Fundamentals of Liquid-Liquid Extractions

Summary

Dr. Frank's video delves into liquid-liquid extraction, a purification technique pivotal in organic synthesis. It hinges on solubility differences and immiscibility of solvents, typically employing water and an organic solvent. The video elucidates the 'like dissolves like' principle, emphasizing polar and non-polar solubility preferences. It also introduces reactive extractions, leveraging acid-base chemistry and pKa values to selectively extract organic compounds into aqueous phases. Practical tips on using separatory funnels and the impact of pH on extraction efficiency are provided, concluding with a strategy for separating a mixture of benzoic acid, naphthalene, and aniline.

Takeaways

• 🌟 Liquid-liquid extraction is a purification technique used in organic synthesis, relying on the differing solubilities of compounds in immiscible solvents.
• 💧 The principle of 'like dissolves like' is crucial; polar solvents dissolve polar molecules better, and non-polar solvents dissolve non-polar molecules better.
• 🔬 Water is often used in liquid-liquid extraction due to its immiscibility with many organic solvents and its high polarity.
• 🧪 A separatory funnel is a common piece of lab equipment used to perform liquid-liquid extractions by physically separating immiscible solvent layers.
• ⏏️ The order of solvent layers (organic on top or bottom) depends on their densities, with water typically being the denser layer.
• 📚 Reactive extractions involve using acid-base chemistry to ionize organic molecules, making them soluble in the aqueous phase for separation.
• 🔄 The acid dissociation constant (pKa) is essential for planning reactive extractions, as it indicates the strength of an acid and its tendency to ionize.
• 🔄 The Henderson-Hasselbalch equation relates the pH of a solution to the pKa of an acid, helping predict the partitioning of acid and its conjugate base.
• ⚖️ Performing multiple extractions with small volumes of solvent is more efficient than a single extraction with a large volume for accumulating the product in its preferred phase.
• 🧪 In a mixture of benzoic acid, naphthalene, and aniline, each compound can be selectively separated based on its pKa and the pH of the extraction solution.

Q & A

What is liquid-liquid extraction?

Liquid-liquid extraction is a purification technique used in organic synthesis, based on the differing solubilities of compounds in immiscible solvents, allowing for the separation of a mixture into distinct layers that can be physically separated.

Why are most organic solvents not suitable for liquid-liquid extraction?

Most organic solvents are miscible with each other, meaning they mix together and do not form separate layers, which is necessary for effective liquid-liquid extraction.

What is the role of water in liquid-liquid extraction?

Water is often used in liquid-liquid extraction because it is immiscible with many organic solvents and has a high polarity, allowing it to dissolve polar impurities and ionic compounds effectively.

How does the separatory funnel facilitate liquid-liquid extraction?

The separatory funnel is a piece of glassware used to mix immiscible solvents, allowing them to separate into distinct layers. It has a valve at the bottom that enables the separate collection of each layer.

What determines whether the organic layer is on top or bottom in a liquid-liquid extraction?

The density of the solvents determines the layering in liquid-liquid extraction. Water, with a density of one gram per milliliter, is typically on the bottom, while less dense organic solvents float on top.

How does the 'like dissolves like' rule apply to solubility in liquid-liquid extraction?

The 'like dissolves like' rule suggests that polar solvents dissolve polar molecules better, and non-polar solvents dissolve non-polar molecules better. This principle is used to predict which solvent will preferentially dissolve a given compound.

Why is it more effective to perform multiple extractions with small volumes rather than a single extraction with a large volume?

Multiple extractions with small volumes allow for the product to accumulate in its preferred phase over time, leading to a higher concentration and more efficient purification compared to a single large volume extraction.

What is reactive extraction and how does it differ from standard liquid-liquid extraction?

Reactive extraction is a process where an organic compound is selectively ionized to become water-soluble, allowing it to be separated from other compounds in the organic phase. This differs from standard extraction, which relies solely on the physical properties of the compounds.

How is the acid dissociation constant (pKa) used in planning reactive extractions?

The pKa value is used to predict the partitioning of a weak acid between its neutral and anionic forms based on the pH of the solution. This information is crucial for determining the conditions under which a compound will be soluble in either the organic or aqueous phase.

What is the Henderson-Hasselbalch equation and how does it relate to liquid-liquid extraction?

The Henderson-Hasselbalch equation is used to predict the ratio of a compound in its ionized form to its neutral form based on the pH of the solution and the compound's pKa. It is used in liquid-liquid extraction to determine the optimal pH for selectively extracting a compound into one phase.

How can the compounds separated by liquid-liquid extraction be recovered in their original form?

After extraction, compounds like anilinium chloride or sodium benzoate can be converted back to their neutral forms by adding an excess of acid or base, respectively. The neutral compounds can then be extracted into an organic solvent or precipitated out of the aqueous solution.

Outlines

00:00

🧪 Fundamentals of Liquid-Liquid Extraction

Dr. Frank introduces liquid-liquid extraction, a purification technique in organic synthesis. The process relies on the differing solubilities of compounds in immiscible solvents, allowing for the separation of a pure product from impurities. Organic solvents are often miscible with each other, but water is immiscible with many organic solvents, making it a common choice for extraction. A separatory funnel is used to physically separate the immiscible solvents into layers, with compounds dissolving preferentially in one layer based on their solubility. The density of the solvents determines the layering, with water typically forming the bottom layer unless the organic solvent is halogenated. The 'like dissolves like' rule is used to predict solubility, with polar solvents dissolving polar molecules better. The video also explains that multiple extractions with smaller volumes are more effective than a single extraction with a large volume.

05:00

💧 The Role of Water in Liquid-Liquid Extraction

Water, being a highly polar solvent, is used in liquid-liquid extraction to remove polar impurities like ionic compounds or salts. These compounds, consisting of cations and anions, are among the most polar and thus dissolve preferentially in water. The video discusses how simple inorganic compounds, such as excess base or acid, or ionic byproducts, can be removed through extraction. However, neutral organic compounds cannot be separated by extraction alone, leading to the concept of reactive extractions. This involves using acid-base chemistry to ionize organic molecules, making them water-soluble and allowing for their separation. The video emphasizes the importance of understanding the acid dissociation constant (pKa) for planning reactive extractions, as it quantifies an acid's strength and helps predict the partitioning of a weak acid between its neutral and anionic forms.

10:02

🔍 Reactive Extractions and the Henderson-Hasselbalch Equation

The video delves into reactive extractions, explaining how organic molecules can be selectively transferred into the aqueous phase by ionizing them. Acid-base chemistry is used to form water-soluble conjugate bases or acids from weak acids or bases, respectively. The Henderson-Hasselbalch equation is introduced to predict the partitioning of a weak acid between its neutral and anionic forms based on the solution's pH and the acid's pKa. The video graphically illustrates how the partitioning changes with pH, showing that at acidic pHs, the neutral form dominates, while at basic pHs, the conjugate base form is prevalent. It is emphasized that to achieve efficient purification, the pH should be adjusted away from the pKa value to ensure that the target molecules remain in a single phase. The video concludes with a practical scenario involving the separation of benzoic acid, naphthalene, and aniline, demonstrating how their differing acidities and basicities can be exploited for selective extraction.

15:04

🌡️ Adjusting pH for Efficient Reactive Extraction

This section focuses on the practical application of pH adjustment for reactive extractions. It explains that to achieve efficient separation, the pH should be set well below the pKa for acids or well above for bases to ensure that the target molecules are almost entirely in one phase. The video uses benzoic acid, naphthalene, and aniline as examples to illustrate how their extraction can be selectively controlled by adjusting the pH. It outlines a step-by-step process for separating these compounds using liquid extraction, starting with the crude mixture in an organic solvent. Aniline is first extracted into the aqueous phase using an acidic solution, followed by the extraction of benzoic acid into the aqueous phase using a basic solution. Naphthalene, remaining neutral and organic-soluble, can be isolated by evaporating the solvent. The video concludes by discussing the regeneration of the neutral forms of aniline and benzoic acid from their respective salts, either by adding excess base or acid, and the subsequent extraction into an organic solvent or precipitation from the aqueous solution.

Keywords

💡Liquid-liquid extraction

Liquid-liquid extraction is a separation technique used in chemistry to isolate compounds based on their differing solubilities in two immiscible liquids, typically an organic solvent and water. It is a core concept in the video, illustrating how impurities can be separated from a desired product by exploiting their preferential solubility in one solvent over the other. The process relies on the principle that 'like dissolves like,' meaning polar compounds tend to dissolve better in polar solvents, and non-polar compounds in non-polar solvents.

💡Solubility

Solubility refers to the ability of a substance to dissolve in a solvent. In the context of the video, solubility is a critical factor in liquid-liquid extraction, as it determines which solvent a compound will preferentially dissolve in. The video explains that different compounds have varying solubilities in different solvents, which is the basis for their separation during extraction.

💡Miscibility

Miscibility is the property of two or more liquids to mix together in all proportions. The video emphasizes that for liquid-liquid extraction to be effective, the solvents used must be immiscible, meaning they do not mix together. This allows for the separation of the solvents and the isolation of the desired product in one phase.

💡Separatory funnel

A separatory funnel is a piece of laboratory glassware used to separate immiscible liquids. The video describes how it is used in liquid-liquid extraction to allow the two phases to separate after mixing. It has a valve at the bottom that enables the separate collection of each layer into different containers.

💡Organic solvent

An organic solvent is a carbon-containing compound that dissolves a wide range of other substances. In the video, organic solvents are used in conjunction with water for extraction because most organic solvents are immiscible with water, which is essential for the separation process.

💡Polar solvents

Polar solvents are solvents that have a significant difference in electronegativity between different atoms, leading to a molecule with a charge separation. The video explains that polar solvents, like water, tend to dissolve polar molecules better due to their ability to form hydrogen bonds and other types of interactions with polar compounds.

💡Non-polar solvents

Non-polar solvents are those where the electron distribution is relatively even, resulting in no significant charge separation. The video mentions that non-polar solvents preferentially dissolve non-polar compounds, which have similar electron distributions and lack significant charge separation.

💡Acid-base chemistry

Acid-base chemistry involves the study of reactions between acids and bases. In the video, this concept is used to explain reactive extractions, where an organic molecule can be converted into a water-soluble form by ionizing it with a strong acid or base, thus allowing it to be extracted into the aqueous phase.

💡pKa

pKa is the acid dissociation constant, a quantitative measure of an acid's strength in solution. The video uses pKa values to predict the partitioning of weak acids between their neutral and anionic forms, which is crucial for planning reactive extractions. A lower pKa indicates a stronger acid, while a higher pKa indicates a weaker acid.

💡Henderson-Hasselbalch equation

The Henderson-Hasselbalch equation is used to predict the ratio of the ionized to non-ionized forms of a weak acid or base in solution as a function of pH. The video explains how this equation is used to determine the pH conditions under which a weak acid will predominantly exist in its neutral form (favoring organic solubility) or its ionized form (favoring aqueous solubility), which is essential for effective extraction.

💡Reactive extractions

Reactive extractions involve the selective transfer of a compound into the aqueous phase by ionizing it, typically through acid-base reactions. The video describes how this technique can be used to separate organic compounds that are otherwise insoluble in water, by temporarily converting them into ionic forms that are soluble in the aqueous phase.

Highlights

Liquid-liquid extraction is a purification technique based on the differing solubilities of compounds in immiscible solvents.

The technique exploits the principle that immiscible solvents will separate into layers when mixed.

Organic solvents are often miscible with each other, making them unsuitable for liquid-liquid extraction.

Water is immiscible with many organic solvents, making it a common choice for liquid-liquid extraction.

A separatory funnel is a glassware used for separating immiscible solvents in liquid-liquid extraction.

The density of solvents determines whether the organic layer is on top or bottom in extraction.

Halogenated solvents, like chloroform, have densities higher than water and will be found underneath the aqueous layer.

The 'like dissolves like' rule helps predict solubility, with polar solvents dissolving polar molecules better.

Most neutral organic molecules preferentially dissolve in organic solvents over water.

Multiple extractions with small volumes of solvent are more efficient than a single extraction with a large volume.

Water can remove polar impurities, including ionic compounds or salts, from organic mixtures.

Reactive extractions involve selectively transferring molecules into the aqueous phase by ionizing them.

Acid-base chemistry can be used to ionize organic molecules, making them soluble in the aqueous phase.

The acid dissociation constant (pKa) is a quantitative measure of an acid's strength and is crucial for planning reactive extractions.

The Henderson-Hasselbalch equation relates the pH of a solution to the pKa of an acid, predicting the partitioning of acid and conjugate base.

Molecules are mostly in the neutral form at pH values below their pKa, and in the conjugate base form at pH values above their pKa.

To ensure efficient purification, avoid intermediate pHs around the pKa value of the target molecule.

Reactive extraction can be used to selectively separate compounds like benzoic acid, naphthalene, and aniline based on their pKa values.

A flow chart summarizes the steps for separating a mixture of benzoic acid, naphthalene, and aniline using liquid-liquid extraction.

Aniline can be selectively extracted into the aqueous phase using an acidic solution, while benzoic acid and naphthalene remain in the organic phase.

Benzoic acid can be converted to its water-soluble form by treating the organic solution with a base, leaving naphthalene in the organic phase.

The salts formed during extraction can be converted back to their neutral forms for purification, using either excess acid or base.

Transcripts

Hi everybody, Dr. Frank here to give you a rundown  on the fundamental theory behind liquid-liquid  

extraction, a useful purification technique in  organic synthesis. Liquid-liquid extraction is a  

purification technique based on two key concepts:  1) The solubility of various compounds differs  

from solvent to solvent. 2) Not all solvents  will mix together; this is what we refer to  

as miscibility. Two solvents that are immiscible  will spontaneously separate themselves if mixed.  

So two immiscible solvents with wildly different  solvating powers can be used to dissolve an impure  

product: in the ideal scenario, all the impurities  will preferentially dissolve in one solvent,  

while the product alone will remain in the  second solvent. Since the solvents won't mix,  

they can be physically separated to  isolate the solution of the pure product.  

While organic solvents can display a wide range of  dissolving power, most of them tend to be miscible  

with each other so most organic solvent pairs are  inadequate for liquid-liquid extraction. Water on  

the other hand is immiscible with many organic  solvents, save for a few very polar solvents.  

As an extremely polar and protic solvent itself,  its dissolving power is also fairly distinct  

than most of the organic solvents. For this  reason, in the overwhelming majority of cases,  

liquid-liquid extraction is performed  using water and an organic solvent.  

Practically speaking, this is easily achieved  with minimal effort in an organic synthesis lab  

using a specialized piece of glassware  known as a separatory funnel,  

or a step funnel. When two immiscible solvents are  mixed therein, they separate into distinct layers;  

compounds found in our mixture will  preferentially dissolve in either phases  

depending on their respective solubilities.  Thanks to the valve at the bottom,  

both layers can then be physically separated by  draining separately into two different containers.  

Distinguishing whether the organic  layer is on top or at the bottom  

is fairly easily achieved, as the relative  ordering depends on the density of each solvent.  

Water has a density of one gram per milliliter:  most organic solvents have densities that are  

inferior to one gram per ml and as such will  be found as the top layer. A very notable  

exception however are halogenated solvents, such  as chloroform and dichloromethane. These solvents  

have densities higher than one gram per ml and as  such will be found underneath the aqueous layer.  

Now that we can distinguish our layers,  we need to determine what will be found  

in each of those layers. The general rule of  thumb when it comes to determining solubility  

is "like dissolves like": polar solvents tend to  dissolve polar molecules better than non-polar  

molecules, and vice-versa. Water is by far the  most polar of solvents commonly encountered  

in the lab and will thus preferentially dissolve  polar compounds, while the organic solvent will  

preferentially dissolve non-polar compounds.  However, most neutral organic molecules can be  

considered as relatively non-polar: sure, some  molecules are definitely more polar than others.  

Take caffeine, for example: with its various  nitrogen atoms and carbonyl moieties, it is  

without a doubt more polar than, say, benzene,  and as a result has better water solubility.  

Yet, caffeine remains better dissolved by many  organic solvents: as a rule of thumb for CHM2123,  

you can consider that all neutral organic  molecules, if given a choice, will preferentially  

dissolve in an organic solvent over water. A  quick comment regarding this rule of thumb:  

you will notice that the word "preferentially"  has been repeatedly used throughout this video,  

instead of the word "exclusively". The reason for  this is fairly simple: let's consider caffeine  

again and its respective solubilities in water  and chloroform. You'll notice that caffeine is  

indeed approximately eight times more soluble  than chloroform than it is in water: if we were  

to add caffeine to a sep funnel containing equal  volumes of chloroform and water, the majority of  

the caffeine would be found in the organic phase.  We wouldn't find, however, ALL of the caffeine,  

since it does have a noticeable solubility in  water. This leads us to rule of thumb number two:  

when performing liquid-liquid extraction, it  is both more efficient and more effective to  

perform several extractions with small volumes of  organic solvent rather than a single extraction  

with a large volume. Over those multiple  extractions, the product will accumulate  

in its preferred phase. With this said, what is  the role of water in a liquid-liquid extraction?  

Being an extremely polar solvent, water can be  used to remove particularly polar impurities,  

notably ionic compounds, or salts. Salts are  compounds consisting of cations and anions;  

because each ion bears an electrical charge due  to the complete transfer of an electron, salts are  

among the most polar compounds typically seen in  chemistry. As a third rule of thumb for CHM2123,  

you can consider that all ionic compounds will  preferentially dissolve in water. In many cases,  

the impurities removed by a liquid extraction  will be relatively simple inorganic compounds;  

for instance, excess base or acid used  in the reaction, or ionic byproducts that  

can result from the reaction, such as the  case in a substitution reaction shown here.  

However, if a crude reaction mixture is  comprised of various neutral organic compounds,  

liquid extraction will typically be powerless to  further separate them. Typically, but not always:  

in some cases, liquid extraction can be used to  further separate organic compounds using a process  

dubbed reactive extractions. Since most organic  molecules tend to be soluble in the organic phase,  

further separation will only occur by selectively  transferring one of our molecules into the aqueous  

phase. How would this be achieved? As mentioned  previously, ionic compounds will preferentially  

dissolve in water, so to push one molecule into  the aqueous phase, it has to be ionized. This  

can be done with organic molecules using acid-base  chemistry: if an organic molecule is a weak acid,  

reacting it with a sufficiently strong base will  form the molecule's conjugate base, which will be  

water soluble. On the other hand, if an organic  molecule is a weak base, reacting it with a  

sufficiently strong acid will form the molecule's  conjugate acid, which will also be water soluble.  

In either cases, the aqueous phase containing the  conjugate derivative can be physically separated.  

Because acid-base chemistry is reversible, we can  isolate the neutral form of whatever we extracted  

into the water by adding an excess of acid  or base to regenerate the original compound.  

To better understand and plan reactive  extractions, it is imperative to have a good  

understanding of the acid dissociation constant,  or pKa, which is a quantitative measure of an  

acid's strength in solution. An acid reaction  can be described as an equilibrium between the  

neutral acid and both its conjugate base and a  proton. Being an equilibrium, this process can  

be quantified using an equilibrium constant Ka,  which is the product of the concentration of the  

products over the concentration of the acid.  For simplicity, we typically use the inverse  

log of this constant (the pKa) which will  in most cases be a number ranging from -10  

to 55. We can define a pKa value for any hydrogen  in a given molecule: this pKa tells us how acidic  

this hydrogen is. The lower the pKa, the more  acid the hydrogen. Typically, for a molecule,  

we will consider the pKa of the most acidic  hydrogen, since it will be the first hydrogen to  

leave in case of an acid-base reaction. Shown here  are the approximate pKas of various functional  

groups and simple molecules: strong acids  such as hydrochloric acid have very low pKas.  

Alkanes have the highest pKas and as a result  are the least acidic compounds you will see in  

organic chemistry. What we are interested in  knowing when doing reactive extractions is the  

partitioning of our weak acid: is it mainly in the  neutral acid form, which would be organic soluble,  

or in the anionic conjugate base  form, which would be water soluble?  

We can easily predict this partitioning by making  use of the pKa value: the key aspect to consider  

here is the relationship between the weak acid's  pKa and the solution's pH. To do so, we start from  

the definition of Ka. By applying a log on each  side of the equation and rearranging the terms,  

we get the Henderson-Hasselbalch equation,  shown here with the pKa and pH highlighted.  

We can graphically plot the partitioning of  both species as a function of the solution's pH:  

unsurprisingly, at acidic pH, almost 100% of the  molecules are in the neutral acid form. Inversely,  

the conjugate base form dominates at basic  pHs. Now, what about this point here,  

where the two lines meet? In this case, exactly  half of the molecules are in a neutral acid form  

and the other half is in the conjugate base form.  What is so special about the pH at this point?  

Let's analyze this using the Henderson-Hasselbalch  equation. Regardless of the actual concentrations  

involved, if both species are found in equal  amounts, then the ratio A-/HA is equal to one.  

The log of one is zero: this tells us that  for both species to be found in equal amounts  

in the solution, the pH of the solution has to  be exactly equal to the pKa of our acid molecule.  

Practically speaking this means that half of the  molecules will tend to dissolve in the organic  

phase, while half of our molecules  will dissolve in the aqueous phase.  

As you might imagine this scenario is not  particularly enviable for purification purposes;  

however, if we decrease the pH by acidifying our  mixture, we find that the equilibrium is shifted  

toward the acid form. This could be demonstrated  with the Henderson-Hasselbalch equation;  

if the pH is inferior to the pKa, log of A-/HA is  negative, which would mean that the concentration  

of A- would be inferior to that of HA. A similar  argument could be made to show that instead,  

by increasing the pH to basic conditions, we  promote the formation of the conjugate base.  

So, for reactive extraction purposes, we want  an almost quantitative partitioning of our acid  

into either organic or aqueous soluble species to  ensure an efficient purification. For this reason,  

we want to avoid intermediate pHs, which  typically correspond to the acid's pKa value,  

plus or minus one unit, to ensure that all of our  target molecules remain in a single phase. Let's  

apply this to a concrete scenario, taking as an  example three different compounds: benzoic acid,  

naphthalene and aniline. The most acidic  proton on benzoic acid is a carboxylic acid,  

with a pKa value of approximately four. What this  tells us is that in the presence of an aqueous  

solution whose pH is inferior to 3, benzoic  acid will be over 99% in the neutral form  

and will dissolve preferentially in the organic  solvent. At pHs superior to 5, over 99% of the  

molecule will be found instead as a benzoate  anion, which is water soluble. Naphthalene bears  

no particularly acidic hydrogens: all of its  hydrogens have pKas of approximately 40 to 45.  

This means that, to be deprotonated, the pH  of water would have to be superior to 45,  

which is impossible. For this reason,  naphthalene will never be deprotonated  

in the presence of water and will always remain  neutral, and thus organic soluble. Finally,  

aniline, which is a bit of a special case. It  bears somewhat acidic hydrogens: the one bound to  

the nitrogen. However, the pKa for such hydrogens  is approximately 30. For similar reasons to what  

was just described for naphthalene, aniline will  never be deprotonated in the presence of water.  

However, aniline is also a base: the nitrogen atom  bears a lone pair that can be used to capture an  

acidic proton and form a conjugate acid. This  acid is indeed stable in the presence of water  

and has a pKa of approximately four. So, in  acidic solutions with a pH inferior to 3,  

the aniline is mostly protonated as the anilinium  and is therefore water soluble. On the other hand,  

in basic solutions, the anilinium is rapidly  deprotonated to form the neutral aniline,  

which is organic soluble. So, considering what  we just discussed, if given a mixture of the  

three compounds, we should easily be able to  separate them using only liquid extraction.  

We will summarize our steps in a table called  a flow chart. Firstly we have a crude mixture  

of the three compounds co-dissolved in an  appropriate organic solvent, such as ethyl  

acetate or dichloromethane. No matter what  we do, naphthalene will always remain in the  

organic phase, while the acid and the aniline  can be selectively pushed into the aqueous phase  

one at a time. It does not really matter which  compound we start with, so we will start by  

removing the aniline. If you remember, aniline can  be made water-soluble in fairly acidic conditions,  

so we will use a 1M hydrochloric acid solution.  At this pH, the aniline is readily extracted  

into the aqueous solution as anilinium chloride,  while the benzoic acid and the naphthalene remain  

neutral and thus organic soluble. Using our sep  funnel, we can physically separate each solution.  

We can then further purify the remaining  organic solution by treating it with base;  

1M sodium hydroxide. In these fairly basic  conditions, the benzoic acid reacts to form  

sodium benzoate, which is water-soluble, and  leaves the naphthalene intact in the organic  

phase. At this point, we have three relatively  pure solutions: two aqueous solutions of anilinium  

chloride and sodium benzoate, respectively,  and an organic solution of naphthalene. If  

naphthalene is the target product, the solvent  can be easily evaporated to yield a pure product.  

However if aniline and/or benzoic acid are  the targets, we have a bit of a problem.  

First off, we currently do not have either  compounds, but instead their respective  

conjugate acid and base. Furthermore, water  is impractical to completely evaporate,  

so you want to finish with your product in a  volatile organic solvent. For both reasons,  

we need to convert our salts back to their  respective neutral form. The anilinium chloride  

can be converted back to aniline by using an  excess of base, to ensure complete regeneration  

of the neutral form, which can then be extracted  into an organic solvent and isolated. Similarly,  

the benzoic acid can be regenerated by adding  an excess of acid: the resulting benzoic acid  

could be extracted using an organic solvent.  However, since the acid itself is a solid, it will  

precipitate from the water upon acidification and  could alternatively be filtered from the solution.

This wraps it up for this video, which  focused on the fundamental theory  

of liquid-liquid extraction,  along with its potential uses.  

Coming up next is a technical video that  will demonstrate how to effectively assemble  

and perform liquid extraction when in a chemistry  undergrad lab here, at the University of Ottawa