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Castor oil is avegetable oil pressed fromcastor beans, the seeds of the plantRicinus communis.[1] The seeds are 40 to 60 percent oil.[2] It is a colourless or pale yellow liquid with a distinct taste and odor. Itsboiling point is 313 °C (595 °F) and itsdensity is 0.961 g/cm3.[3] It includes a mixture oftriglycerides in which about 90 percent of fatty acids arericinoleates.Oleic acid andlinoleic acid are the other significant components.
Some 270,000–360,000 tonnes (600–800 million pounds) of castor oil are produced annually for a variety of uses.[4] Castor oil and its derivatives are used in the manufacturing ofsoaps,lubricants, hydraulic andbrake fluids,paints,dyes,coatings,inks, cold-resistantplastics,waxes and polishes,nylon, andperfumes.[4]
The name probably comes from a confusion between theRicinus plant that produces it and another plant, theVitex agnus-castus.[5][6] An alternative etymology, though, suggests that it was used as a replacement forcastoreum.[7]
Use of castor oil as a laxative is attested to in thec. 1550 BCEEbers Papyrus,[8]and it was in use several centuries earlier.[9]Midwifery manuals from the 19th century recommended castor oil and 10 drops oflaudanum for relieving "false pains".[10]
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Castor oil is well known as a source ofricinoleic acid, amonounsaturated, 18-carbonfatty acid. Among fatty acids, ricinoleic acid is unusual in that it has ahydroxylfunctional group on the 12th carbon atom. This functional group causes ricinoleic acid (and castor oil) to be morepolar than most fats. The chemical reactivity of the alcohol group also allows chemicalderivatization that is not possible with most other seed oils.
Because of its ricinoleic acid content, castor oil is a valuable chemical in feedstocks, commanding a higher price than other seed oils. As an example, in July 2007, Indian castor oil sold for aboutUS$0.90/kg ($0.41/lb),[citation needed] whereas U.S.soybean,sunflower, andcanola oils sold for about $0.30/kg ($0.14/lb).[11]
| Acid name | Range | Type |
|---|---|---|
| Ricinoleic acid | 85–95 | ω−9 |
| Oleic acid | 2–6 | ω−9 |
| Linoleic acid | 1–5 | ω−6 |
| α-Linolenic acid | 0.5–1 | ω−3 |
| Stearic acid | 0.5–1 | saturated |
| Palmitic acid | 0.5–1 | saturated |
| Dihydroxystearic acid | 0.3–0.5 | saturated |
| Others | 0.2–0.5 |
Castor oil has been used orally to relieveconstipation or to evacuate thebowel beforeintestinal surgery.[12] Thelaxative effect of castor oil is attributed toricinoleic acid, which is produced byhydrolysis in thesmall intestine.[12] Use of castor oil for simple constipation is medically discouraged because it may cause violentdiarrhea.[12]
In the food industry, food-grade castor oil is used in food additives, flavorings, candy (e.g.,polyglycerol polyricinoleate inchocolate),[13] as a mold inhibitor, and in packaging. Polyoxyethylated castor oil (e.g.,Kolliphor EL)[14] is also used in the food industries.[15] InIndia,Pakistan, andNepal, food grains arepreserved by the application of castor oil. It stopsrice,wheat, andpulses from rotting. For example, the legumepigeon pea is commonly available coated in oil for extended storage.
Castor oil has been used incosmetic products included in creams and as amoisturizer. It is often combined withzinc oxide to form anemollient andastringent, zinc and castor oil cream, which is commonly used to treat infants fornappy rash.[16][17]Hydrogenated castor oil is also known as trihydroxystearin, which is used in cosmetics and personal care systems.[18]
Castor oil is used as a vehicle for serums administering steroid hormones such asestradiol valerate viaintramuscular orsubcutaneous injection.[19][20]
Despite the lack of evidence, castor oil is sometimes claimed to be able to cure diseases. According to theAmerican Cancer Society, "available scientific evidence does not support claims that castor oil on the skin cures cancer or any other disease."[21]
Despite some undesirable side effects, castor oil is used, topically and orally, for labor induction. There is no high-quality research proving that ingestion of castor oil results incervical ripening orinduction of labor; there is, however, evidence that taking it causesnausea and diarrhea.[22][23] Asystematic review of "three trials, involving 233 women, found there has not been enough research done to show the effects of castor oil on ripening thecervix or inducing labour or compare it to other methods of induction. The review found that all women who took castor oil by mouth felt nauseous. More research is needed into the effects of castor oil to induce labour."[22][23] Castor oil is still used for labor induction in environments where modern drugs are not available; a review of pharmacologic, mechanical, and "complementary" methods of labor induction published in 2024 by theAmerican Journal of Obstetrics and Gynecology stated that castor oil's physiological effect is poorly understood but "given gastrointestinalsymptomatology, aprostaglandin mediation has been suggested but not confirmed."[24] According toDrugs in Pregnancy and Lactation: A Reference Guide to Fetal and Neonatal Risk (2008), castor oil should not be ingested or used topically by pre-term pregnant women.[25] There is no data on the potential toxicity of castor oil for nursing mothers.[25]
Since children commonly strongly dislike the taste of castor oil, some parentspunished children with a dose of it.[26][27] Physicians recommended against the practice because it may associate medicines with punishment and make children afraid of the doctor.[28]
A heavy dose of castor oil could be used as a humiliating punishment for adults. Colonial officials used it in theBritish Raj (India) to deal with recalcitrant servants.[29] Belgian military officials prescribed heavy doses of castor oil inBelgian Congo as a punishment for being too sick to work.[30] Castor oil was also a tool of punishment favored by theFalangist and laterFrancoist Spain during and following theSpanish Civil War.[31] Its use as a form ofgendered violence to repress women was especially prominent.[31][32] This began during the war whereNationalist forces would specifically target Republican-aligned women, both troops and civilians, who lived inRepublican-controlled areas.[31] The forced drinking of castor oil occurred alongside sexual assault, rape, torture and murder of these women.[31][32]
Its most notorious use as punishment came inFascist Italy underBenito Mussolini. It was a favorite tool used by theBlackshirts to intimidate and humiliate their opponents.[33][34][35]Political dissidents were force-fed large quantities of castor oil byfascist squads so as to induce bouts of extreme diarrhea. This technique was said to have been originated byGabriele D'Annunzio orItalo Balbo.[36] This form of torture was potentially deadly, as the administration of the castor oil was often combined withnightstick beatings, especially to therear, so that the resulting diarrhea would not only lead to dangerous dehydration but alsoinfect the open wounds from the beatings. However, even those victims who survived had to bear thehumiliation of the laxative effects resulting from excessive consumption of the oil.[37]
Castor oil is used as a biobasedpolyol in thepolyurethane industry. The average functionality (number ofhydroxyl groups per triglyceride molecule) of castor oil is 2.7, so it is widely used as a rigid polyol and in coatings.[1] One particular use is in a polyurethane concrete where a castor-oil emulsion is reacted with an isocyanate (usually polymericmethylene diphenyl diisocyanate) and acement andconstruction aggregate. This is applied fairly thickly as a slurry, which is self-levelling. This base is usually further coated with other systems to build a resilient floor.[38] Castor oil is not adrying oil, meaning that it has a low reactivity with air compared with oils such aslinseed oil andtung oil. However, dehydration of castor oil yields linoleic acids, which do have drying properties.[1] In this process, the OH group on the ricinoleic acid along with a hydrogen from the next carbon atom are removed, forming a double bond which then has oxidative cross-linking properties and yields the drying oil. It is considered a vital raw material.[39]
Castor oil can react with other materials to produce other chemical compounds that have numerous applications.[40][41][42][43][44]Transesterification followed bysteam cracking givesundecylenic acid, a precursor to specialized polymernylon 11, andheptanal, a component in fragrances.[45] Breakdown of castor oil in strong base gives2-octanol, both a fragrance component and a specialized solvent, and thedicarboxylic acidsebacic acid. Hydrogenation of castor oil saturates the alkenes, giving a waxy lubricant.[1] Castor oil may be epoxidized by reacting the OH groups withepichlorohydrin to make thetriglycidyl ether of castor oil which is useful in epoxy technology.[46] This is available commercially as Heloxy 505.[47]
The production oflithium grease consumes a significant amount of castor oil.Hydrogenation andsaponification of castor oil yields 12-hydroxystearic acid, which is then reacted withlithium hydroxide orlithium carbonate to give high-performance lubricant grease.[48]
Since it has a relatively highdielectric constant (4.7), highly refined and dried castor oil is sometimes used as adielectric fluid within high-performance, high-voltagecapacitors.
Vegetable oils such as castor oil are typically unattractive alternatives topetroleum-derivedlubricants because of their pooroxidative stability.[49][50] Castor oil has better low-temperatureviscosity properties and high-temperature lubrication than most vegetable oils, making it useful as a lubricant injet,diesel, and racing engines.[51] The viscosity of castor oil at 10 °C is 2,420centipoise,[52] but it tends to form gums in a short time, so its usefulness is limited to engines that are regularly rebuilt, such as racing engines. Lubricant companyCastrol took its name from castor oil.
Castor oil has been suggested as a lubricant forbicycle pumps because it does not degrade natural rubber seals.[53]
Turkey red oil, also called sulphonated (or sulfated) castor oil, is made by addingsulfuric acid to vegetable oils, most notably castor oil.[54] It was the first syntheticdetergent after ordinarysoap. It is used in formulatinglubricants, softeners, anddyeing assistants.[54]
Castor oil, like currently less expensive vegetable oils, can be used as feedstock in the production ofbiodiesel. The resulting fuel is superior for cold winters, because of its exceptionally lowcloud point andpour point.[55]
Initiatives to grow more castor for energy production, in preference to other oil crops, are motivated by social considerations. Tropical subsistence farmers would gain acash crop.[56]
Castor oil was the preferred lubricant forrotary engines, such as theGnome engine after that engine's widespread adoption for aviation in Europe in 1909. It was used almost universally in rotary-engined Allied aircraft inWorld War I. Germany had to make do with inferiorersatz oil for its rotary engines, which resulted in poor reliability.[57][58][59]
Themethanol-fueled, two-cycle,glow-plug engines used for aeromodelling, since their adoption bymodel airplane hobbyists in the 1940s, have used varying percentages of castor oil as lubricants. It is highly resistant to degradation when the engine has its fuel-air mixture leaned for maximum engine speed. Gummy residues can still be a problem for aeromodelling powerplants lubricated with castor oil, however, usually requiring eventual replacement ofball bearings when the residue accumulates within the engine's bearing races. One British manufacturer ofsleeve valved four-cycle model engines has stated the "varnish" created[citation needed] by using castor oil in small percentages can improve the pneumatic seal of the sleeve valve, improving such an engine's performance over time.
The castor seed containsricin, a toxiclectin. Heating during the oil extraction process denatures and deactivates the lectin. Harvesting castor beans, though, may not be without risk.[60] The International Castor Oil Association FAQ document states that castor beans contain an allergenic compound called CB1A. This chemical is described as being virtually nontoxic, but has the capacity to affect people with hypersensitivity. The allergen may be neutralized by treatment with a variety of alkaline agents. The allergen is not present in the castor oil itself.[61]
{{cite book}}: CS1 maint: location missing publisher (link)Despite its long history of use for inducing onset of spontaneous labor, castor oil has minimal evidence to support its efficacy and is commonly associated with adverse effects of nausea, vomiting, and diarrhea.
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