Exploiting Liquid-Liquid Extraction to Purify Organic Compounds

Summary

Dr. Frank's video tutorial offers a step-by-step guide on liquid-liquid extraction for purifying organic compounds in a chemistry lab setting. It covers the necessary equipment, the process of shaking and separating phases, and additional purification techniques like aqueous and basic washes. The video also addresses the use of anhydrous sodium sulfate for drying and the strategic application of acid or base to selectively extract charged molecules, ultimately highlighting the technique's efficiency and versatility in organic chemistry.

Takeaways

• 🔬 This video is a practical guide for performing liquid-liquid extractions to purify organic products in a chemistry lab setting.
• 🎓 It is part two of a series and assumes prior knowledge of the theory behind extractions, which was covered in part one.
• 🧪 The process involves using a separatory funnel, erlenmeyers, and various chemicals like solvents, acids, bases, and anhydrous sodium sulfate.
• 🔧 Safety is emphasized by ensuring the extraction setup is secure and performed within a fume hood.
• ⚖️ The extraction technique requires careful shaking of the separatory funnel to maximize the surface area for mass transfer between phases.
• 🌊 Aqueous washes are used to remove water-soluble impurities, and additional basic washes can be performed for further purification.
• 💧 Anhydrous sodium sulfate is used to dry the organic layer by adsorbing water, ensuring a clean product.
• 🔄 The process may include acid-base chemistry to selectively extract compounds into the aqueous layer for purification.
• 🧪 The video demonstrates two scenarios: a simple aqueous wash and a more complex purification involving a basic wash.
• ⏱️ With practice, the entire extraction process, from setup to drying, can be completed in under 20 minutes.

Q & A

What is the main purpose of liquid-liquid extraction in organic chemistry?

The main purpose of liquid-liquid extraction in organic chemistry is to separate and purify organic compounds from a mixture based on their differential solubility in two immiscible liquids, typically an organic solvent and an aqueous solution.

What are the two scenarios demonstrated in the video for liquid-liquid extraction?

The video demonstrates two scenarios: one where a simple aqueous wash is used, and a second where an additional basic wash is performed to further purify the product.

What equipment is necessary for performing liquid extractions as described in the script?

The necessary equipment includes a ring clamp, a separatory funnel, clean 125 milliliter Erlenmeyer flasks, water, extraction solvent, dilute acid or base, anhydrous sodium sulfate, a Buchner funnel, and the reaction mixture to be purified.

Why is it important to shake the separatory funnel vigorously during the extraction process?

Shaking the separatory funnel vigorously is crucial to maximize the surface area between the two immiscible phases, which facilitates mass transfer and ensures effective extraction of the desired compound.

How does the use of anhydrous sodium sulfate aid in the purification process?

Anhydrous sodium sulfate is used to adsorb water from the organic solution, which helps in removing any leftover water-soluble impurities and ensures a drier, purer organic layer.

What is the significance of the color change observed during the basic extraction with sodium hydroxide?

The color change during the basic extraction with sodium hydroxide indicates the selective extraction of a compound into the aqueous layer due to its ionization in the basic environment, which is a key step in separating compounds with different acid-base properties.

Why might one choose to perform an additional acid or base wash in an extraction process?

An additional acid or base wash is chosen to exploit the differential reactivity of compounds with acids or bases, allowing for the selective extraction of certain compounds into the aqueous layer, thus further purifying the product.

How can one convert a compound's conjugate base back to its neutral form during the purification process?

To convert a compound's conjugate base back to its neutral form, one can add excess acid to the aqueous layer until an acidic pH is achieved, followed by extraction with a clean organic solvent to recover the neutral compound.

What is the role of vacuum filtration in the purification of solid products?

Vacuum filtration is used to isolate solid products directly from the aqueous solution when the product precipitates, allowing for its separation without the need for extraction steps.

How long should one expect to perform most extractions from setup to drying according to the video?

The video suggests that once adept, one should be able to perform most extractions from setup to drying in under 20 minutes.

Outlines

00:00

🔬 Liquid-Liquid Extraction for Organic Chemistry

Dr. Frank introduces a tutorial on liquid-liquid extraction, a purification technique used in organic chemistry labs, specifically at the University of Ottawa. The video is a continuation of a series and assumes viewers have a basic understanding of the theory, scope, and limitations of extractions from part one. The video demonstrates two scenarios: a simple aqueous wash and an additional basic wash for further purification. Essential equipment for the procedure includes a ring clamp, a separatory funnel, erlenmeyers, water, extraction solvent, dilute acid or base, anhydrous sodium sulfate, and a Buchner funnel. The process involves attaching the clamp to a fume hood, adding water and reaction mixture to the flask, shaking to maximize surface area for mass transfer, and separating the phases. A common mistake is gently rocking the funnel instead of shaking it vigorously. The video emphasizes the importance of shaking to ensure proper extraction and the use of anhydrous sodium sulfate to dry the organic layer by adsorbing water. In some cases, a basic or acidic wash is performed to exploit the reactivity of the product or impurities with acids or bases, allowing for selective extraction into the aqueous layer.

05:03

🌟 Advanced Extraction Techniques for Organic Compounds

This segment of the video script delves into advanced extraction techniques for separating organic compounds using acid-base chemistry. The process involves repeating the aqueous extraction to ensure full separation of compounds and combining the extracts. The organic layer is then drained into an erlenmeyer, marking the successful separation of two organic products in a short time. If the target product is the blue organic soluble compound, the process can proceed to the drying step as shown in part one. However, if the product is the aqueous soluble orange compound, an additional step is necessary to convert the conjugate base back to the neutral compound by adding excess acid to achieve an acidic pH, followed by extraction with a clean organic solvent. The video also addresses the scenario where the product might precipitate as a solid from the aqueous solution, allowing for the skipping of the extraction step in favor of vacuum filtration for isolation. The tutorial concludes by emphasizing the simplicity and power of liquid-liquid extraction when performed under the right conditions, with the potential to complete most extractions within 20 minutes.

Keywords

💡Liquid-liquid extraction

Liquid-liquid extraction is a method used in chemistry to separate compounds based on their differing solubilities in two immiscible liquids, usually water and an organic solvent. In the context of the video, this technique is central to purifying organic products. The script describes the process of shaking a separatory funnel containing a mixture of an organic layer and an aqueous layer to facilitate the transfer of the desired compound from one phase to the other.

💡Immiscible phases

Immiscible phases refer to two liquids that do not mix together, such as oil and water. In the video, the importance of creating a mass transfer between these two immiscible phases is emphasized for the extraction process to be effective. The script mentions that to achieve this, one must maximize the surface area by shaking the separatory funnel vigorously.

💡Separatory funnel

A separatory funnel is a piece of laboratory equipment used to separate two immiscible liquids. It is a funnel with a stopcock at the bottom that allows the user to control the flow of liquid. In the script, the separatory funnel is used to perform the liquid-liquid extraction, with the operator shaking it to mix and then allowing the layers to separate.

💡Aqueous wash

An aqueous wash is a process in which water is used to wash the organic layer to remove water-soluble impurities. The script describes a scenario where, after the initial extraction, a simple aqueous wash is performed to further purify the product by removing any remaining water-soluble impurities.

💡Basic wash

A basic wash involves the use of a basic solution, such as sodium hydroxide, to selectively extract acidic compounds into the aqueous phase. The video script illustrates this by showing how an orange compound is extracted into a basic aqueous layer, changing the color of the organic layer from green to blue.

💡Anhydrous sodium sulfate

Anhydrous sodium sulfate is a drying agent used to remove water from organic solutions. In the script, it is added to the organic layer after extraction to adsorb any remaining water, ensuring that the organic product is dry before further processing.

💡Dilute acid or base

Dilute acid or base is used to adjust the pH of the solution during the extraction process, which can help in selectively extracting certain compounds. The script mentions using dilute sodium hydroxide for a basic wash and excess acid to convert the conjugate base of a compound back to its neutral form.

💡Buchner funnel

A Buchner funnel is used in conjunction with a vacuum to filter solids from a liquid. Although not a primary focus in the script, it is mentioned as an alternative method to remove anhydrous sodium sulfate from the organic solution if decanting is not feasible.

💡Purification

Purification in the context of the video refers to the process of removing impurities from a chemical compound to obtain a pure product. The entire video is centered around the use of liquid-liquid extraction as a purification technique, with various steps described to ensure the organic product is free from impurities.

💡Reaction mixture

A reaction mixture is a combination of reactants and any products formed during a chemical reaction. In the script, the reaction mixture is the starting material that is subjected to the extraction process to isolate and purify the desired organic product.

💡Vacuum filtration

Vacuum filtration is a method of filtering a liquid through a filter medium under reduced pressure, which speeds up the filtration process. The script briefly mentions vacuum filtration as a potential step if the product is a solid that precipitates from the aqueous solution.

Highlights

Introduction to liquid-liquid extraction for purifying organic products in chemistry labs.

Assumption that viewers are familiar with the theory of extractions from part one of the series.

Emphasis on the variability of extraction steps depending on the reaction.

Overview of equipment needed for liquid extractions, including a separatory funnel and erlenmeyer flasks.

Instructions for setting up the extraction apparatus in a fume hood for safety.

Technique for adding water and reaction mixture to the separatory funnel.

Importance of shaking the funnel vigorously to maximize mass transfer between phases.

Advice on venting the funnel during shaking to prevent pressure build-up.

Step-by-step guide on separating and collecting the organic and aqueous layers.

Description of the washing step to remove water-soluble impurities.

Use of anhydrous sodium sulfate to dry the organic layer by adsorbing water.

Method for decanting the dried organic solution into a clean flask.

Explanation of how to exploit acid-base chemistry for further purification of products.

Demonstration of a basic wash using sodium hydroxide to selectively extract a compound.

Process for converting the conjugate base of a compound back to its neutral form using acid.

Alternative approach for isolating solid products through vacuum filtration.

Conclusion on the efficiency and power of liquid-liquid extraction for organic product purification.

Estimate that proficient extractions can be completed in under 20 minutes.

Transcripts

Hi everybody, Dr. Frank here to show you how to  perform liquid liquid extraction to purify organic  

products when in a chemistry undergrad labs here,  at the University of Ottawa. This video is part  

two of a series on the use of extractions in  the organic lab and assumes that you are already  

familiar with the fundamental theory behind the  technique, as well as its scope and limitations,  

which were the focus of part one. If it is not  already done, I highly suggest that you start by  

watching the theory video first, before proceeding  with this video. Of course, please note that every  

reaction is a little different and the required  steps in liquid extractions will vary accordingly.  

This short film will show you two different  scenarios: one where a simple aqueous wash  

is used, and a second where an additional basic  wash was performed to further purify the product.  

First, a rundown of what equipment you will need  for liquid extractions: a ring clamp, a separatory  

funnel, clean 125 milliliter erlenmeyers,  water along with your extraction solvent,  

dilute acid or base, depending on your mixture to  purify, anhydrous sodium sulfate, a Buchner funnel  

and, of course, your reaction mixture to purify.  Start by attaching your ring clamp tightly to  

a monkey bar in your fume hood, ensuring the  assembly is safe. Insert your sep funnel into  

the ring and close the bottom valve. Put a clean  erlenmeyer under the funnel to catch any dripping,  

if any. Add water into the flask, followed by  your reaction mixture. Rinse your reaction flask  

with a small amount of fresh solvent and pour  into the funnel. Seal with the Teflon stopper,  

grab the funnel and invert it holding the stopper  tightly against the palm of your right hand.  

With your left hand, get a hold of the funnel  near the valve and then SHAKE the funnel. By far,  

the most common mistake during extractions is  that students either rock the funnel very gently,

or simply twirl it around. For extraction to  occur, there has to be a mass transfer between two  

immiscible phases: for this to happen, you need  to maximize the surface area. So again, give it a  

good shake: make sure you vent every few seconds.  Once finished, insert your funnel back into the  

clamp and allow the phases to separate. Remove the  stopper and drain the bottom aqueous layer into a  

clean erlenmeyer. Drain the organic layer into a  second clean erlenmeyer; pour the aqueous layer  

back into the sep funnel and add fresh solvent.  Repeat the shaking step and separate the layers:  

you can combine the organic layers into  the funnel. Drain the excess water,  

then perform a final wash step by adding some  clean water and repeating the extraction and the  

phase separation steps. This washing steps helps  in removing any leftover water-soluble impurities.  

Recuperate the organic layer into an erlenmeyer,  add a few small scoops of anhydrous sodium sulfate  

to the organic solution. This sodium sulfate  adsorbs the water from the solution. Stir  

well and visually inspect the flask; any excess  water left will be visible as either droplets or  

cloudiness. If these are still observable, add a  bit more drying agent and repeat. Once satisfied,  

allow to stand for approximately five minutes  to ensure complete drying. Eliminate the solid;  

because of the size of the sodium sulfate, you  should be able to easily decant the solution  

into a clean flask. Otherwise, you can also filter  it off using a Buchner funnel and a filter paper:  

in this case, a vacuum assembly is seldom  required. In some cases, either your product or an  

impurity might be reactive with acids or bases,  resulting in the formation of an electrically  

charged molecule that can be selectively extracted  into the aqueous layer. This can be exploited to  

further purify your product. To do so, you would  start by performing the same steps as in part one,  

up until right after the water wash. At this  point, instead of drying the organic solution,  

you would need to add either dilute acid or  base (depending on the molecules involved).  

In this example, we have a mixture of two  molecules; one of which is a mild acid. For this  

reason, an extraction with dilute sodium hydroxide  is performed. Notice the color change: the green  

organic layer goes blue as the orange compound is  extracted into the basic aqueous layer. Drain this  

aqueous layer into an erlenmeyer, separate from  the aqueous solution that you've obtained so far.  

Repeat the aqueous extraction step twice, to  ensure full separation of your compounds and  

combine these aqueous extracts as you go. Drain  the organic layer into its respective erlenmeyer:  

you have successfully separated two organic  products in a minimal amount of time using  

only acid-base chemistry. If your target  product is the blue organic soluble compound,  

then you are essentially done and  can proceed with the drying step,  

as shown in part one. However, if your product  is the aqueous soluble orange compound,  

an additional step is required. Currently,  in this erlenmeyer, we have a solution of  

the orange compound's conjugate base, but we want  the neutral compound. We need to convert it back.  

To do so, for this scenario, we need to add excess  acid to the aqueous layer, until an acidic pH  

is achieved. Then, extract the aqueous layers  thrice with clean organic solvent, collecting the  

organic layers into a new erlenmeyer then proceed  to the drying step. If your product is a solid,  

it may very well precipitate from the aqueous  solution; in that case, you can skip this  

extraction step entirely and proceed instead  with a vacuum filtration to isolate your product.  

Lo and behold, this was the process of performing  a liquid liquid extraction: a simple technique,  

it can be immensely powerful to purify an organic  product under the right conditions. Once adept,  

you should be able to perform most extractions  from set up to drying in under 20 minutes.