Salicylic acid derivatives, or salicin, are found in the bark of the willow tree. In the 5th century B. C. , Hippocrates ground the bark into a powder, and later, the Natives Americans chewed on the bark to alleviate fever and pain1. In the 19th century, a German chemist by the name of Felix Hoffman wanted to find a medication that would ease his father’s arthritis without causing irritation to his stomach.
The standard arthritis medication at the time, sodium salicylate, could not be tolerated by many patients, Hoffman’s father included, due to the irritation of the stomach lining brought and by large doses 2, Hoffman synthesized acetylsalicylic acid ‘through some chemical reactions that covered up the acidic portions with an acetyl group’ 3, and was found to alleviate fever, minor pain, and arthritis pain at higher doses. In 1899, the Bayer company sold aspirin for the first time commercially in Germany and in the United States in 1900 4.
In recent years, it has been proven that aspirin helps prevent heart attacks in patients with heart disease and in healthy men over the age of 50. To prevent a heart attack, low dose aspirin (81-325mg) is used. During a heart attack, a 325mg, non-coated aspirin tablet must be chewed to prevent blood platelets from clotting. The tablet must be uncoated due to the aspirin acting slow, and the tablet must be chewed because the healing reactions are fastest with this method (14 minutes chewed vs. 26 minutes swallowed) 5. Reaction Scheme Mechanism.
The purpose of synthesizing aspirin, other than to find a less intestinal irritating pain reliever is to determine if the experiment will work using current methodology and to determine the resulting compound’s purity by obtaining the melting point 6. Aspirin is a common medication for reducing fever, aches, and pains. The scientific name for aspirin is acetylsalicylic acid. The medicinal part of aspirin is salicylic acid, but it is an irritant to the linings of the stomach and the mouth. Salicylic acid is also a major component in acne medications to keep dead cells out of pores by exfoliating the dead cells from inside the pores.
Acetylsalicylic acid is less irritating on the intestines, which contain alkaline fluids that will hydrolyze aspirin into salicylic acid 7. Experimental A 2. 01g (0. 015 mol) sample of salicylic acid, 5. 0mL (0. 053 mol) of acetic anhydride, and 10 drops of concentrated sulfuric acid were placed in a 125mL Erlenmeyer flask. The salicylic acid dissolved, and the flask was heated for 20 minutes, after which, the solution was cooled to room temperature and then placed in an ice bath to cool further. Cold water in the amount of 50mL was added to the flask to complete crystallization.
The crystals were collected through suction filtration. To purify the product, a recrystallization had to be performed. After the suction filtration, the crystals were transferred to a smaller Erlenmeyer flask with 7 mL of ethanol added. The flask was warmed to dissolve the crystals. Warm water in the amount of 17mL was added to the ethanol, and the flask was cooled to room temperature again, and placed into the ice bath again to complete the recrystallization. The crystals were retrieved through suction filtration again.
The crystals were left to dry for a time in order to determine weight and melting point. The resulting weight of the aspirin was 0. 95g with a melting point of 125-131°C, which suggests there are impurities in the aspirin. Results and Discussion The resulting weight of the aspirin obtained was 0. 95g, an actual yield of 35% of the original sample. Theoretically, if the synthesis of the aspirin was perfect, the weight obtained would have been, according to calculations, 2. 70g. The second recrystallization did not work as well as the first recrystallization.
When the second recrystallization was being performed, the aspirin did not recrystallized properly. Therefore, additional time in the freezer was needed for the aspirin to recrystallize. The aspirin crystals were collected through suction filtration, and left to dry until the next lab period. After the crystals had dried, they were white, slightly glossy, and crystalline in appearance. The melting point obtained was in the range of 125-131°C which suggests impurities were present considering that the literature melting point for pure aspirin is 135°C 8.
The sample’s impurities could have been caused by the improper recrystallization of the aspirin, the freezer that the Erlenmeyer flask was stored, or from possible contaminants under the fume hood. Conclusions In the 19th century, aspirin was synthesized to provide a less irritating pain reliever. Today, aspirin is widely used to relieve pain, reduce fever, and helps with heart health. In this experiment, aspirin was synthesized to determine how pure the results would be. The substances used were a mixture of salicylic acid, acetic anhydride, and concentrated sulfuric acid.
Two recrystallizations were performed, with the last one using ethanol. A theoretical yield determined that if the experiment went perfectly, then the amount of aspirin obtained would have been 2. 70g. However, things rarely are perfect, and an actual amount obtained was 0. 95g with an actual percentage yield of 35%. The literature states that the melting point of aspirin is 135°C. The melting point obtained was 125-131°C, supporting that there were possible contaminants in the final product.
Sources 1) ‘Synthesis of Aspirin Course Notes’, homepages. ius. edu/DSPURLOC/c122/asp.htm 2) ‘Synthesis of Aspirin Course Notes’, homepages. ius. edu/DSPURLOC/c122/asp. htm 3) ‘Synthesis of Aspirin Course Notes’, homepages. ius. edu/DSPURLOC/c122/asp. htm 4) www. seriaz. org/downloads/8_aspirin. pdf 5) ‘Aspirin for Heart Attack: Chew or Swallow? ’ www. health. harvard. edy/fhg/updates/update0505a. shtml 6) ‘Synthesis of Aspirin Course Notes’, homepages. ius. edu/DSPURLOC/c122/asp. htm 7) ‘Synthesis of Aspirin Course Notes’, homepages. ius. edu/DSPURLOC/c122/asp. htm 8) CRC Handbook of Chemistry and Physics, 47th Ed, Weast, Richard C. , Ph. D. , pg. C-190.