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Author: Subject: Help for Esterification
stephill92
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[*] posted on 19-3-2019 at 09:05
Help for Esterification


I've recently got into amateur Chemistry and tried doing an esterification of salicylic acid and methanol. I had made about 30ml of methyl salicylate from 50g of salicylic acid, and used molecular sieves to dry it (I needed it to be anhydrous). I used two different brands and it turned pink/red both times (I had to distill it both times to get rid of the color). I used a little MgSO4 to see if I still had water and it bubbled so I don't really know if I did something wrong. Each time I dried it I filled the liquid up with sieves and when it started to get to be more than the liquid I filtered and distilled it. After every attempt to remove the water it still seemed to linger. I now have too little to salvage but I wanted to see if anyone could give me some advice for in the future.
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DraconicAcid
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[*] posted on 19-3-2019 at 10:02


It doesn't look like you need help with the esterification, just with the drying of the product afterwards. You will need to distill it, because there are side reactions during the esterification that give the red/pink/purple colours. Dry it over magnesium sulphate twice before distillation- let it sit over magnesium sulphate for at least an hour before filtering and drying again. Methyl salicylate cannot be dried with more vigorous drying agents such as calcium oxide or alkali metals because it will react with them (I have no opinion on molecular sieves).



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stephill92
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[*] posted on 19-3-2019 at 11:36


I think I may have been confusing in my description. The molecular sieves turned the methyl salicylate pink. I will definitely try drying using magnesium sulfate though.
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DraconicAcid
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[*] posted on 19-3-2019 at 12:20


Now, if you can get some other alcohols, you can get some interesting results. I've managed to make propyl salicylate, which smells surprisingly like celery. Butyl salicylate is supposed to smell like blackberry, but I haven't managed to get that one to work.



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Felab
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[*] posted on 19-3-2019 at 13:35


Where your sieves activated? Did you distill it over the sieves? You tried two different brands of MS or of salicylic acid?

If you distilled the methyl salicylate over the sieves, they might have lost some of their water in the distilation.
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happyfooddance
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[*] posted on 19-3-2019 at 13:36


For minimizing losses when drying esters, I dissolve them in a solvent (usually diethyl ether), this greatly speeds drying, and you can rinse your sieves or drying agent with a little dry solvent.

The colorization you are seeing are (probably several different) reactions catalyzed by the zeolites (alumino-silicates/ mol sieves).

[Edited on 3-19-2019 by happyfooddance]
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DraconicAcid
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[*] posted on 19-3-2019 at 13:45


Quote: Originally posted by happyfooddance  
For minimizing losses when drying esters, I dissolve them in a solvent (usually diethyl ether), this greatly speeds drying, and you can rinse your sieves or drying agent with a little dry solvent.

The colorization you are seeing are (probably several different) reactions catalyzed by the zeolites (alumino-silicates/ mol sieves).

[Edited on 3-19-2019 by happyfooddance]


Good suggestion- the ether greatly reduces the viscosity, and will help it dry a lot faster. Just be careful with your distillation afterwards- the ether is extremely flammable, and you don't want to use a flame to heat your methyl salicylate if there's ether vapours around.




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stephill92
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[*] posted on 19-3-2019 at 16:47


Quote: Originally posted by Felab  
Where your sieves activated? Did you distill it over the sieves? You tried two different brands of MS or of salicylic acid?

If you distilled the methyl salicylate over the sieves, they might have lost some of their water in the distilation.


The sieves were activated, I didn't distill them over the sieves, and I used two different brands of sieves.
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Amos
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[*] posted on 20-3-2019 at 09:49


I've had this same result when trying to remove excess acid with calcium carbonate, even food-grade material. It may be that there's an impurity that changes color when exposed to certain transition metals (phenols like salicylic acid show a brilliant coloration when complex to iron, purple in that specific case) or even high pH. Or maybe your sieves are just dirty. In either case I'd recommend rigorously drying your crude product before distilling and then discarding any drops that come over cloudy as the distillation commences.
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Amos
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[*] posted on 20-3-2019 at 09:49


I've had this same result when trying to remove excess acid with calcium carbonate, even food-grade material. It may be that there's an impurity that changes color when exposed to certain transition metals (phenols like salicylic acid show a brilliant coloration when complexed to iron, purple in that specific case) or even high pH. Or maybe your sieves are just dirty. In either case I'd recommend rigorously drying your crude product before distilling and then discarding any drops that come over cloudy as the distillation commences.

[Edited on 3-20-2019 by Amos]
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