Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: a confused chiral girl on March 21, 2007, 08:19:46 PM
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Hi,
I am using 1-octanol and glacial acetic acid, in excess, to prepare octyl acetate, with the use of sulfuric acid as catalyst. I put the reaction to reflux until it went to completion, and I am wondering besides the octyl acetate, what else is in the reaction flask?
I thought there would be contamination of acetic acid (because it was in excess) and sulfuric acid (since it was the catalyst), and water. but after doing some research on this type of experiment, I found that what should be left in the flask is acetic acid, 1-octanol (alcohol) and water. I am hesitant towards this because it says the catalyst, sulfuric acid would not be one of the products like I proposed. Can anyone confirm this with me? ???
If it was sulfuric acid, would using saturated NaCl to wash the organic layer after extraction (octyl acetate) be able to remove the sulfuric acid?
thank you!!! :D
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I am using 1-octanol and glacial acetic acid, in excess, to prepare octyl acetate, with the use of sulfuric acid as catalyst. [...] what else is in the reaction flask?
[...] I found that what should be left in the flask is acetic acid, 1-octanol (alcohol) and water. I am hesitant towards this because it says the catalyst, sulfuric acid would not be one of the products like I proposed. Can anyone confirm this with me?
- You were right about the sulfuric acid. You put it in, it didn't react, it's still there.
- Yes, there will be acetic acid left, it's in excess. You were right about that too.
- There will be 1-octanol left, because no reaction ever goes to 100% completion. Maybe 95% or 99.9%, but you'll never COMPLETELY get rid of your reactants.
- Water will be in there too, since that's an esterification product.
If it was sulfuric acid, would using saturated NaCl to wash the organic layer after extraction (octyl acetate) be able to remove the sulfuric acid?
I'm not sure how to explain this, or even if I'm right...someone else can probably help out there.
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Washing with saturated NaCl would partially remove the sulfuric acid since is is soluble in water. However, sulfuric acid is also partially soluble in the organic layer so it won't be removed too efficiently. There is another way to extract both the sulfuric acid and the excess acetic acid, however. How would you increase the solubility of these acidic compounds in aqueous solution?
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If it was sulfuric acid, would using saturated NaCl to wash the organic layer after extraction (octyl acetate) be able to remove the sulfuric acid?
Yes. Sulfuric acid is much more soluble in water than in octanol so it will be washed out in the water layer. The reason you use saturated sodium chloride solution is that organic liquids are often sparingly soluble (and sometimes considerably soluble) in pure water, but much less soluble in saturated salt solution. So when you wash the organic extract with saturated salt solution you don't lose some of your organic product in the water layer.
There is also a widly believed myth that washing an organic layer with saturated salt solution (brine) will halp "dry" or remove some of the water from the organic layer. For the rationale I direct your attention to: "The Myth of Saturated Aqueous Sodium Chloride Solution (Brine) for Drying Organic Solutions", James B. Ellern, J. Org. Chem. 1982, 47, 3569.
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Washing with saturated NaCl would partially remove the sulfuric acid since is is soluble in water. However, sulfuric acid is also partially soluble in the organic layer so it won't be removed too efficiently. There is another way to extract both the sulfuric acid and the excess acetic acid, however. How would you increase the solubility of these acidic compounds in aqueous solution?
washing the organic layer with NaHCO3 (sodium bicarbonate) can remove the sulfuric acid as well? then would the equation be NaHCO3 + H2SO4 --> Na2SO4, but can you please balance it..I can't seem to get it balanced properly..
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washing the organic layer with NaHCO3 (sodium bicarbonate) can remove the sulfuric acid as well? then would the equation be NaHCO3 + H2SO4 --> Na2SO4, but can you please balance it..I can't seem to get it balanced properly..
2NaHCO3 + H2SO4 =
It removes the rest of H2SO4 and CH3COOH from organic layer.
Then you can separate alcobol and ester by distillation
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There is also a widly believed myth that washing an organic layer with saturated salt solution (brine) will halp "dry" or remove some of the water from the organic layer. For the rationale I direct your attention to: "The Myth of Saturated Aqueous Sodium Chloride Solution (Brine) for Drying Organic Solutions", James B. Ellern, J. Org. Chem. 1982, 47, 3569.
But this paper does say that brine will remove some of the dissolved water:
In fact, saturated brine can remove
no more than about 25% of dissolved water
No-one ever asserted to me that brine will remove all the water during work-up - this is why you would then use a drying agent such as MgSO4.
The authors seem to be trying to make a big deal out of differentiating between "some" and "much" , and while it interesting to some (or much ;) ) extent, I think this paper is really a waste of time, and essentially just an excuse to get published!
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I had the same reaction to that paper. I have done lots of workups where my cloudy and obviously wet organic layer got nice and clear after a brine wash.
Salt is definitely cheaper than MgSO4 too! Well worth it just based on economics!
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washing the organic layer with NaHCO3 (sodium bicarbonate) can remove the sulfuric acid as well? then would the equation be NaHCO3 + H2SO4 --> Na2SO4, but can you please balance it..I can't seem to get it balanced properly..
Here is a more correct unbalanced equation:
NaHCO3 + H2SO4 --> Na2SO4 + H2O + CO2
This one should be easier to balance.
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Also H2SO4 could be efficently removed with Ba(OH)2 or the cheaper Ca(OH)2:
H2SO4 + Ba(OH)2 --> BaSO4 + 2H2O
H2SO4 +Ca(OH)2 --> CaSO4 + 2H2O
CaSO4 is slightly soluble in water so barite water is better.
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It's better to try to avoid introducing OH-, though, since esters are sensitive to hydrolysis. This is especially true if you plan to distill the ester afterward.
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Then you may introduce BaO or CaO as solid basic oxides :) Initially heterophase reaction though...Filtration and everything will be alright with the product ester. Organic base astriethylamine or pyridine is another choice alternative for neutralization the excess acid i think. Also ion exchange chromatography with some basic polymer resin in a flash chromatography column...Anyway Shotten-Bouman method for esterification is better in preparative chemistry i mean:
ROH + AcCl --> ester and HCl aceptor