p-Cymene
1-Methyl-4-(1-methylethyl)benzene
4-Isopropyl toluene · Dolcymene
化学組成 · Constituent
1-Methyl-4-(1-methylethyl)benzene
4-Isopropyl toluene · Dolcymene
化学組成 · Constituent
p-Cymene is a monocyclic hydrocarbon common in Lamiaceae oils. The compound is also a natural degradation product of other monoterpenes.
Skin. A 4 percent patch test on 25 volunteers caused no irritation or sensitization, although it has been reported as a primary irritant. Undiluted application was moderately irritant to rabbit skin. Among tea tree sensitive patients, one of seven reacted to 1 percent. In a separate group of 11 patients, 5 percent caused no reactions.
Oral and dermal. Acute oral LD50 in rats is 4.75 g/kg; rabbit dermal LD50 exceeds 5 g/kg.
p-Cymene often appears as a degradation product of γ-terpinene, α-terpinene and other monoterpenes. Rising concentration with oil age is a marker of oxidation.
| Black seed | 14.7 – 38.0 % |
| Thyme (thymol CT, carvacrol CT, thymol/carvacrol CT) | 7.2 – 37.7 % |
| Oregano (Mexican) | 7.7 – 28.0 % |
| Camphor (white) | 24.2 % |
| Ajowan | 20.8 – 24.0 % |
| Eucalyptus (polybractea cryptone CT) | 18.3 % |
| Cascarilla | 10.0 – 18.0 % |
| Cumin | 5.9 – 17.5 % |
| Savory (summer + winter) | 0.9 – 14.6 % |
| Pepper (pink) | 2.9 – 11.5 % |
| Pteronia | 11.3 % |
| Bee balm | 2.1 – 11.0 % |
| Oregano | 3.0 – 10.9 % |
| Lime (expressed) | 0.4 – 10.4 % |
| Thyme (spike) | 10.1 % |
| Angelica root | 3.5 – 9.8 % |
| Boldo | 8.6 % |
| Narcissus | 1.3 – 8.5 % |
| Coriander seed | 0 – 8.4 % |
| Tea tree | 0.5 – 8.0 % |
| Elemi | 1.4 – 7.7 % |
| Fir cones (silver) | 0.1 – 7.5 % |
| Southernwood | 7.3 % |
| Pine (dwarf) | 0.4 – 6.9 % |
| Cajuput | 0.7 – 6.8 % |
| Labdanum | 2.1 – 6.3 % |
| Marjoram wild (carvacrol CT) | 5.2 – 6.0 % |
| Marjoram (sweet) | 2.2 – 5.3 % |
p-Cymene shows marked species differences in metabolism, with 23 metabolites identified. The major metabolite in rats is cumic acid; in guinea pigs cuminuric acid. p-Cymen-8-ol and p-cymen-9-ol are minor in both. In rabbits, the compound is metabolized to myrcene-3(10)-glycol, uroterpenol and p-cymene-9-carboxylic acid.
p-Cymene is a marker constituent for thymol- and carvacrol-rich oils. The compound is more stable than its terpene precursors and signals an aged or oxidized oil.
It is also found at low levels in over 200 other essential oils.