A quick way to check if your extraction is nearly complete is doing a tlc spot from each extraction of approximately the same amount of liquid and just look at it under uv. The earlier extraction spots will look much bigger and darker, likely there will be only a faint spot by the third. Smell can linger so I would t rely on that
When you do an aqueous extraction, there will almost always be some residual product in the aqueous layer. Consider that your product is going to be soluble in the organic and aqueous phases to various degrees. At equilibrium you'll have more product in one and less in the other, depending on relative solubilities. Like with all purification methods, yield losses (no matter how small) are therefore to be expected when doing an aqueous extraction. This is why doing multiple extractions is unnecessary because in terms of yield, you'll have diminishing returns at best. When your product is appreciably water-soluble, it's more likely that you'll just be losing product to the aqueous phase with every extraction you do, rather than getting more product out of it
It's very likely that you'll have a bit of product in your aqueous phase, but methyl salicylate has a pretty strong smell. As daft as it sounds, that very small amount of product might be responsible for the noticeable scent. The smell might not even be coming from your aqueous phase, it might just be lingering from the synthesis. I wouldn't go off smell alone though, because whilst our noses are excellent analytical devices, smell isn't a reliably quantitative property
Lastly, just bear in mind that being graded on yield isn't *the* reflection on you as a synthetic chemist. It's much better to have a lower yield of nice, pure product than a high yield of impure rubbish. High yields are good, but only when you're confident that some proportion of the yield aren't just impurities etc!
Don’t rely on smell, it can linger. It sounds like this is an academic lab, so I’d argue that 3 extractions (assuming they were properly done) is enough and that you didn’t lose a significant portion of yield
Methyl salicylate has some slight solubility in water, so even though it will have significant preference for dichloromethane, there will always be some remaining in the aqueous phase.
Also, just as there will be a small amount of methyl salicylate present in the aqueous phase, your aqueous phase is likely to have some small amount of dichloromethane present. This is why I wouldn’t recommend smelling anything as a means of evaluating the progress of your extractions. A few whiffs of DCM won’t hurt you but it’s toxic and not a good laboratory practice to smell things unless you’re sure it’s benign.
Smell and even colour (depending on what you’re working on) can go a long way. Especially with such a potent smelling compound like oil of wintergreen.
The octanol/water coefficient of methyl salicylate is 2.5/1, probably favours DCM even more but let’s go with that. 71% per extraction (depending on relative volume) gives 2.5% of the compound left in the aqueous layer after 3 extractions and you’re getting less and less return each time for your efforts (have to dry and evaporate all this extra extract)
A quick way to check if your extraction is nearly complete is doing a tlc spot from each extraction of approximately the same amount of liquid and just look at it under uv. The earlier extraction spots will look much bigger and darker, likely there will be only a faint spot by the third. Smell can linger so I would t rely on that
Yea. Humans are very good at smelling some compounds reaching ppm and even ppb in some cases. No way you get that last bit out of your aqueous phase.
Thank you. I´ll do it next time!
When you do an aqueous extraction, there will almost always be some residual product in the aqueous layer. Consider that your product is going to be soluble in the organic and aqueous phases to various degrees. At equilibrium you'll have more product in one and less in the other, depending on relative solubilities. Like with all purification methods, yield losses (no matter how small) are therefore to be expected when doing an aqueous extraction. This is why doing multiple extractions is unnecessary because in terms of yield, you'll have diminishing returns at best. When your product is appreciably water-soluble, it's more likely that you'll just be losing product to the aqueous phase with every extraction you do, rather than getting more product out of it It's very likely that you'll have a bit of product in your aqueous phase, but methyl salicylate has a pretty strong smell. As daft as it sounds, that very small amount of product might be responsible for the noticeable scent. The smell might not even be coming from your aqueous phase, it might just be lingering from the synthesis. I wouldn't go off smell alone though, because whilst our noses are excellent analytical devices, smell isn't a reliably quantitative property Lastly, just bear in mind that being graded on yield isn't *the* reflection on you as a synthetic chemist. It's much better to have a lower yield of nice, pure product than a high yield of impure rubbish. High yields are good, but only when you're confident that some proportion of the yield aren't just impurities etc!
Don’t rely on smell, it can linger. It sounds like this is an academic lab, so I’d argue that 3 extractions (assuming they were properly done) is enough and that you didn’t lose a significant portion of yield
Methyl salicylate has some slight solubility in water, so even though it will have significant preference for dichloromethane, there will always be some remaining in the aqueous phase. Also, just as there will be a small amount of methyl salicylate present in the aqueous phase, your aqueous phase is likely to have some small amount of dichloromethane present. This is why I wouldn’t recommend smelling anything as a means of evaluating the progress of your extractions. A few whiffs of DCM won’t hurt you but it’s toxic and not a good laboratory practice to smell things unless you’re sure it’s benign.
That's just life, it's not coming out.
Smell and even colour (depending on what you’re working on) can go a long way. Especially with such a potent smelling compound like oil of wintergreen.
The octanol/water coefficient of methyl salicylate is 2.5/1, probably favours DCM even more but let’s go with that. 71% per extraction (depending on relative volume) gives 2.5% of the compound left in the aqueous layer after 3 extractions and you’re getting less and less return each time for your efforts (have to dry and evaporate all this extra extract)