Preparation of adipic acid from cyclohexene

Experiment 12 Preparation of adipic acid from cyclohexene.

In this laboratory period the cyclohexene prepared in the previous experiment is oxidised to adipic acid. The procedure is written for a specific amount of cyclohexene. Before coming to the laboratory calculate the amounts of reagents required for the amount of cyclohexene you have available. Show these calculations in your laboratory worksheet. Alternatively, you may be supplied with 2 mL of cyclohexene.

Theory:

The cleavage of double bonds by oxidation is useful in the synthesis of acids and ketones and determining structures. Several methods are available including ozonolysis and hot concentrated permanganate. The products obtained depend on the original structure of the olefin. The equations below illustrate the products from cleavage of alkenes:

The balanced equation for the oxidation of cyclohexene with permanganate is shown:

Reference:

T.W.G. Solomons, Organic Chemistry, Fourth Edition, p. 322.

Technical Points

Vacuum Drying of Organic Solids
Organic solids may be dried by allowing air to pass through the filtering apparatus for a few minutes. This, however, only works well when the solvent used for crystallization has a low boiling point. A very effective method of rapidly drying materials isolated from high boiling liquids is to heat them under vacuum. A simple way of carrying out such an operation on a small quantity of material involves using a side arm test tube. The material to be dried is placed in the bottom of such a tube, which is then stoppered with a cork. The side arm is connected to the water aspirator. The vacuum is turned on and the test tube is heated gently in the steam bath. The test tube is shaken regularly until the solid looks dry and no longer sticks to the walls of the tube. Remember to always DISCONNECT the hose from the test tube before turning off the water!

Safety Features:

1. Add concentrated hydrochloric acid to the strongly basic solutionvery cautiously (or erupting may occur). Wash the affected area thoroughly with cold water if acid is spilled on the skin.

2. Handle potassium permanganate carefully. It is a strong oxidising agent. Avoid contact with skin and eyes.

3. Avoid breathing vapours of cyclohexene and methanol.

Procedure:

To a 250 mL Erlenmeyer flask, add water (50 mL), cyclohexene (2 mL, density = 0.81 g cm^-3), and potassium permanganate (8.4 g). Stopper the flask loosely, wrap with a towel and swirl vigorously for 5 minutes. The flask should feel warm.
(If no rise in temperature is detected, remove the stopper, warm the mixture on the steam bath and loosely replace the stopper).
Swirl the flask at frequent intervals for 20 minutes (your yield depends on how well you mix the reactants at this stage).

The temperature of the mixture should be between 35° and 40°.
If the temperature rises above 45°, briefly cool in an ice-water bath. Remove the stopper and place the flask on a steam bath for 15 minutes.
Continue to swirl the flask at frequent intervals.
Make a spot test by withdrawing some of the reaction mixture on the tip of a stirring rod and touching it to a filter paper; permanganate, if present will appear as a purple ring around the dark brown spot of manganese dioxide. If permanganate is still present, add 1 mL of methanol and heat. Repeat this procedure until the permanganate colour has disappeared.
Filter the mixture through a large Buchner funnel (vacuum) into a clean filter flask. Rinse the reaction flask with 10 mL of hot 1% sodium hydroxide solution and pour through the filter. Repeat with a second portion of 10 mL of 1% sodium hydroxide solution.

Place the filtrate and washings in a 250 mL beaker (premarked at 10 mL), add a boiling chip and boil over a flame until the volume of the solution is about 10 mL.

Cool the solution in an ice-water bath and acidify to about pH 1 by cautiously adding concentrated hydrochloric acid dropwise while stirring the solution. (SAFETY GLASSES!) Add an additional 3 mL of acid, stir and allow the beaker to stand in the ice bath for 5 - 10 min to complete the crystallisation.
Collect the acid by vacuum filtration. Recrystallise it from not more than 5 mL of boiling water (if 2 mL of cyclohexene was used). Cool to room temperature, then place in an ice-water bath for 10 minutes.

Filter the product by vacuum (Hirsch funnel) and dry as described under Technical Points. Measure the melting point and yield of product. Calculate the percentage yield. Submit your sample in a labelled vial along with your report.

Infrared Spectroscopy

On your worksheet indicate the important differences in the i.r. spectrum of the starting material and product. Relate the values of these absorptions to the structures of the compounds (see Appendix 3).

Animations of the vibrational modes have been calculated for both cyclohexene and adipic acid.

NOTE: Stains of potassium permanganate and manganese dioxide can be removed from equipment, sinks and hands by washing with a solution of sodium bisulfite (NaHSO₃).

Questions:

1. What reaction is effected by the addition of methanol to unreacted permanganate?

2. Does this reaction affect your product?

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Created and maintained by Prof. Robert J. Lancashire,
The Department of Chemistry, University of the West Indies,
Mona Campus, Kingston 7, Jamaica.

Created Nov 2002. Links checked and/or last modified 19th October 2009.
URL http://wwwchem.uwimona.edu.jm/lab_manuals/c10expt12.html