Chem 1CL Saul Ruiz May 28 2012 Experiment 19 Synthesis of Aspirin and Oil of Wintergreen The overall purpose of this experiment is to synthesize and purify organic molecules and determine the purity through analytical techniques In the first part of the experiment aspirin and oil of wintergreen are synthesized via an esterification reaction Esterification is the production of an ester an organic compound with the general formula where R represents either a hydrocarbon or hydrogen atom and R represents hydrocarbons only The functional group is an ester is the COOR group In esterification reactions a compound containing the hydroxyl group OH reacts with a compound containing a carboxylic acid group COOH This reaction is catalyzed with a strong acid H2SO4 The reaction of salicylic acid and acetic acid to produce aspirin is slow and does not go to completion Instead an equilibrium mixture of the reactants and the products is produced In the reverse reaction however aspirin reacts with water to produce salicylic acid and acetic acid This is shown in the diagram below Here acetic anhydride is used instead of acetic acid to drive the reaction to completion which by combining two acetic acid molecules and eliminating water produces acetic anhydride Since no water is produced in the reaction of salicylic acid and acetic anhydride the reverse reaction will not occur and significantly more aspirin will be produced as seen below 3 006 grams of salicylic acid were weighed and then placed in a 125 mL Erlenmeyer flask Afterwards 5 mL of acetic anhydride were added to the flask as well as 5 drops of concentrated sulfuric acid The flask is placed in a beaker filled with 250 mL of water at 85 C for approximately 25 minutes The flask is then removed and 2 mL of DI water are added which reacts with any excess anhydride to produce acetic acid After the solution cools to about 45 C and 30 mL DI water is added to the flask crystals should form and the flask should be placed in an ice bath for about 30 minutes The final step in this first part of the experiment is using the vacuum filter flask to filter and dry the aspirin crystals The resulting weight for the aspirin was 5 30 grams In the synthesis of the oil of wintergreen or methyl salicylate salicylic acid reacts with methanol to produce methyl salicylate and water as shown by this diagram Equilibrium is established and since there is no simple alternative to methanol to force the reaction to go to completion the product yield of methyl salicylate is maximized by adding an excess of methanol Excess methanol drives the equilibrium to the right which is predicted by Le Chatelier s Principle Moreover an important characteristic of salicylic acid is its bifunctionality which means that it has two different bifunctional groups For instance in synthesis of aspirin the alcohol group on the salicylic acid reacts with a carboxylic acid to form the ester whereas in the production of methyl salicylate the carboxylic acid on the salicylic acid reacts with an alcohol to form an ester In the synthesis of aspirin and methyl salicylate the products are relatively impure with the main impurities being unreacted salicylic acid and acetic acid The acetic acid is soluble in water and thus can be removed by rinsing the aspirin whereas the unreacted salicylic acid is a solid and is therefore insoluble in water Therefore a 1 FeCl3 solution is added as a purity test Three salicylic acid molecules coordinate to the iron III ion to produce a brightly colored magenta complex Cited from lab manual As such both test tubes turned a purple magenta color after adding water and a drop of 1 FeCl3 which indicates the presence of salicylic acid in the aspirin In order to remove it recrystallization is used Through this technique differences in solubility of the components of the crude mixture are utilized to isolate the desired product The crude mixture is dissolved in a warm solvent in which one of the components is more soluble In the next part of the experiment a solution of NaOH is standardized to determine its exact concentration In the standardization process a sample of potassium hydrogen phthalate KHP is accurately weighed and dissolved in water The KHP solution is titrated with the NaOH where 1 mole of NaOH reacts with 1 mole of KHP Thus at the equivalence point the moles of NaOH equal the moles of KHP The average concentration determined from three samples of KHP was 0 97 M whereas the average deviation for these three samples were roughly 0 043 The standardized NaOH is used to determine the exact concentration and compare it to the actual concentration listed as 1 0 M In another part of the experiment the measure point of an organic molecule is determined in order to identify it as every molecule has a unique temperature range in which it changes from a solid to a liquid at a given pressure melting point Here the melting point of aspirin synthesized is compared to the known melting point of aspirin 135 C to ensure the correct molecule was synthesized The melting point can also be used to check for the presence of impurities If a sample is not entirely pure the melting point will be lower and the temperature range at which it melts will be larger Similarly if the melting point of a sample will be lower if an impurity is present due to freezing point depression The calculated melting point of crude and pure aspirin was determined using the melting point apparatus The crude aspirin started to melt at 90 C and completely melted at 100 C whereas the pure aspirin started to melt at 105 C and completely melted at 110 C The differences in the melting points of the synthesized aspirins melting points with the known melting point of 135 C is due to some possible sources of error such as the fact that the thermometer might have inaccurately measured the melting range of the aspirin as the thermometer was non digital through which exact values and could not be visually determined In the last part of the experiment the purity of the aspirin in the recrystallized and crude products is tested Impurities such as salicylic acid and acetic acid are likely to be present and at low temperatures the aspirin can be neutralized according to the following reaction The quantity of aspirin in the sample is determined by titrating the sample with a base The base however will neutralize any acid impurities Therefore from this titration the total moles of acid in the sample can be determined In order