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Author: Subject: Theoretical Borohydride Production using NaK
Mothman
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[*] posted on 27-2-2018 at 11:25
Theoretical Borohydride Production using NaK


Borohydrides begin with alkali metal hydrides which are then reacted with Trimethyl Borate at elevated temperatures to form alkali borohydrides. In another thread regarding the production of Lithium Hydride the OP explained having to scratch the surface of the lithium to make it react, but of course that requires a lot of work to keep the lithium from reacting with the air again, and the yields were reportedly low due to the Lithium not fully reacting. I propose the use of NaK alloy in place of the lithium metal as it would be a liquid which could be agitated and moved around to fully react it with the stream of hydrogen. The issue is that it would be a terrible source of hydrides as potassium hydride is pyrophoric, and pyrophoric reagents under hydrogen are a terrible idea unless you want to lose some eyebrows. To solve the problem of the eventual opening of the container, I would think that a distillation reciever adapter connected both to a hydrogen generator and a container of Trimethyl Borate would be hooked up to the hydride production container. Once the whole apparatus had been flushed with hydrogen and reacted with the alkali metals, Trimethyl Borate would be distilled through the whole thing, thus keeping air out and resulting in a reaction to form a mixture of methoxides and borohydrides, neither of which are pyrophoric and can be further purified for laboratory use.

I have a few ideas as to how this apparatus could be jerry rigged, as it doesn't require excessive heat, just a little bit (no more than 300oC) to keep it going. Normal borosilicate would be able to house it and I bet that the heating could be achieved using the heating elements from eggmaster rollies as tube furnaces, it's not like they have much use otherwise :D, and they are only 30 USD on average. Hydrogen could be generated and dried as discussed in the LiH thread, and the stirring of the Nak could come from a pair of magnets to slosh the stuff back and forth. It ought to be fine as long as the hydrogen is vented away and the whole thing doesn't just bust open halfway through the synthesis...I just wish I had the materials to give this a shot, even making a tube furnace from an egg cooker would be a blast, but sadly I am broke from my habit of buying chemicals like they are going to be banned the next day...like, what if the feds come for the baking soda because it is used in "cookery"? Gotta buy it all now...:D

Feedback on this would be appreciated, if anyone has given the eggmaster rollie tube furnace thing a shot I know I'd sure love to hear about it, it's been an idea I've been thinking of trying as soon as I get some money in the old wallet!

[Edited on 27-2-2018 by Mothman]




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Assured Fish
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[*] posted on 27-2-2018 at 15:17


Seems I dont see the point, sodium metal melts at 98°c which means it will be a liquid at when heated to the apparatus temperature anyway.
The issue with the lithium hydride likely only occurs with lithium due to lithium melting at 450°c, to solve this I suspect a higher reaction temp would be required.

This asuming of coarse that surface area is the actual issue preventing complete hydrogenation of the substrate.
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subskune
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[*] posted on 28-2-2018 at 05:54


I believe tis is very hard to do safe and high yielded on small scale.
I alyways wondered if this could be done in a one pot synthesis. The idea is to reflux a higher temp boiling boric acid ester (eg. triethylborate) and put the metallic sodium directly in, which is molten then.
I know that carbon esters can react with sodium but the reaction involves a carbon radical at the carboxy group which is non present here, but no idea about the borates...
Hydrogen could then be directly bubbled through, with the ester beeing medium and air protection as well as sodium cleaner at once. But as I said this only makes me curious Ive never tried it!




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Mothman
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[*] posted on 28-2-2018 at 13:23


I forgot how low the M.P. of sodium is, had I remembered it then I wouldn't have seen the point either and not posted this, I feel rather silly now...I do hope the mods will either delete this or move it somewhere other than the board dedicated to smart people :P

In terms of your one-pot method subskune, I don't know enough chemistry to accurately predict the actual reaction but it seems to me like it would simply yield high-purity boron and sodium methoxide. But really, if it isn't obvious by now I do not know much, so take everything I say with a kilo of salt...with some added salt for flavor...




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