After first isolation of crude acetaminophen, 1.22g of light, brown shiny, fine Crestline solid emulated, which demonstrated slight less than 0.030g of product was lost from original 0.150g of p-aminophenol. The melting point range of crude acetaminophen ranged from 166.8-167.6°C, when compare to the known melting point of pure acetaminophen which ranged from 169.5-171°C, is slightly depressed. After decolonization of crude acetaminophen 0.060g of a very light tan/pink almost white, fine, shiny crystalline purified acetaminophen was recovered. Significant amount was lost; slightly over half was lost from 0.122g crude acetaminophen. Purified acetaminophen resulted in a much lighter coloration than the crude acetaminophen. Purified acetaminophen was slightly light tan/pink nearly white, whereas crude acetaminophen was light brown. After crystallization of acetaminophen, 0.028g of whiter, shiny, fine crystals resulted with no apparent odor. Slightly less than half of product was lost from 0.060g purified acetaminophen that was crystallized and about 0.122g was lost from the original 0.150g of p-aminophenol started with. The melting point range of the crystallized acetaminophen (166.1-169.8 °C when compared to the known melting point range of pure acetaminophen at 169.5-171°C is clearly depressed and elongated. 169.5-171°C
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% yield of crude product:
x = 0.207g crude acetaminophen
x 100 = 58.7%
% yield of crystallized (final) product
x = 0.207g crude acetaminophen
x 100 = 13.5%
Weigh out about 0.150g p-aminophenol and place this in a %ml conical vial. Note: some amount of product was lost do to spillage. .150g weighted out; p-aminophenol is a dark purple powder containing few small grains. Using pipette, add 0.450ml of water and 0.165ml of acetic anhydride. About 450ml and 0.165ml of water and acetic anhydride weighted out. Addition of water formed dark purple viscous mixture; most p-aminophenol dissolved. Addition of acetic anhydride to the mixture produced a dark brown mixture brown precipitate seemed to have formed at the bottom of the vial. Heat the reaction with an alumina block at about 120°C while stirring gently. After solid precipitate has completely dissolved heat for an addition 20 minutes. Remove vial from heat and allow cooling. Once cool remove the spin vane and air condenser from the conical vial and let cool to room temperature. Once safe to touch put the mixture in an ice bath for 15-20 minutes allowing for crystallization.
Collect crystals through vacuuming through Hirsch funnel for 5-10 minutes allowing for air to go through. Once dry add weight the crude product and do melting point range test 166.8-167.6°C compared to the know melting point range of 169.5-171°C. Dissolve 0.2g of sodium Dithionite in 1.5ml of water in a 5ml conical vial. Weight out about 0.204g of sodium dithionite, a grey- white solid powder, add the crude product to the vial and heat up the mixture at about 100°C for 15 minutes. After heating the crude product completely dissolved producing a light tan translucent solution. Note: spillage occurred when transferring crude product into conical vial. Cool mixture in an ice bath for about 10 minutes. Collection of crystals are done by vacuuming with the Hirsch funnel, once dry weight the purified acetaminophen 0.060g resulted. The purified acetaminophen resulted in a much lighter coloration than the crude. Place purified acetaminophen in a craig tube.
Crystallize the material from a solvent mixture composed of 50% water 50% methanol by volume. Set up the Craig tube apparatus described in technique 11, section11.4. Add drops of hot solvent until solid is dissolved. When product has dissolved, place the Craig tube into a 10ml Erlenmeyer flask, insert the inner plug of the Craig tube and allow solution to cool. Place in ice bath for several minutes to allow acetaminophen to crystallize. After crystallization has occurred collect crystals using apparatus shown in technique 8 figure 8.11, place assembly in centrifuge for several minutes collect crystals on watch glass weight it at 0.028g and find the melting point range of 166.1-169.8°C. Questions:
1. Most compounds have lower solubility’s at lower temperatures. You can obtain more product y crystallization at lower temperature. 3. Product can be lost through Hirsch funnel if over washed.
4. x = 0..180g crude acetaminophen
x = 0.00119g mol acetaminophen
Through the main reaction between 0.150g of p-aminophenol with acetic anhydride, 0.122g of crude acetaminophen was produced along with some acetic acid. This indicates a 58.7 percent yield of crude acetaminophen. This is a fair percent yield considering a slight amount of p-aminophenol was lost due to spillage in the transferring process into conical vail and slight amount of crude acetaminophen was lost when trying to remove crystallized crude acetaminophen from conical vial.
Percent yield is 58.7% indicating loss of reactants or spillage of products. There is possible error when performing suction filtration; too much washing of product can cause product to fall through filter ultimately decreasing overall percent yield. also overheating may have caused a loss of product; some of the product may have been splattered out of the reaction vessel when heating. 1005 yield would mean that one has carried out the lab activities perfectly producing the predicted amount of product. Given the 58.7% yield actually obtained, it is evident that experimental procedures be accurately followed for further improvement. It is in the transferring process of p-aminophenol to a 5mL conical vial. Where error is most critical and product can be readily lost.
After decolorization process, 0.060g of decolorized/purified acetaminophen was obtained indicating a significant loss of product. Prior to decolorization process, 0.122g of crude acetaminophen solid was present, meaning half of product was lost in the decolorization process. It is important to note that a significant amount of product was lost due to spillage when transferring crude acetaminophen into conical vial to decolorization. Error may also be present if mixture is overheated and product is evaporated off.
After crystallization process of purified acetaminophen, 0.028g of white final acetaminophen resulted indicating a 13.5% yield. this is a poor percent yield. this indicates slightly less than half of 0.060g of purified acetaminophen was lost. Such a low percent yield can be attributed to the loss of product throughout the crystallization process. It is important o note that a significant amount of product was lost within supernatant after centrifugation, also, product was lost when trying to remove product from Craig tube and plug.
Purity of final product of acetaminophen was tested through qualitative observation of coloration and by comparing obtained melting point ranges of crude and final acetaminophen to the literature melting point range of pure acetaminophen. Because crude solid acetaminophen contains dark impurities carried along with p-aminophenol we can qualitatively compare the level of impurity before and after decolorization. As for the second test for impurity, the melting point range of the crude acetaminophen, 166.8-167.6°C is slightly depressed when compared to the known melting point range of pure acetaminophen 169.5-171°C. Crude acetaminophen melting point range is depressed by 2.7°C. A difference of less than 5°C indicates a good melting point range was obtained for crude acetaminophen this indicating a minimal amount of impurity present. The melting point range of final crystallized acetaminophen, 166.1-169.8°C is slightly depressed and elongated when compared to the known melting point range of pure acetaminophen 169.5-171°C.
It is depressed by 3.4°C and elongated by 2.2°C. A difference of less than 5°C indicates a good melting point range was obtained, though impurities may still be present. When crystals are isolated by filtration from a solvent, it is important to allow complete drying/evaporation of the solvent in order to minimize impurities and get a good melting range. Residual solvent may also function as an impurity and will depress/broaden the melting range for acetaminophen. When two chemicals are mixed, side reactions may take place and produce by-products which can serve as impurities ultimately lowering and elongating the melting point range. For further reference, one must meticulously carry out experimental procedures to ensure that neither reactants nor product is lost and higher percent yield is obtained.