General Description
Colorless liquid with a mild pleasant odor. Floats on water.
Reactivity Profile
Vigorous reactions, sometimes amounting to explosions, can result from the contact between aromatic hydrocarbons, such as CYMENE, and strong oxidizing agents. They can react exothermically with bases and with diazo compounds. Substitution at the benzene nucleus occurs by halogenation (acid catalyst), nitration, sulfonation, and the Friedel-Crafts reaction.
Air & Water Reactions
Insoluble in water.
Health Hazard
Inhalation causes impairment of coordination, headache. Contact with liquid causes mild irritation of eyes and skin. Ingestion causes irritation of mouth and stomach.
Fire Hazard
HIGHLY FLAMMABLE: Will be easily ignited by heat, sparks or flames. Vapors may form explosive mixtures with air. Vapors may travel to source of ignition and flash back. Most vapors are heavier than air. They will spread along ground and collect in low or confined areas (sewers, basements, tanks). Vapor explosion hazard indoors, outdoors or in sewers. Runoff to sewer may create fire or explosion hazard. Containers may explode when heated. Many liquids are lighter than water.
Occurrence
Widespread in nature; reported in the oils of cypress, Artemisia cina Bg., Ceylon cinnamon, boldo leaf, cascarilla,
Cuminum cyminum L. and lemon; in the oils for seeds of coriander and Cicuta virosa; in the ether-extracted oils of Monarda
fisulosa and Monarda puncata; in the star anise and nutmeg essential oils. Note that p-cymene reported in essential oil may be
formed from the conversion of a cyclic terpene; its presence is indicative of aging in lemon essential oil. Reported found in citrus
juices and peel oils, guava, papaya, black currant, pineapple, blueberry, blackberry, carrot, tomato, celery seed, cumin seed, mace,
ginger, coriander seed, anise, nutmeg, mace, parsley, cardamom, cinnamon root and bark, pepper, peppermint oil, spearmint oil,
cassia leaf and Thymus vulgaris.
Definition
ChEBI: A monoterpene that is toluene substituted by an isopropyl group at position 4.
Preparation
Obtained chiefly from the wash water of sulfite paper.
Aroma threshold values
Aroma characteristics at 1% EtoH: harsh chemical, woody and terpy-like with an oxidized citrus lemon
note. It has spicy nuances reminiscent of cumin, oregano and cilantro
Taste threshold values
Taste characteristics at 1 to 10 ppm: terpy and rancid with slightly woody, oxidized citrus notes. It has spice
nuances of green pepper and oregano.
Flammability and Explosibility
Flammable
Chemical Reactivity
Reactivity with Water: No reaction; Reactivity with Common Materials: No reaction; Stability During Transport: Stable; Neutralizing Agents for Acids and Caustics: Not pertinent; Polymerization: Not pertinent; Inhibitor of Polymerization: Not pertinent.
Metabolism
In this compound both an isopropyl and a methyl group occur together and the available evidence shows that only the methyl group is oxidized, cumic acid (pisopropylbenzoic acid) and its conjugate (cuminuric acid) being the main metabolites in dogs and in sheep (Williams, 1959). Following inhalation, only a small part is excreted unchanged, the remainder being oxidized to water-soluble metabolites. As early as 1873, Ziegler suggested that the readily oxidized propyl side-chain formed a -COO H group (Browning, 1965): The ultimate product in the case of dogs and sheep is cumic acid, which is probably excreted as a conjugate with glycine (Gerarde, 1960).
Purification Methods
Wash p-cymene with cold, conc H2SO4 until there is no further colour change, then repeatedly with H2O, 10% aqueous Na2CO3 and H2O again. Dry it over Na2SO4, CaCl2 or MgSO4, and distil it. Further purification steps include steam distillation from 3% NaOH, percolation through silica gel or activated alumina, and a preliminary reflux for several days over powdered sulfur. Store it over CaH2. [Beilstein 5 IV 1060.]
