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Author: Subject: Preparation of NaH from sodium metal.
draculic acid69
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[*] posted on 29-6-2021 at 00:44


What is RM R2M RMX?
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[*] posted on 29-6-2021 at 02:41


Quote: Originally posted by draculic acid69  
What is RM R2M RMX?

R - a carbon chain
M - metal
X - a halogen
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S.C. Wack
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[*] posted on 29-6-2021 at 14:16


It's a sign that beta-hydride elimination is a deep organometallic rabbit hole.



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[*] posted on 30-6-2021 at 04:49


Might the same concept apply to more easily obtained alkoxides? Equivalent beta elimination would give a carbonyl and hydride, right?



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[*] posted on 30-6-2021 at 07:54


Quote: Originally posted by njl  
Might the same concept apply to more easily obtained alkoxides? Equivalent beta elimination would give a carbonyl and hydride, right?

It would give a hydroxide and an alkene if it happened the same way.

[Edited on 30-6-2021 by Jenks]
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[*] posted on 30-6-2021 at 12:55


No, elimination of a beta hydrogen + electron from an alkoxide would give a carbonyl and hydride, elimination of hydroxide from an alkoxide is different and would give the alkene. I'm asking if beta hydride elimination with alkoxides is a viable path for hydrides ie elimination of hydride from methoxide to give formaldehyde.



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[*] posted on 22-7-2021 at 17:59


Quote: Originally posted by S.C. Wack  
Quote: Originally posted by draculic acid69  
I think that Li reacts with the H2 around 60'c which is a bit easier than molten metals.


500

The easiest route to hydrides (not in the literature as a preparative method AFAIK) is by heating RM (R2M or RMX for Mg, etc) in oil.

[Edited on 28-6-2021 by S.C. Wack]


You can't stop there, especially when youve said the method cant be found in the lit (and this from the lit guru, one is inclined to believe you)
So dont be coy, time for shyness is over, off with your pants, what do you know, is it a huge one you are hiding, i dare say it is, as rm, rmgx's are a bit of a no brainer to make

Sorry if the sexual reference offends any....
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[*] posted on 22-7-2021 at 18:05


Quote: Originally posted by S.C. Wack  
It's a sign that beta-hydride elimination is a deep organometallic rabbit hole.


oh and then this.....haha

here ill make it easy

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S.C. Wack
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[*] posted on 23-7-2021 at 16:07


It would be one of those reactions listed under formation (Bildung) rather than preparation (Darstellung), if it's listed anywhere at all. Yes, many organometallics are easy to make if the perfectly inert environment is provided for, and easy to decompose with enough heat (let's say 150-200C), this is what I know.

This elimination has been a noted reaction of all kinds of expensive organometallics when people are trying to make something else with maybe a little too much heat. No clue of the yield or purity of any hydride (when a metal hydride is formed) from the process, because AFAIK the hydride is completely ignored because no one cares, except maybe for noting that something found to be the hydride was identified. This is going back to at least 190-something (for Mg), if not earlier.




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S.C. Wack
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[*] posted on 24-7-2021 at 21:57


Quote: Originally posted by Panache  
(and this from the lit guru, one is inclined to believe you)


I've read very little of the organometallic original literature (none at all in German or French) however, and am as infallible as Catch-22's protagonist: ‘You’re going to be all right, kid,’ Yossarian assured him, patting his arm comfortingly. ‘Everything’s under control.’ Snowden shook his head feebly. ‘I’m cold,’ he repeated, with eyes as dull and blind as stone. ‘I’m cold.’
‘There, there,’ said Yossarian, with growing doubt and trepidation.


...but I'm good at quoting fiction. There's no doubt that hydrides can be formed in this way, but whether they should is unclear.

A brief search gave an example where the yield of metal cpd. is given. It's 95% but unfortunately there's no beta carbon, much less hydrogen, and thus no hydride. Heating methyllithium to 225C, etc., gives CH2Li2 and methane. If they still had Star Trek conventions, one could make an impression, and get the bomb squad called and venue evacuated, with (amorphous) (methylene)dilithium "crystals".




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[*] posted on 10-8-2021 at 14:50


With the more reactive metals, hydrides can be made without heat from RM and H, easily, sometimes, says JACS 60, 2336 (1938). This works with sodium but is better with the heavier alkalis. BTW previous articles from that year are interesting...at p. 1019 (EtMgBr, vacuum, 220C, using the residue to reduce benzophenone) and p. 2333, where phenyllithium is added to slightly hydrogenated rings and refluxed in ether, producing the aromatic and LiH.



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[*] posted on 11-8-2021 at 00:09


Quote: Originally posted by rockyit98  
Thoisoi2 - Chemical Experiments! uploaded: This Chemical is Not from Our Planet! shows how dangerous NaH is


Demonstration of NaH starts at 08.40,

https://youtu.be/4EkbcBJnJk4?t=520
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[*] posted on 2-10-2021 at 18:57


Quote: Originally posted by Bedlasky  
Quote: Originally posted by Monoamine  
Quote: Originally posted by rockyit98  
Sodium react with hydrogen to produce sodium hydride. This reaction takes place at a temperature near 300 ° C.
needs catalysts. maybe naphthalene.


Not too familiar with catalysts. Why is naphthalene a catalyst for this reaction?


Sodium react with naphtalene to form sodium naphtenide, which than react with hydrogen gas to produce NaH.

2Na + 2C10H8 --> 2NaC10H7 + H2

NaC10H7 + H2 --> NaH + C10H8


Thank you again for this suggestion. I ran quite a few experiments (sadly without success) but I think I still learned a bit about this whole approach.
First off, to form the salt NaC10H7 the choice of solvent is very important. I tried hexane and paraffin (C16-C18 alkanes according to the MSDS), but the salt barely forms in them, although it may form very very slowly in the paraffin when heated so that the Na melts.
NaC10H7 does however form very well in tetrahydrofuran (THF). The problem with THF, however, is that there seem to be quite a few side reactions and after running the reaction for a few hours you are left with a brown/black goop which seems to react with water.

In either case, if the reaction NaC10H7 + H2 --> NaH + C10H8 proceeds at all, it does so very very slowly.

In an attempt to get some results I also tried adding a 10% Pd/C catalyst (in the hopes that this might help the H2 react with the salt). It's possible that this does slightly work, but the problem here is that the Pd/C seems to react with the Na in THF (at room temperature). It also seems to react with the Na in paraffin, but only at around 80-100oC.

Another issue I realized is that since naphthalene sublimes at around 80oC, it will actually sublime out of solution when you heat the paraffin to that temperature. This is a bit of a catch-22, since the only time I thought I got the reaction to slightly work was when I heated the Na with naphthalene and Pd/C catalyst above the melting point of sodium (around 97.8oC). On the other hand this could also be used as a purification strategy to remove the naphthalene if the reaction is ever successful.

The last thing I tried was just adding a molar equivalent of naphthalene rather than treat it as a true catalyst (since mothballs aren't too pricey), but it seems that if you add that much then the Na just destroys the paraffin and you end up with brown goop.

Am I just doing this completely wrong? At this point I just want to see if this can work...

[Edited on 3-10-2021 by Monoamine]
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[*] posted on 2-10-2021 at 19:04


Quote: Originally posted by rockyit98  
Sodium react with hydrogen to produce sodium hydride. This reaction takes place at a temperature near 300 ° C.
needs catalysts. maybe naphthalene.


Might work under some conditions, but one problem is that naphthalene sublimes out of solution at around 80oC
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[*] posted on 2-10-2021 at 19:46
Just for fun


All this talk about beta-eliminations made me drop a small piece of Na into EtBr and cover it with paraffin. Look's like the Na is floating in the middle right? It's suspended between a layer of paraffin (top) and a layer of EtBr (bottom) (and slowly reacting with the EtBr, but I don't see a precipitate, only bubbles probably ethene (so then where's the NaH or the NaBr??)



EtBr_Na_Paraffin.jpg - 4.6MB

[Edited on 3-10-2021 by Monoamine]

[Edited on 3-10-2021 by Monoamine]
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[*] posted on 2-10-2021 at 21:13


Sodium is melted and shaken in xylene if one wants reactive sodium. But the reaction in this case would be at best the Wurtz, and if ethylsodium was made it would react with the halide, to make not-ethylsodium...which explains why someone might want or make an amount of alkylmercury...just for fun.



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[*] posted on 3-10-2021 at 08:04


Monoamine - is it possible that the brown/black goop formed during the reaction in THF could be due to some impurities? I also found this paper that preformed the synthesis in THF, Dimethyl ether and Glyme/DME. For some reason the reactions doesn't work in diethyl ether.

https://pubs.acs.org/doi/10.1021/ja01303a022

I suspect that diglyme might work as a higher boiling point solvent. If so It might be possible to form the sodium naphthalene in diglyme stoichiometrically, Then bubble hydrogen to precipitate out NaH.

With Na + Pd/C + NaC10H7 + H2 would this not preferentially hydrogenate naphthalene to tetralin, killing it as a catalyst?

[Edited on 3-10-2021 by walruslover69]
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[*] posted on 3-10-2021 at 20:57


Quote: Originally posted by S.C. Wack  
Sodium is melted and shaken in xylene if one wants reactive sodium. But the reaction in this case would be at best the Wurtz, and if ethylsodium was made it would react with the halide, to make not-ethylsodium...which explains why someone might want or make an amount of alkylmercury...just for fun.


Oh I didn't know that. Thanks! I haven't tried any aromatic solvent yet but I might give that a shot. I wonder if toluene might also work (I don't think at these temperature we have to worry about a Birch reduction). If the reaction is refluxed it might also help to solve the naphthalene sublimation issue, since some of the crystals could be washed back into solution by the condensing toluene vapours (maybe...).
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[*] posted on 3-10-2021 at 21:16


Quote: Originally posted by walruslover69  
Monoamine - is it possible that the brown/black goop formed during the reaction in THF could be due to some impurities? I also found this paper that preformed the synthesis in THF, Dimethyl ether and Glyme/DME. For some reason the reactions doesn't work in diethyl ether.

https://pubs.acs.org/doi/10.1021/ja01303a022

I suspect that diglyme might work as a higher boiling point solvent. If so It might be possible to form the sodium naphthalene in diglyme stoichiometrically, Then bubble hydrogen to precipitate out NaH.

With Na + Pd/C + NaC10H7 + H2 would this not preferentially hydrogenate naphthalene to tetralin, killing it as a catalyst?

[Edited on 3-10-2021 by walruslover69]


Neat idea, in that case I'll look into diglyme. Could be interesting to try to make it. Also thanks for the thought about hydrogenating naphthalene with the Pd/C catalyst, this probably did happen to some extent and would explain why there was at most a very short window in which it worked, because the catalysts were probably destroyed soon after.

In terms of impurities, this is of course possible, but the only sources would be the naphthalene, which I got from mothballs, but I played around with subliming it a bit, and it sublimed and crystalized cleanly so I think the mothballs were pure naphthalene- or from the Pd/C catalyst. On the other hand, the brown goop did form in the THF both with Pd/C and without. With Pd/C after a few hours, without Pd/C after a few days.
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[*] posted on 4-10-2021 at 04:57


I reproduce here the relevant section of the book Small Scale Synthesis of Laboratory Reagents pp. 77-78.

Quote:

A quartz test tube about 30 mm in diameter and at least 200 mm long is placed inside a sealed tube oven or a circular opening in a box oven, and inclined upwards at 5°–8° to the horizontal. About 3–4 g of sodium metal, which has been shaken under ether to remove the last traces of paraffin, is placed inside a stainless steel tube, closed at one end, and inserted into the quartz reactor. A measured amount of steel wool at the bottom of the quartz test tube is used to adjust the location of the steel tube opening so it lies just inside the oven at the point where a temperature gradient is expected to commence. A side arm on the quartz tube leads to a U-tube containing several sections filled with P2O5 and separated by glass wool. The other end of the U-tube is connected to a hydrogen cylinder through a flow-rate adjusting valve. A long-arm stainless steel spatula (which can be fashioned out of a thin- diameter S/S pipe) is inserted through a seal so that its end lies just outside the zone where NaH is expected to be formed. The spatula runs through a fairly long section of straight tube prior to reaching the active zone in order to minimize the angular movement of the spatula and disturbance to the seal when removing the product. The outlet gases from the reactor are passed through an empty washbottle and an oil bubbler, which both isolates the reactor and serves as an indicator of the pressure inside.

The air inside the reactor is purged by opening the hydrogen valve until no oxygen is evident in the outlet gas, and the oven temperature is raised in the range 610°C– 640°C (corresponding to a tube temperature of about 550°C–580°C). Hydrogen absorption commences at about 570°C as evidenced by a slow rise of oil inside the washbottle capillary, and the hydrogen valve is opened so that the level in the capil- lary remains about constant. There is some nonuniformity in hydrogen absorption with time, and the hydrogen feed rate should be adjusted on the high-side, which leads to some loss of hydrogen. Alternatively, a hydrogen balloon can be used.

The sodium hydride starts forming immediately outside the tube opening where the local temperature is below its decomposition temperature at 1 atm hydrogen pressure. Figure 6.2 shows the result after about 20 min of operation. After about 2 h, a wool-like plug of sodium hydride needles completely occupies the temperature region suitable for hydride formation and hydrogen absorption slows. The hydrogen flow rate can be increased at this point to produce positive pressure inside the reac- tor, and the spatula can be inserted into the active region and rotated to remove the plug into the low-temperature region of the reactor where the hydride is stable. This operation is repeated every few hours, resulting in an NaH formation rate of about 0.2–0.3 g/h. When sufficient NaH has formed, the quartz tube is withdrawn from the reactor and allowed to cool to near room temperature. At that point, the hermi- ticity of the apparatus can be broken, and the sodium hydride removed in the open atmosphere. The author has found that no spontaneously ignitable sublimates form in the reaction.

Raising the reactor temperature above about 640°C does not lead to an increased rate of hydride formation; rather, a gray color appears in the product corresponding to condensed unreacted sodium. Higher temperatures still lead to decomposition of the hydride already formed and its reformation in the section of the reactor, which now has the appropriate temperature. However, the higher evaporation rate also leads to sodium globules forming in the NaH matrix as well as condensation of liquid sodium on the walls of the quartz reactor. This is deleterious to the quartz tube because of the danger of liquid sodium flowing into the high temperature region and reducing the quartz in depth. Gaseous sodium on the other hand does not seriously attack quartz, producing just a superficial discoloration, which disappears (due to the silicon being oxidized back to silica) on exposure to air.
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[*] posted on 4-10-2021 at 16:06


Quote: Originally posted by Monoamine  
a brown/black goop which seems to react with water.


BTW phenylsodium is black. The not particularly convenient reference for naphthalene, Na, and H is US2073973...the active product is described as a black mixture of hydride and "hydrocarbide" which could be used to produce more tetralin from additional naphthalene and hydrogen. US2372671 says that said catalyst can be ball-milled with Na and H at >300C for NaH, which doesn't make much sense, given that US2372670 and US1796265 use the same apparatus and simpler substances such as just about any inert solid.

Quote: Originally posted by Monoamine  
Oh I didn't know that.


Both subjects are described in Vogel.

Quote: Originally posted by Keras  
I reproduce here the relevant section of the book Small Scale Synthesis of Laboratory Reagents pp. 77-78.


It's not clear if len1 investigated any "surface active agents" with wet NaH synthesis as cited at the bottom of page 72, including oleic acid.




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[*] posted on 5-10-2021 at 06:55


Quote: Originally posted by S.C. Wack  

Quote: Originally posted by Keras  
I reproduce here the relevant section of the book Small Scale Synthesis of Laboratory Reagents pp. 77-78.


It's not clear if len1 investigated any "surface active agents" with wet NaH synthesis as cited at the bottom of page 72, including oleic acid.


I have no idea. I find disappointing that this book had no second, expanded edition. It's a good book, overall.
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[*] posted on 5-10-2021 at 08:24


In the case of ethyllithium its thermal decomposition to the hydride is indeed discussed in the literature, as it is also the discovery of the basic catalysis of ethylene polymerization, by one Ziegler whom you may have heard of (cf. "Ziegler-Natta catalyst"):

Quote:
The discovery of the hydroalumination reaction by Ziegler and Gellert in 1949 was the culmination of a series of experiments on the thermal stability of metal alkyls begun by Karl Ziegler in the early 1930s.7 During an attempt to distill ethyllithium, Ziegler found that the compound decomposed over 100 °C into ethylene and lithium hydride; the ethylene reacted, in steps, with the ethyllithium to give higher n–al– kyllithiums and these, in turn, eliminated lithium hydride to produce a mixture of higher α–alkenes (Scheme 1).8


Comprehensive Organic Synthesis, J.J. Eisch, 1991. IIRC a temperature of 120 C is recommended for this transformation. The generation of polymers might lead to foaming, although papers do not describe foaming.

Isopropyllithium appears to decompose a little more easily and for steric reasons should be a less avid polymer former. See particularly:

https://pubs.acs.org/doi/pdf/10.1021/jo01346a044

I don't know about the alkylsodiums -- these are difficult to prepare due to the competing Wurtz coupling, IIRC.




[Edited on 04-20-1969 by clearly_not_atara]
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