O-Cresol

Natural occurrences

o-Cresol is one of the chemical compounds found in castoreum. This compound is gathered from the beaver's castor glands and found in the white cedar consumed by the beaver.

o-Cresol is a constituent of tobacco smoke.

Production

Together with many other compounds, o-cresol is traditionally extracted from coal tar, the volatile materials obtained in the production of coke from coal. A similar source material is petroleum residues. These residue contains a few percent by weight of phenol and isomeric cresols. In addition to the materials derived from these natural sources, about two thirds of the Western world's supply is produced by methylation of phenol using methanol. The alkylation is catalysed by metal oxides: :C6H5OH + CH3OH → CH3C6H4OH + H2O Over-methylation gives xylenol. Many other production methods have been examined, including oxidative decarboxylation of salicylic acid, oxygenation of toluene, and hydrolysis of 2-chlorotoluene.

Applications

o-Cresol is mainly used as a precursor to other compounds. Chlorination and etherification gives members of commercially important herbicides, such as 2-methyl-4-chlorophenoxyacetic acid (MCPA). Nitration gives dinitrocresol, a popular herbicide. Kolbe–Schmitt carboxylation gives o-cresotinic acid, a pharmaceutical intermediate. Carvacrol, essence of oregano, is derived by alkylation of o-cresol with propene. The muscle relaxant mephenesin is an ether derived from o-cresol.

Health effects

Most exposures to cresols are at very low levels that are not harmful although, like phenols, cresols are skin irritants. When cresols are inhaled, ingested, or applied to the skin at very high levels, they can be harmful. Breathing high levels of cresols for a short time results in irritation of the nose and throat. Aside from these effects, very little is known about the effects of breathing cresols at lower levels over longer times. The acute LD50 for oral ingestion by mice is 344 mg/kg.

References

References

1. {{IDLH. cresol. Cresol (o, m, p isomers)
2. {{PGCH. 0154
3. Helmut Fiegein "Cresols and Xylenols" in Ullmann's Encyclopedia of Industrial Chemistry" 2007; Wiley-VCH, Weinheim. {{doi. 10.1002/14356007.a08_025
4. The Beaver: Its Life and Impact. Dietland Muller-Schwarze, 2003, page 43 ([https://books.google.com/books?id=HZ5WjXB5Pr8C&dq=Castoreum+beekeeping&pg=PA43 book at google books])
5. (2011). "Hazardous Compounds in Tobacco Smoke". International Journal of Environmental Research and Public Health.