p-Cymene

Description

November is flavor and aroma month!
It’s almost Thanksgiving! Among the holiday treats that most of us enjoy is cranberry sauce, whether it’s full of whole berries or simply a wiggly gelatin. What compounds are in cranberries that make the sauce taste so good?
According to the Science and Food program at the University of California, Los Angeles, the primary flavor compounds are ethyl benzoate, p-cymene, α-terpineol, and 1,8-cineole (aka eucalyptol). The latter two are former Molecules of the Week, so the first two take center stage this year.
Ethyl benzoate is a simple ester of benzoic acid with a sweet, fruity aroma. It has been known since the late 19th century; it is found in fruits such as apples, bananas, cherries, and of course, cranberries. Synthetic ethyl benzoate is made by esterifying benzoic acid and ethanol with an acid catalyst such as hydrochloric or sulfuric acid. It is used as an ingredient in perfumes and artificial fruit-flavoring agents.
p-Cymene is a dialkyl aromatic hydrocarbon. In addition to being a flavor component in cranberries, it is abundant in several essential oils, notably the oils of cumin and thyme. Its aroma and flavor have been described as having hints of citrus, earth, and wood. It can be synthesized from petrochemicals (e.g., the alkylation of toluene with propylene) or from natural terpenes (e.g., by microwave irradiation of limonene). Like ethyl benzoate, p-cymene is used as a flavoring agent; but it also has medicinal uses (in cough syrup) and as a starting material for manufacturing pesticides.
Needless to say, while you’re enjoying your Thanksgiving dinner, you won’t be focusing on any of this. Have a happy holiday!

Chemical properties

p-Cymene is a monoterpene that is found in a variety of plants, including C. sativa, and has diverse biological activities, including antimicrobial, anticancer, antioxidant, anti-inflammatory, antinociceptive, and anxiolytic properties.p-Cymene inhibits the growth of S. typhimurium, E. coli, L. monocytogenes, S. epidermidis, and S. aureus with MIC values ranging from 0.266 to 0.608% v/v.It decreases the invasive activity of HT-1080 human fibrosarcoma cells in vitro by 87% when used at a concentration of 600 μM.In mouse hippocampus, p-Cymene (50 mg/kg, i.p.) reduces lipid peroxidation and nitrite content by 65.5 and 71.2%, respectively, and increases superoxide dismutase (SOD) and catalase activities by 22.7 and 119.3%, respectively, compared to vehicle control animals.Formulations containing p-cymene have been used as flavoring agents.

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.

The Uses of p-Cymene

As a diluent for lacquers, varnishes, and dyes; in the production of resins; as a component of fragrances; also found as a byproduct in the manufacture of sulfite paper pulp

The Uses of p-Cymene

It is used in heat-exchange media, metal polishes, and thinners for lacquers/varnishes. Also used to make para-cresol, carvacrol, and synthetic resins. It is also used as a component of commercial terpene solvent mixtures.

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.

Synthesis Reference(s)

Journal of the American Chemical Society, 95, p. 982, 1973 DOI: 10.1021/ja00784a090

General Description

Colorless liquid with a mild pleasant odor. Floats on water.

Air & Water Reactions

Insoluble in 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.

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.

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.

Safety Profile

Mildly toxic by ingestion. Humans sustain central nervous system effects at low doses. A skin irritant. Flammable liquid. Explosion Hazard: Slight in the form of vapor. To fight fire, use foam, CO2, dry chemical. When heated to decomposition it emits acrid smoke and fumes.

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.]