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Author Topic:   The MeNO2-Al-Hg reductive amination according to Methyl Man
Methyl Man
Hive Bee
posted 01-27-2000 01:36 PM     Click Here to See the Profile for Methyl Man      Reply w/Quote
Since the appearance of Ritter's writeup of this method in Total Synthesis II, much discussion has taken place about it but, it has sometimes seemed, little has been clarified. This is due in large measure to the sensitivity of this reaction to even the most minor changes in its many variables. With this writeup, I hope to provide a clearer view of the method and to allow others to benefit from the hard-won experience of someone (not me) whom we'll call Mr. A. Ritter's original writeup, while inspiring, lacked details about the many nuances that, once understood, allow the amateur chemist to really understand this reaction's dynamics. Thus I have tried with this writeup to help the neophyte who has only physical observations and scant written material to guide him (although I suspect and hope that it may even help a few more seasoned cooks as well).

The first thing I'd like you to look at is the array of interrelating variables in this reaction that make it so delicate. They are as follows:

1) the thickness/type of the aluminum
2) the consistency (i.e. flat, ground, etc.)
3) the amount of HgCl2 used in relation to the amount of aluminum
4) the addition rate of the MeNO2/MDP-2-P
5) the size of the reaction vessel in relation to the scale of the reaction
6) the ability to effectively stir the reaction
7) the coldness of the water through the reflux condenser (yes, even that!)

The above factors are sort of submitted in an order of importance (#1 being most important), but in reality they are all inextricably related. I observed firsthand the trials and tribulations of Mr. A as he struggled to match up the correct combination of ratios and conditions that would allow a smooth, consistent reaction and predictable results every time. Finally, after lots of frustration, confusion, losses, and---in the end---a revelation, the perfect set of elements was hit upon and recorded.

The scale Mr. A chooses to perform this reaction on is half-scale to the scale in the Ritter writeup, which was 55g aluminum and 50g MDP-2-P. Therefore this writeup will illustrate the reaction on a scale of 27.5g aluminum and 25g MDP-2-P. The subject found for his own personal reasons that this smaller scale was much easier to manage (not the least of which is that even with a huge 4-liter separatory funnel, at this smaller scale it gets pretty filled up!). There's no doubt that the original larger scale can be successfully applied, although it would require adjustments in the glassware capacity, stirring method, and probably other elements.

MATERIALS and APPARATUS:
* 27.5g Reynolds Wrap Heavy Duty aluminum foil
* 25g MDP-2-P
* 20 mL MeNO2 of 99+% purity
* 750 mL MeOH + 50 mL more for addition funnel + additional small amounts that will be needed later to thin the mixture
* 400mg HgCl2
* 2-liter 2-neck flat bottom flask
* reflux condenser (400mm preferable)
* 250mL or 500mL addition or separatory funnel
* cooling setup (bucket, water pump, tubing, 1 bag ice)

METHOD:
1. Weigh 27.5g of Reynolds Wrap Heavy Duty aluminum foil (NOTE: it HAS to be Reynolds and it MUST be the heavy duty stuff) and then tear it by hand or cut it with scissors into small rectangles approximately 1" by .75". Settle down with this task with a good CD or TV show because it is tedious and will take about 30-40 minutes.
2. With a coffee grinder, "grind" these pieces of foil for durations of about 10 seconds. Fill the coffee grinder only loosely (about two thirds full---don't stuff it! That will adversely change the consistency of the ground foil). It will probably take about 4 to 5 "loads" in your grinder to do the whole 25g of foil, depending on the size of your grinder. (In actuality, the foil does not get "ground," but rather, each individual piece just gets compacted and compressed. If it is compressed too heavily, the inner surfaces of the foil nuggets may be rendered inaccessible to the Hg/MeOH solution, changing the timing of the amalgamation and maybe even causing an incomplete or failed reaction.) When properly done, the foil should be in gnarled little nuggets about the size of sunflower seeds (shell included) and should NOT look super-tight and small.
3. Place a 3" stirbar in your 2L flat bottom flask and onto your stirplate. Add the foil nuggets to the flask and then proceed to set up your glass, support and clamps so that the reflux condenser and addition/sep funnel are securely affixed and your flask is well-centered on the stirplate (this will be critical when you begin to attempt stirring!). Also, prepare your cooling, i.e. attach the inflow and outflow tubes to the reflux condenser.
4. Carefully add the 400mg HgCl2 to 750mL MeOH to a tightly sealable bottle and shake to dissolve all HgCl2. Set this solution aside.
5. Combine the 25g MDP-2-P, 20mL MeNO2, and 50mL MeOH and pour them into the addition/sep funnel. Rinse your beaker (or whatever you used) with a tiny bit of additional MeOH to get the residual ketone and add it to this MDP-2-P/MeNO2/MeOH solution.
6. Very slowly and carefully (w/gloves, glasses, long sleeves and a Hail Mary if you're Catholic), using a large funnel, pour the HgCl2/MeOH solution from step 4 down the condenser.
7. Turn the stirring on full blast for a 5-second burst to intimately mix the solution and the foil. If you have prepared the foil as described above, it will easily stir. Give it a few more 5-second stirs over the next few minutes. I believe that doing this really helps facilitate the amalgamation process that is about to occur.
8. After about 5 minutes or so, you will begin to see bubbles popping up on the surface of the MeOH solution. At first they will be tiny, like champagne bubbles. Then after a few minutes you will see them joined by larger bubbles closer to the size of those seen in boiling water. It is around this same time that the appearance of the aluminum will change from its normal shiny silver color and start to take on a dull gray look, accompanied by a gray cloudy look that begins forming in the MeOH. This is the magic moment when you want to begin dripping in your MDP-2-P/MeNO2/MeOH mixture. Set a drip rate of approximately 1 drop per second at this point and no faster. You can speed it up a bit later to accelerate the reaction if desired.
9. Place about 3 lbs ice into your bucket. When you can feel exothermic warmth begin by feeling the outside of the flask, quickly add about 2.5 liters water to the bucket (or an appropriate amount to make very ice-heavy ice water) and plug in the pump.
10. While monitoring the growing intensity of the bubbling amalgamation, turn on/off the stirring intermittently as you did earlier. This time it is to assure distribution of the added ketone/nitromethane in the reaction flask but also because the amalgamation seems to gain its vital momentum more effectively if given some significant blocks of time (meaning about 30 seconds at a time) in between "stirring bursts." When the reaction is clearly starting to get vigorous and hot, crank the stirring to 10 and leave it on.

NOTE: This is where you can take advantage of Mr. A's trial and error regarding this reaction's parameters. If you used the kind of foil specified, prepared it as specified, used no more than the specified 400mg HgCl2, and used a 2-liter and NOT a smaller flask, you can breathe easy knowing that the reaction is going to hum along nicely but will not get out of control, and will result in perfectly processed aluminum amalgam sludge. You may think that a 2-liter flask is oversized for this reaction, but that is precisely the point. The extra headroom in the glass provides a nice zone of "breathing room" for the reaction and facilitates good refluxing. I've seen this reaction get out of hand in a 1000mL flask, and it isn't pretty, believe me. Use the 2-liter.

11. As the reaction progresses only a few minutes after the addition was started, you will observe that the aluminum is breaking up fairly rapidly. This is good, as long as you have the ketone/nitro mixture dripping in at a good rate of about 1drop per second. But be careful with the addition rate at this point, as a rate that is much faster than this could easily send the reaction into overdrive (not good). Your reflux should be unnervingly vigorous as the amalgamation really starts to pick up speed, with the MeOH literally pouring down out of the condenser. I know it's hard to believe, but this is what you want, this is good. I'm telling you, LOTS of trial and error came before this writeup. Trust me. You will also see sludge already starting to settle at the bottom and forming a ring on the glass around the top surface of the spinning mess. The consistency will get thicker by the minute. Add more ice to your bucket as needed.
12. At this point you can sort of control the reaction rate by slowing down or speeding up the addition rate a bit. Of course the reaction is already barreling along, so you won't want to speed it up much. The concept here is that you want the addition of the ketone/nitromethane to be paced neck-and-neck, as it were, with the breakdown of the foil as it amalgamates and gets turned into sludge. In other words, you have to watch those two things and sort of adjust the addition so that they proceed at approximately the same rate. It's tricky, and imprecise, but with a little experience and intuition you'll get the hang of it. Sure, you could be lazy and just leave the addition at a steady 1 drop/second the whole time, but if the amalgamation peters out way before your addition is finished, and you find yourself adding your beautiful ketone to impotent sludge, don't cry to me. The addition should take about 40-45 minutes in total, and as it's finishing, the state of the aluminum should be about 95% broken down. In fact the reaction should by now (~45 minutes after addition was started) look like a really thick, steely-gray chowder with only minor small slivers of undissolved aluminum visible if any at all. You will probably even need to add an extra 20-30mL of MeOH down the condenser at this point (or before) to help it keep stirring effectively. This is no problem.

A note about color at this point is helpful too. Comparing successful reactions to failed ones, I have observed that there is a distinctive color to the mixture early on that indicates healthy amalgamation and foretells a successful run. At a point maybe 30 minutes or so post-addition, the reaction takes on a color that I would describe as being "light steely gray with blue overtones." It is a hard thing to describe shades of gray, but I will try. It is a light shade, akin to the color of common gray sweat pants, but like I say with a very slight suggestion of a blue hue in there as well. This is in contrast to what I saw in failures resulting from using too thick of aluminum and not enough HgCl2, where a dark metallic gray with definite green overtones (from unreacted ketone) was noted.

NOTE: Another point I would like to make about the timing of the addition against the breakdown of the aluminum is that Mr. A found that there was a definite "spike" curve to the amalgamation reaction which was easily observed by watching the reflux rate. That is to say, there is a peak that it builds up to and then comes down from. At this scale, and using the exact materials described herein, that buildup to peak and subsequent slowdown occurs over approximately 25 minutes or so---very fast. So at only about 20-25 minutes after you first started feeling the amalgamation heating up, it will have slowed to a reflux of about 2 drops per second, after having been at a peak with a reflux rate so furious it is a stream, not drops. At one hour and 15 minutes after you first started the addition, the reflux will have slowed to a very calm 1 drop per 2 seconds or so. Finally, when...

A) the reflux has slowed to almost no reflux at all
B) if you stop the stirring you do not see any small bubbles anymore
C) no "uneaten" aluminum is visible and the solution is a thick, uniform gray soup,

...the reaction has essentially finished. It will reach this state at about one hour 45 minutes to two hours after addition was started. Nevertheless, you will leave it stirring happily for a total of three hours after the addition was finished to assure that the reaction has run its full course and the conversions that you desire have had ample time to take place. You could add a bit of external heat at this point but it's probably not even needed (Mr. A does it just to be sure). One reason I bring this all up is that there has been lots of talk about how this reaction needs 8 hours or 24 hours or even 36 hours to run! But those time frames apply only in cases where much thicker aluminum is used, and/or in variations using methylamine and not nitromethane. Mr. A was never successful in using thicker aluminum, and doesn't want to be! Why would someone want to make a reaction take any more time than it needs? Beats me! I'm mystified! The approach illustrated in this writeup optimizes this reaction to finish in 3 hours 45 minutes from beginning to end, and it probably doesn't even need that much time.

13. If you chose to apply external heat, turn it off at 30 minutes before the targeted finish time. Otherwise you will have to wait an extra 30 minutes for it to cool for the next steps.
14. When finish time has arrived, dismantle your setup, set aside your reaction flask, and make 750 mL of a 35% NaOH solution (750 mL H2O + 262.5g NaOH) and let it cool to room temp or below (safety glasses!).
15. Into a separatory funnel no smaller than 2000mL capacity, pour your beautiful gray reaction mixture, being very careful to KEEP THE STIRBAR FROM FALLING IN to the sep funnel and breaking it (that would be ugly). If your mixture is really thick, you may need to add small amounts of MeOH to thin it to a pourable consistency. This is perfectly fine. Wash the final residue out of the reaction flask with a few mLs of MeOH and add it to the funnel also.
16. Slowly pour the NaOH solution into the sep funnel (gloves and glasses! no excuses!). That's right, don't dump it in wholesale. Basifying should be a gentle process. If you bully those molecules they may decide they're being disrespected and choose not to cooperate. Adding the NaOH will cause the mixture to warm up a bit as the very last bits of the aluminum are dissolved, which is fine. Swirl it a couple times and give it about 10 minutes to cool down to something closer to ambient temperature. That yummy stinky methylamine smell tells you that the reaction was successful.
17. When the mixture in the sep funnel has cooled down, extract it once with 400mL toluene followed by once with 100mL toluene. These are the critical moments for your yield now, so you be sure to shake long and hard (at least 3 minutes) during these extractions (I don't have to tell you to vent do I?!). The toluene/product layer will of course be on top since toluene floats on water. Also, be sure to give the separations ample time to happen (at least 15 minutes); it is easy to tell when it's okay to separate because the interface of small toluene bubbles finally resolves and you have a nice clean line between the layers. If you like, do as Mr. A does and finish off with a final small extraction of 50-60 mL toluene just to get the last of the stuff.

NOTE: Your extractions will contain a tiny amount of the base/metal/garbage from the bottom layer; this is inevitable but easily worked around in this way: when you have collected your combined toluene/product extractions in a bottle, chill that bottle in the freezer for 30 minutes or so. When cold, the garbage gets a lot less mobile and it is easy to decant the toluene away from it. Just be vigilant while pouring the last 50 mL or so and avoid letting that glob of crap rejoin the toluene. Yeah, you will lose the very last 2 or 3 mL, but that's life. Alternatively, you could filter it through a paper towel, but you will still lose the same amount when the towel absorbs it. Just get over it and move on!

18. If you haven't already, drain the garbage layer out of your sep funnel into a storage bottle or something, and wash the garbage residue out your sep funnel with water.
19. Wash the toluene/product 4 times (or more) in your sep funnel with 400 or 500mL H2O and a final time with 500mL of a saturated NaCl solution to remove any traces of solvated HgCl2.
20. Dry your toluene/product solution with 30g of your favorite drying agent (MgSO4 recommended) in an acetone-cleaned, heat-dried bottle for no less than 30 minutes (Mr. A is superstitious so he lets it sit for an hour). Shake it a few times during this period.
21. Filter the solution and gas it with that good ol' HCl bubbler setup. Be smart and use just enough muriatic (31% HCl) to wet the salt but not enough to make any puddles, and put a wad of drying agent wrapped in tissue paper in line somehow between the reaction flask and the tube leading to your pipette end. Weep with joy as a bumper crop of white precipitate crashes out of solution.

Expected yield: approximately 20-21.5g raw odoriferous product that will purify via careful recrystallization to 17-18g of beautiful snow-white MDMA! Ain't life grand?

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

pSillyMan
NewBee
posted 01-27-2000 02:01 PM     Click Here to See the Profile for pSillyMan      Reply w/Quote
MM: Beautiful! I've been waiting for this puppy! One question sir: where does Mr. A get his MeNO2?

Methyl Man
Hive Bee
posted 01-27-2000 02:04 PM     Click Here to See the Profile for Methyl Man      Reply w/Quote
Racing fuels supplier. 99.7%.

Methyl Man
Hive Bee
posted 01-27-2000 04:20 PM     Click Here to See the Profile for Methyl Man      Reply w/Quote
One thing that I want to mention in hindsight here since I know it's probably going to come up, is the issue of added water.

It's been emphatically stated several times that some water is needed in this reaction for imine formation etc. etc. That may be true, but I know for a fact that it doesn't need to be added. That is to say, maybe there is some trace water in the MeOH Mr. A uses (Heet) that is fulfilling this function, and maybe it's even in all MeOH except expensive absolute anhydrous stuff. I don't know. But he doesn't add it anymore and it definitely doesn't hurt anything.

Before, Mr. A was adding about 25 mL, and maybe it was not a good thing. But he likes how it's going now.

hellman
Hive Bee
posted 01-27-2000 07:10 PM     Click Here to See the Profile for hellman      Reply w/Quote
Methyl Man,

Everybody has been waiting for such a detailed description of the Amalgamation process,;Ever since Zwitt's pleasured us, there still has been little bit's missing,.
You have truly filed the gaps, and you deserve no less respect and honour than the great man himself,.

We don't exactly know who you are, for all intensive purposes we don't need to, But you ARE A VERY KIND AND GENEROUS MAN, not cripled by greed or sacasctic materialism.

I am tingling, just as I know all other bees are,.

Thankyou Methyl Man

From everybody,

Hellman

Niels Bohr
Hive Bee
posted 01-27-2000 10:25 PM     Click Here to See the Profile for Niels Bohr      Reply w/Quote
I like those yields; 17 to 18 g from 25 g starting material

One other dumb question...what make and model coffee grinder do you suggest? This is probably as important as the oversized flasks.

Niels Bohr
Hive Bee
posted 01-27-2000 10:27 PM     Click Here to See the Profile for Niels Bohr      Reply w/Quote
...in fact, lets get real anal here...what size stirbar and how many RPM's (guess)?

Methyl Man
Hive Bee
posted 01-28-2000 02:23 AM     Click Here to See the Profile for Methyl Man      Reply w/Quote
Hi Niels!

Regarding the coffee grinder, it's a Black & Decker "Coffee Mill" (CAT. NO. CBM-1 TYPE 2) although I doubt it matters.

Stirbar is standard 3" and the stirplate a wimpy old Fisher standard 7" x 7".

Hellman: you brought a tear to my eye. What can I say, I'm just trying to return the kindness and helpfulness that has been shown to me...

sunlight
Hive Bee
posted 01-28-2000 03:30 AM     Click Here to See the Profile for sunlight      Reply w/Quote
A few days ago I threw away two broken cofee grinders (Philips). I like to make all kind of things with them, but it seems they don't like to make everything. Anyway they are cheap.

patrick
NewBee
posted 01-28-2000 06:19 AM     Click Here to See the Profile for patrick      Reply w/Quote
Can somebody give me the thickness of the Reynolds Wrap Heavy Duty aluminum foil. We don't have this brand in Europe.

Thanks a lot

Methyl Man
Hive Bee
posted 01-28-2000 12:06 PM     Click Here to See the Profile for Methyl Man      Reply w/Quote
Wow, that's right I just realized how "Americentric" that writeup must appear to some European bees. Okay the task is clear, we have to dig up that old post by---who was it, Xerxes??---where he called Reynolds Wrap company and got the thicknesses of their products. If you do a search on "Al-Hg" (no quotes) it will be in there... I know, cause I've done it many times. Then, when that thickness is known, you guys in Europe can contact makers of your big national brands and zero in on the ones that are about the same.

Someone else do the search, I'm too tired...

scwam
Hive Bee
posted 01-30-2000 03:17 PM     Click Here to See the Profile for scwam      Reply w/Quote
its something like .025mm to .04mm thick

skazy_haze
NewBee
posted 01-31-2000 06:54 PM     Click Here to See the Profile for skazy_haze      Reply w/Quote
Methyl Man,
i would like to thank you for this meticulous description of the Al/Hg procedure. Bill Clinton will be trying it very soon in conjunction with your benzo wacker write up.
However, he has a few quick questions about said procedures before attempting them.

1) The Whitehouse is a conspicuous place to cook in, so Bill doesn't want to take any chances with HCl gas. So he was planning, at step#19 of the above procedure, to take the toluene/honey mixture and not dry it but add muriatic acid to the mix until pH5 was attained. At this point, he would get Hillary or some other wench to heat the mixture over a hotplate at around 110C until
everything boils off except the honey. He then hopes to cool the honey down to room temp, then add 4 volumes of ice cold acetone, mix around a bit and stuff the product into the freezer. Can Bill expect fluffy white foodstuffs to emerge with this arrangement?

2) when refluxing, is it necessary to use a reflux condenser or will a regular leibig condenser suffice? what about in the benzo wacker procedure?

3) the cooling setup you describe above has skaze a little hazed...are you describing a bucket with water and ice to feed through the reflux condenser? if so, how good of a pump does Bill need for this? will plain old cold tap water do the trick?

thank you Methyl Man for your excellent postings and researches into the apiary sciences.

Methyl Man
Hive Bee
posted 02-08-2000 07:23 PM     Click Here to See the Profile for Methyl Man      Reply w/Quote
#1: Sounds good, sounds like the sunlight method. No one I know has done it, but it sounds good.

#2: Liebigs and Allihns are almost exactly the same. I would think they could be used interchangably.

#3: Yeah a bucket with ice water and a little ol' 150 GPH pump would work great.

All times are CT (US)

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