Hydrolysis of Oil of Wintergreen

Hydrolysis of Oil of Wintergreen - Hydrolysis of Oil of...

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Hydrolysis of Oil of Wintergreen 1 Authors: D. Afzal, A. E. Moody and J. M. McCormick* Last Update: March 15, 2006 Introduction Oil of wintergreen is an essential oil obtained from wintergreen leaves or sweet birch bark. The primary constituent of oil of wintergreen is methyl salicylate (its structure is shown in Fig. 1), which has a fragrant smell and is responsible for the wintergreen flavor in foods and beverages. Because of the high demand in the food industry for methyl salicylate most of it is made synthetically, which is both cheaper and easier than extracting it from the natural sources. Figure 1. Structure of methyl salicylate. Methyl salicylate undergoes hydrolysis in the presence of H+ or OH-. An hydrolysis reaction is where something is broken apart by water ( hydro - = water, - lysis = splitting). In the experimental procedure that you will follow, the methyl salicylate will be first reacted with a concentrated NaOH solution (the source of OH - ) to give compound Y , which we will not isolate (compound Y is an example of a synthetic intermediate ). A sulfuric acid (H 2 SO 4 ) solution will be added as a H + source to convert compound Y into compound X , which we will collect and characterize. The reaction’s two steps are shown in Scheme 1.
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Scheme 1. Unbalanced chemical equations for the hydrolysis of methyl salicylate to give Compound X . When these two steps are added together, we get the overall chemical equation for the hydrolysis of methyl salicylate shown in Scheme 2 ( More Info ). It is important for you realize that none of the reactions in either scheme are complete! We are missing products, and we do not know the identity of either compound Y or compound X . Scheme 2. Overall unbalanced chemical equation for the hydrolysis of methyl salicylate. You will hydrolyze oil of wintergreen in Week 1 of this exercise and then in Week 2 you will use chemical, physical and spectroscopic means to identify compound X . First you will demonstrate that compound X is an acid, and then you will titrate a known amount of X with a standardized base to determine its molar mass. You will also compare the melting point of impure and recrystallized X . A substance's melting point is one of the older methods for assessing purity. Pure substances have unique and distinct melting points, while impure substances (mixtures) usually do not have a unique melting point; rather they melt over a range of temperatures. Thus, a melting point determination is a quick and easy way to determine the purity of a substance, if its melting point is neither too high (as is the case with many ionic compounds) nor too low (as for most gases).
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In this exercise and in the previous one , we have seen how compounds are characterized by their chemical and physical properties, and until the 1960’s these were the primary ways to characterize new compounds. Starting in the 1960’s new methods, based on the interaction of matter with electromagnetic radiation, revolutionized
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Hydrolysis of Oil of Wintergreen - Hydrolysis of Oil of...

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