Introduction:
What is acetaminophen? Acetaminophen, or more commonly known as Tylenol, is a widely used over the counter medicine. This is mostly because it is a very powerful analgesic (relieves pain) and antipyretic (reduces fever). This is the medicine that people turn to when they have a fever, headache, or minor aches and pains. It is easily accessible because of its affordable price, useful because of its low toxicity when used properly, and has few side effects. So, it is a pretty well trusted medicine.
The chemistry behind acetaminophen:
Acetaminophen is formed when the amine group of a p-aminophenol is acetylated (introduce an acetyl-functioning group to) by acetic anhydride to form an amide functional group. Acetic acid is the byproduct of the chemical reaction.
After the reaction, acetaminophen is isolated as an impure crude solid. The crude solid was purified using a recrystallization technique. Recrystallization is a method of purification that involves dissolving a solid and then causing it to recrystallize, to precipitate as a crystal solid, from the solution. In a recrystallization procedure, the crude solid is dissolved by heating it in a minimal amount of a solvent (recrystallization solvent). The hot solution is cooled to room temperature and then in an ice water bath, where crystals solidify out of the saturated solution. The formation of crystals upon cooling was done slowly, without disrupting the solution—no swirling or stirring allowed. The crystals obtained after the recrystallization are more pure than the crude solid because most of the impurities remain dissolved in the cold solution. Therefore, recrystallization is a rare reaction that involves no side-product or contaminants in the product
The purpose of the experiment was to discover the purity of the recovered products were measured and analyzed using the method of melting point determinations. This was done using the MelTemp apparatus, to analyze and observe both the crude and purified products.
Procedure:
The experimental procedure used in this experiment was outlined in the CHEM 123L lab manual, 2013, experiment #1. All the steps were followed without deviation.
Experimental Observations:
Taken from data sheet
Volume of Water used: 32 mL
Temperature of water: 67 degrees Celsius
Name of substance/ object being measured Mass (g)
Qualitative properties (if any) p-aminophenol 3.05 Solid, white
Acetic anhydride 4.37 Erlenmeyer flask 100.21 Erlenmeyer flask and crude 103.41 Crude 3.2 Gloopy, thick
Dish 30.19 glassDish and crude 32.37 Purified crude 2.08 White, fine, crystalline
Compound Temperature measured from MelTemp (degrees Celsius)
Crude 165
Purified/recrystallized product 166.5
Results and Calculations:
Full molecular equation of chemical reaction between p-Aminophenol and acetic anhydride
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Determining the theoretical yield of acetaminophen:
Original mass of p-aminophenol = 3.05g
Molar mass of p-aminophenol (C6H7 NO):
= (12.01*6)g/mol + (1.008*7)g/mol + 14.01g/mol + 16.00g/mol
= 109.13 g/molMolar mass of acetic anhydride (C4H6O3):
= (12.01*4)g/mol + (1.008*6)g/mol + (16.00*3)g/mol
= 102.09 g/molVolume of acetic anhydride used: 4.04 mL
Density of acetic anhydride: 1.082 g/cm^3
Mass of acetic anhydride used (assuming that 1 mL of solution is equivalent to approximately 1 g in mass): 4.04 mL * 1.082 g/cm^3 = 4.37 g
Find the limiting reagent by comparing the molar ratio of p-aminophenol and acetic anhydride:
Moles of p-aminophenol = mass/molar mass = 3.05g/ 109.13g mol-1 = 0.02795 molMoles of acetic anhydride = mass/molar mass = 4.37g/ 102.09g mol-1 = 0.04281 molEach compound in the chemical equation reacts on a 1:1 ratio with each other. The limiting reagent here is p-aminophenol because there are less moles of it, meaning it is limited so it will run out first. So, we will use the moles of p-aminophenol to find out the moles of acetaminophen. Since the equation is