Cresols (also hydroxytoluene or cresylic acid) are a group of aromatic

organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. T ...

s. They are widely-occurring

phenols In organic chemistry, phenols, sometimes called phenolics, are a class of chemical compounds consisting of one or more hydroxyl groups (— O H) bonded directly to an aromatic hydrocarbon group. The simplest is phenol, . Phenolic compounds are ...

(sometimes called ''phenolics'') which may be either natural or manufactured. They are also categorized as methyl

phenol Phenol (also called carbolic acid) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile. The molecule consists of a phenyl group () bonded to a hydroxy group (). Mildly acidic, it ...

s. Cresols commonly occur as either solids or liquids because their

melting point The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depen ...

s are generally close to room temperature. Like other types of phenols, they are slowly oxidized by exposure to

air The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing f ...

, and the resulting impurities often give the samples a yellow to brownish red tint. Cresols have an odor characteristic to that of other simple phenols, reminiscent to some of a "

coal tar Coal tar is a thick dark liquid which is a by-product of the production of coke and coal gas from coal. It is a type of creosote. It has both medical and industrial uses. Medicinally it is a topical medication applied to skin to treat psorias ...

" smell. The name "cresol" is an adduct of phenol and their traditional source,

creosote Creosote is a category of carbonaceous chemicals formed by the distillation of various tars and pyrolysis of plant-derived material, such as wood or fossil fuel. They are typically used as preservatives or antiseptics. Some creosote types were ...

Structure and production

In its

chemical structure A chemical structure determination includes a chemist's specifying the molecular geometry and, when feasible and necessary, the electronic structure of the target molecule or other solid. Molecular geometry refers to the spatial arrangement of ...

, a

molecule A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioche ...

of cresol has a

methyl group In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula . In formulas, the group is often abbreviated as Me. This hydrocarbon group occurs in ma ...

substituted onto the ring of phenol. There are three forms (

isomers In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers. ...

) of cresol: ''ortho''-cresol ( ''o''-cresol), ''meta''-cresol ( ''m''-cresol), and ''para''-cresol ( ''p''-cresol). These forms occur separately or as a mixture, which can also be called cresol or more specifically, tricresol. About half of the world's supply of cresols are extracted from coal tar. The rest is produced by hydrolysis of

chlorotoluene Chlorotoluene is a group of three isomeric chemical compounds. They (''ortho''-chlorotoluene, ''meta''-chlorotoluene, and ''para''-chlorotoluene) consist of a disubstituted benzene ring with one chlorine atom and one methyl group. Properties The ...

s or the related sulfonates. Another method entails methylation of phenol with methanol over a solid acid catalyst, often comprising magnesium oxide or alumina. Temperatures above 300 °C are typical. Anisole converts to cresols under these conditions.

Applications

Cresols are precursors or synthetic intermediates to other compounds and materials, including plastics, pesticides, pharmaceuticals, and dyes.Helmut Fiegein "Cresols and Xylenols" in Ullmann's Encyclopedia of Industrial Chemistry" 2007; Wiley-VCH, Weinheim. For cresol bactericides or disinfectants the mechanism of action is due to the destruction of bacterial cell membranes. Most recently, cresols have been used to create a breakthrough in manufacturing

carbon nanotubes A scanning tunneling microscopy image of a single-walled carbon nanotube Rotating single-walled zigzag carbon nanotube A carbon nanotube (CNT) is a tube made of carbon with diameters typically measured in nanometers. ''Single-wall carbon na ...

at scale that are separated and not twisted, without additional chemicals that change the surface properties of the nanotubes.

Commercial examples

* Creolin, a 19th-century disinfectant. * Carbolic soap, 19th-century. * The original

Lysol Lysol (; spelled Lizol in India) is a brand of American cleaning and disinfecting products distributed by Reckitt, which markets the similar Dettol or Sagrotan in other markets. The line includes liquid solutions for hard and soft surfaces, ai ...

formulation, essentially a water solution of carbolic soap. "Lysol" has been used as a generic trademark to refer to such a cresol soap solution and remains used as such in some professional settings. The CAS number is 12772-68-8.

Derivatives

Derivatives of ''p''-cresol include: * Butylated hydroxytoluene, a common antioxidant Derivatives of ''o''-cresol include: *

Indo-1 Indo-1 is a popular calcium indicator similar to Fura-2. In contrast to Fura-2, Indo-1 has a dual emissions peak. The main emission peak in calcium-free solution is 475 nm while in the presence of calcium the emission is shifted to 400 ...

, a popular calcium indicator * MCPA, (4-chloro-2-methylphenoxy)acetic acid * MCPB, 4-(4-chloro-2-methylphenoxy)butanoic acid *

Mecoprop Mecoprop (also known as methylchlorophenoxypropionic acid and MCPP) is a common general use herbicide found in many household weed killers and "weed-and-feed" type lawn fertilizers. It is primarily used to control broadleaf weeds.amine In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen Hydrogen is the chemical element wi ...

atomoxetine, (3''R'')-''N''-methyl-3-(2-methylphenoxy)-3-phenylpropan-1-amine *the diol

mephenesin Mephenesin ( INN) is a centrally acting muscle relaxant. It can be used as an antidote for strychnine poisoning. Mephenesin however presents with the major drawbacks of having a short duration of action and a much greater effect on the spinal co ...

, 3-(2-methylphenoxy)propane-1,2-diol Derivatives of ''m''-cresol include: *

Amylmetacresol Amylmetacresol (AMC) is an antiseptic used to treat infections of the mouth and throat. It is used as an active pharmaceutical ingredient in Strepsils, Cēpacol, Gorpils and Lorsept throat lozenges, typically in combination with dichlorobenzy ...

, an

antiseptic An antiseptic (from Greek ἀντί ''anti'', "against" and σηπτικός ''sēptikos'', "putrefactive") is an antimicrobial substance or compound that is applied to living tissue/skin to reduce the possibility of infection, sepsis, or putre ...

* Bevantolol, (''RS'')- -(3,4-dimethoxyphenyl)ethyl2-hydroxy-3-(3-methylphenoxy)propyl]amine *

Bromocresol green Bromocresol green (BCG) is a dye of the triphenylmethane family (triarylmethane dyes). It belongs to a class of dyes called sulfonephthaleins. It is used as a pH indicator in applications such as growth mediums for microorganisms and titrations. ...

* Bupranolol, a non-selective

beta blocker Beta blockers, also spelled β-blockers, are a class of medications that are predominantly used to manage abnormal heart rhythms, and to protect the heart from a second heart attack after a first heart attack ( secondary prevention). They are ...

* Chloro-''m''-cresol which is used as a household disinfectant * Tolimidone, 5-(3-methylphenoxy)pyrimidin-2(1''H'')-one

Health effects

When cresols are inhaled, ingested, or applied to the

skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other animal coverings, such as the arthropod exoskeleton, have different de ...

, they can be very harmful. Effects observed in people include irritation and burning of skin, eyes, mouth, and

throat In vertebrate anatomy, the throat is the front part of the neck, internally positioned in front of the vertebrae. It contains the pharynx and larynx. An important section of it is the epiglottis, separating the esophagus from the trachea (windpip ...

; abdominal pain and vomiting;

heart The heart is a muscular organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide to t ...

damage;

anemia Anemia or anaemia (British English) is a blood disorder in which the blood has a reduced ability to carry oxygen due to a lower than normal number of red blood cells, or a reduction in the amount of hemoglobin. When anemia comes on slowly, t ...

;

liver The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it ...

and

kidney The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; blo ...

damage; facial paralysis; coma; and

death Death is the irreversible cessation of all biological functions that sustain an organism. For organisms with a brain, death can also be defined as the irreversible cessation of functioning of the whole brain, including brainstem, and brain ...

. 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, for example, at lower levels over longer times. Ingesting high levels results in kidney problems, mouth and throat burns, abdominal pain, vomiting, and effects on the

blood Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the cir ...

and

nervous system In biology, the nervous system is the highly complex part of an animal that coordinates its actions and sensory information by transmitting signals to and from different parts of its body. The nervous system detects environmental changes ...

. Skin contact with high levels of cresols can burn the skin and damage the kidneys, liver, blood,

brain A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a ve ...

, and lungs. Short-term and long-term studies with animals have shown similar effects from exposure to cresols. No human or animal studies have shown harmful effects from cresols on reproduction. It is not known what the effects are from long-term ingestion or skin contact with low levels of cresols. The Occupational Safety and Health Administration has set a permissible exposure limit at 5 ppm (22 mg/m³) over an eight-hour time-weighted average, while the

National Institute for Occupational Safety and Health The National Institute for Occupational Safety and Health (NIOSH, ) is the United States federal agency responsible for conducting research and making recommendations for the prevention of work-related injury and illness. NIOSH is part of the C ...

recommends a limit of 2.3 ppm (10 mg/m³).Documentation for Immediately Dangerous To Life or Health Concentrations (IDLHs) - Cresol (o, m, p isomers)
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References