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Myeou
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[*] posted on 25-2-2013 at 10:23
Acetamide Synthesis


So i tried to make acetamide from the reaction of Ethyl acetate and NH3 .
I poured both of them in to the flask waited 3 days for mixng them. After that , i made a reflux and than distilled it.
First thing come from disttilation was amonnia . Than ethyl acetate came. It was still smells like amonnia too. After that water came it was also smeell like amonnia. And in the there in the flask there was a Yellow colored chemical which i cant recognize. It was liquid so it is not acetamide. It was more viscose than water and smells like acetic acid but not pungent as acetic acid.

Here is a picture from that yellow liquid.

From what i read , this reaction should reveal acetamide and ethanol. But thing i get was something different.

The thing that weird for me is , i tried different method to make acetamide , from heating amonnium acetate , i still get the same weird liquid .

What am i doing wrong ? Is that liquid a solution of acetamide with amonnia and water ???

[Edited on 25-2-2013 by Myeou]

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[*] posted on 25-2-2013 at 18:34


Acetic acid is one of the products from the reaction between ethyl acetate and ammonia.

CH3COOC2H5 + NH3 ---> CH3CONH2 + C2H5COOH

Try removing the acetic acid with a base + liquid-liquid extraction with a suitable organic solvent.

Collect the organic layer and dry down.
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Myeou
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[*] posted on 26-2-2013 at 07:11


Quote: Originally posted by bananaman  
Acetic acid is one of the products from the reaction between ethyl acetate and ammonia.

CH3COOC2H5 + NH3 ---> CH3CONH2 + C2H5COOH

Try removing the acetic acid with a base + liquid-liquid extraction with a suitable organic solvent.

Collect the organic layer and dry down.


wow that is suprising for me because i thought that the raction mechanism goes same as NaOH and CH3COOC2H5 .

Could you explain the mechanism to me ?
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[*] posted on 26-2-2013 at 07:31


Quote: Originally posted by bananaman  
Acetic acid is one of the products from the reaction between ethyl acetate and ammonia.

CH3COOC2H5 + NH3 ---> CH3CONH2 + C2H5COOH

Try removing the acetic acid with a base + liquid-liquid extraction with a suitable organic solvent.

Collect the organic layer and dry down.


No it is not.
You have just magicked up an extra carbon and two oxygen atoms.
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Myeou
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[*] posted on 26-2-2013 at 07:39


Quote: Originally posted by ScienceSquirrel  
Quote: Originally posted by bananaman  
Acetic acid is one of the products from the reaction between ethyl acetate and ammonia.

CH3COOC2H5 + NH3 ---> CH3CONH2 + C2H5COOH

Try removing the acetic acid with a base + liquid-liquid extraction with a suitable organic solvent.

Collect the organic layer and dry down.


No it is not.
You have just magicked up an extra carbon and two oxygen atoms.



Could we be clear that reaction between ethyl acetate and amonnia yields acetamide and ethanol..

If this is true why is the yellow solution smells like acetic acid ?
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[*] posted on 26-2-2013 at 08:15


A competing reaction is hydrolysis of the ethyl acetate to yield ethanol and acetic acid. The acetamide will also hydrolyse.
What you have is an aqueous solution of acetamide with traces of acetic acid. Acetamide is extremely soluble in water, 2000g per litre, so even small amounts of water will make it into a solution.
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[*] posted on 26-2-2013 at 09:04


Quote: Originally posted by Myeou  
It was liquid so it is not acetamide.

It should be liquid. I can't see it possible to obtain pure and thus solid acetamide without a redistillation with a distillation column. Keep in mind that water will form from the thermolysis of the ammonium acetate side product during the first distillation and it is thus not possible to obtain an anhydrous acetamide this way. Also, ammonium acetate decomposes also to ammonia and acetic acid which is unlikely to condense in a 1:1 ratio, thus causing contamination with acetic acid and ammonium acetate.

What is the reference of this procedure and how do the authors isolate acetamide? Are you sure they did not fractionate the crude product?




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[*] posted on 26-2-2013 at 17:33


Sorry for the mistakes previously. Attached is a relevant paper regarding the preparation of acetamide from ethyl acetate and ammonia.

Attachment: Preparation of Acetamide by the Action of Ammonium Hydroxide and Ethyl Aetate.pdf (738kB)
This file has been downloaded 2670 times

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[*] posted on 6-5-2013 at 13:03


So I did a very quick synthesis of acetamide this week following this discussion, by simply mixing aqueous ammonia (household grade, 9%) with what is supposedly 99% ethyl acetate (dubious source). I simple mixed stoichiometric amounts, about 9.1 grams ethyl acetate with 20 mL 9% ammonia. Approximately 100 mmol of both reagents. The solution initially forms two separate layers as the ethyl acetate has a low solubility in water (8.3 g/dL).

I left the solution on the magnetic stirrer for 24 hours, at about 700 rpm. At this point there were no longer two separate layers, so it's safe to assume that a reaction had taken place. I simple poured the resulting solution into an evaporating dish and left it at room temperature for 3 days, when crystals finally started forming. The crystals were collected and placed in a desiccator with phosphorus pentoxide for another 24 hours. A simple melting-point test did give confirmation that the product is relatively pure acetamide with a melting point at ~80 C, all of the product melted to a clear liquid not exceeding 90 C.

This procedure clearly seems like a success. I forgot to weigh my final product, so I don't know any yields at this moment, but I could do that if anybody is interested.

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[*] posted on 6-5-2013 at 13:54


Very nice results, Polesch! Taking into consideration that you used just 9% ammonia... Nice :)



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[*] posted on 7-5-2013 at 00:54


Quote: Originally posted by Adas  
Very nice results, Polesch! Taking into consideration that you used just 9% ammonia... Nice :)


When I used what is 'most likely' a saturated solution of ammonia in ice-cold water, I did get a much higher yield, as I used about the same volume of solution - but obtained much more crystals:

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[*] posted on 18-9-2013 at 18:18


I tried making acetamide with 30% ammonia and 98.5% ethyl acetate. After evaporating the solution at about 60C. The solution started turning yellow and it smelled like acetic acid so I let it cool to room temperature and crystals started forming. I didn't weigh the crystals so I don't know the yield but it certainly was very low.
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[*] posted on 18-9-2013 at 19:15


Usually the anhydrous ammonia gas is first dissolved in pure ethanol, and this is then reacted with the ethyl acetate. Otherwise, ammonia is not very soluble in ethyl acetate.

Another method is to heat ammonium acetate in a sealed tube under flame.
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[*] posted on 6-11-2013 at 07:02


Would this also work with primary amines or their salts? Could anybody try this with ammonium chloride?



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[*] posted on 11-4-2015 at 11:45


Acetamide is an interesting compound and making it from something so common as Ethyl Acetate would be excellent. However, I have serious doubts about this procedure.

Polesch, how do you know that you don't simply have Ammonium Acetate crystals? Acetamide melts at 79ºC, Ammonium Acetate melts at 110ºC, I believe, while starting to slowly decompose. How accurate was your melting point measurement?

We all know that Ethyl Acetate hydrolyzes readily in water, as follows:
Ethyl Acetate(l) + Water(l) --> Acetic Acid(aq) + Ethanol(aq)

Ammonia readily forms Ammonium Hydroxide in water:
NH3(aq) + H2O(l) <--> NH4+(aq) + OH-(aq)

Ammonium Hydroxide and Acetic Acid react to form Ammonium Acetate. The equilibrium of the hydrolysis of Ethyl Acetate shifts to the right and proceeds to completion. We should be left with Ammonium Acetate, Water and Ethanol.

I can't thing of a way this process could actually work.
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[*] posted on 11-4-2015 at 11:58


There is a procedure in Vogel, 3rd edition page 403. Ethyl acetate will not hydrolyze simply by placing it into water, it either needs refluxing with an acid catalyst or the addition of a stoichiometric amount of base(typically hydroxide). The base acts by nucleophilically attacking the carbonyl in ethyl acetate with the ethoxide then acting as a leaving group and being protonated by the now acidic hydrogen originally present on the hydroxide. In ammonia, I doubt that the hydroxide concentration is high enough for this to happen at any appreciable rate. The free ammonia in solution can instead act as a nucleophile itself, this still results in ethoxide as the leaving group, but it leaves acetamide rather than acetate as the final product.
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[*] posted on 11-4-2015 at 12:48


@gdflp,

Quote:

Ethyl acetate will not hydrolyze simply by placing it into water, it either needs refluxing with an acid catalyst or the addition of a stoichiometric amount of base(typically hydroxide).


The equilibrium constant for the hydrolysis of Ethyl Acetate is around 0,25. So yes, Ethyl Acetate hydrolyzes just by coming in contact with water (of course, only a part of it gets hydrolyzed).

Adding a stoichiometric amount of base will, as you said, make the equilibrium go into completion.


Quote:

The base acts by nucleophilically attacking the carbonyl in ethyl acetate with the ethoxide then acting as a leaving group and being protonated by the now acidic hydrogen originally present on the hydroxide. In ammonia, I doubt that the hydroxide concentration is high enough for this to happen at any appreciable rate



The hydroxide concentration in ammonia is probably low, as you said:
NH3(aq) + H2O(l) <--> NH4+(aq) + OH-(aq)

However, the neutralization reaction between Acetic Acid and Ammonium Hydroxide (an acid/base reaction) happens much much much more easily than the reaction between free ammonia and Ethyl Acetate.

As both Ammonium Hydroxide and Acetic Acid disappear, the ammonia equilibrium will shift to the right making more Ammonium Hydroxide and the equilibrium of the hydrolysis of Ethyl Acetate will also shift to the right, producing more Acetic Acid.

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[*] posted on 11-4-2015 at 13:18


Quote: Originally posted by HgDinis25  

Quote: Originally posted by gdflp  

Ethyl acetate will not hydrolyze simply by placing it into water, it either needs refluxing with an acid catalyst or the addition of a stoichiometric amount of base(typically hydroxide).


The equilibrium constant for the hydrolysis of Ethyl Acetate is around 0,25. So yes, Ethyl Acetate hydrolyzes just by coming in contact with water (of course, only a part of it gets hydrolyzed).

Adding a stoichiometric amount of base will, as you said, make the equilibrium go into completion.

Where did you get this number? Also this gives no information about the rate of this uncatalyzed hydrolysis reaction, I would expect it to be extremely slow.
Quote: Originally posted by HgDinis25  

Quote: Originally posted by gdflp  

The base acts by nucleophilically attacking the carbonyl in ethyl acetate with the ethoxide then acting as a leaving group and being protonated by the now acidic hydrogen originally present on the hydroxide. In ammonia, I doubt that the hydroxide concentration is high enough for this to happen at any appreciable rate



The hydroxide concentration in ammonia is probably low, as you said:
NH3(aq) + H2O(l) <--> NH4+(aq) + OH-(aq)

However, the neutralization reaction between Acetic Acid and Ammonium Hydroxide (an acid/base reaction) happens much much much more easily than the reaction between free ammonia and Ethyl Acetate.

As both Ammonium Hydroxide and Acetic Acid disappear, the ammonia equilibrium will shift to the right making more Ammonium Hydroxide and the equilibrium of the hydrolysis of Ethyl Acetate will also shift to the right, producing more Acetic Acid.


The issue is that, as I explained above, not much free acetic acid will be present in the solution at any given time. In addition, the equilibrium between acetic acid and ammonia, a weak acid and a weak base, is not overly favorable to begin with and ammonia acetate will decompose to acetic acid and ammonia on prolonged standing, this is the reason that ammonium acetate can not simply be made by mixing ammonia and vinegar. No doubt, some ammonium acetate will be formed but this is not a significant problem for the reaction as most of it will dehydrate to acetamide when the mixture is distilled during workup.

[Edited on 4-11-2015 by gdflp]
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[*] posted on 11-4-2015 at 13:26


Quote: Originally posted by HgDinis25  
The equilibrium constant for the hydrolysis of Ethyl Acetate is around 0,25. So yes, Ethyl Acetate hydrolyzes just by coming in contact with water (of course, only a part of it gets hydrolyzed).

The equilibrium constant for the reaction of ethyl acetate with water is totally irrelevant for the ammonolysis of ethyl acetate. You are confusing the kinetics with thermodynamics.
Quote:
Adding a stoichiometric amount of base will, as you said, make the equilibrium go into completion.

Only if the base as such is non-nucleophilic in water, thus making only the hydroxide ions as the only relevant nucleophilic species present. Otherwise, other reaction pathways could prevail. And the reaction rate would still be determined by the kinetics and not thermodynamics.
Quote:
The hydroxide concentration in ammonia is probably low, as you said:NH3(aq) + H2O(l) <--> NH4+(aq) + OH-(aq)

It is not just about the hydroxide concentration being low, it is about it being very low in relation to the concentration of ammonia.
Quote:
However, the neutralization reaction between Acetic Acid and Ammonium Hydroxide (an acid/base reaction) happens much much much more easily than the reaction between free ammonia and Ethyl Acetate.

It takes acetic acid for deprotonating acetic acid. Since there is no acetic acid, the reaction cannot give a solution of ammonium acetate as the main product. The acetate can only form by the hydrolysis of ethyl acetate, a reaction that is of minor importance considering the wast majority of the nucleophiles in the system is ammonia molecules.

Consider it this way. You have plenty of ammonia and only very little of hydroxide. Both are comparably nucleophilic. So why would you expect the acetate as the main product? It makes more logic for the acetamide to be the main product. (And experimentally acetamide is the main product!)

Essentially, you are using a faulty logic. Instead of looking at the entire system, you look just at one tiny component of the system (the hydroxide) and misuse thermodynamic data by ignoring the kinetic aspects. In chemistry you need to evaluate every problem holistically, like evaluating the entire system, not just parts of it.

Furthermore, reacting acyl chlorides by adding them to aqueous ammonia gives the corresponding carboxamides as main product in addition to ammonium chloride byproduct. So why would you expect the way less reactive ethyl acetate undergoing the hydrolysis pathway rather than the ammonolysis? So even without using any logical thinking, merely using deduction makes your conclusion that ammonium acetate should be the main product appear quite unusual.




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[*] posted on 11-4-2015 at 13:39


Quote: Originally posted by Nicodem  

Consider it this way. You have plenty of ammonia and only very little of hydroxide. Both are comparably nucleophilic.

Are they? I was under the impression that since hydroxide was a negatively charged nucleophile, it was better nucleophile than neutral nucleophiles such as ammonia, even though the nitrogen equivalent, amide, is a better nucleophile than hydroxide.

[Edited on 4-11-2015 by gdflp]
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[*] posted on 11-4-2015 at 14:04


Quote: Originally posted by gdflp  
Are they? I was under the impression that since hydroxide was a negatively charged nucleophile, it was better nucleophile than neutral nucleophiles such as ammonia, even though the nitrogen equivalent, amide, is a better nucleophile than hydroxide.

Just because a nucleophile is charged, it does not mean that it is stronger that any neutral nucleophile. A negative charge here is merely a lone electron pair. A charge on a poorly polarizable ion can even reduce the nucleophilicity in protic solvents. For example, the hydroxide ion is very strongly solvated in water due to its excellent H-bonding ability. For this reason its nucleophilicity in water is not particularly high.

According to Meyr et al. measurements (see his database), hydroxide in water is just slightly more nucleophilic than ammonia in water:

ammonia in water
N Parameter: 9.48
SN Parameter: 0.59

OH- in water
N Parameter: 10.47
SN Parameter: 0.61

In addition, ammonia can react with ethyl acetate in both phases while hydroxide can only react with ethyl acetate in the aqueous phase. It would be interesting to measure the kinetics of the ammonolysis in each phase.




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[*] posted on 11-4-2015 at 14:24


@Nicodem,


Quote:
The equilibrium constant for the reaction of ethyl acetate with water is totally irrelevant for the ammonolysis of ethyl acetate. You are confusing the kinetics with thermodynamics.


I was merely stating that Ethyl Acetate can hydrolyze just by coming in contact with water because of gdflp's claim "Ethyl acetate will not hydrolyze simply by placing it into water"

Careful with your conclusions. Before saying I'm confusing kinetics with thermodynamics (I don't even know why you brought them up on such an easy argument to understand):
Person 1 - Ethyl Acetate needs more than just water to hydrolyze.
Person 2 - Actually, the equilibrium constant is 0,25 (not 0,000001 for instance). Therefore the reaction happens. The rate may be slow but it is there.

Everything else you said does make sense. However, I would expect the rate of reaction to form acetamide would be much slower than the acid/base reaction between Acetic Acid and Ammonium Hydroxide.


Quote:

Essentially, you are using a faulty logic. Instead of looking at the entire system, you look just at one tiny component of the system (the hydroxide) and misuse thermodynamic data by ignoring the kinetic aspects. In chemistry you need to evaluate every problem holistically, like evaluating the entire system, not just parts of it.


I was focusing on the hydroxide part, as you said, because I thought the rate of the acid/base reaction to be much greater than the rate of Acetamide formation. I may be wrong, though. Anyway, let's elaborate on this:
misuse thermodynamic data by ignoring the kinetic aspects

Where did I misuse thermodynamic data, as you claim? And ignored kinteic aspects?
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[*] posted on 11-4-2015 at 14:33


Quote: Originally posted by HgDinis25  

Careful with your conclusions. Before saying I'm confusing kinetics with thermodynamics (I don't even know why you brought them up on such an easy argument to understand):
Person 1 - Ethyl Acetate needs more than just water to hydrolyze.
Person 2 - Actually, the equilibrium constant is 0,25 (not 0,000001 for instance). Therefore the reaction happens. The rate may be slow but it is there.
...
Where did I misuse thermodynamic data, as you claim? And ignored kinteic aspects?


The equilibrium constant is thermodynamic data. Whether or not the reaction will occur at *any* rate in the absence of a catalyst is a kinetics question.

There are many, many reactions that are thermodynamically favourable, but do not occur under standard conditions, even on the geological time scale. Diamond converting to graphite has a favourable Gibb's Free Energy change (it has no eq'm constant), but it does not occur. Hydrogen mixed with oxygen will not react in the absence of a spark or catalyst, despite its sky-high eq'm constant.

The reaction 2 Ag+(aq) + 2 I-(aq) = 2 Ag(s) + I2(s) has a very high eq'm constant, but that reaction also simply doesn't happen upon mixing the two reactants, for obvious reasons, and no catalyst in the world will make it happen.




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[*] posted on 11-4-2015 at 14:40


Quote: Originally posted by HgDinis25  

I was merely stating that Ethyl Acetate can hydrolyze just by coming in contact with water because of gdflp's claim "Ethyl acetate will not hydrolyze simply by placing it into water"

Careful with your conclusions. Before saying I'm confusing kinetics with thermodynamics (I don't even know why you brought them up on such an easy argument to understand):
Person 1 - Ethyl Acetate needs more than just water to hydrolyze.
Person 2 - Actually, the equilibrium constant is 0,25 (not 0,000001 for instance). Therefore the reaction happens. The rate may be slow but it is there.

Everything else you said does make sense. However, I would expect the rate of reaction to form acetamide would be much slower than the acid/base reaction between Acetic Acid and Ammonium Hydroxide.

I was talking about this instance, the ethyl acetate hydrolysis will not occur at a rate fast enough to introduce acetic acid and interfere with the reaction. Again, the aminolysis in this case will be preferred because the ammonia is present in such a large concentration as compared to the hydroxide, both of which have reasonably comparable nucleophilicity in water as shown by the data Nicodem provided.

Quote: Originally posted by HgDinis25  

I was focusing on the hydroxide part, as you said, because I thought the rate of the acid/base reaction to be much greater than the rate of Acetamide formation. I may be wrong, though. Anyway, let's elaborate on this:
misuse thermodynamic data by ignoring the kinetic aspects

Where did I misuse thermodynamic data, as you claim? And ignored kinteic aspects?

By quoting equilibriums, you are using thermodynamic data which is less relevant in this case. When determining the favored product when dealing with a mixture with competing reactions, kinetic data is often far more important, of which you provided none.

@Nicodem
Thank you for that data, my post wasn't intended to disagree with you, I was merely curious as I have always been taught that negatively charged nucleophiles were better nucleophiles than neutral nucleophiles.
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[*] posted on 11-4-2015 at 14:40


Quote: Originally posted by HgDinis25  
Acetamide is an interesting compound and making it from something so common as Ethyl Acetate would be excellent. However, I have serious doubts about this procedure.

Here's a reference from 1907. They find only traces of ammonium salt.
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