mysteriusbhoice
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Can KBH4 substitute NaBH4 in ethanol/methanolic solutions for reduction of ketones to alcohol.
I found that KBH4 is half the price of NaBH4 (which is always out of stock) atleast where im at and I wonder if I can directly substitute it for this
application.
few things I wonder.
1. Why is it cheaper as usually wouldnt the potassium salts cost more.
2. Can this be used in other reductions
3. IK it cannot be used in solvents like THF due to bad solubility but can it be converted to NaBH4 or LiBH4 or can addition of some NaOH perhaps
still favor some sort of ion exchange.
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EF2000
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OwO, what happened to poisoned palladium?
Not as useful+lower demand+less notorious (not watched by DEA for example)
If you find a suitable solvent, it should act just as NaBH4. JACS article quoted lower reports similiar yields for reduction of methyl ethyl
ketone, chloral hydrate and m-nitrobenzaldehyde.
Not only THF. It's "insoluble in ethanol, ether and tetrahydrofuran", says Alfa Aesar. 1954 paper in JACS adds:
| Quote: |
One hundred grams of 95% ethanol dissolved 0.25 g. of potassium borohydride at 25 [degrees]. The compound is insoluble (<0.01%) in isopropylamlne,
benzene, hexane, ether, dioxane, tetrahydrofuran and acetonitrile. |
Given that KBH4 can be made from NaBH4 and KOH, I doubt that reverse reaction can be done.
About LiBH4, "Metal Tetrahydroborates" says (read "hydroborate" as "borohydride"):
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Potassium hydroborate and lithium salts (bromide, iodide, and nitrate) may be used but the resultant yield of the lithium hydroborate is low (~10%)
except in the reaction involving lithium chloride in i-amyl alcohol when a 30% yield was claimed (419,420). Other patents have described the use of
dimethylformamide (122), ethanol (302), and ether (357) in similar reactions. The action of calcium hydroborate on lithium chloride in refluxing
tetrahydrofuran also yields lithium hydroborate (253). |
Attachment: Metal Boro[hydrides].pdf (2.4MB)
This file has been downloaded 150 times
[Edited on 13-1-2024 by EF2000]
Wroom wroom
"The practice of pouring yourself alcohol from a rocket fuel tank is to be strongly condemned encouraged"
-R-1 User's Guide
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Lionel Spanner
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I should think it'd be a suitable substitute for sodium borohydride, provided that you account for the difference in molecular weight; the active
species is the borohydride, not the metal cation.
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clearly_not_atara
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I would guess that the difference in MW is why it's cheaper. The borohydride ion is going to be way more expensive than the potassium or sodium.
You're just getting more inactive ion.
In general, potassium salts of inorganic ions are less soluble than sodium salts of the same ion, while for organic or fluorine ions this is reversed
and the potassium ions are more soluble. In a few cases, such as perchlorate (Na >>> K) or oxalate (K >>> Na), this difference is
very large. Potassium borohydride appears to be less soluble, which would be the only major problem. I would also hazard a guess it's a little more
stable.
It's plausible that KBH4 could be converted to NaBH4 by comproportionation with NaClO4, or a similar conversion with LiClO4. The use of perchlorate as
a counterion to precipitate potassium is not mentioned in the above review. But this requires the perchlorates.
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woelen
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Mixing perchlorate and borohydride may be risky. In aqueous solution, I do not expect any issues, but when an intimate solid mix is prepared of the
two ions, you may run the risk of unwanted ignition. BH4(-) ion is a very strong reductor, while ClO4(-) is a strong oxidizer! Keep that in mind. When
preparing NaBH4 from NaClO4 and KBH4, I absolutely would recrystallize the resuling NaBH4 a second time, to be absolutely sure that no significant
amounts of perchlorate remain in the solid. And also: first try with small quantities (at most one gram).
I don't think you can use NH4ClO4 to get rid of the potassium ions as a first step. Ammonium ion may be too acidic for combination with borohydride.
So, if you don't have NaClO4 (which most likely is the case if you are in the EU) and only can get NH4ClO4, then you first have to convert that,
before attempting to make NaBH4.
BTW: It is doubtful whether this thread belongs to the organic chemistry section. The initial question makes it fit to this section, but how this
threads develops is more towards inorganic chemistry.
[Edited on 15-1-24 by woelen]
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clearly_not_atara
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I agree with moving the thread. And the concerns about solid mixtures of borohydride and perchlorate seem well founded.
On further consideration of the above evidence, I think that the salt metathesis of KBH4 with LiCl in isopropanol, possibly refluxing, is worth
considering. Isopropanol is considered unreactive with sodium borohydride:
https://pubs.acs.org/doi/pdf/10.1021/ja01628a044
It also probably dissolves KBH4 better than isoamyl alcohol, giving a faster reaction, but has a similarly low solubility of KCl.
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woelen
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Thread Moved
31-1-2024 at 00:18 |
EF2000
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A bit off-topic, but still related to potassium borohydride. There was an article Potassium borohydride on Wikipedia, but it was deleted for some stupid reason. It's a waste, cause the article was good, with a lot of sources.
Maybe someone with a "good standing" there can request un-deletion?
Wroom wroom
"The practice of pouring yourself alcohol from a rocket fuel tank is to be strongly condemned encouraged"
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clearly_not_atara
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^I think you'd have a better time contributing to the Sciencemadness Wiki. Wikipedia usually wants "secondary sources", i.e. not just studies, which
are not always so easy to find, although I did find one:
https://pubs.acs.org/doi/pdf/10.1021/ie50574a021
Incidentally, this article seems to clear up some of the confusion in the OP. It mentions that KBH4 is much more air-stable than NaBH4 or LiBH4, which
probably makes it cheaper to supply.
This stability suggests that KOH might give better results and easier work-up in the preparation of borohydrides from MgB2:
https://www.sciencemadness.org/whisper/viewthread.php?tid=31...
Incidentally, I wonder if you could improve the process by including some additional Mg metal in the rxn mixture since MgB2 contains too much boron
and not enough electrons.
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