Extractions

walking into a department store you're often hit by a variety of smells coming from the perfume department how do they make all these different scents well one way they do that is by separating out chemical compounds and mixing them in different ways to get their own brands specific formula but in order to isolate the chemical compounds one of the techniques that's frequently used is known as extraction extraction can be done in your organic chemistry lab using these two main pieces of glassware the first which is shown in blue is known as the separatory funnel or the SEP funnel for short at the top of this this has an opening through which you can pour in liquid at the bottom you have the stopcock currently shown in the closed position which prevents liquid from flowing freely from the SEP funnel then into this out as you shake the shuttle urine funnel and allow the mixture to settle when you pour in a mixture of liquids what you'll often notice is that you get two different layers one on the bottom and one on top this happens after you shake the separatory funnel and allow the mixture to settle down well what does this mean this means that these liquids or solvents have different densities with the higher density being on the bottom and the lower density floating on top often these will represent the organic phase and the aqueous phase the aqueous phase contains water and other charged species or ions whereas the organic phase contains uncharged species or neutral compounds so how exactly do we do an extraction well first of all you need to open the stopcock and when you do that you'll see that although you still have your organic phase up here the aqueous phase is now able to flow down the SEP funnel and into the flask and once you've collected all of your aqueous layer and the flask you can close the stopcock again which will leave you with just the organic phase in the SEP funnel now that we know how to do this in lab let's look at compounds we'd be able to separate for example take hexane and propane amine what do we know about these two compounds well hexane is pretty neutral and propane amine is basic because of its amino group so in order to get one of these into the organic layer and one of them into the aqueous layer we'd want to make sure that we can produce an ion and leave one other compound uncharged to do that we can add an acid by adding something like hydrochloric acid what you'll find is that this amino group the nitrogen these electrons can deprotonate the HCL and leave behind just a chloride anion which means that in your aqueous layer you would have a charged amino group whereas in your organic layer you would just have hexane there you've done your first extraction so next in this example you have hexane and phenol phenol is weakly acidic this means that in order to get phenol into the aqueous layer you would want to add a base we can use a base like sodium hydroxide which is a strong base and what you'd find is that these electrons would be able to deprotonate the phenol meaning that in the aqueous layer this time you would be left with the phenolate anion and in the organic phase you would just have the hexane okay let's do something a little bit more complicated what if instead you had three compounds this time hexane phenol and acetic acid well in this case if we took the approach we took previously which was trying to add a base to get these assets into the aqueous layer if we tried adding NaOH we'd find that since this is a strong base you would easily be protonate not only the siddik acid but even the phenol so let's try using something else instead if instead we had a somewhat milder base like sodium bicarbonate and I'll show it structure here you have this anion with the sodium cation and since this is a mild base it won't be able to deprotonate very weak acids meaning it won't be able to deprotonate the phenol but it will be able to deprotonate the acetic acid this means that in your aqueous layer this time you would have the acetate anion while in your organic layer you have hexane and you have phenol how do we separate these last two well we've already done that in the previous example so to get just one compound into the aqueous layer again we would want to add a base but this time we can use sodium hydroxide the hydroxide at these electrons here would deprotonate the phenol giving you again the phenolate anion along with the hexane in your organic layer and now we've learned how to do extractions so when you're actually doing this in the lab you'd want to make sure that you save each and every layer what happens if you accidentally toss one out into the waste container while actually using a multi-step extraction you would be able to recover your product from the waste container