Phenol (also known ascarbolic acid,phenolic acid, orbenzenol) is anaromaticorganic compound with the molecularformulaC₆H₅OH.^[5] It is a whitecrystallinesolid that isvolatile. The molecule consists of aphenyl group (−C₆H₅) bonded to ahydroxy group (−OH). Mildlyacidic, it requires careful handling because it can causechemical burns.^[5]

Phenol

Names
Preferred IUPAC name Phenol[1]
Systematic IUPAC name Benzenol
Other names Carbolic acid Phenolic acid Phenylic acid Hydroxybenzene Phenic acid Phenyl alcohol Phenyl hydroxide
Identifiers
CAS Number	108-95-2 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:15882 Y
ChEMBL	ChEMBL14060 Y
ChemSpider	971 Y
DrugBank	DB03255 Y
ECHA InfoCard	100.003.303
KEGG	D00033 Y
PubChemCID	996
RTECS number	SJ3325000
UNII	339NCG44TV Y
UN number	2821 (solution) 2312 (molten) 1671 (solid)
CompTox Dashboard(EPA)	DTXSID5021124
InChI InChI=1S/C6H6O/c7-6-4-2-1-3-5-6/h1-5,7H Y Key: ISWSIDIOOBJBQZ-UHFFFAOYSA-N Y InChI=1/C6H6O/c7-6-4-2-1-3-5-6/h1-5,7H
SMILES Oc1ccccc1
Properties
Chemical formula	C6H6O
Molar mass	94.113 g/mol
Appearance	Transparent crystalline solid
Odor	Sweet and tarry
Density	1.07 g/cm3
Melting point	40.5 °C (104.9 °F; 313.6 K)
Boiling point	181.7 °C (359.1 °F; 454.8 K)
Solubility in water	8.3 g/100 mL (20 °C)
logP	1.48[2]
Vapor pressure	0.4 mmHg (20 °C)[3]
Acidity (pKa)	9.95 (in water), 18.0 (in DMSO), 29.1 (in acetonitrile)[4]
Conjugate base	Phenoxide
UV-vis (λmax)	270.75 nm[5]
Dipole moment	1.224 D
Pharmacology
ATC code	C05BB05 (WHO)D08AE03 (WHO),N01BX03 (WHO),R02AA19 (WHO)
Hazards
GHS labelling:
Pictograms	[6]
Signal word	Danger
Hazard statements	H301,H311,H314,H331,H341,H373[6]
Precautionary statements	P261,P280,P301+P310,P305+P351+P338,P310[6]
NFPA 704 (fire diamond)	3 2 0
Flash point	79 °C (174 °F; 352 K)
Explosive limits	1.8–8.6%[3]
Lethal dose or concentration (LD, LC):
LD50 (median dose)	317 mg/kg (rat, oral) 270 mg/kg (mouse, oral)[7]
LDLo (lowest published)	420 mg/kg (rabbit, oral) 500 mg/kg (dog, oral) 80 mg/kg (cat, oral)[7]
LC50 (median concentration)	19 ppm (mammal) 81 ppm (rat) 69 ppm (mouse)[7]
NIOSH (US health exposure limits):
PEL (Permissible)	TWA 5 ppm (19 mg/m3) [skin][3]
REL (Recommended)	TWA 5 ppm (19 mg/m3) C 15.6 ppm (60 mg/m3) [15-minute] [skin][3]
IDLH (Immediate danger)	250 ppm[3]
Safety data sheet (SDS)	[1]
Related compounds
Related compounds	Thiophenol Sodium phenoxide
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Phenol was first extracted fromcoal tar, but today is produced on a large scale (about 7 million tonnes a year) frompetroleum-derived feedstocks. It is an important industrialcommodity as aprecursor to many materials and useful compounds.^[8] It is primarily used to synthesizeplastics and related materials. Phenol and its chemicalderivatives are essential for production ofpolycarbonates,epoxies,explosives such aspicric acid,Bakelite,nylon,detergents,herbicides such asphenoxy herbicides, and numerouspharmaceutical drugs.^[9]

Phenol is an organic compound appreciablysoluble in water, with about 84.2 g dissolving in 1000 ml (0.895M). 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.^[5]

Phenol is a weak acid. In aqueous solution in the pH range ca. 8 - 12 it is in equilibrium with thephenolateanionC₆H₅O⁻ (also calledphenoxide orcarbolate):^[10]

C₆H₅OH ⇌ C₆H₅O⁻ + H⁺

Phenol is more acidic than aliphatic alcohols. Its enhanced acidity is attributed toresonance stabilization ofphenolate anion. In this way, the negative charge on oxygen is delocalized on to theortho and para carbon atoms through the pi system.^[11] An alternative explanation involves the sigma framework, postulating that the dominant effect is theinduction from the more electronegativesp² hybridised carbons; the comparatively more powerful inductive withdrawal of electron density that is provided by the sp² system compared to an sp³ system allows for great stabilization of the oxyanion. In support of the second explanation, thepK_a of theenol ofacetone in water is 10.9, making it only slightly less acidic than phenol (pK_a 10.0).^[5] 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.

Incarbon tetrachloride and in alkane solvents, phenolhydrogen bonds with a wide range of Lewis bases such aspyridine,diethyl ether, anddiethyl sulfide. The enthalpies of adduct formation and the−OH IR frequency shifts accompanying adduct formation have been compiled.^[12] Phenol is classified as ahard acid.^[13][14]

Phenol exhibitsketo-enol tautomerism with its unstable keto tautomer cyclohexadienone, but the effect is nearly negligible. The equilibrium constant for enolisation is approximately 10⁻¹³, which means only one in every ten trillion molecules is in the keto form at any moment.^[15] 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.^[16] 4,4' Substituted cyclohexadienone can undergo adienone–phenol rearrangement in acid conditions and form stable 3,4‐disubstituted phenol.^[17]

For substituted phenols, several factors can favor the keto tautomer: (a) additional hydroxy groups (seeresorcinol) (b) annulation as in the formation ofnaphthols, and (c) deprotonation to give the phenolate.^[18]

Phenoxides areenolates stabilised byaromaticity. 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".^[19]

Phenol is highly reactive towardelectrophilic aromatic substitution. The enhanced nucleophilicity is attributed to donationpi electron density from O into the ring. Many groups can be attached to the ring, viahalogenation,acylation,sulfonation, and related processes.

Phenol is so strongly activated that bromination and chlorination lead readily to polysubstitution.^[20] The reaction affords 2- and 4-substituted derivatives. The regiochemistry of halogenation changes in strongly acidic solutions wherePhOH₂]⁺ predominates. Phenol reacts with dilute nitric acid at room temperature to give a mixture of 2-nitrophenol and 4-nitrophenol while with concentrated nitric acid, additional nitro groups are introduced, e.g. to give2,4,6-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), andcyclohexanones give respectively 4-adamantylphenol, a bis(2-hydroxyphenyl) derivative, and a 4-cyclohexylphenols.Alcohols andhydroperoxides alkylate phenols in the presence ofsolid acidcatalysts (e.g. certainzeolite).Cresols and cumyl phenols can be produced in that way.^[21]

Aqueous solutions of phenol are weakly acidic and turn blue litmus slightly to red. Phenol is neutralized bysodium hydroxide forming sodium phenate or phenolate, but being weaker thancarbonic acid, it cannot be neutralized bysodium bicarbonate orsodium carbonate to liberatecarbon dioxide.

C₆H₅OH + NaOH → C₆H₅ONa + H₂O

When a mixture of phenol andbenzoyl chloride are shaken in presence of dilutesodium hydroxide solution,phenyl benzoate is formed. This is an example of theSchotten–Baumann reaction:

C₆H₅COCl + HOC₆H₅ → C₆H₅CO₂C₆H₅ + HCl

Phenol is reduced tobenzene when it is distilled withzinc dust or when its vapour is passed over granules of zinc at 400 °C:^[22]

C₆H₅OH + Zn → C₆H₆ + ZnO

When phenol is treated withdiazomethane in the presence ofboron trifluoride (BF₃),anisole is obtained as the main product and nitrogen gas as a byproduct.

C₆H₅OH + CH₂N₂ → C₆H₅OCH₃ + N₂

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 thecumene process, also calledHock process. It involves the partialoxidation ofcumene (isopropylbenzene) via theHock rearrangement:^[8] 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.^[23][24] In 2010, worldwide demand for acetone was approximately 6.7 million tonnes, 83 percent of which was satisfied with acetone produced by the cumene process.

A route analogous to the cumene process begins withcyclohexylbenzene. It isoxidized to ahydroperoxide, akin to the production ofcumene hydroperoxide. Via the Hock rearrangement, cyclohexylbenzene hydroperoxide cleaves to give phenol andcyclohexanone. Cyclohexanone is an important precursor to somenylons.^[25]

The direct oxidation ofbenzene (C₆H₆) to phenol is possible, but it has not been commercialized:

C₆H₆ + O → C₆H₅OH

Nitrous oxide is a potentially "green" oxidant that is a more potent oxidant than O₂. Routes for the generation of nitrous oxide however remain uncompetitive.^[26][23][25]

Anelectrosynthesis employingalternating current gives phenol from benzene.^[27]

The oxidation oftoluene, as developed byDow Chemical, involves copper-catalyzed reaction of molten sodium benzoate with air:

C₆H₅CH₃ + 2 O₂ → C₆H₅OH + CO₂ + H₂O

The reaction is proposed to proceed via formation of benzyoylsalicylate.^[8]

Autoxidation ofcyclohexylbenzene gives thehydroperoxide. Decomposition of this hydroperoxide affordscyclohexanone and phenol.^[8]

Early methods relied on extraction of phenol from coal derivatives or the hydrolysis of benzene derivatives.

The original commercial route was developed byBayer andMonsanto in the early 1900s, based on discoveries byWurtz andKekulé. The method involves the reaction of a strong base withbenzenesulfonic acid, proceeded by the reaction of hydroxide withsodium benzenesulfonate to give sodium phenoxide. Acidification of the latter gives phenol. The net conversion is:^[28]

C₆H₅SO₃H + 2 NaOH → C₆H₅OH + Na₂SO₃ + H₂O

Chlorobenzene can be hydrolyzed to phenol using a base (Dow process) or steam (Raschig–Hooker process):^[24][25][29]

C₆H₅Cl + NaOH → C₆H₅OH + NaCl

C₆H₅Cl + H₂O → C₆H₅OH + HCl

These methods suffer from the cost of the chlorobenzene and the need to dispose of the chloride byproduct.

Phenol is also a recoverable byproduct ofcoal pyrolysis.^[29] In theLummus process, the oxidation of toluene tobenzoic acid is conducted separately.

Phenyldiazonium salts hydrolyze to phenol. The method is of no commercial interest since the precursor is expensive.^[30]

C₆H₅NH₂ + HCl + NaNO₂ → C₆H₅OH + N₂ + H₂O + NaCl

Salicylic acid decarboxylates to phenol.^[31]

The major uses of phenol, consuming two thirds of its production, involve its conversion to precursors for plastics.Condensation with acetone givesbisphenol-A, a key precursor topolycarbonates andepoxide resins. Condensation of phenol, alkylphenols^{[citation needed]}, or diphenols^{[citation needed]} withformaldehyde givesphenolic resins, an example of which isBakelite. Partialhydrogenation of phenol givescyclohexanone,^[32] a precursor tonylon. Nonionicdetergents are produced by alkylation of phenol to give thealkylphenols, e.g.,nonylphenol, which are then subjected toethoxylation.^[8]

Phenol is also a versatile precursor to a large collection of drugs, most notablyaspirin but also manyherbicides andpharmaceutical drugs. Phenol is a component inliquid–liquidphenol–chloroform extraction technique used inmolecular biology for obtainingnucleic acids from tissues or cell culture samples. Depending on the pH of the solution eitherDNA orRNA can be extracted.

Phenol is so inexpensive that it also attracts many small-scale uses. It is a component of industrialpaint strippers used in the aviation industry for the removal of epoxy, polyurethane and other chemically resistant coatings.^[33] Safety concerns have caused it to be banned from use in cosmetic products in theEuropean Union^[34][35] andCanada.^[36][37]

Concentrated liquid phenol can be usedtopically as a localanesthetic forotology procedures, such asmyringotomy andtympanotomy tube placement, as an alternative to general anesthesia or other local anesthetics.^[38] Phenol spray, with phenol as the active ingredient, is used medically to treat sore throat.^[38] It is the active ingredient in some oralanalgesics.^[38]

Concentrated phenol liquids are used for permanent treatment of ingrown toe and finger nails, a procedure known as a chemicalmatrixectomy. The procedure was first described by Otto Boll in 1945.^{[citation needed]} Since then, phenol has become the agent of choice for chemical matrixectomies performed bypodiatrists.^{[medical citation needed]}

Phenol is used as a chemicaldenervation agent inanalgesia treatment, such as forspasticity, arthritis, or cancer pain.^[39] Its effect on the nerve is todenature protein, diminish nerve fat andmyelin content, and interrupt sensory transmission to the brain.^[39] If successful, pain relief may last for weeks to two years.^[39] Complications may include pain on injection, bleeding, or infection.^[39]

Clinical studies from 2023-25 reported that local injection of phenol (1.5–3 ml of 6% phenol in sterile water) at three to fivesensory knee nerves was effective as aneurolytic treatment to relieve pain associated with chronicosteoarthritis.^[40][41] The phenol method may be used for people who did not experience pain relief fromradiofrequency ablation of knee nerves.^[40][41]

Phenol was discovered in 1834 byFriedlieb Ferdinand Runge, who extracted it (in impure form) fromcoal tar.^[43] Runge called phenol "Karbolsäure" (coal-oil-acid, carbolic acid). Coal tar remained the primary source until the development of thepetrochemical industry. French chemistAuguste Laurent extracted phenol in its pure form, as a derivative of benzene, in 1841.^[44] In 1836, Auguste Laurent coined the name "phène" for benzene;^[45] this is the root of the word "phenol" and "phenyl". In 1843, French chemistCharles Gerhardt coined the name "phénol".^[46]

Theantiseptic properties of phenol were used by SirJoseph Lister in his pioneering technique of antiseptic surgery. Lister decided that the wounds had to be thoroughly cleaned. He then covered the wounds with a piece of rag or lint^[47] 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 contemporaryLouis Pasteur in sterilizing various biological media. He theorized that if germs could be killed or prevented, no infection would occur. Lister reasoned that a chemical could be used to destroy the micro-organisms that cause infection.^[48]

Meanwhile, inCarlisle, England, officials were experimenting withsewage treatment using carbolic acid to reduce the smell of sewagecesspools. 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 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 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.^[49]

By 16 March 1867, when the first results of Lister's work were published in 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

— Richard Hollingham,Blood and Guts: A History of Surgery, p. 62^[49]

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 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

— Richard Hollingham,Blood and Guts: A History of Surgery, p. 63^[50]

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 caseCarlill v Carbolic Smoke Ball Company. In the tort law case ofRoe v Minister of Health, phenol was used to sterilizeanaesthetic packed inampoules, in which it contaminated the anaesthetic through invisible micro-cracks and causedparaplegia to the plaintiffs.

Thetoxic effect of phenol on 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.^[51] Injections of phenol were used as a means of individual execution byNazi Germany during theSecond World War.^[52] It was originally used by the Nazis in 1939 as part of the mass-murder of disabled people underAktion T4.^[53] The Germans learned that extermination of smaller groups 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 inAuschwitz when he volunteered to die in place ofa stranger. Approximately one gram is sufficient to cause death.^[54]

Phenol is a normal metabolic product, excreted in quantities up to 40 mg/L in human urine.^[51] Thetemporal gland secretion of maleelephants showed the presence of phenol and4-methylphenol duringmusth.^[55][56] It is also one of the chemical compounds found incastoreum. This compound is ingested from the plants the beaver eats.^[57]

Phenol is a measurable component in the aroma and taste of the distinctiveIslay scotch whisky,^[58] generally ~30 ppm, but it can be over 160 ppm in the maltedbarley used to producewhisky.^[59] This amount is different from and presumably higher than the amount in the distillate.^[58]

Cryptanaerobacter phenolicus is a bacterium species that producesbenzoate from phenol via4-hydroxybenzoate.^[60]Rhodococcus phenolicus is a bacterium species able to degrade phenol as sole carbon source.^[61]

Phenol and its vapors are corrosive to the eyes, the skin, and the respiratory tract.^[62] Its corrosive effect on skin and mucous membranes is due to a protein-degenerating effect.^[51] Repeated or prolonged skin contact with phenol may causedermatitis, or even second and third-degree burns.^[63] Inhalation of phenol vapor may cause lungedema.^[62] The substance may cause harmful effects on the central nervous system and heart, resulting indysrhythmia,seizures, andcoma.^[64] Thekidneys may be affected as well. Long-term or repeated exposure of the substance may have harmful effects on theliver andkidneys.^[65] There is no evidence that phenol causescancer in humans.^[66] Besides itshydrophobic effects, another mechanism for the toxicity of phenol may be the formation ofphenoxylradicals.^[67]

Since phenol is absorbed through the skin relatively quickly, systemic poisoning can occur in addition to the local caustic burns.^[51] 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. TheLD₅₀ 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.^[51] 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.^[68]

Chemical burns fromskin exposures can be decontaminated by washing withpolyethylene glycol,^[69]isopropyl alcohol,^[70] or perhaps even copious amounts of water.^[71] Removal of contaminated clothing is required, as well as immediatehospital treatment for large splashes. This is particularly important if the phenol is mixed withchloroform (a commonly used mixture in molecular biology forDNA andRNA purification).^{[citation needed]} Phenol is also a reproductive toxin causing increased risk of miscarriage and low birth weight indicating retarded development in utero.^[5]

Phenol, which is produced and hence transported in large volumes, is shipped in a molten state below 70 °C (158 °F). The melting point is lowered and corrosive nature enhanced in the presence of small amounts of water. Typically stainless steel containers and nitrogen-blanketing are required to prevent discoloration.^[8]

The wordphenol is also used to refer to any compound that contains a six-memberedaromatic ring, bonded directly to ahydroxyl group (-OH). Thus, phenols are a class oforganic compounds of which the phenol discussed in this article is the simplest member.

• Bamberger rearrangement
• Claisen rearrangement
• Cresol
• Fries rearrangement
• Polyphenol

• International Chemical Safety Card 0070
• Phenol Material Safety Data Sheet
• National Pollutant Inventory: Phenol Fact Sheet
• NIOSH Pocket Guide to Chemical Hazards
• CDC - Phenol - NIOSH Workplace Safety and Health Topic
• IARC Monograph: "Phenol"
• Arcane Radio Trivia outlines competing uses for Phenol circa 1915