Phenol
Phenol (also known as carbolic acid, phenolic acid, or benzenol) is an aromatic organic compound with the molecular formula C6H5OH.[5] It is a white crystalline solid that is volatile. The molecule consists of a phenyl group (−C6H5) bonded to a hydroxy group (−OH). Mildly acidic, it requires careful handling because it can cause chemical burns.[5]
This article is about the molecule. For the group of chemicals that contains a phenol group, see Phenols.Phenol was first extracted from coal tar, but today is produced on a large scale (about 7 million tonnes a year) from petroleum-derived feedstocks. It is an important industrial commodity as a precursor to many materials and useful compounds.[8] It is primarily used to synthesize plastics and related materials. Phenol and its chemical derivatives are essential for production of polycarbonates, epoxies, explosives, Bakelite, nylon, detergents, herbicides such as phenoxy herbicides, and numerous pharmaceutical drugs.[9]
Occurrences[edit]
Phenol is a normal metabolic product, excreted in quantities up to 40 mg/L in human urine.[49] The temporal gland secretion of male elephants showed the presence of phenol and 4-methylphenol during musth.[53][54] It is also one of the chemical compounds found in castoreum. This compound is ingested from the plants the beaver eats.[55]
Phenol is a measurable component in the aroma and taste of the distinctive Islay scotch whisky,[56] generally ~30 ppm, but it can be over 160ppm in the malted barley used to produce whisky.[57] This amount is different from and presumably higher than the amount in the distillate.[56]
Biodegradation[edit]
Cryptanaerobacter phenolicus is a bacterium species that produces benzoate from phenol via 4-hydroxybenzoate.[58] Rhodococcus phenolicus is a bacterium species able to degrade phenol as sole carbon source.[59]
Toxicity[edit]
Phenol and its vapors are corrosive to the eyes, the skin, and the respiratory tract.[60] Its corrosive effect on skin and mucous membranes is due to a protein-degenerating effect.[49] Repeated or prolonged skin contact with phenol may cause dermatitis, or even second and third-degree burns.[61] Inhalation of phenol vapor may cause lung edema.[60] The substance may cause harmful effects on the central nervous system and heart, resulting in dysrhythmia, seizures, and coma.[62] The kidneys may be affected as well. Long-term or repeated exposure of the substance may have harmful effects on the liver and kidneys.[63] There is no evidence that phenol causes cancer in humans.[64] Besides its hydrophobic effects, another mechanism for the toxicity of phenol may be the formation of phenoxyl radicals.[65]
Since phenol is absorbed through the skin relatively quickly, systemic poisoning can occur in addition to the local caustic burns.[49] Resorptive poisoning by a large quantity of phenol can occur even with only a small area of skin, rapidly leading to paralysis of the central nervous system and a severe drop in body temperature. The LD50 for oral toxicity is less than 500 mg/kg for dogs, rabbits, or mice; the minimum lethal human dose was cited as 140 mg/kg.[49] The Agency for Toxic Substances and Disease Registry (ATSDR), U.S. Department of Health and Human Services states the fatal dose for ingestion of phenol is from 1 to 32 g.[66]
Chemical burns from skin exposures can be decontaminated by washing with polyethylene glycol,[67] isopropyl alcohol,[68] or perhaps even copious amounts of water.[69] Removal of contaminated clothing is required, as well as immediate hospital treatment for large splashes. This is particularly important if the phenol is mixed with chloroform (a commonly used mixture in molecular biology for DNA and RNA purification). Phenol is also a reproductive toxin causing increased risk of miscarriage and low birth weight indicating retarded development in utero.[5]