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Student Name

Laboratory Date:

Date Report Submitted:

___________________________

Student ID

Experiment Number and Title

Experiment 731: Esters

Experiment 731: Esters

Section 1: Purpose and Summary of experiment

Many molecules containing the ester functional group have pleasant, sometimes fruity, fragrances. The synthesis of an ester can be accomplished in one of several ways. In this lab, esterification occurs when an alcohol and a carboxylic acid are reacted in the presence of an acid catalyst, such as concentrated sulfuric acid.

Example of an esterification reaction:

Other synthetic pathways to esters also exist. Acid chlorides react with alcohols to yield an ester and hydrochloric acid. A small amount of pyridine or other base is usually added to the reaction mixture to neutralize the resulting acid. Acid anhydrides can also react with alcohols to produce esters.

Artificial flavors often contain esters. In this lab, isoamyl acetate (banana) and methyl salicylate (wintergreen) work best but also try others to see if you like their odors. Sometimes; however, the carboxylic acids and alcohols may not react completely, and these compounds may contaminate the reaction products such that their foul odors may mask the fragrances of the esters.

Section 2: Safety Precautions and Waste Disposal

Safety Precautions:

Wear your safety goggles.

Sulfuric acid can cause chemical burns that may seriously damage skin and/or eyes. Wear goggles and gloves and avoid contact. If contact occurs, wash with copious amounts of water. A paste made with baking soda (sodium bicarbonate) and water can also be applied to the skin to neutralize the acid.

The carboxylic acids and alcohols used in this experiment can be irritating with foul odors. Keep all reagents in the fume hood to minimize odors.

Waste Disposal:

The residual amounts of amounts of organic compounds used in this lab are safe to dispose down the drain. However, anything larger than 1 milliliter should be captured in the liquid organic waste stream.

Tip: After rinsing the sink with water, check for the pleasant odors of the esters that might remain in the sink!

Pre-Lab Questions:

1) What precautions are necessary when:

A) using sulfuric acid

B) using a warm-water bath

C) smelling the odor of esters

2) What is the purpose of sulfuric acid in today’s experiment?

3) Why should test tubes be dry in today’s reactions? (Hint: Esterification is an equilibrium reaction.)

4) Butyl alcohol (CH₃CH₂CH₂CH₂OH) reacts with acetic acid (CH₃CO₂H) to form an ester.

A) Draw a balanced equation for this reaction.

B) What is the name of this ester?

Section 3: Procedure

Part 1: Synthesize the Esters

Set up a warm water bath by obtaining a 250 mL or larger beaker and filling it half-full with tap water. Set the beaker on a hot plate and heat the water to 60-65^oC.

Obtain 6 DRY (water will hinder the reaction), small test tubes. The small test tubes are the ones that contain a volume of about 10 ml. Label the test tubes 1-6.

Choose 6 esters to make from Table 1.

On the DATA SHEET (below) write down the ester that you will prepare in each test tube.

Using the quantities listed in Table 1, add the listed amounts of each carboxylic acid and each alcohol to the appropriate test tubes.

Carefully add 5 drops of concentrated sulfuric acid to each test tube.

Heat all the test tubes together in the warm water bath (60-65^oC) for 10 minutes or longer.

Be sure to monitor the temperature to maintain it within the specified range.

Using a test tube clamp, remove the test tubes from the warm water bath and place them in a test tube rack to cool.

When cooled to room temperature, use a plastic dropper to add 2 mL (about 40 drops) or more of laboratory water to each test tube and mix well. Two layers will form (like oil and water). The ester will be in the top layer.

Use a pipet to remove a few drops of the top layer. Transfer the drops to a clean watch glass and carefully waft (use your hand to fan the odors towards your nose) to smell the ester.

Record a description of the actual odor on the DATA SHEET (below). If the odor does not match the odor listed, describe the odor as best you can. (It is possible that the ester may be contaminated by the odors of the carboxylic acid or alcohol!)

Table 1 Synthesis and Characteristics of Esters (choose 6) ester
Carboxylic Acid	Alcohol	Ester	Odor
Salicylic acid (0.1 g)	Methyl alcohol (10 drops)	Methyl salicylate	wintergreen
Acetic acid (10 drops)	Isoamyl alcohol (3-methyl-1-butanol) (20 drops)	Isoamyl acetate	banana
Acetic acid (8 drops)	Octyl alcohol (20 drops)	Octyl acetate	orange
Acetic acid (10 drops)	Propyl alcohol (10 drops)	Propyl acetate	pear
Acetic acid (10 drops)	Ethyl alcohol (10 drops)	Ethyl acetate	nail polish remover
Acetic acid (10 drops)	Benzyl alcohol (10 drops)	Benzyl acetate	jasmine
Propanoic acid (10 drops)	2-methyl-1-propanol (older name is isobutyl alcohol) (10 drops)	Isobutyl propionate	fruity rum smell

Part 2: Identify an Unknown Ester

Obtain an unknown ester. If it is labeled with a number or code, record the number or code on the DATA SHEET (below).

Use a pipet to remove a few drops of the unknown ester. Transfer the drops to a clean watch glass and carefully waft (use your hand to fan the odors towards your nose) to smell the ester.

Record a description of the actual odor on the DATA SHEET (below).

Use the odors listed in Table 1 to identify the unknown ester. Write the name of the ester on the DATA SHEET (below).

Return the unused portion of the unknown ester.

Part 3: Clean up (and re-analyze the esters)

Empty each test tube one-at-a-time in the sink and rinse with plenty of water. Waft the odors from the sink for a second chance to analyze the odor of each ester.

Data Sheet: Lab group Member(s) ___________________________________________
Test Tube Number	Name of Ester	Odor listed in Table 1	Actual Odor
1
2
3
4
5
6
Unknown Ester (List number or code here)

Post-Lab Questions:

1) A student reacts benzyl alcohol with salicylic acid.

A) What is the name of the ester product?

B) Draw the structure of the ester product.

2) Another student made isopropyl benzoate (structure shown here).

A) Draw the structures of the carboxylic acid and alcohol used to synthesize isopropyl benzoate.

B) Write the names of the carboxylic acid and alcohol underneath your drawings.

3) Draw balanced equations for the reactions that took place in each of your 6 test tubes from today’s lab.