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Author Topic: Lithium Borohydride / Lithium Aluminium Hydride  (Read 199 times)

no1uno

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Lithium Borohydride / Lithium Aluminium Hydride
« on: July 22, 2010, 11:37:30 AM »
I'd like to see a decent hydride synthesis available, utilizing the pretty-much 1g/AA battery of Lithium that is OTC (or 7 batteries per mole).

There really are two routes, but both require the preparation of Lithium Hydride, then that is treated with ethereal AlCl3 or ethereal BF3 to give either the LiAlH4 or LiBH4, either of which would be a nice addition to the arsenal.

Has anyone got a synthesis for Lithium Hydride? I'm going through the Inorganic Syntheses Volumes (I'm sure I've seen it), but as Li has a melting point just under 200'C, then passing INCREDIBLY dry H2 into the molten metal in a solvent would be the obvious route...

The Boron Trifluoride is WAY easier to make than the Aluminium trichloride (although the Schlessinger procedure using HCl(g) seems easier than most), so the LiBH4 would probably be way easier to make (although none of this is overly easy).

EDIT

OK - I've got some papers - had to grab them out of Brauer, Vol.1

Preparation of Alkali Metal Hydrides (LiH looks like a biatch), Diborane and the Borohydrides, plus I have requested bulk articles in the reference request thread:
« Last Edit: July 22, 2010, 01:54:06 PM by no1uno »
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Sedit

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Re: Lithium Borohydride / Lithium Aluminium Hydride
« Reply #1 on: July 22, 2010, 02:18:25 PM »
LiH is formed from the direct combination of its elements the only issue I forsee its the Melted Lithium attacking any vessle you try to put it in.

Lithium nitride, Made from N2 and Li, readily reacts with H2 to yeild LiH and LiNH2 so theres a possible means, and density could possibly be used to seperate the two by stirring in an unreactive solvent that straddles the the two densitys. One sinks, one floats ect.

Im tryin to make AlCl3 right now as my pet project and its not going as easy as it sounds like it should. Im opting for Cl2 now because this HCl shit just isn't cuting it. Im thinking strong light to dissasociate the Chlorine should make it a cake walk as long as it does not blow up in my face.
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no1uno

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Re: Lithium Borohydride / Lithium Aluminium Hydride
« Reply #2 on: July 22, 2010, 09:44:50 PM »
Looks like a pipe-bomb type arrangement - only 600'C shouldn't be that big a stretch. Dissolve the LiH in THF and treat it with a THF solution of BF3 (given off whenever HF reacts with B2O3) and that will be that. Fuck AlCl3 for mine. I think there is a misprint in Brauer, IIRC the hydrogenation takes place at fairly high (even autogeneous pressure) pressure.
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Re: Lithium Borohydride / Lithium Aluminium Hydride
« Reply #3 on: July 23, 2010, 01:44:44 AM »
The solvent method discussed in the first paper for making LiH looks very sexy and given Lithiums reactivity 200C seems more then reasonible. I lik the idea of heptane since its very easy to get rather pure in arts and crafts store but its low BP could pose a problem.

Personally I would be looking towards Ca(AlH4)2 since its hydride could be made from Calcium oxide and Mg under a stream of H2. CaO + Mg + H2 ? CaH2 + MgO. At first glance it would appear more bang for your buck as far as hydrogen storage goes but it has some solubility issues that LiAlH4 does not have.
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Vesp

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Re: Lithium Borohydride / Lithium Aluminium Hydride
« Reply #4 on: July 23, 2010, 08:11:58 PM »
Do you know of anyone who has add luck with producing BF3, and how they did it exactly? That sounds like a great lewis acid to make/use for various things - but it also sounds like it is one of those synthesis that might be difficult to do in the laboratory in decent yield. I don't see that uploaded anywhere here so hopefully I didn't over look one of the papers.

Quote
A multistage process for preparing pure BF3 from hexafluorosilicic acid, H2 SiF6, comprises reacting H2 SiF6 with oxygen acids of boron and/or boron oxide in the first stage to give hydroxyfluoroboric acid and silica, filtering off the silica and concentrating the hydroxyfluoroboric acid, adding oleum to the concentrate and then heating to form gaseous BF3.
- http://www.freepatentsonline.com/4830842.html

That might be useful if sodium pyrosulfate/Na2S2O7 could be used in place of the SO3. hydroxyfluoroboric acid is produced by the reaction of BF3 and H2O - which I think implies that the H2SO4/B2O3 and fluoride method alone will not produce great yields, as the forming water will likely react with some of the forming BF3 producing hydroxyfluoroboric acid - so a very strong dehydrating agent must be mixed with it as well, such as polyphosphoric acid (as shown on SM its ability to make SO3 out of H2SO4) or perhaps a pyrosulfate, as they decompose into SO3 upon heating and react with water to form NaHSO4.

If BF3 can be produce in an effective and safe manner, it will have more uses than this - such as Friedel-Crafts reactions,  transalkylation, etc
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no1uno

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Re: Lithium Borohydride / Lithium Aluminium Hydride
« Reply #5 on: July 24, 2010, 04:35:02 AM »
Boron Trifluoride (BF3) is the product of adding Boron Oxide (aka Boric acid) to HF - even the shitty HF solution you buy at the car-detailing shops for cleaning wheel rims, it is a gas (bp.-100'C or so). It ain't a problem to generate, getting it pure might be a bit more of an issue, but that can be dealt with by using pure HF:

6HF + B2O3 ==> 3H2O + 2BF3

I've been going through the routes to hydrides and the "easiest" route to LiH is the thermal decomposition of alkyl lithium's - which is known to give the correspondent alkene and LiH (it is why there is a white deposit in old-ish bottles of alkyl lithiums)... For our purposes,

CH3CH2Cl + 2Li ==> LiCl + EtLi =(filter)=> EtLi

(analogous to the preparation of methyl lithium (from orgsyn)).

CH3CH2Li + Heat ==> C2H4 + LiH

Which saves a fucking shitload of fucking around with high temperature/high pressure apparatus. What to do with the ethene I don't know, personally I'd get it as far away as possible from the source of heat and fuck it off, although it can be useful). The only possible use I could think of would be the preparation of dichloroethane which would of course be quite a useful preparation in and of itself (a most useful looking chlorinated solvent, more to the point one which is unobtanium most places). I must have a look around for the preparation details, I know they involve CuCl2 (feel free to post the preparation here if you have it).

I'm about to try and get some papers on the studies of the thermal degradation of alkyl lithiums so that I can see precisely how the reaction works, the better we can understand that, the better we can control the outcomes. Personally I think the home lab-technician should be able to handle making alkyl lithiums from chloroethane (which is just ethanol with HCl/ZnCl2 (the chloroethane boils at about 12'C) distilling straight into the lithium/solvent).
« Last Edit: July 24, 2010, 04:43:33 AM by no1uno »
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Vesp

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Re: Lithium Borohydride / Lithium Aluminium Hydride
« Reply #6 on: July 24, 2010, 05:15:37 AM »
ethene is so easily synthesis that there is no point in focusing on it as a useful by-product in this reaction. All you have to do is make diethyl ether wrong to get ethene ;)

Anyways, BF3 reacts with water doesn't it? I do not believe it is as easy as you are making it sound. A dilute HF solution with the addition of boron oxide (which isn't boric acid, but the anhydride of it) will form BF3, yes -- but than that will almost immediately form the flouroboric acid, which is BF3- H+ -- I have a feeling that it will not be easy to get that back into BF3 -- it isn't with any other lewis acid - maybe I am missing something? I personally think you'll need to heat NaF, H2SO4, B2O3, and Na2S2O7 - or polyphosophric acid (essentially create SO3 in situation)  in order to get decent and pure BF3..
Though, I've never done it, just seems like it would react with water at any possible chance it gets based on the fact that it fumes in air due to vapor...



CH3CH2Cl + 2Li ==> LiCl + EtLi =(filter)=> EtLi

This method looks awesome, however it is unfortunate that it sacrifices half of the lithium, but that might be able to be over came by producing something like MgEt2 and later reacting that with the Li. Perhaps to dangerous to mess with, but Li isn't the cheapest thing.


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no1uno

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Re: Lithium Borohydride / Lithium Aluminium Hydride
« Reply #7 on: July 24, 2010, 12:56:26 PM »
Yeah, it sacrifices half the lithium (just in the formation of the EtLi), but then you sacrifice 3 equivalents of the hydride to form the relevant LiBH4/LiAlH4. The joy of it is, that 7-8 batteries = 1 mole of Li, kind of puts things into perspective doesn't it? 1 mole of the N-(2-methoxybenzyl)-4-chloro-2,5-dimethoxyphenethylamine will weigh approximately, what - 2-CC is ~216 g/mol and methyl salicylate is about ~152g/mol, so we are looking at what at least 350-400g/mol (and the methyl salicylate's availability is why a hydride reducing agent is imperative).

Yeah, it ain't going to be cheap, not by a long-shot, but if it allows access to previously unavailable, extremely useful reagents (that until now we've had to try and work around), it will be worth every fucking penny. Anyway, I don't believe that small purchasers of hydride reagents would get their hands on them for much less than this will cost, with the added benefit of staying WELL under the radar.

As to the BF3, etc. I've attached the relevant excerpt from Brauer - remember it forms a complex with ether (I think it also does with THF - I know borane does).
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Buzzoff

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Re: Lithium Borohydride / Lithium Aluminium Hydride
« Reply #8 on: August 09, 2010, 07:14:35 PM »
It isn't for neophytes, but if you can obtain a Parr High Pressure Reactor, or similar device....

Making your own NaAlH4 (or thereby LiAlH4) is do-able.  It requires access to the pyrophoric catalyst Triethylaluminum, but otherwise the ingredients can, with some searching, be  acquired.

US Patent 4512966

http://www.google.com/patents/about?id=QZY1AAAAEBAJ&dq=us+patent+4512966

There a several interesting discussions on the matter at ScienceMadness.
http://www.sciencemadness.org/talk/viewthread.php?tid=11845&page=2#pid150198
« Last Edit: August 09, 2010, 07:57:52 PM by Buzzoff »
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