Synthesis of Banana Oil

Synthesis of Banana Oil - Laboratory D: The Synthesis of...

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Laboratory D: The Synthesis of Banana Oil Laboratory Techniques: Refluxing a reaction p. 203-204 Performing an extraction or washing p. 128-140 Drying agents p. 80-83 Organic Chemistry Concepts: Esterification of Carboxylic acids FF p. 612-614 Jones p. 986-996 Carey p. 635-637 Equilibrium Reactions Jones p. 351-367 In the first experiment, you used acetic anhydride to prepare the corresponding acetate ester from salicylic acid. In this lab, you will use a Fischer esterification to prepare isopentyl acetate. Many esters have pleasant, fruity flavors. Isopentyl acetate is no exception: it is often known as banana oil because it gives bananas part of their characteristic taste, and it is also used to prepare artificial coffee, butterscotch, and honey flavorings. This is in stark contrast to acetic acid, which is the smelly component of vinegar. The Fischer esterification is an acid catalyzed equilibrium reaction between a carboxylic acid and an alcohol to give the corresponding ester and water. O OH OH O O + +H 2 O We will be using sulfuric acid to catalyze the reaction. While this is a very simple reaction, the limitation of the reaction is that it is an equilibrium reaction. The equilibrium constant is approximately 4.2, which means that starting with equimolar concentrations of each reactant, the reaction only goes about 2/3 of the way to completion. Not only would this give us a low yield, but it would leave us with the difficult job of separating a mixture of unreacted acetic acid, isopentyl alcohol and isopentyl acetate. In order to purify this reaction mixture we will need to learn another purification technique, extraction . In this procedure, water and an organic solvent are combined in a separatory funnel . Because they are not soluble in each other, two layers are formed, and the compounds in solution move to the layer in which they are most soluble. In this case when water is added to the reaction mixture, the isopentyl alcohol and isopentyl acetate will form an organic layer. The concentrated sulfuric acid that was used as the catalyst will partition to the aqueous layer. The acetic acid is soluble in both water and organic compounds and will partition between the two layers. In order to remove all of the acetic acid, we can take advantage of the fact it is a carboxylic acid. Carboxylic acids typically have pKa values near 5, and can be easily
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deprotonated. Therefore, we will wash the organic layer with sodium bicarbonate. The reaction with sodium bicarbonate will produce sodium acetate. Since it is now a salt, sodium acetate has very little solubility in the organic layer and in this way we can move all of the acetic acid (in the form of sodium acetate) to the aqueous layer. Be very careful with the sodium bicarbonate washes. The deprotonation reaction that is occurring generates carbon dioxide, making it incredibly important to vent your separatory funnel frequently.
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This note was uploaded on 03/24/2009 for the course CHEMISTRY 030.225 taught by Professor Janegreco during the Spring '09 term at Johns Hopkins.

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Synthesis of Banana Oil - Laboratory D: The Synthesis of...

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