Paracymene (PCM)

p-Cymene, is a naturally occurring aromatic organic compound. It is classified as an alkylbenzene related to a monoterpene. Its structure consists of a benzene ring para-substituted with a methyl group and an isopropyl group. There are two less common geometric isomers. o-Cymene, in which the alkyl groups are ortho-substituted, and m-cymene, in which they are meta-substituted. p-Cymene is the only natural isomer. All three isomers form the group of cymenes. p-Cymene is insoluble in water, but miscible with ethanol and diethyl ether. It is a constituent of a number of essential oils, most commonly the oil of cumin and thyme. Significant amounts are formed in sulfite pulping process from the wood terpenes. p-Cymene is a common ligand for ruthenium. The parent compound is [(η6-cymene)RuCl2]2. This half-sandwich compound is prepared by the reaction of ruthenium trichloride with the terpene α-phellandrene.