Camphor synthesis of camphor by retro-synthesis?

Answer 1

Expmt # 803 The Synthesis of Camphor from

Camphene:

Carbocation Rearrangment & Jones Oxidation

Adapted from "Experiments in Organic Chemistry: From Microscale to Macroscale" by Jonathon S. Nimitz,

Prentice-Hall, 1991.

You may recall that the order of carbocation stability obeys the following trend:

Next to O or N > tertiary, allylic, or benzylic > secondary > primary > methyl

In fact, it is extremely difficult to form a primary carbocation and virtually impossible to

form a methyl carbocation in solution. If a secondary carbocation can rearrange to form

a tertiary carbocation by shifting an alkyl, aryl, or hydride group from a neighboring

carbon, it is likely to do so. Carbocation rearrangements are also often observed in ring

systems as is seen in the synthesis of camphor from camphene (shown below).

CH2

HOAc

Camphene

H

O

O

Isobornyl acetate

OH-, H2O

H

HO

Isoboneol

CrO3

H2SO4

O

Camphor

This experiment involves the three-step synthesis of camphor from camphene as shown.

You will be required to do background reading on camphor; pertinent information is to be

included in the Introduction section of your final report. The mechanism of this route

(beginning with camphene through camphor) is also to be determined and included in

the Discussion section of the final report.

Procedure A: Rearrangement of Camphene to Isobornyl Acetate

In a 100-mL beaker, place glacial acetic acid (400 mmol) and camphene (80 mmol).

Heat the mixture for 15-20 minutes on a hot plate, keeping the temperature within the

range 90-100°C. Add 15 mL of cold water and cool the beaker in an ice bath. Place the

mixture in a separatory funnel and remove the aqueous layer, keeping the upper layer of

isobornyl acetate in the funnel. Wash with 10 mL of water, then with 10 mL of 10%

aqueous sodium carbonate. Dry the organic layer over anhydrous sodium sulfate, filter,

and weigh the product. Calculate % yield of this step. Take IR and 1H NMR and

melting point of this product.

Procedure B: Hydrolysis of Isobornyl Acetate to Isoborneol

Set up a 100-mL round-bottomed flask with a water-cooled condenser and heating

mantle. In the flask, place isobornyl from step A. Now, based on the mass of your

product, calculate and add 2.5 mL of 2.5 M KOH in 75% ethanol/25% water for every

gram of isobornyl acetate used.

Reflux the mixture for 45-60 minutes. Cool the flask to room temperature using an ice

bath, and pour the reaction mixture slowly with swirling into a beaker containing 50 mL of

a mixture of ice and water. The isoborneol precipitates; collect the solid by suction

filtration and wash it with cold water. Leave the crude solid in an open beaker in the

hood (labeled) or in your locker to draw until the next lab period. At that time, take a

melting point, an IR and 1H NMR of this product. Also, weigh and calculate % yield

Procedure C: Jones Oxidation Isoborneol to Camphor

For each gram of crude isoborneol obtained in step B, place into a beaker 1.75 mL of

Jones reagent. Jones reagent consists of CrO3 in aqueous H2SO4, which forms the

strong oxidizing agent chromic acid, H2CrO4. The solution is 2.67 M in Cr6+. In a

separate Erlenmeyer flask, dissolve the isoborneol in 10 mL of acetone. Over the

course of 10 minutes, add the Jones reagent dropwise to the isoborneol solution with

swirling. Let the mixture stand for 30 minutes with occasional stirring.

At the end of this time, pour the solution onto 250 mL of an ice-water mixture in a large

beaker. Stir well, then vacuum filter to collect the precipitated camphor. Allow the

product to air dry at room temperature by placing it on a large filter paper on a

watchglass. Once dry, weigh the crude product.

Sublime the crude camphor product. (Information on sublimation can be found in

Chapter 6 on page 139 of the Lab Guide). Weigh pure product and take a melting point.

Analyze by 1H and 13C NMR and IR.

Final Report

Be sure to annotate all spectral data. Include the mechanism of each step of the

reaction scheme in the Discussion section of your final report.