Synthesis of Methyl Benzoate by Fisher Esterification

Organic Chemistry II

Experiment Title:

Synthesis of Methyl Benzoate by Fisher Esterification

Experiment Date:

02/02/16

Submission Date:

30/02/2016

Name

Jayne Moorhead

Student Number

C14344116

Class Name

DT420/2

Introduction.

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Image 1- Mechanism of the Synthesis of Methyl Benzoate by Fisher Esterification

In this experiment Methyl Benzoate was prepared from Benzoic Acid. Methanol and Sulfuric Acid were used as catalysts for the reaction. This is known as Fishers Esterification. In this Esterification as can be seen from Image 1 The carbonyl group of the acid loses its lone pair. The acid catalyst works by increasing the positive charge on the carboxyl carbon this increases its reactivity towards nucleophiles. In the second step the oxygen has too many bonds and so takes an electron off the carbon. The most important step in the reaction is the addition of methanol which is a nucleophile to the carbonyl carbon to the protonated nucleophile. In this step a C-O bond is formed which is the Ester bond. The oxygen attached to alcohol has too many bonds, it takes an electron from the Hydrogen. There is another addition of acid which attracts an OH group, this forms the water molecule. The water is formed from the hydrogen of the alcohol and the hydroxyl of the acid.  In the next step water is eliminated, for this to happen an -OH group must be protonated to improve its leaving-group capacity. The elimination of the water forms the ester, converting benzoic acid to methyl benzoate. The acid catalyst serves two purposes. First, it makes the carbonyl carbon a better electrophile and also allows for the loss of H2O as a leaving group which is a much stronger leaving group than HO3. The aim of this experiment is to convert Benzoic Acid into Methyl Benzoate. This will be achieved by using Fishers Esterification. This is a reversible reaction and will therefore reach a point of equilibrium on both ends of the reaction. Fishers Esterification is named after Emil Fisher, who developed the Method.

Esters formed from the reaction of a carboxylic acid and an alcohol, as done in this experiment. An ester is a sweet smelling substance that are often used in food flavorings, perfume and fragrances. Esters can also be converted in polymers called polyesters these polyesters can be used to make plastic bottles or they can be converted into fibers to make clothing. Recycled polyesters are used to make fleece clothing.1 Methyl benzoate is a crystalline solid or a solid dissolved in a liquid. It is denser than water. Contact with the chemical may slightly irritate skin, eyes and mucous membranes. It also may be slightly toxic by ingestion. Its main use is that it is used to make other chemicals.2 Its boiling point is 196.65

Method

Part 1

5 grams of benzoic acid and 25mL of methanol was places in a 100mL round-bottomed flask. The mixture was cooled on ice and 1.5mL of concentrated sulfuric acid was slowly and carefully poured down the walls of the flask. It was swirled to mix the components. A reflux condenser was fitted with a water inlet tubing, 3 boiling chips were added and the mixture was gently refluxed for one hour.

Part 2 ( Isolation and Purification)

The solution was cooled to room temperature and then decanted into a separatory funnel containing 25mL of water, the flask was rinsed with 25mL of diethyl ether. This ether was added to the separatory funnel and shaken thoroughly, the water layer was drained off, which contained the sulfuric acid and the bulk of the methanol. The ether was washed in the separatory funnel with 25mL of water followed by 25mL of 10% sodium bicarbonate which removed the unreacted benzoic acid. It was shaken with frequent release of pressure by inverting the separatory funnel and opening the stopcock, until no further reaction appeared. The bicarbonate layer was drained into a beaker. The ether layer was dried in the separatory funnel with saturated sodium chloride solution, the ether solution was separated. The ether solution was dried over anhydrous calcium chloride in a 125mL Erlenmeyer flask. Sufficient anhydrous calcium chloride was added so that it no longer clumped together on the bottom of the flask. After 10 minutes, the dry ether solution was decanted into a dry 50-mL Erlenmeyer flask, the drying agent was washed with an addition 5mL of ether and decanted again. The ether was removed by evaporation in the hood. It was then weighed and an actual, theoretical and percentage yield was got.

Results.

Actual Yield – 1.9mL / 2.052g 

Theoretical Yield – 5.5744g

Percentage Yield – 36.81%

Discussion.

This lab involved the production of an ester from the reaction of a carboxylic acid and alcohol. The main aim of the lab was to produce methyl benzoate from the reaction of Benzoic acid and Methanol using Fisher Esterification.When conducting an esterification reaction, the acid used for the proton source must be strong enough to protonate the carboxylic acid in the first step. In this experiment, 5 grams of benzoic acid was reacted with 25 mL of methanol to product methyl benzoate. Sulfuric acid was then added to the mixture of benzoic acid and methanol. The reason excess methanol was used in this reaction is because Fisher esterification reaction is an equilibrium, which means the forward and reverse reaction is occurring at the same time. Each step as shown in Image 1 is reversible. By adding more methanol the reaction is drove to the right to create more product. Fishers Esterification takes advantage of Le Chateliers Principle by changing the concentration of the methanol it shifts the reaction to the right therefore creating more methyl benzoate to use up the increased amount of methanol and return the equilibrium to normal. The other method involves the removal of water.4 Ether, sodium bicarbonate and saturated sodium chloride were used respectively to wash the reaction mixture, due to their ability to remove excess sulfuric acid, methanol and unreacted benzoic acid. The ether solution was dried with anhydrous Calcium Chloride, as this is a dehydrating agent which removes excess water from the solution. The results obtained were 2.052g of Methyl Benzoate and a percentage yield of 36.81%. This was a disappointingly low result to have obtained. There are many reasons to why this low percentage may have been got firstly due to human error, it is possible that before weighing the final product that some of it was left in the container and also some spilled onto the desk before weighing. If this experiment was to be repeated more care would be taken whilst transferring the product to the clock glass to be weighed. Perhaps not enough methanol was added at the beginning to ensure enough product was formed, if this was to be repeated the experiment could be tried using more ethanol. Also whilst removing the waste layers during the experiment perhaps part of the product was removed whilst removing the layer. This would require more accuracy in future trials of the experiment.

In conclusion although the experiment was a success in that methyl benzoate was created a very low percentage yield was got meaning that the experiment could definitely be improved upon.