Sciencemadness Discussion Board

Sodium ethoxide with NaOH and ethanol

Ninja - 22-7-2011 at 05:55

Hi!

When you heat NaOH with ethanol (~95%)you get a yellow to red sticky mass,
which has to contain sodium ethoxide since it's formed in an dynamic equilibrium at even low temperatures just by mixing them.
At first it becomes a yellow fluid and then it becomes dark red (thanks to oxidation of ethoxide?) mass (which is in the beginning also yellow).
How can one easily measure the amount of ethoxide formed? Simple titration is not possible here...

Thanks, Ninja

1911 - 22-7-2011 at 06:35

The equilibrium is always more inclined to the ethanol and and hydroxide rather than ethoxide and water. AFAIK if you just mix ethanol and hydroxide that's not called ethoxide but alcoholic potash instead. The equilibrium must be driven to right in order to ethoxide to form. This can be done by refluxing alcoholic potash solution under a appropriate drying agent like wikipedia suggests.
Another potential, simplier way could be using sodium oxide instead of hydroxide. Oxide would first react with small amounts of water present in ethanol to sodium hydroxide. The hydroxide would then react with ethanol forming ethoxide and more water which in turn reacts with sodium oxide. One problem though is that as ethanol must be used as a solvent and thus in excess the reaction would always form some sodium hydroxide and thus water aswell. So pure ethoxide can't be obtained by this way. For most applications requiring sodium ethoxide this should be still fine.

Ninja - 23-7-2011 at 05:24

Quote: Originally posted by 1911  
The equilibrium is always more inclined to the ethanol and and hydroxide rather than ethoxide and water. AFAIK if you just mix ethanol and hydroxide that's not called ethoxide but alcoholic potash instead. The equilibrium must be driven to right in order to ethoxide to form. This can be done by refluxing alcoholic potash solution under a appropriate drying agent like wikipedia suggests.
Another potential, simplier way could be using sodium oxide instead of hydroxide. Oxide would first react with small amounts of water present in ethanol to sodium hydroxide. The hydroxide would then react with ethanol forming ethoxide and more water which in turn reacts with sodium oxide. One problem though is that as ethanol must be used as a solvent and thus in excess the reaction would always form some sodium hydroxide and thus water aswell. So pure ethoxide can't be obtained by this way. For most applications requiring sodium ethoxide this should be still fine.

Yes, i knew this.
I have also pure sodium and no problem with the preparation of anhydrous ethanol.
But i am interested in measuring the concentration of sodium ethoxide produced by the described method. How can one titrate the concentration of this solution?
All methods i can think of change the concentration of it substantially.

Thanks anyway, Ninja

Nicodem - 23-7-2011 at 13:48

Quote: Originally posted by Ninja  
But i am interested in measuring the concentration of sodium ethoxide produced by the described method. How can one titrate the concentration of this solution?

You don't have to measure it. It already was measured - the pKa values of hydroxide and ethoxide in ethanol are known (UTFSE for the article, unless I'm mistaken and it was about methoxide in methanol instead). So you just calculate the ratio by inserting your concentrations values in the equilibrium equation.
The ethoxide/hydroxide equilibrium of a solution of NaOH in ethanol is in favour of the ethoxide, just as one would intuitively guess by applying the solvation theory.
For most reactions where the presence of water is of no consequence, a NaOH/EtOH solution behaves similarly as a NaOEt/EtOH solution. For example, if you want to make an ethyl ether via the Williamson reaction, you can just use NaOH/EtOH. If you need a more anhydrous solution of NaOEt/EtOH you can always just dry a NaOH/EtOH solution with excess NaOH or precipitate the NaOEt out using acetone or other appropriate antisolvent (UTFSE for references).

Ninja - 7-6-2012 at 01:33

How can i purify this so prepared sodium ethoxide?

Has anyone information of the polymer formation and properties of old sodium ethoxide solutions?

Thanks, Ninja

Dr.Bob - 11-6-2012 at 09:46

It is very difficult to "purify" strong base solutions, whether alkoxides or lithium bases. That is why it is best to make them pure from the start. It will be difficult to purify any alkoxide solution containing 5% water to get pure sodium ethoxide. For methanol, it is easier to get close, since the initial methanol can be obtained nearly anhydrous, so there is only 1 molar equivalent of water in the solution, whereas ethanol containing 5% water has a large amount more water than that. You can do the math is you want to check this, I have done it before and don't care to repeat it. That (the 5% water in most ethanol) is one of several reasons that making ethanol based biodiesel via transesterification is very difficult compared to methanol based biodiesel.

The same way, it is hard to purify say, butyl lithium, as it is too reactive to really isolate-if you evaporate it, you get a complex aggregate of material which may never redissolve well again, and the material may react with the remaining solvent (especially THF) to form new compounds.

Adas - 11-6-2012 at 10:28

The red sticky mass was probably due to ketones present in the alcohol and the ketones condensed via aldol condensation at high pH.

Nicodem - 12-6-2012 at 10:03

Quote: Originally posted by Dr.Bob  
It will be difficult to purify any alkoxide solution containing 5% water to get pure sodium ethoxide. For methanol, it is easier to get close, since the initial methanol can be obtained nearly anhydrous, so there is only 1 molar equivalent of water in the solution, whereas ethanol containing 5% water has a large amount more water than that. You can do the math is you want to check this, I have done it before and don't care to repeat it. That (the 5% water in most ethanol) is one of several reasons that making ethanol based biodiesel via transesterification is very difficult compared to methanol based biodiesel.

Isolating sodium ethoxide from ethanolic NaOH solutions is relatively easy, because it can be precipitated using acetone as the antisolvent. This topic and the pertaining patent has already been discussed in the ethoxide thread. If needed, the water in saturated ethanolic NaOH can be removed by drying over NaOH pellets. All of this has already been discussed ad nauseam, but unfortunately there are always new members who are too lazy to UTFSE and thus threads like this one keep on resurfacing all the time. It is generally not worth replying to questions like this, because if someone is too lazy to search and read, it is likely that the laziness extends also to the experimental work, meaning the answer will never be applied.

The answer to the Ninja's question is to throw away the decomposing solution and prepare a fresh one.

kmno4 - 13-6-2012 at 23:34

Quote: Originally posted by Nicodem  

Isolating sodium ethoxide from ethanolic NaOH solutions is relatively easy, because it can be precipitated using acetone as the antisolvent. This topic and the pertaining patent has already been discussed in the ethoxide thread.

As far I remember, NO experimental conditions and results have been given for this procedure in mentioned thread.
So, value of such a discussion is rather none (sorry).

Nicodem - 14-6-2012 at 09:47

Quote: Originally posted by kmno4  
Quote: Originally posted by Nicodem  

Isolating sodium ethoxide from ethanolic NaOH solutions is relatively easy, because it can be precipitated using acetone as the antisolvent. This topic and the pertaining patent has already been discussed in the ethoxide thread.

As far I remember, NO experimental conditions and results have been given for this procedure in mentioned thread.
So, value of such a discussion is rather none (sorry).

Actually it has be successfully tried by gsus and me and reported at the old Hive forum. It immediately gives a crystalline precipitate just as claimed in the patent (thus obviously not the amorphous NaOH, which is also thermodynamically an unlikely precipitate from such a system). Gsus did a more thorough verification, while I never did a use test for the product to confirm its quality because NaOEt is simply too cheap to bother using a homemade product. I'm however sure there are members who do not have easy access to commercial sources and could use this procedure. Care needs to be taken to wash off the acetone residues from the product, else it self-condenses. And to do the filtration in the absence of moist air, obviously.

S.C. Wack - 14-6-2012 at 16:10

A good reason why no explicit directions would be posted is because they aren't necessary. People who've tested this may have done so just for hahas to see if it works. Quick careless tests tend to end in meh unless pursued further, but those interested in the subject might have plenty of sodium they have no other use for.

kmno4 - 15-6-2012 at 14:10

Quote: Originally posted by S.C. Wack  
A good reason why no explicit directions would be posted is because they aren't necessary...

:o
Quote:
Gsus did a more thorough verification, while I never did a use test for the product to confirm its quality because NaOEt is simply too cheap to bother using a homemade product.

:o
Exceptional curiosity of these statements does not let me comment them.
Have I mistaken forums ? It is sciencemadness.org or kindergarden.com ??

[Edited on 15-6-2012 by kmno4]

S.C. Wack - 15-6-2012 at 16:10

XXX explicit then: follow directions in http://www.google.com/patents/US1978647
Optimize in your hands with your equipment. Calculate yield and cost and dismiss.
It takes minutes, and could be done by a kindergartener.

If you want more explicit directions, we're not stopping you from doing this and posting them?

EDIT: Clarification on yield if the earlier post was not clear enough: yields by people who performed this quite casually and really don't care are only so relevant. In other words, we wouldn't know how high they are because AFAIK no one has tried to see how high they could go.

[Edited on 16-6-2012 by S.C. Wack]

Nicodem - 16-6-2012 at 06:54

S.C. Wack is correct. The procedure is so simple that there really is nothing to discuss about it. I don't see any reason on why would anyone bother discussing this patent on any forum. All the details are already clearly described in the examples. At the time I checked it, that must have been eight years ago, I had plenty of commercial quality sodium ethoxide available and saw no other value in that patent, except for the curiosity and simplicity of the procedure - it is the simplest method to get solid sodium ethoxide that I ever saw anywhere.

anomolous - 13-6-2013 at 20:47

Quick question. I precipitated sodium ethoxide salts per US patent 1978647 and was wondering how easily they will go back into solution in absolute ethanol? Has anyone made an ethanolic solution from the sodium ethoxide salts before? Should be fine, right?

Thanks

Dr.Bob - 14-6-2013 at 11:05

That should work just fine. It should be soluble but some NaOH and Na2CO3 may form from air and CO2 getting into the base, and they will not be as soluble. Most people just make NaOEt as they need it, since it is not easy to keep it perfectly dry.

anomolous - 16-6-2013 at 21:51

Thanks, Dr Bob. The sodium ethoxide salts have been stored in a vacuum desiccator over CaCl, so they should be nearly anhydrous. Adding them to absolute ethanol under an inert atmosphere will hopefully keep those impurities to a minimum. This is the only way I could see to make a pure sodium ethoxide solution from NaOH. But perhaps Organikum's method from US patent 2796443 would be better? I thought I might get a purer product precipitating the salts first, and then redissolving them in pure ethanol, rather than trying to convert the remaining NaOH in solution to ethoxide.

Ninja - 9-12-2014 at 08:27

Is a good option for making sodium ethoxide with NaOH to use aluminium powder to drive the equilibrium more to the ethoxide? or will it become impure? Al-hydroxides should'nt be soluble in ethanol, right?

JAVA - 28-12-2014 at 05:01

What is the strongest base: sodium hydroxide or sodium ethoxide ?

Write the reaction mechanism: H2O is released, what happens if you put some water in your "sodium ethoxide" mixture ?


Fact is that sodium ethoxide can be prepared by reacting sodium metal in anhydrous EtOH, which is slightly hygroscopic.

Nicodem - 29-12-2014 at 06:20

Quote: Originally posted by JAVA  
What is the strongest base: sodium hydroxide or sodium ethoxide ?

It depends. In water they are of comparable strength, the ethoxide being about twice more basic than hydroxide. But this is an exception due to solvation effects, because in most solvents, the hydroxide is more basic. For example, in ethanol it is the opposite to water, the hydroxide is slightly more basic than the ethoxide. In DMSO the hydroxide is about 40 times stronger a base than the ethoxide.