Esters: Aspirin and Wintergreen

Lab Esters: Aspirin and Wintergreen

Objectives:  synthesize the ester organic functional group  synthesize aspirin  synthesize wintergreen

Introduction: Esters are an organic functional group. The general structure of an ester is a carbonyl carbon bonded to an oxygen.

O O R' C O C R R O H R' C O C R R' C O H ester ether carboxylic acid alcohol

Esters are quite often fragrant in a pleasant manner. This is not to say that all esters have a scent or that all esters smell nice, because they all don’t, but many of the good smells you encounter are due to the ester functional group. Esters are very important in the perfume industry!

Esters are produced by the dehydration of an alcohol and a carboxylic acid. This reaction proceeds much faster with the addition of sulfuric acid, acting as a catalyst.

Sample esterification reaction: carboxylic acid alcohol ester O H H O H H H2SO4 H2O CH3 C OH HO C C H CH3 C O C C H H H H H acetic acid ethanol ethyl ethanoate

Aspirin, acetylsalicylic acid, is possibly the oldest known pharmaceutical. First, synthesized by Charles Gerhardt in 1850, the Bayer Company purchased the patent in 1893. Gerhardt extracted an organic molecule named salicin from the herb meadowsweet and the bark of a white willow. Gerhardt’s experiment was not just a good guess, herbalists had been advising people suffering with headaches and other ailments to chew on the white willow bark or eat meadowsweet for centuries.

The standard tablet contains 325mg of aspirin, the remainder is a structural binder. You need not spend the extra money on purchasing Bayer aspirin, because in the United States the FDA requires all drugs sold to meet certain purity standards. So by law, generic brand aspirin is the same as the more expensive Bayer.

Aspirin is sold as a painkiller (analgesic), anti-inflammatory and a fever reducer (antipyretic). More recently it has been touted to reduce the incident of heart attacks and strokes by preventing blood clotting. Alone, the United States consumes over 20 tons of aspirin a day, making aspiring the most used drug in the world. Wintergreen is an oil composed of salicylic acid and methanol and is named methylsalicylate. Wintergreen is commonly thought of as a flavoring.

Aspirin O O C OH O C OH O O OH C CH 3 O C CH3 CH C OH O 3 C CH3 O salicylic acid acetic anhydride acetylsalicylic acid acetic acid

O O C OH C O CH3 OH H+ OH H2O CH3OH

methanol salicylic acid methylsalicylate

Procedure Aspirin: 1. Set up a warm water bath between 45 and 50C and an ice bath. 2. Measure out 2.8 grams of salicylic acid and place it in a 125mL Erlenmeyer flask. 3. Add 5.0mL of acetic anhydride to this flask. 4. Add 4 drops of concentrated H2SO4, sulfuric acid and stir. 5. Place this flask in the warm water bath for 7 minutes. 6. Stir or swirl frequently to ensure all compounds remain dissolved. 7. Remove the flask from the warm water and allow it to cool to room temperature. 8. A precipitate will begin to form, add 50mL of deionized water. 9. If any solid lumps form break them up with a scupula or stirring rod. 10.Allow the mixture to stand for 5 minutes after the water is added then chill in the ice bath for 5 minutes. 11.Pre-mass a piece of filter paper. 12.Collect the solid using a funnel. 13.Allow the filter paper and solid to dry overnight.

Procedure Wintergreen: 1. Set up a warm water bath between 45 and 50C and an ice bath. 2. Measure out 2.8 grams of salicylic acid and place it in a 125mL Erlenmeyer flask. 3. Add 5.0mL of methanol to this flask. 4. In the hood, add 4 drops of concentrated H2SO4, sulfuric acid. 5. Stir this mixture thoroughly. 6. Place this flask in the warm water bath for 7 minutes. 7. Stir or swirl frequently to ensure all compounds remain dissolved. 8. Remove the flask from the warm water and allow it to cool to room temperature. 9. Use the wafting technique to smell your compound.