Synthesis of Salicylic Acid from Oil of Wintergreen

Our fourth experiment of the semester is a gratifying one on several levels. First, it illustrates how chemists can transform one naturally occurring compound (oil of wintergreen) into another (salicylic acid, found in willow bark). Second, it shows how a minor modification in molecular structure, changing O-CH3 into O-H, can transform a sticky, gooey, colorless liquid noteworthy for its characteristic mint-fresh odor into a mass of needle-shaped white crystals that have no odor at all. What a huge difference an extra hydrogen bond between molecules can make!

The experiment utilizes several standard practices of the synthetic laboratory. “Reflux” is used to warm materials at a constant temperature in order to induce a chemical reaction. Acid-base chemistry is used to control the ionization states and solubility of molecules. Vacuum filtration is used to separate precipitates from unwanted liquids, and recrystallization is used to further purify the precipitated material.

Time required: 2 laboratory sessions 

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