Limonene
Properties
| State | Liquid (colorless to pale yellow with strong citrus odor) |
| Color | Colorless to pale yellow |
| Solubility | Insoluble in water; miscible with ethanol, ether, and most organic solvents |
| Melting Point | -74°C |
| Boiling Point | 176°C |
About Limonene
Limonene is a cyclic monoterpene that biosynthesis builds from two isoprene units, and which orange-juice processors recover by the truckload from the peel residue left after juicing — over 70,000 tonnes a year, making it the largest single terpene byproduct on the world market. Cold-pressed orange peel oil is roughly 95% (R)-(+)-limonene, while turpentine and conifer extracts give mixed and (S)-(-)-rich material. The chirality matters: (R)-limonene smells like fresh orange peel, (S)-limonene smells distinctly piney or turpentine-ish, and the difference is one of the cleanest demonstrations in olfaction that human odorant receptors are themselves chiral and discriminate enantiomers without the help of a derivatization step. Industrially, limonene's appeal is that it dissolves polystyrene foam and most polyolefin oils on contact while being biodegradable in soil and water within weeks (BOD5 ~150 mg O2/g) — Styrofoam packing peanuts will collapse into a sticky liquid in a beaker of D-limonene at ten times their starting volume, the standard demo for green-chemistry recycling pitches. Lab uses include adhesive removal, paraffin-wax dewaxing in histology slides (it replaces xylene with much lower neurotoxicity), and as a bio-based feedstock for Vandeurzen-style polylimonene carbonate plastics from CO2. The flash point at 48 °C and the tendency of oxidized limonene to form skin-sensitizing hydroperoxides are the two hazards that come up first in every safety brief.
Where you'll encounter it
If you've ever scratched an orange peel and gotten that bright citrus burst right under your nose, or used a 'natural' citrus degreaser to lift grease off a stovetop, you've handled D-limonene at near-100% concentration. Florida and Brazilian orange-juice processors recover over 70,000 tonnes of D-limonene per year by steam-distilling it from the peel residue left after juicing, and that recovery stream feeds everything from the citrus-scented degreasers under your kitchen sink (which work because limonene dissolves grease as effectively as mineral spirits) to the bio-based PLA additives in compostable cutlery. Histology labs replace toxic xylene with limonene for paraffin section dewaxing because it does the same job without the neuropathy risk. And green-chemistry classroom demos use it to dramatically dissolve Styrofoam packing peanuts on contact — a beaker swallows ten times its volume of foam in seconds.
Common Uses
- Citrus flavor and fragrance principal in orange-, lemon-, and grapefruit-scented products
- Biodegradable degreaser and parts-washer solvent (replaces mineral spirits)
- Polystyrene-foam dissolution and EPS recycling stream feedstock
- Histology dewaxing solvent replacing xylene in paraffin section processing
- Adhesive remover for stickers, labels, and asphalt roofing residues
- Monomer for polylimonene carbonate bio-based plastics synthesized with CO2
- Carrier solvent in agricultural pesticide and herbicide formulations
- Teaching example for chirality, olfaction, and renewable feedstock chemistry
Safety Information
GHS: Flam. Liq. 3 (H226, flash point 48 °C), Skin Irrit. 2 (H315), Skin Sens. 1 (H317), Aquatic Acute 1/Chronic 1 (H400/H410). Fresh limonene is a mild skin irritant; the skin-sensitization hazard kicks in once limonene oxidizes during storage to limonene-1-hydroperoxide and limonene-2-hydroperoxide, which are potent contact allergens responsible for many fragrance dermatitis cases. Store under nitrogen or with antioxidants. GRAS for food use at typical flavoring concentrations (FEMA 2633). Not classified as carcinogenic to humans (IARC Group 3).
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.