Thin Layer Chromatography

Comparing the relative polarity of Menthol, Methyl salicylate, Eugenol and Vanillin  against five solvents using Thin Layer Chromatography

Abstract

Thin Layer Chromatography (TLC) is a separation technique that includes a stationary (TLC plate) and a moving (solvent and compound) phase. The purpose of this practical was to use TLC to determine the rate of flow of four compounds in the presence of five solvents with varying polarity. The five solvents being used were Hexane, Ethyl Acetate, 90-Hexane 10-Ethylacetate, 80-Hexane 20-Ethylacetate, and 70-Hexane 30-Ethylacetate. The four compounds being used were Menthol, Methyl salicylate, Eugenol and Vanillin. During the practical it was seen that all the compounds except Menthol seemed to have appeared as dots under the Ultra Violet(UV) light or after the TLC sheet was placed in Iodine, the compounds had either moved up or stayed at their initial point after they were introduced to the solvents.

Results

Table 1: A list of the compounds and solvents used in the TLC experiment.

• Hexane

[pic 1]

Rf(M) = 0mm/37mm=0

Rf(MS) = 6mm/37mm=0.16

Rf(EU) = 0mm/37mm=0

Rf(V) = 0mm/37mm=0

The Rf values indicate that the polarity of Menthol, Eugenol and Vanillin are all greater than Hexane (which is a non-polar molecule) because the solvent is unable to pull the compounds that stick to the surface of the silica. It can be seen in the drawing that Eugenol and Vanillin moved up slightly, but Methyl Salicylate on the other hand is pulled up to a greater distance by Hexane, this may be due to the fact that Methyl Salicylate has a lower polarity compared to the compounds present on the TLC plate and it is also has a lower polarity compared to Hexane.

• 90-Hexane 10-Ethylacetate

[pic 2]

Rf(M) = 0mm/40mm=0

Rf(MS) = 28mm/40mm=0.7

Rf(EU) = 21mm/40mm=0.53

Rf(V) = 8mm/40mm=0.2

The Rf  values indicate that the polarity of Menthol is greater than the polarity of 90-Hexane 10-Ethylacetate (which is non-polar due to the fact that it contains large amounts of Hexane). In this case Methyl Salicylate is the least polar compound due to the fact that it has the highest Rf  value, whereas Menthol has the highest polarity because it has the lowest Rf  value. The fact that 90-Hexane 10-Ethylacetate was able to pull Methyl Salicylate, Vanillin, and Eugenol up means that all these compounds have a low polarity compared to 90-Hexane 10-Ethylacetate.