Chapter G, Problem 1PP

Practice Problem G.1

When farnesol is treated with sulfuric acid, it is converted to bisabolene. Outline a possible mechanism for this reaction.

Interpretation Introduction

Interpretation:

The mechanism for the formation of Bisabolene from Farnesol in presence of is to be outlined.

Concept introduction:

Farnesol is a compound that is formed from isoprene compounds. In general, when geranyl pyrophosphate reacts with isopenenyl pyrophosphate, farnesyl pyrophosphate (intermediate for the synthesis of sesquiterpenes) is formed. This, on oxidation can give farnesol.

Concentrated sulfuric acid acts as a strong dehydrating agent and removes the water molecule from alcohols to form unsaturated hydrocarbon.

Answer to Problem 1PP

Solution:

The mechanism for the synthesis of Bisabolene is explained as follows:

Explanation of Solution

During the first step, Farnesol (unsaturated alcohol) reacts with acid (HA = ) to form a hydrated product. Then, the hydrated product formed loses one water molecule to form a carbocation. Consequently, this carbocation rearranges to form a more stable carbocation. At last, the base ( ) abstracts the hydrogen ion from the molecule, forming Bisabolene.

The whole mechanism can be depicted as:

Hence, Bisabolene has been formed from Farnesol in the presence of concentrated sulfuric acid.

Conclusion

The Bisabolene has been synthesized from Farnesol in the presence of concentrated sulfuric acid. The mechanism for the synthesis of Bisabolene is outlined as: