[lukas.stib]

Hello, I need to advise what I did wrong.

I was producing propyl acetate from propan-1-ol and acetic acid, and unfortunately the layers were not separated during cleaning in a separating funnel.

I made: 100 g of propan-1-ol
             106 g of acetic acid
             about 30-40 ml of sulfuric acid (I always use a lot of sulfuric acid to make water).

I carried out a reflux for about 2.5 hours (the solution turned to beige color) then poured into a separating funnel and poured 50 ml of cold water. Two layers should be created, but nothing has been done. So I mixed up and added a little more water, but still nothing. So I still poured a soda solution into it (it was very bubbling!) but two layers were still not forming. So I destroyed it...
I want to ask what I did wrong?
Next time, it would not be better to carry out the distillation immediately after reflux, collect everything up to about 104°C, and then wash with a small amount of water, sodium bicarbonate and then carry out the final distillation?
For more soluble esters in water, I think this method would be better (I had a similar problem in producing methyl acetate).

I don't want to clean the product with sodium hydroxide, ether... I don't need it so clean product, I'm just doing it for fun, so I stay with baking soda and water.

Thank you very much.

[wildfyr]

That is a HUGE amount of sulfuric acid?!? To make water? What does that mean? I am so confused.

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.

[lukas.stib]

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%.

[hypervalent_iodine]

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.

[clarkstill]

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.

[rolnor]

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).

[clarkstill]

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.

[kriggy]

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

[rolnor]

Its difficult to separate propylacetat and Et2O completely even with fractional distillation.
If less H2SO4 is used neutralization is no problem.

[lukas.stib]

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.

[lukas.stib]

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.

[rolnor]

Great!