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Ricinoleic acid is a hydroxy fatty acid — systematic name 12-hydroxy-9-cis-octadecenoic acid — that makes up about 85–90% of castor oil. Its formula is C₁₈H₃₄O₃ and its CAS number is 141-22-0. What sets it apart is a hydroxyl (–OH) group on its carbon chain, on top of the usual acid group and a double bond. That gives it three reactive sites instead of one, which is why castor oil behaves so differently from every other vegetable oil.
A fatty acid is a long carbon chain with an acid group at one end. Ricinoleic acid follows that pattern — an 18-carbon chain — but adds something rare: a hydroxyl group on the 12th carbon. It occurs naturally and abundantly only in castor oil, which is exactly why castor is such a valued industrial crop. Strip the oil down and you are essentially working with ricinoleic acid.
The reason chemists prize ricinoleic acid is its tri-functional structure. On a single molecule you have:
Most fatty acids offer only the first of these. Having all three on one chain is what makes ricinoleic acid a flexible building block rather than just an oil component.
| Fatty acid | Chain | Hydroxyl group? | Key trait |
|---|---|---|---|
| Ricinoleic | C18, 1 double bond | Yes (C-12) | Tri-functional, reactive, high viscosity |
| Oleic | C18, 1 double bond | No | Common, stable, low reactivity |
| Stearic | C18, saturated | No | Fully saturated, waxy, inert |
The only structural difference between oleic and ricinoleic acid is that hydroxyl group — and yet it changes the behaviour of the molecule completely.
Because of its reactivity, ricinoleic acid (and its derivatives) appears in bio-lubricants and estolides, alkyd and epoxy-ester resins, polyurethanes and bio-polymers such as nylon-11, cosmetics and surfactants, and as the basis of sulphated (Turkey Red) oil for textiles. For the commercial specification and supply details, see our ricinoleic acid product page.
It helps to be precise: castor oil is a triglyceride — three fatty acids attached to a glycerol backbone, mostly ricinoleic acid. Ricinoleic acid is the free fatty acid you get when that triglyceride is split. So castor oil is the raw material; ricinoleic acid is one of the most useful things you can make from it. Curious how the oil itself is produced? See what is castor oil.
A hydroxy fatty acid (12-hydroxy-9-cis-octadecenoic acid) making up ~85–90% of castor oil. Formula C₁₈H₃₄O₃, CAS 141-22-0. Its hydroxyl group gives castor oil its distinctive behaviour.
It has three reactive sites — an acid group, a double bond and a hydroxyl group — where most fatty acids have only one. That lets it be esterified, oxidised, polymerised and turned into urethanes.
No. Castor oil is a triglyceride containing ricinoleic acid; ricinoleic acid is the free fatty acid released when the oil is split, and it is more reactive.
Bio-lubricants, resins, polyurethanes and bio-polymers, cosmetics and surfactants, and as the basis of sulphated (Turkey Red) oil.
