Camphor
Properties
| State | Solid (white or translucent waxy crystalline solid with strong aromatic odor) |
| Color | White to translucent |
| Solubility | Slightly soluble in water (1.2 g/L at 25°C); freely soluble in ethanol, ether, and acetone |
| Melting Point | 175-177°C |
| Boiling Point | 204°C (sublimes readily) |
About Camphor
Camphor is a bicyclic monoterpene ketone built on the norbornane (bicyclo[2.2.1]heptane) skeleton with a carbonyl at C2 and three methyl groups locked onto the bridgehead carbons. That rigid cage geometry is what makes the molecule chemically interesting — it cannot pucker or relax, every substituent has a fixed exo or endo face, and the C=O is approached by nucleophiles with strong facial selectivity that depends on whether they attack from the convex exo face (kinetically preferred) or the more hindered endo face. This made camphor and its derivatives the test bed for one of the longest-running arguments in physical organic chemistry: the Winstein–Brown debate of the 1950s through 1970s over whether the 2-norbornyl cation, the carbocation generated by ionizing camphor-derived sulfonates, was a classical secondary cation rapidly equilibrating between two structures or a non-classical bridged cation with three-center two-electron σ delocalization. The argument was finally settled in 2013 by low-temperature X-ray crystallography of the cation in superacidic media, which showed the bridged structure outright. Beyond the carbocation history, the same molecule is the active counterirritant in Vicks VapoRub and Tiger Balm at 3 to 11 percent loading, where it activates TRPV3 warm receptors and TRPA1 in sensory neurons to produce a warming sensation that masks underlying pain. Natural (R)-(+)-camphor is steam-distilled from the wood of Cinnamomum camphora; synthetic racemic camphor is made from α-pinene through the Wagner–Meerwein rearrangement that turns pinene into bornyl chloride and then to camphor by oxidation.
Where you'll encounter it
If you have ever rubbed Vicks on a kid's chest at 2 a.m. or reached for a Tiger Balm tin for sore shoulders, that warming smell coming off the salve is camphor. In an organic teaching lab, camphor sublimes cleanly at atmospheric pressure — drop a few crystals on a watch glass and within hours you have rebuilt them as needles on the underside of an inverted funnel, which is how undergraduates first see the technique. In medicinal chemistry, (1R)-camphorsulfonic acid (CSA) is one of the standard chiral resolving agents on the shelf for separating enantiomers of basic amines through diastereomeric salt formation, and Oppolzer's camphorsultam — built from camphor — is a workhorse chiral auxiliary in asymmetric synthesis.
Common Uses
- Counterirritant in topical analgesics like Vicks VapoRub and Tiger Balm at 3 to 11 percent loading
- Chiral auxiliary precursor for Oppolzer's camphorsultam in asymmetric aldol and Diels–Alder chemistry
- (1R)-Camphorsulfonic acid as a chiral resolving agent for amines via diastereomeric salt formation
- Plasticizer in nitrocellulose lacquers and historically in celluloid film stock
- Moth and clothing-pest repellent, sublimation-active in closed wardrobes and boxes
Safety Information
GHS: H228 (flammable solid), H301 (toxic if swallowed), H319 (eye irritation), H335 (respiratory irritation). Pediatric ingestion is the dangerous scenario — as little as 1 g (the contents of one or two over-the-counter camphor preparations) can trigger seizures in a child, and ingestion of 50 to 500 mg/kg is potentially lethal. Topical concentrations above 11 percent are restricted in the US by FDA. Vapors from heating camphor are CNS-depressant; ensure ventilation when subliming. Skin absorption is real — wear nitrile gloves when handling solid material in bulk.
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. We deliberately do not publish occupational exposure limits or other regulatory thresholds: those values are revised over time and differ between jurisdictions, so the only correct source is the current SDS and the regulations that apply where you work.