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Making Scents of Esters

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Making Scents of Esters Lesson Plan Making Scents of Esters Lesson Objectives: 1. The student will be able to distinguish between alcohol, carboxylic acid, and ester compounds by identifying the functional groups characteristic to each. 2. The student will be able to describe the process of esterification. 3. The student will be able to name ester compounds. 4. The student will be able to describe the applications of organic chemistry to the food industry. QCC Objectives: Grade: 9-12 Science Chemistry 4 Topic: Inquiry, Process and Problem Solving Standard: Gives examples of industrial processes that have been derived from scientific research and describe the impact on society. 17 Topic: Organic Chemistry Standard: Uses the structure of methane as a model structure to draw configurations of, and name, representative classes of organic compounds. Discusses the solubility properties of such compounds. 17.1 Describes the applications of organic chemistry to modern industry, such as the pharmaceuticals and plastics industries. Total Duration: Roughly 60 minutes (adaptable to class schedule) Materials and/or Equipment Needed: Per class: food flavorings small zipper-type plastic bag or 35-mm film canister for each flavoring cotton ball for each flavoring (optional) food coloring 2/3 cup sweetened condensed milk 4 ½ cups confectioner’s sugar real vanilla extract imitation vanilla flavor unsalted saltine crackers large mixing bowl wooden spoon or hand mixer measuring cups measuring spoons serving plates labels markers Per group: 4 small test tubes 400-mL beaker 4 125-mL Erlenmeyer flasks hot plate test tube holder goggles aprons 100 mL concentrated sulfuric acid 4 alcohol/carboxylic pairs (isoamyl alcohol/acetic acid, octyl alcohol/acetic acid, methyl alcohol/salicylic acid, propyl alcohol/acetic acid) Opening Moments of Class: The teacher introduces students to a variety of organic compounds, including esters, by asking them to smell and describe different food flavorings using the wafting procedure. Getting Ready: Prepare a set of bags or canisters for each group or a set for the class to share. Label the bags or canisters with a number or letter code. Place a small amount of each flavor (5-10 drops) on a cotton ball and place it in the bag or canister, keeping a key that indicates where each flavor is located. If the coloring of the flavoring would give the answer to the students, you may want to add a small amount of food color to the cotton ball to hide the natural color of the flavoring. Once the cotton balls have been placed in the plastic bags or canisters, keep them closed to minimize students’ pre- exposure to the odors. Procedures: 1. The teacher reviews with students the definitions of organic compounds and functional groups. • Organic compounds are often simplified to include those compounds that contain the element carbon. For example, aspirin, C9H8O4, is an organic compound. Organic compounds do contain carbon, and most organic compounds also contain hydrogen. Those compounds that consist solely of carbon and hydrogen are called hydrocarbons. Butane, C4H10, is an example of a hydrocarbon. Other organic compounds may contain oxygen, nitrogen, sulfur, phosphorus, or one of the halogens. These groups of atoms containing elements other than carbon and hydrogen constitute functional groups. Each functional group is important because it is this group of elements that provides the compound as a whole with unique chemical properties. Furthermore, organic compounds are commonly classified by the functional groups they contain. 2. The teacher reviews with students the functional groups characteristic to alcohols, carboxylic acids, and esters. • Alcohol Æ -OH Carboxylic Acid Æ -COOH Ester Æ -COO 3. The teacher describes to students the properties of esters and the process of esterification (see introduction to attached laboratory handout). 4. The teacher demonstrates to students the naming of ester compounds. • Step 1: When “alcohol” is included in the name of the alcohol, drop it. Step 2: Remove from the name of the carboxylic acid “ic acid,” and add “ate.” Step 3: Combine the remaining names, beginning with the alcohol Ex. ethyl alcohol + acetic acid Æ ethyl acetate 5. The teacher describes in detail to students the laboratory exercise to be performed, stressing the safety precautions associated with the experiment. • Concentrated sulfuric acid (18M H2SO4) is a very dangerous chemical, which can cause severe chemical burns when in contact with skin. In addition, unknown chemicals should never be held directly under the nose when smelling; instead, the wafting procedure should be used. Carefully smell by waving a hand across the mouth of the container, pushing the vapors toward the nose. 6. The students perform the “Making Scents of Esters” laboratory experiment (see the attached laboratory handout). Closing Moments of Class: The teacher presents students with food samples made with real vanilla extract and imitation vanilla flavoring. Students are asked to distinguish between the two samples, citing the noted differences. Getting Ready: Measure 2/3 cup sweetened condensed milk into a mixing bowl. Gradually add 4 ½ cups confectioner’s sugar and mix. The mixture should be crumbly. Separate the crumbly mixture into 2 batcches. Add ½ tsp. real vanilla extract to one batch. Mix well. This is batch A. Add ½ tsp. imitation vanilla flavor to the other batch. Mix well. This is batch B. Shape the mixture into small balls about the size of marbles. Keep the two batches separate. When tasting, provide students with crackers to cleanse their palates between samples. • Real vanilla contains well over 100 chemicals, one of which is vanillin. Imitation vanilla is made from very few chemicals, often only vanillin and ethyl vanillin. Ethyl vanillin is not found in vanilla plants, and it has a taste similar to vanillin but about 5 times stronger. Many people can taste the difference between real vanilla extract and imitation vanilla flavoring. This is because they notice the taste of the other chemicals in real vanilla or because the taste of the imitation vanilla is too strong. A question to pose to students… Why are natural flavorings (such as chocolate) sometimes preferable to artificial? *Some artificial flavorings can be produced to taste just like natural flavors (ex. oil of wintergreen). Other natural flavorings (such as (chocolate) are such complex mixtures of chemicals that scientists have yet to make an artificial flavor that tastes just like the natural one (ex. chocolate is comprised of 1200 chemicals and coffee 450). Attempts have been made to replicate such complex mixtures (ex. oresh orange juice is comprised of 250 chemicals while TANG has only 5 or 6). Making Scents of Esters Introduction: An ester is an organic compound that is formed, in addition to water, when a carboxylic acid reacts with an alcohol. This process is called esterification. General Reaction: Specific Reaction: Esterification typically requires a catalyst to speed it, and for decades, concentrated sulfuric acid (18M H2SO4) has been used to do so. Sulfuric acid is a very dangerous chemical, which can cause severe chemical burns when in contact with skin, and therefore, the utmost care should be taken when working with sulfuric acid. When carboxylic acids are esterified (combined with an alcohol to form an ester), the resulting esters are liquids with fruity flavors. These synthetic esters are used in the food industry as flavorings. In many cases, the synthetic esters produced in the laboratory are nearly the same molecules that give fruits their characteristic flavors. Materials: 4 small test tubes 400-mL beaker 4 125-mL Erlenmeyer flasks hot plate test tube holder goggles apron 4 alcohol/carboxylic acids pairs concentrated sulfuric acid (18M H2SO4) Procedure: *Record all data in the attached data table. 1. Add about 200 mL water to the 400-mL beaker. Heat the water until it boils and then turn off the hot plate. 2. Add 10 drops iosamyl alcohol to a clean, dry test tube. Label the test tube “1.” 3. Add 10 drops octyl alcohol to a second clean, dry test tube. Label the test tube “2.” 4. Add 20 drops methyl alcohol to a third clean, dry test tube. Label the test tube “3.” 5. Add 10 drops propyl alcohol to a fourth clean, dry test tube. Label the test tube “4.” 6. To test tubes 1, 2, and 4, add 30 drops acetic acid. 7. To test tube 3, add 0.5g salicylic acid. Gently swirl the test tube to ensure the salicylic acid to go into solution. 8. Add 2 drops of the concentrated sulfuric acid to each of the 4 test tubes. 9. Using a test tube holder, place the test tubes into the beaker of near-boiling water. Let the test tubes stand in the hot-water bath for 5 minutes. 10. Label the 125-mL Erlenmeyer flasks “1,” “2,” “3,” and “4.” Add water to each until it is about 1/3 full. 11. Pour the contents of the test tubes into the correctly labeled flask and swirl. 12. Carefully smell the ester by waving a hand across the mouth of the flask to push the vapor toward your nose. Describe the odor of the sample in the table below. 13. Rinse the contents of the flasks down the drain with water. Table 1: Alcohol/Carboxylic Acid Pairs and Resulting Esters Test Carboxylic Ester Odor of Tube Alcohol Amount Acid Amount Produced Ester 1 2 3 4 Questions: 1. Write the chemical reactions for each of the esters produced in the above procedures. 2. Isoamyl alcohol, octanol, methanol, and propanol contain what functional group characteristic of all alcohols? 3. Acetic acid and salicylic acid contain what functional group characteristic of all carboxylic acids? 4. The esters produced in this laboratory experiment contain what functional group characteristic of all ester? 5. Isobutyl alcohol and formic acid combine to produce a raspberry odor.
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