Synthesis of Ethyl Acetate

Introduction

Ethyl Acetate is a broadly used solvent. It has a sweet smell similar to pear drops (according to Wikipedia). I’m going to be making it using the classical Fischer Esterification reaction. This is an excellent synthesis to carry out when studying Organic Chemistry.

Ethyl Acetate has many uses, both as a solvent and as a reagent. It can be used to make Acetamide or Ethyl Acetoacetate, for instance. It has also gained some use as a Nail Polish Remover.

Reagents

• Ethanol (can be the 96% stuff found in every store);
• Glacial Acetic Acid;
• Sulfuric Acid 98%;
• Distilled Water (Tap Water works just fine);

Dangers

This reaction doesn’t have any particular danger. The Ethyl Acetate produced is flammable, though. The entire procedure should be carried out in a well ventilated area.

• Ethanol can cause severe intoxication, usually after the fifth drink.
• Acetic Acid is mildly corrosive and has a pungent odor, which I hate. Gloves and goggles are recommended. Working in a well ventilated area is also recommended.
• 98% Sulfuric Acid is highly corrosive. Wear gloves and goggles when handling it.

Procedure

Weight about 46 grams of Ethanol and 70 grams of Acetic Acid into a reaction vessel. Then, add about 5mL of Sulfuric Acid.

Set up an apparatus for simple reflux.

Note: The brown stuff you see on those pictures are my boiling stones.

Reflux the mixture for about 1 hour.

After 1 hour, take it of heating. If you smell the mixture (carefully) you will notice a new odor (Ethyl Acetate).

Now, set up for simple distillation.

The first drops of distillate should appear at about 70ºC.

The temperature will continue to rise, steadily.

When it reaches 80ºC it will start to rise much more rapidly and will reach the 90ºC mark very quickly. Stop the distillation as soon as it reaches about 93ºC.

Now you have a mixture that mostly contains Ethyl Acetate, Ethanol and Water. Pour it into a separatory funnel.

Now add 10mL of water. Sake thoroughly and allow the two phases to separate. Once there are two distinctive layers, drain the bottom one (it’s normal for the top layer to be cloudy).

Repeat this process five times so that the total volume of water used is 50mL.

Once you’re done you’re left with a mixture of Ethyl Acetate and Water. You need to use a dehydrating agent to remove the water. I recommend Anhydrous Calcium Chloride. Weight about 30 grams of Anhydrous Calcium Chloride and place it into the mixture (this is a huge excess of Calcium Chloride, you can use less but I prefer to always use an excess of it).

Let the mixture sit for about half an hour. Occasionally, shake the flask.

After half an hour, set up again for simple distillation (the Calcium Chloride inside the flask serves as boiling stones).

Note: If you want an almost water-free product remember to dry your distillation apparatus carefully.

My distillation took about an hour. The vapor should come over at around 77ºC.

Here is a picture about 40 minutes later:

Here is a picture of the mixture vessel when I stopped heating, to finish distilling:

My final product should be at least 98% pure Ethyl Acetate. The main contaminant is moisture.

I was able to obtain 68,2g of Ethyl Acetate.

Note: What you see on the scale isn’t a liquid. It is actually a stain that I haven’t cleaned properly yet.

Theory

As already stated, this reaction is a classical example of a Fischer Esterification reaction. This terminology is employed to describe a reaction between a Carboxylic Acid and an Alcohol, with an acid catalyst, under reflux.

For a better understanding of the theory behind this reaction, I’m going to divide this section into 3 sub-sections: general, distillation and purification.

• General

Molar Masses

Ethanol – 46,068 g/mol

Acetic Acid – 60,05 g/mol

Ethyl Acetate – 88,11 g/mol

In this case, Acetic Acid reacts with Ethanol, using Sulfuric Acid as a catalyst, to produce Ethyl Acetate and Water. This is an equilibrium reaction:

Acetic Acid + Ethanol <–> Ethyl Acetate + Water

Because this is an equilibrium, simply adding the reagents won’t produce a good yield of Ethyl Acetate. However, by refluxing and by having an acid catalyst, one can obtain a significant amount of Ethyl Acetate. Still, the reaction will be far from completion. That’s why it is important to do a simple distillation after the reflux, which I will now explain.

• Distillation

Boiling Points

Ternary Azeotrope (Ethyl Acetate/Water/Ethanol) – 70,3ºC – 7,8% Water, 9% Ethanol, 83,2% Ethyl Acetate

Azeotrope (Water/Ethyl Acetate) – 70,4ºC – 91,9% Ethyl Acetate

Azeotrope (Ethanol/Ethyl Acetate) – 71,8ºC – 69,2% Ethyl Acetate

Ethyl Acetate – 77,1ºC

Azeotrope (Ethanol/Water) – 78,1ºC – 95,5% Ethanol

Ethanol – 78,4ºC

Water – 100ºC

Acetic Acid – 118ºC

As you can see, after reflux one is left with a mixture of Ethyl Acetate, Water, Acetic Acid and Ethanol. This allows for a multitude of azeotropes.

When the distillation is started, the first thing to come out is the ternary azeotrope. Thus, a mixture of Ethanol, Water and Ethyl Acetate comes over. You could ask, of course, wouldn’t that diminish the yield, as Ethanol is being removed? This would shift the equilibrium to the left and remove some of the reagent. Well, yes and no. The Ethanol that gets removed doesn’t form any Ethyl Acetate, so it gets “wasted”. However, the percentage of Ethanol that comes over is way too low compared to the percentage of Ethyl Acetate and Water that comes over. This effectively shifts the equilibrium to the right.

At some point, almost all Ethanol is going to be consumed as it either it gets distilled away or it reacts to form Ethyl Acetate. That’s one of the reasons it is good to have excess Acetic Acid present, which allows for more Ethanol to react in the equilibrium.

At this point, the azeotropic mixture of Ethyl Acetate and Water should start to distill off. Notice that the percentage of Ethyl Acetate that distills over in both azeotropic mixtures is much higher than any other compound. At some point, the Ethyl Acetate is going to get all distilled over.

When all Ethyl Acetate is distilled, the temperature suddenly rises. This is because water is going to start to be distilled over (100ºC). It is at this point that one should stop the distillation. The relatively high boiling point of Acetic Acid prevents it from distilling over.

The Ethyl Acetate that is collected is contaminated with Water and Ethanol (some Acetic Acid may be present). The Ethanol present aids preventing the hydrolysis of Ethyl Acetate.

• Purification

Many procedures for this synthesis call for the neutralization of Ethyl Acetate with Sodium Carbonate, in order to remove the Acetic Acid present. Because my method doesn’t involve the contamination of Ethyl Acetate with Acetic Acid, this is unnecessary.

Ethyl Acetate is mildly soluble in water, about 8,3 g/100mL (20ºC). In order to remove the Ethanol and Water present in the Ethyl Acetate, I washed my distillate with water. This effectively removes the Ethanol present. Of course, some of the product gets lost.

After removing the Ethanol, it is necessary to remove the water present. I did so by distilling with a drying agent. Calcium Chloride can form a multitude of hydrated species effectively absorbing the water from the Ethyl Acetate. In this case, Calcium Chloride forms the dihydrate, which only decomposes at around 175ºC. This allows us to distill the Ethyl Acetate and effectively remove the Water from it.

Note: 15 grams of Calcium Chloride can absorb approximately 5 grams of water, in the conditions given. This is more than enough. However, I doubled the quantity just to make sure my product gets as anhydrous as possible. Also, I recycle my Calcium Chloride.

The collected product is pure Ethyl Acetate. I was able to obtain 68,2g. This represents an yield of 77,4% based on Ethanol.

Final Notes

It’s always interesting to produce smelly esters in the lab. Keep an eye here for I might use this compound on future posts.