Sauron - 29-12-2008 at 22:08
Hard to find any info on these compounds.
Brauer, nothing.
Inorg.Syn., nothing.
Merck Index, nothing.
Paquette, nothing
Acros and Alfa, nada.
Aldrich, nix on Ba(BH4)2. They do sell Ca(BH4)4, but in 1 gr quantity and horrendous price.
Aldrich also has complex w/THF
What gives? Is the prep so much more difficult than Li, Na, K borohydrides?
Anyone have a clue?
sparkgap - 29-12-2008 at 22:15
You have seen this and this, among other things?
Also this patent?
sparky (~_~)
Sauron - 29-12-2008 at 23:01
I had not seen US 2784053, but a few minutes ago found a later electrochemical prep patent US4808282
Here that one is and I will go get the earlier one from freepatentsonline.com
Thanks
The patent you pointed me to claims facile prep by metathesis with NaBH4 in DMF or ethanolamine, in which the alkiline earth chlorides and sulfates
are soluble, but the sodium sulfates or chlorides are not.
So if this works, the Ba or Ca borohydrides are easily prepared.
I will give it a try.
Thanks again
[Edited on 30-12-2008 by Sauron]
Attachment: US4808282.pdf (454kB)
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Sauron - 30-12-2008 at 01:05
Here's the patent sparkie was referring to.
Looks like it nails this one down.
[Edited on 30-12-2008 by Sauron]
Attachment: US2784053.pdf (168kB)
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vulture - 30-12-2008 at 02:25
Might I ask what your specific interest is in these borohydrides?
Sauron - 30-12-2008 at 02:50
The borohydrides prepared according to that aboveposted wet=lab US patent method are described as solvated crystalline solids after removal of DMF or
ethanolamine by vacuum evaporation at room temperature.
I saw another paper where Ca(BH4)2 was obtained from its THF complex by vacuum at 130 C.
And I have a paper from Phys.Rev. reporting the prep of several alkiline earth borohydrides by dry-milling (in a ball mill) LiBH4 and anhydrous
chlorides of Mg, Zn, Zr, Hf, and Cd for five hours - although they did not explain how LiCl was seperated from the product, they did reference a
German paper preparing Zn and Zr borohydrides same way, which probably does include that little detail.
DMF and ethanolamine boil a lot higher than THF. Perhaps, at least in the case of Ca(BH4)2 which I know forms an adduct with THF, taking up the
solvated solid in THF would displace the DMF or ethanolamine? But, on evaporation I suppose we will be back to square one.
I think I had better find out how the Ca(BH4)2 bis-THF adduct is prepared. If it is prepared by metathesis of NaBH4 and CaCl2 in THF, then this would
be the way to go. Because the adduct is definitely busted at 130 under reduced pressure.
[Edited on 31-12-2008 by Sauron]
Sauron - 30-12-2008 at 21:07
Here's the state of play as of now:
1.
LiCl + NaBH4 -> LiBH4 + LiCl.
Isopropylamine solvent; LiCl precipitates and is filtered off. Amine removed, LiBH4 taken up in Et2O and that is also evacuated off. A much nicer prep
than usual one as shown in Brauer (LiH + BF3-etherate).
H.C.Brown in JACS
LiBH4 can also be purchased, but it is a lot costlier than NaBH4 so why?
2. 2 LiBH4 + CaCl2 (anhydrous) dry milled 5 hours yield Ca(BH4)2 and LiCl
No details on separation but product is solvent free
Phys Rev B
Alternate prep:
2 NaBH4 + CaCl2 -> Ca(BH4)2 + 2 NaCl
in DMF or ethanolamine
US Patent discussed upthread. Product is recovered solvated, and solvent of crystallization needs to be driven off in vacuo w/heat.
A 1955 letter to the journal Nature (London) 175, 346 reported prep of Ca(BH4)2 by same reagents in dry THF, Reaction time 4-8 hrs. Brown in
1980 improved on this by use of his "glass bead ball mill" approach and reduced time to 1 hr.
In a 1980 communication to Inorg.Chem. 20 4454 Brown indicted his own prep of LiBH4 above as requiring high temperature to remove IPA solvent,
as I feared might be the case. He advocated using LiBr rather than LiCl and Et2O or THF rather than IPA and reported a convenient procedure for
effecting solutions of LiBH4 in these solvents, NaBr ppts out.
[Edited on 31-12-2008 by Sauron]
Attachment: BoronBrown.pdf (419kB)
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Sauron - 31-12-2008 at 02:37
And here is the end of the story, the 1955 Nature report of the calcium borohydride prep by Hungarian workers, later improved by Brown a quarter
century on.
LiBH4 not required. The reaction uses CaCl2 and NaBH4 in THF. All reactants and solvent need to be anhydrous. After separation of the Ca(BH4)2
solution from NaCl precipitate, by filtration or centrifugatioin, the THF is removed in vacuo leaving the solid borohydride-bis(THF) adduct from which
the borohydride can be isolated by heating to 130 C in vacuo to constant weight.
The salient feature of calcium borohydride is its ability to reduce esters directly to primary carbinols (alcohols) which is something NaBH4 usually
fails to do.
It is also highly selective for reduction of conjugated terminal alenes.
R-C(=O)-OR -> RCH2-OH
R-CH=CH-CH2-CH=CH2 -> R-CH=CH-CH2-CH2-CH3