[halo364]

Hi everyone. I have a orgo question that has stumped me and a couple of my classmates for a while now. Basically, we've been asked to create a procedure for obtaining pure Methyl salicylate from a sweet birch tree without using any kind of man-made materials (for example, no glassware, no pure chemicals, no thermometers... only things that could be found in nature).

What we have so far is this: we can create a fire and use it to heat water. We can then place crushed up pieces of birch bark into the water for a few hours and let them create wintergreen oil. We can then filter out the pieces of bark (perhaps using a scrap of clothing) and boil off the water. This will give us a compound that is 98% Methyl salicylate.

What we've been struggling with is how to get rid of that extra 2%. We can't use steam distillation, we think, because that involves a ton of relatively complex glassware. The wording of the question suggests that we need to add something (an acid or base of some kind) to the compound and do a liquid-liquid separation-type-thing, but we can't think of a way to get an acid/base that is strong enough to do this. Plus, although we think that Methyl salicylate is acidic, we don't know that the other components of wintergreen oil are basic or neutral.
 
Are we thinking along the right lines? Are we missing some angle entirely? Any help would be greatly appreciated!

- Evan G.

[AWK]

Probably water dissolved in wintergreen oil is the rest 2 %.

[halo364]

Probably water dissolved in wintergreen oil is the rest 2 %.

A couple sources (like http://en.wikipedia.org/wiki/Wintergreen) have said that the remaining 2% is composed of a mixture of a-pinene, myrcene, delta-3-carene, limonene, 3,7-guaiadiene, and delta-cadinene. We're assuming that this is at least mostly true, but we're struggling to figure out how to get rid of all of those extra components without resorting to techniques that heavily utilize man-made objects or chemicals.

[fledarmus]

You have a phenol present in your methyl salicylate. What is the pKa of a phenol group?

Look at the structures of the other compounds you listed. What do they all have in common? Think about the elements present...

[halo364]

You have a phenol present in your methyl salicylate. What is the pKa of a phenol group?

Look at the structures of the other compounds you listed. What do they all have in common? Think about the elements present...

The pKa of phenol in water is 9.95
And all the of other compounds are similar (I think) in that they don't have any oxygens in them...

Should we add an acid to the mixture and try to do a liquid-liquid separation?

EDIT: Just remembered that pKa doesn't = pH
So now I'm back to having no idea..

[fledarmus]

A pKa of 9.95 is not acidic in water, but it is acidic enough that a proton can be pulled using a relatively weak base. This is a typical method of separating and identifying phenols. Sodium carbonate is a strong enough base to pull phenol protons, and the resulting sodium salt of the phenol can be extracted into water. Since none of the impurities you mention have any acidic functionalities, they will remain in the organic layer. Then you can re-protonate your phenol with a weak acid, like acetic acid, and extract it back into the organic layer.

[orgopete]

Potash?

[AWK]

Much easier is using more pure compound obtained by synthesis.

[AWK]

Purification of commercial reagents is a very difficult or even impossible task.
And you want to it doing nothing!