Sciencemadness Discussion Board

Minty Smell

aga - 31-5-2015 at 14:53

Today i tried the esterification of salicylic acid to form methyl salicylate according to this utoob vid : https://www.youtube.com/watch?v=lJLP2bcXDqY

Half the amounts were used.

Big smile after 1.5 hours as there was a distinct minty listerine smell.

On washing with ice cold water, all the nice oil disappeared and semi-solid chewing-gum like lumps appeared.

Undeterred, the chewing gum was washed with sodium bicarbonate to remove acid and distillation attempted (reasoning=oils go to waxy solids when cold)

NO result other than a pile of dirty glassware, a blocked stop-cock in a sep funnel and a shed full of listerine smell.

I'll try again, after paying my wife the money i bet that i could do it easily, and today.

blogfast25 - 31-5-2015 at 15:05

How cold was that water? The MP of methyl salicylate is only - 9 C. Perhaps it goes quite viscous at low temperature?

aga - 31-5-2015 at 15:09

The water was above zero, maybe 5 to 8 degrees.

As soon as the oil hit the water, chewing gum appeared.

Still smelt minty, but nowhere near as strong as before the water was added.

blogfast25 - 31-5-2015 at 15:24

Sounds like unreacted salicylic acid then. I haven't watched the Utoob though. Is it 'worth' watching?

j_sum1 - 31-5-2015 at 15:52

Yep. NileRed is good here. As is MrHomeScientist on the same topic. (NR uses salycylic acid. MHS uses aspirin.)
It is on the to do list.

Amos - 31-5-2015 at 16:20

I followed Nile Red's procedure to the letter, but interestingly enough, after boiling off most of the excess ethanol, upon decanting the reaction mixture into water, the methyl salicylate FLOATED. So be sure that the layer you're extracting in the sep funnel step is the correct one.

blogfast25 - 31-5-2015 at 16:55

Quote: Originally posted by Amos  
I followed Nile Red's procedure to the letter, but interestingly enough, after boiling off most of the excess ethanol, upon decanting the reaction mixture into water, the methyl salicylate FLOATED. So be sure that the layer you're extracting in the sep funnel step is the correct one.


Salt in your water, pushing up density?

cyanureeves - 31-5-2015 at 16:57

i got the gummy stuff too and it was just as nice smelling as the liquid so i kept it.one time i did get the oil though but i lost track of what i did different.i used cheap o'reilley's part store brake line antifreeze which was blue on all runs but on some runs i used different aspirins.also on some runs i used salicylic and on some runs i just used acetylsalicylic acid(plain aspirin).i got equally smelling products so i was happy.my yields were very little compared to all the three videos on youtube. i used a sandwich baggy for sep funnel and sometimes left them over night trying to sep more oil.on some runs the gum would go to the bottom so i would decant because it would not float like the oil. the water i would separate from was also minty smelling so my garage and tool shed smelled nice and tooth pastey.correction: the oil is supposed to sink but sometimes it would would only form a thin layer on top that i would decant. i recall also having to cap the stuff because the smell would really get strong and irritating.

[Edited on 6-1-2015 by cyanureeves]

Amos - 31-5-2015 at 17:20

Quote: Originally posted by blogfast25  
Quote: Originally posted by Amos  
I followed Nile Red's procedure to the letter, but interestingly enough, after boiling off most of the excess ethanol, upon decanting the reaction mixture into water, the methyl salicylate FLOATED. So be sure that the layer you're extracting in the sep funnel step is the correct one.


Salt in your water, pushing up density?


Nope, it was initially just cold distilled water. I suspect that the cold methyl salicylate was just too viscous and the addition funnel's inside area was too small to allow the methyl salicylate layer to move itself underneath the water.

aga - 31-5-2015 at 23:17

Thinking about it, the video states that this an equilibrium reaction, and uses Le Chatelier's principle to push the reaction to the right by adding an excess of methanol.

Once the methanol has been boiled off and a large amount of water is added, surely the same principle holds true, pushing the equilibrium back to the left.

Is the reverse reaction a lot quicker than the forward reaction ?

There were certainly many oily blobs in the beaker before the water was added.

I'll try it again and neutralise the acid catalyst first.

Doh. Need to distill some more methanol for that.

Oscilllator - 1-6-2015 at 01:26

Quote: Originally posted by aga  
Once the methanol has been boiled off and a large amount of water is added, surely the same principle holds true, pushing the equilibrium back to the left.

Well I think we can safely assume that methyl salicylate is stable at room temperature, since otherwise Listerine would become contaminated with methanol over time. It *might* decompose in hot water, but if it was dumped in cold water the decomposition should be negligible.

DFliyerz - 1-6-2015 at 07:19

I actually have experienced something like this when dissolving acetylsalicylic acid in "denatured alcohol" (it was actually about 50/50 ethanol/methanol), where I got a very distinct minty smell and after washing the flask with water, I ended up with a goopy gum-like thing that I still have a bit of stuck to the bottom of my wash basin.

Texium - 1-6-2015 at 07:45

I had problem with the methyl salicylate mixing with the salted water, because the density of a saturated Na2SO4 solution is almost exactly that of methyl salicylate. So be cautious as you neutralize the solution. It can make it very messy, with little bubbles of the oil floating up and down in the funnel if you need to add too much. I thought little of it until I realized that it wasn't separating nicely, and ended up settling for having some dissolved in methanol until I make another attempt at it.