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Author: Subject: Sodium benzoate + ammonium chloride → Ammonium benzoate + Salt?
Keras
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[*] posted on 29-4-2024 at 10:41
Sodium benzoate + ammonium chloride → Ammonium benzoate + Salt?


I just wonder if the reaction above is likely to take place.

I want to get ammonium benzoate to make benzamide by dehydration, and from that aniline using a Hofmann rearrangement (it’s more a proof of concept).

However, the idea of combining directly benzoic acid and ammonia doesn’t really work, because benzoic acid is only soluble in hot water whereas for ammonia it’s exactly the opposite. So my idea was to use the salts instead.

Thanks!
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[*] posted on 29-4-2024 at 11:25


Quote: Originally posted by Keras  

However, the idea of combining directly benzoic acid and ammonia doesn’t really work, because benzoic acid is only soluble in hot water whereas for ammonia it’s exactly the opposite.

It works, apparently. In this paper in Thermochimica Acta, ammonium benzoate is prepared by dissolving benzoic acid in concentrated ammonia (25%, I guess): https://doi.org/10.1016/j.tca.2010.01.021

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clearly_not_atara
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[*] posted on 29-4-2024 at 11:48


Benzoic acid is more soluble in water when there is some kind of alkali present to deprotonate it. I expect that adding solid benzoic acid in small portions to aqueous ammonia with stirring and chilling would achieve the desired results.



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[*] posted on 29-4-2024 at 21:38


Quote: Originally posted by clearly_not_atara  
Benzoic acid is more soluble in water when there is some kind of alkali present to deprotonate it. I expect that adding solid benzoic acid in small portions to aqueous ammonia with stirring and chilling would achieve the desired results.


Well I tried that initially, proceeding from the same rationale, bubbling ammonia produced from boiling a commercial 30% solution. It simply didn't work. The acid never dissolved entirely. I evaporated the resulting solution, got some white crystals and when I tried to pyrolyse them, all I got was tiny (and beautiful) flakes of benzoic acid, which sublimed out of the flask. It was a flat out fiasco.
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[*] posted on 30-4-2024 at 04:37


Quote: Originally posted by Keras  
I just wonder if the reaction above is likely to take place.

In a solvent in which both sodium and ammonium benzoate are soluble and sodium chloride is not. Ethanol or methanol, for example.

Quote: Originally posted by Keras  
I want to get ammonium benzoate to make benzamide by dehydration, and from that aniline using a Hofmann rearrangement (it’s more a proof of concept).

However, the idea of combining directly benzoic acid and ammonia doesn’t really work, because benzoic acid is only soluble in hot water whereas for ammonia it’s exactly the opposite.

Someone else had the same issues with benzoic acid almost four years ago:
Quote: Originally posted by SplendidAcylation  

A few months ago, I got quite excited when I found out that benzonitrile could be made by dehydrating benzamide, which can be made via thermal dehydration of ammonium benzoate, using P2O5.

The dehydration of the amide should be just the same as dehydrating formamide or acetamide, and the preparation of the amide itself, by heating the ammonium carboxylate, should also be as easy as the other ones, however the preparation of the ammonium benzoate is a lot more straight forward than either the formate or acetate, because the benzoate is much more stable, and less soluble in water.

So, with these things in mind, and a reckless desire to waste phosphoric anhydride, I went about it.

I made the ammonium benzoate simply by dissolving benzoic acid in an excess 25% ammonia solution.

The dissolution was extremely slow, so I ended up recrystallizing the benzoic acid first to increase its surface area; then it dissolved fairly quickly.

Once dissolved, I heated the solution in a dish on a water bath, once the water was all gone I had an almost quantitative yield of the salt.

The dry salt was then sealed in a glass tube and heated, immersed in sand, to around 200c for an hour.

Upon cooling, I found that the dry white salt had turned into a light brown, wet, waxy substance, presumably benzamide.
The substance melted readily, and was thus poured out of the tube.


Another route you can try is aminolysis of a benzoate ester to give benzamide directly. But then, where would be the fun?




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[*] posted on 30-4-2024 at 10:53


Quote: Originally posted by bnull  
Quote: Originally posted by Keras  
I just wonder if the reaction above is likely to take place.

In a solvent in which both sodium and ammonium benzoate are soluble and sodium chloride is not. Ethanol or methanol, for example.


Fair enough. But water would be more than sufficient. I did some eyeballing, and 1 mol of benzoic acid + one mol of ammonium chloride in 175 mL of boiling water should do the trick. There will be some ammonium benzoate lost in the process, but the salt should remain in solution. Not a big deal, given the price of the reactants.

Quote: Originally posted by bnull  

Another route you can try is aminolysis of a benzoate ester to give benzamide directly. But then, where would be the fun?


I have no experience with aminolysis. But then, why bother create some ester, as you say.
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[*] posted on 30-4-2024 at 11:50


Esters are easy enough.



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[*] posted on 30-4-2024 at 21:53


Quote: Originally posted by DraconicAcid  
Esters are easy enough.

Sure.
Well at this point I've ordered benzoyl chloride. So I can both make esters and benzamide directly by treating with ammonia :p
Still, I’ll try the first route.
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[*] posted on 29-5-2024 at 01:22


Ok, I tried that. 0.55 mol of sodium benzoate and ammonium chloride into a random amount of boiling water (~ 150 mL), boiled down until something began to precipitate then left out. Got a thick white paste of whatever.

Tried to pyrolyse that to benzamide at ~ 200 °C. Got nothing. As the paste is heated, exactly like the first time I tried, benzoic acid sublimes out forming a stream of tiny flakes, and then in the flask I was left with an off-white crystalline substance that looked promising, but turned out to be some sort of dirty ammonium chloride (probably [EDIT] or salt?). So at the end, nothing was left.

Either ammonium benzoate reverts to benzoic acid and ammonia when heated, or there is something wrong with the reaction. If ammonium benzoate can really be dehydrated into benzamide, I wonder what's the correct process.

[Edited on 29-5-2024 by Keras]
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[*] posted on 29-5-2024 at 02:35


If you compare you experiment with the one above made by SplendidAcylation there are some differences.
He dried the salt to get rid of all water and then put it in a sealed tube and heated to 200°C for an hour.
Maybe make sure all water is gone then try it in a sealed glass tube.
I would guess that its important its really dry and also the sealing in a tube could make it work.
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[*] posted on 29-5-2024 at 03:39


Yeah, I was thinking about that. Maybe the reversion to benzoic acid is caused by water still present.
I’ll try to do that in a sealed RBF, but I’m very wary of sealed environments
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[*] posted on 29-5-2024 at 06:22


What about ammonium benzoate from ammonium bicarbonate and benzoic acid? There would be no sodium chloride to mess things up and, because ammonium bicarbonate decomposes above 40 °C, any excess of the latter would just disappear on heating.



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[*] posted on 29-5-2024 at 07:56


My memory from some time ago is that the analogous pyrolysis of ammonium acetate happens in two stages: first, ammonium acetate decomposes losing ammonia to give ammonium diacetate. Then, ammonium diacetate decomposes to acetamide and the excess acetic acid and water boil off.

In other words, the 1:1 salts are just not stable at temperatures high enough to form amides. It's plausible that benzoic acid doesn't form a very stable anion dimer (BzO)2H- due to sterics so that ammonium benzoate just decomposes to benzoic acid.

Alternative possibilities include heating benzoic acid (bp 250 C) with ammonium sulfate (decomp 280 C) or heating benzoic acid with urea.




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[*] posted on 29-5-2024 at 08:21


Heating benzoic acid with urea is a possibility, but what would be the stoichiometry?
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[*] posted on 29-5-2024 at 09:08


My estimate is:
BzOH + NH2CONH2 >> BzNH2 + CO2 + NH3 (g)

The rxn between BzOH and the second equivalent of NH3 should be much slower than boiling away of formed NH3 so not very important.




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[*] posted on 29-5-2024 at 09:35


Quote: Originally posted by clearly_not_atara  
Alternative possibilities include heating benzoic acid (bp 250 C) with ammonium sulfate (decomp 280 C) or heating benzoic acid with urea.

Benzamide from benzoic acid and urea, with boric acid as catalyst: Benzoic Acid, Carbamid>Benzamid>Anilin?

@Keras: You may also want to read the references given in Wagner and Zook's Synthetic Organic Chemistry, page 297. They are "The Preparation of Benzamide", by C. H. Kao and Shao-Yuan Ma (J. Chem. Soc., 2788 (1930) ), and "The Preparation of Aromatic Acid Amides", again by Kao and Ma (J. Chem. Soc., 443 (1931)). A little hard to find but quite interesting.




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[*] posted on 29-5-2024 at 09:57


Quote: Originally posted by bnull  

@Keras: You may also want to read the references given in Wagner and Zook's Synthetic Organic Chemistry, page 297. They are "The Preparation of Benzamide", by C. H. Kao and Shao-Yuan Ma (J. Chem. Soc., 2788 (1930) ), and "The Preparation of Aromatic Acid Amides", again by Kao and Ma (J. Chem. Soc., 443 (1931)). A little hard to find but quite interesting.

The first one is in the "Notes" section of 1930 volume: on page 6.
The second one is in the "Notes" section of 1931 volume: second page.

Maybe folks from National Tsing Hua University published longer, more detailed articles in some local journal, but given the conditions in 1930s Republic of China and what happened later, they are a bit more harder to find.




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[*] posted on 29-5-2024 at 11:59


Quote: Originally posted by bnull  
Quote: Originally posted by clearly_not_atara  
Alternative possibilities include heating benzoic acid (bp 250 C) with ammonium sulfate (decomp 280 C) or heating benzoic acid with urea.

Benzamide from benzoic acid and urea, with boric acid as catalyst: Benzoic Acid, Carbamid>Benzamid>Anilin?

@Keras: You may also want to read the references given in Wagner and Zook's Synthetic Organic Chemistry, page 297. They are "The Preparation of Benzamide", by C. H. Kao and Shao-Yuan Ma (J. Chem. Soc., 2788 (1930) ), and "The Preparation of Aromatic Acid Amides", again by Kao and Ma (J. Chem. Soc., 443 (1931)). A little hard to find but quite interesting.


Thanks for the pointers. I have boric acid I never used, will do as soon as I can, and maybe report on my own findings.
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[*] posted on 2-6-2024 at 11:37


Besides, I suddenly realised I could sacrifice a small part of my benzoyl chloride to make benzamide :p

Not very economical, though, for more than a dozen of grams.

[Edited on 2-6-2024 by Keras]
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