Methyl Salicylate (Oil of Wintergreen) Lab Procedure PDF

# Methyl Salicylate (Oil of Wintergreen) ## Synthesis of an ester - Heating under reflux - Extraction - Vacuum distillation In this experiment, you will prepare a familiar-smelling organic ester, oil of wintergreen. Methyl salicylate was first isolated in 1843 by extraction from the wintergreen pl...

# Methyl Salicylate (Oil of Wintergreen) ## Synthesis of an ester - Heating under reflux - Extraction - Vacuum distillation In this experiment, you will prepare a familiar-smelling organic ester, oil of wintergreen. Methyl salicylate was first isolated in 1843 by extraction from the wintergreen plant (Gaultheria). It was soon found that this compound had analgesic and antipyretic character almost identical to that of salicylic acid (see the essay "Aspirin") when taken internally. This medicinal character probably derives from the ease with which methyl salicylate is hydrolyzed to salicylic acid under the alkaline conditions found in the intestinal tract. Salicylic acid is known to have analgesic and antipyretic properties. Methyl salicylate can be taken internally or absorbed through the skin; thus, it finds much use in liniment preparations. Applied to the skin, it produces a mild tingling or soothing sensation, which probably comes from the action of its phenolic hydroxyl group. This ester also has a pleasant odor, and it is used to a small extent as a flavoring principle. - C-O-H - OH - C-O-CH3 - OH - H+ - + CH3OH - + H2O Methyl salicylate will be prepared from salicylic acid, which is esterified at the carboxyl group with methanol. You should recall from your organic chemistry lecture course that esterification is an acid-catalyzed equilibrium reaction. The equilibrium does not lie far enough to the right to favor the formation of the ester in high yield. More product can be formed by increasing the concentrations of one of the reactants. In this experiment, a large excess of methanol will shift the equilibrium to favor a more complete formation of the ester. This experiment also illustrates the use of distillation under reduced pressure for purifying high-boiling liquids. Distillation of high-boiling liquids at atmospheric pressure is often unsatisfactory. At the high temperatures required, the material being distilled (the ester, in this case) may partially or even completely decompose, causing loss of product and contamination of the distillate. When the total pressure inside the distillation apparatus is reduced, however, the boiling point of the substance is lowered. In this way, the substance can be distilled without being decomposed. ## Special Instructions - The experiment must be started at the beginning of the laboratory period because a long reflux time is needed to esterify salicylic acid and obtain a respectable yield. - Perform a supplementary experiment during the reaction period or complete work that is pending from previous experiments. Enough time should remain at the end of the period to perform the extractions, place the product over the drying agent, assemble the apparatus, and perform the vacuum distillation. ## Caution - Handle the concentrated sulfuric acid carefully; it can cause severe burns. - When a distillation is conducted under reduced pressure, it is important to guard against the dangers of an implosion. Inspect the glassware for flaws and cracks and replace any that is defective. - Wear your safety glasses. ## Suggested Waste Disposal - The aqueous extracts from this experiment should be placed in the container designated for this purpose. Place any remaining methylene chloride in the container designated for halogenated waste. ## Procedure - Assemble equipment for reflux using a 5-mL conical vial and a water-cooled condenser (Technique 7, Figure 7.6A). Top the apparatus with a calcium chloride drying tube. - Use a hot plate with an aluminum block. Place 0.65 g of salicylic acid, 2.0 mL of methanol (d = 0.792 g/mL), and a spin vane in the vial. Stir the mixture until the salicylic acid dissolves. - Carefully add 0.75 mL of concentrated sulfuric acid, in small portions, to the mixture in the vial while stirring. A white precipitate ## Isopentyl Acetate (Banana Oil) - Esterification - Heating under reflux - Extraction - Simple distillation - Microscale boiling point In this experiment you will prepare an ester, isopentyl acetate. This ester is often referred to as banana oil because it has the familiar odor of this fruit. - CH3 - H - CH3-C-OH + CH3-CH-CH2CH2-OH - Acetic acid - (excess) - Isopentyl alcohol - CH3 - CH3-C-O-CH2CH2-CH-CH3 + H2O - Isopentyl acetate Isopentyl acetate is prepared by the direct esterification of acetic acid with isopentyl alcohol. Because the equilibrium does not favor the formation of the ester, it must be shifted to the right, in favor of the product, by using an excess of one of the starting materials. Acetic acid is used in excess because it is less expensive than isopentyl alcohol and more easily removed from the reaction mixture. In the isolation procedure, much of the excess acetic acid and the remaining isopentyl alcohol are removed by extraction with sodium bicarbonate and water. After drying with anhydrous sodium sulfate, the ester is purified by distillation. The purity of the liquid product is analyzed by performing a microscale boiling point determination or infrared spectroscopy.