Esterification
At the end of this lab, students should know...
What is the general structure of an ester?
An ester consists of a carbonyl with an alkyl or aryl group on one side and an oxygen bound to another alkyl or aryl group on the other side.
What effect does alkyl chain length and different groups have on a simple ester?
Simple esters, or those with short alkyl chains, have smells and flavors of fruits and flowers. The structure of the alkyl chain influences the sm...
Source: Lara Al Hariri at the University of Massachusetts Amherst, MA, USA
- Preparation of the Laboratory
Here, we show the laboratory preparation for 10 students working in pairs, with some excess. Please adjust quantities as needed.
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First, put on a lab coat, safety glasses, and nitrile gloves. Note: Some of the reagents are volatile or have unpleasant odors, so you will handle them in a fume hood.
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Ensure that you have glass and organic waste containers and that each sink has paper towels.
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Follow the table to designate codes for the carboxylic acids and alcohols used in this lab. The carboxylic acids are coded A through C, and the alcohols are coded D through I. The students will use a 3:1 molar ratio of alcohol to carboxylic acid in the reaction.
Code Compound MW
(g/mol)Density at RT (g/cm3) Moles per vial Grams per vial cm3 per vial Number of vials A Acetic acid 60.05 1.049 0.07 4.2035 4.0 3 B Butyric acid 88.11 0.953 0.07 6.1677 6.5 3 C Anthranilic acid 137.14 - 0.07 9.5998 - 1 D 1-Propanol 60.10 0.803 0.21 12.6210 15.7 1 E Isoamyl alcohol 88.15 0.810 0.21 18.512 22.8 1 F 1-Butanol 74.12 0.810 0.21 15.565 19.2 1 G Ethanol 46.07 0.789 0.21 9.6747 12.3 1 H Methanol 32.04 0.791 0.21 6.7284 8.5 2 I 1-Octanol 130.23 0.830 0.21 27.348 32.9 1 -
Prepare the three carboxylic acids: acetic acid, butyric acid, and anthranilic acid. Each group will need 0.07 moles of their assigned carboxylic acid in a vial.
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Tare a 10-mL glass vial on an analytical balance in a fume hood. Use a Pasteur pipette to measure 4.2035 g of acetic acid, which will be about 4 mL. Cap the vial and label it ‘A’. Prepare two more labeled vials of acetic acid in the same way.
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Weigh 6.1677 g of butyric acid, which will be about 6.5 mL, in a tared 10-mL vial. Cap the vial and label it ‘B’. Prepare two more vials of butyric acid in the same way.
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Use a small spatula to weigh 9.5998 g of solid anthranilic acid in a tared 10-mL vial. Cap the vial and label it ‘C’. You should now have a total of seven vials of carboxylic acid.
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Prepare the 7 alcohols. Each group will need 0.21 moles of their assigned alcohol in a vial. Use the table as a guide to prepare and label one vial of each alcohol. Prepare and label two vials of methanol.
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You should now have a total of seven vials of alcohol. Keep the reagent vials in the instructor's hood for now and put away the stock bottles of the carboxylic acids and alcohols.
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Assign each student group one of these seven combinations of reagents.
Ester code Carboxylic acid Alcohol Ester product Scent AD Acetic acid 1-Propanol Propyl acetate Pear AE Acetic acid Isoamyl alcohol Isoamyl acetate Banana AI Acetic acid 1-Octanol Octyl acetate Orange BF Butyric acid 1-Butanol Butyl butyrate Pineapple BG Butyric acid Ethanol Ethyl butyrate Strawberry BH Butyric acid Methanol Methyl butyrate Apple CH Anthranilic acid Methanol Methyl anthranilate Grape -
Prepare or obtain seven vials of the fruit scents and label them with the fruit names as references.
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Set out the following glassware and equipment at each student lab station (we suggest that students work in pairs):
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Put bottles of saturated sodium bicarbonate and 3 M sulfuric acid in a dedicated fume hood, along with a roll of plastic paraffin film and scissors.
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Set out filter paper and Pasteur pipettes in a central area so that every student group can easily access them.
1Lab stand 23-prong clamps 1Stir plate 1Lab jack 1Heating mantle 1Temperature controller 2Pieces of tubing (for condenser) 1Joint clip 1Tube of vacuum grease 1Box of laboratory wipes 110-mL graduated cylinder 1600-mL beaker 150-mL round-bottom flask and flask stand 1Standard condenser 1Small stir bar 1Glass rod 1Package of pH paper 2Pasteur pipette bulbs -
Just before the lab, fill a large insulated cooler with crushed ice. Place the cooler and an ice scoop in a central area in the lab.
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When the students arrive, show them how to safely waft vapors before giving them their assigned reagents.
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View the full transcript and gain access to JoVE Lab Manual videos
Q1: What safety equipment is required before starting an esterification lab?
Before beginning esterification work, put on a lab coat, safety glasses, and nitrile gloves. Since many reagents are volatile or have unpleasant odors, you will handle them in a fume hood. Ensure glass and organic waste containers are available, and verify that each sink has paper towels for cleanup.
Q2: How do you prepare carboxylic acid vials for an esterification experiment?
Tare a 10-mL glass vial on an analytical balance in a fume hood. Use a Pasteur pipette to measure the required mass of liquid carboxylic acid, or use a small spatula for solid compounds like anthranilic acid. Cap and label each vial with its assigned code. Prepare the specified number of vials for each carboxylic acid according to the lab protocol.
Q3: What is the molar ratio of alcohol to carboxylic acid in esterification reactions?
Students use a 3:1 molar ratio of alcohol to carboxylic acid in the esterification reaction. This means each group needs 0.21 moles of their assigned alcohol and 0.07 moles of their assigned carboxylic acid. The specific masses and volumes for each reagent are provided in the preparation table based on molecular weight and density.
Q4: How many different ester products can be made from the available reagents?
Seven different ester products can be synthesized by combining three carboxylic acids with various alcohols. These include propyl acetate, isoamyl acetate, octyl acetate, butyl butyrate, ethyl butyrate, methyl butyrate, and methyl anthranilate. Each ester has a characteristic fruit scent, ranging from pear to grape, making the products easily identifiable.
Q5: What glassware setup is needed at each student lab station for esterification?
Each station requires a lab stand, heating mantle with temperature controller, stir plate, 50-mL round-bottom flask, standard condenser, lab jack, and supporting equipment like clamps and tubing. Additionally, students need graduated cylinders, beakers, glass rods, Pasteur pipettes, and pH paper. A tube of vacuum grease and laboratory wipes should also be available for assembly and maintenance.
Q6: Where should volatile reagents and ice be stored during an esterification lab?
Bottles of saturated sodium bicarbonate and sulfuric acid should be placed in a dedicated fume hood along with plastic paraffin film and scissors. A large insulated cooler filled with crushed ice should be set up in a central area of the lab with an ice scoop for easy access by all student groups during the experiment.
Q7: How should students be prepared before receiving their assigned esterification reagents?
Before students arrive, instructors should demonstrate how to safely waft vapors to smell chemical compounds without direct inhalation. This technique is essential because many esterification reagents are volatile or have strong odors. Once students understand proper vapor-wafting technique, they can safely receive their assigned carboxylic acid and alcohol vials for the reaction.