Methyl Benzoate Lab Report

The aim of this experiment is to carry out a reaction that results in the synthesis of Methyl Benzoate by Fischer Esterification. Methyl Benzoate is an organic compound, it is an Ester with the chemical formula C6H5COOCH3 and it is formed by the condensation of methanol and benzoic acid. Methyl Benzoate is strongly reminiscent of the fruit of the feijoa tree, and it is used in the making of perfumes. (6)
(2)An Ester is a functional group which is derived from carboxylic acids, they are sweet and fruity smelling compounds. The lower the molecular weight of the ester the more pleasant the smell. They are often used in the food industry for artificial flavours or fragrances. An Ester is a product of the reaction of a carboxylic acid and an alcohol

(the hydrogen of the acid R-COOH is replaced by an alkyl group R') that are heated in the presence of an acid catalyst. Esters mainly result from the condensation of a carboxylic acid and an alcohol, for instance, in this experiment it is the condensation of methanol and carboxylic acid. Benzoic acid contributes a hydroxyl group and methanol contributes a hydrogen atom to form a water molecule, therefore the water is removed once the ester is formed.This reaction can be catalyzed by the presence of H+ ions. Sulfuric acid, H2SO4, is used as a catalyst for this reaction. The process is called Esterification or Fischer Esterification.
This Fisher Esterification will be carried out under reflux and it is a reversible process where equilibrium between reactant and products will be reached. The opposite of the esterification process is hydrolysis, this can be carried out by the addition of water to the link on the ester which would break it down to the carboxylic acid (benzoic acid) and the alcohol (methanol). Hydrolysis would also require the presence of a catalyst. Esterification is very complicated reaction and so it is a very slow reaction but it is even slower for amides.
The mechanism for this reaction is the acid catalyzed nucleophilic acyl substitution mechanism. It is not a direct substitution reaction, instead it is an addition reaction followed by an elimination reaction. The mechanism begins with protonation of the carbonyl group of the carboxylic acid, which is then attacked by the alcohol. Proton transfer and the subsequent release of water result in an oxygen cation with three bonds. A final deprotonation (removal of a proton) step provides the ester product. A more detailed description of this mechanism is as follows and it can be seen in Figure 1.
(4)In the first part of the mechanism the benzoic acid accepts a proton from the acid catalyst, it then binds to the carbonyl oxygen atom. Since the inorganic sulfuric acid is a strong acid it forces the weaker benzoic acid to act as a base and accept the proton. The protonation increases the positive charge on the carboxyl carbon and enhances its reactivity. Then a lone pair of electrons on the methanol (nucleophile) oxygen atom attack the carbonyl carbon atom of benzoic acid and a tetrahedral intermediate is formed. This is where the ester bond is formed. A hydrogen shifts from one oxygen atom to another, these steps are equilibria and are reversible, and then the water molecule leaves, this can only happen when a hydroxyl group is protonated so that its leaving group capacity is improved. The proton that’s just been bonded to the carbonyl oxygen atom leaves which regenerates the catalyst (sulfuric acid) and the ester Methyl Benzoate is released.