By reacting a carboxylic acid with an alcohol we synthesize an ester, in this case isoamyl acetate.
- Obtain 8.5 mL of isoamyl alcohol and 15.0 mL of acetic acid in a 100-mL round-bottomed flask.
- Add dropwise 5 mL of concentrated sulfuric acid with boiling chips and reflux for one hour.
- At the end of the reflux cool the round-bottomed flask in a cold water bath.
- Pour the contents of the flask into a beaker with 40mL of ice water.
- Pour the beaker contents into a separatory funnel and mix with occasional venting. If the two layers do not separate add 2-3 g of solid sodium chloride to increase the density of the aqueous layer which will separate the two layers.
- Separate the organic layer and wash with 15 mL sodium bicarbonate. Keep washing with sodium bicarbonate until it is neutral or slightly basic.
- This might take 1 to 2 more washings.
- After the last washing, wash again with 15 mL of distilled water.
- Transfer the organic layer to a dry flask and add 1-2 g of anhydrous magnesium sulfate. Stopper the flask and occasionally stir.
Gravity filter the solution into a 100 mL round-bottomed flask and perform a simple distillation. Collect the portion that distills between 130oC and 145oC into a pre-weighed vial. 10) Record the refractive index, mass, and percent yield.
Data: Percent Yield: Hypothetical 8.5 mL isoamyl alcohol x .81g/mL = 6.9 g isoamyl alcohol 6.9 g x 1 mol isoamyl alcohol/88 g = .0781 mol isoamyl alcohol 1 mol isoamyl alcohol : 1 mol isoamyl acetate .0781 mol isoamyl acetate x 130 g/ 1mol = 10.1530 g isoamyl acetate Actual 12.4344 g 6.6333 g 5.8011 g Percent Yield = Actual / Hypothetical = 5.8011 g/ 10.1530 g = 57.14 % Refractive Index: Measured refractive index: 1.400 at 20oC Merck Index refractive index: 1.405 at 20oC
Discussion: The reaction that took place, carboxylic acid with an alcohol forming an ester, can be done two different ways: The one used in this lab was method A. The R group in this case is a methyl group and the R is the (CH3) 2CH(CH2)2 group.
The acid used is sulfuric acid. This method does not present as high yields as method B. The reason for this is that the reaction is reversible. To help increase yield in this method an excess of one of the primary reactants is used. In this case the acetic acid. The isoamyl alcohol is a limiting reactant and is used to calculate the percent yield.
The first step in the reaction mechanism is that the carboxylic acid is protonated. The double bonded O is reacted with the acid H+ and the double bond between the carbon and the oxygen goes to the oxygen molecule to a pair of electrons and with the acid H+ ion, an OH+ forms. In the same step the O from the OH group on the alcohol attaches to the C atom of the carboxylic acid giving the carbon atom 4 bonds after it lost one by giving the other oxygen an electron pair. The H+, from the newly added alcohol, is then separated with the oxygen taking the electron pair. Then the H+ attaches to the side OH group forming H2O.
This H2O is then removed, leaving one OH group, which in turn returns to its primary state by losing an H+ and forming the double bond again (giving carbon 4 bonds).
Research: The product has many uses. These uses include being a component in pear oil and banana oil, and pear flavor in mineral water, syrups, and lacquers. Isoamyl Acetate is also used in photography, bronzing, and dyeing of artificial silk.
It aids in the manufacturing of artificial silk. The product is one of many ingredients used in cigarettes, and it also is used as a pheromone. Its characteristics make it a very popular compound. Its smell has been argued to be that of pear, apple, or banana, yet most popularly banana. It also has gives flavor of pear.
These characteristics make it popular to be used as a fragrance, and flavor additives. It can be found naturally in pears, apples, and bananas and so is very popular in artificial flavoring. There have been complaints that this compound can cause fatigue, headache, and mucous membrane irritation. In cigarettes it is only one of six hundred different ingredients used. Primarily it might seem harmless, yet among this many different chemicals can react readily especially when lit up. One of the most interesting uses of isoamyl acetate can be its use as a pheromone.
A pheromone is a chemical that an organism produces to elicit a specific response to usually others of the same species. Isoamyl acetate is a pheromone to the honeybee. The chemical is evoked when a honeybee attacks or stings and intruder. This chemical signals the rest of the hive to come and join in the attack.
It is used as a form of communication. This form of communication can also have a negative effect. In this case, the chemical is present in pears and apples, which come to be a problem when farmers need bees to pollinate their trees. The bees do not pollinate the trees as well as some of the other type of trees, which can cause smaller crops and bees that are more likely to strike those who are in the area, because of their readiness to attack. Now in a recent article published by Good Fruit Grower, scientists have found a way to increase the pollination count in fruit trees.
The scientists extracted a mixture of five chemicals from the mandibular glands in the queen bee. This mixture has been found to act as a pheromone to the honeybees also. By synthetically making these chemicals and spraying them on the trees, there was a forty- percent increase found in the amount of pollinated pear and apple trees. The pheromone works over the isoamyl acetate and rouses the bees to pollinate the trees. This has also been used to help increase pollination yields in those fruit trees other than apples and pears and is also successful.
Conclusion: When the experiment was done there was an expected low yield because of the method we used to form the ester, yet I feel that my product was quite high. The refractive index was only off by .0005, which shows the product is pure. There was a lot of transferring and separating of the product, which helps loss along the way. This lab was interesting; by the way of how we distinguished the organic layer by its smell (banana).