What Is D-Limonene?
D-limonene, a monocyclic monoterpene, is a key component of essential oils found in citrus peels, characterized by its optically active forms, including D- and L-limonene. The D-form is particularly noted for its lemony fragrance, whereas dipentene refers to the racemic mixture of these isomers. D-limonene predominates in oils from orange peel, lemon, and bergamot, L-limonene in pine needle and huckleberry oils, and dipentene in camphor and turpentine oils.
Physicochemical Properties of D-Limonene
As a cyclic terpene, D-limonene is renowned for its distinct citrus aroma, found primarily in citrus peel. Its properties make it an effective solvent in various applications, capable of dissolving fats and oils.
1. Name
English Name: Limonene
IUPAC Name: 1-methyl-4-(1-methylethenyl)-cyclohexene
2. Molecular Formula
C10H16
3. Molecular Weight
136.23 g/mol
4. Melting Point
-74.35°C
5. Solvent Solubility
Insoluble in water, but soluble in alcohols
Uses of D-Limonene
D-limonene finds extensive use as a flavoring agent in food, beverages, and bath products, and as a solvent in industrial applications due to its unique aroma and solvent properties.
1. Use as a Flavoring Agent
It is a popular flavoring agent in citrus-flavored foods and beverages, and is used in soaps, detergents, cosmetics, and air fresheners due to its fragrance. Its effectiveness in dissolving oily substances also makes it a valuable ingredient in hand soaps and kitchen detergents.
2. Use as a Synthetic Chemical Raw Material
Its ability to dissolve oils has led to its widespread use as a solvent in paints, printing inks, and other industrial applications.
3. Structural Similarity With Styrene and Use as a Styrofoam Recovery Agent
Due to its structural similarity to styrene, D-limonene can dissolve styrene foam, making it a useful recycling agent for styrofoam.
Structure of D-Limonene
D-limonene is a chiral molecule with two enantiomers, existing primarily in citrus peels. Its molecular formula is C10H16. The D-enantiomer is responsible for the strong citrus odor, whereas the racemic form is known as dipentene.
It features two unconjugated C=C double bonds, contributing to its reactivity and susceptibility to oxidation.
Other Information on D-Limonene
How D-Limonene Is Produced
D-limonene is naturally extracted from citrus peels through mechanical squeezing, steam distillation, or chemical synthesis, yielding an oil rich in D-limonene along with other components such as carboxylic acids, aldehydes, and ketones.
(1) Extraction
The essential oil is extracted from citrus peels through mechanical squeezing and distillation.
(2) Steam Distillation
This process involves steam distilling the citrus peel, then cooling the vapor to separate the oil.
(3) Chemical Synthesis
Chemical synthesis methods include the dehydration of ethanoic acid, hydrohalogenation of isoprene, and hydrolysis of β-pinene.