Granular Aluminum

bio · Working Bee

I was wondering if anyone has experience using amalgamated granular Al for reductive amination and could offer some advice.

Neighbor Joe came into 2Kg RA grade granular Al (pricey stuff) purported to be 10 mesh (confusing) by the supplier @ .012 inch size. which would be .3mm (300 micron). The actual size distribution is quite wide, quessing 100-500 microns.

Due to the large surface area compared to foil or sheet tests indicate about 3g/L HgCl2 is needed for amalgamation. Joe said he uses 1g/L for extra heavy duty foil.

A 100mm reduction is about to be performed to see how this works. Surprisingly enough the grains take many hours to dissolve in MeOH forming the methoxide however placed into 5% NaOH the reaction is very vigorous and totally dissolves in less than 30 minutes.

Any input is appreciated and Joe is considering adding the grains in maybe 3 or 4 portions over a couple of hours then continuing at reflux until completely dissolved using 2moles Al to 1mole ketone and 3mole alcoholic MeNH2.

loki · guinea pig

when making amalgam isn't the idea to have the Hg adsorbing onto the aluminium? sorry if that's a stupid question, i just recall all the hoo har about aluminium thickness for amalgamations and assumed this meant that it wasn't to be dissolved, otherwise thin foil would have been reccommended (which dissolves more readily due to surface area). if i'm wrong about that, then aluminium powder would be better than grains.

possibly a finer grade such as 50-100 micron would be more suitable? A way to turn those bigger beads into thinner material would be to put them between two sheets of steel and press them flat with a vise or by putting two pieces of wood either side and slamming the thing for dear life - that'd get them a bit skinnier.

primathon · modified

I think you should be VERY careful about the amount of heat that much surface area may produce. Proceed cautiously...

Pastor John Hagee · Mon Jul 11, 2005 6:49 am

Why not add it in four portions over time, with addition of 1/4th of your total portion of HgCl2 before each portion of the Al?

The_Dude · Mon Jul 11, 2005 6:56 am

Joe is an environmental hazard.

Joe can use about a tenth of the amount of Hg salt.

Joe should keep that Al powder for fun things, like thermite.

Pastor John Hagee · Mon Jul 11, 2005 7:15 am

.. or making finely divided Urushibara Ni maybe?

bio · Working Bee

Keep them cards and letters coming. Here are some comments.

................when making amalgam isn't the idea to have the Hg adsorbing onto the aluminium? .........................

The HgCl2 reacts with the oxide coating thereby allowing the active Al to react.
Thicker sheets, .2-.3mm, will dissolve much more slowly which is better for a few reasons. Thin or even thick foil reacts so fast that larger aminations are hard to control.

.............possibly a finer grade such as 50-100 micron would be more suitable? A way to turn those bigger beads into thinner material would be to put them between two sheets of steel and press them flat with a vise or by putting two pieces of wood either side and slamming the thing for dear life - that'd get them a bit skinnier.................

He wants the larger grains but thought of the vise idea or hammering into a mold to conglomerate them but I told him this may screw up the amalgamation due to trapped oxide.

........I think you should be VERY careful about the amount of heat that much surface area may produce. Proceed cautiously...............

Good thinking! Three progressively larger scale tests so far have given a feel for the reaction rate and when to apply heat. He'll keep a bucket of ice water handy and use a waaay oversized vessel.

To reduce the surface area Joe is considering straining out the smaller grains.

................Why not add it in four portions over time, with addition of 1/4th of your total portion of HgCl2 before each portion of the Al?.......................

Was thinking along these lines of three to five additions over 2 hours but amalgamating all but the first portion separately for 15-20 minutes then adding carefully with the solution. This was done succesfully with foil.

I wonder if adding the HgCl2 directly to the reaction followed by the Al as you suggested would work as well as preamalgamating. As it is simpler it would be preferable to lazy Joe!

Have you had good results doing this?

........Joe is an environmental hazard..................

Maybe you are dumping the stuff but Joe recovers all his Hg.

.......Joe can use about a tenth of the amount of Hg salt............

Not necessarily Dude!

This depends on the thickness of the oxide layer, the surface area obviously and other factors. Grains have hundreds of times more surface than sheet. Do you think maybe perhaps it has more oxide proportionaly to the weight compared to foil? You can't use too much but can use too little.

Also the amalgamating solution is only a little more than it takes to cover the Aluminum. Two kilos fit in a 1.5L jar and a 100grams of foil balls half fills a 6L flask. 300mg/L might work for 1/4mm sheet but it ain't working for this stuff.

..................Joe should keep that Al powder for fun things, like thermite.........

It;s not powder BTW read the post again. Welding with thermite is no fun to me or watching it burn for the hell of it.

.. or making finely divided Urushibara Ni maybe?.............

Now that's a good idea. Maybe Raney nickel too with the sieved finer grains.
Al Isopropoxide anyone?

Thanks for all the input folks and Joe will keep you posted. That is, if he lets me know what's going on as he hinted this should be kept secret.
Surprised

bio · Working Bee

Contrary to popular opinion, including mine, reduction with this form of aluminum is NOT difficult to control. In fact foil reacts much faster, the reaction rate is comparable to sheet metal in the .3-.5mm range. I'm not sure I understand why this is, these are the observations:

The aluminum granules were sieved to about .2-.3mm sized grains. This was approx 1/3 of the purported 10 mesh size RA product.. Observed with a magnifying glass the particles range from rough spherical to jagged irregular shape. There are some flakes also. Without cleaning or other preparation the grains were amalgamated with HgCl2 (3g/L) in wet MeOH (.5% water added) using 15ml/g. The first portion in-situ and the 2nd and 3rd separately. Incremental addition was found to be not required.

In a 1L FBBF directly on the hotplate stirrer was added 1.5g Al and 67.5ml amalgamating solution. Hydrogen evolution began in 5 min and after 10 min
was gray/murky with some internal heating. At 15 min, 147mM methylimine in 250ml MeOH containing 300mM excess methylamine, was added over 10 min.
At the 30min mark 1.5g of amalgamated Al with the solution was added. Gentle heat was started at 45min and 1.5g amalgam was added to the refluxing mixture at the 60min mark.

At the 12 hour mark much Al remained and 2ml 50% NaOH added. Then another
2ml at 14hours. Some Al metal remained at 18hours and the reaction was terminated.

Workup returned slightly less than the usual yield of the expected product.
This was determined to be due to not all the Al dissolving, insufficient excess and perhaps delayed heating?? The imine also was in the refrigerator for 24hours but I doubt this would affect anything??

Next run will be larger with a few modifications! More excess, longer time etc.

Any input out there to help me tweak this baby??
It's much appreciated from those with much experience in this type reaction.

bio · Working Bee

OK, got it figured out and working much better.

Using a 2% HgCl2 solution, just enough to cover (1ml/g Al), amalgamated the Al in 10 minutes. Boiled on the exotherm in 15min and on it's own for 90 minutes with the granuals lasting about 12 hours.

Runs hot and fast like foil lasts like sheet and is easy to control! Traces of cutting oil were discovered and removed with hexane. This caused some problems prior.

icecool · Insistent Chemist

SWIM always uses thin foil, which has been shredded in the mixer.
But he doesn't get that great yields.
Could it be because of the too thin Al foil, he does stirr it very well, so all the foam that would evolve gets mixed into the liquid and thus bubbles threw it....

bio · Working Bee

Problem with foil (even the extra heavy duty) is that it dissolves too fast.

There are two ways around this. Run the reaction as fast and hot as possible (addition rate). The reflux condensor if 24/40 should be almost choking. If the reactants are added when the foil is almost gone it does no good.

Adding the nuggetized foil in portions (say 3 over 90min) will keep the reaction going long enough. Preamalgamate the foil, timed just right, then dump it in solution and all.

You should be able to get over 80% yields.

icecool · Insistent Chemist

Hmm, okay I get it a bit could you descripe it a bit better since this is the only problem I have and that would solve it and I would be very happy with it.
So next time SWIM'll reduce 10g 2,5-dimethoxynitrostyrene, how would he go about amalgamation.
SWIM has never done pre-amalgamation if you could explain that a bit more on how to go about that.
And if the foil is too thin it will dissolve too quickly, does that matter then, I thought when all the Al is dissolved it all reacted so all the nitropropene or nitrostyrene is reduced?
And when heating it up like you say, wouldn't that be the same as using thin foil at a lower temperature or adding it more slowely.
At the moment normally SWIM grinds thin kitchen Al foil to little shreds and adds a part of it and then adds more later on in 3 portions, so when everything has dissolved he adds more...
The reaction takes about 2-3 hours normally and then most of the Al is dissolved and he uses the double amount of Al as the nitrostyrene/propene.
So for 5g P2NP he uses 10g Al foil same goes for the 2,5-dimethoxynitrostyrene.

bio · Working Bee

.................never done pre-amalgamation.....then adds more later on in 3 portions, so when everything has dissolved he adds more...

This simply means to amalgamate the Al separately from the reaction when adding in portions. The Al must be "activated" before it will react.

...............I thought when all the Al is dissolved it all reacted so all the nitropropene or nitrostyrene is reduced?............

The Al will react with the water and/or alcohol also so this is not necessarily true.

...................when heating it up like you say, wouldn't that be the same as using thin foil at a lower temperature or adding it more slowely..............

The idea here is to have all the reagent added before the Al is mostly gone. The Al will boil the alcohol without heat added in the beginning. So you can't run any cooler than the boiling point of the solvent.

................The reaction takes about 2-3 hours normally and then most of the Al is dissolved and he uses the double amount of Al as the nitrostyrene/propene..........

It depends on the particular reaction parameters and I'm not really that familiar with the PNP reduction. For a 1 electron reduction generally 1.5-3 Al:1.0 substrate
in MOLES is enough, any other way of measuring it is meaningless.