In the course of investigating the preparation of LAH from sodium aluminum hydride it came to my attention that triethylaluminum is useful as a
catalyst in prep of the sodium compound.
The most straightforward prep of the triethylaluminum is from ethyl bromide and turnings of an alloy of 70 Al 30% Mg. Upon digging up the original
publication it came out that this is or was a Dow Chemical product under the trade name Magnalium.
Further it appears that a 50/50 alloy of same name is used in fireworks and is sold packaged as a mix on powder of various mesh, and turnings.
I am only interested in the turnings and not in the 50/50 alloy but in Al 69-70/Mg 30-31.
Anyone have any suggestions on sourcing?DJF90 - 1-4-2009 at 06:33
Can you not use the 50/50 magnalium turnings with additional aluminium turnings to make it up to 70/30?Sauron - 1-4-2009 at 10:15
J reckon not. *f I could do so then I could simply use a mix od Mg turnings and Al granules, couldn't I? There would be no need for an alloy at all.
"Magnalium" ps a;;egedly made in compositions from 5% Mg to 50% Mg the rest Al. garage chemist - 1-4-2009 at 10:35
Alloy the elements yourself, using a protective molten salt cover over the melt.
Melt the Al in a crucible under NaCl+KCl+NaF (this salt mix can dissolve Al2O3 when molten, making it an excellent flux), add the Mg in solid form,
let it melt, stir it a bit, let cool.
Drill into or grind the ingot to make turnings.
Go to the backyard metalcasting website and forums if you need inspiration on how to make a propane fired Al melting furnace.
[Edited on 1-4-2009 by garage chemist]Sauron - 1-4-2009 at 11:12
g c, this has been an off the shelf product since the 1930s and I do not wish to turn it into a DIY metallurgy project. Should I buy a lathe to make
my own turnings?
If the alloy is elusibe I will buy triethylaluminum instead.
Or just react ethyl bromide with Al granules and reduce the "sesquibromide" with Na. That works. The point of the alloy turnings is, fewer
steps/higher yield.DJF90 - 1-4-2009 at 13:28
Ok another suggestion for you sauron. React the aluminium with the ethyl bromide to afford the sesquibromide. Using dioxane as the solvent, the
schlenk equilibrium may be shifted to favour the aluminium trihalides, as it does with grignard reagents:
3 RAlX2 <=> 2 AlX3 + AlR3
and
3 R2AlX <=> AlX3 + 2 AlR3
The equilibrium can be shifted further by distilling off the trialkylaluminium from the mixture. However you may face troubles with this as the
dioxane boils lower. Perhaps the trihalides are insoluble? This would also shift the equilibrium.
Just an idea, but perhaps it could lead somewhere. Maybe not.Fleaker - 1-4-2009 at 13:52
Goodness gracious! This can all be done easily. Sauron can simply melt the aluminum and magnesium in a muffle furnace. Flush it with SF6, flux with
what garage chemist suggest to remove surface oxides. This must be done in a graphite crucible.
The alloy is exceedingly brittle and can be broken cold or when hot short into nice pieces, which ball mill well, or can be wrapped in a heavy cloth
bag and pounded on with a heavy hammer.
Probably would take all of an hour to do.chemoleo - 1-4-2009 at 14:04
Quote:
The most straightforward prep of the triethylaluminum is from ethyl bromide and turnings of an alloy of 70 Al 30% Mg.
How is the reaction carried out? Reflux of the allow in excess EtBr?
I didn't realise that Al-alkanes are obtained so easily!Sauron - 1-4-2009 at 14:16
Trialkylaluminums form etherates so ethers are undesirable as solvents.
If it were not so one could form the Et3Al quantitatively from AlCl3 and 3 EtMgBr or 3 EtMgI but we do not want and cannot use the etherate as
catalyst in the prep of NaAlH4 in toluene. What is needed is the neat Et3Al or (commercially available) its soln in toluene.
Actually the sesquihalide is not so unusable. From the mixture of EtAlBr2 and Et2AlBr, by reducing the dibromide with Na the pure Et2AlBr can be had
in 50-60% yield. This is then further reduced with Na to Et3Al. Having the Al/Mg alloy just makes things simpler and more efficient.
Garage chemist's suggestion is not that bad either, Mg melts 110 C lower than Al, Al melts at 660 C, the alloy will likely be lower melting than
either. I have an 1100 C tube furnace 2" x 12" so a vycor tube abd a boat and an inert atmosphere and we are all set. The alloy ought to be brittle.
Sorry, fleaker, I did not see yur post till after writing this,
Chemoleo, the JOC paper and the Brauer pages based on it are posted above.
Yes, alkylaluminums are easy if you can handle the pyrophoricity. I just looked at the ATBOIC volume on organometallics (1930s) and the lit. goes far
back. The earliest preps were from R2Hg which I would rather not work with. But the simple reaction with RX and Al to obtain a mix of RAlX2 and R2AlX
is, as the 1940 JOC article mentions, long known but mostly ignored.
That all changed when Et3Al was found to catalyze the low pressure polymerization of ethylene. By the way the industrial prep of Et3Al is from
ethylene, Al and H2. Pressure of course.
I hope Fluka or another European vendor offers triethylaluminum in toluebe. From USA this would be a hazmat deal killer. Been down that road before.
[Edited on 1-4-2009 by Sauron]watson.fawkes - 1-4-2009 at 15:12
"In aluminum-rich alloys, the eutectic temperature is 450 °C (840 °F) and the concentration is 35% magnesium." from <i>Aluminum: properties
and physical metallurgy</i>, by John E. Hatch.
Found with Google by searching for "aluminum-magnesium-eutectic".Sauron - 1-4-2009 at 15:30
Thanks. As I surmised. The melt could be done in pyrex with likely sacrifice of the flask. 30/70 is not far from the 35/65 eutectic. How much Si will
enter the melt at the softening point of the borosilicate?
Thanks.zed - 1-4-2009 at 22:16
You might Inquire to the folks at Firefox. They have a pretty impressive inventory. They don't list the 70%+30% Alloy, but they might have some, and
since you only require turnings......Shipping should be no problem. http://www.firefox-fx.com/a_bab - 2-4-2009 at 00:31
Firstly, I really doubt that the 70:30 Al:Mg has any use in pyrotechnics, hence Firefox is *very* unlikely to carry it.
Secondly, this alloy it's not going to be brittle at all. Starting from 55% of either the Al or Mg in the alloy, the britleness is drastically
reduced. Pretty much like trying to crush a Zn bar. Kind of brittle, but it won't break when pounded.
Making the alloy yourself is not that difficult, but it may be.
It's hard to heat the pyrex while avoiding the softening, because in order to achieve the needed 600 degrees C you need a hot flame, and especially a
large flame. I'd say the glass is out of question.
A metal can should be used instead (thats the classical way), and the most elegant solution would be either an adaptation of a microwave oven (with a
ferrite crucible) or an electric oven.
But somehow I suspect that although Sauron has the experience to do it, his age (no offence intended), location for experimentation and God knows what
other factors might not allow him to do it, because after all it's a smelly dirty job to melt metals. It may also draw unwanted attention.
As an idea, there are plenty of (pyro) forumites around here with enough experience of making magnalium who may be willing to help our valuable
member.Sauron - 2-4-2009 at 03:41
Perhaps, a-bab, your callowness and lack of insight (no offense intended) can be fprgiven. Pyrex may be out, vycor is not, flame is not required, I
have a 1100 C tube furnace with a 2" x 12" bore, so keep your metal can. 600 C is a cakewaalk for this furnace.
I have melted metals before. I have melted Ag, and I used to cast my own bullets out of Pb/Sb wheelweight alloy. I have melted NaCN/KCN to case harden
steel.
If the pyro suppliers don't carry this alloy, then they don'y get my money.
There's a Taiwanese company called Magnalium that specializes in Al/Mg alloys from 5-50% Mg and I am a lot closer to Waiwan than to Europe or USA. I
guess I will drop them an email.
There are still lots of options on the table.
I requested an alloy quote from the Taiwan company.
Also found that Alfa sells triethylaluminum, 94% 100 g $150 in nonreturnable cylinder. I will see if I can buy from their European office to avoid
hazmat. If not I am sure some other non US supplier will sell it, and as a typical catalyst charge for a run to produce 250 g NaAlH4 is 2 to 4 ml, it
will be a while before I would need to reorder. 100 g is c.125 ml, d 0.83 Enough to make 8 to 15 lbs LAH.
[Edited on 2-4-2009 by Sauron]a_bab - 2-4-2009 at 09:21
In no way I wanted to offend you. I'm already starting to feel old, probably too old hence my issue. But it certainly looks like you are not very keen
about making the alloy yourself, and that would be understood, as I wouldn't too if I were you.
With your electric furnace, it should be a piece of cake. And don't forget that the shavings can be obtained by drilling the block of your alloy with
a good metal drill bit. Certainly cheaper than buying a lathe...
Al 69-70%/Mg 30-31%
argyrium - 2-4-2009 at 09:47
Sauron,
You might try contacting Bonnie or Ken Kosanke. They consult and publish to the energetics community, amongst other things.
Years ago, I received a set of obscure alloy combinations from them for testing (in pyrotechnics). They may be able to steer you towards a source.
[Edited on 2-4-2009 by argyrium]Sauron - 2-4-2009 at 11:21
Not to worry, a_bab. My aversion is to unnecessary DIY when a little legwork will turn up either the alloy, or a triethylaminum sorce. Or a
worksround prep that needs no allow. As it happens I will probably have all three options.
I do own a small drill press, having sold my big floor standing drill press when I opted to get out of cabinetmaking while still in possesion of all
my fingers. It was the least of my machine tools. A milling machine would be the best way to reduce the Al/Mg to chips. Even a tabletop mill/drill
would do it. But silly to go buy one for this.
Al and ethyl halide (sans solvent, under N2, bone dry and O2 free) the so called ethylaluminum sesquihalide Et3Alx3 which is really a mixture of
EtAlX2 and Et2AlX. These can't be fractionated. So far I have found three ways to obtains the Et2AlX which is what is needed to get the Et3Al.
1. Use the Mg/Al alloy, this reduces EtAlX2 in situ
2. Reduce sesquihalide with Na
3. At least in the case of the sesquichloride, EtAlCl2 complexes with NaCl, Et2AlCl does not, so now fractionation succeeds.
Ref. Ann. vol 629, p.33
The Mg/Al alloy is the most efficient way but in the end, Al and ethyl halide (sdp the chloride and bromide) are cheap so who cares? I only need 100
gl triethylaluminum and it isn't the sort of thing you would want to have in bulk anyway.
And thanks for the link, argyrium.Sauron - 2-4-2009 at 12:49
It is probably time to start a thread on preparation of LAH
