Cresols (also known as hydroxytoluene, toluenol, benzol or cresylic acid) are a group of aromatic

organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...

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 ar ...

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

phenol Phenol (also known as carbolic acid, phenolic acid, or benzenol) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile and can catch fire. The molecule consists of a phenyl group () ...

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 of matter, state from solid to liquid. At the melting point the solid and liquid phase (matter), phase exist in Thermodynamic equilib ...

s are generally close to room temperature. Like other types of phenols, they are slowly oxidized by exposure to air, and the resulting impurities often give the samples a yellow to brownish red tint. Cresols have an

odor An odor (American English) or odour ( Commonwealth English; see spelling differences) is a smell or a scent caused by one or more volatilized chemical compounds generally found in low concentrations that humans and many animals can perceive ...

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 psoria ...

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

Structure and production

In its

chemical structure A chemical structure of a molecule is a spatial arrangement of its atoms and their chemical bonds. Its determination includes a chemist's specifying the molecular geometry and, when feasible and necessary, the electronic structure of the target m ...

, a

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

of cresol has a methyl group substituted onto the ring of phenol. There are three forms ( 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 Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution reaction, substitution, elimination reaction, elimination, and solvation reactions in which water ...

of chlorotoluenes 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. Another

isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, the same number of atoms of each element (chemistry), element – but distinct arrangements of atoms in space. ''Isomerism'' refers to the exi ...

of cresol is called Benzyl alcohol, or ''alpha''-cresol (α-cresol). Benzyl alcohol has a hydroxy group inside a methyl group on the

benzene Benzene is an Organic compound, organic chemical compound with the Chemical formula#Molecular formula, molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar hexagonal Ring (chemistry), ring with one hyd ...

ring.

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 carbon nanotube (CNT) is a tube made of carbon with a diameter in the nanometre range (nanoscale). They are one of the allotropes of carbon. Two broad classes of carbon nanotubes are recognized: * ''Single-walled carbon nanotubes'' (''SWC ...

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 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 Antioxidants are Chemical compound, compounds that inhibit Redox, oxidation, a chemical reaction that can produce Radical (chemistry), free radicals. Autoxidation leads to degradation of organic compounds, including living matter. Antioxidants ...

Derivatives of ''o''-cresol include: * Indo-1, a popular calcium indicator * MCPA, (4-chloro-2-methylphenoxy)acetic acid * MCPB, 4-(4-chloro-2-methylphenoxy)butanoic acid * Mecoprop, (''RS'')-2-(4-chloro-2-methylphenoxy)propanoic acid * the amine

atomoxetine Atomoxetine, formerly sold under the brand name Strattera, is a selective norepinephrine reuptake inhibitor (sNRI) medication used to treat attention deficit hyperactivity disorder (ADHD) and, to a lesser extent, cognitive disengagement syndr ...

, (3''R'')-''N''-methyl-3-(2-methylphenoxy)-3-phenylpropan-1-amine * the diol mephenesin, 3-(2-methylphenoxy)propane-1,2-diol Derivatives of ''m''-cresol include: * Amylmetacresol, an antiseptic * Bevantolol, (''RS'')- -(3,4-dimethoxyphenyl)ethyl -hydroxy-3-(3-methylphenoxy)propylmine * Bromocresol green * 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 ( arrhythmia), and to protect the heart from a second heart attack after a first heart attack ( secondary prevention ...

* 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 ...

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

mouth A mouth also referred to as the oral is the body orifice through which many animals ingest food and animal communication#Auditory, vocalize. The body cavity immediately behind the mouth opening, known as the oral cavity (or in Latin), is also t ...

, and

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

; abdominal pain and vomiting;

heart The heart is a muscular Organ (biology), organ found in humans and other animals. This organ pumps blood through the blood vessels. The heart and blood vessels together make the circulatory system. The pumped blood carries oxygen and nutrie ...

damage; anemia;

liver The liver is a major metabolic organ (anatomy), organ exclusively found in vertebrates, which performs many essential biological Function (biology), functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of var ...

and

kidney In humans, the kidneys are two reddish-brown bean-shaped blood-filtering organ (anatomy), organs that are a multilobar, multipapillary form of mammalian kidneys, usually without signs of external lobulation. They are located on the left and rig ...

damage; facial paralysis;

coma A coma is a deep state of prolonged unconsciousness in which a person cannot be awakened, fails to Nociception, respond normally to Pain, painful stimuli, light, or sound, lacks a normal Circadian rhythm, sleep-wake cycle and does not initiate ...

; and

death Death is the end of life; the irreversible cessation of all biological functions that sustain a living organism. Death eventually and inevitably occurs in all organisms. The remains of a former organism normally begin to decompose sh ...

. 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 and

nervous system In biology, the nervous system is the complex system, highly complex part of an animal that coordinates its behavior, actions and sense, sensory information by transmitting action potential, signals to and from different parts of its body. Th ...

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

brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

, and

lung The lungs are the primary Organ (biology), organs of the respiratory system in many animals, including humans. In mammals and most other tetrapods, two lungs are located near the Vertebral column, backbone on either side of the heart. Their ...

s. 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 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