Sciencemadness Discussion Board

One-pot, quick-and-dirty tetrabutylammonium bromide (TBAB) preparation

Melgar - 8-5-2017 at 14:45

Lab space has recently become somewhat of a luxury for me, so I've been looking at various syntheses that don't really require chemistry glassware, or extensive purification. TBAB seems to be one of the few things that can be made this way, since getting an exact quantity is less important than getting the emulsion to form and dissipate like you expect it to. So from a solution, it can just slowly be added until it performs like you think it should, assuming the solution is unreactive to your reaction conditions. That being said, here goes:

You will need:



  1. Begin with about 1/5 the volume of your bottle of butyl alcohol, or about 1/8 its volume of 2-butoxyethanol.
  2. Measure out 1.5 molar equivalents of bromide salt for the quantity of butyl compound you plan to use. 2-butoxyethanol requires three times as much bromide per mole as n-butanol. Combine both in the bottle, then add roughly the same volume of nonpolar solvent as you have for your butyl compound.
  3. Add 1.5 molar equivalents (based on sulfur or phosphorus acids) of your oxoacid, and cap it.
  4. Let any evolved heat dissipate, then shake it well. Keep repeating this step until heat stops evolving.
  5. If the solids aren't going into solution, cool the bottle down to freezer temperatures, then open it and add a small quantity (about 10-20% the volume of your oxoacid) of water. There should be at least a third the volume of the bottle empty.
  6. Cap the bottle, and carefully heat it, keeping it below water's boiling point. Depending on the nature of your reagents, the alcohol/alcohol ether should dissolve some of your acid and salt, and the acid should dehydrate your alcohol, turning it into an alkyl bromide, which should migrate to the nonpolar layer. Swirl the bottle occasionally, to make sure there is a thorough mixing of the reagents in the aqueous/acid layer.
  7. I have not tried this procedure with 2-butoxyethanol, however the HBr should cleave the ether bond, and then additional HBr should brominate the resulting hydroxyl groups. I see no reason that this wouldn't happen, but feel free to correct me if I'm wrong.
  8. When the layers stop changing size and/or color, allow the bottle to cool, then carefully open it, wearing gloves, and with a rag or paper towel over the cap to prevent spray. None of the contents should have an extremely high vapor pressure at these temperatures, but regardless, it's prudent to release any gases slowly, so they don't cause the contents to foam out of the bottle.
  9. Use a separatory funnel to remove the lower layer, and put the upper layer back into the bottle. Or pipette the lower layer into a waste container, or do whatever works to remove most of the lower layer. You do not have to be extremely thorough here.
  10. Add solid sodium carbonate until there's no more bubbling, then add a small quantity more, at least enough to indicate when an acid is being neutralized.
  11. Figure out what to do with the 1,2 dibromoethane if you used 2-butoxyethanol. I haven't tried this myself, so I can only speculate.
  12. Add your ammonium salt or aqueous ammonia solution, dropwise. Add a few drops, then mix the solution and wait for a few minutes. Keep doing this until the solution has an ammonia or amine odor to it that doesn't quickly subside. If at any point, the lower layer becomes acidic, add more sodium carbonate. You should now notice the solution become a characteristic emulsion upon stirring, which separates after a minute or so.
  13. Acidify the lower layer with a ~50% solution of your oxoacid. This will form salts with any non-quaternary amines in the upper layer, bringing them to the lower layer.
  14. Your upper layer should consist mostly of TBAB and whatever solvent you used. In many cases, it can be pipetted from this layer directly, and used as-is.


Any thoughts or suggestions?

Aqua-regia - 9-5-2017 at 11:17

Do you have some reference about this, or just an invention? This stuff is very useful phase transfer catalist. What a coincidence your post, because i have just searched some good and easy way to prep. it. (havent found easy way)

Melgar - 9-5-2017 at 14:55

TBAB is just a quaternary ammonium salt that's obviously been prepared by exhaustively alkylating ammonia with 1-bromobutane. It could also be considered the unwanted product that you'd inevitably get if you reacted 1-bromobutane and ammonia to try to make 1-butylamine. Seeing as quaternary amines are so easy to accidentally make, I figured they'd be about as easy to deliberately make, which is more or less true. I keep running into the same issues though, which stem from the fact that it's hard to brominate all of your butanol without a full glassware setup with magnetic stirring and reflux and distillation. I'm almost certainly getting butanol in my organic layer, but it doesn't react with ammonia, so I should be fine there, even if the yields aren't as good as they could be. I know that there's probably butanol in the organic layer, and maybe a small amount of HBr forming hydrogen bonds with the butanol, but if I wanted to remove them, I suppose I could always just evaporate whatever I could from that layer.

I'm also not sure what else might be out there that would hydrolyze or otherwise cleave into n-butanol or 1-bromobutane. 2-butoxyethanol seems to be in a large number of products, although I haven't tested it to see how well it'd work. Dibutyl ether should work well, if anyone can get ahold of it. So should butyl esters, but I don't know of any that are easily obtained OTC.

Corrosive Joeseph - 9-5-2017 at 16:54

Unless you are hellbent on synthesis, this looks like the quickest, dirtiest way to quat salts -
http://www.bonnymans.co.uk/products/product.php?categoryID=1...

Or something like it. As good as "Aliquat 336", apparently............
"OTC PTC" - http://www.sciencemadness.org/talk/viewthread.php?tid=9496

Still interested. Would love to hear more


/CJ



byko3y - 9-5-2017 at 17:11

- No proportions for the second step, no yields for both steps.
- Purity of the product was not verified, neither idendity.
- Product separation seems questionable for me. TBAB is much more soluble in water than in organic solvents.

JJay - 9-5-2017 at 17:18

There are numerous quaternary disinfectant concentrates on the market. Several of these may require some purification, although the one suggested by Corrosive Joeseph looks like it may be low in impurities. Also, bear in mind that while quaternary ammonium salts are far more toxic to plants and microorganisms than most mammals, they can kill you:

http://www.reckittprofessional.com/productpromain/ProductSea...




[Edited on 10-5-2017 by JJay]

Corrosive Joeseph - 9-5-2017 at 17:33

You might also need a business address. Biocides are slowly getting regulated over here.
Who knows how long this will last................


/CJ

Melgar - 9-5-2017 at 20:22

The easiest source of quaternary ammonium salts that I'm aware of is "Quat-Tabs", which are tablets of quaternary disinfectant used by restaurants. Tablets are a few grams each, are about 50% quaternary salt, and the rest mostly dye, so as to indicate when the substance is present. However, dimethyl quaternary compounds tend to form more of an emulsion, and maintain a stronger bond with their ions in the organic phase. They're cheap as hell though:

http://www.ebay.com/itm/122324045647

As far as my synthesis, I actually already have 250 grams of TBAB that I bought, so I know what it does when you add it to a two-phase mixture and agitate it. The stuff I made does the exact same thing, although it's mixed with butanol and so is liquid and not solid. It should be pretty trivial to make TBAB with a full glassware setup. 1-bromobutane is a pretty standard undergraduate lab demonstrating an SN2 reaction, here's one of four undergraduate lab sheets I found detailing its preparation:

http://chemistry.csudh.edu/faculty/noel/CHE317L/Preparation%...

The next step would obviously be to add ammonia, which would be immediately alkylated, all the way to its quaternary salt if there was enough base present to neutralize the evolved acid. Hence, the sodium carbonate. Without the base, the amines would form salts with the HBr, preventing their further reaction.

@byko3y: TBAB is more soluble in butanol than it is in water, even though butanol will form a layer on top of water, and is miscible with virtually all nonpolar solvents. In my case, the lower layer was saturated with sodium carbonate too, which would have severely limited TBAB's solubility.

[Edited on 5/10/17 by Melgar]

byko3y - 10-5-2017 at 06:01

Tributylamine hydrobromide is soluble in butanol in order of 10g/100ml. TBAB is not miscible with nonpolar solvents e.g. slightly soluble in toluene: http://onlinelibrary.wiley.com/wol1/doi/10.1002/047084289X.r...
Both TBAB and tributylamine have low solubility in saturated Na2CO3 water solution.
Traces of TBAB will lead to the formation of emulsion, this fact shows that TBAB is present, but we have no idea how much if it is present.

Melgar - 10-5-2017 at 15:05

A mixture of naphtha and butanol will easily dissolve a large amount of TBAB. Of course, naphtha by itself will dissolve little if any, but I'm quite certain that there was a substantial amount of butanol in the nonpolar layer. I also put about 0.5 mL of the nonpolar layer into a 250 mL flask that I wanted to test with, and it formed a substantial emulsion there too. After sitting for a while, the amine smell in the organic layer goes away, presumably as it's further alkylated, albeit more slowly since the reaction concentration is lower. Seeing as tributylamine is described as having a strong odor, and TBAB has none, that seems like it'd be an adequate test for non-quaternary amines.