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Problem in synthesis of propyl acetate
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Mark Gallaway
Problem in synthesis of propyl acetate
Hello chemists,
I made a second synthesis of propyl acetate, and I am very satisfied. The previous synthesis was probably unsuccessful due to the large amount of sulfuric acid. I did the synthesis in the same amount of reactants, 106 g acetic acid, 100 g propan-1-ol but sulfuric acid I used about 17 ml. I started to warm up, and after a few minutes the solution became cloudy, but as the temperature rises, the haze disappeared (and color was not brown as in the previous synthesis, but colorless). I carried out the reflux for 2 hours, allowed to cool, and then rinsed three times with 20 ml of cold solution of NaHSO4, and the last rinse with 20 ml of cold water. Of course, traces of acids will be in solution, but I don't need high purity. Now I have about 190 ml of crude propyl acetate, which is dried with calcium chloride. Next time I distill.
Thank you very much for your advice on my question.
I made a second synthesis of propyl acetate, and I am very satisfied. The previous synthesis was probably unsuccessful due to the large amount of sulfuric acid. I did the synthesis in the same amount of reactants, 106 g acetic acid, 100 g propan-1-ol but sulfuric acid I used about 17 ml. I started to warm up, and after a few minutes the solution became cloudy, but as the temperature rises, the haze disappeared (and color was not brown as in the previous synthesis, but colorless). I carried out the reflux for 2 hours, allowed to cool, and then rinsed three times with 20 ml of cold solution of NaHSO4, and the last rinse with 20 ml of cold water. Of course, traces of acids will be in solution, but I don't need high purity. Now I have about 190 ml of crude propyl acetate, which is dried with calcium chloride. Next time I distill.
Thank you very much for your advice on my question.
Thank you all for your answers (I didn't expect so many). I will try the synthesis again and use a smaller amount of H2SO4 (about 15 ml) and wash in a small amount of cold water and soda bicarbonate.
I don't have other solvents and I don't want to order them.
Thank you all for your answers (I didn't expect so many). I will try the synthesis again and use a smaller amount of H2SO4 (about 15 ml) and wash in a small amount of cold water and soda bicarbonate.
I don't have other solvents and I don't want to order them.
I think you should neutralize the acid in the workup before washing with water. I strongly vote against adding any solvent this will be very difficult to remove. Use sat. NaHCO3 (aq).
I think you should neutralize the acid in the workup before washing with water. I strongly vote against adding any solvent this will be very difficult to remove. Use sat. NaHCO3 (aq).
I dont think the amount of sulfuric acid would cause any problems per se - I generally use 10% v/v sulfuric acid:alcohol for a Fischer and it works fine. Why do you think using more would cause the ester to hydrolyse? You wouldn't expect acid catalysed hydrolysis of a propyl ester, and the quantity of acid ensures there's no water around anyway. I'd also doubt if propyl acetate is water soluble (since ethyl acetate isnt!)
Next time I would try using another (reasonably volatile) solvent in your work-up. The product should be soluble in hydrocarbon solvents (probably even petrol, but definitely ether). I would do the following after the reaction:
-Add a large amount of water (maybe 500 mL) cautiously and with cooling (bear in mind H2O reacts exothermically with anhydrous H2SO4) -Once cooled, add a decent amount of organic solvent (maybe 500 mL again) and separate off the aqueous layer. -The organic solvent will still contain some acetic acid, so so then do a couple of washes with aq. NaHCO3 (bearing in mind the residual acid will produce CO2, so make sure the sep funnel is left open to vent. I've got a 3 inch scar on my right hand from an exploding sep funnel!) - Vac off the organic solvent (carefully, propyl acetate has a bp of 102 C)
If you need a high yield you could introduce a few back-extractions.
I dont think the amount of sulfuric acid would cause any problems per se - I generally use 10% v/v sulfuric acid:alcohol for a Fischer and it works fine. Why do you think using more would cause the ester to hydrolyse? You wouldn't expect acid catalysed hydrolysis of a propyl ester, and the quantity of acid ensures there's no water around anyway. I'd also doubt if propyl acetate is water soluble (since ethyl acetate isnt!)
Next time I would try using another (reasonably volatile) solvent in your work-up. The product should be soluble in hydrocarbon solvents (probably even petrol, but definitely ether). I would do the following after the reaction:
-Add a large amount of water (maybe 500 mL) cautiously and with cooling (bear in mind H2O reacts exothermically with anhydrous H2SO4) -Once cooled, add a decent amount of organic solvent (maybe 500 mL again) and separate off the aqueous layer. -The organic solvent will still contain some acetic acid, so so then do a couple of washes with aq. NaHCO3 (bearing in mind the residual acid will produce CO2, so make sure the sep funnel is left open to vent. I've got a 3 inch scar on my right hand from an exploding sep funnel!) - Vac off the organic solvent (carefully, propyl acetate has a bp of 102 C)
If you need a high yield you could introduce a few back-extractions.
I'm sorry, I wrote it wrong. I think more sulfuric acid the better, because sulfuric acid binds water during esterification. Acetic acid is 99% and propan-1-ol is 99.5%.
I'm sorry, I wrote it wrong. I think more sulfuric acid the better, because sulfuric acid binds water during esterification. Acetic acid is 99% and propan-1-ol is 99.5%.
I think the problem is that acetic acid is likely soluble in propylacetate and propanol therefore the layers are not separating. Adding more water or brine should help but IMO the best is just to slowly dilute with aq. base to neutralize the acids which should suffice for the separation of both layers
I think the problem is that acetic acid is likely soluble in propylacetate and propanol therefore the layers are not separating. Adding more water or brine should help but IMO the best is just to slowly dilute with aq. base to neutralize the acids which should suffice for the separation of both layers
I'm sorry, I wrote it wrong. I think more sulfuric acid the better, because sulfuric acid binds water during esterification. Acetic acid is 99% and propan-1-ol is 99.5%.
You absolutely do not need to add that much. Get a Dean-Stark trap to help with water removal if it's a concern (sometimes you can get away without).
Probably your main issues are 1.) you're hydrolysing your ester through the completely unnecessary amount of acid you've added and, 2.) your reaction components are all miscible in water.
I'm sorry, I wrote it wrong. I think more sulfuric acid the better, because sulfuric acid binds water during esterification. Acetic acid is 99% and propan-1-ol is 99.5%.
You absolutely do not need to add that much. Get a Dean-Stark trap to help with water removal if it's a concern (sometimes you can get away without).
Probably your main issues are 1.) you're hydrolysing your ester through the completely unnecessary amount of acid you've added and, 2.) your reaction components are all miscible in water.
I disagree. Wash out the bulk of the acid as aq. H2SO4, then the NaHCO3 wash will be a lot less frisky, as the bulk of the acid is gone. Otherwise you will spend about half a day doing dropwise additions until gas evolution ceases.
An alternative would be to work-up using NaOH carefully to neutral pH. At least there would be no gas evolution (but still a big exotherm).
Why do you think Et2O would be hard to get rid of? Theres a pretty massive difference in boiling point with the product. That said, in principle it should be unnecessary, particularly when the reaction is on a decent scale - it should phase separate without additional solvent. However, clearly the OP was having difficult achieving phase separation so I hoped this suggestion would help.
I disagree. Wash out the bulk of the acid as aq. H2SO4, then the NaHCO3 wash will be a lot less frisky, as the bulk of the acid is gone. Otherwise you will spend about half a day doing dropwise additions until gas evolution ceases.
An alternative would be to work-up using NaOH carefully to neutral pH. At least there would be no gas evolution (but still a big exotherm).
Why do you think Et2O would be hard to get rid of? Theres a pretty massive difference in boiling point with the product. That said, in principle it should be unnecessary, particularly when the reaction is on a decent scale - it should phase separate without additional solvent. However, clearly the OP was having difficult achieving phase separation so I hoped this suggestion would help.
I made a second synthesis of propyl acetate, and I am very satisfied. The previous synthesis was probably unsuccessful due to the large amount of sulfuric acid. I did the synthesis in the same amount of reactants, 106 g acetic acid, 100 g propan-1-ol but sulfuric acid I used about 17 ml. I started to warm up, and after a few minutes the solution became cloudy, but as the temperature rises, the haze disappeared (and color was not brown as in the previous synthesis, but colorless). I carried out the reflux for 2 hours, allowed to cool, and then rinsed three times with 20 ml of cold solution of NaHSO4, and the last rinse with 20 ml of cold water.
Of course, traces of acids will be in solution, but I don't need high purity.
Now I have about 190 ml of crude propyl acetate, which is dried with calcium chloride. Next time I distill.
Thank you very much for your advice on my question.
I made a second synthesis of propyl acetate, and I am very satisfied. The previous synthesis was probably unsuccessful due to the large amount of sulfuric acid. I did the synthesis in the same amount of reactants, 106 g acetic acid, 100 g propan-1-ol but sulfuric acid I used about 17 ml. I started to warm up, and after a few minutes the solution became cloudy, but as the temperature rises, the haze disappeared (and color was not brown as in the previous synthesis, but colorless). I carried out the reflux for 2 hours, allowed to cool, and then rinsed three times with 20 ml of cold solution of NaHSO4, and the last rinse with 20 ml of cold water.
Of course, traces of acids will be in solution, but I don't need high purity.
Now I have about 190 ml of crude propyl acetate, which is dried with calcium chloride. Next time I distill.
Thank you very much for your advice on my question.
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I don't have other solvents and I don't want to order them.
I don't have other solvents and I don't want to order them.
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Next time I would try using another (reasonably volatile) solvent in your work-up. The product should be soluble in hydrocarbon solvents (probably even petrol, but definitely ether). I would do the following after the reaction:
-Add a large amount of water (maybe 500 mL) cautiously and with cooling (bear in mind H2O reacts exothermically with anhydrous H2SO4)
-Once cooled, add a decent amount of organic solvent (maybe 500 mL again) and separate off the aqueous layer.
-The organic solvent will still contain some acetic acid, so so then do a couple of washes with aq. NaHCO3 (bearing in mind the residual acid will produce CO2, so make sure the sep funnel is left open to vent. I've got a 3 inch scar on my right hand from an exploding sep funnel!)
- Vac off the organic solvent (carefully, propyl acetate has a bp of 102 C)
If you need a high yield you could introduce a few back-extractions.
Next time I would try using another (reasonably volatile) solvent in your work-up. The product should be soluble in hydrocarbon solvents (probably even petrol, but definitely ether). I would do the following after the reaction:
-Add a large amount of water (maybe 500 mL) cautiously and with cooling (bear in mind H2O reacts exothermically with anhydrous H2SO4)
-Once cooled, add a decent amount of organic solvent (maybe 500 mL again) and separate off the aqueous layer.
-The organic solvent will still contain some acetic acid, so so then do a couple of washes with aq. NaHCO3 (bearing in mind the residual acid will produce CO2, so make sure the sep funnel is left open to vent. I've got a 3 inch scar on my right hand from an exploding sep funnel!)
- Vac off the organic solvent (carefully, propyl acetate has a bp of 102 C)
If you need a high yield you could introduce a few back-extractions.
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Acetic acid is 99% and propan-1-ol is 99.5%.
Acetic acid is 99% and propan-1-ol is 99.5%.
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If less H2SO4 is used neutralization is no problem.
If less H2SO4 is used neutralization is no problem.
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Typically perhaps half a mL would sulfuric acid would suffice to catalyze a Fischer esterification at this scale.
Do the basic neutralization first, otherwise the extra acetic acid will be distilled at a somewhat similar temp and could contaminate.
Are your solvents very wet? A pretty small amount of water can grind an esterification to a halt.
Typically perhaps half a mL would sulfuric acid would suffice to catalyze a Fischer esterification at this scale.
Do the basic neutralization first, otherwise the extra acetic acid will be distilled at a somewhat similar temp and could contaminate.
Are your solvents very wet? A pretty small amount of water can grind an esterification to a halt.
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You absolutely do not need to add that much. Get a Dean-Stark trap to help with water removal if it's a concern (sometimes you can get away without).
Probably your main issues are 1.) you're hydrolysing your ester through the completely unnecessary amount of acid you've added and, 2.) your reaction components are all miscible in water.
You absolutely do not need to add that much. Get a Dean-Stark trap to help with water removal if it's a concern (sometimes you can get away without).
Probably your main issues are 1.) you're hydrolysing your ester through the completely unnecessary amount of acid you've added and, 2.) your reaction components are all miscible in water.
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VOTE
An alternative would be to work-up using NaOH carefully to neutral pH. At least there would be no gas evolution (but still a big exotherm).
Why do you think Et2O would be hard to get rid of? Theres a pretty massive difference in boiling point with the product. That said, in principle it should be unnecessary, particularly when the reaction is on a decent scale - it should phase separate without additional solvent. However, clearly the OP was having difficult achieving phase separation so I hoped this suggestion would help.
An alternative would be to work-up using NaOH carefully to neutral pH. At least there would be no gas evolution (but still a big exotherm).
Why do you think Et2O would be hard to get rid of? Theres a pretty massive difference in boiling point with the product. That said, in principle it should be unnecessary, particularly when the reaction is on a decent scale - it should phase separate without additional solvent. However, clearly the OP was having difficult achieving phase separation so I hoped this suggestion would help.
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