Purification by recrystallization : Synthesis of ...
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 Mass of Acetaminophen (g)
Volume of Water added (mL) Melting Temperatures (degrees Celsius)
Initial mass of p-aminophenol: 3.09g
Purified Product after Recrystallization Mass of purified product:
Mass of 125mL flask : 54.39 g Mass of 125ml flask and crude product: 57.15g Mass of crude product: 2.76g 27.7mL 163-167 degrees
164-169 degrees celsius
When p-aminophenol was headed at a temperature of 70-74 degrees Celsius, the colour changed from clear to a slight pink. When Acetic anhyride was added, the colour changed to a yellow, and a foul vinegar odour was produced.
The melting point is 169172 degrees Celsius (Handbook of Chemistry, n.d.)
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
Molar mass (g/mol)
p-aminophen
acetic anhydride
acetaminophen
(C6H7NO)
(C4H6O3)
(C8H9NO2)
109.126g/mol
102.089 g/mol
151.163 g/mol
Density ( g/mL) Starting materials = 3.09 g Volume of H20 = 27.7ml Volume of acetic anhydride = 4 ml
1.082 g/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 The theoretical yield is 4.281 g acetaminophen. The Percent Yield Percentage yield = (mass of actual yield / mass of theoretical yield) x 100% = (actual yield / 4.281g ) x 100% = Discussion The melting point of the purified product has a sharp melting point due to the strucutral lattice of the crystals. There is a uniform shape, with little impurities, allowing all the atoms/molecules to melt at the same time. In the results of the experiment, a sharp melting point was not achieved, as we had a range(Stathopulos, 2013). In addition, the percentage yield of the reaction was very low due to inaccuracies in the experiment. The theoretical yield is 4.281 g of acetaminophen, and the actual yield is much lower than that, . Therefore the percentage yield is %. In the hot filtration step, crystallized material was lost on the filter paper. Unintentional spills may reduce the amount of product.
The minimum amount of water was not used to rinse the filter while transferring the solid to the Buchner funnel. An excess of water may have dissolved some of the product, making it necessary to recrystallized it again(Stathopulos, 2013). Therefore the cause of the low yield may be water getting into the reaction. Faulty equipment that is non-calibrated may decrease the yield. The melting point is affected by the purity of the pure product. The results show that the melting point of the crude and pure product are similar. This is inaccurate, as the pure product melts at a sharper temperature range due to its lack of impurities. A reasonable for this would be the failure to dry the product completely. Water molecules may not have fully evaporated, leaving impurities, and thus a larger range of melting points(Stathopulos, 2013). The melting range of the purified solid was close to the literature value of 169-172 degrees Celsius. However, due to these sources of observed errors, the accuracy of the results is not 100%. Questions 1. Acetaminophen was purified by recrystallization, answer the following questions regarding the technique of recrystallization: a) 10ml of water was added for every 1g of crude product. What could happen if 20ml of water was added for every 1g of crude product? The mass of the extra water will contribute to the overall mass of the crude product. The water will dissolve some product, creating the need to recrystallized the product again. b) What could happen if 5mL of water was added for every 1g of crude product? If 5mL of water was added for every 1g of crude product instead of 10mL, the amount of product produced will be limited. The water solvent is needed in order to carry out the experiment. Therefore, a decrease in the solvent means that the mass will be greatly reduced in the final calculations. c) Cold solvent was used to aid in the transfer of the recrystallized product. What could happen if room temperature solvent was used? The solute is recrystallized in the cold solvent. The low temperature reduces the ability of the water to contain the dissolved substances. The lowered solubility means the solid precipitates out more quickly or crystallizes. In summary, the crystallization is faster if you cool the solution because the solubility is reduced.
2. This experiment is an example of an organic synthesis reaction; in this case an amide was synthesized from an amine: a) What is an organic compound? An organic compound is any compound of solid, liquid, or gas state, which contains the carbon molecule. b) What is an amine? An amine is an organic compound derived from ammonia that has a hydrogen atom replaced by organic radicals. c) What is an amide? An amide is a compound derived from ammonia that has a hydrogen atom replaced by the anion NH2. 3. Perhaps the most well known brand of acetaminophen in North America is Tylenol. How did Tylenol get it's name? Tylenol gets it name from it's chemical formula. The chemical formula for acetaminophen is para-acetylaminophenol, containing a tyl- and -enol, forming Tylenol Conclusion The melting point range of the recrystallized material was not narrow, implying a range of melting points. Although the experimental value of 164-169 degrees is near the literature value of 169-172 degrees Celsius, due to experimental inaccuracies, a sharp melting point was not achieved. The percentage yield for Acetaminophen is %. Therefore the experiment conducted was not effective nor reliable. References Kelter, P., Mosher, M., & Scott, A. (2009). Chemistry: The practical science. Boston, MA: Houghton Mifflin. Melting Points. (n.d.). Handbook of Chemistry and Physics. Retrieved February 7, 2013, from http://www.hbcpnetbase.com/ Stathopulos, S. (2013). Chem123l laboratory manual
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 Mass of Acetaminophen (g)
Volume of Water added (mL) Melting Temperatures (degrees Celsius)
Initial mass of p-aminophenol: 3.09g
Purified Product after Recrystallization Mass of purified product:
Mass of 125mL flask : 54.39 g Mass of 125ml flask and crude product: 57.15g Mass of crude product: 2.76g 27.7mL 163-167 degrees
164-169 degrees celsius
When p-aminophenol was headed at a temperature of 70-74 degrees Celsius, the colour changed from clear to a slight pink. When Acetic anhyride was added, the colour changed to a yellow, and a foul vinegar odour was produced.
The melting point is 169172 degrees Celsius (Handbook of Chemistry, n.d.)
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
Molar mass (g/mol)
p-aminophen
acetic anhydride
acetaminophen
(C6H7NO)
(C4H6O3)
(C8H9NO2)
109.126g/mol
102.089 g/mol
151.163 g/mol
Density ( g/mL) Starting materials = 3.09 g Volume of H20 = 27.7ml Volume of acetic anhydride = 4 ml
1.082 g/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 The theoretical yield is 4.281 g acetaminophen. The Percent Yield Percentage yield = (mass of actual yield / mass of theoretical yield) x 100% = (actual yield / 4.281g ) x 100% = Discussion The melting point of the purified product has a sharp melting point due to the strucutral lattice of the crystals. There is a uniform shape, with little impurities, allowing all the atoms/molecules to melt at the same time. In the results of the experiment, a sharp melting point was not achieved, as we had a range(Stathopulos, 2013). In addition, the percentage yield of the reaction was very low due to inaccuracies in the experiment. The theoretical yield is 4.281 g of acetaminophen, and the actual yield is much lower than that, . Therefore the percentage yield is %. In the hot filtration step, crystallized material was lost on the filter paper. Unintentional spills may reduce the amount of product.
The minimum amount of water was not used to rinse the filter while transferring the solid to the Buchner funnel. An excess of water may have dissolved some of the product, making it necessary to recrystallized it again(Stathopulos, 2013). Therefore the cause of the low yield may be water getting into the reaction. Faulty equipment that is non-calibrated may decrease the yield. The melting point is affected by the purity of the pure product. The results show that the melting point of the crude and pure product are similar. This is inaccurate, as the pure product melts at a sharper temperature range due to its lack of impurities. A reasonable for this would be the failure to dry the product completely. Water molecules may not have fully evaporated, leaving impurities, and thus a larger range of melting points(Stathopulos, 2013). The melting range of the purified solid was close to the literature value of 169-172 degrees Celsius. However, due to these sources of observed errors, the accuracy of the results is not 100%. Questions 1. Acetaminophen was purified by recrystallization, answer the following questions regarding the technique of recrystallization: a) 10ml of water was added for every 1g of crude product. What could happen if 20ml of water was added for every 1g of crude product? The mass of the extra water will contribute to the overall mass of the crude product. The water will dissolve some product, creating the need to recrystallized the product again. b) What could happen if 5mL of water was added for every 1g of crude product? If 5mL of water was added for every 1g of crude product instead of 10mL, the amount of product produced will be limited. The water solvent is needed in order to carry out the experiment. Therefore, a decrease in the solvent means that the mass will be greatly reduced in the final calculations. c) Cold solvent was used to aid in the transfer of the recrystallized product. What could happen if room temperature solvent was used? The solute is recrystallized in the cold solvent. The low temperature reduces the ability of the water to contain the dissolved substances. The lowered solubility means the solid precipitates out more quickly or crystallizes. In summary, the crystallization is faster if you cool the solution because the solubility is reduced.
2. This experiment is an example of an organic synthesis reaction; in this case an amide was synthesized from an amine: a) What is an organic compound? An organic compound is any compound of solid, liquid, or gas state, which contains the carbon molecule. b) What is an amine? An amine is an organic compound derived from ammonia that has a hydrogen atom replaced by organic radicals. c) What is an amide? An amide is a compound derived from ammonia that has a hydrogen atom replaced by the anion NH2. 3. Perhaps the most well known brand of acetaminophen in North America is Tylenol. How did Tylenol get it's name? Tylenol gets it name from it's chemical formula. The chemical formula for acetaminophen is para-acetylaminophenol, containing a tyl- and -enol, forming Tylenol Conclusion The melting point range of the recrystallized material was not narrow, implying a range of melting points. Although the experimental value of 164-169 degrees is near the literature value of 169-172 degrees Celsius, due to experimental inaccuracies, a sharp melting point was not achieved. The percentage yield for Acetaminophen is %. Therefore the experiment conducted was not effective nor reliable. References Kelter, P., Mosher, M., & Scott, A. (2009). Chemistry: The practical science. Boston, MA: Houghton Mifflin. Melting Points. (n.d.). Handbook of Chemistry and Physics. Retrieved February 7, 2013, from http://www.hbcpnetbase.com/ Stathopulos, S. (2013). Chem123l laboratory manual
