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Purification by recrystallization.docx

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CHEM 123
Christine Dupont

Purification by recrystallization : Synthesis of Acetaminophen Date Lab was conducted: Jan 24th 2013 Date of submission: Feb 7th 2012 Name: Lucy Low ID: 20486564 TA: Quan Partner's Name: Farrah Khan Section #: 10 Introduction The purpose of this experiment is to determine the purity of a recovered product through the melting point determinations. This is done through a process of purification called crystallization, which removes impurities from a sample (Stathopulos, 2013). When the amine group of p-aminophenol is acetylated with acetic anhydride, an amide group is added to form acetaminophen. Acetic acid is the by-product in the reaction. The equation of the rate is shown below: p-aminophen + acetic anhydride ---> acetaminophen + acetic acid C6H7NO + C4H6O3 ---> C8H9NO2 + C2H4O2 The acetaminophen is isolated from the products as a crude solid. Recrystallization is a process of purification where a solid is dissolved and recrystallized. Another common term for recrystallization is fractional crystallization. Recrystallization occurs when the crystal solid precipitates out of the solution. When the crude solid is recrystallized, the Acetaminophen is isolated to form a pure solid. Crystals in the pure form contain no impurities of the compound Acetaminophen (Kelter & Mosher, 2009). The saturation point is the concentration in which no additional solute will dissolve into the solvent at a certain temperature. By heating the solution, the temperature and solubility of the substance increases. The solubility can increase up to its saturation point. When cooled, the temperature lowers the solubility. The purity of the material obtained can be correlated to the sharpness of the melting point (Stathopulos, 2013). A pure compound is a structure with molar symmetry, and organization of atoms. An impurity is random and a poorly organized structure. If the impurities are present with the pure compound, the melting point will deviate because melting point is also dependent on the high symmetry and organization of molecular structures, just as the vapor pressure (Stathopulos, 2013).Therefore impurities causes the melting point of a substance to expand, creating a melting range. The melting points of the crude and purified products can be determined through a MelTemp melting point apparatus. The melting point of acetaminophen is 169-172 degrees Celsius for C8H3NO2 (Handbook of Chemistry, n.d.). Procedure The experimental procedure used for this experiment was outlined in the Chem 123L lab manual, experiment #1. All steps were followed without deviation(Stathopulos, 2013). Experimental Observations *Purification of Acetaminophen Data Table Crude Product Purified Product after Recrystallization Mass of Initial mass of p-aminophenol: 3.09g Mass of purified product: Acetaminophen (g) Mass of 125mL flask : 54.39 g Mass of 125ml flask and crude product: 57.15g Mass of crude product: 2.76g Volume of Water 27.7mL added (mL) Melting 163-167 degrees 164-169 degrees celsius Temperatures (degrees Celsius) When p-aminophenol was headed at a The melting point is 169- temperature of 70-74 degrees Celsius, the 172 degrees Celsius colour changed from clear to a slight pink. (Handbook of Chemistry, When Acetic anhyride was added, the colour n.d.) changed to a yellow, and a foul vinegar odour was produced. Results and Calculations The reaction equation for the formation of acetaminophen and the by-produce acetic acid: p-aminophen + acetic anhydride ---> acetaminophen + acetic acid C6H7NO + C4H6O3 ---> C8H9NO2 + C2H4O2 p-aminophen acetic anhydride acetaminophen (C6H7NO) (C4H6O3) (C8H9NO2) Molar mass (g/mol) 109.126g/mol 102.089 g/mol 151.163 g/mol Density ( g/mL) 1.082 g/mL Starting materials = 3.09 g Volume of H20 = 27.7ml Volume of acetic anhydride = 4 ml The Theoretical Yield P-Aminophen 3.09 g C6H7NO x ( 1 mol C6H7NO / 109.1 g C6H7NO) x ( 1 mol acetaminophen / 1 mol C6H7NO) =2.832 x 10^-2 mol p-aminophen Acetic Anhydride 4 mL C4H6O3 x (1.082 g C4H6O3 / 1 mL C4H6O3) x (1 mol C4H6O3 / 102.1 g C4H6O3) x ( 1 mol acetaminophen / 1 mol C4H6O3) = 4.239 x 10^-2 mol acetic anhydride The limiting reactant is p-aminophen with 2.832 x 10^-2 mol p-aminophen. 2.832 x 10^-2 mol C8H9NO2 x (151.163 g C8H9NO2 / 1 mol C8H9NO2) = 4.281 g acetaminophen
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