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Isopentyl acetate (C7H14O2) is one example of a pheromone. It is an acetate ester pheromone and is one of dozens of honey bee pheromones. It has been known since the 1960s that isopentyl acetate acts as an alarm pheromone for honey bees.
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Isopentyl acetate is a clear ester with a pleasant aroma. It is also called banana oil because of its characteristic strong, banana-like odor. Isopentyl acetate has a molecular weight of 130.2 g/mol and is a highly volatile compound. Volatility is typical of alarm pheromones. The boiling point of isopentyl acetate is 142 °C. Other physical properties of the compound are shown in table below. The compound is also known as isoamyl acetate and 3-methylbutyl acetate.
Table. Chemical and physical properties.
Isopentyl acetate can be synthesized in many different ways. The most common method is to synthesize it from isoamyl alcohol and acetic acid using acid-catalyzed Fischer esterification, for example, which is an important organic reaction. Picture 2 shows the chemical equation of the synthesis, and picture 3 illustrates the reaction mechanism.
Picture 2. Chemical reaction equation
There are six steps in the reaction.
- Steps 1, 3, 4 and 6 are acid-base reactions in which rapid proton transfer takes place.
- In steps 2 and 5, bonds between carbon and oxygen are formed and broken. The activation energies of steps 2 and 5 are much higher than those of the proton transfer steps. Acid-catalyzed esterification has the advantage of being a simple process, but the high temperature and strong acid catalyst required can make it an impossible reaction to carry out with sensitive substrates. The synthesis has an 80 % yield. Simple distillation in an oil bath at a boiling point of 142 ° C is sufficient to separate the product from the final mixture .
The –C–CO 2R stretch characteristic of an ester is visible in the isopentyl acetate IR spectrum in the 1735–1745 cm -1 range. The –C–H stretches are visible just below 3000 cm -1, and the –C–O and –CO 2 stretches appear as several peaks in the 1050–1300 cm -1 range.
Picture 4. IR spectrum of isopentyl acetate.
In addition to functioning as an alarm pheromone in honey bees, naturally occurring isopentyl acetate also acts as a pheromone and kairomone in some flies and as a pheromone, kairomone and allomone in some beetles.
Isopentyl acetate is also used as an artificial sweetener in foods and beer, for example, and as an artificial perfume to mask unpleasant odors in products such as shoe polish.