MagicJigPipe
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Synthesis of LiAlH4 Starting from "Scratch"
Searching revealed (surprisingly) a very small amount of threads about lithium aluminum hydride (LAH) and none concerning it's "complete" synthesis.
I found this strange because of (a) How expensive it is and (b) how difficult it is to obtain.
After some quick research I have come to the conclusion that the easiest way for an ametuer to produce the compound is via LiH and AlCl3, both of
which should be able to be easily made in an ametuer lab.
LiH
Does anyone have any specifics (or experience) on the reaction between H2 and Li?
LAH
Does anyone have any actual experience with preparing this compound via LiH and AlCl3? If so, what is your experience?
Is this feasible in practice or just in theory? From reading some older texts (and Rhodium, why is it on there? A certain stimulant?) I know the
reaction is supposed to work. I'm just trying to find out if anyone has tried it and, if so, if they would share their experiences and/or discuss
it's feasibility. This would be an excellent reagent to have around the lab. Especially, if it could be produced for a fraction of the "retail"
price.
Also, if there is a reference I am missing it would be great if someone could point me towards it. I simply looked through the references I have on
my computer as I didn't think there would be too much information about this "old" reaction on google.
(My apologies if there is a thread on this already, I really did search the forum under the "General Chemistry" section)
[Edited on 5-28-2008 by MagicJigPipe]
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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Sauron
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Rhodium has a page on the preparation of LAH from LiH and AlCl3.
The problem devolves to obtaining lithium hydride.
You might look in Brauer and see how to prepare LiH from the elements.
Can you purchase lithium metal where you are? I have a couple of hundred grams in oil.
But I also have about a Kg of LAH so I won't have to make any from my precious lithium.
Obviously in the prep of LAH you will need scrupulously anhydrous reagents, equipment and conditions. The usual LAH solvents are required (Et2O, THF).
You had best be well prepared for the possibility of a nasty fire.
[Edited on 30-5-2008 by Sauron]
Sic gorgeamus a los subjectatus nunc.
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garage chemist
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There are detailed instructions for the preparation of LiH and LAH from this in Brauer. Look in the library.
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Nick F
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What about using NaAlH4 and LiX instead of LAH? Sodium metal is generally much cheaper and easier to get than lithium. Would you perhaps run into
solubility problems? If you can dissolve them in your ether then I imagine NaX would just ppte.
I know the Li is important, because LAH is much less effective in the presence of 12-crown-4.
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MagicJigPipe
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Wow, duh! That is the one reference I didn't look at. Not on purpose, though. I have so many books I just somehow skipped over Brauer.
Thanks for the advice.
From Brauer:
| Quote: |
Lithium Aluminum Hydride
LiAIH4
I. 4 LiH + A1C18 = LiAlH4 + 3LiCl
For the reaction between LiH and A1C13 to occur to a noticeable
extent, the thick, hard lumps of lithium hydride must be ground to
a very fine powder and then sieved. This treatment is performed
under nitrogen. A very reactive ether suspension of LiH is obtained
if the material is wet-ground with anhydrous ether in a special ball
mill (K. Ziegler et al.) and used immediately.
A fresh suspension of 23.5 g. (2.96 moles) of LiH in 200 ml. of
ether is introduced (with exclusion of moisture) into a threeneck
flask provided with a dropping funnel, a reflux condenser and
a stirrer. A solution of 71.2 g. (0.534 mole) of A1C13 in 300 ml. of
ether is then added in drops with vigorous stirring. The reaction
starts immediately, as shown by the boiling of the ether. The rate
is kept uniform by adjustment of the addition rate. When all the
A1C13 solution has been added, stirring is continued until the reaction
has subsided, and the mixture is left to stand for some
time. The contents of the flask are then filtered, using nitrogen
pressure, through a fritted glass filter, and the clear filtrate is
concentrated at atmospheric pressure until it has a syrupy consistency.
The residual ether may be evaporated in vacuum at
70°C. The yield of LiAlH4, based on A1C13, is about 85%.
Insufficient grinding of the LiH may prevent the reaction from
starting spontaneously, or from going to completion, and lead to
sudden, explosive bursts of renewed activity; in such cases the
reaction is started by adding 200 ml. of ether, followed by a solution
of 3 g. of LiAlH4 in 30 ml. of ether, to the finely divided LiH.
The subsequent procedure is the same as described above. According
to Wiberg, a slight quantity of iodine may be used as an
initiator instead of the LiAlH4.
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After reading it I realize that it may not be as easy as I thought but still doable.
Apparently a glovebox would be good to have for grinding the LiH under dry N2. Alternatively it suggests that you ball mill the LiH while wet with
Et2O. IMO, that would be the easiest thing to do. All that would be needed is a ball mill "cylinder" that could be either purged with inert gas or
made completely sparkless and designed to hold ether. Of course the former two are already done on a regular basis but the latter, IMO, should be
quite easy to accomplish. Also, I assume the ether must be dried with Na. I expected that, however.
It appears that Rhodium simply copied (almost verbatim in some parts) Brauer.
Now, on to LiH preparation.
EDIT
Also, Sauron, AFAIK none of the alkali metals can be purchased in my area (along with most other chemicals) so I would have to purchase it online,
which is not a problem. Of course I could get it from lithium batteries but that's stupidly expensive. The only thing that would thwart that is to
resort to stealing which I am not prepared to do.
I wonder if the difference in cost between sodium and lithium would be worth the extra trouble to make NaH? Of course, the increased reactivity of
sodium compared to lithium would be another thing to take into consideration.
[Edited on 5-29-2008 by MagicJigPipe]
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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DJF90
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How does NaAlH4 stack up against LiAlH4 in terms of physical and chemical properties. I expect them to have similar reducing ability, solubility will
probably vary to some degree, and one of them might be more reactive (I know sodium metal is more reactive than Li, but is this also true for the
tetrahydridoaluminates?) Sodium is much easier to obtain either by ordering or made via electrolysis of molten salts, as documented in the "hot
electrochemical sodium" thread (and also a few other methods), and so from that point of view NaAlH4 is more "accessible" to the home chemist.
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MagicJigPipe
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I read the Brauer synthesis of alkali hydrides and even though LiH requires a higher temperature, it is less reactive towards O2 (apparently NaH
ignites in air at 260C). Isn't lithium just as easy to produce electrolytically?
I'm still not convinced that Na would be easier to deal with.
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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Sauron
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Rhodium copied (archived) from Hive, Hive contributor copied from Brauer or the literature, Brauer cadged from the literature, with attribution of
course.
Try Alfa Aesar, VWR, Fisher for LiH, Li metal, Lithium tetrahydridoaluminate, anhydrous AlCl3 etc. VWR for example might be skittish about selling
organics to individuals but none of these are organic. I do not know what may or may not be on any DEA "list" or DHS "chemicals of concern" list, or
even if the latter has been put into force yet. I do know that any of the alkili hydrides and certainly LAH will be DOT classed as flammable solids
at least and so you will face stupid hazmat fees.
I got my glove box off LabX from a seller in Springfield MO for c.$300. It is a larger Labconco job and as you are in an adjacent state would have
been cheap to ship to you. If I were you I'd be searching for one. A new pair of neoprene glovebox gloves will cost you more than the box will, if
you buy it right. Tip: wear thin citton gloves inside the neoprene gloves. More comfortable.
Sic gorgeamus a los subjectatus nunc.
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MagicJigPipe
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If the damn gas prices were like they were in the early and mid '90s it would be worth it to drive even a few states over to pick up something like
that. I remember, when I was about 7, driving by a gas station and seeing the price at $.96. A 300% increase in 17 years is definitely not good
seeing as though the mininum wage has only increased by 60%.
Okay, enough OTness.
I'm going to try this with lithium first. It will take me a while to get some of the apparatus. Until then I'll be looking for a source for the
chemicals. I will look into those companies, Sauron.
I'm still wondering why noone has tried this considering it apparently has "illigitimate" uses. Perhaps I shall go ask over at WetDreams but I
really, really, really don't want to go over there.
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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panziandi
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This pdf is a technical bulletin on NAH it appears that the reaction rates of some reductions are higher with this reagent vs LAH but also vice
versa... So in some instances it may be better to use NAH!
http://www.albemarle.com/tds/fine_chemistry_services/sc2035f...
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