Hypochlorite Oxidation of Menthol

Lab 6 - Hypochlorite Oxidation of Menthol

Staley, Briana

April 29th, 2019

Chem 12B 31187

Introduction:

The oxidation of alcohols provides the most general method for preparing carbonyl compounds, and in this particular experiment the secondary alcohol in (-)-Menthol oxidizes into a ketone and produces menthone.

Household bleach (NaOCl) is used as an alternative oxidizing agent, but this reaction is slow in neutral or alkaline solutions, and so acetic acid is added as a catalyst.

Furthermore, the mechanism for this reaction is somewhat unknown, however kinetics and other studies suggests that alcohol is first converted into the alkyl hypochlorite. It then undergoes an E2 elimination with water as the base.

Materials:

Compounds Mass Volume

Menthol 5.085 g x

Glacial Acetic Acid x 10.0 mL

Dichloromethane x 41.0 mL

Sodium Sulfate 3.00 g x

Sodium Carbonate 9.27 g x

Experimental Procedure:

A buret was rinsed twice with 5 mL portions of bleach, and then filled with bleach until the 0.0 mL mark. The bleach in the buret was added dropwise to a 250 mL E-flask containing 5.0805 g menthol, a magnetic stir bar, 10 mL of glacial acetic acid, and a thermometer centered positioned and hovering within the mixture. As bleach was being added, the mixture was stirred, and the temperature slowly began to rise, but hovered around 40°C. After, the E-flask was covered by foil and stirred for an additional 30 minutes. Quickly after the 30 minutes had elapsed, the reaction mixture was tested for Cl2 by adding a drop of the reaction’s solution on a starch-iodine paper. Na2CO3, of which was determined to be 9.27 g, was then added to the reaction mixture to neutralize the acetic acid, and immediately after the aqueous layer was extracted 3 times with 10 mL of CH3Cl2 for each extraction. The CH2Cl2 layers were combined with 3.00 g of Na2SO4, corked, and placed into the lab locker next lab sessions.

On the next day of lab, a gravity filtration apparatus was erected to remove the Na2SO4 by gravity filtration. 11.0 mL of dichloromethane was poured through the product in the funnel and collected into a pre-weighed RBF. After filtering, the flask was rotovaped, weighed, and finally placed into the lab locker, uncorked, for over spring break and until the next lab session. After spring break, the theoretical and percent yield were calculated, and the NMR and IR spectrums of the products obtained.

Results:

Mass of product 4.0512 g

Percent yield 81%

Theoretical yield:

(0.03254 mol menthol) x (1 mol menthone / 1 mol menthol) x (154.25 g / 1 mol menthone) = 5.019295 g menthone

Actual yield:

4.0512 g menthone

Percent yield:

(4.0512