Dipentene is a monoterpene olefin having potential applications in polymer and fuel chemistry. It is also widely used as a flavoring and fragrance agent. It is derived from the oil of citrus fruit peels. It is a racemic of limonene, D-limonene occurs more naturally in nature and has the fragrance of oranges, while the less common L-limonene has a piny, turpentine-like odor.
In nature, limonene is formed from the molecule geranyl pyrophosphate, via cyclization of a neryl carbocation or its equivalent as shown in the equation below:
In the final step, the C=C double bond is formed through the loss of a proton from the carbocation.
Commercially, d-limonene is obtained from citrus fruits through the process of steam distillation and centrifugal separation. Commonly, orange oil is extracted as a by-product of orange juice production by centrifugation. The orange oil obtained composes greater than 90% of d-limonene. Further separation takes place via steam distillation, where steam is passed through the orange oil to distill lemonene. Limonene is relatively stable and can be distilled without decomposition, but at elevated temperatures it cracks to form isoprene. The limonene extracted is commonly D-limonene, but at 300°C it racemizes to dipentene.
Flavor and fragrance industry:
Used as a fragrance in perfumery, aftershave lotions, bath products and other personal care products. It is also added to cleaning products such as hand cleansers to give a lemon or orange fragrance and for its ability to dissolve oils.
D-limonene is used in food manufacturing and to mask the bitter taste of alkaloids. It is also commonly used as a dietary supplement.
Limonene is used as a solvent for cleaning purposes, such as removing oil from machine parts, because it is produced from a renewable source, such as the by-product of orange juice production. It also has applications as a paint stripper, and as a fragrant alternative to turpentine.