PRODUCTS

D LIMONENE

CAS No. : 138-86-3
EC No. : 227-813-5

Synonyms:
1-Methyl-4-(1-methylethenyl)cyclohexene; 4-Isopropenyl-1-methylcyclohexene; p-Menth-1,8-diene; Racemic: dl-Limonene; Dipentene; 1-Methyl-4-(prop-1-en-2-yl)cyclohex-1-ene; limonene; limonen; D-Limonen; -Limonene; 5989-27-5; (R)--Limonene; -(4R)-Limonene; -carvene; (4R)-Limonene; D--Limonene; (D)-Limonene; (R)-Limonene; (R)-p-Mentha-1,8-diene; Citrene; -p-Mentha-1,8-diene; (R)-4-Isopropenyl-1-methyl-1-cyclohexene; D-Limonen; Carvene; Glidesafe; Glidsafe; Kautschiin; Refchole; -R-Limonene; Cyclohexene, 1-methyl-4-(1-methylethenyl)-, (4R)-; d-p-Mentha-1,8-diene; Limonene, D-; -4-Isopropenyl-1-methylcyclohexene; -Dipentene; (4R)-4-isopropenyl-1-methylcyclohexene; D-LIMONENE; D-Limonene; D-LİMONEN; D-Limonen; D-LIMONENE; D-Limonene; D-LİMONEN; D-Limonen; (R)--p-Mentha-1,8-diene; Biogenic SE 374; -alpha-Limonene; d-Limonene (natural); d-Limoneno [Spanish]; Limonene, -; (R)-1-Methyl-4-(1-methylethenyl)cyclohexene; -(R)-Limonene; Hemo-sol; (4R)--Limonene; CCRIS 671; r--limonene; D-LIMONENE; D-Limonene; D-LİMONEN; D-Limonen; D-LIMONENE; D-Limonene; D-LİMONEN; D-Limonen; FEMA No. 2633; EC 7; (R)-1-Methyl-4-(prop-1-en-2-yl)cyclohex-1-ene; HSDB 4186; D-1,8-p-Menthadiene; NCI-C55572; EINECS 227-813-5; p-Mentha-1,8-diene, (R)--; 4betaH-p-mentha-1,8-diene; -1,8-para-Menthadiene; AI3-15191; CHEBI:15382; 1-Methyl-4-(1-methylethenyl)cyclohexene, (R)-; Limonene; (4R)-1-methyl-4-(prop-1-en-2-yl)cyclohex-1-ene; Cyclohexene, 1-methyl-4-(1-methylethenyl)-, (R)-; (4R)-1-methyl-4-isopropenylcyclohex-1-ene; (R)--4-Isopropenyl-1-methylcyclohexene; (4R)-1-methyl-4-(1-methylethenyl)cyclohexene; -Limonene, stabilized with 0.03% tocopherol; Cyclohexene, 1-methyl-4-(1-methylethenyl)-, (theta)-; -Limonene, 96%, unstabilized; d-Limoneno; D LIMONENE; D-Limonene; D-LİMONEN; D-Limonen; D-limonene [JAN]; (4R)-4-isopropenyl-1-methyl-cyclohexene; Citrus stripper oil; Terpenes and Terpenoids, limonene fraction; Sulfate turpentine, distilled; Dextro-limonene; D-Limonene; citre ne; 65996-98-7; EINECS 266-034-5; limonene, (R)-isomer; D-Limonene Reagent Grade; DSSTox_CID_778; (4R)-1-methyl-4-prop-1-en-2-ylcyclohexene; D-LIMONENE; D-Limonene; D-LİMONEN; D-Limonen; D-LIMONENE; D-Limonene; D-LİMONEN; D-Limonen; (4R)-limonene derivatives; EC 227-813-5; CHEMBL449062; PARA-MENTHA-1,8-DIENE; (R)--Limonene, 95%; (R)--Limonene, 97%P; (R)--Limonene, >=93%; (R)--Limonene, analytical standard; (4R)-1-Methyl-4-(prop-1-en-2-yl)cyclohexene; (4R)-1-methyl-4-(1-methylvinyl)cyclohex-1-ene; J-502148; W-105295; Q27888324; (R)--Limonene, primary pharmaceutical reference standard; UNII-9MC3I34447 component; D-LIMONENE; D-Limonene; D-LİMONEN; D-Limonen; D-LIMONENE; D-Limonene; D-LİMONEN; D-Limonen; (R)--Limonene, purum, >=96.0% (sum of enantiomers, GC); (R)--Limonene, technical, ~90% (sum of enantiomers, GC); LEMOSOL; POLY/CLEAR SOLVENT; -(4R)-Limonene; -1,8-p-menthadiene,(R)--limonene; -4-isopropenyl-1-methylcyclohexene; -limonen; (4R)--limonene; (gamma)-Carvene; (R)--1-methyl-4-(1-methylethenyl)cyclohexene; (r)--p-mentha-8-diene; (R)-1-methyl-4-(1-methylethenyl)cyclohexene; (r)-cyclohexen; (theta)-cyclohexen; 1-methyl-4-(1-methylethenyl)-,(R)-Cyclohexene; 4-isopropenyl-1-methyl-cyclohexen; 4-isopropenyl-1-methylcyclohexene; D-LIMONENE; D-Limonene; D-LİMONEN; D-Limonen; D-LIMONENE; D-Limonene; D-LİMONEN; D-Limonen; citrene; Cyclohexene, 1-methyl-4-(1-methylethenyl)-, (R)-; cyclohexene,1-methyl-4-(1-methylethenyl)-,(R)-; Dextro-limonene; carvene; D-citrene; -limonene; -(4R)-limonene; -alpha-limonene; -R-limonene; (4R)--limonene; (R)--limonene; citrus D-limonene; D-limonene; D'limonene; D’limonene; D'limonene (high purity, low odor); D-limonene citreatt; limonene D pure; limonene dextro redistilled; D-limonene high purity low odor; D-limonene natural; D’limonene natural; D-LIMONENE; D-Limonene; D-LİMONEN; D-Limonen; D-LIMONENE; D-Limonene; D-LİMONEN; D-Limonen; dextro-limonene natural; D-limonene P&F; limonene R+ SP natural; limonene R+ ST; D-limonene Rectified; dextro-limonene redistilled; -p-mentha-1,8-diene; -para-mentha-1,8-diene; (R)--para-mentha-1,8-diene; D-para-mentha-1,8-diene; dextro-para-mentha-1,8-diene; -1,8-para-menthadiene; 1,8 9-p-menthadiene; 1,8 9-para-menthadiene; (R)-1-methyl-4-(1-methyl ethenyl) cyclohexene; (R)-1-methyl-4-(1-methyl vinyl) cyclohexene; D-Limonene; D-LİMONEN; D-Limonen; (R)-1-methyl-4-(1-methylethenyl)cyclohexene; (R)-1-methyl-4-(1-methylvinyl)cyclohexene; (R)-1-methyl-4-isopropenyl-1-cyclohexene; (4R)-1-methyl-4-prop-1-en-2-ylcyclohexene; -4-iso propenyl-1-methyl cyclohexene; 4-iso propenyl-1-methyl cyclohexene; -4-iso propenyl-1-methylcyclohexene; 4-iso propenyl-1-methylcyclohexene

D Limonene

D limonene is a colorless liquid aliphatic hydrocarbon classified as a cyclic monoterpene, and is the major component in the oil of citrus fruit peels.[1] The d-isomer, occurring more commonly in nature as the fragrance of oranges, is a flavoring agent in food manufacturing.[1][2] It is also used in chemical synthesis as a precursor to carvone and as a renewables-based solvent in cleaning products.[1] The less common l-isomer is found in mint oils and has a piny, turpentine-like odor.[1] The compound is one of the main volatile monoterpenes found in the resin of conifers, particularly in the Pinaceae, and of orange oil.
D limonene takes its name from French limon ("lemon").[3] D limonene is a chiral molecule, and biological sources produce one enantiomer: the principal industrial source, citrus fruit, contains d-D limonene (-D limonene), which is the (R)-enantiomer.[1] Racemic D limonene is known as dipentene.[4] d-D limonene is obtained commercially from citrus fruits through two primary methods: centrifugal separation or steam distillation.

Chemical reactions
D limonene is a relatively stable monoterpene and can be distilled without decomposition, although at elevated temperatures it cracks to form isoprene.[5] It oxidizes easily in moist air to produce carveol, carvone, and D limonene oxide.[1][6] With sulfur, it undergoes dehydrogenation to p-cymene.
D limonene occurs commonly as the d- or (R)-enantiomer, but racemizes to dipentene at 300 °C. When warmed with mineral acid, D limonene isomerizes to the conjugated diene α-terpinene (which can also easily be converted to p-cymene). Evidence for this isomerization includes the formation of Diels–Alder adducts between α-terpinene adducts and maleic anhydride.
It is possible to effect reaction at one of the double bonds selectively. Anhydrous hydrogen chloride reacts preferentially at the disubstituted alkene, whereas epoxidation with mCPBA occurs at the trisubstituted alkene.
In another synthetic method Markovnikov addition of trifluoroacetic acid followed by hydrolysis of the acetate gives terpineol.

Biosynthesis
In nature, D limonene is formed from geranyl pyrophosphate, via cyclization of a neryl carbocation or its equivalent as shown.[8] The final step involves loss of a proton from the cation to form the alkene.
The most widely practiced conversion of D limonene is to carvone. The three-step reaction begins with the regioselective addition of nitrosyl chloride across the trisubstituted double bond. This species is then converted to the oxime with a base, and the hydroxylamine is removed to give the ketone-containing carvone.[2]

In plants
d-D limonene is a major component of the aromatic scents and resins characteristic of numerous coniferous and broadleaved trees: red and silver maple (Acer rubrum, Acer saccharinum), cottonwoods (Populus angustifolia), aspens (Populus grandidentata, Populus tremuloides) sumac (Rhus glabra), spruce (Picea spp.), various pines (e.g., Pinus echinata, Pinus ponderosa), Douglas fir (Pseudotsuga menziesii), larches (Larix spp.), true firs (Abies spp.), hemlocks (Tsuga spp.), cannabis (Cannabis sativa spp.),[9] cedars (Cedrus spp.), various Cupressaceae, and juniper bush (Juniperus spp.).[1] It contributes to the characteristic odor of orange peel, orange juice and other citrus fruits.[1][10] To optimize recovery of valued components from citrus peel waste, d-D limonene is typically removed.[11]

Safety and research
d-D limonene applied to skin may cause irritation from contact dermatitis, but otherwise appears to be safe for human uses.[12][13] D limonene is flammable as a liquid or vapor and it is toxic to aquatic life.[1]

Uses
D limonene is common as a dietary supplement and as a fragrance ingredient for cosmetics products.[1] As the main fragrance of citrus peels, d-D limonene is used in food manufacturing and some medicines, such as a flavoring to mask the bitter taste of alkaloids, and as a fragrance in perfumery, aftershave lotions, bath products, and other personal care products.[1] d-D limonene is also used as a botanical insecticide.[1][14] d-D limonene is used in the organic herbicide "Avenger".[15] It is added to cleaning products, such as hand cleansers to give a lemon or orange fragrance (see orange oil) and for its ability to dissolve oils.[1] In contrast, l-D limonene has a piny, turpentine-like odor.

D limonene is used as a solvent for cleaning purposes, such as adhesive remover, or the removal of oil from machine parts, as it is produced from a renewable source (citrus essential oil, as a byproduct of orange juice manufacture).[11] It is used as a paint stripper and is also useful as a fragrant alternative to turpentine. D limonene is also used as a solvent in some model airplane glues and as a constituent in some paints. Commercial air fresheners, with air propellants, containing D limonene are used by philatelists to remove self-adhesive postage stamps from envelope paper.[16]
D limonene is also used as a solvent for fused filament fabrication based 3D printing.[17] Printers can print the plastic of choice for the model, but erect supports and binders from HIPS, a polystyrene plastic that is easily soluble in D limonene. As it is combustible, D limonene has also been considered as a biofuel.
In preparing tissues for histology or histopathology, d-D limonene is often used as a less toxic substitute for xylene when clearing dehydrated specimens. Clearing agents are liquids miscible with alcohols (such as ethanol or isopropanol) and with melted paraffin wax, in which specimens are embedded to facilitate cutting of thin sections for microscopy.

D limonene is one of the most common terpenes in nature. It is a major constituent in several citrus oils (orange, lemon, mandarin, lime, and grapefruit). D limonene is listed in the Code of Federal Regulations as generally recognized as safe (GRAS) for a flavoring agent and can be found in common food items such as fruit juices, soft drinks, baked goods, ice cream, and pudding. D limonene is considered to have fairly low toxicity. It has been tested for carcinogenicity in mice and rats. Although initial results showed D limonene increased the incidence of renal tubular tumors in male rats, female rats and mice in both genders showed no evidence of any tumor. Subsequent studies have determined how these tumors occur and established that D limonene does not pose a mutagenic, carcinogenic, or nephrotoxic risk to humans. In humans, D limonene has demonstrated low toxicity after single and repeated dosing for up to one year. Being a solvent of cholesterol, D limonene has been used clinically to dissolve cholesterol-containing gallstones. Because of its gastric acid neutralizing effect and its support of normal peristalsis, it has also been used for relief of heartburn and gastroesophageal reflux (GERD). D limonene has well-established chemopreventive activity against many types of cancer. Evidence from a phase I clinical trial demonstrated a partial response in a patient with breast cancer and stable disease for more than six months in three patients with colorectal cancer.

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D limonene is the oil extracted from the peels of oranges and other citrus fruits (1).
People have been extracting essential oils like D limonene from citrus fruits for centuries. Today, D limonene is often used as a natural treatment for a variety of health issues and is a popular ingredient in household items.
However, not all of D limonene’s benefits and uses are supported by science.
This article examines D limonene’s uses, potential benefits, side effects, and dosage.

What is D limonene?
D limonene is a chemical found in the rind of citrus fruits, such as lemons, limes, and oranges. It is especially concentrated in orange peels, comprising around 97% of this rind’s essential oils (2Trusted Source).
It’s often referred to as d-D limonene, which is its main chemical form.
D limonene belongs to a group of compounds known as terpenes, whose strong aromas protect plants by deterring predators (3Trusted Source).
D limonene is one of the most common terpenes found in nature and may offer several health benefits. It has been shown to possess anti-inflammatory, antioxidant, anti-stress, and possibly disease-preventing properties.

SUMMARY
D limonene is an essential oil found in citrus fruit peels. It belongs to a class of compounds called terpenes.
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Common uses of D limonene
D limonene is a popular additive in foods, cosmetics, cleaning products, and natural insect repellants. For example, it’s used in foods like sodas, desserts, and candies to provide a lemony flavor.
D limonene is extracted through hydrodistillation, a process in which fruit peels are soaked in water and heated until the volatile molecules are released via steam, condensed, and separated (4).
Due to its strong aroma, D limonene is utilized as a botanical insecticide. It’s an active ingredient in multiple pesticide products, such as eco-friendly insect repellents (5).
Other household products containing this compound include soaps, shampoos, lotions, perfumes, laundry detergents, and air fresheners.
Additionally, D limonene is available in concentrated supplements in capsule and liquid form. These are often marketed for their supposed health benefits.
This citrus compound is also used as an aromatic oil for its calming and therapeutic properties.

SUMMARY
D limonene is used in a range of products, including food, cosmetics, and eco-friendly pesticides. It can also be found in supplement form, as it may boost health and fight certain diseases.
Linked to several health benefits
D limonene has been studied for its potential anti-inflammatory, antioxidant, anticancer, and heart-disease-fighting properties.
However, most research has been conducted in test tubes or on animals, making it difficult to fully understand the role of D limonene in human health and disease prevention.
Anti-inflammatory and antioxidant benefits
D limonene has been shown to reduce inflammation in some studies (6Trusted Source, 7Trusted Source).
While short-term inflammation is your body’s natural response to stress and is beneficial, chronic inflammation can harm your body and is a major cause of illness. It’s important to prevent or reduce this type of inflammation as much as possible (8Trusted Source).
D limonene has been shown to reduce inflammatory markers that relate to osteoarthritis, a condition characterized by chronic inflammation.

A test-tube study in human cartilage cells noted that D limonene reduced nitric oxide production. Nitric oxide is a signaling molecule that plays a key role in inflammatory pathways (9Trusted Source).
In a study in rats with ulcerative colitis — another disease characterized by inflammation — treatment with D limonene significantly decreased inflammation and colon damage, as well as common inflammatory markers (10Trusted Source).
D limonene has demonstrated antioxidant effects as well. Antioxidants help reduce cell damage caused by unstable molecules called free radicals.
Free radical accumulation can lead to oxidative stress, which may trigger inflammation and disease (11Trusted Source).
One test-tube study revealed that D limonene may inhibit free radicals in leukemia cells, suggesting a decrease in inflammation and cellular damage that would normally contribute to disease (12Trusted Source).

Although promising, these effects need to be confirmed by human studies.
May have anticancer effects
D limonene may have anticancer effects.
In a population study, those who consumed citrus fruit peel, the major source of dietary D limonene, had a reduced risk of developing skin cancer compared to those who only consumed citrus fruits or their juices (13Trusted Source).
Another study in 43 women recently diagnosed with breast cancer experienced a significant 22% reduction in breast tumor cell expression after taking 2 grams of D limonene daily for 2–6 weeks (14Trusted Source).
Additionally, research in rodents found that supplementing with D limonene inhibited the growth of skin tumors by preventing inflammation and oxidative stress (15Trusted Source).
Other rodent studies indicate that D limonene may fight other types of cancer, including breast cancer (16Trusted Source).
What’s more, when given to rats alongside the anticancer drug doxorubicin, D limonene helped prevent several common side effects of the medication, including oxidative damage, inflammation, and kidney damage (17Trusted Source).
Although these results are promising, more human studies are needed.

May boost heart health
Heart disease remains the leading cause of death in the United States, accounting for nearly one in four deaths (18Trusted Source).
D limonene may lower your risk of heart disease by reducing certain risk factors, such as elevated cholesterol, blood sugar, and triglyceride levels.
In one study, mice given 0.27 grams of D limonene per pound of body weight (0.6 grams/kg) showed reduced triglycerides, LDL (bad) cholesterol, fasting blood sugar, and fat accumulation in the liver, compared to a control group (19Trusted Source).
In another study, stroke-prone rats given 0.04 grams of D limonene per pound of body weight (20 mg/kg) exhibited significant reductions in blood pressure compared to rats of similar health status that did not receive the supplement (20Trusted Source).
Keep in mind that human studies are needed before strong conclusions can be drawn.

Other benefits
Aside from the benefits listed above, D limonene may:

Reduce appetite. The scent of D limonene has been shown to significantly reduce appetite in blowflies. However, this effect has not been studied in humans (21Trusted Source).
Decrease stress and anxiety. Rodent studies suggest that D limonene could be used in aromatherapy as an anti-stress and anti-anxiety agent (22Trusted Source).
Support healthy digestion. D limonene may protect against stomach ulcers. In a study in rats, citrus aurantium oil, which is 97% D limonene, protected nearly all of the rodents against ulcers caused by medication use (23Trusted Source).
SUMMARY
D limonene may offer antioxidant, anti-inflammatory, anticancer, and anti-heart-disease benefits, among others. However, more research in humans is needed.

Safety and side effects
D limonene is considered safe for humans with little risk of side effects. The Food and Drug Administration (FDA) recognizes D limonene as a safe food additive and flavoring (5).
However, when applied directly to the skin, D limonene may cause irritation in some people, so caution should be used when handling its essential oil (24Trusted Source, 25).
D limonene is sometimes taken as a concentrated supplement. Because of the way your body breaks it down, it’s likely safe consumed in this form. That said, human research on these supplements is lacking (26Trusted Source).
Notably, high-dose supplements may cause side effects in some people. What’s more, insufficient evidence exists to determine whether D limonene supplements are acceptable for pregnant or breastfeeding women.
It’s best to consult your healthcare practitioner before taking D limonene supplements, especially if you’re taking medications, are pregnant or breastfeeding, or have a medical condition.

SUMMARY
Aside from possible skin irritation associated with direct application, D limonene is likely safe for most people to use and consume in moderation.
Potentially effective dosages
Because few D limonene studies exist in humans, it’s difficult to provide a dosage recommendation.
Nonetheless, dosages of up to 2 grams daily have been safely used in studies (9Trusted Source, 14Trusted Source).
Capsule supplements that can be purchased online contain dosages of 250–1,000 mg. D limonene is also available in liquid form with typical dosages of 0.05 ml per serving.
However, supplements aren’t always necessary. You can easily obtain this compound by eating citrus fruits and peels.
For example, fresh orange, lime, or lemon zest can be used to add D limonene to baked goods, drinks, and other items. What’s more, pulpy citrus juices, such as lemon or orange juice, boast D limonene, too (27Trusted Source).

SUMMARY
While dosage recommendations don’t exist for D limonene, 2 grams daily has been safely used in studies. In addition to supplements, you can obtain D limonene from citrus fruits and zest.

Other names of D limonene:
D limonene
Orange peel oil
Citrus peel oil
Citrine
p-mentha-1,8-diene (scientific name)

What is D limonene? What are the health effects of D limonene?
Terpene compounds, which are obtained from the peel of citrus fruits, mostly in lemon peel, and give these plants their scent, are called D limonene. Intense citrus consumption is thought to be one of the reasons for less cancer and cardiovascular diseases in people eating a Mediterranean diet.
Cancer of D limonene with it has not been prevented or treated.
Anti-inflammatory, wound-healing and tumor-shrinking therapy in laboratory studies. Again, in laboratory studies, it has been shown that D limonene affects the growth signal pathways in cancer cells and can lead to apoptosis. In animal studies, D limonene slowed the growth of pancreatic, stomach, colon, skin and lung cancers. It also slowed the formation and progress of animals exposed to cancer-causing substances. However, this has not been seen in anti-cancer patients.

For which medicinal medicine is D limonene tried?
To prevent and treat cancer
In laboratory studies, a combination of D limonene and the chemotherapy drug called docetaxel increases the effectiveness against prostate cancer cells. A community study (epidemiological) study reported an inverse association between citrus consumption and squamous cell cancer of the skin. However, these results could not be supported by clinical studies. More research is needed to find that D limonene is not the prevention or treatment of cancer.
To treat heartburn and reflux
Although it has been tried intensively to concentrate, the limits to support this use, even the D limonene cause stomach complaints. More are needed in this area.

Side effects of D limonene
Nausea
Vomiting
Diarrhea
Allergic skin rash
Trigger asthma

WHAT IS D limonene?
D limonene, also known as Citrus Terpenes, is the main chemical constituent found in the cold-pressed peel oils that can be derived from all edible citrus fruits, namely oranges, lemons, and limes. After the first pressing of the peels, it is obtained from the resultant oil through the process of distillation. The two chemical forms of D limonenee are D limonene, which is found largely in orange peels, and L-D limonenee, which is found largely in lemon peels. D limonenee gets its name from the botanical name for “Lemon” – Citrus limon – due to the richness of this natural compound in lemon peels.

Its wide range of beneficial applications has made D limonene one of the most prominent natural Terpenes. With a light, pleasantly dry, and refreshingly-sweet citrusy scent, it is valued for its aroma and is mostly used in fragrances as well as green cleaning products rather than for therapeutic applications. NDA’s D limonene Raw Material is a thin, clear, colorless, oily fluid that is derived from steam distilled citrus rinds. It is safer to use, works more effectively, and is more environmentally-friendly than most commercial and industrial cleaners.

HOW DOES D limonene WORK?
D limonene is a fragrance agent, a degumming agent, and a gentle yet powerful cleaner that is reputed to effectively remove stains, grease, tar, and more, thus making a natural replacement for more popular solvents, which usually contain chlorine or petroleum. Its mildness has also made it a popular ingredient in water-free hand soaps, in which it is said to not only cleanse but to also leave the hands smelling fresh. When applied to various types of hard surfaces, such as counter tops, windows, mirrors, floors, bath tubs, refrigerators, cars, and electronic items, D limonene is reputed to bring a high shine to all cleaned items.

APPLICATIONS FOR D limonene
D limonene may be used at full strength, that is without dilution, as an eco-friendly detergent; however, direct application to painted surfaces, plexiglass, plastics, or fiberglass is not recommended. Conversely, it may be added to wetting agents, such as water or vinegar bases, to achieve better solubilization. Either method will make for a natural yet equally effective industrial-strength “green” surface disinfectant that is ideal for household cleaning.

D limonenee is a colorless liquid aliphatic hydrocarbon classified as a cyclic monoterpene, and is the major component in the oil of citrus fruit peels. The D-isomer, occurring more commonly in nature as the fragrance of oranges, is a flavoring agent in food manufacturing. It is also used in chemical synthesis as a precursor to carvone and as a renewables-based solvent in cleaning products. The less common L-isomer is found in mint oils and has a piny, turpentine-like odor. The compound is one of the main volatile monoterpenes found in the resin of conifers, particularly in the Pinaceae, and of orange oil.
D limonenee takes its name from French limon ("lemon"). D limonenee is a chiral molecule, and biological sources produce one enantiomer: the principal industrial source, citrus fruit, contains D limonene ((+)-D limonenee), which is the (R)-enantiomer. Racemic D limonenee is known as dipentene. D limonene is obtained commercially from citrus fruits through two primary methods: centrifugal separation or steam distillation.

Chemical reactions
D limonenee is a relatively stable monoterpene and can be distilled without decomposition, although at elevated temperatures it cracks to form isoprene. It oxidizes easily in moist air to produce carveol, carvone, anD limonene oxide. With sulfur, it undergoes dehydrogenation to p-cymene.
D limonenee occurs commonly as the D- or (R)-enantiomer, but racemizes to dipentene at 300 °C. When warmed with mineral acid, D limonenee isomerizes to the conjugated diene α-terpinene (which can also easily be converted to p-cymene). Evidence for this isomerization includes the formation of Diels–Alder adducts between α-terpinene adducts and maleic anhydride.
It is possible to effect reaction at one of the double bonds selectively. Anhydrous hydrogen chloride reacts preferentially at the disubstituted alkene, whereas epoxidation with mCPBA occurs at the trisubstituted alkene.
In another synthetic method Markovnikov addition of trifluoroacetic acid followed by hydrolysis of the acetate gives terpineol.

Biosynthesis
In nature, D limonenee is formed from geranyl pyrophosphate, via cyclization of a neryl carbocation or its equivalent as shown. The final step involves loss of a proton from the cation to form the alkene.
The most widely practiced conversion of D limonenee is to carvone. The three-step reaction begins with the regioselective addition of nitrosyl chloride across the trisubstituted double bond. This species is then converted to the oxime with a base, and the hydroxylamine is removed to give the ketone-containing carvone.

In plants
D limonene is a major component of the aromatic scents and resins characteristic of numerous coniferous and broadleaved trees: red and silver maple (Acer rubrum, Acer saccharinum), cottonwoods (Populus angustifolia), aspens (Populus grandidentata, Populus tremuloides) sumac (Rhus glabra), spruce (Picea spp.), various pines (e.g., Pinus echinata, Pinus ponderosa), Douglas fir (Pseudotsuga menziesii), larches (Larix spp.), true firs (Abies spp.), hemlocks (Tsuga spp.), cannabis (Cannabis sativa spp.),[9] cedars (Cedrus spp.), various Cupressaceae, and juniper bush (Juniperus spp.). It contributes to the characteristic odor of orange peel, orange juice and other citrus fruits. To optimize recovery of valued components from citrus peel waste, D limonene is typically removed.

Safety and research
D limonene applied to skin may cause irritation from contact dermatitis, but otherwise appears to be safe for human uses. D limonenee is flammable as a liquid or vapor and it is toxic to aquatic life.

Uses
D limonene is common as a dietary supplement and as a fragrance ingredient for cosmetics products. As the main fragrance of citrus peels, D limonene is used in food manufacturing and some medicines, such as a flavoring to mask the bitter taste of alkaloids, and as a fragrance in perfumery, aftershave lotions, bath products, and other personal care products. D limonene is also used as a botanical insecticide. D limonene is used in the organic herbicide "Avenger". It is added to cleaning products, such as hand cleansers to give a lemon or orange fragrance (see orange oil) and for its ability to dissolve oils. In contrast, L-D limonene has a piny, turpentine-like odor.

D limonene is also used as a solvent for fused filament fabrication based 3D printing. Printers can print the plastic of choice for the model, but erect supports and binders from HIPS, a polystyrene plastic that is easily soluble in D limonene. As it is combustible, D limonene has also been considered as a biofuel.
In preparing tissues for histology or histopathology, D limonene is often used as a less toxic substitute for xylene when clearing dehydrated specimens. Clearing agents are liquids miscible with alcohols (such as ethanol or isopropanol) and with melted paraffin wax, in which specimens are embedded to facilitate cutting of thin sections for microscopy.

D limonene is a colourless liquid hydrocarbon classified as a cyclic terpene possessing a strong smell of oranges. It is used in chemical synthesis as a precursor to carvone and as a renewably-based solvent in cleaning products. D limonene takes its name from the lemon, as the rind of the lemon, like other citrus fruits, contains considerable amounts of this compound, which contributes to their odor. D limonene is a chiral molecule, and biological sources produce one enantiomer: the principal industrial source, citrus fruit, contains D-li D limonene is common in cosmetic products. As the main odor constituent of citrus (plant family Rutaceae), D limonene is used in food manufacturing and some medicines, e.g., bitter alkaloids, as a flavoring; it is also used as botanical insecticide. It is added to cleaning products such as hand cleansers to give a lemon-orange fragrance (see orange oil). In contrast, L-D limonene has a piney, turpentine-like odor. D limonene is increasingly being used as a solvent for cleaning purposes, such as the removal of oil from machine parts, as it is produced from a renewable source (citrus oil, as a byproduct of orange juice manufacture). It also serves as a paint stripper when applied to painted wood. D limonene is also used as a solvent in some model airplane glues. All-natural commercial air fresheners, with air propellants, containing D limonene are used by philatelists to remove self-adhesive postage stamps from envelope paper. As it is combustible, D limonene has also been considered as a biofuel. D limonene can be used to dissolve polystyrene, and is a more ecologically friendly substitute for acetone. Safety D limonene and its oxidation products are skin and respiratory irritants, anD limonene-1,2-oxide (formed by aerial oxidation) is a known skin sensitizer. Most reported cases of irritation have involved long-term industrial exposure to the pure compound, e.g. during degreasing or the preparation of paints. However a study of patients presenting dermatitis showed that 3% were sensitized to D limonene.

D limonene is a chemical found in the peels of citrus fruits and in other plants. It is used to make medicine.
D limonene is used for obesity, cancer, and bronchitis, but there is no good scientific evidence to support these uses.
In foods, beverages, and chewing gum, D limonene is used as a flavoring.
In pharmaceuticals, D limonene is added to help medicinal ointments and creams penetrate the skin.
In manufacturing, D limonene is used as a fragrance, cleaner (solvent), and as an ingredient in household cleaning products, cosmetics, and personal hygiene products.

D limonene
D limonene is one of the most abundant terpenes in cannabis, and it may be found in concentrations as high as 16% of the essential oil fraction. Ubiquitous in citrus rind, D limonene is a monoterpene commonly used in perfumes, household cleaners, food, and medicines. D limonene has numerous medicinal benefits demonstrated in human and animal studies. D limonene is among a number of plant essential oils that have been identified as having antioxidant and anticancer properties. D limonene has therefore been suggested as an excellent dietary source for cancer prevention (Aggarwal and Shishodia, 2006)

Orange oil is an essential oil produced by cells within the rind of an orange fruit (Citrus sinensis fruit). In contrast to most essential oils, it is extracted as a by-product of orange juice production by centrifugation, producing a cold-pressed oil. It is composed of mostly (greater than 90%) D limonene, and is often used in place of pure D limonene. D limonene can be extracted from the oil by distillation.

Composition
The compounds inside an orange oil vary with each different oil extraction. Composition varies as a result of regional and seasonal changes as well as the method used for extraction. Several hundred compounds have been identified with gas chromatograph-mass spectrometry. Most of the substances in the oil belong to the terpene group with D limonene being the dominant one. Long chain aliphatic hydrocarbon alcohols and aldehydes like 1-octanol and octanal are second important group of substances.
Orange oil is used as a cleaner. It is also used as an additive to certain wax finish/polish such as Howard's Feed-N-Wax Wood Polish & Conditioner.

Biological pest control
Orange oil can be used in green pesticides for biological pest control. It can kill ants, and by erasing their scent-pheromone trail indicators disrupts re-infestation.
Orange oil is also known to be useful to control, but not exterminate Drywood termites (Incisitermes.), killing only those who come into direct contact with it.

Aromatherapy material for humans
In the practice of aromatherapy, orange oil is described as providing various benefits, including the possibility of "reducing stress", controlling "anxiety", enabling "relaxation" and "lifting mood". Aromatherapy is a pseudoscience, and much of the purported evidence cited for these claims comes from research which is not double-blinded or controlled.

Hazards
The D limonene which is the main component of the oil is a mild irritant, as it dissolves protective skin oils. D limonene and its oxidation products are skin irritants, anD limonene-1,2-oxide (formed by aerial oxidation) is a known skin sensitizer. Most reported cases of irritation have involved long-term industrial exposure to the pure compound, e.g. during degreasing or the preparation of paints. However a study of patients presenting dermatitis showed that 3% were sensitized to D limonene.
D limonene is also flammable.

Use: Dipentene is a terpene liquid found in various volatile oils such as cardamon, mace, nutmeg , turpentine oil. Dipentene is mainly composed of D limonene, beta phellandrene, myrcene and other terpenes. Dipentene is used as a solvent for resins, alkyds and waxes and to make paints, enamels, lacquers and polishes. Dipentine is used as a perfumery composition for soaps, personal care products and cosmetics. It is used as an intermediate for terpene resins, carvone, terylene, and rubber chemicals. It is used as an oils dispersant, metal dryer. It is used as a substitute for chlorinated solvents in degreasing metals for cleaning in the electronic industry and the printing industry while it can also be used as starting material for the synthesis of terpene resin. alpha-D limonene has been used as a gallstone solubilizer in pharmaceutical industry.

D limonene, (+)- is an oral dietary supplement containing a natural cyclic monoterpene and major component of the oil extracted from citrus peels with potential chemopreventive and antitumor activities. Although the mechanism of action has yet to be fully elucidated, D limonene and its metabolites perillic acid, dihydroperillic acid, uroterpenol anD limonene 1,2-diol may inhibit tumor growth through inhibition of p21-dependent signaling and may induce apoptosis via the induction of the transforming growth factor beta-signaling pathway. In addition, they inhibit post-translational modification of signal transduction proteins, resulting in G1 cell cycle arrest as well as differential expression of cell cycle- and apoptosis-related genes.

Use: D limonene is found in citrus essential oil, the contents can be up to 90%. (-)-D limonene is naturally found in Pine needle oil, Turpentine, Cajeput oil and other essential oils. It appears liquid and has orange smell. It is make from Terpenes of orange oils by the method of fractionation.
(4R)-D limonene is an optically active form of D limonene having (4R)-configuration. It has a role as a plant metabolite. It is an enantiomer of a (4S)-D limonene.

D limonene is a tricarboxylic acid found in citrus fruits. D limonene is used as an excipient in pharmaceutical preparations due to its antioxidant properties. D limonene maintains stability of active ingredients and is used as a preservative. D limonene is also used as an acidulant to control pH and acts as an anticoagulant by chelating calcium in blood.

General description of D limonene
D limonene is an organic acid. Its molar enthalpy of solution in water has been reported to be ΔsolHm (298.15K, m = 0.0203molkg-1) = (29061±123)Jmol-1.[2] It can be produced by crystallization from mother liquor of citric acid solution at 20-25°C during citric acid synthesis. An investigation of its crystal growth kinetics indicates that growth is linearly dependent on size.

Application of D limonene
D limonene was used in the preparation of citric acid solution employed in the acetone method of 68Ga pre-purification and radiolabeling technique.
D limonene may be used:
• As release-modifying agent to improve the release of diltiazem hydrochloride from melt extruded Eudragit RS PO tablets.
• To prepare citrate buffer for use in the preparation of platelets for intravital microscopy.
• To prepare Tris-citrate buffer employed for the electrophoresis of bacterial enzymes.

D limonene is a weak organic acid that has the molecular formula C6H8O7. It occurs naturally in citrus fruits. In biochemistry, it is an intermediate in the D limonene cycle, which occurs in the metabolism of all aerobic organisms.
More than two million tons of D limonene are manufactured every year. It is used widely as an acidifier, as a flavoring and a chelating agent.
A citrate is a derivative of D limonene; that is, the salts, esters, and the polyatomic anion found in solution. An example of the former, a salt is trisodium citrate; an ester is triethyl citrate. When part of a salt, the formula of the citrate anion is written as C6H5O3−7 or C3H5O(COO)3−3.

Natural occurrence and industrial production of D limonene
Lemons, oranges, limes, and other citrus fruits possess high concentrations of D limonene
D limonene exists in a variety of fruits and vegetables, most notably citrus fruits. Lemons and limes have particularly high concentrations of the acid; it can constitute as much as 8% of the dry weight of these fruits (about 47 g/l in the juices[10]).[a] The concentrations of D limonene in citrus fruits range from 0.005 mol/L for oranges and grapefruits to 0.30 mol/L in lemons and limes; these values vary within species depending upon the cultivar and the circumstances in which the fruit was grown.
D limonene was first isolated in 1784 by the chemist Carl Wilhelm Scheele, who crystallized it from lemon juice.
Industrial-scale D limonene production first began in 1890 based on the Italian citrus fruit industry, where the juice was treated with hydrated lime (calcium hydroxide) to precipitate calcium citrate, which was isolated and converted back to the acid using diluted sulfuric acid. In 1893, C. Wehmer discovered Penicillium mold could produce D limonene from sugar. However, microbial production of D limonene did not become industrially important until World War I disrupted Italian citrus exports.

In 1917, American food chemist James Currie discovered certain strains of the mold Aspergillus niger could be efficient D limonene producers, and the pharmaceutical company Pfizer began industrial-level production using this technique two years later, followed by Citrique Belge in 1929. In this production technique, which is still the major industrial route to D limonene used today, cultures of A. niger are fed on a sucrose or glucose-containing medium to produce D limonene. The source of sugar is corn steep liquor, molasses, hydrolyzed corn starch, or other inexpensive, sugary solution.[14] After the mold is filtered out of the resulting solution, D limonene is isolated by precipitating it with calcium hydroxide to yield calcium citrate salt, from which D limonene is regenerated by treatment with sulfuric acid, as in the direct extraction from citrus fruit juice.
In 1977, a patent was granted to Lever Brothers for the chemical synthesis of D limonene starting either from aconitic or isocitrate/alloisocitrate calcium salts under high pressure conditions; this produced D limonene in near quantitative conversion under what appeared to be a reverse, non-enzymatic Krebs cycle reaction.
Global production was in excess of 2,000,000 tons in 2018. More than 50% of this volume was produced in China. More than 50% was used as an acidity regulator in beverages, some 20% in other food applications, 20% for detergent applications, and 10% for applications other than food, such as cosmetics, pharmaceuticals, and in the chemical industry.

Chemical characteristics of D limonene
Speciation diagram for a 10-millimolar solution of D limonene
D limonene can be obtained as an anhydrous (water-free) form or as a monohydrate. The anhydrous form crystallizes from hot water, while the monohydrate forms when D limonene is crystallized from cold water. The monohydrate can be converted to the anhydrous form at about 78 °C. D limonene also dissolves in absolute (anhydrous) ethanol (76 parts of D limonene per 100 parts of ethanol) at 15 °C. It decomposes with loss of carbon dioxide above about 175 °C.
D limonene is a tribasic acid, with pKa values, extrapolated to zero ionic strength, of 2.92, 4.28, and 5.21 at 25 °C.[17] The pKa of the hydroxyl group has been found, by means of 13C NMR spectroscopy, to be 14.4.[18] The speciation diagram shows that solutions of D limonene are buffer solutions between about pH 2 and pH 8. In biological systems around pH 7, the two species present are the citrate ion and mono-hydrogen citrate ion. The SSC 20X hybridization buffer is an example in common use.[19] Tables compiled for biochemical studies[20] are available.
On the other hand, the pH of a 1 mM solution of D limonene will be about 3.2. The pH of fruit juices from citrus fruits like oranges and lemons depends on the D limonene concentration, being lower for higher acid concentration and conversely.
Acid salts of D limonene can be prepared by careful adjustment of the pH before crystallizing the compound. See, for example, sodium citrate.

The citrate ion forms complexes with metallic cations. The stability constants for the formation of these complexes are quite large because of the chelate effect. Consequently, it forms complexes even with alkali metal cations. However, when a chelate complex is formed using all three carboxylate groups, the chelate rings have 7 and 8 members, which are generally less stable thermodynamically than smaller chelate rings. In consequence, the hydroxyl group can be deprotonated, forming part of a more stable 5-membered ring, as in ammonium ferric citrate, (NH4)5Fe(C6H4O7)2·2H2O.
D limonene can be esterified at one or more of its three carboxylic acid groups to form any of a variety of mono-, di-, tri-, and mixed esters.

Biochemistry of D limonene
D limonene cycle
Main article: D limonene cycle
Citrate is an intermediate in the TCA cycle (aka TriCarboxylic Acid cycle, or Krebs cycle, Szent-Györgyi), a central metabolic pathway for animals, plants, and bacteria. Citrate synthase catalyzes the condensation of oxaloacetate with acetyl CoA to form citrate. Citrate then acts as the substrate for aconitase and is converted into aconitic acid. The cycle ends with regeneration of oxaloacetate. This series of chemical reactions is the source of two-thirds of the food-derived energy in higher organisms. Hans Adolf Krebs received the 1953 Nobel Prize in Physiology or Medicine for the discovery.
Some bacteria (notably E. coli) can produce and consume citrate internally as part of their TCA cycle, but are unable to use it as food because they lack the enzymes required to import it into the cell. After tens of thousand of evolutions in a minimal glucose medium that also contained citrate during Richard Lenski's Long-Term Evolution Experiment, a variant E. coli evolved with the ability to grow aerobically on citrate. Zachary Blount, a student of Lenski's, and colleagues studied these "Cit+" E. coli[23][24] as a model for how novel traits evolve. They found evidence that, in this case, the innovation was caused by a rare duplication mutation due to the accumulation of several prior "potentiating" mutations, the identity and effects of which are still under study. The evolution of the Cit+ trait has been considered a notable example of the role of historical contingency in evolution.

Other biological roles of D limonene
Citrate can be transported out of the mitochondria and into the cytoplasm, then broken down into acetyl-CoA for fatty acid synthesis, and into oxaloacetate. Citrate is a positive modulator of this conversion, and allosterically regulates the enzyme acetyl-CoA carboxylase, which is the regulating enzyme in the conversion of acetyl-CoA into malonyl-CoA (the commitment step in fatty acid synthesis). In short, citrate is transported into the cytoplasm, converted into acetyl CoA, which is then converted into malonyl CoA by acetyl CoA carboxylase, which is allosterically modulated by citrate.
High concentrations of cytosolic citrate can inhibit phosphofructokinase, the catalyst of a rate-limiting step of glycolysis. This effect is advantageous: high concentrations of citrate indicate that there is a large supply of biosynthetic precursor molecules, so there is no need for phosphofructokinase to continue to send molecules of its substrate, fructose 6-phosphate, into glycolysis. Citrate acts by augmenting the inhibitory effect of high concentrations of ATP, another sign that there is no need to carry out glycolysis.[25]
Citrate is a vital component of bone, helping to regulate the size of apatite crystals.[26]

Applications of D limonene
Food and drink
Powdered D limonene being used to prepare lemon pepper seasoning
Because it is one of the stronger edible acids, the dominant use of D limonene is as a flavoring and preservative in food and beverages, especially soft drinks and candies.[13] Within the European Union it is denoted by E number E330. Citrate salts of various metals are used to deliver those minerals in a biologically available form in many dietary supplements. D limonene has 247 kcal per 100 g.[27] In the United States the purity requirements for D limonene as a food additive are defined by the Food Chemicals Codex, which is published by the United States Pharmacopoeia (USP).

D limonene can be added to ice cream as an emulsifying agent to keep fats from separating, to caramel to prevent sucrose crystallization, or in recipes in place of fresh lemon juice. D limonene is used with sodium bicarbonate in a wide range of effervescent formulae, both for ingestion (e.g., powders and tablets) and for personal care (e.g., bath salts, bath bombs, and cleaning of grease). D limonene sold in a dry powdered form is commonly sold in markets and groceries as "sour salt", due to its physical resemblance to table salt. It has use in culinary applications, as an alternative to vinegar or lemon juice, where a pure acid is needed. D limonene can be used in food coloring to balance the pH level of a normally basic dye.

Cleaning and chelating agent of D limonene
Structure of an iron(III) citrate complex.
D limonene is an excellent chelating agent, binding metals by making them soluble. It is used to remove and discourage the buildup of limescale from boilers and evaporators.[13] It can be used to treat water, which makes it useful in improving the effectiveness of soaps and laundry detergents. By chelating the metals in hard water, it lets these cleaners produce foam and work better without need for water softening. D limonene is the active ingredient in some bathroom and kitchen cleaning solutions. A solution with a six percent concentration of D limonene will remove hard water stains from glass without scrubbing. D limonene can be used in shampoo to wash out wax and coloring from the hair. Illustrative of its chelating abilities, D limonene was the first successful eluant used for total ion-exchange separation of the lanthanides, during the Manhattan Project in the 1940s. In the 1950s, it was replaced by the far more efficient EDTA.
In industry, it is used to dissolve rust from steel and passivate stainless steels.

Cosmetics, pharmaceuticals, dietary supplements, and foods
D limonene is used as an acidulant in creams, gels, and liquids. Used in foods and dietary supplements, it may be classified as a processing aid if it was added for a technical or functional effect (e.g. acidulent, chelator, viscosifier, etc.). If it is still present in insignificant amounts, and the technical or functional effect is no longer present, it may be exempt from labeling <21 CFR §101.100(c)>.
D limonene is an alpha hydroxy acid and is an active ingredient in chemical skin peels.
D limonene is commonly used as a buffer to increase the solubility of brown heroin.[31]
D limonene is used as one of the active ingredients in the production of facial tissues with antiviral properties.[32]

Other uses of D limonene
The buffering properties of citrates are used to control pH in household cleaners and pharmaceuticals.
D limonene is used as an odorless alternative to white vinegar for home dyeing with acid dyes.
Sodium citrate is a component of Benedict's reagent, used for identification both qualitatively and quantitatively of reducing sugars.
D limonene can be used as an alternative to nitric acid in passivation of stainless steel.[33]
D limonene can be used as a lower-odor stop bath as part of the process for developing photographic film. Photographic developers are alkaline, so a mild acid is used to neutralize and stop their action quickly, but commonly used acetic acid leaves a strong vinegar odor in the darkroom.
D limonene/potassium-sodium citrate can be used as a blood acid regulator.
Soldering flux. D limonene is an excellent soldering flux,[35] either dry or as a concentrated solution in water. It should be removed after soldering, especially with fine wires, as it is mildly corrosive. It dissolves and rinses quickly in hot water.

Synthesis of solid materials from small molecules
In materials science, the Citrate-gel method is a process similar to the sol-gel method, which is a method for producing solid materials from small molecules. During the synthetic process, metal salts or alkoxides are introduced into a D limonene solution. The formation of citric complexes is believed to balance the difference in individual behavior of ions in solution, which results in a better distribution of ions and prevents the separation of components at later process stages. The polycondensation of ethylene glycol and D limonene starts above 100°С, resulting in polymer citrate gel formation.

Safety of D limonene
Although a weak acid, exposure to pure D limonene can cause adverse effects. Inhalation may cause cough, shortness of breath, or sore throat. Over-ingestion may cause abdominal pain and sore throat. Exposure of concentrated solutions to skin and eyes can cause redness and pain.[36] Long-term or repeated consumption may cause erosion of tooth enamel.
D limonene is an acidic compound from citrus fruits; as a starting point in the Krebs cycle, citrate is a key intermediate in metabolism. Citric acid is one of a series of compounds responsible for the physiological oxidation of fats, carbohydrates, and proteins to carbon dioxide and water. It has been used to prepare citrate buffer for antigen retrieval of tissue samples. The citrate solution is designed to break protein cross-links, thus unmasking antigens and epitopes in formalin-fixed and paraffin embedded tissue sections, and resulting in enhanced staining intensity of antibodies. Citrate has anticoagulant activity; as a calcium chelator, it forms complexes that disrupt the tendency of blood to clot. May be used to adjust pH and as a sequestering agent for the removal of trace metals.
Additional forms available:
Citric Acid, Anhydrous (sc-211113)
Sodium Citrate, Dihydrate (sc-203383)
Citric Acid Trisodium Salt (sc-214745)
Sodium citrate monobasic (sc-215869)
Sodium citrate tribasic hydrate (sc-236898)
Citrate Concentrated Solution (sc-294091)
This monograph for Citric Acid, Anhydrous, and Citric Acid, Monohydrate provides, in addition to common physical constants, a general description including typical appearance, applications, change in state (approximate), and aqueous solubility. The monograph also details the following specifications, corresponding tests for verifying that a substance meets ACS Reagent Grade specifications including: Assay, Insoluble Matter, Residue after Ignition, Chloride, Oxalate, Phosphate, Sulfur Compounds (as SO, Iron, Lead, and Substances Carbonizable by Hot Sulfuric Acid (Tartrates, etc.).

Citric acid is a naturally occurring fruit acid, produced commercially by microbial fermentation of a carbohydrate substrate. Citric acid is the most widely used organic acid and pH-control agent in foods, beverages, pharmaceuticals and technical applications.
D limonene occurs as colourless crystals or as white, crystalline powder with a strongly acidic taste. It is efflorescent in dry air, very soluble in water, freely soluble in ethanol (96 %) and sparingly soluble in ether.
D limonene is non-toxic and has a low reactivity. It is chemically stable if stored at ambient temperatures. D limonene is fully biodegradable and can be disposed of with regular waste or sewage.

D limonene is found naturally in citrus fruits, especially lemons and limes. It’s what gives them their tart, sour taste.
A manufactured form of D limonene is commonly used as an additive in food, cleaning agents, and nutritional supplements.
However, this manufactured form differs from what’s found naturally in citrus fruits.
For this reason, you may wonder whether it’s good or bad for you.
This article explains the differences between natural and manufactured D limonene, and explores its benefits, uses, and safety.
What Is D limonene?
D limonene was first derived from lemon juice by a Swedish researcher in 1784.
The odorless and colorless compound was produced from lemon juice until the early 1900s when researchers discovered that it could also be made from the black mold, Aspergillus niger, which creates D limonene when it feeds on sugar.
Because of its acidic, sour-tasting nature, D limonene is predominantly used as a flavoring and preserving agent — especially in soft drinks and candies.
It’s also used to stabilize or preserve medicines and as a disinfectant against viruses and bacteria.
D limonene is a compound originally derived from lemon juice. It’s produced today from a specific type of mold and used in a variety of applications.

Natural Food Sources
Citrus fruits and their juices are the best natural sources of D limonene.
In fact, the word citric originates from the Latin word citrus.
Examples of citrus fruits include:
lemons, limes, oranges, grapefruits, tangerines, pomelos
Other fruits also contain D limonene but in lesser amounts. These include:
pineapple, strawberries, raspberries, cranberries, cherries, tomatoes
Beverages or food products that contain these fruits — such as ketchup in the case of tomatoes — also contain D limonene.
While not naturally occurring, D limonene is also a byproduct of cheese, wine, and sourdough bread production.
The D limonene listed in the ingredients of foods and supplements is manufactured — not what’s naturally found in citrus fruits.
This is because producing this additive from citrus fruits is too expensive and the demand far exceeds the supply.
Lemons, limes, and other citrus fruits are the predominant natural sources of D limonene. Other fruits that contain much less include certain berries, cherries, and tomatoes.
Artificial Sources and Uses
The characteristics of D limonene make it an important additive for a variety of industries.
Food and beverages use an estimated 70% of manufactured D limonene, pharmaceutical and dietary supplements use 20%, and the remaining 10% goes into cleaning agents.

Food Industry
Manufactured D limonene is one of the most common food additives in the world.
It’s used to boost acidity, enhance flavor, and preserve ingredients (5).
Sodas, juices, powdered beverages, candies, frozen foods, and some dairy products often contain manufactured D limonene.
It’s also added to canned fruits and vegetables to protect against botulism, a rare but serious illness caused by the toxin-producing Clostridium botulinum bacteria.

Medicines and Dietary Supplements
D limonene is an industrial staple in medicines and dietary supplements.
It’s added to medicines to help stabilize and preserve the active ingredients and used to enhance or mask the taste of chewable and syrup-based medications.
Mineral supplements, such as magnesium and calcium, may contain D limonene — in the form of citrate — as well to enhance absorption.

Disinfecting and Cleaning
D limonene is a useful disinfectant against a variety of bacteria and viruses.
A test-tube study showed that it may be effective in treating or preventing human norovirus, a leading cause of foodborne illness.
D limonene is commercially sold as a general disinfectant and cleaning agent for removing soap scum, hard water stains, lime, and rust.
It’s viewed as a safer alternative to conventional disinfectant and cleaning products, such as quat and chlorine bleach.
D limonene is a versatile additive for food, beverages, medicines, and dietary supplements, as well as cleaning and disinfecting products.

Health Benefits and Body Uses
D limonene has many impressive health benefits and functions.
Metabolizes Energy
Citrate — a closely related molecule of D limonene — is the first molecule that forms during a process called the D limonene cycle.
Also known as the tricarboxylic acid (TCA) or Krebs cycle, these chemical reactions in your body help transform food into usable energy.
Humans and other organisms derive the majority of their energy from this cycle.

Enhances Nutrient Absorption
Supplemental minerals are available in a variety of forms.
But not all forms are created equal, as your body uses some more effectively.
D limonene enhances the bioavailability of minerals, allowing your body to better absorb them.
For example, calcium citrate doesn’t require stomach acid for absorption. It also has fewer side effects — such as gas, bloating, or constipation — than another form called calcium carbonate.
Thus, calcium citrate is a better option for people with less stomach acid, like older adults.
Similarly, magnesium in the citrate form is absorbed more completely and is more bioavailable than magnesium oxide and magnesium sulfate.
D limonene also enhances the absorption of zinc supplements.

May Protect Against Kidney Stones
D limonene — in the form of potassium citrate — prevents new kidney stone formation and breaks apart those already formed.
D limonene protects against kidney stones by making your urine less favorable for the formation of stones.
Kidney stones are often treated with D limonene as potassium citrate. However, consuming foods high in this natural acid — like citrus fruits — can offer similar stone-preventing benefits.
Safety and Risks
Manufactured D limonene is generally recognized as safe (GRAS) by the Food and Drug Administration (FDA) (5).
No scientific studies exist investigating the safety of manufactured D limonene when consumed in large amounts for long periods.
Still, there have been reports of sickness and allergic reactions to the additive.
One report found joint pain with swelling and stiffness, muscular and stomach pain, as well as shortness of breath in fo