Extended Essays 2021

an aromatic ester, the oil can also be characterised by its strong ‘peppermint’ scent and is used often for the flavouring/scent of candy and fragrances 3 .

The synthesis of Methyl Salicylate from salicylic acid ( 7 6 3 ) with methanol ( 3 ) and conc. Sulfuric acid ( 2 4 ) , is shown in Figure #1 . This reaction is extremely slow under STP, and like other esterification reactions requires significant energy to facilitate. As a condensation reaction, heat is required to remove the water molecule formed by the acid and alcohol mixture ( + ion from the acid and − ion from the alcohol), to form the ester product. Hence, energy in

the form of high heat/temperature can be used to accelerate the reaction via a reflux system. In

this system, the mixture is heated with a heating mantle, allowing for the reaction to reach its

boiling point. As the mixture is connected to a cooling condenser, the evaporated products or

reactants are condensed back into the mixture preventing any escape of vapour. This allows for

the reaction to proceed at a higher rate. Extending the time under reflux allows the reaction to go

further towards completion, liberating more water molecules and therefore producing a higher concentration/yield of the desired ester 4 . Moreover, rate is also increased using a catalyst (in this case, H 2 4 ) which in addition to high temperatures, is used to speed up the reaction by lowering the activation energy (energy required to initiate a reaction) 5 .

Figure #1: The reaction between salicylic acid and methanol to form methyl salicylate 6

The mechanism for this reaction is outlined in 5 steps as listed and shown below 7 ( Figure #2 ) 1. Cation formation: salicylic acid loses an electron to the catalyst ( + ion), breaking its

oxygen-carbon double bond and forming a carbocation.

2. Delocalized Carbocation: the carboxyl oxygen of the methanol is protonated by the

carbocation - gives the carbocation a delocalized electron, making it a better electrophile.

3. Proton Transfer: A proton from one of the hydroxyl groups is transferred to the oxygen

carboxyl, swapping the hydrogen to the proton donor.

3 (Jill Seladi-Schulman, 2020) 4 (Barnes, 2017) 5 (Oxford University Press, 2014)

6 (Lab Monk, 2020) 7 (BYJUS'S, 2021)

4