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Pinene

Pinene is a bicyclic monoterpene hydrocarbon with the molecular formula C₁₀H₁₆, occurring naturally as two primary structural isomers, α-pinene and β-pinene, which are major constituents of the essential oils in pine trees and other conifers.^[1]^[2] α-Pinene features an endocyclic double bond in its bicyclo[3.1.1]hept-2-ene structure, while β-pinene has an exocyclic double bond.^[1]^[2] Both exist as enantiomers that influence their optical activity and biological interactions.^[3] These isomers are colorless liquids with a characteristic turpentine-like odor, insoluble in water but soluble in organic solvents, and they play essential roles as plant metabolites in species such as Pinus trees and Camellia sinensis.^[1]^[2] Pinene's abundance in nature makes it a principal component of turpentine oil, from which it is extracted for industrial use as a solvent, flavoring agent, and fragrance ingredient in products like perfumes and food additives.^[2] Beyond commercial applications, pinenes exhibit notable biological activities, including antimicrobial, anti-inflammatory, and antioxidant properties, positioning them as promising natural compounds for therapeutic development, such as in combating bacterial infections or reducing oxidative stress.^[4]^[3] Their chemical versatility also serves as a scaffold in organic synthesis for pharmaceuticals and insecticides, highlighting their significance in both natural ecosystems and human innovation.^[5]

Properties

Physical Properties

Pinene has the molecular formula C₁₀H₁₆ and a molar mass of 136.23 g/mol for both its α- and β-isomers.^[1]^[6] Both isomers appear as clear, colorless liquids at room temperature, often exhibiting a pale yellow tint in commercial samples, and possess a characteristic pine-like or turpentine odor.^[1]^[6] They are sparingly soluble in water, with solubility values around 2.5 mg/L at 25 °C for α-pinene, but readily dissolve in organic solvents including ethanol, diethyl ether, chloroform, benzene, and glacial acetic acid.^[1]^[6] The physical constants differ slightly between the isomers, as summarized below:

Property	α-Pinene	β-Pinene
Density	0.858 g/cm³	0.860 g/cm³ at 25 °C
Boiling Point	156 °C at 760 mmHg	166 °C at 760 mmHg
Melting Point	-62.5 °C	-61.5 °C

These values reflect standard conditions and contribute to the isomers' volatility and handling in industrial applications.^[1]^[6] As chiral molecules, the enantiomers of pinene display optical activity; for example, (+)-α-pinene has a specific rotation of +33.52° (in ethanol at 20 °C), while (+)-β-pinene shows +28.6°.^[1]^[6]

Chemical Properties

Pinene is an unsaturated bicyclic monoterpene hydrocarbon with the molecular formula C₁₀H₁₆, characterized by a bicyclo[3.1.1]heptane skeleton featuring one or more carbon-carbon double bonds. This structure imparts strain to the ring system, contributing to its distinctive reactivity profile.^[5] Pinene exhibits chirality due to its asymmetric carbon atoms, existing in enantiomeric forms for both α- and β-isomers. The α-pinene enantiomers are (1R,5R)-(+)-α-pinene (CAS 7785-70-8) and (1S,5S)-(−)-α-pinene (CAS 7785-26-4), while the β-pinene enantiomers are (1R,5R)-(+)-β-pinene (CAS 19902-08-0) and (1S,5S)-(−)-β-pinene (CAS 18172-67-3).^[7]^[8]^[9]^[10] Under normal ambient conditions, pinene is relatively stable as a clear, colorless liquid, but it is sensitive to oxidation—particularly photooxidation in the presence of atmospheric oxidants like ozone and hydroxyl radicals—and decomposes upon heating, releasing acrid fumes. It also shows vulnerability to light-induced degradation, which can accelerate oxidative changes.^[11]^[12] As a non-polar hydrocarbon with a topological polar surface area of 0 Å² and no hydrogen bond donors or acceptors, pinene is highly lipophilic, evidenced by its logP value of approximately 4.8 for α-pinene and 4.2 for β-pinene, rendering it insoluble in water but miscible in organic solvents. This lipophilicity underpins its role as a predominant volatile component in essential oils from coniferous plants, where it contributes to the oils' non-aqueous, hydrophobic nature.^[4] The chemical reactivity of pinene stems from its endocyclic or exocyclic double bonds and the strained four-membered ring bridge, making it susceptible to acid- or thermally induced isomerization (e.g., α- to β-pinene or to camphene), cationic polymerization via carbocation intermediates, and electrophilic addition reactions across the unsaturated sites.^[5]^[13]^[14]^[15]

Isomers

α-Pinene

α-Pinene is a bicyclic monoterpene hydrocarbon with the molecular formula C₁₀H₁₆, characterized by a bicyclo[3.1.1]heptane skeleton featuring bridges of three, one, and one carbon atoms, resulting in a fused four-membered ring system. The structure includes three methyl groups attached at positions 2, 6, and 6, and an endocyclic double bond located between carbons 2 and 3 within the larger ring.^[1]^[16] This compound exists as a pair of enantiomers due to chiral centers at the bridgehead carbons 1 and 5. The naturally occurring dextrorotatory form is (1R,5R)-(+)-α-pinene, while the levorotatory enantiomer is (1S,5S)-(−)-α-pinene, with both forms common depending on the source; the (−) form predominates in European pine essential oils, while the (+) form is more abundant in North American ones.^[17]^[18] The enantiomers exhibit optical rotations of approximately +51° and –51° for the (+) and (–) forms, respectively.^[19] α-Pinene is more abundant in nature compared to its isomer β-pinene, constituting a major component of many plant-derived essential oils and recognized as one of the most widespread terpenoids. In many conifer essential oils, α-pinene typically constitutes 50-70% of total pinenes.^[20]^[18]^[1] Its systematic IUPAC name is 2,6,6-trimethylbicyclo[3.1.1]hept-2-ene. Characteristic spectroscopic data include ¹H NMR signals in CDCl₃ showing a methyl singlet at δ 1.67 (3H, =C-CH₃), gem-dimethyl singlet at δ 1.26 (6H), along with olefinic proton at δ 4.95–5.05 (1H, br s).^[1]

β-Pinene

β-Pinene is a bicyclic monoterpene distinguished from its α-isomer by the presence of an exocyclic double bond at carbon 2, forming a methylene group (=CH₂) that extends outside the ring system. This structural feature is part of a bicyclo[3.1.1]heptane core with geminal methyl groups at the 6-position, resulting in a more open configuration and differing ring strain compared to α-pinene's endocyclic double bond between carbons 2 and 3.^[6]^[16] The IUPAC name for β-pinene is 6,6-dimethyl-2-methylidenebicyclo[3.1.1]heptane.^[6] β-Pinene possesses two stereogenic centers at carbons 1 and 5, yielding a pair of enantiomers: (1R,5R)-(+)-β-pinene and (1S,5S)-(−)-β-pinene. The (1S,5S)-(−)-enantiomer predominates in natural sources.^[21]^[22]^[23] In essential oils, β-pinene occurs less frequently and in lower concentrations than α-pinene, often comprising 20-40% of the total pinene content.^[24]^[6] Unique spectroscopic identifiers for β-pinene include the characteristic signals of its exocyclic methylene protons in the ¹H NMR spectrum, appearing as two closely spaced singlets near 4.65 and 4.70 ppm (in CDCl₃), which differ from the olefinic proton signal of α-pinene around 5.0 ppm. In IR spectroscopy, the exocyclic C=C stretch appears at approximately 1640 cm⁻¹, providing another means of distinction from α-pinene's endocyclic counterpart.^[6]

Biosynthesis

Natural Biosynthesis

The natural biosynthesis of pinene occurs primarily in plants through a specialized branch of the isoprenoid pathway, starting with the formation of geranyl pyrophosphate (GPP), a C10 precursor, via the condensation of isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP) catalyzed by geranyl diphosphate synthase (GPPS). GPP then isomerizes to linaloyl pyrophosphate (LPP), an activated intermediate, in a process facilitated by pinene synthase (PS). This enzyme promotes the cyclization of LPP to yield the bicyclic carbocation intermediate characteristic of pinene, which loses a proton to form either α-pinene or β-pinene depending on the PS variant and stereochemistry.^[5] Pinene synthase enzymes, belonging to the terpene synthase family, are highly specific and often produce pinene as the major product alongside minor monoterpenes; for instance, a PS from Artemisia annua converts GPP predominantly to (-)-β-pinene (94%) with trace (-)-α-pinene. GPPS ensures the availability of GPP, and both enzymes are encoded by plant nuclear genes, with PS typically featuring a plastid-targeting transit peptide. These enzymes exhibit regioselectivity and stereospecificity, enabling the production of enantiomerically pure pinenes essential for their biological functions.^[5]^[25] This biosynthetic process is localized in the plastids of plant cells, where the methylerythritol phosphate (MEP) pathway predominates for generating IPP and DMAPP, though cross-talk with the cytosolic mevalonate pathway can supplement precursors. Pinenes produced serve an evolutionary role as defense compounds, repelling herbivores and inhibiting microbial pathogens through their volatility and antimicrobial properties, thereby enhancing plant survival in natural ecosystems.^[25]^[5]^[26]

Microbial Biosynthesis

Microbial biosynthesis of pinene involves the engineering of microorganisms, primarily Escherichia coli and yeast species, to produce this monoterpene through synthetic biology approaches that mimic aspects of the natural terpenoid pathway.^[27] Researchers heterologously express plant-derived enzymes such as pinene synthases (PS) from species like Pinus taeda and geranyl diphosphate synthases (GPPS) to convert precursors like geranyl diphosphate (GPP) into pinene, often optimizing the mevalonate or methylerythritol phosphate pathways for enhanced precursor supply.^[27] Combinatorial expression strategies, including fusion proteins of GPPS and PS, have been employed to improve efficiency by channeling intermediates directly to product formation.^[27] A seminal study in 2014 by researchers at the Georgia Institute of Technology and the Joint BioEnergy Institute demonstrated the feasibility of pinene production in E. coli through combinatorial expression of three PS variants (P. taeda, Abies grandis, Picea abies) and three GPPS enzymes from the same sources, achieving titers up to 32 mg/L with an A. grandis GPPS-PS fusion— a sixfold improvement over prior efforts.^[27] This work highlighted the importance of enzyme compatibility and fusion designs for yield optimization in bacterial hosts.^[27] Post-2020 advances have focused on pathway optimization and genetic tools to boost titers and stability. In 2023, engineering E. coli by bioprospecting efficient PS (PtPS1 Q457L variant) and GPPS (AgGPPS), combined with N-terminal truncation of PS for better solubility, resulted in α-pinene titers of 1.035 g/L in a 1.3 L fed-batch bioreactor.^[28] Similarly, a 2025 study utilized CRISPR/Cas9 and lambda-Red recombineering to chromosomally integrate the pinene pathway in E. coli DH411, optimizing gene copy ratios and fermentation conditions to reach 436.68 mg/L in a 5 L fermenter, emphasizing stable, high-density production.^[29] Efforts in yeast, such as Saccharomyces cerevisiae, have also progressed with dynamic regulation of competing pathways, achieving a titer of 1.8 g/L in a 3-L bioreactor in an optimized strain reported in 2025.^[30] These microbial systems offer advantages for sustainable pinene production, utilizing renewable feedstocks like glucose to generate the compound without relying on chemical solvents or plant extraction, potentially enabling scalable, eco-friendly alternatives for industrial applications as of 2025.^[28]^[29]

Occurrence

In Plants

Pinene, particularly its α- and β-isomers, is widely distributed in the Pinaceae family, which includes coniferous trees such as pines (Pinus species), where it constitutes a major component of essential oils from needles and resins.^[31] This distribution extends to various herbs and angiosperms, including members of the Lamiaceae and Rutaceae families, reflecting its role in diverse plant taxa.^[32] In conifers like Pinus species, pinene is abundant in pine needle oils, with concentrations reaching up to 60%, as seen in Pinus flexilis where α-pinene comprises 37.1% and β-pinene 21.9%.^[31] Turpentine oil derived from pine resins is dominated by α-pinene, typically at 58-65%, underscoring its prevalence in these sources.^[1] Other notable plant sources include Cannabis sativa, where α-pinene is a primary constituent of essential oils alongside myrcene and β-ocimene.^[33] Salvia officinalis (sage) exhibits varying α-pinene levels depending on chemotype, ranging from 2% in low producers to over 20% in high-α-pinene variants.^[34] Similarly, Sideritis species, such as S. bilgerana, contain high levels of β-pinene (up to 51.2%) and α-pinene (30.2%) in their essential oils.^[32] In makrut lime (Citrus hystrix) leaves, β-pinene is prominent at approximately 27.4% of the essential oil composition.^[35] Ecologically, pinene serves as a key defense compound in plants, acting as an insect repellent by deterring herbivores and pests through its volatile emissions, and exhibiting antimicrobial properties that inhibit bacterial and fungal growth on plant surfaces.^[36] This biosynthetic production via the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway enables plants to synthesize pinene as part of their terpenoid defenses.^[5]

In Other Sources

Pinene, particularly its α- and β-isomers, occurs in various non-plant natural sources, though in lower abundances compared to its prevalence in terrestrial vegetation.^[37] Microbial production of pinene serves as a secondary metabolite in certain bacteria and fungi. Terpene synthases capable of generating pinene are widely distributed across bacterial genomes, enabling natural synthesis in diverse prokaryotic species.^[38] Soil actinomycetes, including genera like Streptomyces and Nocardia, also produce biologically active terpenoids such as pinene as part of their metabolic repertoire.^[39] In animal sources, pinene appears in trace amounts through metabolic processes or as components of pheromones. Insects, particularly bark beetles like the mountain pine beetle (Dendroctonus ponderosae), metabolize α-pinene via cytochrome P450 enzymes such as CYP6DE1 to produce aggregation pheromones like trans-verbenol.^[40] In mammals, including humans and rodents, pinene is metabolized following dietary intake from plant sources, yielding primary metabolites such as verbenol, myrtenol, and pinocarveol, often detected in urine after exposure.^[41]^[42] As a volatile organic compound (VOC), pinene is emitted into the atmosphere from forest ecosystems, where it plays a key role in secondary organic aerosol (SOA) formation through oxidation processes.^[37] These emissions, primarily α-pinene, arise from soil, litter, and vegetative sources, contributing to atmospheric chemistry and particle nucleation in boreal regions.^[43] Pinene is rarely detected in algae and other marine organisms, but trace occurrences have been noted in red macroalgae, where α- and β-pinene represent common bicyclic monoterpenes among volatile emissions.^[44] Marine measurements over ocean blooms have also shown correlations between α-pinene and other monoterpenes, suggesting limited biogenic production by phytoplankton.^[45]

Production

Natural Extraction

Pinene, particularly its α and β isomers, is primarily extracted from natural sources such as the resin and needles of coniferous trees through physical separation techniques that isolate the volatile terpenes without chemical alteration.^[1] The production of turpentine, a key source of pinene, traces back to ancient civilizations, where resin from pine trees was collected and distilled for use in medicine and as a solvent.^[46] In modern times, extraction has evolved to include systematic tapping of live pines and fractional distillation to separate pinene isomers from the crude mixture.^[46] Steam distillation remains the predominant method for isolating pinene from pine resin and needles, involving the passage of steam through the plant material to volatilize the essential oils, which are then condensed and separated. This process is widely applied to produce gum turpentine from tapped resin of species like Pinus palustris, yielding an oil where α-pinene constitutes 58-65% and β-pinene about 30%.^[1] For pine needles, such as those from Pinus pinaster, steam distillation at atmospheric pressure for over an hour extracts essential oils with α-pinene comprising 22.5-40.5% of the isolated oil, depending on material freshness.^[47] Following initial distillation, fractional distillation under vacuum refines the mixture, enabling separation of α-pinene (boiling point ~155°C) from β-pinene and other terpenes based on their differing volatilities.^[48] Solvent extraction serves as an alternative or complementary approach, particularly for essential oils from herbaceous plants containing pinene, using non-polar solvents like hexane or polar ones like ethanol to dissolve and recover the terpenes. For instance, a 1:1 hexane-acetone mixture at room temperature extracts terpenoids from pine tissues, while ethanol is employed for compounds like α-pinene from sources such as rosemary leaves, offering faster kinetics than distillation in some cases.^[49]^[50] Extraction yields and pinene content vary significantly due to factors like seasonal changes and plant part used; resin from tapped pines generally provides higher α-pinene concentrations (up to 65%) compared to needles (around 25-40%), as resin is richer in oleoresin.^[1]^[47] Seasonal fluctuations influence composition and yields. These variations underscore the importance of timing and source selection in commercial operations to maximize efficiency.^[51]

Chemical Synthesis

Pinene, particularly α-pinene, is commonly synthesized chemically through the isomerization of β-pinene, leveraging the greater thermodynamic stability of the α-isomer. This classical method employs either acid or base catalysts to facilitate the rearrangement. For instance, base-catalyzed isomerization using potassium 3-aminopropylamide (KAPA) at 25°C converts (−)-β-pinene to (−)-α-pinene in 93% yield with >92% enantiomeric excess, preserving chirality from the natural precursor under inert atmosphere conditions.^[52] Acid-catalyzed variants, such as with phosphoric acid or aluminum-supported catalysts, achieve similar conversions but often require higher temperatures (up to 200°C) and may produce side products like camphene, with selectivities toward α-pinene exceeding 80% under optimized heterogeneous catalysis.^[53]^[54] Another classical route involves the cyclization of myrcene, an acyclic monoterpene, under cationic conditions to form the bicyclic pinene structure. Acid catalysts, such as Lewis acids or protic acids, promote the electrophilic addition and ring closure, though this pathway suffers from competing rearrangements leading to limonene or other isomers. Yields for pinene are typically modest due to limited regioselectivity. Laboratory-scale total syntheses, such as the 1978 route by Thomas and Fallis, provide a de novo approach starting from simple acyclic precursors via sequential alkylation, cyclization, and elimination steps to yield racemic α- and β-pinene, establishing a general framework for bicyclic terpenes but with low overall yields due to multi-step complexity.^[55] Modern synthetic strategies emphasize asymmetric synthesis to access enantiopure pinenes, crucial for applications requiring specific stereochemistry. Chiral catalysts enable enantioselective cyclizations or allylations with high enantiomeric excesses in targeted steps, though overall yields for pure enantiomers often remain moderate owing to purification challenges and side reactions. Catalytic hydrogenation of related precursors like limonene epoxides has been explored to generate pinane skeletons, followed by dehydration, but stereocontrol is inconsistent without chiral ligands.^[56] Key challenges in pinene synthesis include achieving high stereoselectivity amid the molecule's four chiral centers and minimizing skeletal rearrangements, which reduce yields in non-isomerization routes. Recent developments focus on green chemistry, such as flow reactor systems for continuous isomerization of β-pinene using reusable heterogeneous catalysts, enhancing efficiency and reducing waste compared to batch processes. One-pot tandem catalysis with MgO and mesoporous supports has enabled selective transformations to pinene derivatives with 63% yields, promoting sustainability in terpene chemistry.^[57]^[58]

Chemical Reactions

Reactions of α-Pinene

α-Pinene, with its endocyclic double bond, undergoes a variety of chemical transformations that exploit its strained bicyclic structure, leading to valuable intermediates in terpene chemistry.^[16] Oxidation of α-pinene is a key reaction, typically targeting the double bond or allylic positions to yield products such as verbenone and pinene oxide. Epoxidation to pinene oxide proceeds stereospecifically with peracids such as m-chloroperbenzoic acid (m-CPBA), yielding high selectivity under mild conditions, where the reaction occurs preferentially on the bottom face of the molecule.^[16] Catalytic epoxidation using air over nanosized Co₃O₄ at 70 °C achieves up to 70.75% conversion with 87.68% selectivity to pinene oxide, alongside minor verbenol and verbenone.^[16]^[59] Allylic oxidation to verbenone can be achieved using air or molecular oxygen in the presence of catalysts. This transformation, often mediated by transition metals like silica-titania co-gels with tert-butyl hydroperoxide, achieves approximately 60% selectivity to verbenone. A representative catalytic process is illustrated by the equation:

\alpha\text{-Pinene} + \ce{O2} \xrightarrow{\text{catalyst}} \text{verbenone}

Isomerization of α-pinene under acidic conditions rearranges the carbon skeleton to form monocyclic or bicyclic isomers such as camphene and limonene. The conversion to camphene is efficiently catalyzed by heterogeneous acids like carbon-based solid acids or ion-exchange resins, with conversions exceeding 99% and selectivities up to 80% in solvent-free systems at moderate temperatures.^[60]^[61] This reaction proceeds via carbocation intermediates, where protonation of the double bond leads to skeletal rearrangement, and is enhanced by Lewis acids such as Ce/SnO₂ in solvents like acetone.^[16] Limonene formation occurs as a parallel pathway under similar acidic catalysis, though with lower selectivity compared to camphene in optimized systems.^[62] Hydrogenation of α-pinene saturates the endocyclic double bond to produce pinane, predominantly the cis isomer, using heterogeneous metal catalysts under mild pressures. Nickel-based catalysts, such as those prepared via electroless deposition or coated with ionic liquids, facilitate stereoselective hydrogenation with high cis-pinane yields (up to 95%) at 50–100°C and 1–10 atm of H₂.^[63]^[64] Palladium on carbon (Pd/C) also proves effective, with reaction kinetics showing first-order dependence on hydrogen pressure and α-pinene concentration at 0–100°C, enabling quantitative conversions.^[65] Ruthenium catalysts further enhance selectivity for cis-pinane in continuous processes.^[66] Polymerization of α-pinene involves cationic initiation to form dimers and higher oligomers used in resin production, leveraging the molecule's reactivity toward carbocation propagation. Lewis acidic ionic liquids, such as those with alkyl carboxylate groups, catalyze the process at room temperature, yielding terpene resins with controlled molecular weights and up to 90% conversion.^[67] Traditional aluminum halide systems (e.g., AlCl₃/SbCl₃ at -15°C) promote dimer formation with 80–90% yields and minimal higher oligomers, while incremental addition of monomer minimizes side reactions.^[68]^[69] These reactions typically produce low-molecular-weight polymers suitable for adhesives and coatings.^[16]

Reactions of β-Pinene

β-Pinene, distinguished by its exocyclic double bond, undergoes a variety of chemical transformations that exploit this structural feature, leading to valuable terpenoid derivatives. These reactions include isomerization to α-pinene, thermal decomposition to acyclic monoterpenes, electrophilic additions across the double bond, and selective oxidations yielding functionalized products such as nopinone, nopol, and myrtenal. Unlike α-pinene, the reactivity of β-pinene often favors ring-opening or cleavage at the exocyclic methylene, enabling industrial applications in fragrance and polymer precursor synthesis.^[16] Isomerization of β-pinene to α-pinene is typically facilitated by acid catalysts, such as hierarchical zeolites like MCM-22, which promote skeletal rearrangement under mild conditions (e.g., 100% conversion and 93.7% selectivity to α-pinene at 423 K). This process involves protonation of the exocyclic double bond, followed by 1,2-hydride shift and deprotonation to form the endocyclic isomer. While thermal isomerization can occur at higher temperatures (above 500 K), catalytic methods enhance efficiency and selectivity, avoiding side products like limonene.^[70]^[71] Pyrolysis of β-pinene at elevated temperatures (573–873 K) under low pressure yields myrcene as the primary product via a concerted retro-Diels-Alder mechanism, where the four-membered ring cleaves to form the acyclic diene. This endothermic reaction (ΔH ≈ +50 kJ/mol) proceeds without catalysts and is industrially significant for producing myrcene, a key precursor in synthetic rubber and fragrance synthesis, with yields up to 80% at 873 K. Minor byproducts include limonene and menthadienes from competing isomerization pathways. The reaction can be represented as:

\ce{β-pinene ->[pyrolysis, 400-600°C] (CH3)2C=CH2-C4H6-CH(CH3)-CH=CH2}

where the product is myrcene.^[72]^[73] Electrophilic addition reactions target the electron-rich exocyclic double bond of β-pinene. For instance, ozonolysis involves initial [3+2] cycloaddition of ozone, followed by cleavage to yield nopinone, a bicyclic ketone used in perfume synthesis, with high efficiency using ozone in low-temperature solvents (e.g., dichloromethane at -78°C). Similarly, the Prins reaction with formaldehyde under acid catalysis (e.g., ZnCl₂ or metal-exchanged zeolites) adds the hydroxymethyl group, producing nopol (2-(4-(hydroxymethyl)-1-methylcyclohex-3-en-1-yl)propan-2-ol) with selectivities over 90% at 353 K, serving as an intermediate for insecticides and surfactants.^[74]^[75]^[76] Oxidation of β-pinene also highlights its reactivity, producing myrtenal through allylic oxidation or epoxide rearrangement. Photooxidation or selenium dioxide-mediated processes selectively functionalize the double bond to form myrtenal (an α,β-unsaturated aldehyde) with yields around 50-70%, depending on conditions like solvent and oxidant concentration. This compound finds use in flavorings and as a synthetic building block. Nopinone emerges as a common product in broader oxidation schemes, such as with performic acid or atmospheric OH radicals, underscoring β-pinene's role in aerosol formation studies.^[77]^[78]^[79]

Applications

Industrial and Commercial Uses

Pinene, particularly α-pinene, serves as the primary component of turpentine, comprising 60-80% of its composition and enabling its widespread use as a solvent in oil-based paints, varnishes, and enamels.^[80] This solvency arises from pinene's ability to dissolve resins, waxes, and oils effectively, making it a key thinner for achieving desired consistencies in coatings and a cleaner for industrial equipment and brushes.^[81] In the chemical industry, turpentine-derived pinene acts as a raw material for further processing into varnishes and related products.^[82] In the fragrance and flavor sectors, α-pinene imparts a characteristic fresh, pine-like scent, finding applications in perfumes, colognes, and cleaning products.^[83] Its refreshing aroma also masks undesirable flavors in consumer goods such as chewing gum and confections, enhancing palatability while contributing subtle herbal notes to beverages and candies.^[84] β-Pinene similarly supports flavor profiles in food-grade additives, leveraging its woody, resinous qualities.^[85] As a polymer precursor, pinene undergoes dimerization and polymerization to form terpene resins used in adhesives and synthetic materials. β-Pinene-derived polymers, for instance, serve as tackifiers in hot-melt adhesives, providing biodegradability and renewability while improving adhesion and thermal stability.^[86] These resins are also incorporated into pressure-sensitive adhesives and coatings, offering tunable properties from natural sources.^[87] In pharmaceutical manufacturing, pinene acts as a key intermediate; for example, (−)-β-pinene is converted to (−)-menthol through industrial routes involving hydrogenation and cyclization.^[88] Similarly, α-pinene is isomerized to camphene and oxidized to produce camphor, a compound used in medicinal formulations.^[89] Global production of pinene, primarily extracted from turpentine, reaches approximately 100,000 tons per year (as of 2023), driven by sulfate turpentine yields of around 255,000 metric tons annually, with about 34% suitable for high-purity recovery.^[90]

Biofuel Uses

Pinene, particularly α-pinene, has been investigated as a high-energy-density biofuel suitable for spark-ignition engines due to its non-oxygenated hydrocarbon structure, offering a gravimetric energy content comparable to conventional gasoline. Pinene-derived fuels, such as its dimers, have an energy density similar to that of the high-performance jet fuel JP-10, making them promising renewable alternatives for transportation fuels.^[27] In a 2016 study by the Society of Automotive Engineers, α-pinene was tested in a single-cylinder spark-ignition engine, demonstrating stable combustion with reduced emissions of carbon monoxide and hydrocarbons compared to gasoline, while maintaining comparable power output and efficiency.^[91] Derivatives such as pinene dimers and polymers have been developed as high-density hydrocarbons specifically for aviation fuels, exhibiting a heating value of approximately 43 MJ/kg, which aligns closely with the requirements for sustainable aviation fuel (SAF) standards.^[92] These compounds serve as drop-in replacements for fossil-based jet fuels, requiring no engine modifications due to their compatible physicochemical properties, and are derived from renewable biomass sources like pine resin.^[27] The chemical stability of pinene-derived fuels supports reliable combustion performance in high-temperature environments.^[93] In the 2020s, advancements in microbial engineering have accelerated the production of pinene for SAF applications, with engineered bacteria enabling scalable biosynthesis from sugars, as highlighted in reviews of isoprenoid-derived biofuels. Recent efforts as of 2025 include rational engineering of Escherichia coli strains for stable and efficient α-pinene production.^[94]^[95] Pilot-scale demonstrations of these microbial pathways aim to integrate pinene into blended SAF formulations, potentially reducing lifecycle greenhouse gas emissions compared to petroleum-derived fuels.^[94]

Biological Activities

Pharmacological Effects

α-Pinene exhibits anxiolytic properties by modulating the GABAergic system, enhancing non-rapid eye movement sleep and reducing anxiety-like behaviors in animal models through interaction with GABAA receptors.^[96] In mice, oral administration of α-pinene has demonstrated hypnotic effects via GABAA-benzodiazepine receptor modulation, supporting its potential in alleviating anxiety disorders.^[96] The neuroprotective effects of pinene isomers, particularly β-pinene, have been observed in models of Alzheimer's disease, where it ameliorates pathology induced by intracerebroventricular streptozotocin through restoration of neurotransmitter balance and reduction of neuroinflammation.^[97] Recent preclinical studies have shown improved cognitive function and neuroprotection with β-pinene in animal models of Alzheimer's, though human clinical trials remain limited. Pinene demonstrates anti-tumor activity by inducing apoptosis in various cancer cells, such as those in human ovarian and cervical cancers, primarily through caspase activation and mitochondrial pathways.^[98]^[99] A 2022 study demonstrated that α-pinene promotes caspase-dependent cell death and inhibits proliferation in cervical cancer cells without significant toxicity to normal cells.^[99] Gastroprotective effects of α-pinene-rich extracts from pine sources protect against gastric damage in Helicobacter pylori infection models by inhibiting H. pylori growth in gastric tissue, thereby reducing mucosal damage.^[100] Research from 2019 indicates that these effects are associated with α-pinene's antimicrobial and gastroprotective properties.^[101] As a cytoprotective agent, pinene provides antioxidant defense against oxidative stress, scavenging reactive oxygen species like hydrogen peroxide and preventing cellular damage in various tissues.^[101] This property contributes to its broader protective role, overlapping with mild anti-inflammatory mechanisms in neuronal and gastric contexts.^[102]

Antimicrobial and Anti-inflammatory Effects

Pinene isomers, particularly α-pinene and β-pinene, exhibit notable antimicrobial properties against various bacterial and fungal pathogens. α-Pinene demonstrates inhibitory effects against Staphylococcus aureus, including methicillin-resistant strains (MRSA), and Escherichia coli, with minimum inhibitory concentrations (MICs) in the range of 0.25–0.5% for susceptible isolates. β-Pinene similarly shows activity against E. coli, including multi-resistant variants, and contributes to broader monoterpene efficacy against Gram-negative bacteria. These compounds also possess antifungal activity; for instance, β-pinene inhibits Candida species by interfering with cell wall synthesis via interaction with Δ-14-sterol reductase, while α-pinene effectively targets Candida albicans with MIC values around 0.125–0.25%. The primary mechanism involves disruption of microbial cell membranes, where α-pinene reduces membrane integrity, alters fluidity, and induces ion leakage, leading to cytoplasmic content release and cell death.^[103]^[56]^[4]^[104]^[105]^[106]^[107] In terms of anti-inflammatory effects, α-pinene suppresses pro-inflammatory cytokines such as tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in cellular models, reducing their production in lipopolysaccharide-stimulated macrophages. This modulation occurs primarily through inhibition of the NF-κB signaling pathway, which downregulates inflammatory mediator expression and nitric oxide release. Studies from 2020 confirmed these effects in rat models of myocardial inflammation, where pretreatment with α-pinene significantly lowered TNF-α, IL-6, and NF-κB levels in cardiac tissue compared to controls. β-Pinene shares similar cytokine-suppressive properties, contributing to overall terpene-mediated anti-inflammatory action.^[108]^[4]^[109]^[110] Pinene enhances the efficacy of conventional antibiotics against resistant strains through synergistic interactions. For example, α-pinene potentiates ciprofloxacin and mupirocin against MRSA and enteropathogenic E. coli, reducing MICs by up to 33-fold in combination therapies. This modulation likely stems from increased membrane permeability, facilitating antibiotic influx into bacterial cells. Such effects have been observed against multidrug-resistant (MDR) Gram-positive and Gram-negative pathogens, positioning pinene as a potential adjuvant in combating antimicrobial resistance.^[111]^[112]^[113]^[114] In vivo studies provide evidence of pinene's anti-inflammatory benefits in animal models of systemic inflammation. Administration of α-pinene in rodent models of induced inflammation, such as hypoxia or lipopolysaccharide challenge, reduced cytokine levels and improved tissue responses, with effects linked to NF-κB inhibition. Recent 2024 research via molecular docking suggests β-pinene's potential antiviral activity against SARS-CoV-2 by targeting viral proteases, highlighting its broader role in infection-related inflammation.^[115]^[116]^[117]

Safety and Toxicology

Toxicity Profile

Pinene exhibits low acute toxicity via oral administration, with an LD50 of 3.7 g/kg for α-pinene and 4.7 g/kg for β-pinene in rats, indicating minimal risk from single ingestions at typical exposure levels.^[6]^[1] Dermal exposure at high concentrations can cause skin irritation, potentially leading to allergic contact dermatitis in sensitive individuals, though this is uncommon at low doses used in consumer products.^[118] Inhalation of vapors may result in eye irritation and mild respiratory discomfort, with sensory irritation observed in human volunteers at concentrations around 450 mg/m³.^[119] Chronic exposure to pinene shows potential for respiratory sensitization, particularly in occupational settings with prolonged inhalation, though evidence is primarily from irritation rather than true allergic responses. In animal models, repeated dosing does not indicate carcinogenicity, as supported by 90-day inhalation studies in rats showing no tumor formation or genotoxic effects.^[120] Reproductive toxicity is minimal, with only questionable findings of reduced sperm counts in high-dose rat inhalation studies, and no significant developmental effects observed. Metabolically, pinene undergoes hepatic oxidation primarily via cytochrome P450 enzymes to form metabolites such as myrtenol and verbenol, which are rapidly excreted in urine, contributing to its low bioaccumulation potential.^[121] In humans, pinene is considered safe at low doses, holding Generally Recognized as Safe (GRAS) status from the FDA for use as a flavoring agent in food, with rapid elimination half-life of about 1.4 hours for key metabolites. However, high occupational exposure has been linked to dermatitis cases, emphasizing the need for ventilation and protective measures in industrial handling.^[122]

Regulatory Aspects

Pinene, encompassing both α-pinene and β-pinene isomers, is registered under the European Union's REACH regulation, requiring manufacturers and importers to provide detailed safety data for volumes exceeding one tonne per year to ensure risk assessment and control measures.^[123]^[124] In the United States, the Food and Drug Administration (FDA) affirms α-pinene and β-pinene as generally recognized as safe (GRAS) for use as flavoring agents in food products, typically at low concentrations consistent with good manufacturing practices to maintain safety margins.^[125] As a volatile organic compound (VOC), pinene contributes to the formation of ground-level ozone and photochemical smog through atmospheric reactions with nitrogen oxides under sunlight, prompting inclusion in air quality management frameworks.^[126] Environmental regulations, such as the U.S. Environmental Protection Agency's (EPA) National Volatile Organic Compound Emission Standards for Aerosol Coatings, impose limits on VOC content in consumer products containing pinene to mitigate ozone nonattainment, with reactivity values assigned (e.g., 4.51 for α-pinene) to guide formulation compliance.^[127] Similarly, California's Air Resources Board regulates VOC emissions from consumer products, restricting pinene in categories like air fresheners and cleaners to reduce smog precursors. Occupational exposure to pinene, often evaluated through turpentine (a primary source containing 50-70% pinene), is governed by the Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL) of 100 ppm (560 mg/m³) as an 8-hour time-weighted average to prevent respiratory and skin irritation.^[128] Handling guidelines emphasize engineering controls like local exhaust ventilation, personal protective equipment (PPE) including chemical-resistant gloves and respirators for concentrations above the PEL, and monitoring to ensure compliance in industrial settings such as solvent and fragrance production.^[129] Internationally, pinene is subject to standards from the International Fragrance Association (IFRA), which recommends unrestricted use in most fragrance applications but requires monitoring of oxidation products like pinene oxide due to potential sensitization risks, based on safety assessments by the Research Institute for Fragrance Materials (RIFM).^[130] For biofuel applications, pinene derivatives serve as precursors in sustainable fuel production, falling under emerging export controls. As of 2025, regulatory updates under the EU's REACH CoRAP (Community Rolling Action Plan) 2025-2027 initiative include evaluations of terpenes like pinene to address potential environmental persistence, encouraging registrants to update dossiers with sustainability data by March 2025 to support bio-based production incentives aligned with the European Green Deal.^[131] These developments favor sustainable sourcing, such as from managed forestry or microbial synthesis, to meet criteria for low-carbon certifications in bioeconomy regulations.^[132]

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Neuroprotective effects of essential oils in animal models ... - PubMed
This systematic review evaluates recent advancements in understanding the neuroprotective role of EOs against Alzheimer's disease (AD) …
[98]
α-Pinene Induces Apoptotic Cell Death via Caspase Activation in ...
Sep 4, 2019 · The apoptosis results reveal, that the cancer cells at the human ovary with alpha-pinene induces the significant populations of apoptotic cells.
[99]
α-Pinene inhibits the growth of cervical cancer cells through its ...
Sep 8, 2022 · Our experiment proved that α-Pinene promoted apoptosis, which will be used to hopefully maximize the therapeutic strategies in clinical studies ...
[100]
Gastroprotective effect of phytoncide extract from Pinus ... - PubMed
Jun 12, 2020 · Phytoncide significantly inhibited the growth of H. pylori in gastro tissue, possibly due to the abundant α-pinene present in the phytoncide as detected by ...
[101]
Therapeutic Potential of α- and β-Pinene: A Miracle Gift of Nature
Nov 14, 2019 · This article aims to summarize the most prominent effects of α- and β-pinene, namely their cytogenetic, gastroprotective, anxiolytic, cytoprotective, ...
[102]
https://doi.org/10.3390/molecules17066305
[103]
Antibacterial Activity and Time-kill Kinetics of Positive Enantiomer of ...
The purpose of this research is to evaluate the antimicrobial activity of the positive enantiomer of α-pinene against strains of Staphylococcus aureus ATCC ...
[104]
β-pinene Enantiomers Against Candida SPP - PubMed
(+)-β-pinene has antifungal activity and most likely acts through interference with the cell wall; through molecular interaction with Delta-14-sterol reductase.
[105]
Antifungal effect of α-pinene alone and in association with ...
Mar 27, 2022 · Thus, this study strengthens α-pinene as a promising antifungal agent, as it exhibited strong inhibitory activity against Candida albicans ...
[106]
Antibiotic resistance modulation and modes of action of (-)-α-pinene ...
Apr 1, 2015 · Additionally, (-)-α-pinene decreases membrane integrity, which suggests that enhanced microbial influx is a secondary mode of action of (-)-α- ...
[107]
[PDF] Investigation of antifungal activity mechanisms of alpha- pinene ...
It has a wide range of biological activities, including antibacterial effects against. E.coli and S. aureus; antifungal effects against. C. albicans (Salehi ...
[108]
The effects of alpha-pinene on inflammatory responses and ...
The study found that α-pinene effectively reduces the production of inflammation markers such as IL-6, TNF-α, and nitric oxide. Additionally, α-pinene ...
[109]
Alpha-Pinene-encapsulated lipid nanoparticles diminished ...
Oct 29, 2024 · Additionally, α-pinene have also been shown to suppress the activation of inflammatory mediators including NF-κB, tumor necrosis factor α (TNF-α) ...
[110]
Protective effect of alpha-pinene against isoproterenol-induced ...
Jun 30, 2020 · Our results indicated that the pretreatment with AP significantly diminished TNF-α, IL-6, and NF-κB in the heart tissue when compared to control ...<|separator|>
[111]
Potentiation of the Activity of Antibiotics against ATCC and MDR ...
The present research aimed to evaluate the antibacterial and antibiotic-modulating activity of (+)-α-pinene and (-)-borneol against MDR bacterial strains.
[112]
Antibiotic potentiating action of α-PINENE and borneol against ...
The α-pinene and borneol showed a low antimicrobial action against EPEC and ETEC. •. Synergism was observed associating the substances with ciprofloxacin ...
[113]
[PDF] New Synergistic Combination Therapy of Mupirocin and α-Pinene ...
As a result, combinatory mixtures caused a 33-fold reduction of the MBC of the topical antibiotic when it was used against strains of multidrug-resistant MRSA.
[114]
[PDF] Biological Activities of α-Pinene and β-Pinene Enantiomers
In combination with commercial antimicrobials, ciprofloxacin plus (+)-α-pinene or (+)-β- pinene presented synergistic activity against MRSA whereas an ...
[115]
Alpha-Pinene-encapsulated lipid nanoparticles diminished ...
Oct 28, 2024 · Our results suggest that with the help of lipid nanoparticle encapsulation, APLNs possess a better pharmacological effect in anti-inflammation.
[116]
Alpha-pinene ameliorate behavioral deficit induced by early ... - Nature
Mar 17, 2024 · Alpha-pinene may have a protective effect via anti-inflammatory properties against the negative impacts of hypoxia on the developing brain.
[117]
[PDF] Molecular docking insights in beta pinene's fight against corona virus
Nov 3, 2024 · This study presents a novel approach by focusing on beta-pinene's potential as an antiviral agent specifically against the SARS-CoV- 2 main ...
[118]
[PDF] Pinene is a FLAMMABLE - Hazardous Substance Fact Sheet
▻ Very high exposure may affect the nervous system causing loss of coordination, dizziness, confusion, seizures and coma. ▻ alpha-Pinene may cause a skin ...
[119]
NTP Technical Report on the Toxicity Studies of α-Pinene (CASRN ...
This Toxicity Study Report summarizes the results of 2-week and 3-month inhalation toxicity studies with α-pinene in F344/N rats and B6C3F1/N mice.
[120]
[PDF] Safety Data Sheet - EPA OSC Response
Feb 15, 2023 · Carcinogenicity: Based on a 90-day toxicity study in rat, alpha-pinene is not expected to be carcinogenic for humans. Reproductive toxicity:.
[121]
Endothelial-dependent relaxation of α-pinene and two metabolites ...
Exposure of Mice to α-Pinene Increased Urinary Excretion of Two Oxidized Metabolites: Myrtenol and Verbenol. Following α-pinene inhalation exposure (1 ppm, 6 h ...
[122]
alpha-Pinene - Hazardous Agents - Haz-Map
"Turpentine and the monoterpenes (alpha-pinene, beta-pinene, 3-carene) are skin and mucous membrane irritants, and in high concentrations, are central nervous ...
[123]
https://echa.europa.eu/registration-dossier/-/registered-dossier/14724
[124]
https://echa.europa.eu/registration-dossier/-/registered-dossier/15934
[125]
Substances Added to Food (formerly EAFUS)
... GRAS status of flavoring substances. The FEMA number is provided here as a reference to FEMA's GRAS assessments. The GRAS Pub. No. is the FEMA GRAS ...Missing: dermatitis | Show results with:dermatitis
[126]
[PDF] Final Rule: Aerosol Coatings National Volatile Organic Compound ...
Jan 6, 2025 · Section 183(e) requires the EPA to control VOC emissions from certain categories of consumer and commercial products for purposes of reducing ...
[127]
National Volatile Organic Compound Emission Standards for ...
Jan 17, 2025 · ... VOC emissions contributing to ozone formation and ozone nonattainment. ... a-Pinene (Pine Oil), 80-56-8, 4.51. Methyl Methacrylate, 80-62-6 ...
[128]
Turpentine - NIOSH Pocket Guide to Chemical Hazards - CDC
OSHA PEL. TWA 100 ppm (560 mg/m3). Measurement Methods. NIOSH 1551. See: NMAM or OSHA Methods. Physical Description. Colorless liquid with a characteristic odor ...
[129]
https://www.osha.gov/chemicaldata/702
[130]
[PDF] RIFM fragrance ingredient safety assessment, α-pinene, CAS ...
Nov 25, 2021 · α-Pinene has been registered under REACH and additional data is available: 11.2.4.1. For CAS # 80-56-8 (ECHA, 2011a). A biodegradation test.<|separator|>
[131]
China to Launch First Marine Biofuel Export Quotas in 2025 to ...
China plans to issue its first export quotas for marine bunker fuel blended with biodiesel, aiming to bolster domestic biofuel producers affected by European ...
[132]
CoRAP 2025-2027 project: assessment of 28 chemical substances
Jan 6, 2025 · ECHA invites registrants to update their REACH registration dossiers with all relevant information before March 2025. Substances to be assessed: ...
[133]
Alpha-Pinene Market Trends | Future Outlook & Opportunities 2032
In December 2023, Braskem inaugurated a sustainable bio-based alpha-pinene production line in Brazil, integrating supercritical CO2 extraction technology and ...