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
brand-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 and into the flask,
shown here in pink. This happens after you shake
the sep 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. But what does this mean? This means that these
liquids or solvents have different densities,
with a 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
the 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 in 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 propanamine. What do we know about
these two compounds? Well, hexane is pretty
neutral and propanamine 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 to 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. 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
acids into the aqueous layer. If we tried adding
NaOH, we'd find that since this
is a strong base, you would easily deprotonate not
only the acetic 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 its structure here-- you have this anion
with a 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, 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? Well actually, using a
multi-step extraction, you'd be able to recover
your product from the waste container.