Synthesis of Adipic Acid

Introduction:

Oxidative cleavage of alkenes is a well known reaction. Several reagents are known to react with alkenes which result in complete breaking of the both bonds to the carbon atoms. Depending on the reagents chosen, different oxidation states can be achieved. For example, the reaction of an alkene with ozone followed by zinc results in the formation of two aldehydes. Reaction of the same alkene with potassium permanganate under basic conditions results in oxidation to the carboxylic acid. It is this latter type of reaction that will be investigated in today’s experiment.
Purpose:

The purpose of this experiment is to synthesis adipic (hexanedioic)acid through the permanganate oxidization of cyclohexene.  This is actually a very complicated redox reaction and the mechanism is not well understood, however, the stoichiometry is as follows:

Adipic acid is an important commercial product, since it can be  reacted with 1,6-hexanediamine (hexamethylenediamine) to form the first commercially successful polymer:  Nylon-6,6.

Procedure:

Before you come into lab, make sure you have filled in your table of reagents and products.  You will need these values (particularly the molecular formula and molecular weight) to determine the identity of your products and to calculate your final yield.  Obtain IR's of cyclohexene and adipic acid from the SDBS web as part of your pre-lab activities. Make sure you understand the each step of the procedure before arriving at the lab.

1. Add approximately 50 mL of water, and 9 g of potassium permanganate to a 250 mL Erlenmeyer flask.
2. Determine the volume required to achieve 1.6g cyclohexene and add the appropriate volume via a graduated pipet. Cyclohexene has an objectionable odor, so keep it contained in the hood or under your snorkel hood.
3. Add a magnetic stirring bar and your thermometer to the flask and place on a magnetic stirring motor.
4. Set the motor for vigorous stirring, but DO NOT allow it to splatter.
5. After 5 minutes, check to see if the flask feels warm.  If not heat it to about 30 °C.
6. Keep stirring and heating for another 30 minutes.  The temperature of the mixture needs to be maintained between 35 °C - 40 °C.  If it rises above 45 °C,  place the Erlenmeyer flask in an ice bath briefly.
7. Raise the temperature of the flask to 55 °C - 60 °C and continue to stir for another 30 minutes.  DO NOT allow the temperature to approach the boiling point of cyclohexene.
8. Check for the presence of excess permanganate by withdrawing a drop from the reaction mixture and touching it on a paper towel.  If you see a purple ring around a brown center (manganese dioxide), permanganate is still present.
9. If permanganate is still present, add approximately 1 mL of methanol and heat and stir for several minutes.  Repeat until permanganate is no longer present. Note, this step is very exothermic.
10. Filter the hot mixture using a Buchner funnel into a CLEAN filter flask.
11. Rinse the Erlenmeyer flask with 10 mL of hot 1% sodium hydroxide solution and pour through the filter.
12. Repeat with a second portion of 10 mL of hot 1% sodium hydroxide solution. The filtrate should be clear and colorless, if not refilter.
13. Transfer the filtrate and washing into a 150 mL beaker that has been pre marked at 10 mL.
14. Add a boiling chip and boil off the water until less than 10 mL remain.
15. Cool the solution to room temperature and then place it into an ice bath. Let it cool to well below room temperature.
16. Carefully add 10 mLs of concentrated hydrochloric acid and allow the beaker to stand in the ice bath for as long as possible (minimum of 15 - 20 minutes). Your yield is largely determined by how long you let it cool at this stage.
17. Use vacuum filtration to collect the product.
18. Dry the crystals in an 110 °C - 125 °C oven for 10 minutes. Weigh the product and return to the oven for an additional 10-15 minutes. Repeat until a constant weight is obtained.
19. Determine the melting point of your product. Note how it compares to the literature value.
20. Determine your yield, purity (m.p., and FTIR), and turn in the product in a properly labeled vial:

Your Name:	Class/Section:	Date:
Compound:	M.P./ B.P.:
Actual Yield (g):	Theoretical Yield (g):	Percent Yield:

Conclusions:

• Calculate the theoretical, actual, and percent yields of your product.
• How pure is your product?  How can you tell?
• Why was the methanol added?  Did it have any effect on your yield or purity?
• Give a detailed analysis of your FTIR.  How does the product compare with the starting materials?

 (Updated 2/7/04 by C.R. Snelling)

 (Updated 2/1/09 by J. Neilan)