Sciencemadness Discussion Board

Making n-butyl bromide (1-bromobutane) for TBAB (Tetrabutylammonium bromide) synthesis

Keras - 25-4-2021 at 02:20

Folks,

I've been trying to make TBAB, because I read it can be used as a phase transfer catalyst to significantly enhance the yield of benzyl alcohol oxidation by bleach into benzaldehyde (Wang M-L., Huang T-H.: Kinetic Study of Benzyl Alcohol Oxidation Under Phase Transfer Catalysis Conditions. Chem. Eng. Comm., 194:618–634, 2007. DOI: 10.1080/00986440600992685). At pH = 9.5, the authors report over 90% yield under reflux in 40 mn starting with 10% bleach and using TBAB and sodium bicarbonate to speed up the reaction.

So far, I've successfully (I think, I had no time to really test it) obtained n-butyl bromide starting from homebrewed HBr (d = 1.41 following NileRed) using the process described in Vogel p. 561 (experiment 5.54), using 1/5 of the stated quantities. For whom it may concern, the initial addition of sulphuric acid to hydrobromic acid produced a strong browish/reddish colour due to the oxidation of HBr into elemental bromine. After addition of n-butanol, more sulphuric acid and refluxing at around 120 °C, the brown colour faded out in like one hour, leaving a clear colourless layer. I kept refluxing one more hour as suggested in Vogel. I let cool and had only so much time to collect the upper layer of butyl bromide floating over the denser acid layer. I must have tallied around 25 ml that I placed into a small amber glass vial. Vogel's theoretical yield of 95% translates into 31 mg or 24 ml circa, so I suppose it worked quite well (Butyl bromide separation from the aqueous layer containing Br⁻ and BuOH must drive the reaction forward).

Next step (after maybe washing and distilling) is TBAB from n-butyl bromide, which I suppose is just a matter of reacting ammonia with it. Does it need ammonia gas bubbling, or will it work with a standard aqueous NH₃ solution?

There's also this old thread about TBAB, where it is mentioned that quaternary ammonium salts are readily obtained.

Thanks!

[Edited on 25-4-2021 by Keras]

njl - 25-4-2021 at 07:29

I'd say avoid bubbling lest you end up with less substituted products. Bubbling NH3 will make it very difficult to control the amount of NH3 actually reacting, and since you absolutely need an excess of BuBr over NH3 it would be best to use a solution of NH3. That said, the solubility's of BuBr and NH3 don't have too much overlap so water might not work as a solvent.

Keras - 25-4-2021 at 07:43

Quote: Originally posted by njl  
I'd say avoid bubbling lest you end up with less substituted products. Bubbling NH3 will make it very difficult to control the amount of NH3 actually reacting, and since you absolutely need an excess of BuBr over NH3 it would be best to use a solution of NH3. That said, the solubility's of BuBr and NH3 don't have too much overlap so water might not work as a solvent.


I was planning to titrate a commercial bottle of aqueous ammonia, measure out the right amount of it and drive it to boiling, feeding the vapour into the BuBr. That way, the amount of gaseous ammonia is fairly well controlled.

njl - 25-4-2021 at 07:59

In that case you would know the absolute maximum amount of ammonia available to react, but it would be impossible to guarantee the actual amount reacted since some will inevitably escape the reaction vessel. In my opinion gas bubbling should be reserved for reactions where the gas is used in excess. This is not to say that bubbling won't work, just that it would likely have lower selectivity for TBAB over less substituted products. If NH3 gas addition is slow enough you might be able to increase the proportion of fully alkylated products but at that point you are basically making a solution of NH3 during the reaction.

Keras - 25-4-2021 at 10:55

Quote: Originally posted by njl  
In my opinion gas bubbling should be reserved for reactions where the gas is used in excess.


What about bubbling NH₃ into methanol, titrate the mix by measuring the weight increase, and then using the right volume of this methanol/ammonia mixture with BuBr?

njl - 25-4-2021 at 14:48

That sounds like an excellent solution! Good thinking.

Keras - 25-4-2021 at 22:56

Quote: Originally posted by njl  
That sounds like an excellent solution! Good thinking.


Thanks! :) I'll go ahead and do this when I can go back to my lab.
Thanks for the enlightening thread!

njl - 26-4-2021 at 05:51

Just remember gas solubilities increase as temperatures decrease, and it may be beneficial to add a base in order to neutralize the formed HBr.

AvBaeyer - 26-4-2021 at 18:30

You might want to consider looking at this article which can be freely accessed on the Sigma-Aldrich website:

Sjöberg, K., Aldrichim. Acta 1980, 13, 55.

Generally, tetrabutylammonium bromide (TBAB) is made in a stepwise procedure by the alkylation of tributylamine with butyl bromide. Your proposal to do the synthesis in "one bucket" will in all likelihood provide you with an intractable mess.

Just as a suggestion, TBAB has been available on Amazon in the US off and on for some time. If your interest is in PTC reactions this may be a better start than trying to make the stuff yourself.

A survey of TBAB chemistry can be found here:

sci-hub.se/10.1002/047084289X.rt011.pub2

Have fun,

AvB

DraconicAcid - 26-4-2021 at 20:55

Quote: Originally posted by AvBaeyer  
Just as a suggestion, TBAB has been available on Amazon in the US off and on for some time. If your interest is in PTC reactions this may be a better start than trying to make the stuff yourself.


Seriously? Amazon.ca offers nothing but homeopathic crap for any tetraalkylammonium bromide I've checked it for.

monolithic - 27-4-2021 at 04:22

Quote: Originally posted by AvBaeyer  
Just as a suggestion, TBAB has been available on Amazon in the US off and on for some time. If your interest is in PTC reactions this may be a better start than trying to make the stuff yourself.


This is where I bought mine from. https://www.amazon.com/HiMedia-GRM5456-250G-Tetrabutylammoni...

njl - 27-4-2021 at 04:27

I can recommend Himedia, but their stock is all over the place. Sometimes I can't find a product the day after I find it in the first place. So Keras if you just want TBAB HiMedia is a good source, but I get the feeling you are more interested in making it.

Fery - 27-4-2021 at 12:08

here iodide
https://chemcraft.su/product/24516
bromide sold out:
https://chemcraft.su/product/23302

DraconicAcid - 27-4-2021 at 12:33

Quote: Originally posted by Fery  
here iodide
https://chemcraft.su/product/24516
bromide sold out:
https://chemcraft.su/product/23302

That's a cool site- thank you for the link. Have people had good experiences with it?

njl - 27-4-2021 at 17:00

There are good reviews for chemcraft in one of the reagents acquisition threads.

Uvxtal76 - 8-5-2021 at 13:23

TBAB and no not some homeopathic pilled up crap is easily had from Amazon... Yes HiMedia, and cheap too!

Keras - 8-5-2021 at 22:37

Quote: Originally posted by DraconicAcid  
Quote: Originally posted by Fery  
here iodide
https://chemcraft.su/product/24516
bromide sold out:
https://chemcraft.su/product/23302

That's a cool site- thank you for the link. Have people had good experiences with it?


I’ve ordered only once from Chemcraft. Barring the fact that the parcel was quarantined because of idiotic CoVID rules, it arrived fine. Products are carefully packaged, excellent price/quality ratio. Highly recommended.

And yes, now that I know that solubility of ammonia in methanol is around 17%, I’ll try and finish the synthesis. Probably tomorrow.

EDIT: I should get about 30 g of butyl bromide, that’s 220 mmol.
I need seven times that amount of ammonia, I suppose.

[Edited on 9-5-2021 by Keras]