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Overview of α-Phellandrene and β-Phellandrene

Phellandrene is a monocyclic monoterpene organic compound. It is a colorless to pale yellow oily liquid, with a pair of isomers with similar molecular structures and similar chemical properties: α-Phellandrene (α-PA) and β-Phellandrene (β-PA). Both isomers have two optical activities, left-handed and right-handed, and their boiling points differ very little. Therefore, α-Phellandrene and β-Phellandrene usually as a mixture of exist in plants. α-PA is easily decomposed by distillation at atmospheric pressure, and its optical rotation will also decrease significantly after prolonged exposure to air, so it needs to be stored in a sealed container.

Natural phellandrene, its dextrorotatory form is commonly found in plant oils such as cinnamon oil, ginger oil, elemi oil, and cumin oil. The levorotatory form is commonly found in eucalyptus oil, star anise oil, bay leaf oil, and pepper oil. According to research¹, natural α-Phellandrene has a higher content in volatile oils such as eucalyptus leaf oil, bay leaf oil, fennel oil, and Chinese fir oil. β-Phellandrene has a higher content in tree species such as pine and hemlock.

The synthesis of α-Phellandrene can be achieved through catalytic production using carvone. Recent study has shown that a high-throughput synthesis of α-Phellandrene can be achieved through A Three-step Sequential Continuous-flow Reaction Process². β-Phellandrene is synthesized via the pyrolysis of β-Pinene or by a series of reactions starting with Cyclohexene as the raw material.

Fine Chemical Applications – Flavors and Fragrances

Natural phellandrene is often accompanied by a natural aroma, which is characterized by citrus, fresh mint, pepper spicy, and woody scents³. It is used as a precursor in the synthesis of fragrances. The flavor industry mainly uses α-Phellandrene as a primary raw material commodity, which meets the regulatory requirements for the use of food flavors in various countries.

Phellandrene has highly reactive conjugated double bonds. α-Phellandrene can be added to inner-ring conjugated double bond to produce a compound containing Meng’s alkane glycol, which creates a cooling sensation on the skin and is often used in personal care product formulations. The oxidation product of the exocyclic double bond of β-Phellandrene possesses woody and fresh mint notes. Due to its conjugated double bonds, Phellandrene can be used in the synthesis of advanced fragrances such as Butenone, Methyl acrylate, and Acrylic aldehyde through Diels-Alder reactions and addition reactions with dienes⁴.

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Fine Chemical Applications – Stereochemistry

The conjugated double bond structure of phellandrene, especially α-Phellandrene, makes it easily undergo Diels-Alder reactions with dienes, providing C₁₀ molecular skeletons, as well as internal and external double bonds. This characteristic makes phellandrene highly valuable in the fields of intermediate synthesis application and Asymmetric Catalysis.

The synthetic Menthol is an important raw material to produce fine fragrance and medicinal compounds. Menthol can be synthesized by converting α-Phellandrene or β-Phellandrene into Menthone or Menthenone, both of which contain a menthol skeleton^{5, 6}. Another synthesis route involves the hydrogen chloride addition of β-Phellandrene, followed by a series of reactions and hydrogenation to produce (-)-Menthone, which can then be reduced to synthesize Menthol⁷.

Chiral ligands are an important tool in asymmetric catalysis for constructing chiral compounds. (R)-(-)-α-Phellandrene can undergo a [4+2] cycloaddition reaction with 2-naphthyl acetylenecarboxylate to synthesize Chiral Dienes that can be used as ligands in rhodium-catalyzed asymmetric addition reactions⁸. It can also react with Ethyl propiolate and Dimethylaluminum chloride for the preparation of chiral diene-rhodium (Rh) metal catalysts⁹.

Agricultural Application – Feed Additives

Phellandrene has medicinal value. Currently, it has been shown that α-Phellandrene can inhibit the growth of human liver cancer cells¹⁰. Orange blossom essential oil containing α-Phellandrene and β-Phellandrene is used in health supplements to improve sleep and memory impairment¹¹. Purified terpenes containing phellandrene can be combined with gymnosporine (Psilocybin) to form new derivatives for antidepressant potential and the treatment of anxiety disorders¹². As an active terpene compound, phellandrene is more widely used in agriculture.

Currently, α-Pinene has been proven to have significant antitussive and expectorant effects. It can also kill fungi and inhibit common pathogenic bacteria in livestock such as Staphylococcus aureus and Escherichia coli by inhibiting the biosynthesis of fungal DNA, RNA, polysaccharides, and ergosterol. When combined with phellandrene, its synergistic effect becomes even more prominent.

Relevant experiments have shown that¹³ feeding pig feed containing α-Pinene (with a content of 50 ppm) had the lowest incidence of common diseases compared to the control group. On the other hand, α-Phellandrene, as a traditional flavoring, can promote animal feeding, while β-Phellandrene has an anti-parasitic effect. Comparative experiments have shown that the feed additive compound of phellandrene and α-Pinene has significantly improved the unsaturated fatty acid content of pork and improved its taste compared to the antibiotic control group and the blank control group. In comparative experiments for poultry breeding enhancement¹³, the feed additive containing α-Pinene and phellandrene significantly reduced the incidence of bronchitis in chickens, greatly improved their survival rate, and effectively improved the meat’s taste.

The natural activity of volatile organic compounds (VOCs) from plant is also applied in plant protection and fungicide formulations. Research on the bacteriostatic mechanism of α-Phellandrene against blue mold and gray mold on tomato plants has shown that¹⁴ α-Phellandrene changes the permeability of the cell membrane of pathogen, degrades the cell wall, and then destroys the cell membrane, causing leakage of intracellular substances and ultimately exerting a bacteriostatic effect.

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Agricultural Application – Pests Control

Thrips, a common pest in mango, strawberry, and flower cultivation, can threaten almost all vegetable and flower crops. Thrips can carry viruses, such as Tomato spotted wilt virus (Tospovirus), which can cause incurable damage to tomatoes. Currently, one method for controlling thrips is to use insecticides containing potassium soap or pyrethroid plant extracts for extermination. However, since thrips can hide under leaf veins, large amounts of insecticide are required, and not all pests can be effectively contacted. Another method of control is to use biological control, by using natural enemy from the Amblyseius genus to hunt and kill thrips. These traditional methods may have issues such as excessive pesticide use with incomplete elimination of pests or secondary pest problems.

A newer method of pest control is to use semi-synthetic antibiotic microemulsion products containing Methylamino avermectin. The products have a strong target specificity and is environmentally degradable. It can effectively kill populations of thrips. Natural repellents containing α-Phellandrene and α-Pinene have also become a new development direction.

In research with relevant plant volatiles¹⁵, the avoidance rates of α-Pinene and α-Phellandrene on adult thrips were 63.33% and 78.33%, respectively. In mangoes, the volatile monoterpenoid with the highest avoidance rate against thrips was 3-Carene, reaching up to 80.00%¹⁵. Compound formular of several terpenoid monomers are expected to become the main biobased ingredients of natural repellents against thrips in the future. These products may be used in conjunction with Methylamino avermectin insecticide microemulsion to effectively prevent damage caused by thrips infestations.

One of the main components of lavender, β-Phellandrene, shows a defensive effect against aphids. Through odor selection research on the main pest of lavender Rhopalosiphum padi and its natural enemy Harmonia axyridis in the flower bud stage, it was found that¹⁶ β-Phellandrene, β-Caryophyllene, and Limonene have significant effects in repelling aphids and attracting ladybugs. After spraying with Methyl jasmonate solution, the number of terpenes in lavender significantly increased, with β-Phellandrene content increasing by 500%, β-Caryophyllene by 150%, and Limonene by 250%. Compared to the blank control group, the avoidance effect was enhanced by 15.3%. The higher the percentage of the three monomers, the more prominent the avoidance effect. Additionally, β-Phellandrene showed a more significant attraction effect towards Harmonia axyridis¹⁶.

Anoplophora glabripennis (Motsch.) causes serious damage to protective forests and fast-growing forests. In China, protective forests are mostly destroyed by the beetle’s harm¹⁷, which directly leads to a 25% drop in timber prices due to the insect holes it creates in standing trees. Currently, the main methods for controlling the beetles include spraying with deltamethrin solution, using imidacloprid powder, or using maple trees (Acer negundo L. and Acer tataricum subsp. ginnala) as bait wood for trapping. Research have shown that¹⁸ a formula composed of α-Phellandrene, Nonanal, Geranyl acetone, and 2-undecyloxy-1-ethanol (a male insect pheromone of the Monochamus alternatus Hope beetle) had the best lure effect.

In lure research conducted on Empoasca vitis, α-Phellandrene, γ-Terpinene, Eucalyptol, cis-3-hexenyl acetate, 3-Octanone, and Caryophyllene were found to effectively attract the insect, with α-Phellandrene displaying a significant attractant effect¹⁹. The six-component blend of the above monomers was more effective in attracting Empoasca vitis than individual components. Empoasca vitis is one of the main bugs of tea trees, and adult insects feed on the buds and leaves, causing tea trees growth retardation, wilting, and severe damage to tea production and quality. Currently, chemical control is the main method of prevention and control, with strict requirements on pesticide dosage. Plant-based attractants have the potential to replace traditional color plate trapping methods and more accurately lure and kill bugs.

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