In This Laboratory Activity You Will Separate Orange Oil From

In this laboratory activity you will separate orange oil from orange peel by the technique of steam distillation. Introduction: In this experiment we will be extracting D – limonene (4-Isopropeny-1methyl-cyclohexene) from orange peel by use of steam distillation. Limonene belongs to a class of compounds called terpenes. Terpenes are a large and varied class of hydrocarbons, produced primarily by a wide variety of plants, particularly conifers. They are the major components of resin, and of turpentine produced from resin. The name "terpene" is derived from the word "turpentine". When terpenes are modified chemically, such as by oxidation or rearrangement of the carbon skeleton, the resulting compounds are generally referred to as terpenoids. Terpenes and terpenoids are the primary constituents of the essential oils of many types of plants and flowers. Essential oils are used widely as natural flavor additives for food, as fragrances in perfumery, in aromatherapy, and in traditional and alternative medicines. Synthetic variations and derivatives of natural terpenes and terpenoids also greatly expand the variety of aromas used in perfumery and flavors used in food additives. The building block of all terpenes is an isoprene unit. A limonene molecule contains two isoprene units.

“Isoprene” Units The terpene D-limonene is the major chemical component in orange oil and has a variety of uses. As the main odor constitutent of the citrus family, D – limonene can be used as an additive to impart an orange-like fragrance or flavor to foods, toiletries, and cleaning products. Pure limonene is used as a

solvent to replace other solvents such as toluene, mineral spirits, turpentine, acetone, etc. Flea and tick shampoos also contain D-limonene as do some insecticides. Limonene is an irritant to the skin and eyes.

There are two isomers (same chemical formula but different structure) of limonene, D and L limonene. A quick glance at the structural representations of limonene above reveals that both of these isomers have the same connection of atoms. How can they be isomers? D and L limonene are stereoisomers, specifically, enantiomers or optical isomers. Stereoisomers are structures that differ only in the spatial arrangement of atoms. Enantiomers, such as D and L – limonene, are non-superimposable mirror images of each other (as you will see later on in the lab). Two compounds that are enantiomers of each other have the same physical properties, except for the direction in which they rotate polarized light and how they interact with different enantiomers of other compounds. In nature, only one enantiomer of most biological compounds, such as amino acids (L), is present. As a result, different enantiomers of a compound may have substantially different biological effects. In the structures above, the wedge line in the D isomer represents a bond projecting out of the plane of the paper. The dashed line in the L – limonene structure represents a bond projecting behind the plane of the paper. Distillation is a method used to separate substances based on differences in their boiling temperatures (volatilities). Steam distillation is a special case of the distillation of an aqueous mixture. A mixture of water and an organic

material is boiled in a distillation apparatus causing vaporized water (steam) and organic liquid to distill into a receiver. Steam distillation allows the separation of this organic liquid from its parent plant material at a temperature well below its boiling point so that there is little chance of decomposition. Many essential oils are separated from plant materials by steam distillation. Some essential oils have components that are too fragile even for steam distillation. Other methods of recovering essential oils include cold pressing and chemical extraction.