a very long time (almost an hour). He undertands more about this reaction now, i.e. that the bubbling is a separate thing and not an indicator of amalgamation per se, but can you give him any guidance at all regarding  what to expect on the longer timing using (thin) pie tins? One concern is that he has a day job and therefore can't babysit a 24-hour reflux.

Thanks mucho...

 
 
 
 
    Osmium
(Moderator)
12-21-99 03:07
No 105383
      Re: What about this variation of the nitro/Al reaction??  Bookmark   

You don't have to babysit the whole reaction, once you know how it works. O. usually left his Al/Hg reactions alone over night, for 12 hours or more, and nothing bad ever happened.

I don't know what your problem is with the amalgamation. The Al surface does look different when amalgamated. Another good sign is the turbidity generated by the Al sludge. Once there's that Al sludge, amalgamation was apparently successful. Let me tell you this: throw the Hg compound into the Al/alcohol mixture, stir for half an hour or so and proceed. The amalgamation is the least critical step, it works all the time. Especially with thick foil or even sheet.

 
 
 
 
    Methyl Man
(Member)
12-21-99 03:54
No 105384
      Re: What about this variation of the nitro/Al reaction??  Bookmark   

Osmium: I say "babysit" because this precedure is done as a reflux, no? To reflux one needs to assure ice-cold water thru the condenser, no? And for me, that means chucking more ice in the bucket every 20 minutes to keep the reflux constant. Are you saying that it's okay to leave it running with the reflux petered out? I thought the reaction had to have external heat applied once the exothermic action has ceased (but does it ever even get exothermic with the slow-reacting thicker aluminum??). And if one applies heat, well, the alcohol is going to reflux, leading us back to the need for constant ice water!! Do you see my problem? Am I all wet here or what? What am I missing?

Thank you! 

 
 
 
 
    Methyl Man
(Member)
12-21-99 10:38
No 105386
      Re: What about this variation of the nitro/Al reaction??  Bookmark   

Well K.C., it's like this. His main trip is that he really really likes the concept of cutting out one whole procedure by combining it with another. It appeals to his sense of efficiency, or something. Also, because it is the first and only reduction he has ever attempted, he feels a certain drive to master it. He would like to feel he has it pretty well down before moving on. Call it a work ethic if you want.

He also tried making MeNH2 via the Sumerian vac reflux thing and failed, and I guess he feels a little intimidated and frustrated by it (at least that reaction), making the in-situ deal look that much better. I know it's not logical, but what can I say.

I suppose he'd be willing to try the other methylamine synth that's supposed to be pretty easy, which one is it, the formaldehyde and ammonium chloride one? And I'm sure he'll find it to be a breeze, but damn, he just would like to get this nitro/Al/Hg thing down if possible.

So a mild 50C reflux eh? Shit, not possible with Reynolds Hotbags---that reaction just goes too nuts and the aluminum is 90% broken down within 40 minutes or so. And that's even with the aluminum ground into little nuggets; if it was left as open squares it would be way too crazy. At the peak moment, the refluxing MeOH is *pouring* down from the condenser!

It has become obvious that he needs to use some thicker aluminum than foil, but still doesn't have enough info to visualize what's going to happen with it. Can you give an overview of roughly what one should expect in the way of the timing when using pie plates? This would help a lot. For example: with pie-plate thickness aluminum, will it

A) never bubble at all
B) only bubble slightly
C) only bubble slightly, but after 3 hours
C) end up bubbling hard, but after 3 hours

etc. etc. Know what I mean? I need to know what's going to happen so that he doesn't think it's not working and cancel it or something. And no one really states these physical/timing details. My concern is that since I've read that the critical part of the reaction is over when the bubbling stops. SO I assume that one would to have all their ketone in by that time.

Am I making any sense?? I really need to understand the timing of this (with thicker Al)!

 
 
 
 
    K.C. Nicolaou
(Member)
12-21-99 11:43
No 105387
      Re: What about this variation of the nitro/Al reaction??  Bookmark   

Well, I can't give you an exact desription of what's going to happen because there's so many variables going on and because SGIDK never done a Al/Hg reduction with nitromethane. But, when adding a premixed solution of MeAm/ketone/MeOH to thick-ass(like 1/16") Al sheet that had been pre-amalgamated in MeOH, some gas evolution/exothermicity was noticed, but not enough to heat the solution much or cause it to start boiling vigorously. When heated to 50C, slow gas evolution was observed, but that may have been from boiling solvent/MeAm. Al dissolves slowly, with most of it being consumed over the first 3-5hr, but continuing for 8-10hr. Mag stirring is very difficult and can only be properly acheived late in the rxn. Super-thick Al sheet can be had from a metal suppy type place for dirt cheap.

As for making methylamine(the hexamine, formaldehyde/ammonium chloride, paraformaldehyde/ammonium chloride methods are all fundamentally the same), assuming you can heat the rxn for extended periods of time without the temp going over 104C, the only hard part is separating the ammonium chloride from the methylamine. If you can get nBuOH, this is not really a problem, but it can get a little bit tricky when using IPA or EtOH. Not hard at all once you get a hang of it, plus it can be done with totally OTC and very cheap materials. You also should realize that you can make methylamine seperately with Al/Hg and then use that in a new Al/Hg reduction with ketone. This has the advantage of not requiring new crystalization skills and using the starting materials you've already got. I believe there is a link on Rhodium's page or an old thread that describes how to do that. I'm all for efficiency too, but my idea of efficiency is such that I'd rather do a little extra work for a lot more yield.

 
 
 
 
    Osmium
(Moderator)
12-21-99 13:26
No 105388
      Re: What about this variation of the nitro/Al reaction??  Bookmark   

Methyl man, use some common sense: using sheet which might be 20 times thicker than foil will produce a reaction roughly 20 times slower, because the reaction takes place at the metal surface. The same energy will be released during much longer time, so the reaction will not heat up like the one using Al foil. External heat is applied to speed things up, otherwise you'd have to wait forever and a day for the reaction to finish. The yield with externally produced MeNH2 will always be higher, I can assure you that. It is usually worth it to go the extra mileage, yield-wise.

Don't use sheet that is too thick, I have posted the thickness I used before. I'll try to find out again in case you can't find it anymore (I think it was something like 0.2-0.3mm, not 100% sure about that right now).
I usually left the reaction alone, cooling was provided by ice water. I used big 10kg ice pieces and some water plus a circulating pump. They will keep things cold for the better part of a night. Or simply use tap water, you don't need a high flow rate at all, a very slow water flow is all that's needed. Hell, you might waste like 50 gallons of water, but who cares? That's about a bathtub full, and it's not really expensive compared to the other chems you already used 

 
 
 
 
    Methyl Man
(Member)
12-21-99 18:26
No 105389
      Re: What about this variation of the nitro/Al reaction??  Bookmark   

Thanks guys, I think I've got it now. That little bit of extra explanation was what I was after. I do appreciate it. I can be a little slow on the uptake... but I finish the course eventually.  

About making the MeNH2 via Al/Hg, yeah I've been thinking about that a lot, but I keep coming back to the thought that it's sort of like repeating a step. For me I guess it depends on the improvement in yield... if it (using externally made amine) results in a huge improvement in yield---like from 50% to 80%---that would probably be worth it to him, but if it were like from 50% to 60%, it would not. I think he feels that if he has to make the amine separately, he may as well just go the NaCNBH3 route.

As you struggle to help me understand this stuff, I hope you guys are bearing in mind that there are probably 1,000 others out there who are benefiting from the info in these posts also.

That's it for me on this subject. I'll leave y'all alone about it now.

Happy Holidaze

------------------
O+O+O+O+O+O+O+O+O+O+O+O+O
"There's a methyl to my madness"

 
 
 
 
    K.C. Nicolaou
(Member)
12-21-99 21:10
No 105385
      Re: What about this variation of the nitro/Al reaction??  Bookmark   

You don't really want a vigorous reflux. If you can set it up so that you can hold the temperature at ~50C, you're good. As for ice water, it's nice, but probably not absolutely necessary if you have an efficient condensor. Not to pry MM, but why are you so opposed to making MeNH2 seperately?
 
 
 
 
    Methyl Man
(Member)
12-22-99 11:44
No 105390
      Re: What about this variation of the nitro/Al reaction??  Bookmark   

Oops, well I thought that was all... but tonight Mr. Adigk tried aluminum roasting pan aluminum (~4 mil thick) and tried dripping in 90% of the MeNO2 first. Something did not work, because the ketone remained unconverted after 6 hours of stirring in the flask with the aluminum and the nitro, and no methylamine smell was ever detectable. Only ketone smell. Shit! Now he needs to figure out how to maybe salvage that ketone.

Mainly, he wonders if it's safe to distill off the methanol at 65C... data suggests that MeNO2 is volatile, but I know its BP is 101C, well above MeOH. Couldn't he just gently distill off the MeOH and salvage his ketone/nitro mixture that way? Or is it risky? I don't see why it would be any worse than running the reduction at 65C, which he does routinely.

Thanks for any help... 

 
 
 
 
    Osmium
(Moderator)
12-22-99 15:19
No 105391
      Re: What about this variation of the nitro/Al reaction??  Bookmark   

???
Forgot to add the Hg?
The MeOH and MeNO2 will distill together, as an azeotrope, at about the usual boiling point of MeOH. Strange, isn't it?
Did the Al dissolve? Why did you add the ketone at all when there was no fishy smell? Should have told you that something's wrong.

 
 
 
 
    psychokitty
(Member)
12-22-99 16:31
No 105392
      Re: What about this variation of the nitro/Al reaction??  Bookmark   

You were able to stir an aluminum pie pan mix?  Wow.  Anyway, if forgetting to add the HgCl2 is not the problem, then I suggest adding the 25 mL of water to get the reaction going.  This will add to the overall efficiency of the reaction while at the same time cut down the time it needs to finish.  If you just want to salvage the ketone/MeOH/nitro mix, then just filter the whole mess so that it can be reused in another fresh Al reaction (be sure to wash the filter cake with a little alcohol).  After filtering, however, if you are a little edgy about the dilution, just VAC distill most of the alcohol until you reach the desired volume. Then proceed from there as usual (amalgamation followed by dripping over one hour the ketone/nitro mix).

Good luck

--PK

 
 
 
 
    psychokitty
(Member)
12-22-99 16:55
No 105393
      Re: What about this variation of the nitro/Al reaction??  Bookmark   

Shit!  I forgot about the azeotrope.  Okay, isolate the alcoholic mixture through filtration as described before, and then VAC distill.  If you run into anything that distills at a higher temperature than the major fraction does, then you know you've got either your nitromethane or an azeotrope.  Either way, continue to VAC distill (being sure to keep the separate fractions in different flasks away from eachother) until all you have is your ketone.  Measure the volume of the suspected nitromethane/azeotrope fraction.  If it is more than the amount of nitromethane that you used initially, then it is probably an azeotrope.  In any case, calculate the amount of nitromethane that is in there (subtract the volume of nitromethane used at the beginning of the reaction from the volume of the fraction isolated).  If there is less nitromethane present than was originally  added, then simply raise the volume to standard.  If everything is as it should be, then great.  But if in doubt,add about 5 mL more of nitromethane just for good measure.  Proceed from there as usual.

Oh, yes, if the ENTIRE fraction distills over at one temperature (making it virtually impossible to separate the methanol from the nitromethane) then distill all of it away and then dispose of it.  Next add the correct amount of methanol and nitromethane to the ketone, and start all over.

--PK

 
 
 
 
    Methyl Man
(Member)
12-22-99 18:52
No 105394
      Re: What about this variation of the nitro/Al reaction??  Bookmark   

Thanks again guys. No no, he would not forget the Hg. He's not that out of it! Os, he was following your advice in this same thread where you said to just let the Al/MeOH/Hg stir about a half-hour, then begin dripping (in this case, 90% of the MeNO2 first). Yeah, he should have sniffed to see where things were before adding ketone I guess, but figuring that the whole thing might take 12 hours or so, he just went ahead. The Al was being affected by the Hg, but it never broke down at all into grey sludge; it just released a little gray color into the solution and got dull-looking. I don't know, but it sure does appear to me that the exothermic part is what reduces the nitro to the amine.

Something about the thick aluminum just ain't happenin' for him. BTW he was only able to stir it about 10% of the time. The rest of the time he was able to agitate it by trying to stir, which made the the stir bar sort of flutter and agitate it a bit.

This kind of does it for him though---he's going to concentrate on learning to make MeNH2 so that he can eventually advance by learning the NaCNBH3 reduction. For strictly production purposes, he'll settle for the "50%" he gets with what he knows how to do (the nitro/Al with its nutty, angry phase using shredded Reynolds Hotbags).

I suppose he was due for some kind of failure, as he hadn't  really had one yet... 

 
 
 
 
    K.C. Nicolaou
(Member)
12-22-99 23:33
No 105395
      Re: What about this variation of the nitro/Al reaction??  Bookmark   

I know psychokitty already said this, but did you add water at any point? I know I posted the amount of water required for the reduction of the nitromethane and ketone somewhere, so I'll try to find it and convert the numbers into a useful form for a non mole-calculating mofo like yourself.
 
 
 
 
    Methyl Man
(Member)
12-23-99 01:30
No 105396
      Re: What about this variation of the nitro/Al reaction??  Bookmark   

Yeah I didn't mention it but he had ~25mL of water in there also. I really don't think that's it at all though. When he does this reaction with the thinner aluminum, he can smell right away that the methylamine is being made as the mixture really starts bubbling furiously. I don't know shit, but this sure suggests to me that the heat is facilitating that conversion. Last night he saw essentially no heat being created, and no MeNO2-->MeNH2 conversion.

Could the fact that he only used 180mg of HgCl2 with much thicker Al have something to do with it? maybe there just wasn't enough Hg for a vigorous reaction? At any rate, it doesn't matter much because he's tired of tinkering with this reduction.

 
 
 
 
    DarthKitty
(Member)
12-23-99 06:24
No 105397
      Re: What about this variation of the nitro/Al reaction??  Bookmark   

Well, at least finish the reaction to see what you get. Add a little more HgCl2 and water and see what happens.  Better than just ditching the whole messload.  Just jump-start the reaction any way you can.  You've got nothing to lose anyway.

DK

 
 
 
 
    philley
(Member)
12-23-99 21:47
No 105398
      Re: What about this variation of the nitro/Al reaction??  Bookmark   

Metyl Mann, it has been said that std al pie plates will need more than 180mg for a decent rate. 300-500mg has been used on pie plates where it takes a good 30 minutes for it too start reaction (quicker w/applied heat) and concurrent w/the amount of Hg added. With 400mg expect bubling to start in 30 minutes and for it to become rapid and only about 2/3 or the foil to be devoured after 20 hours w/50c temps on strong overhead stirring. The important thing is not to let the reaction before adding the ketone to get to advance and break down to much al before you even get started. Give it a try w/300mg in 300ml MeOH and wait 45 minutes, 180mg will show almost no major changes.

Denny of Canada

 
 
 
 
    philley
(Member)
12-23-99 21:49
No 105399
      Re: What about this variation of the nitro/Al reaction??  Bookmark   

BTW, if you have an addition funnel and use to min 24hour stirring, I would add the MeN02 about 2 to 3 hours before the ketone and drip the ketone in over a minimum of 4 hours for optimum conversion.
Thanks Bro,
 
 
 
 
    sparks
(Member)
12-25-99 14:03
No 105400
      Re: What about this variation of the nitro/Al reaction??  Bookmark   

I tried to post this before, but something went wrong.
Anyways, why don't you do it the nitroway n'til the end?
It's easy and troubleless.
It may be a bit more exotermic than expected, but if you live in the northern hemisphere you have lotsa snow to keep it contollable with.
All in all, a very nice and useful reaction.
(just think about where you're putting that mercury waste, otherwise your karma goes to hell, and that we don't want, do we?)
 
 
 
 
    lab_bitch
(Hive Bee)
10-07-02 06:32
No 365305
      Re: Oops, well I thought that was all...  Bookmark   


Oops, well I thought that was all... but tonight Mr. Adigk tried aluminum roasting pan aluminum (~4 mil thick) and tried dripping in 90% of the MeNO2 first. Something did not work, because the ketone remained unconverted after 6 hours of stirring in the flask with the aluminum and the nitro, and no methylamine smell was ever detectable. Only ketone smell. Shit! Now he needs to figure out how to maybe salvage that ketone




Did the addition of the MeNO2 cause the aluminum to break down?  Did the aluminum turn dull grey (amalgamated) b/f you added the nitro?  If you don't first let the Hg reduce on the aluminum surface b/f adding other reagents, they will complex with the Hg and prevent amalgamation.  Perhaps you added the nitro too early.

 
 
 
 
    lab_bitch
(Hive Bee)
10-07-02 06:39
No 365314
      Re: Could the fact that he only used 180mg of ...  Bookmark   


Could the fact that he only used 180mg of HgCl2 with much thicker Al have something to do with it?




With thicker foil, you have less surface area and thus need less HgCl2.  I am pretty sure that adding more HgCl2, changes the reduction potential of the metal, making it less energetically favorable for the aluminum to oxidize.  This slows the rate of reduction.  On the other hand, more HgCl2 increases the rate of reduction of the nitro/ketone b/c it serves as a catalyst.  The reduction will not occur if HgCl2 is not added.  Even if the oxidative coating was removed from the aluminum, it would only react with the solvent.

 
 
 
 
    lab_bitch
(Hive Bee)
10-07-02 06:46
No 365318
      Re: It may be a bit more exotermic than expected, ...  Bookmark   


It may be a bit more exotermic than expected, but if you live in the northern hemisphere you have lotsa snow to keep it contollable with.




Antarctica is in the southern hemisphere, and has more snow than you've ever seen in your life.laugh

 
 
 
 
    Diggity
(Hive Bee)
10-07-02 06:50
No 365323
      The reduction will not occur if HgCl2 is not ...  Bookmark   

The reduction will not occur if HgCl2 is not added. Even if the oxidative coating was removed from the aluminum, it would only react with the solvent.

Im confused.. why does the "preparation of AL/hg" by Eleusis describe AL being amalgamated, then the Hg containing solvent poured off the al, then non hg containg solvent poured back over, and stored to be used at a later date?

Prepare a ~2% Mercuric (II) Chloride solution by dissolving 1g of HgCl2 in 50mL of distilled water.

Cut 40g of aluminum foil into small squares approximately .5cm a side.

Place the aluminum into a large beaker or other suitable glass container and cover with the sodium hydroxide solution. Heat gently in a well ventilated area until hydrogen gas evolves vigorously for about 3 minutes. Strain the foil through a plastic colander and wash first with distilled water, then with denatured alcohol. Pat dry then add to a beaker with the 2% HgCl2 solution. Allow to amalgamate for 2 minutes then pour off the supernatant. It is unethical to pour mercury compounds down the drain, but you'll probably do it anyway ;-). Now wash the foil in the colander as before, with distilled water, ethanol, and then a little bit of ether. Submerge the aluminum amalgam in ether to store until use.


[edit] OOps.. this method uses Naoh in dh20, not hg in solvent.. but still uses Hg..

../rhodium/chemistry /eleusis/aluminum.html

& I'm, somethin of a phenom, no need for da cron, I'm un-stopable.   
 
 
 
 
 
 
    lab_bitch
(Hive Bee)
10-07-02 07:14
No 365339
      Amalgamation means that the Hg is adsorbed on the ...  Bookmark   

Amalgamation means that the Hg is adsorbed on the Al surface, so the water doesn't really contain any HgCl2.
 
 
 
 
    Disciple
(Stranger)
12-17-02 01:24
No 390109
      Al powder addition  Bookmark   

I've got shitloads of Al powder(fine) lying around and was wondering whether it would be worth trying to boost efficientcy by combining this with the ketone dripping it in. So that the reaction only proceeds at the same rate as the addition. What do you Think
 
 
 
 
    SPISSHAK
(Hive Bee)
12-17-02 01:35
No 390110
      careful!  Bookmark   

Aluminum powder reacts real exothermically in this reaction, try it and let us know how it works, but try to avoid run away reactions.
 
 
 
 
    Aurelius
(Hive Addict)
12-17-02 01:52
No 390115
      powder addition  Bookmark   

powder additions are usually not made as slurries in small scale production.  it's hard to keep the suspension up- the aluminum will settle and clog your addition funnel.  try adding it through a wide center condensor and wash it down with a couple mls (5-10) of methanol each time.
 
 
 
 
    Disciple
(Stranger)
12-18-02 03:07
No 390382
      emulsion??  Bookmark   

Yeh I was wondering how would be best to keep the al powder suspended. would it be possible to make an emulsion or something or am i just talking outta my ass.
How do you mean to add it through a wide center condensor.
THanks.
 
 
 
 
    goiterjoe
(Title on BackOrder)
12-18-02 08:12
No 390453
      amalgation procedure  Bookmark   

Wouldn't you want the aluminum to be amalgated before the reduction begins, or is there an advantage to letting the aluminum amalgate during the reaction?  I was under the impression that you want all of the aluminum to amalgate before the reaction.  On the other hand, you wouldn't want to use aluminum powder for nitromethane as it would get way too hot.

If at first you don't succeed, try, try again. Then give up. There's no use being a fool about it.
 
 
 
 
    SPISSHAK
(Hive Bee)
12-18-02 08:31
No 390457
      Mercuric  Bookmark   

Salts have a tendancy to complex with a lot of things, especially amines, so it would make sense to so this first, rinse the excess off with water, then procedd with reduction, and not to amalgamate in-situ.
 
 
 
 
    Aurelius
(Hive Addict)
12-18-02 19:13
No 390545
      suggestion  Bookmark   

aurelius only meant to give a suggestion on how the addition could be performed.  didn't mean to suggest that this was a viable or preferred method.  the suggestion is only there if somebody would like to try this variation.  - come to think of it, it probably wouldn't help at all and would probably cause a couple of problems with the cleanup.  the aluminum added later wouldn't have any mercury salts to amalgamate it after the start of the reduction. (excess washed off the pre-prep'd aluminum)  so you'll just have excess aluminum powder floating around.