Laboratory Synthesis of Aspirin

Summary

This video script details a laboratory demonstration of synthesizing aspirin from salicylic acid using acetic anhydride, catalyzed by sulfuric acid and heated to促成 reaction. The process includes crystallization for purification and a qualitative test with iron(III) chloride to confirm the absence of the phenol group in the final product, indicating successful synthesis and purification of aspirin.

Takeaways

• 🧪 The lab session focuses on an organic synthesis experiment to create aspirin.
• 💊 Aspirin, known as acetylsalicylic acid, is used for pain and inflammation relief.
• 🔬 Aspirin can be synthesized from salicylic acid and acetic anhydride in a single step.
• 🔍 The process involves using a strong acid as a catalyst and heating the reaction mixture.
• 🌡️ A hot water bath is used for even heating, reaching temperatures around 80-90°C.
• ⏱️ The reaction is left to proceed for about 10 minutes before cooling to room temperature.
• 💠 Crystallization is initiated by scratching the sides of the beaker or adding cold water.
• 🧊 An ice water bath is used to ensure complete crystal formation.
• 🕳️ Aspirin crystals are collected by vacuum filtration using a Büchner funnel.
• 🔄 Recrystallization is performed to purify the product, dissolving in ethanol and hot water.
• 🧪 A qualitative test using iron(III) chloride confirms the presence and purity of aspirin by color change.

Q & A

What is the main objective of the video?

The main objective of the video is to demonstrate an actual organic synthesis of aspirin, a drug used to reduce pain and inflammation.

What is the chemical name of aspirin?

The chemical name of aspirin is acetylsalicylic acid.

How is aspirin synthesized from salicylic acid?

Aspirin is synthesized from salicylic acid by reacting it with acetic anhydride to introduce the acetyl group.

What role does acetic anhydride play in the synthesis of aspirin?

Acetic anhydride is used to acetylate salicylic acid, thereby converting it to acetylsalicylic acid, which is aspirin.

What is the purpose of using a strong acid as a catalyst in the synthesis?

A strong acid, such as sulfuric acid, is used as a catalyst to speed up the reaction between salicylic acid and acetic anhydride.

Why is a hot water bath used instead of direct heating?

A hot water bath is used for even heating of the reaction mixture, preventing localized overheating that could occur with direct heating.

What is the significance of the crystallization step in the synthesis process?

The crystallization step is used to isolate and purify the synthesized aspirin from the reaction mixture.

How is the aspirin product collected after crystallization?

The aspirin product is collected by vacuum filtration after the crystallization step.

Why is recrystallization necessary in the purification process?

Recrystallization is necessary to further purify the aspirin product by removing any remaining impurities or starting materials.

What is the purpose of the qualitative test using iron(III) chloride at the end of the synthesis?

The qualitative test with iron(III) chloride is used to confirm the presence and purity of aspirin by checking for the absence of the phenol ring, which would indicate the presence of salicylic acid.

What is the final step to confirm the successful synthesis of aspirin?

The final step to confirm the successful synthesis of aspirin is to perform a qualitative test with iron(III) chloride, which should show no color change in the purified product, indicating the absence of salicylic acid.

Outlines

00:00

🧪 Organic Synthesis of Aspirin

This paragraph describes the process of synthesizing aspirin, a drug used for pain and inflammation relief, from salicylic acid. The synthesis involves a one-step reaction with acetic anhydride to introduce an acetyl group. A strong acid catalyst is used, and the reaction is heated to completion. Crystallization steps follow to isolate and purify the aspirin. Safety precautions are emphasized due to the use of irritants and strong acids. The process includes setting up a hot water bath, adding reagents, heating, cooling, and using vacuum filtration. Recrystallization is performed to further purify the product.

05:03

🔍 Confirming Aspirin Synthesis with Qualitative Assay

This paragraph outlines the final steps of the aspirin synthesis process, including drying the product and weighing it to determine the mass of the purified sample. It also describes a simple qualitative test using iron(III) chloride to confirm the presence and purity of aspirin. The test checks for the phenol ring, which is present in salicylic acid but not in aspirin. The results of the test show that the starting material turns purple, while the purified aspirin remains brown, indicating successful synthesis and purification. The paragraph concludes by emphasizing the simplicity of the synthesis and hints at more complex techniques to be explored in the future.

Keywords

💡Organic Synthesis

Organic synthesis refers to the process of chemically combining a few simpler compounds to form a more complex molecule. In the context of the video, organic synthesis is the main theme, as the lab procedure demonstrates the synthesis of aspirin from simpler compounds like salicylic acid and acetic anhydride. This process is crucial in organic chemistry and is used to create a wide array of products, from pharmaceuticals to industrial chemicals.

💡Aspirin

Aspirin, also known as acetylsalicylic acid, is a common anti-inflammatory drug used to relieve pain and reduce inflammation. The video focuses on the synthesis of aspirin as an example of a straightforward organic synthesis process. Aspirin is highlighted as a significant molecule due to its widespread use in medicine, which underscores the importance of organic synthesis in pharmaceutical applications.

💡Salicylic Acid

Salicylic acid is a organic compound that serves as the starting material for aspirin synthesis in the video. It is a white crystalline solid and a precursor in the production of aspirin. The script describes how salicylic acid reacts with acetic anhydride to form acetylsalicylic acid, demonstrating the role of starting materials in organic synthesis.

💡Acetic Anhydride

Acetic anhydride is the reagent used to introduce the acetyl group to salicylic acid, thus transforming it into aspirin. It is a colorless liquid and a reactive chemical used as an acetylating agent. In the script, acetic anhydride is combined with salicylic acid in the presence of a catalyst to perform the synthesis, illustrating a typical use of anhydrides in organic chemistry.

💡Catalyst

A catalyst is a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change. In the video, a strong acid like sulfuric acid acts as a catalyst to speed up the reaction between salicylic acid and acetic anhydride. The use of a catalyst exemplifies a common strategy in organic synthesis to improve reaction efficiency.

💡Crystallization

Crystallization is a technique used to purify a substance by forming solid crystals from a solution. In the video, crystallization is used to isolate aspirin from the reaction mixture after the synthesis. The process involves cooling the solution to induce crystal formation, which is a critical step in obtaining a pure product.

💡Recrystallization

Recrystallization is a purification technique that involves dissolving a substance in a solvent at high temperature and then allowing it to recrystallize at lower temperatures. The script describes a recrystallization step to further purify the synthesized aspirin, emphasizing the importance of purification in organic synthesis.

💡Vacuum Filtration

Vacuum filtration is a method of filtering a liquid through a filter (like filter paper) using a vacuum to draw the liquid through the filter, leaving the solid material behind. In the video, vacuum filtration is used to collect the aspirin crystals after crystallization, showcasing a common laboratory technique for isolating solid products.

💡Qualitative Assay

A qualitative assay is a type of chemical test used to determine the presence or absence of a particular compound. In the video, iron(III) chloride is used in a qualitative assay to test for the presence of the phenol ring in salicylic acid, which aspirin lacks. This test helps confirm the successful synthesis and purification of aspirin.

💡Phenol Ring

A phenol ring is a hydroxylated aromatic ring structure that is characteristic of phenolic compounds. In the script, the phenol ring is mentioned in relation to salicylic acid, which contains this structure and reacts with acetic anhydride to form aspirin. The absence of the phenol ring in aspirin is confirmed using a qualitative assay with iron(III) chloride.

💡Hot Water Bath

A hot water bath is a technique used to gently heat a chemical reaction. In the video, a hot water bath is set up to heat the reaction mixture containing salicylic acid and acetic anhydride. This method provides even heating and is safer than direct heating, which is important for controlling reaction conditions.

Highlights

Introduction to organic synthesis lab techniques

Synthesis of aspirin from salicylic acid

Aspirin's chemical name is acetylsalicylic acid

One-step synthesis of aspirin using acetic anhydride

Use of strong acid as a catalyst in the reaction

Heat the reaction to completion

Crystallization steps for aspirin isolation and purification

Qualitative test to confirm aspirin synthesis

Safety precautions with reagents like ethyl acetate and sulfuric acid

Setting up a hot water bath for even heating

Preparation of reaction mixture with salicylic acid and acetic anhydride

Addition of concentrated sulfuric acid and swirling for mixing

Heating the reaction in a hot water bath

Cooling the solution to initiate aspirin crystal formation

Use of a glass rod to scratch the beaker for crystallization

Adding cold water to halt the reaction

Collecting aspirin crystals by vacuum filtration

Rinsing the flask and filter paper with ethanol

Recrystallization to purify the product

Dissolving impure aspirin in ethanol and hot water

Formation and collection of aspirin crystals

Using vacuum system to dry the product

Weighing the purified aspirin sample

Qualitative assay using iron(III) chloride to confirm product

Observation of color change in the presence of phenol ring

Confirmation of successful aspirin synthesis and purification

Completion of the first organic synthesis

Transcripts

We’ve gone over a number of laboratory techniques in this series.

But now it’s time to do something different.

We are going to do an actual organic synthesis.

We are going to build an organic molecule.

As we have discussed in the lecture series, a big part of organic chemistry involves pathways

that scientists have used over the years to synthesize specific organic molecules.

These are used to synthesize everything from biomolecules to industrial materials to drugs.

Today we will synthesize aspirin.

Aspirin is a drug used to reduce pain and inflammation, which we covered in detail over

in the pharmacology series.

Aspirin’s chemical name is acetylsalicylic acid, and it is synthesized quite easily in

one step from salicylic acid.

As you can see in this scheme, we can convert salicylic acid to acetylsalicylic acid by

reacting with acetic anhydride to introduce the acetyl group.

The hydroxyl group on salicylic acid attacks protonated acetic anhydride to pick up the

acetyl group.

This is what we’re doing in the lab.

We’ll add the anhydride to salicylic acid, use a strong acid as a catalyst, and heat

the reaction to completion.

We’ll then perform crystallization steps to isolate and purify our aspirin.

To finish, we’ll use a simple qualitative test to see whether or not we have made and

purified aspirin.

Reagents will include ethyl acetate, an irritant, and sulfuric acid, an extremely strong acid,

so make sure you are using all the appropriate safety gear and precautions.

To start, let’s set up a hot water bath.

We’ll put water in a 500 milliliter beaker and start heating it on a hot plate.

While that heats, let’s prepare our reaction.

We’ll put about 2 grams of salicylic acid in a 125 milliliter Erlenmeyer flask, making

sure to record the precise mass on our datasheet.

Let’s add 5 milliliters of acetic anhydride to the powder.

Let’s also add 5 drops of concentrated sulfuric acid.

Swirl the mixture to make sure that everything is well mixed.

We’re now ready to heat our reaction vessel.

To get even heating, we’ll dip our flask in the hot water beaker, instead of putting

it directly on a hot plate.

To do this, let’s use a ring stand and a clamp to secure our flask.

Heat the water until it reaches around 80 or 90 degrees Celsius, and then leave the

reaction flask partially submerged in the hot water for about 10 minutes.

With our reaction complete, let’s take it out of the hot water.

We’ll then let our solution cool down to room temperature.

Aspirin crystals should start to form as the solution cools down.

As we covered in the recrystallization tutorial, you can use a glass rod to scratch the sides

of the beaker to initiate crystallization if necessary.

The glass particles scratched off will provide a surface for crystals to start forming.

If you still do not see crystals, add about 10 milliliters of cold water to the reaction

mixture.

This will halt the reaction.

To make sure all the crystals have been formed, let’s dip our beaker in an ice water bath.

Leave it there for 10 minutes.

That should be enough for all the crystals to form.

After we’ve formed aspirin crystals, let’s collect them by vacuum filtration.

Place some filter paper in the Büchner funnel, and then add the solution.

Be sure to rinse the flask with cold water to get all of the product out, and also to

wash with water to remove impurities.

Let’s run the vacuum for a few minutes to make sure that everything is dry.

Let’s then collect our product in another vessel.

We’ll make sure to save all our product by rinsing the filter paper with ethanol into

our beaker.

Even though we’ve collected our product, it is not totally pure.

This is because it still has trace amounts of the starting materials.

We’ll have to perform recrystallization to purify our product.

Let’s start by dissolving the impure aspirin in 5 milliliters of ethanol.

While we do that, let’s heat up some water on our hot plate.

We’ll then add 50 milliliters of hot water to the crude sample.

This will start to dissolve.

Let’s then add the vessel to the hot plate and start adding more solvent.

After everything has dissolved, it is time to recrystallize.

Let’s take our vessel off of the hot plate and place it at room temperature.

Over time, we’ll start to see crystals of aspirin form.

Give it time for all the crystals to form, and we can also scratch the sides to initiate

crystallization.

Finally, put the vessel in an ice bath as before to make sure we’ve crystallized all

of our product.

Let’s bring in the vacuum system again to dry our product one last time.

Before we do that, we’ll weigh our filter paper and watch glass, as this will be used

to measure the mass of our product.

Now, let’s add the same filter paper to the vacuum system and start filtering.

Let this go for a few minutes to make sure it’s dry.

We can then put our filter paper with our product on the watch glass and leave it at

room temperature to air dry, or use the oven at 65 degrees Celsius for 20 minutes.

After you get a dry product, let’s place it on a scale to weigh it.

The mass of your purified sample is calculated by taking this number and subtracting the

mass of the watch glass plus the filter paper that you measured earlier.

Once you’re done with a synthesis, you have to make sure that the product you’ve made

is the correct product.

In a typical chemistry lab, we use melting point analysis, IR, NMR, TLC, and more.

But today, we’ll use a simple qualitative assay to confirm the presence and purity of

our product.

To do that, we’ll use iron(III) chloride.

This compound changes color from brownish-red to purple in the presence of a phenol ring.

Now, let’s look at our starting material, salicylic acid, and our product, acetylsalicylic

acid.

Which one has a phenol ring?

As you can see, salicylic acid has a phenol ring and aspirin doesn’t.

So, if we add both the starting material and our product to tubes and introduce iron(III)

chloride, the salicylic acid should turn purple and aspirin should remain brown.

So if we have made and purified our aspirin, it shouldn’t change color.

If it does, either we didn’t make any aspirin, or we’ve made it but didn’t correctly

separate it from the starting material.

So let’s test our products.

Here we have a tube of our starting material, a tube of our crude product after the first

crystallization, and a tube of our final product.

We’ve also added a tube of pure water as our control to make sure that our test works

correctly.

Now, after adding FeCl3 to each of our samples, let’s look at the results.

The starting material turned purple as expected.

Then the crude product may turn purple, which would mean that there is still some starting

material in there.

But it may not, if the product was cleaned enough that no significant impurities reside

even within the crude product.

The pure product, as you can see, is brown, which is good news.

That means that we have successfully made aspirin and adequately purified it from the

starting material.

The control here is also brown, meaning that our test works as expected.

And with that you have now completed your first organic synthesis.

This is about as simple as it gets for synthesis, so hopefully we can look at much more complicated

synthetic techniques in

the future.