kazaa81
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The official Aluminum alkyl derivates (pyrophorics) thread!
Hallo all,
as I'm doing some research in pyrophoric aluminum derivates, I've seen there isn't anything specific in the forum, just something about
"methyl aluminum chlorides".
In the net there aren't so much info about prep. and precautions about these substances; an example is:
http://en.wikipedia.org/wiki/Trimethylaluminium
So, if anyone can share procedures about the synthesis of alkyl aluminum compounds, this is the right thread!
Thanks all for help! 
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BromicAcid
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The relevent thread you talk of is titled Preparation of CH3AlCl2 so although not strictly organic it is still relevent because from this the trialkyl derivatives can be made. The
prepartion described there produces "an equimolar mixture" of dimethyl aluminum chloride and methyl aluminum dichloride. Separation of the
two is possible though chemical means, sodium chloride being able to complex with MeAlCl<sub>2</sub> but not
Me<sub>2</sub>AlCl. Anyway, this synthesis is interesting with respect to trimethyl aluminum because they can be reduced to the trialkyl
derivative, the dichloride being particularly susceptible to the converstion, the reduction as carried out with sodium metal affording trimethyl
aluminum, aluminum metal, and sodium chloride as the products. Excess sodium should not be used. (Or you can replace the chloride on the aluminum
atom on a monochloro alkyl aluminum compound by treating it with sodium fluoride then treat that with excess sodium fluoride to give a complex salt
that disproportionates at 200-300C to give cyolite and the trialkyl aluminum compound.)
The same reaction described in the other thread yields tiralkyl aluminum directly if instead of aluminum metal, an alloy consisting of 2 mol Al to 3
mol Mg is susbstitued, in that case the products are the trialkyl aluminum and magnesium chloride. Additionally the trialkyl compound can be
synthesised in a classical manner from the regular reaction of aluminum with dimethyl mercury  or there is usually some way to make these types of compounds through a Grignard in a simple chemical reaction but
electrolysis of a Grignard reagent with aluminum electrodes also yields the trialkyl compounds.
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mick
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This is just a guess. If you reacted dry aluminium with dry chlorine with no air, AlCl3 with no water. React with methane with dry molecular sieve to
absorb HCl it could be possible to end up with pyrophoric trialkylalumium compounds.
mick
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stygian
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| Quote: |
The same reaction described in the other thread yields tiralkyl aluminum directly if instead of aluminum metal, an alloy consisting of 2 mol Al to 3
mol Mg is susbstitued, in that case the products are the trialkyl aluminum and magnesium chloride. Additionally the trialkyl compound can be
synthesised in a classical manner from the regular reaction of aluminum with dimethyl mercury or there is usually some way to make these types of compounds through a Grignard in a simple chemical reaction but
electrolysis of a Grignard reagent with aluminum electrodes also yields the trialkyl compounds. |
I wonder if an AlB12 electrode were used, could one produce a TEA-TEB mix close to the one used for aerospace purposes?
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kazaa81
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Thank all for the replies!
Don't forget this thread, Al-pyrophoric fans!
I was wondering if it's possible to synthetize alkyl aluminum by electrolysis...I'm also thinking about storage of such substances, under a
light solvent (in case of liquid Al alkyls, density less than the liquid alkyl).
Any pyrophoric Aluminum procedure welcomed!
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stygian
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I've read that even dilute ether solutions of organoaluminums are still pyrophoric, unlike boranes, which are just really flammable below 18
percent.
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mick
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An even better way to make them would be to mix the alkane with chlorine, dry. Add clean Al in a well sealed container and move to a safe distance. It
might need a bit of heat to start the reaction.
mick
They are pyrophoric and when dissolved in organic solvents they could ignite the solvent after exposure to air very fast.
[Edited on 23-11-2005 by mick]
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BromicAcid
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I mentioned in my post the ability to produce trialkyl aluminum compounds via electrolysis. Alkyl radicals will attack aluminum metal to give alkyl
aluminum compounds, hence the electrolysis of a Grignard reagent with aluminum electrodes (or at least an anode) will result in the preparation of the
respective trialkyl compound. Of course the reaction mixture has to be non-aqueous due to the reactivity of alkyl aluminum compounds with water, so
that limits some of the possiblities. [Note that electrolysis of Grignard reagents is carried out with high voltages due to the limited conductance
in ether solutions]. So the key is to find solutions that when electrolyzed yield radicals, such as the electrolysis of ethyl sodium in diethyl zinc,
a 75-87% yield of triethyl aluminum from this situation.
There are of course non-electrolytic methods to prepare alkyl radicals such as the decomposition of aryldiazonium chlorides and the decomposition of
other organo metallics, most famously tetramethyl or ethyl lead which were used in leaded gasoline for just that reason.
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kazaa81
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I was not talking about storing Al alkyls in solution, but under a liquid in which they aren't soluble and/or in contact with air.
Like H2O and chloroform that form 2 separate layers!
Any procedure about Al alkyls welcomed! Personal experience too!
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garage chemist
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kazaa81... first hydrogen fluoride, then mercaptans, then boron hydrides, now aluminium alkyls.
Not one of those experiments was successful, the latter two are pretty much out of reach of most hobby labs, including mine.
From your earlier posts, I conclude that you don't even have a distillation setup, which is crucial for any of your desired substances.
Don't you think you should start with something with which you actually have a CHANCE for success?
[Edited on 24-11-2005 by garage chemist]
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BromicAcid
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Yeah, come on Kazaa, you said at the opening of this thread that you were doing research but all you did was link us to a wikipedia entery on the
subject. Where is the research in that  I mean, you should do considerably
more research, a simple MSDS check on Al(CH<sub>3</sub> <sub>3</sub> states that it 'explodes' on contact with water, so your storage of it in a chloroform layer beneath a water
layer is fundamentally flawed, even if they are not miscible there will still be interaction at the surface, furthermore trimethyl aluminum solutions
are avalible in hexane as a solvent, if you decide to use chloroform as a solvent I would hazard a guess that you might get a vigorous reaction
resulting in aluminum chloromethane compounds and such.
As garage chemist pointed out these are difficult procedures to follow, but we encourage open thought here, just reading about these compounds even if
I never ever attempt their synthesis is interesting enough, but just do some of your own research on them first, it is more rewarding that way.
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kazaa81
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Hi,
with HF I've dissolved some glass when making it, with mercaptanes some was succesful....boron hydrides are still out of reach!
No, I've a distillation apparatus, even if the flask is small (250 ml)...
Sorry, but chloroform and water was just an example of how an Al alkyl would be stored, under a layer of something! Probably this wasn't clear to
you. A better example is white phosphorous under water.
I've see some MSDS and knew of explosion with H2O.
Yes, I hadn't explained very well some things because I had little time at work, but next time be less harsh! 
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kazaa81
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Some data about these compounds...
TriMethylAluminum
Al(CH3)3
CAS # 75-24-1
Mol. 72,09 g/mol
M.P 15°C
B.P 125°C
Density 0,752 g/cm3
Pyrophoric, explode with water
TriEthylAluminum
Al(C2H5)3
Mol. 114,17 g/mol
M.P -52°C
B.P 194°C
Density 0,835 g/cm3
Pyrophoric (forms Al2O3), explode with water, caustic on skin
TriIsoButylAluminum was the pyrophoric igniter used in some napalm bombs in Vietnam (called TIBA or TIBAL).
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liwenbinyk
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,hallo,I am so glad learn some from here, thank you.
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