Extended Essays 2021

4. pi bond formation & water molecule liberation: a pi bond (from the carbon-oxygen double

bond) is formed as the hydroxy group’s alcohol oxygen atom donates a pair of electrons to

the carbon atom, removing the water molecule from the alcohol-acid mixture.

5. Esther Formation: Methyl salicylate is formed as the hydrogen attached to the oxygen in the

pi bond is swapped with a pair of electrons from the anion catalyst.

Figure #2: The Mechanism of the esterification of salicylic acid to form methyl salicylate 8

Credited reports thus far have shown that the concentration of methyl salicylate can be

determined through a multitude of methods, including Nuclear Magnetic Resonance Spectroscopy, TLC 9 , Ultraviolet Spectrophotometry 10 and HPLC methods 11 . The most recent

method was published by the Journal of Applied Pharmaceutical Science (Vol.4), where the

concentration of methyl salicylate in bulk or semi-solid formulations was tested through

colorimetric quantification. Prior to this report, there has not been an established method of

colorimetry, as varying concentrations of methyl salicylate (being colourless) , don’t produce

different absorbance values in the visible spectrum.

To solve this, the report used a ferric chloride solution ( 3 ) , that when reacted with phenols (organic compounds with a hydroxyl attached to the carbon atom of an aromatic ring), produce

a purple-coloured solution. Hence by application of Beers law, it was found that the concentration

of methyl salicylate is directly proportional to the intensity of the purple colour in the final solution and therefore the recorded absorbance at 515nm 12 . Once graphed, the calibration curve can determine the concentration of the unknown product and therefore the absorbance (Au) measured by the UV spectrophotometer 13 .

8 (Lab Monk, 2020) 9 (Springs, n.d.) 10 (Dorwal, 2012) 11 (Technologies, 2018)

12 (Sajin Kattuvilakam Abbas, 2014) 13 (Sajin Kattuvilakam Abbas, 2014)

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