Experiment 8: Acetylsalicylic Acid Experiment

Topics: Aspirin, Acetic acid, Acetic anhydride Pages: 6 (1650 words) Published: February 13, 2013
Monica Perez
Experiment 8: Acetylsalicylic Acid Experiment
CHM Lab- 2211 Sec 0016
Instructor: Jennifer Reed

Commonly used as Aspirin, acetylsalicylic acid is an analgesic (pain reliever), which is one of the products of the esterification reaction between salicylic acid and acetic anhydride. This esterification occurs since the hydroxyl group from the salicylic acid reacts with acetic anhydride to form an ester. In this experiment, we will be able to recreate this acid catalyzed reaction, using sulfuric acid as our catalyst in order to produce acetylsalicylic acid and acetic acid. The final product of this reaction will be some crystals, which will be mainly composed of acetylsalicylic acid. In order to purify our products, we will have to add water to our crystals so that the acetylsalicylic acid can be dissociated from impurities. Using a technique called vacuum filtration, crystals will be held on a filtration paper while the liquid portion of reagents will drained into an Erlenmeyer flask. To purify our crystals even more, we will have to perform a procedure called re-crystallization, using ethyl acetate as our solvent instead of water in order to prevent decomposition of our products, and then once again we will use vacuum filtration to separate the crystals from the solvent. After we have finished with the experiment, we will be testing for the presence of salicylic acids in our crystals. Salicylic acid is a phenol and it will react with a mixture of Ferric Chloride by changing the color of the solution into a dark purple. If our crystals change color, it will mean that we still have some impurities and the melting point of the acetylsalicylic acid may be affected by the presence of these impurities.


Table 1.1: Acetylation of Salicylic Acid
Weight of Salicylic Acid | 2.00 g|
Mass of Watch glass + filter paper| 32.43g|
Mass of Watch glass + filter paper and product of re- crystallization| 35.55 g| Mass of product of re-crystallization| 35.55 g – 32.43g = 3.12 g| Melting point recorded of Acetylsalicylic Acid | 128- 130 ° C| Literature melting point of Acetylsalicylic Acid | 135-136 ° C| Actual yield of Acetylsalicylic Acid | 1.56 g|

Theoretical yield of acetylsalicylic Acid | 2.61 g|
Percent yield of acetylsalicylic acid | 60 %|

Table 1.2: Observations during phenol test
Sample| Color|
Salicylic acid | Purple |
Crude crystals | Light Purple |
Recrystallization wet products | Orange|
Solvent (distilled water)| Clear yellow |
*Polymerization may have occurred as a possible side product because of too much heat applied. Calculations for Acetylation of Salicylic Acid:
1. Catalyst: Sulfuric Acid 5 drops
2. Limiting Reagent: Salicylic Acid
2.00g (1 mol salicylic acid) (1 mol acetylsalicylic acid) = 0.0145mol Acetylsalicylic Acid (138.10g) (1 mol Salicylic Acid) 3. Excess Reagent: Acetic Anhydride

Acetylsalicylic Acid 5. 00 mL (1.082g) (1 mol Acetic Anhydride) (I mol Acetylsalicilyc Acid) = 0.0530 mol (1 mL) (102.10 g) (1 mol Acetic Anhydride)

4. Theoretical Yield:
0.0145 mol Acetylsalicylic Acid (180.2g Acetylsalicylic acid) = 2.61 g Acetylsalicylic Acid (1 mol Acetylsalicylic acid) 5. Actual yield:

Actual yield = (1/2) x (3.12 g crude product) = 1.56g Acetylsalicylic acid

6. Percent Yield:

(1.56 g) x 100% = 59.77 % ≈ 60%
(2.61 g)

Through our calculations we were able to determine salicylic acid as our limiting reagent, which means that the amount of acetylsalicylic acid produced will be determined by the amount...
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