DL-Limonene

Description

D-limonene, which is a volatile oil, constitutes approximately 98% of orange peel oil by weight and has moderately good knockdown activity against ectoparasites of companion animals. The insecticidal activity of both d-limonene and linalool is enhanced when synergized by piperonyl butoxide. Apart from toxicoses reported in cats (65), d-limonene generally has a high margin of safety.

Description

(±)-Limonene is a cyclic monoterpene that has been found in various plant oils and Cannabis and has antifungal activity. It completely inhibits mycelial growth and aflatoxin B₁ production in A. flavus when used at concentrations of 500 and 250 ppm, respectively. (±)-Limonene also inhibits the growth of various additional fungi in vitro, including S. cerevisiae, R. glutinis, and K. thermotolerans (MICs = 500-4,000 μg/ml). It has been identified as a contact dermatitis allergen in honing oil, paint thinner, and turpentine. Formulations containing (±)-limonene have been used as fragrance and flavoring ingredients.

Chemical properties

colourless or light yellow liquid

Chemical properties

Limonene (4R)-(+)-limonene and (4S)-(?)-limonene as well as the racemate (dipentene) occur abundantly in many essential oils.The(+) isomer is present in citrus peel oils at a concentration of over 90%; a low concentration of the (?) isomer is found in oils from the Mentha species and conifers.
Limonene is a liquid with lemon-like odor. It is a reactive compound; oxidation often yields more than one product. Dehydrogenation leads to p-cymene. Limonene can be converted into cyclic terpene alcohols by hydrohalogenation, followed by hydrolysis. Nitrosyl chloride adds selectively to the endocyclic double bond; this reaction is utilized in the manufacture of (?)-carvone from (+)- limonene.
(+)-Limonene is obtained in large amounts as a by-product in the production of orange juice; (?)-limonene is isolated in relatively small quantities from essential oils. Racemic limonenes, which are commercially available under the name dipentene, are formed as by-products in many acid-catalyzed isomerizations of α- and β-pinene. Distillation of the so-called dipentene fraction yields limonenes in varying degrees of purity.
The limonenes are used as fragrance materials for perfuming household products and as components of artificial essential oils.

Chemical properties

d-, l- or dl-Limonene has a pleasant, lemon-like odor free from camphoraceous and turpentine-like notes. Limonene is the most important and widespread terpene; it is known in the d- and l- optically active forms and in the optically inactive dl-form (known as dipentene).

Occurrence

It has been reported found in more than 300 essential oils in amounts ranging from 90 to 95% (lemon, orange, mandarin) to as low as 1% (palmarosa); the most widespread form is the d-limonene, followed by the racemic form and then l-limo nene. Also reported found in ginger, nutmeg, pepper, mace, hop oil, coriander seed, calamus, dill herb, caraway seed and rosemary.

The Uses of DL-Limonene

d-Limonene is a flavoring agent that is a liquid, colorless with a pleasant odor resembling mild citrus. It is miscible in alcohol, most fixed oils, and mineral oil; soluble in glycerin; and insoluble in water and propylene glycol. It is obtained from citrus oil. It is also termed d-p-mentha-1,8,diene and cinene.

Toxicology

D-limonene is a clear colorless mobile liquid with a pleasant lemon-like odor. （(4R)-limonene is an optically active form of limonene having (4R)-configuration. It has a role as a plant metabolite. It is an enantiomer of a (4S)-limonene.）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.

The Uses of DL-Limonene

Limonene is an antioxidant and flavoring agent that occurs in lemons, oranges, and pineapple juice, being obtained from the oils. It is a colorless liquid which is insoluble in water and propylene glycol, very slightly soluble in glycerin, and miscible with alcohol, most fixed oils, and mineral oil. It prevents or delays enzymatic browning-type oxidation.

Definition

ChEBI: A monoterpene that is cyclohex-1-ene substituted by a methyl group at position 1 and a prop-1-en-2-yl group at position 4 respectively.

Preparation

d-Limonene may be obtained by steam distillation of citrus peels and pulp resulting from the production of juice and cold pressed oils, or from deterpenation of citrus oils; it is sometimes redistilled.

Production Methods

Limonene occurs in the oil of many plants and is the main constituent (≤86%) of the terpenoid fraction of fruit, flowers, leaves, bark, and pulp from shrubs, annuals, or trees including anise, mint, caraway, polystachya, pine, lime, and orange oil. It occurs as a by-product in the manufacture of terpineol and in various synthetic products made from α-pinene or turpentine oil. It is found in the gas phase of tobacco smoke and has been detected in urban atmospheres.

Aroma threshold values

Detection: 4 to 229 ppb

Taste threshold values

Taste characteristics at 30 ppm: sweet, orange, citrus and terpy.

Synthesis Reference(s)

Canadian Journal of Chemistry, 39, p. 1860, 1961 DOI: 10.1139/v61-249
Tetrahedron Letters, 20, p. 3519, 1979 DOI: 10.1016/S0040-4039(01)95450-4

General Description

A colorless liquid with an odor of lemon. Flash point 113°F. Density about 7.2 lb /gal and insoluble in water. Hence floats on water. Vapors heavier than air. Used as a solvent for rosin, waxes, rubber; as a dispersing agent for oils, resins, paints, lacquers, varnishes, and in floor waxes and furniture polishes.

Air & Water Reactions

Flammable. Insoluble in water.

Reactivity Profile

Cinene may react vigorously with strong oxidizing agents. May react exothermically with reducing agents to release hydrogen gas.

Health Hazard

Liquid irritates eyes; prolonged contact with skin causes irritation. Ingestion causes irritation of gastrointestinal tract.

Fire Hazard

Behavior in Fire: Containers may explode.

Chemical Reactivity

Reactivity with Water No reaction; Reactivity with Common Materials: No reaction; Stability During Transport: Stable; Neutralizing Agents for Acids and Caustics: Not pertinent; Polymerization: Not pertinent; Inhibitor of Polymerization: Not pertinent.

Pharmaceutical Applications

Many studies have reported that D-limonene effectively plays a valuable role in the prevention of several chronic and degenerative diseases. This review provides worthy information about the beneficial effects of D-limonene such as antioxidant, antidiabetic, anticancer, anti-inflammatory, cardioprotective, gastroprotective, hepatoprotective, immune modulatory, anti-fibrotic, anti-genotoxic etc. This could in turn help in the application of D-limonene for clinical studies. Various plant families contain Terpenes as their secondary metabolites. Monoterpenes constitute an important part of these secondary metabolites. D-limonene is a well-identified monoterpene that is commonly applied as a fragrance ingredient in essential oils. D-limonene is known to possess remarkable biological activities. It can be effectively used for treating various ailments and diseases. Due to its diverse functions, it can be efficiently utilized for human health.
Numerous data on animal studies have highlighted the potential effects of D-limonene. D-limonene is well tolerated in experimental animals and protective effects of limonene were observed in several preclinical models. Animal studies showing the cardio protective and hepatoprotective effects of D-limonene are found to be inadequate. Moreover, studies exploring the anticancer efficacy of D-limonene on animal models are also found to be limited. The study on the effect of D-limonene on humans is also extremely limited. Therefore, our present review will open new avenues to undertake further research on D-limonene in preclinical models and for subjecting this compound to effective clinical trials.

Contact allergens

Dipentene corresponds to a racemic mixture of d-limonene and l-limonene. Dipentene can be prepared from wood turpentine or by synthesis. It is used as a solvent for waxes, rosin and gums, in printing inks, perfumes, rubber compounds, paints, enamels, and lacquers. An irritant and sensitizer, dipentene caused contact dermatitis mainly in painters, polishers, and varnishers

Contact allergens

Limonene is a racemic form of dand l-limonene. d-Limonene is contained in Citrus species such as citrus, orange, mandarin, and bergamot. l-Limonene is contained in Pinus pinea. The racemic form (dand l-limonene) is also named dipentene.

Anticancer Research

Tested as promising antitumor molecules in induced tumor on rat tissues, D-limonenewas tested in preclinical studies in patients with advanced cancer. Limonene inhibitsthe activity of HMG-CoA reductase, subsequently reducing the possibility of cancergrowth. The mechanism of action involves the inhibition of prenyltransferases withthe activation of glutathione-S transferase and uridine diphospho-glucuronosyltransferase.More interest was pointed on the principal metabolite:perillyl alcohol which is more potent than limonene. The interest on perillyl alcoholis based on the necessity of a very high dosage of D-limonene in preclinical studies(about 1000 mg/kg/day in human mammary tumor) that can cause notably importantside effects. The more active perillyl alcohol and the less low active doseshypothesized this molecule as a clinical candidate (Pattanayak et al. 2009; Chenet al. 2013; Fontes et al. 2013; Rani and Sharma 2013).

Safety Profile

A skin irritant. Flammable when exposed to heat or flame; can react vigorously with oxidzing materials. When heated to decomposition it emits acrid smoke and irritating fumes.

Toxicology

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.

Potential Exposure

Dipentene is used as a solvent; in rubber compounding and reclamation; and to make paints,enamels, lacquer, and perfumes.

First aid

If this chemical gets into the eyes, remove anycontact lenses at once and irrigate immediately for at least15 min, occasionally lifting upper and lower lids. Seek medical attention immediately. If this chemical contacts theskin, remove contaminated clothing and wash immediatelywith soap and water. Seek medical attention immediately. Ifthis chemical has been inhaled, remove from exposure,begin rescue breathing (using universal precautions, including resuscitation mask) if breathing has stopped and CPR ifheart action has stopped. Transfer promptly to a medicalfacility. When this chemical has been swallowed, get medical attention. Give large quantities of water and inducevomiting. Do not make an unconscious person vomit

Carcinogenicity

Induction of kidney neoplasias has been observed in male rats of strains that have significant concentrations of the protein a2u-globulin (158a). This protein is not expressed in females or species other than the rat; therefore, limonene carcinogenicity appears to be limited to the male of specific strains of this species. Subcutaneous injection of the compound or its hydroperoxide into C57BL/6 mice decreased the incidence of dibenzopyrene- induced tumors appreciably. Given orally either 15 min or 1 h prior to nitrosodiethylamine, D-limonene reduced forestomach tumor formation by about 60% and pulmonary adenoma formation by about 35%. Reduction of cancer incidence and metastasis by limonene has also been reported in other systems (158b).

Environmental Fate

Limonene is insoluble and is stable in water. Substances like limonene that are monoterpenes are released in large amounts mainly to the atmosphere. The chemical and physical properties of limonene also indicate that limonene is distributed mainly to air. Based on the physical and chemical properties of limonene, when this substance is released to ground, it has low to very low mobility in soil. The soil adsorption coefficient (Koc), calculated on the basis of the solubility (13.8 mg l^-1 at 25 ℃) and the log octanol/water partition coefficient (4.232), ranges from 1030 to 4780.3. Henry’s Law constant indicates that limonene rapidly volatilizes from both dry and moist soil; however, its strong adsorption to soil may slow this process. In the aquatic environment, limonene is expected to adsorb to sediment and suspended organic particles to rapidly volatilize to the atmosphere, based on its physical and chemical properties. The estimated half-life for volatilization of limonene from a model river (1 m deep, flow 1 ms^-1, and wind speed 3 ms^-1) is 3.4 h. The bioconcentration factor, calculated on the basis of water solubility and the log octanol/water partition coefficient, is 246–262, suggesting that limonene may accumulate in fish and other aquatic organisms.

storage

Color Code—Red: Flammability Hazard: Store ina flammable liquid storage area or approved cabinet awayfrom ignition sources and corrosive and reactive materials.Store in tightly closed containers in a cool, well-ventilatedarea. Before entering confined space where this chemicalmay be present, check to make sure that an explosive concentration does not exist. Store in tightly closed containersin a cool, well-ventilated area away from heat and incompatible materials. Sources of ignition, such as smoking andopen flames, are prohibited where this chemical is used,handled, or stored in a manner that could create a potentialfire or explosion hazard. Metal containers involving thetransfer of 5 gallons or more of this chemical should begrounded and bonded. Drums must be equipped with selfclosing valves, pressure vacuum bungs, and flame arresters.Use only nonsparking tools and equipment, especially whenopening and closing containers of this chemical.

Shipping

This compound requires a shipping label of“FLAMMABLE LIQUID.” It falls in Hazard Class 3 andPacking Group II.

Toxicity evaluation

D-Limonene can cause a renal syndrome in male rats. Male rats have a background of spontaneous protein droplets in the proximal tubule, particularly within the cells of the P2 segment. D-Limonene can increase the formation of protein droplets, and experiments show that the only protein accumulating is α2u-globulin. α2u-Globulin is synthesized in the liver, then it is released into the general circulation and reabsorbed by renal proximal tubule cells. Synthesis of α2u-globulin occurs only in adult male rats and to understand the critical role of α2uglobulin in the renal effects of D-limonene the absence of histopathological changes can be studied in female rats, since they cannot produce α2u-globulin. It was concluded from these studies that D-limonene does not have a renal toxicity effect on species that do not synthesize α2u-globulin, for example, female rats, male and female mice, and dogs.
To develop nephropathy, there is a prerequisite step in which an agent binds to α2u-globulin and in the case of D-limonene, this agent is 1,2-epoxide. Binding of this agent to α2u-globulin reduces the rate of degradation relative to that of native protein, thereby causing it to accumulate. Accumulation of α2u-globulin can be observed after a single oral dose of D-limonene and continued treatment results in additional histological changes in the kidney. Renal function can be observed by increasing the amount of α2u-globulin in urine. These functional changes occur only in male rats and only at doses that exacerbate protein droplet formation. In response to the cell death and functional changes, there is an increase in cell proliferation in the kidney. With continued treatment, cell proliferation persists but it does not restore renal function. Increasing cell proliferation is directly related to the development of renal tubular tumors and is dependent on the presence of α2u-globulin. α2u-Globulin nephropathy and renal cell proliferation occur at the same doses consistent with those that produce renal tubular tumors.
α2u-Globulin is one type of superfamily proteins that bind and transport a variety of agents. Many of these proteins are synthesized in mammalian species, including humans. The protein that can be found in human urine is very different from that in rat urine. About 1% of the protein concentration in male rat urine can be found in human urine. Human urinary protein is predominantly a species of high molecular mass, and there is no protein in human plasma or urine identical to α2u-globulin and there is no protein-like α2u-globulin detected in human kidney tissue. Even though the binding of D-limonene- 1,2-epoxide to α2u-globulin can be shown in vitro, other superfamily proteins, especially those synthesized by humans, do not bind 1,2-epoxide.
There is no verification that any human protein can contribute to a renal syndrome similar to α2u-globulin nephropathy, and consequently no evidence can be found that D-limonene is carcinogenic in humans by a mechanism similar to α2u-globulin nephropathy. The initiation of renal cell tumors in male rats by binding to agents that act through an α2u-globulin-associated response is not projected as a carcinogenic hazard to humans. This can be concluded based on an extensive evidence that the presence of α2u-globulin is an absolute requirement for the carcinogenic activity. Therefore, D-limonene has no carcinogenic activity in human since neither α2u-globulin nor any protein that can function like α2uglobulin is synthesized by humans.