Date of Experiment: September 10th, 2013
Organic Chemistry II – CHLB330
Name: Symone E. MoxeyLab Partner: Lynden Cooper
Synthesis of Aspirin (Acetylsalicylic Acid)
Aspirin (acetylsalicylic acid) is produced experimentally in the lab. The resulting percentage yield is 65.5%. The purity of the obtained product is tested using the melting point and Ferric Chloride Test (FCT). The aspirin was massed, and the melting point was determined. Based on the data collected, there was a total yield of 1.757g of purified aspirin, which had a melting point range of 125°C-130°C. Results of the Ferric Chloride test showed that no unreacted salicylic acid present. The product is too impure for human consumption. Introduction:-
Most drugs are chemical compounds which are described as “organic compounds” because they are comprised primarily of the elements carbon, hydrogen and oxygen. The following experiment will be the synthesis of a widely used prescription drug known as aspirin. The common chemical name is acetylsalicylic acid. Aspirin is a versatile drug that is consumed in huge quantities worldwide. It is a non-steroidal anti-inflammatory drug (NSAID)1 with a range of physiological effects8. Aspirin has a very interesting history. For years, the bark and leaves of willow trees have been used as a pain killer. In the 5th century B.C. Hippocrates first used a bitter powder obtained from the ground willow bark to ease aches and to reduce fever5. However, the active component (salicylic acid) found in these willow trees can cause harm. The problem with these chemicals was that they upset the users’ stomach badly. This is because its acidity (pKa = 2.97) can be higher than the pH of the human stomach (pH ~4 after digestion is complete)3.
Figure 1: Salicylic Acid
Salicylic acid is a diprotic (an acid that contains 2 hydrogen atoms capable of dissociating) organic acid, with two acidic functional groups: a carboxylic acid and a phenol. In comparison, acetylsalicylic acid (monoprotic) known as aspirin is less acidic (pKa = 4.57). Unlike salicylic acid, an ester has replaced the acidic phenol in acetylsalicylic acid.
Figure 2: Acetylsalicylic Acid
The synthesis of aspirin from salicylic acid results in the formation of an ester functional group and therefore the process is called esterification. Esterification is mainly the reaction between alcohols and carboxylic acids to make esters1. The first step in the esterification is to create a suspension of salicylic acid (solid at room temperature) in an excess of acetic anhydride (liquid at room temperature). In this reaction acetic acid or sometimes called ethanoic acid serves as both a limiting reactant and a solvent.
Figure 3: Ethanoic Anhydride
A catalyst is required for this reaction. Concentrated sulfuric acid, H2SO4 , donates an H+ which binds to the reaction complex. As a catalyst, H+ is not consumed but regenerated by the end of this reaction. As the reaction takes place, the solid salicylic acid disappears and the acetylsalicylic acid product remains dissolved in the hot solution. Once all solid has vanished (all the salicylic acid has been consumed) the reaction is completed5.
Figure 4: Formation of Acetylsalicylic Acid
Once complete, the excess ethanoic anhydride must be hydrolysed (separated by the addition of water) to acetic (ethanoic) acid. Because acetic acid is highly reactive toward water, hydrolysis must be done slowly-water should be added drop-wise.
Figure 5: Hydrolysis of Ethanoic Acid
After this process, more water is then added to the solution and the flask is placed in an ice bath to lower the solubility and precipitate the aspirin product. The aspirin product is not very soluble in water so the aspirin product will precipitate when water is added4. The crude product is then collect via filtration and recrystallized to further purify the product. Equations:-
DATA TABLE 1
Mass of Erlenmeyer Flask 81.5 g
Mass of Flask and Salicylic...
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