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DraconicAcid
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Recrystallize it from water. It dissolves in hot water, precipitates from cold.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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Paddywhacker
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While brine is often useful for assisting separations, I think that in this case it is causing problems.
Firstly, the excess methanol is decreasing the solubility of salt, causing it to crash out of solution, and secondly, brine is denser than water,
making the aqueous phase closer in density to the heavy methyl salicylate. The closer the difference in density, the more difficult the separation.
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ChemSwede
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Quote: Originally posted by Paddywhacker  | While brine is often useful for assisting separations, I think that in this case it is causing problems.
Firstly, the excess methanol is decreasing the solubility of salt, causing it to crash out of solution, and secondly, brine is denser than water,
making the aqueous phase closer in density to the heavy methyl salicylate. The closer the difference in density, the more difficult the separation.
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That's good information! Maybe some of the milky stuff was NaCl that crashed out of solution.
But shouldn't methyl salicylate combine with ethyl acetate anyway, leaving methanol and NaCl in the aqueous layer?
I clearly saw two phases when I added ethyl acetate.
I'm actually a bit uncertain about how to extract my product with the best yield.
There are a few threads about Me-salicylate here on SM, which I have read.
Some suggest boiling off the methanol before adding water/brine. Others state that that would concentrate the H2SO4, leading to problems. I suppose
the acid could hydrolyze the ester.
Some just add water and then ethyl acetat. The methanol goes in the water phase and the product into the ethyl acetate.
What's optimal?
Also I'm wondering about increasing yield during reflux. Since it's an equilibrium I suppose that removing water would create more product. For
instance, I have a Dean Stark trap, but I'm not sure if it's any good here, since methanol is soluble in water.
Adding more H2SO4 might get rid of some water, but then the ester might hydrolyze.
How about adding some drying agent?
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ChemSwede
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Sounds good if that works. I can't seem to find any data on solubility in hot water, but it would be much more convenient to use that method.
[Edited on 27-12-2013 by ChemSwede]
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DraconicAcid
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| Quote: Originally posted by ChemSwede |
Sounds good if that works. I can't seem to find any data on solubility in hot water, but it would be much more convenient to use that method.
[Edited on 27-12-2013 by ChemSwede] |
It works- my grade-11-equivalent students do it every year, to separate it from a mixture containing salt, sand, MnO2 and glycerol. I can
look up the solubilities when I'm back in my office.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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ChemSwede
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| Quote: Originally posted by DraconicAcid | | Quote: Originally posted by ChemSwede |
Sounds good if that works. I can't seem to find any data on solubility in hot water, but it would be much more convenient to use that method.
[Edited on 27-12-2013 by ChemSwede] |
It works- my grade-11-equivalent students do it every year, to separate it from a mixture containing salt, sand, MnO2 and glycerol. I can
look up the solubilities when I'm back in my office. |
I just found this page:
http://www.ce.gxnu.edu.cn/organic/net_course/content/Crystal...
It says that the solubility for salicylic acid in water at 100 C is 6,67g/10ml.
So I will prepare some pure salicylic acid and then go for the methyl salicylate again.
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ChemSwede
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Attempting to synthesize methyl salicylate again.
I've kind of failed once using 5,6g salicylic acid (prepared from sodium salicylate), 20ml methanol and 2ml conc. H2SO4.
I refluxed for 1½h at 70C.
Afterwards there was a strong smell of methyl salicylate, so I added ethyl acetate and water. Separated the organic layer and evaporated the ethyl
acetate. I was left with a lot of white crystals with a strong scent of my ester.
i could not isolate any product since there was so much unreacted salicylic acid left.
I have now dissolved the unreacted salicylic acid from my last attempt in 40ml methanol. I added 3ml H2SO4 and a few boiling chips.
The mixture is refluxing at 70C, and I'm planning to do that for 2h this time.
Any ideas on how to make all the salicylic acid react? Temp, reflux time, adding more methanol during reflux?
How do I isolate the product most efficiently? Adding water and recover the ester at the bottom or boil away the methanol and add water f ex? There
are a few suggestions on the forum.
Some say that boiling away the methanol concentrates the remaining acid, which is not good for the product.
Would be nice to isolate the product this time. Wonderful smell.
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Mailinmypocket
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Try using dichloromethane or chloroform, if you can, instead of ethyl acetate
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ChemSwede
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Update on the synthesis.
I left the reaction for ½h, and when I returned the boiling had stopped, but the temp was still 70C.
Did the methanol react or boil away?
Perhaps I should run the reflux at 60C since methanol boils at around 70C. My Liebig condenser is just 20cm so perhaps it cannot keep the methanol
from boiling away.
I added another 25ml of methanol and the boiling started again. Still refluxing at 70C.
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ChemSwede
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I have DCM, but I'm a bit reluctant to use it since it's hard to get, and since it's cancerogenous.
It should work with ethyl acetate I guess. I know it has a higher boiling point than DCM, and it can be hard to make it form two layers with water
sometimes.
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Mailinmypocket
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You might want to consider it. Check out this link here for solubility of salicylic acid in ethyl acetate vs dichloromethane:
http://lxsrv7.oru.edu/~alang/onsc/solubility/allsolvents.php...
You will barely get any unreacted salicylic acid in your solvent phase. The low boiling point of DCM makes it easier to strip from the methyl
salicylate afterwards. But if it is hard to get you can always redistill the DCM and recycle it...
[Edited on 9-3-2014 by Mailinmypocket]
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