Synthesis of Fragrant Esters

Transcription

1 Synthesis of Fragrant Esters Introduction: An ester is an organic compound that is formed when a carboxylic acid reacts with an alcohol. In addition to an ester being form, water is another product of the reactions. Esterification typically requires a catalyst to speed the reaction. For years concentrated sulfuric acid (H 2 SO 4 ) has been used to do so. Sulfuric acid is a very dangerous chemical, which can cause severe chemical burns when in contact with all human tissues. The utmost care needs to be taken when working with sulfuric acid. When carboxylic acids are esterified (combined with an alcohol to form an ester), some of the resulting esters are liquids with fruity scents or flavors. These synthetic esters produced in the laboratory are nearly the same molecules that give fruits their characteristic flavors. Materials Various Alcohols: Various Organic Acids: Test tubes (5-8) Hot Plate Gloves Goggles Pipets Stiring rods Part A: Synthesis of The Oil of Wintergreen Methylsalicylate (oil of wintergreen) is an ester in which the carboxyl group of salicylic acid has reacted with the alcohol group of methyl alcohol. Oil of wintergreen is used both as a topical analgesic in rubs for sore muscle and a flavoring agent. salicyclic acid Methanol (Methyl Alcohol) methyl salicylate Wintergreen Anthranilic Acid Methanol (Methyl Alcohol) methyl anthranilate Grape

2 Procedure 1. Place 0.2 grams of salicylic acid into a clean, dry 10-cm test tube. 2. Add 6 drops of methyl alcohol and agitate the tube until the contents are well mixed. 3. Then add 1 drop of concentrated sulfuric acid. off any contacted area with cool water. 4. Agitate the tube contents and place the tube in a beaker of boiling water for three minutes. 5. After heating is complete remove the tube from the bath and add 15 drops of water to the tube contents. 6. Cautiously note the odor of the products in the test tube by wafting the scent to your nose. Do this until you can detect an odor. Record the odor. Part B: Synthesis of Grape 1. Place 0.2 grams of anthranilic acid into a clean, dry 10-cm test tube. 2. Add 6 drops of methyl alcohol and agitate the tube until the contents are well mixed. 3. Then add 1 drop of concentrated sulfuric acid. off any contacted area with cool water. 4. Agitate the tube contents and place the tube in a beaker of boiling water for three minutes. 5. After heating is complete remove the tube from the bath and add 15 drops of water to the tube contents. 6. Cautiously note the odor of the products in the test tube by wafting the scent to your nose. Do this until you can detect an odor. Record the odor.

3 Part C: Synthesis of Pear, Banana, and Orange A number of other commercially important esters can also be synthesized using a similar procedure that yielded oil of wintergreen. In this experiment, you will synthesize three esters used commercially as flavorings, using acetic acid. Acetic acid n-propyl n-propyl acetate Pear Acetic acid Isoamyl Isoamyl acetate Banana Acetic Acid Octyl alcohol n-octyl acetate Orange Procedure 1. Prepare n-propyl acetate by putting 6 drops on n-propyl alcohol in a clean, dry 10-cm test tube. 2. Add 2 drops of glacial acetic acid. 3. Add 1 drop of concentrated sulfuric acid, agitate the tube to mix the contents, and place the test tube in boiling water bath for 3 minutes. off any contacted area with cool water. Both glacial acetic acid and concentrated sulfuric acid will vigorously attack tissue. Avoid contact and wash any contacted area immediately with large amounts of cool water. 4. When heating is completed, remove the test tube from the bath, and add 20 drops of water to the test tube contents. Agitate to mix. 5 Cautiously note the odor of the product, using the method described in step 6 of the procedure for the oil of wintergreen (Part A). Record the odor in the data table. 6. Repeat Steps 1 to 5 twice using the following pairs of alcohols and acid: isoamyl alcohol plus glacial acetic acid, and octyl alcohol plus glacial acetic acid. 7. Note and record the odor of the produced esters. Do not worry about having the correct odor for a particular ester. Descriptions of odors often vary with people, and some odors hard to describe.

4 Part D: Synthesis of Pineapple, Strawberry and Apple Although the procedure for the following ester is much the same as in Part C, special attention must be paid when using butyric acid. The use of a fume hood is necessary because of butyric acid strong unpleasant odor. Butyric Acid n-butyl n-butyl butyrate Pineapple Butyric Acid Ethyl ethyl butyrate Strawberry Butyric Acid Methanol (Methyl Alcohol) methyl butyrate Apple Procedure 1. Prepare n-butyl butyrate by putting 6 drops of n-butyl alcohol in a clean, dry 10-cm test tube. 2. Wearing chemically resistant gloves to avoid contact with skin, add 2 drops of butyric acid. 3. Add 1 drop of concentrated sulfuric acid, agitate the tube to mix the contents, and place the test tube in boiling water bath for 3 minutes. off any contacted area with cool water. Concentrated sulfuric acid will vigorously attack tissue. Avoid contact and wash any contacted area immediately with large amounts of cool water. 4. When heating is completed, remove the test tube from the bath, and add 20 drops of water to the test tube contents. Agitate to mix. 5 Cautiously note the odor of the product, using the method described in step 6 of the procedure for the oil of wintergreen (Part A). Record the odor in the data table. 6. Repeat Steps 1 to 5 twice using the following pairs of alcohols and acid: ethyl alcohol plus butyric acid, and methyl alcohol plus butyric acid. 7. Note and record the odor of the produced esters. Do not worry about having the correct odor for a particular ester. Descriptions of odors often vary with people, and some odors hard to describe.

5 Data Acid and Alcohol Reacted Salicyclic Acid and Methyl Alcohol Anthranilic Acid and Methyl Alcohol Acetic Acid and n-propyl Alcohol Acetic Acid and Isoamyl Alcohol Acetic Acid and Octyl Alcohol Butyric Acid and n-butyl Alcohol Butyric Acid and Ethyl Alcohol Butyric Acid and Methyl Alcohol Product Odor Questions 1. What role does sulfuric acid play in the production of the esters in lab? 2. Name three commercial products that contain oil of wintergreen. i. ii. iii. 3. What is the difference between artificial Flavoring and natural flavoring? 4. Explain how the esters made in this lab could or could not be used in the following: a. Coloring agents b. Flavoring agents c. Analgesics