Isolation and Epoxidation of a Natural Product: Limonene

Introduction

Natural products are compounds produced by living organisms. Recently a great deal of exploration has been done involving the use of natural products in pharmaceutical drug discovery and drug design. Extraction of natural products from organisms is an important part of modern organic chemistry. One commonly performed natural product isolation is the extraction of R-(+)-limonene from the fruit of Citrus sinensis, i.e. the orange tree. This enantiomeric form of the molecule is responsible for the characteristic odor of citrus fruits.

Many natural products, like R-(+)-limonene, have chiral centers making them optically active. In this experiment, you will isolate limonene and purify it via an epoxidation reaction. Epoxidation is a key transformation in an organic chemist’s arsenal. This particular epoxidation is carried out under “green” conditions, since it uses water as the solvent. Finally, you will compare the optical purity of your product to a neat sample using polarimetry.

Objectives

In this experiment, you will

• Isolate R-(+)-limonene from oranges by performing a fractional distillation.
• Perform an epoxidation reaction, under “green” conditions, to generate the pure R-(+)-limonene.
• Compare the enantiomer of the synthesized limonene to neat limonene using polarimetry.