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Just for fun!
Synthesis of Aspirin
Organic chemistry is heavily involved in the production of many everyday items, such as, plastics, petroleum, and pharmaceuticals. Aspirin is the most commonly used drug in the United States, with more than 40 million pounds produced each year. The chemical name for aspirin is Acetylsalicylic acid. Aspirin is known to be an analgesic (pain reliever) and an antipyretic (fever reducer). The multi-step synthesis of aspirin that you will be attempting is shown below (These structures are written in shorthand. Every unlabeled vertex is a carbon, and hydrogens need to be added until each carbon has 4 bonds):
You will be performing several common organic synthetic techniques in creating aspirin. In the first step, you will be performing a hydrolysis of methyl salicylate, otherwise known as, Oil of Wintergreen. In the second step, you will be performing a condensation reaction to produce your final product, acetylsalicylic acid. In each of these steps, certain pieces of each molecule are changing, while the core of the molecule remains unchanged. These reaction sites are commonly referred to as functional groups. Each functional group exhibits unique chemistry. Methyl Salicylate is composed of an ester (RCOOR) (R indicates a carbon-containing group) and a phenol (C6H5OH). In the presence of sodium hydroxide the hydrolysis of the ester takes precedence over any chemical change in the phenol. Although the phenol is acidic and will react with the sodium hydroxide, once sulfuric acid is added, the phenol will reappear unchanged, while the ester becomes a new functional group known as a carboxylic acid (RCOOH). In the presence of acetic anhydride, the carboxylic acid is less reactive than the phenol. The phenol of salicylic acid is converted to the acetyl ester in the presence of acetic anhydride, therein; the common name of Acetylsalicylic acid is used for the final structure of aspirin.
Not only is the synthesis of aspirin a great demonstration of our ability to change functional groups on organic molecules, but the three organic molecules involved exhibit some unique chemical bonding principles. Due to the different functional groups being synthesized, we will be able to use Infrared spectroscopy to confirm the synthesis of each new compound in our 2-step synthesis of aspirin.
Functional groups within molecules can be observed to have distinctive IR absorptions, similar to the gaseous compounds we observed in the Global Warming lab. The IR absorptions can help us distinguish one type of bond from another. Experimentally, you will be obtaining an infrared spectrum for each product you synthesize to help confirm the creation of each compound. Table 1 gives the absorption values for certain bonds in the functional groups that you will be seeing in this lab. A range of absorption values is given for each bond because the environment surrounding each bond can influence the final position in the IR spectrum. At the end of this lab is an infrared spectrum with a complete analysis, in Table 2, of your starting material, Methyl Salicylate. Every IR spectrum for this lab should include a complete analysis, similar to that shown for Methyl Salicylate. Use Table 2 at the end of this lab to help track the changes seen from one compound’s IR spectrum to the next compound's IR spectrum.
Table 1: Principal IR Absorptions of Solids and Liquids for Certain Functional Groups
Throughout this lab and the Computational Chemistry lab that follows, we hope to investigate the bonding characteristics of our three main organic molecules in the overall synthesis of aspirin. We will do this using hand-held molecular model kits and HyperChem. We will use IR spectroscopy and other experimental data to compare the various models we use to represent the bonding taking place in these molecules.
Equipment and Materials:
ATR-FTIR Spectrum One Spectrometer
For Step 1: Synthesis of Salicylic Acid
For Step 2: Synthesis of Acetylsalicylic Acid
PreparationClick here for prelab worksheet. Please print using double-sided printer.
Multi-Step Synthesis of Aspirin
Work in pairs and wear gloves when handling the chemicals.
Step 1: Synthesis of Salicylic Acid from Oil of Wintergreen (Methyl Salicylate)
Cool the beaker in an ice bath until it is completely cool, approximately 5 minutes (The bottom of the beaker will cool before the solution. When checking temperature, swirl liquid around a little bit before touching the bottom of the beaker.). While the solution is still on the ice bath, slowly add 50.0 mL of 9M H2SO4 while stirring continuously with a glass stirring rod. Let the reaction cool in the ice bath with occasional stirring for an additional 3 minutes. Isolate the product using a Buchner funnel and vacuum filtration. Leave the product under vacuum for 10-15 minutes to dry out your product. Weigh the dry solid in a watchglass or weighing boat before beginning of the next step. You will obtain an FTIR spectrum of your salicylic acid at the end of lab today.
Step 2: Synthesis of Acetylsalicylic Acid (Aspirin) from Salicylic Acid
Stir in 3.0 mL of Acetic Anhydride and 2-5 drops of Concentrated Phosphoric Acid (85% H3PO4). Mix thoroughly with a glass stirring rod and allow to sit at room temperature to cool. After approximately 2 minutes, cover the beaker with a watch glass and place the covered beaker into the microwave oven. Heat the beaker in the microwave oven on the "Low" setting for 5-7 minutes. Do not microwave more than one beaker at a time. Remove the beaker using paper towels to protect your fingers from the hot beaker and allow the beaker to sit at room temperature in the hood for approximately one minute. Then, add 2 mL of distilled water. Swirl the beaker and let it sit for approximately 5 minutes. To help precipitate your aspirin from the solution, add 15 mL of distilled water and stir continuously for approximately one minute. Add an additional 10 mL of distilled water while stirring and then put your beaker on ice for approximately 5 minutes to help induce recrystallization.
Collect your solid product in a vacuum filtration apparatus with a Buchner funnel. Rinse out the beaker with a small portion of cold distilled water and allow your final product to dry under vacuum for 10 – 15 minutes. Weigh the dry solid.
Take FTIR spectra of both your salicylic acid and aspirin products.
Click here for results worksheet. Please print on double-sided printer.
Click to open a printable version of this figure
Table 2: Analysis of FTIR Spectra from Aspirin Lab [from 4000-1400cm-1]
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Created By: Adilia James '07 and Sarah Coutlee '07
Maintained By: Nick Doe
Date Created: July 3, 2006
Last Modified: June 6, 2007
Expiration Date: July 3, 2007