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82-556: 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. 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 . Phenol

164-469: A generic medication and over the counter . Coal tar is used in medicated shampoo , soap and ointment . It demonstrates antifungal , anti-inflammatory , anti-itch , and antiparasitic properties. It may be applied topically as a treatment for dandruff and psoriasis , and to kill and repel head lice . It may be used in combination with ultraviolet light therapy . Coal tar may be used in two forms: crude coal tar ( Latin : pix carbonis ) or

246-628: A recommended exposure limit (REL) of 0.1 mg/m cyclohexane -extractable fraction over an 8-hour workday. At levels of 80 mg/m , coal tar pitch volatiles are immediately dangerous to life and health . When used as a medication in the United States, coal tar preparations are considered over-the-counter drug pharmaceuticals and are subject to regulation by the Food and Drug Administration (FDA). Electrophilic aromatic substitution Electrophilic aromatic substitution ( S E Ar )

328-553: A bis(2-hydroxyphenyl) derivative, and a 4-cyclohexylphenols. Alcohols and hydroperoxides alkylate phenols in the presence of solid acid catalysts (e.g. certain zeolite ). Cresols and cumyl phenols can be produced in that way. Aqueous solutions of phenol are weakly acidic and turn blue litmus slightly to red. Phenol is neutralized by sodium hydroxide forming sodium phenate or phenolate, but being weaker than carbonic acid , it cannot be neutralized by sodium bicarbonate or sodium carbonate to liberate carbon dioxide . When

410-462: A chemical could be used to destroy the micro-organisms that cause infection. Meanwhile, in Carlisle , England, officials were experimenting with sewage treatment using carbolic acid to reduce the smell of sewage cesspools . Having heard of these developments, and having previously experimented with other chemicals for antiseptic purposes without much success, Lister decided to try carbolic acid as

492-521: A coal tar solution ( Latin : liquor picis carbonis, LPC ) also known as liquor carbonis detergens (LCD). Named brands include Denorex, Balnetar, Psoriasin, Tegrin, T/Gel, and Neutar. When used in the extemporaneous preparation of topical medications, it is supplied in the form of coal tar topical solution USP , which consists of a 20% w/v solution of coal tar in alcohol , with an additional 5% w/v of polysorbate 80  USP; this must then be diluted in an ointment base, such as petrolatum . Coal tar

574-622: A complex mixture of three or more membered condensed ring aromatic hydrocarbons , was listed on 13 January 2010 as a substance of very high concern by the European Chemicals Agency . Exposure to coal tar pitch volatiles can occur in the workplace by breathing, skin contact, or eye contact. The Occupational Safety and Health Administration (OSHA) has set the permissible exposure limit ) to 0.2 mg/m benzene -soluble fraction over an 8-hour workday. The National Institute for Occupational Safety and Health (NIOSH) has set

656-419: A derivative of benzene, in 1841. In 1836, Auguste Laurent coined the name "phène" for benzene; this is the root of the word "phenol" and " phenyl ". In 1843, French chemist Charles Gerhardt coined the name "phénol". The antiseptic properties of phenol were used by Sir Joseph Lister in his pioneering technique of antiseptic surgery. Lister decided that the wounds had to be thoroughly cleaned. He then covered

738-437: A key precursor to polycarbonates and epoxide resins. Condensation of phenol, alkylphenols, or diphenols with formaldehyde gives phenolic resins , a famous example of which is Bakelite . Partial hydrogenation of phenol gives cyclohexanone , a precursor to nylon . Nonionic detergents are produced by alkylation of phenol to give the alkylphenols , e.g., nonylphenol , which are then subjected to ethoxylation . Phenol

820-633: A member of the aromatic ring, which substantially stabilizes the cationic intermediate. Examples of electrophilic substitutions to pyrrole are the Pictet–Spengler reaction and the Bischler–Napieralski reaction . Electrophilic aromatic substitutions with prochiral carbon electrophiles have been adapted for asymmetric synthesis by switching to chiral Lewis acid catalysts especially in Friedel–Crafts type reactions . An early example concerns

902-425: A mixture of 2-nitrophenol and 4-nitrophenol while with concentrated nitric acid, additional nitro groups are introduced, e.g. to give 2,4,6-trinitrophenol . Friedel Crafts alkylations of phenol and its derivatives often proceed without catalysts. Alkylating agents include alkyl halides, alkenes, and ketones. Thus, adamantyl-1-bromide , dicyclopentadiene ), and cyclohexanones give respectively 4-adamantylphenol,

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984-492: A mixture of phenol and benzoyl chloride are shaken in presence of dilute sodium hydroxide solution, phenyl benzoate is formed. This is an example of the Schotten–Baumann reaction : Phenol is reduced to benzene when it is distilled with zinc dust or when its vapour is passed over granules of zinc at 400 °C: When phenol is treated with diazomethane in the presence of boron trifluoride ( BF 3 ), anisole

1066-580: A procedure known as a chemical matrixectomy . The procedure was first described by Otto Boll in 1945. Since that time phenol has become the chemical of choice for chemical matrixectomies performed by podiatrists. Concentrated liquid phenol can be used topically as a local anesthetic for otology procedures, such as myringotomy and tympanotomy tube placement, as an alternative to general anesthesia or other local anesthetics. It also has hemostatic and antiseptic qualities that make it ideal for this use. Phenol spray, usually at 1.4% phenol as an active ingredient,

1148-411: A substituent group (other than hydrogen). The entering group may displace that substituent group but may also itself be expelled or migrate to another position in a subsequent step. The term ' ipso -substitution' is not used, since it is synonymous with substitution. A classic example is the reaction of salicylic acid with a mixture of nitric and sulfuric acid to form picric acid . The nitration of

1230-419: A wide range of Lewis bases such as pyridine , diethyl ether , and diethyl sulfide . The enthalpies of adduct formation and the −OH IR frequency shifts accompanying adduct formation have been compiled. Phenol is classified as a hard acid . Phenol exhibits keto-enol tautomerism with its unstable keto tautomer cyclohexadienone, but the effect is nearly negligible. The equilibrium constant for enolisation

1312-416: A wound antiseptic. He had his first chance on August 12, 1865, when he received a patient: an eleven-year-old boy with a tibia bone fracture which pierced the skin of his lower leg. Ordinarily, amputation would be the only solution. However, Lister decided to try carbolic acid. After setting the bone and supporting the leg with splints, he soaked clean cotton towels in undiluted carbolic acid and applied them to

1394-634: Is a positive charge on the carbon bearing the electron-withdrawing group (i.e., ortho or para attack) is less stable than the others. Therefore, these electron-withdrawing groups are meta directing because this is the position that does not have as much destabilization. The reaction is also much slower (a relative reaction rate of 6×10 compared to benzene) because the ring is less nucleophilic. Although discussions of directing groups usually focus on electronic effects (e.g. EWG vs EDGs), steric effect can prove influential. Thus, nitration of toluene gives approximately 2:1 ortho vs para-nitrotoluene . In

1476-416: Is a special type of EAS with special ortho directors . Non-halogen groups with atoms that are more electronegative than carbon, such as a carboxylic acid group (-CO 2 H), withdraw substantial electron density from the pi system. These groups are strongly deactivating groups . Additionally, since the substituted carbon is already electron-poor, any structure having a resonance contributor in which there

1558-420: 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 psoriasis and seborrheic dermatitis (dandruff). It may be used in combination with ultraviolet light therapy . Industrially it is a railroad tie preservative and used in

1640-422: Is a weak acid (pH 6.6). In aqueous solution in the pH range ca. 8 - 12 it is in equilibrium with the phenolate anion C 6 H 5 O (also called phenoxide or carbolate ): Phenol is more acidic than aliphatic alcohols. Its enhanced acidity is attributed to resonance stabilization of phenolate anion. In this way, the negative charge on oxygen is delocalized on to the ortho and para carbon atoms through

1722-402: Is absorbed through the skin relatively quickly, systemic poisoning can occur in addition to the local caustic burns. 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 LD 50 for oral toxicity is less than 500 mg/kg for dogs, rabbits, or mice;

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1804-464: Is achieved via the action of the nitronium ion as the electrophile. The sulfonation with fuming sulfuric acid gives benzenesulfonic acid . Aromatic halogenation with bromine , chlorine , or iodine gives the corresponding aryl halides. This reaction is typically catalyzed by the corresponding iron or aluminum trihalide. The Friedel–Crafts reaction can be performed either as an acylation or as an alkylation . Often, aluminium trichloride

1886-402: Is also a versatile precursor to a large collection of drugs, most notably aspirin but also many herbicides and pharmaceutical drugs . Phenol is a component in liquid–liquid phenol–chloroform extraction technique used in molecular biology for obtaining nucleic acids from tissues or cell culture samples. Depending on the pH of the solution either DNA or RNA can be extracted. Phenol

1968-404: Is an organic reaction in which an atom that is attached to an aromatic system (usually hydrogen) is replaced by an electrophile . Some of the most important electrophilic aromatic substitutions are aromatic nitration , aromatic halogenation , aromatic sulfonation , alkylation Friedel–Crafts reaction and acylation Friedel–Crafts reaction. The most widely practised example of this reaction

2050-536: Is an organic compound appreciably soluble in water, with about 84.2 g dissolving in 1000 ml (0.895 M ). Homogeneous mixtures of phenol and water at phenol to water mass ratios of ~2.6 and higher are possible. The sodium salt of phenol, sodium phenoxide , is far more water-soluble. It is a combustible solid (NFPA rating = 2). When heated, phenol produces flammable vapors that are explosive at concentrations of 3 to 10% in air. Carbon dioxide or dry chemical extinguishers should be used to fight phenol fires. Phenol

2132-535: Is approximately 10, which means only one in every ten trillion molecules is in the keto form at any moment. The small amount of stabilisation gained by exchanging a C=C bond for a C=O bond is more than offset by the large destabilisation resulting from the loss of aromaticity. Phenol therefore exists essentially entirely in the enol form. 4, 4' Substituted cyclohexadienone can undergo a dienone–phenol rearrangement in acid conditions and form stable 3,4‐disubstituted phenol. For substituted phenols, several factors can favor

2214-553: Is available as a generic medication and over the counter . Side effects include skin irritation, sun sensitivity, allergic reactions , and skin discoloration. It is unclear if use during pregnancy is safe for the baby and use during breastfeeding is not typically recommended. The exact mechanism of action is unknown. It is a complex mixture of phenols , polycyclic aromatic hydrocarbons (PAHs), and heterocyclic compounds . It demonstrates antifungal , anti-inflammatory , anti-itch , and antiparasitic properties. Coal tar

2296-434: Is believed that their metabolites bind to DNA, damaging it. The PAHs found in coal tar and air pollution induce immunosenescence and cytotoxicity in epidermal cells. It's possible that the skin can repair itself from this damage after short-term exposure to PAHs but not after long-term exposure. Long-term skin exposure to these compounds can produce " tar warts ", which can progress to squamous cell carcinoma . Coal tar

2378-411: Is consistent with low yields of meta-substituted product. Other substituents, such as the alkyl and aryl substituents , may also donate electron density to the pi system; however, since they lack an available unshared pair of electrons, their ability to do this is rather limited. Thus, they only weakly activate the ring and do not strongly disfavor the meta position. Directed ortho metalation

2460-606: Is highly reactive toward electrophilic aromatic substitution . The enhanced nucleophilicity is attributed to donation pi electron density from O into the ring. Many groups can be attached to the ring, via halogenation , acylation , sulfonation , and related processes. Phenol is so strongly activated that bromination and chlorination lead readily to polysubstitution. The reaction affords 2- and 4-substituted derivatives. The regiochemistry of halogenation changes in strongly acidic solutions where PhOH 2 ] predominates. Phenol reacts with dilute nitric acid at room temperature to give

2542-563: Is incorporated into some parking-lot sealcoat products used to protect the structural integrity of the underlying pavement. Sealcoat products that are coal-tar based typically contain 20 to 35 percent coal-tar pitch. Research shows it is used throughout the United States of America , however several areas have banned its use in sealcoat products, including the District of Columbia; the city of Austin, Texas; Dane County, Wisconsin;

Phenol - Misplaced Pages Continue

2624-448: Is obtained as the main product and nitrogen gas as a byproduct. Phenol and its derivatives react with iron(III) chloride to give intensely colored solutions containing phenoxide complexes. Because of phenol's commercial importance, many methods have been developed for its production, but the cumene process is the dominant technology. Accounting for 95% of production (2003) is the cumene process , also called Hock process . It involves

2706-448: Is possible, but it has not been commercialized: Nitrous oxide is a potentially "green" oxidant that is a more potent oxidant than O 2 . Routes for the generation of nitrous oxide however remain uncompetitive. An electrosynthesis employing alternating current gives phenol from benzene. The oxidation of toluene , as developed by Dow Chemical , involves copper-catalyzed reaction of molten sodium benzoate with air: The reaction

2788-861: Is produced through thermal destruction ( pyrolysis ) of coal . Its composition varies with the process and type of coal used – lignite , bituminous or anthracite . Coal tar is a mixture of approximately 10,000 chemicals, of which only about 50% have been identified. Most of the chemical compounds are polycyclic aromatic hydrocarbon : Others: benzene , toluene , xylenes , cumenes , coumarone , indene , benzofuran , naphthalene and methyl-naphthalenes , acenaphthene , fluorene , phenol , cresols , pyridine , picolines , phenanthracene, carbazole , quinolines , fluoranthene . Many of these constituents are known carcinogens. Various phenolic coal tar derivatives have analgesic (pain-killer) properties. These included acetanilide , phenacetin , and paracetamol aka acetaminophen . Paracetamol may be

2870-464: Is proposed to proceed via formation of benzyoylsalicylate. Autoxidation of cyclohexylbenzene give the hydroperoxide . Decomposition of this hydroperoxide affords cyclohexanone and phenol. Early methods relied on extraction of phenol from coal derivatives or the hydrolysis of benzene derivatives. The original commercial route was developed by Bayer and Monsanto in the early 1900s, based on discoveries by Wurtz and Kekule. The method involves

2952-398: 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. Coal tar Coal tar

3034-584: Is safe for the baby and use during breastfeeding is not typically recommended. According to the National Psoriasis Foundation , coal tar is a valuable, safe and inexpensive treatment option for millions of people with psoriasis and other scalp or skin conditions. According to the FDA , coal tar concentrations between 0.5% and 5% are considered safe and effective for psoriasis. Long-term, consistent exposure to coal tar likely increases

3116-586: Is so inexpensive that it also attracts many small-scale uses. It is a component of industrial paint strippers used in the aviation industry for the removal of epoxy, polyurethane and other chemically resistant coatings. Due to safety concerns, phenol is banned from use in cosmetic products in the European Union and Canada . Phenol was widely used as an antiseptic , and it is used in the production of carbolic soap . Concentrated phenol liquids are used for permanent treatment of ingrown toe and finger nails,

3198-400: Is sometimes exploited synthetically, particularly the case of replacement of silyl by another functional group ( ipso attack). However, the loss of groups like iodo or alkyl is more often an undesired side reaction. Both the regioselectivity —the diverse arene substitution patterns —and the speed of an electrophilic aromatic substitution are affected by the substituents already attached to

3280-430: Is the ethylation of benzene. Approximately 24,700,000 tons were produced in 1999. (After dehydrogenation and polymerization, the commodity plastic polystyrene is produced.) In this process, acids are used as catalyst to generate the incipient carbocation. Many other electrophilic reactions of benzene are conducted, although on a much smaller scale; they are valuable routes to key intermediates. The nitration of benzene

3362-502: Is unknown. Coal tar is a complex mixture of phenols , polycyclic aromatic hydrocarbons (PAHs), and heterocyclic compounds . It is a keratolytic agent, which reduces the growth rate of skin cells and softens the skin's keratin . Coal tar is on the World Health Organization's List of Essential Medicines , the most effective and safe medicines needed in a health system . Coal tar is generally available as

Phenol - Misplaced Pages Continue

3444-485: Is used medically to treat sore throat. It is the active ingredient in some oral analgesics such as Chloraseptic spray, TCP and Carmex . Phenol was discovered in 1834 by Friedlieb Ferdinand Runge , who extracted it (in impure form) from coal tar . Runge called phenol "Karbolsäure" (coal-oil-acid, carbolic acid). Coal tar remained the primary source until the development of the petrochemical industry . French chemist Auguste Laurent extracted phenol in its pure form, as

3526-688: Is used, but almost any strong Lewis acid can be applied. For the acylation reaction a stoichiometric amount of aluminum trichloride is required. The overall reaction mechanism, denoted by the Hughes–Ingold mechanistic symbol S E Ar , begins with the aromatic ring attacking the electrophile E (2a). This step leads to the formation of a positively charged and delocalized cyclohexadienyl cation , also known as an arenium ion , Wheland intermediate, or arene σ-complex (2b). Many examples of this carbocation have been characterized, but under normal operating conditions these highly acidic species will donate

3608-483: The amino group of aniline , are strongly activating (some time deactivating also in case of halides ) and ortho/para -directing by resonance. Such activating groups donate those unshared electrons to the pi system, creating a negative charge on the ortho and para positions. These positions are thus the most reactive towards an electron-poor electrophile. This increased reactivity might be offset by steric hindrance between activating group and electrophile but on

3690-425: The nitrogen atom can donate electron density to the pi system (forming an iminium ion ), giving four resonance structures (as opposed to three in the basic reaction). This substantially enhances the stability of the cationic intermediate. When the electrophile attacks the meta position, the nitrogen atom cannot donate electron density to the pi system, giving only three resonance contributors. This reasoning

3772-424: The p K a of the enol of acetone in water is 10.9, making it only slightly less acidic than phenol (p K a 10.0). Thus, the greater number of resonance structures available to phenoxide compared to acetone enolate seems to contribute little to its stabilization. However, the situation changes when solvation effects are excluded. In carbon tetrachloride and in alkane solvents, phenol hydrogen bonds with

3854-485: The 2 position involves the loss of CO 2 as the leaving group. Desulfonation in which a sulfonyl group is substituted by a proton is a common example. See also Hayashi rearrangement . In aromatics substituted by silicon, the silicon reacts by ipso substitution. Compared to benzene, furans , thiophenes , and pyrroles are more susceptible to electrophilic attack. These compounds all contain an atom with an unshared pair of electrons ( oxygen , sulfur , or nitrogen ) as

3936-572: The Lancet, he had treated a total of eleven patients using his new antiseptic method. Of those, only one had died, and that was through a complication that was nothing to do with Lister's wound-dressing technique. Now, for the first time, patients with compound fractures were likely to leave the hospital with all their limbs intact Before antiseptic operations were introduced at the hospital, there were sixteen deaths in thirty-five surgical cases. Almost one in every two patients died. After antiseptic surgery

4018-408: The addition of chloral to phenols catalyzed by aluminium chloride modified with (–)-menthol . A glyoxylate compound has been added to N,N-dimethylaniline with a chiral bisoxazoline ligand – copper(II) triflate catalyst system also in a Friedel–Crafts hydroxyalkylation : In another alkylation N-methylpyrrole reacts with crotonaldehyde catalyzed by trifluoroacetic acid modified with

4100-628: The amount in the distillate. Cryptanaerobacter phenolicus is a bacterium species that produces benzoate from phenol via 4-hydroxybenzoate . Rhodococcus phenolicus is a bacterium species able to degrade phenol as sole carbon source. Phenol and its vapors are corrosive to the eyes, the skin, and the respiratory tract. Its corrosive effect on skin and mucous membranes is due to a protein-degenerating effect. Repeated or prolonged skin contact with phenol may cause dermatitis , or even second and third-degree burns. Inhalation of phenol vapor may cause lung edema . The substance may cause harmful effects on

4182-405: The benzene ring. In terms of regioselectivity, some groups promote substitution at the ortho or para positions, whereas other groups favor substitution at the meta position. These groups are called either ortho–para directing or meta directing , respectively. In addition, some groups will increase the rate of reaction ( activating ) while others will decrease the rate ( deactivating ). While

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4264-428: The carcinogenicity of PAHs some municipalities, such as the city of Milwaukee, have banned the use of common coal tar-based road and driveway sealants citing concerns of elevated PAH content in groundwater. Coal tar causes increased sensitivity to sunlight , so skin treated with topical coal tar preparations should be protected from sunlight. The residue from the distillation of high-temperature coal tar, primarily

4346-453: The case of tert-butylbenzene, however, the selectivity is reversed:73% of the product is 4-nitro-tert-butybenzene]]. Compared to benzene, the rate of electrophilic substitution on pyridine is much slower, due to the higher electronegativity of the nitrogen atom. Additionally, the nitrogen in pyridine easily gets a positive charge either by protonation (from nitration or sulfonation ) or Lewis acids (such as AlCl 3 ) used to catalyze

4428-433: The central nervous system and heart, resulting in dysrhythmia , seizures , and coma . The kidneys may be affected as well. Long-term or repeated exposure of the substance may have harmful effects on the liver and kidneys . There is no evidence that phenol causes cancer in humans. Besides its hydrophobic effects, another mechanism for the toxicity of phenol may be the formation of phenoxyl radicals . Since phenol

4510-620: The central nervous system causes sudden collapse and loss of consciousness in both humans and animals; a state of cramping precedes these symptoms because of the motor activity controlled by the central nervous system. Injections of phenol were used as a means of individual execution by Nazi Germany during the Second World War . It was originally used by the Nazis in 1939 as part of the mass-murder of disabled people under Aktion T4 . The Germans learned that extermination of smaller groups

4592-565: The chloride byproduct. Phenol is also a recoverable byproduct of coal pyrolysis. In the Lummus process , the oxidation of toluene to benzoic acid is conducted separately. Phenyldiazonium salts hydrolyze to phenol. The method is of no commercial interest since the precursor is expensive. Salicylic acid decarboxylates to phenol. The major uses of phenol, consuming two thirds of its production, involve its conversion to precursors for plastics. Condensation with acetone gives bisphenol-A ,

4674-461: The cumene process. A route analogous to the cumene process begins with cyclohexylbenzene . It is oxidized to a hydroperoxide , akin to the production of cumene hydroperoxide . Via the Hock rearrangement, cyclohexylbenzene hydroperoxide cleaves to give phenol and cyclohexanone . Cyclohexanone is an important precursor to some nylons . The direct oxidation of benzene ( C 6 H 6 ) to phenol

4756-401: The electron density especially at positions 2, 4 and 6, leaving positions 3 and 5 as the ones with comparably higher reactivity, so these types of groups are meta directors (see below). Halogens are electronegative, so they are deactivating by induction, but they have lone pairs, so they are resonance donors and therefore ortho/para directors. Groups with unshared pairs of electrons, such as

4838-410: The keto tautomer: (a) additional hydroxy groups (see resorcinol ) (b) annulation as in the formation of naphthols , and (c) deprotonation to give the phenolate. Phenoxides are enolates stabilised by aromaticity . Under normal circumstances, phenoxide is more reactive at the oxygen position, but the oxygen position is a "hard" nucleophile whereas the alpha-carbon positions tend to be "soft". Phenol

4920-428: The minimum lethal human dose was cited as 140 mg/kg. 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. Chemical burns from skin exposures can be decontaminated by washing with polyethylene glycol , isopropyl alcohol , or perhaps even copious amounts of water. Removal of contaminated clothing

5002-437: The nitrogen atom, being electronegative, can hold the negative charge by itself. Another way is to do an oxidation before the electrophilic substitution. This makes pyridine N -oxide , which due to the negative oxygen atom, makes the reaction faster than pyridine, and even benzene. The oxide then can be reduced to the substituted pyridine. The attachment of an entering group to a position in an aromatic compound already carrying

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5084-410: The only coal-tar derived analgesic still in use today. Industrial phenol is now usually synthesized from crude oil rather than coal tar. Coal tar derivatives are contra-indicated for people with the inherited red cell blood disorder glucose-6-phosphate dehydrogenase deficiency (G6PD deficiency), as they can cause oxidative stress leading to red blood cell breakdown. The exact mechanism of action

5166-438: The other hand there are two ortho positions for reaction but only one para position. Hence the final outcome of the electrophilic aromatic substitution is difficult to predict, and it is usually only established by doing the reaction and observing the ratio of ortho versus para substitution. In addition to the increased nucleophilic nature of the original ring, when the electrophile attacks the ortho and para positions of aniline,

5248-416: The other hand, deactivating substituents destabilize the intermediate cation and thus decrease the reaction rate by either inductive or resonance effects. They do so by withdrawing electron density from the aromatic ring. The deactivation of the aromatic system means that generally harsher conditions are required to drive the reaction to completion. An example of this is the nitration of toluene during

5330-466: The partial oxidation of cumene (isopropylbenzene) via the Hock rearrangement : Compared to most other processes, the cumene process uses mild conditions and inexpensive raw materials. For the process to be economical, both phenol and the acetone by-product must be in demand. In 2010, worldwide demand for acetone was approximately 6.7 million tonnes, 83 percent of which was satisfied with acetone produced by

5412-432: The patterns of regioselectivity can be explained with resonance structures , the influence on kinetics can be explained by both resonance structures and the inductive effect . Substituents can generally be divided into two classes regarding electrophilic substitution: activating and deactivating towards the aromatic ring. Activating substituents or activating groups stabilize the cationic intermediate formed during

5494-400: The pi system. An alternative explanation involves the sigma framework, postulating that the dominant effect is the induction from the more electronegative sp hybridised carbons ; the comparatively more powerful inductive withdrawal of electron density that is provided by the sp system compared to an sp system allows for great stabilization of the oxyanion. In support of the second explanation,

5576-434: The presence of phenol and 4-methylphenol during musth . It is also one of the chemical compounds found in castoreum . This compound is ingested from the plants the beaver eats. Phenol is a measurable component in the aroma and taste of the distinctive Islay scotch whisky , generally ~30 ppm , but it can be over 160ppm in the malted barley used to produce whisky . This amount is different from and presumably higher than

5658-448: The production of trinitrotoluene (TNT). While the first nitration, on the activated toluene ring, can be done at room temperature and with dilute acid, the second one, on the deactivated nitrotoluene ring, already needs prolonged heating and more concentrated acid, and the third one, on very strongly deactivated dinitrotoluene, has to be done in boiling concentrated sulfuric acid . Groups that are electron-withdrawing by resonance decrease

5740-525: The proton attached to the sp carbon to the solvent (or any other weak base) to reestablish aromaticity. The net result is the replacement of H by E in the aryl ring (3). Occasionally, other electrofuges (groups that can leave without their electron pair ) beside H will depart to reestablish aromaticity; these species include silyl groups (as SiR 3 ), the carboxy group (as CO 2 + H ), the iodo group (as I ), and tertiary alkyl groups like t -butyl (as R ). The capacity of these types of substituents to leave

5822-415: The reaction of strong base with benzenesulfonic acid , proceeding by the reaction of hydroxide with sodium benzenesulfonate to give sodium phenoxide. Acidification of the latter gives phenol. The net conversion is: Chlorobenzene can be hydrolyzed to phenol using base ( Dow process ) or steam ( Raschig–Hooker process ): These methods suffer from the cost of the chlorobenzene and the need to dispose of

5904-439: The reaction. This makes the reaction even slower by having adjacent formal charges on carbon and nitrogen or 2 formal charges on a localised atom. Doing an electrophilic substitution directly in pyridine is nearly impossible. In order to do the reaction, they can be made by 2 possible reactions, which are both indirect. One possible way to do a substitution on pyridine is nucleophilic aromatic substitution. Even with no catalysts,

5986-594: The risk of non-melanoma skin cancers . Evidence is inconclusive whether medical coal tar, which does not remain on the skin for the long periods seen in occupational exposure , causes cancer, because there is insufficient data to make a judgment. While coal tar consistently causes cancer in cohorts of workers with chronic occupational exposure, animal models, and mechanistic studies, the data on short-term use as medicine in humans has so far failed to show any consistently significant increase in rates of cancer. Coal tar contains many polycyclic aromatic hydrocarbons , and it

6068-474: The state of Washington; and several municipalities in Minnesota and others. In modern times, coal tar is mostly traded as fuel and an application for tar, such as roofing. The total value of the trade in coal tar is around US$ 20 billion each year. Side effects of coal tar products include skin irritation, sun sensitivity, allergic reactions , and skin discoloration. It is unclear if use during pregnancy

6150-425: The substitution by donating electrons into the ring system, by either inductive effect or resonance effects . Examples of activated aromatic rings are toluene , aniline and phenol . The extra electron density delivered into the ring by the substituent is not distributed evenly over the entire ring but is concentrated on atoms 2, 4 and 6, so activating substituents are also ortho/para directors (see below). On

6232-467: The surfacing of roads. Coal tar was listed as a known human carcinogen in the first Report on Carcinogens from the U.S. Federal Government, issued in 1980. Coal tar was discovered circa 1665 and used for medical purposes as early as the 1800s. Circa 1850, the discovery that it could be used as the main raw material for the synthesis of dyes engendered an entire industry. It is on the World Health Organization's List of Essential Medicines . Coal tar

6314-441: The wound, covered with a layer of tin foil, leaving them for four days. When he checked the wound, Lister was pleasantly surprised to find no signs of infection, just redness near the edges of the wound from mild burning by the carbolic acid. Reapplying fresh bandages with diluted carbolic acid, the boy was able to walk home after about six weeks of treatment. By 16 March 1867, when the first results of Lister's work were published in

6396-434: The wounds with a piece of rag or lint covered in phenol. The skin irritation caused by continual exposure to phenol eventually led to the introduction of aseptic (germ-free) techniques in surgery. Lister's work was inspired by the works and experiments of his contemporary Louis Pasteur in sterilizing various biological media. He theorized that if germs could be killed or prevented, no infection would occur. Lister reasoned that

6478-433: Was a component of the first sealed roads. In its original development by Edgar Purnell Hooley , tarmac was tar covered with granite chips. Later the filler used was industrial slag . Today, petroleum derived binders and sealers are more commonly used. These sealers are used to extend the life and reduce maintenance cost associated with asphalt pavements, primarily in asphalt road paving, car parks and walkways. Coal tar

6560-535: Was introduced in the summer of 1865, there were only six deaths in forty cases. The mortality rate had dropped from almost 50 per cent to around 15 per cent. It was a remarkable achievement Phenol was the main ingredient of the "carbolic smoke ball," an ineffective device marketed in London in the 19th century as protection against influenza and other ailments, and the subject of the famous law case Carlill v Carbolic Smoke Ball Company . The toxic effect of phenol on

6642-563: Was more economical by injection of each victim with phenol. Phenol injections were given to thousands of people. Maximilian Kolbe was also murdered with a phenol injection after surviving two weeks of dehydration and starvation in Auschwitz when he volunteered to die in place of a stranger . Approximately one gram is sufficient to cause death. Phenol is a normal metabolic product, excreted in quantities up to 40 mg/L in human urine. The temporal gland secretion of male elephants showed

6724-592: Was one of the first chemical substances proven to cause cancer from occupational exposure, during research in 1775 on the cause of chimney sweeps' carcinoma . Modern studies have shown that working with coal tar pitch, such as during the paving of roads or when working on roofs, increases the risk of cancer. The International Agency for Research on Cancer lists coal tars as Group 1 carcinogens , meaning they directly cause cancer. The U.S. Department of Health and Human Services lists coal tars as known human carcinogens. In response to public health concerns regarding

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