Solvent extraction.
Solvent extraction,
also known as liquid,
liquid extraction, is a separation technique.
It can be used to transfer an analyte from
one liquid phase to another liquid phase in contact with it.
It is based on the relative solubility of an analyte
in 2 immiscible or partially miscible liquids.
One of which is usually an aqueous solution,
and the other is an organic solvent.
Let's take a closer look at the miscibility
of two common solvent pairs.
One pair is dichloromethane and water,
and the other pair is diethyl ether.
And water. The miscibility chart shows us
that dichloromethane and water are immiscible.
ether is also immiscible with water.
The target analyte
partition's between two liquid phases.
to establish equilibrium,
the extraction efficiency depends on the partition ratio,
also known as the distribution constant.
The partition ratio is the ratio of
the concentration of an analyte in a single defined form.
In an organic phase,
to its concentration in the same form in
the aqueous phase, at equilibrium.
The equation relates to an organic-aqueous system,
where the aqueous phase forms the feed.
Solvent extraction includes nine steps.
As there are important things to
remember about these steps.
First, the stopper and
the plug of the stopcock must be
well fitted to prevent leakage of solution.
Next, a separatory funnel should
never be more than three-quarters full.
And then the funnel should not be shaken too
vigorously because it may cause formation of emulsion.
Emulsion is the dispersion
of droplets in an immiscible liquid.
If an emulsion has formed near
the interface between two liquid layers
we could wait for few minutes to
see if separation will occur on its own.
Sometimes gentle swirling and
stirring is enough to destroy it.
Another method is to add brine or salt water to the solution.
It will increase the density of
the aqueous layer, thereby forcing separation.
And it will help break the emulsion.
Then we need to know which layer is
organic and which one is aqueous.
The layers can be identified using
a simple technique as demonstrated later in this video,
only the bottom layer
should be drained for the stopcock.
This allows us to minimise contamination as
only one layer touches the stem of the sep funnel.
Usually the solution containing the solid,
is extracted three times,
using fresh portions of the extraction solvent
After separation of
the organic and the aqueous layers
the organic layer will be wet.
It will contain water.
Water can be removed from
the organic layer by treating it with a suitable desiccant
desiccants are drying agents that
absorb water due to
their chemical and physical properties.
The two common types of desiccants are zeolite
molecular sieves, types A and X,
and anhydrous inorganic salts,
such as magnesium sulphate and sodium sulphate.
Desiccants have varying properties and applications.
Not all desiccants can absorb the same amount of
water and can dry an organic layer to the same extent,
Capacity is the amount of water a desiccant will absorb per its weight
Completeness, is the effectiveness of a desiccant in
removing all the water from an organic layer by the time
equilibrium has been established.
Rate is the rate of drying.
For example, zeolites,
also commonly known as molecular sieves,
have high capacity and extremely high completeness.
Zeolites are aluminosilicate minerals
that can carry water.
Zeolites are made up of tetrahedral building units.
Their pore openings are used to
absorb molecules smaller than the pore size,
and reject molecules larger than the pore size.
It is important to select
the right zeolite for a given application.
Type A zeolites have distinct capabilities of adsorption,
whereas Type X offer
much larger pore openings than type A, for example,
4A molecular sieve has a pore opening of
approximately four angstroms. If
the sodium ion is exchanged with the larger potassium ion,
the pore opening, is reduced to 3 angstroms.
On ion exchange with calcium
the pore opening increases to five angstroms
Type 13X is a sodium,
modified molecular sieve.
with a pore diameter of 10 angstroms
For example, type 4A molecular sieve
is suitable for drying diethyl ether
since the pore size excludes the entry of ether
but does not exclude the entry of water.
Anhydrous
inorganic salts, such as magnesium sulphate and
sodium sulphate are suitable
for general purpose applications,
including drying ethyl layer.
These salts can absorb a large amount of water.
Also, magnesium sulphate is
faster and can dry an organic layer more completely.
It is slightly acidic.
So for example, it works well in diethyl ether,
but not as well for ethyl acetate. As for sodium sulphate,
It works well for both solvents,
Although sodium sulphate will not free
an organic layer completely of water,
it has been considered the best of salt desiccants.
Once the drying task is complete,
the desiccant should be removed by gravity
filtration.
Using a separation funnel is a good way
to extract and wash organic products.
Setup, you will need the following.
A retort stand with a retort
ring, a separation funnel of
appropriate size with a lid that fits tightly, a waste beaker,
a collection flask and a conical flask.
Once you have these and the setup as shown,
you are ready to start using the separation funnel.
Carefully, add your liquid to the funnel,
making sure not to fill it over halfway.
Now you can add the other liquid.
If the method wants you to extract,
you will need to use an organic solvent.
If it wants you to wash, add water.
In this case, I wish to extract
so I put in an organic solvent.
Now you can place the cap on
and give it a slight twist to
secure it. Place the cap into the palm of
your hand and point the tip of the separation funnel to
the back of the fume hood. Using a rocking motion,
Move the separation funnel and at
regular intervals release the valve to release pressure.
Continue to do this until you cannot
hear the sound of pressure releasing.
Now return it to the ring and remove
the lid. Wait until you
can clearly see the separation between the layers.
Now you need to collect your sample.
The liquids are separated based on density.
So the highest density will be on the bottom.
In this case, DCM was used,
which has a higher density than water.
So the product is on the bottom.
Place the collection flask under the funnel
and carefully open the valve to let the liquid out,
making sure to stop it just before the boundary
between the layers as to not contaminate your product.
The remaining liquid is a raffinate.
The extraction steps can be repeated twice or more times.
with fresh solvent.
To ensure complete extraction.
The top layer should be
removed from the top of the funnel
It is best to keep
both layers until the analyte
of interest has been isolated.
If you're not sure whether the aqueous layer is
above or below the organic layer
add a few drops of Milli-Q water,
the water droplets may enter either the top layer.
or the bottom layer, in any case,
shall enter the aqueous layer.
For example, since the densities
of halogenated organic solvents
such as DCM are higher than that of water.
DCM will rest on
the bottom and the water layer will be above it.
So the water droplets will mix,
with the top layer. The densities
of non-halogenated organic solvents,
such as diethyl ether
are lower than that of water.
So a non-halogenated solvent,
like ether, will float on top of the aqueous layer.
We can see that the water droplets
fall in through the upper layer into the lower layer.
This means that the aqueous layer
is below the organic layer.
After extraction, it's essential to remove
the residual water from
the organic layer by adding the proper desiccant.
we are going to add sodium sulphate in small amounts.
will cause absorption
of our product and may also
lead to its loss. After adding
a small amount swirl the mixture in the flask.
we can see the sodium sulphate clumps
together sticking to the bottom of the flask.
Since the majority of the sodium sulphate has clumped,
we need to add a bit more.
Now, the desiccant, swirls loosely
when the flask is shaken, it's not clumped.
We want to let it set for ten minutes
to make sure that all the water is absorbed
out of an organic layer
the solution will become clear when it is dry.
To remove the dessicant we should perform
a gravity filtration through fluted filter paper.
Then ideally, we need to rinse the desiccant three
times with the minimum amount of dry solvent.
adding each of these rinses to the flask
at the end of the extraction,
we have our compound of interest
dissolved exclusively in the organic solvent.