Exploiting Liquid-Liquid Extraction to Purify Organic Compounds
Summary
TLDRDr. 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
🔬 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.
🌟 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.
Mindmap
Keywords
💡Liquid-liquid extraction
💡Immiscible phases
💡Separatory funnel
💡Aqueous wash
💡Basic wash
💡Anhydrous sodium sulfate
💡Dilute acid or base
💡Buchner funnel
💡Purification
💡Reaction mixture
💡Vacuum filtration
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.
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