preparation of isopentyl acetate :: essays research papers

INTRODUCTION Isopentyl acetate, "banana oil", is a naturally occurring compound that possesses a distinctive odor. It is found in bananas, as well as many other organisms. This experiment attempts to produce isopentyl acetate by heating under reflux, which involves heating the mixture in a flask with a condenser placed vertically in the neck since any escaping vapours condense and run back into the flask, by combining isopentyl alcohol with acetic acid and an acid catalyst. The product was isolated using a combination of techniques -- acid-base extraction, drying, and distillation -- and was characterized by its boiling temperature and its refractive index. Esterification is a condensation reaction where two molecules are joined together to form a larger molecule with the simultaneous loss of water. This ester in this experiment is isopentyl acetate formed from acetic acid and isopentyl alcohol. The reaction is catalyzed by hydrochloric acid, a Fisher esterification process, (McMurry, p780-781) but the catalyst affects only the rate of reaction, and not the extent of reaction. The desired product accumulates only if the equilibrium constant is favorable. As it happens, the equilibrium constant for this reaction is rather small (~4) (comparing bond energies in the reactants and products will tip you off as to why the equilibrium constant is so small). Therefore, simply mixing equal amounts of the starting materials will convert only about 67% of the starting material into product. To drive the equilibrium forward Le Chatelier's principle is used, in this case there are two ways to adjust reagent concentrations to force isopentyl alcohol to become isopentyl acetate. One way is to remove product as it forms. The other way is to use a large excess of acetic acid. This experiment is based on the latter approach, but it raises two issues. We can use excess acetic acid only if acetic acid is cheap, and if unreacted acetic acid can be removed easily from the product mixture (Organic chemistry lab. Manual, p32). In this lab had to use acid- base extraction process. Since isopentyl acetate is soluble in diethyl ether, but acetic acid is soluble in both solvents. Therefore, a simple extraction procedure would remove only some of the acetic acid from isopentyl acetate, but it would not completely separate the two compounds. An acid-base extraction improves on the simple two-solvent extraction scheme by using acid-base reactions to change acetic acid into another compound with different solubility behavior. Hence, we convert acetic acid into, sodium acetate, and obtain a compound that is soluble in water, but not in diethyl ether.