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

aromatic In organic chemistry, aromaticity is a chemical property describing the way in which a conjugated system, conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibits a stabilization stronger than would be expected from conjugati ...

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 In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula (whereas normal methane has the formula ). In formulas, the group is often abbreviated as ...

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 Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...

by exposure to

air An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...

, 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 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 w ...

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 In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula (whereas normal methane has the formula ). In formulas, the group is often abbreviated a ...

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

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

) 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 ...

chlorotoluene Chlorotoluenes are aryl chlorides based on toluene in which at least one aromatic hydrogen atom is replaced with a chlorine atom. They have the general formula C7H8–''n''Cl''n'', where ''n'' = 1–5 is the number of chlorine atoms. Monochlorotol ...

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 Anisole, or methoxybenzene, is an organic compound with the formula . It is a colorless liquid with a smell reminiscent of anise seed, and in fact many of its derivatives are found in natural and artificial fragrances. The compound is mainly ...

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 Benzyl alcohol (also known as α-cresol) is an aromatic alcohol with the formula C6H5CH2OH. The benzyl group is often abbreviated "Bn" (not to be confused with "Bz" which is used for benzoyl), thus benzyl alcohol is denoted as BnOH. Benzyl a ...

, 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 The cell membrane (also known as the plasma membrane or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of a cell from the outside environment (the extra ...

. 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 Creolin (which is also called Creolina) is a generic name for disinfectants whose composition varies according to origin. It is extracted from the dry distillation of wood. The residue remaining in the autoclave vessel is a dark, syrupy mass called ...

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

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

formulation, essentially a water solution of carbolic soap. "Lysol" has been used as a

generic trademark A generic trademark, also known as a genericized trademark or proprietary eponym, is a trademark or brand name that, because of its popularity or significance, has become the generic term for, or synonymous with, a general class of products or ...

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 Butylated hydroxytoluene (BHT), also known as dibutylhydroxytoluene, is a lipophilic organic compound, chemically a derivative of phenol, that is useful for its antioxidant properties. BHT is widely used to prevent free radical-mediated oxidation ...

, 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 Indo-1 is a popular dye that is used as a ratiometric calcium indicator similar to Fura-2. In contrast to Fura-2, Indo-1 has a dual emissions peak and a single excitation. The main emission peak in calcium-free solution is 475 nm while in ...

, a popular calcium indicator *

MCPA MCPA (2-methyl-4-chlorophenoxyacetic acid) is a widely used phenoxy herbicide introduced in 1945. It selectively controls broad-leaf weeds in pasture and Cereal, cereal crops. The mode of action of MCPA is as an auxin, which are growth hormones t ...

, (4-chloro-2-methylphenoxy)acetic acid *

MCPB MCPB, 2,4-MCPB, 4-(4-chloro-o-tolyloxy)butyric acid (IUPAC), or 4-(4-chloro-2-methylphenoxy)butanoic acid ( CAS) is a phenoxybutyric herbicide. In the United States it is registered for use on pea crops before flowering, for post-emergence contr ...

, 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 organic compounds that contain carbon-nitrogen bonds. Amines are formed when one or more hydrogen atoms in ammonia are replaced by alkyl or aryl groups. The nitrogen atom in an amine possesses a lone pair of elec ...

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 A diol is a chemical compound containing two hydroxyl groups ( groups). An aliphatic diol may also be called a glycol. This pairing of functional groups is pervasive, and many subcategories have been identified. They are used as protecting gro ...

mephenesin Mephenesin (INN), also called myanesin, 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 ef ...

, 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, Cofsils and Lorsept throat lozenges, typically in combination with dich ...

, an

antiseptic An antiseptic ( and ) is an antimicrobial substance or compound that is applied to living tissue to reduce the possibility of sepsis, infection, or putrefaction. Antiseptics are generally distinguished from ''antibiotics'' by the latter's abil ...

* Bevantolol, (''RS'')- -(3,4-dimethoxyphenyl)ethyl -hydroxy-3-(3-methylphenoxy)propylmine *

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 ( 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 Irritation, in biology and physiology, is a state of inflammation or painful reaction to allergy or cell-lining damage. A stimulus or agent which induces the state of irritation is an irritant. Irritants are typically thought of as chemical age ...

and burning of skin,

eye An eye is a sensory organ that allows an organism to perceive visual information. It detects light and converts it into electro-chemical impulses in neurons (neurones). It is part of an organism's visual system. In higher organisms, the ey ...

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 Anemia (also spelt anaemia in British English) is a blood disorder in which the blood has a reduced ability to carry oxygen. This can be due to a lower than normal number of red blood cells, a reduction in the amount of hemoglobin availabl ...

;

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 A nose is a sensory organ and respiratory structure in vertebrates. It consists of a nasal cavity inside the head, and an external nose on the face. The external nose houses the nostrils, or nares, a pair of tubes providing airflow through the ...

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 is com ...

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 The Occupational Safety and Health Administration (OSHA; ) is a regulatory agency of the United States Department of Labor that originally had federal visitorial powers to inspect and examine workplaces. The United States Congress established ...

has set a

permissible exposure limit The permissible exposure limit (PEL or OSHA PEL) is a legal limit in the United States for exposure of an employee to a chemical substance or physical agents such as high level noise. Permissible exposure limits were established by the Occupational ...

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 List of United States federal agencies, United States federal agency responsible for conducting research and making recommendations for the prevention of work-related occ ...

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)
/ref>

References