Oxidation of Cyclohexanol to Cyclohexanone

Introduction:

There are four basic types of chemical reactions in organic chemistry:  combination, elimination, substitution, and rearrangement.  Today, you will be conducting a  rearrangement reaction in which you will convert cyclohexanol into cyclohexanone (oxidation).  Although some of the finer points of this reaction are not totally understood, it is generally agreed that it proceeds as follows:



As you will no doubt recall from general chemistry, oxidation/reduction reactions involve the shifting of electrons from one species to another.  The species that losses electrons is said to have been oxidized and is therefore the reducing agent.  The species that gains electrons is said to have been reduced and is therefore the oxidizing agent.  Like any other type of chemical reaction there must be mass balance, so the number of electrons lost by one species must equal the number of electrons gained by another.  In organic chemistry, the species being oxidized shows a loss of hydrogen and/or a gain in oxygen, while the species being reduced shows a loss of oxygen and/or a gain in hydrogen.  You need to prove to yourself that these two views are complimentary.

Our oxidation of cyclohexanol begins by generating the hypochlorous acid which will be our oxidizing agent.  As you can see from its formula, the chlorine in hypochlorous acid has an oxidation state of +1.  Recall that chlorine normally has an oxidation number of -1.  This deficiency of electrons makes this particular species very reactive.  Since this is a very strong oxidizing agent, we will be generating it in situ through the reaction of acetic acid and sodium hypochlorite (regular household bleach).

In the next step, the hydrogen on the hypochlorous acid undergoes nucleophilic attack by the oxygen of the cyclohexanol to form protonated cyclohexanol and  a hypochlorite ion.  This is followed by nucleophilic attack by the hypochlorite ion and displacement of water.  The water then abstracts a hydrogen which initiates a cascade that results in the chlorine leaving as chloride ion and the generation of cyclohexanone. 

Note that the actual oxidizing agent was Cl+ which was reduced to Cl-.  It is also interesting to note that the oxygen atom on the cyclohexanone is not the same oxygen atom that was initially present on the cyclohexanol.  Where did it go, and how do you think you could prove this?


Purpose:

The purpose of this lab is produce cyclohexanone through the hypochlorite oxidation of cyclohexanol.  As before, you will use gas chromatography (GC), refractive index (RI), and infrared spectrometry (IR) to determine the purity of your product.   In addition, you will produce a specific derivative of your product to prove its identify.


Procedure
:

Before you come into lab, make sure you have filled in your table of reagents and products.  You will need these values to determine the identify of your products and to calculate your final yield.  You will also need to come to lab with IRs of both cyclohexanol, and cyclohexanone already in your notebooks (this link may be helpful:   http://webbook.nist.gov/chemistry/name-ser.html).  Finally, it is important that you know exactly what you are going to be doing so you can work more efficiently.



  1. Accurately weigh approximately 10 g of cyclohexanol into a clean, dry 500 mL round bottom flask.
  2. Add 2-3 mL of glacial acetic acid, and a magnetic stirrer to the round bottom flask.
  3. Fit the flask with a Claisen adapter and insert your thermometer into the side arm of the flask (see figure above).  Position the thermometer so it is immersed but is not hit by the magnetic stirring bar.  Remember to lubricate all ground glass joints with a minimal amount of silicon grease.  Make sure that all joints are secured (blue clips) and that the whole apparatus is properly clamped.
  4. Fit a 250 mL separatory funnel onto the Claisen adapter (see figure above) and add 180 mL of commercial bleach to it.  The concentration of commercial bleach will vary, but is typically about 5%. 
  5. Support your apparatus on a magnetic stir motor and adjust the speed of the motor so that the contents of the flask are stirred vigorously.
  6. Add the bleach drop wise but as rapidly as possible to the flask.  The addition should take about 10-15 minutes.  Monitor the temperature as the reaction proceeds.
  7. Keep stirring the flask after the addition is complete for an additional 15-20 minutes.
  8. Transfer the reaction mixture to a 400 mL beaker.
  9. Add approximately 50 grams of NaCl to the mixture and heat to 50 °C on a hot plate.  Keep stirring the mixture for 5-10 minutes.
  10. Allow the excess NaCl to settle out and transfer the liquid to a 250 mL separatory funnel.
  11. Extract with 25 mL of hexane.  Use proper technique and beware of gas pressure!
  12. Transfer the hexane to a 100 mL beaker.
  13. Extract the reaction product with an additional 15 mL of fresh hexane.
  14. Add this hexane to the previous extract and dry them with a small amount of anhydrous MgSO4.
  15. Carefully transfer this dried hexane to a 250 mL round bottom flask.
  16. Attach the round bottom flask to the rotary evaporator and strip off the hexane.  Remember to note the rotary evaporator conditions.
  17. Determine the mass and purity of your product (micro boiling point, GC, RI, and FTIR).  Be sure to include your GC and FTIR traces in your lab report.
  18. Turn in your product in a labeled, tightly sealed container.  Be sure to include the following information on the label:

Your Name:
Class/Section:
Date:
Compound:
M.P./ B.P.:
R.I.:
Actual Yield (g):
Theoretical Yield (g):
Percent Yield:
Purity (GC):
Purity (RI):
Purity (IR):

Conclusions:


 (Updated 12/22/03 by C.R. Snelling)