Sciencemadness Discussion Board

Distilling esters with very high boiling points?

Cou - 13-8-2020 at 13:38

Butyl salicylate has a boiling point of 270 C
The problem with vacuum distilllation is that I find it difficult to control. You can't see the atmospheric pressure boiling point of the distillate so that you could confirm its purity. Crude butyl salicylate is contaminated with 1-butanol which is easiest to separeate by simple distillation.

Can you just go ahead and crank up the hot plate to 10 and distill at like 300 C? If decomposition was an issue, you would see it in the distillate temperature.

outer_limits - 13-8-2020 at 13:46

1-butanol has boiling point at 118 C. Evaporate it, there is no need to heat the mixture to 300 C

DraconicAcid - 13-8-2020 at 16:27

Can you deprotonate it without hydrolyzing it?

HeYBrO - 13-8-2020 at 22:05

maybe you could try steam distillation?

DavidJR - 14-8-2020 at 05:50

Yeah, steam distillation is the obvious choice here. Just make sure there is no residual acid.

Cou - 14-8-2020 at 10:58

I'll consider steam distillation.

I encountered an annoying issue with vacuum distillation yesterday that made me discard 40 mL of butyl salicylate. The ground glass joint vacuum grease gets inside the distillate, causing severe foaming that I couldn't stop with silicone oil. This can be remedied by greasing the joints with whatever you're distilling.

[Edited on 8-14-2020 by Cou]

Syn the Sizer - 14-8-2020 at 16:58

Honestly I agree with outer_limits. Use an excess of alcohol, to convert as much acid to the ester as possible, neutralize the remaining acid with bicarb solution, rinse and dry with suitable drying agent. Then distill off the remaining alcohol, should what is left in the distilling flask not be the ester?

Is there a reason this method is not viable?

Cou - 14-8-2020 at 19:13

Quote: Originally posted by Syn the Sizer  
Honestly I agree with outer_limits. Use an excess of alcohol, to convert as much acid to the ester as possible, neutralize the remaining acid with bicarb solution, rinse and dry with suitable drying agent. Then distill off the remaining alcohol, should what is left in the distilling flask not be the ester?

Is there a reason this method is not viable?


Fisher esterification reactions often produce tar and discoloration. After using the dean-stark technique to make butyl salicylate, the resulting mixture is almost black. so the crude ester needs to be purified by some kind of distillation.

Yea, after washing the reaction mixture with water (to remove 1-butanol) and sodium carbonate solution (to remove salicylic acid), what's left is a discolored ester containing organic crap.

In the past I had issues with vacuum distillation because the vacuum grease on the ground glass joints would contaminate the ester, causing severe foaming. I realized you can just grease the joints with the crude ester.

Syn the Sizer - 15-8-2020 at 21:41

Ok, that makes sense, basically high temps in atmospheric oxygen forms tar.

DavidJR - 17-8-2020 at 03:55

Quote: Originally posted by Cou  

Fisher esterification reactions often produce tar and discoloration. After using the dean-stark technique to make butyl salicylate, the resulting mixture is almost black. so the crude ester needs to be purified by some kind of distillation.


It depends on what catalyst you use. If you use sulphuric acid, then tar is very often formed. Especially if you distill the reaction mixture without first neutralising the acid, but some still forms if you do. However, if you use p-toluenesulfonic acid, you don't usually get tar formation. I haven't tried phosphoric acid, maybe that would be better too.

Cou - 17-8-2020 at 17:55

I found that high boiling salicylate esters, where the alcohol used in the reaction is 5 carbons or fewer, can be purified like this:

1: Add reaction mixture to a sep funnel with a large volume of water to get ester layer on bottom.

2: wash ester layer with sat. Sodium carbonate until there is no fizzing. Removes acids

3: wash with a large volume of water to remove the alcohol*

4: wash with saturated sodium chloride to extract most water

5: dry with anhydrous magnesium chloride powder

6: vacuum distill (the round bottom flask needs to be big to avoid splashing liquid spilling over. I used a 500 mL flask for 50 mL




*Only alcohols with 5 or fewer carbons are easily extracted with water. for alcohols with low solubility I would somehow estimate how much alcohol might be left over, then use the alcohol solubility to decide if a reasonable volume of water can extract it. If water extraction won't work, I would heat the crude ester to above the BP of the alcohol to expel it before doing any washes.

[Edited on 8-18-2020 by Cou]

[Edited on 8-18-2020 by Cou]

outer_limits - 17-8-2020 at 20:54

Quote:

6: vacuum distill (the round bottom flask needs to be big to avoid splashing liquid spilling over. I used a 500 mL flask for 50 mL


Do you use air bleeder or strong stirring? Both are great reducers of splashing and bumping.