Materials Included In Kit

Additional Materials Required

Safety Precautions

Sulfuric acid is severely corrosive to eyes, skin and other tissue. Acetic acid is corrosive to skin and tissue, is a moderate fire risk and is moderately toxic by ingestion and inhalation. Salicylic acid is moderately toxic by ingestion. Isopentyl alcohol is slightly toxic by ingestion and inhalation, a moderate fire risk and may form explosive peroxides. Methyl alcohol is a dangerous fire risk and is toxic by ingestion. Ethyl alcohol is a dangerous fire risk; addition of denaturant makes the product poisonous—it cannot be made nonpoisonous. Please review current Safety Data Sheets for additional safety, handling and disposal information. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Final solutions from the microcentrifuge tubes may be disposed of according to Flinn Scientific Suggested Disposal Method #24a. All the ester solutions may be combined and neutralized together to save time.

Teacher Tips

• Enough materials are provided in this Super Value Kit for 5 classes of 30 students each, working in pairs (75 total student groups).
• Place only about 50 mL of hot water into the water bath cup. This will allow the water level of the bath to be low; thus, when the microcentrifuge tubes are placed into the cup, they will be deep enough to be supported by the cup itself and not fall out.
• For a class of 15 groups (30 students), heat 1 L of water to about 80 °C. Heat the water before the class begins the experiment and keep it ready for immediate use. This will help move the experiment along and will certainly save time.
• When adding the methyl alcohol to the salicylic acid, about 15 drops of the alcohol will be required to dis­solve the solid. The solid will reappear when the sulfuric acid is added.
• Cut the polystyrene cup in half so the microcentrifuge tubes stand up more easily.
• Remember the crude “ester” is still quite acidic due to the concentrated sulfuric acid. Caution should be taken when examining the ester.
• The microcentrifuge tubes may be labeled with tape or wax pencil.

Sample Data

Answers to Questions

1. Using the information in the Background section, determine the name of the ester produced in each microcentrifuge tube, and enter the name in the data table.

   See “Name of Ester” column in data table.

2. Compare the odors of the three esters produced to the odors of the starting materials. How are they different?

   Most of the esters have pleasant smells. The alcohols have medicinal smells while the acids are sharp, biting and unpleasant. The odors of the ester products are described in the sample data table.

3. Were the esters easily identified as a specific fragrance (e.g., apple, banana)? In the case where a specific fragrance was detected, how does the odor compare to the natural fragrance?

   There were some very distinct odors that were easily identified. The isopentyl acetate (banana) and methyl salicylate (wintergreen) stand out. The odors of these compounds, while very distinct, were stronger and less subtle than the natural fragrances.

Introduction

The purpose of this kit is to prepare and identify several types of esters.

Concepts

• Esters
• Dehydration synthesis

Background

Many esters have the characteristic property of a pleasant odor. As such, they are used as artificial flavors and perfumes. The flavors from products such as peppermint gum or banana-flavored ice cream most likely originate from organic compounds known as esters. Not all esters have odors, but most volatile esters do. An example of an odorless ester would be vegetable oil.

Esters are formed by the process of dehydration synthesis using an alcohol with an acid. The name of the ester is formed from the alcohol and acid used in their making. For example, when making the ester methyl salicylate (oil of wintergreen), the alcohol and acid used would be methyl alcohol and salicylic acid, respectively. This ester has a pleasant “peppermint” odor. Another example would be the ester butyl formate which is produced when reacting butyl alcohol with formic acid.

When an organic acid (RCOOH) reacts with an alcohol (R*OH), water is produced and an ester is formed. This process is an example of dehydration synthesis. Unfortunately, the reverse reaction also occurs, so keeping a large excess of alcohol and minimizing the amount of water helps increase the yield of esters.

For example: Some artificial flavors are formed by the mixing of esters in an attempt to duplicate the flavor or odor of a natural substance. For example, the odor of raspberries originates from a mixture of isobutyl formate and isobutyl acetate. In this experiment three different esters having the characteristic odors of banana, peppermint and fruit essences will be made. The product formed will be quite crude; however, the three different odors will be detected, and the basic method of producing esters will be performed.

Materials

Safety Precautions

Sulfuric acid is severely corrosive to eyes, skin and other tissue. Acetic acid is corrosive to skin and tissue, is a moderate fire risk and is moderately toxic by in gestion and inhalation. Salicylic acid is moderately toxic by ingestion. Isopentyl alcohol is slightly toxic by ingestion and inhalation and a moderate fire risk. Methyl alcohol is a dangerous fire risk and is toxic by ingestion. Ethyl alcohol is a dangerous fire risk; addition of denaturant makes the product poisonous—it cannot be made nonpoisonous. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory.

Procedure

1. Obtain three microcentrifuge tubes. Make sure each microcentrifuge tube is clean and dry. Label the microcentrifuge tubes I, E and M.
2. Using a clean, thin-stem pipet, place 10 drops of isopentyl alcohol into microcentrifuge tube “I.”
3. Using a clean, thin-stem pipet, place 10 drops of glacial acetic acid into microcentrifuge tube “I” containing the isopentyl alcohol.
4. Add one drop of concentrated sulfuric acid into microcentrifuge tube “I.”
5. Close the microcentrifuge tube top and set aside.
6. Using a clean, thin-stem pipet, place 10 drops of ethyl alcohol in the microcentrifuge tube labeled “E.”
7. Using a clean, thin-stem pipet, add 10 drops of glacial acetic acid to microcentrifuge tube “E.” Note: You may use the same pipet used to add glacial acetic acid to microcentrifuge tube “I” if quantities are limited.
8. Repeat steps 4 and 5 for microcentrifuge tube “E.”
9. Using a balance, measure 0.15 g of salicylic acid and add to microcentrifuge tube “M.”
10. Using a clean, thin-stem pipet, add 12 drops of methyl alcohol to dissolve the salicylic acid.
11. Cautiously add 3 drops of concentrated sulfuric acid to microcentrifuge tube “M.”
12. Close the microcentrifuge tube “M” top and set aside.
13. Place all three microcentrifuge tubes in a polystyrene cup containing hot water. The water used should be between 70 ˚C and 80 ˚C (see Figure 1). Use caution as the water is hot.
    {12173_Procedure_Figure_1}
14. After ten minutes, open the microcentrifuge tubes and carefully waft the odor of each ester separately (see Figure 2). Before wafting the odor of microcentrifuge tube “M,” add 3 drops of water to the ester. Note: If the odor of the ester is not easily distinguished, pour solution into a watch glass before wafting.
    {12173_Procedure_Figure_2}
15. In the data table, record the names of the alcohol and acid used in each microcentrifuge tube as well as the odor of the ester produced.
16. See instructor for disposal procedures.

Student Worksheet PDF

12173_Student1.pdf