Lab 21-1 Synthesize Methyl Salicylate from Aspirin.txt

[Kenji Totsuka]

I'm reading the procedure for Lab 21-1, but am a little confused.  I think the two questions below are related.  Any help is greatly appreciated. 

- What are the two layers?

    - At the end of the synthesis I'm supposed to have brown solution, which contains impurities such as ethanol.   I think I'm supposed to add water to the brown solution and expect to get two layers.  What are the two layers?  At first, I thought I would get aqueous layer (water) and organic layer (ethanol), but ethanol is miscible with water, so I don't think I'll get ethanol layer.  But I think Methyl Salicylate dissolves in methanol, which dissolves in water, ....but that aqueous layer is thrown away???

- How is the methanol removed?

   - At the end of "Isolate and purify the product" section, I'm supposed to wash the brown solution with water and then with sodium bicarbonate solution.  How is methanol removed from the brown solution? Is it removed with the water wash?  But I thought methanol is what the Methyl Salicylate dissolves in, so I would think you want to keep the methanol.  But then I don't see any step to remove methanol.  It seems to me, at the end of the sodium bicarbonate wash, you retain the layer that contain the Methyl Salicylate, or is that layer IS the Methyl Salicylate?

Thank you very much for your help. 

Kenji

[The Home Scientist]

The brown solution is a mixture of methyl salicylate with unreacted methanol and aspirin along with the sulfuric acid (which as a catalyst is not consumed) and various byproducts. When you add water, the water-soluble parts of the reaction mixture migrate from the organic (methyl salicylate) layer to the aqueous layer. Methyl salicylate is denser than water, so the bottom layer is organic and the top layer aqueous.

Repeated water washes remove the unreacted methanol, sulfuric acid, and other water-soluble contaminants from the methyl salicylate layer. The sodium bicarbonate reacts with any traces of sulfuric acid still present to yield extremely soluble sodium sulfate. After several washes/neutralizations, what you're left with is a bottom layer of raw but reasonably pure methyl salicylate.

[Kenji Totsuka]

That makes a lot of sense.  I read that Methyl salicylate is freely soluble in methanol, so I just kept assuming that Methyl salicylate remains in methanol.  But since methanol is miscible with water, and methyl salicylate is insoluble in water, methanol moves to the aqueous layer leaving methyl salicylate behind.   Thank you very much for your help.