Toluene (/ˈtɒl.juiːn/), also known astoluol (/ˈtɒl.ju.ɒl,-ɔːl,-oʊl/), is asubstitutedaromatic hydrocarbon^[15] with thechemical formulaC₆H₅CH₃, often abbreviated asPhCH₃, where Ph stands for thephenyl group. It is a colorless,water-insoluble liquid with the odor associated withpaint thinners. It is a mono-substitutedbenzene derivative, consisting of amethyl group (CH₃) attached to aphenyl group by asingle bond. As such, its systematicIUPAC name ismethylbenzene. Toluene is predominantly used as an industrialfeedstock and asolvent.

Toluene

Names
Preferred IUPAC name Toluene[2]
Systematic IUPAC name Methylbenzene
Other names Methyl benzene[1] Benzylane Phenylmethane Toluol Anisen
Identifiers
CAS Number	108-88-3 Y
3D model (JSmol)	Interactive image
Abbreviations	PhMe MePh BnH Tol
ChEBI	CHEBI:17578 N
ChEMBL	ChEMBL9113 Y
ChemSpider	1108 Y
DrugBank	DB01900 N
ECHA InfoCard	100.003.297
IUPHAR/BPS	5481
KEGG	C01455 Y
PubChemCID	1140
RTECS number	XS5250000
UNII	3FPU23BG52 Y
UN number	1294
CompTox Dashboard(EPA)	DTXSID7021360
InChI InChI=1S/C7H8/c1-7-5-3-2-4-6-7/h2-6H,1H3 Y Key: YXFVVABEGXRONW-UHFFFAOYSA-N Y InChI=1/C7H8/c1-7-5-3-2-4-6-7/h2-6H,1H3 Key: YXFVVABEGXRONW-UHFFFAOYAT
SMILES Cc1ccccc1
Properties
Chemical formula	C6H5CH3
Molar mass	92.141 g·mol−1
Appearance	Colorless liquid[3]
Odor	sweet, pungent,benzene-like[4]
Density	0.8623 g/mL (25 °C)[1]
Melting point	−95.0 °C (−139.0 °F; 178.2 K)[1]
Boiling point	110.60 °C (231.08 °F; 383.75 K)[1]
Solubility in water	0.54 g/L (5 °C) 0.519 g/L (25 °C) 0.63 g/L (45 °C) 1.2 g/L (90 °C)[5]
logP	2.73[6]
Vapor pressure	2.8 kPa (20 °C)[4]
Magnetic susceptibility (χ)	−66.1·10−6 cm3/mol[7]
Thermal conductivity	0.1310 W/(m·K) (25 °C)[8]
Refractive index (nD)	1.4941 (25 °C)[1]
Viscosity	0.560 mPa·s (25 °C)[9]
Structure
Dipole moment	0.375D[10]
Thermochemistry[11]
Heat capacity(C)	157.3 J/(mol·K)
Std enthalpy of formation(ΔfH⦵298)	12.4 kJ/mol
Std enthalpy of combustion(ΔcH⦵298)	3.910 MJ/mol
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	highly flammable
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H225,H304,H315,H336,H361d,H373
Precautionary statements	P210,P240,P301+P310,P302+P352,P308+P313,P314,P403+P233
NFPA 704 (fire diamond)	2 3 0
Flash point	4 °C (39 °F; 277 K)[12]
Autoignition temperature	480[12] °C (896 °F; 753 K)
Explosive limits	1.1–7.1%[12]
Threshold limit value (TLV)	50 mL/m3, 190 mg/m3
Lethal dose or concentration (LD, LC):
LC50 (median concentration)	>26700 ppm (rat, 1 h) 400 ppm (mouse, 24 h)[13]
LCLo (lowest published)	55,000 ppm (rabbit, 40 min)[13]
NIOSH (US health exposure limits):
PEL (Permissible)	TWA 200 ppm C 300 ppm 500 ppm (10-minute maximum peak)[4]
REL (Recommended)	TWA 100 ppm (375 mg/m3) ST 150 ppm (560 mg/m3)[4]
IDLH (Immediate danger)	500 ppm[4]
Safety data sheet (SDS)	SIRI.org
Related compounds
Relatedaromatic hydrocarbons	benzene xylene naphthalene
Related compounds	methylcyclohexane methylcyclohexene
Supplementary data page
Toluene (data page)
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

As the solvent in some types ofpaint thinner,permanent markers,contact cement and certain types of glue, toluene is sometimes used as a recreationalinhalant^[16] and has the potential of causing severe neurological harm.^[17][18]

The compound was first isolated in 1837 through a distillation ofpine oil byPierre Joseph Pelletier andFilip Neriusz Walter, who named itrétinnaphte.^[19][20] In 1841,Henri Étienne Sainte-Claire Deville isolated a hydrocarbon frombalsam of Tolu (an aromatic extract from the tropical Colombian treeMyroxylon balsamum), which Deville recognized as similar to Walter'srétinnaphte and to benzene; hence he called the new hydrocarbonbenzoène.^[21][22][23] In 1843,Jöns Jacob Berzelius recommended the nametoluin.^[24] In 1850, French chemistAuguste Cahours isolated from a distillate of wood a hydrocarbon which he recognized as similar to Deville'sbenzoène and which Cahours namedtoluène.^[25][26]

The distance between carbon atoms in the toluene ring is 0.1399 nm. The C-CH₃ bond is longer at 0.1524 nm, while the average C-H bond length is 0.111 nm.^[27]

Toluene reacts as a normalaromatic hydrocarbon inelectrophilic aromatic substitution.^[28][29][30] Because themethyl group has greater electron-releasing properties than ahydrogen atom in the same position, toluene is more reactive thanbenzene toward electrophiles. It undergoessulfonation to givep-toluenesulfonic acid, andchlorination byCl₂ in the presence ofFeCl₃ to give ortho and paraisomers ofchlorotoluene.

Nitration of toluene gives mono-, di-, and trinitrotoluene, all of which are widely used. Dinitrotoluene is the precursor totoluene diisocyanate, a precursor topolyurethane foam.Trinitrotoluene (TNT) is an explosive.

Completehydrogenation of toluene givesmethylcyclohexane. The reaction requires a high pressure of hydrogen and acatalyst.

The C-H bonds of the methyl group in toluene arebenzylic, therefore they are weaker than C-H bonds in simpler alkanes. Reflecting this weakness, the methyl group in toluene undergoes a variety offree radical reactions. For example, when heated withN-bromosuccinimide (NBS) in the presence ofAIBN, toluene converts tobenzyl bromide. The same conversion can be effected with elementalbromine in the presence of UV light or even sunlight.

Toluene may also be brominated by treating it with HBr and H₂O₂ in the presence of light.^[31]

C₆H₅CH₃ + Br₂ → C₆H₅CH₂Br + HBr

Benzoic acid andbenzaldehyde are produced commercially bypartial oxidation of toluene withoxygen. Typical catalysts includecobalt ormanganesenaphthenates.^[32] Related but laboratory-scale oxidations involve the use ofpotassium permanganate to yieldbenzoic acid andchromyl chloride to yieldbenzaldehyde (Étard reaction).

The methyl group in toluene undergoes deprotonation only with very strong bases; itspK_a is estimated using acidity trends to be approximately 43 indimethyl sulfoxide (DMSO)^[33][34] and its ion pair acidity is extrapolated to be 41.2 incyclohexylamine (Cesium Cyclohexylamide) using a Bronsted correlation.^[35][36]

Toluene ismiscible (soluble in all proportions) withethanol,benzene,diethyl ether,acetone,chloroform, glacialacetic acid andcarbon disulfide, but immiscible with water.^[37]

Toluene occurs naturally at low levels in crude oil and is a byproduct in the production ofgasoline by acatalytic reformer orethylenecracker. It is also a byproduct of the production ofcoke fromcoal. Final separation and purification is done by any of thedistillation orsolvent extraction processes used forBTX aromatics (benzene, toluene, and xylene isomers).^[15]

Toluene can be prepared by a variety of methods. For example,benzene reacts withmethanol in presence of asolid acid to give toluene and water:^[15]

${\displaystyle {\text{C}}_6^{}{\text{H}}_6^{}+{\text{CH}}_3^{}\text{OH}\stackrel{t^o}{\to }{\text{C}}_6^{}{\text{H}}_5^{}{\text{CH}}_3^{}+{\text{H}}_2^{}\text{O}}$ 

Toluene is one of the most abundantly produced chemicals. Its main uses are (1) as a precursor to benzene andxylenes, (2) as a solvent for thinners, paints,lacquers, adhesives, and (3) as an additive for gasoline.^[15]

Toluene is converted to benzene viahydrodealkylation:

C₆H₅CH₃ + H₂ → C₆H₆ + CH₄

Itstransalkylation gives a mixture of benzene andxylenes.

Toluene is widely used in the paint,dye, rubber, chemical, glue, printing, and pharmaceutical industries as a solvent.^[38] Nail polish, paintbrush cleaners, and stain removers may contain toluene. Manufacturing of explosives (TNT) uses it as well. Toluene is also found in cigarette smoke and car exhaust. If not in contact with air, toluene can remain unchanged in soil or water for a long time.^[39]

Toluene is a commonsolvent, e.g. forpaints, paint thinners, strippers, silicone sealants,^[40] manychemical reactants,rubber,printing ink,adhesives (glues),lacquers,leather tanners, anddisinfectants.^[15]

Toluene is anoctane booster ingasoline fuels forinternal combustion engines as well asjet fuel andturbocharged engines inFormula One.^[41]

InAustralia in 2003, toluene was found to have been illegally combined with petrol in fuel outlets for sale as standard vehicular fuel. Toluene incurs no fuel excise tax, while other fuels are taxed at more than 40%, providing a greaterprofit margin for fuel suppliers. The extent of toluene substitution is claimed to be 60%.^[42][43]

In the laboratory, toluene is used as a solvent for carbon nanomaterials, including nanotubes and fullerenes, and it can also be used as afullerene indicator. The color of the toluene solution of C₆₀ is bright purple. Toluene is used as a cement for finepolystyrenekits (by dissolving and then fusing surfaces) as it can be applied very precisely by brush and contains none of the bulk of an adhesive. Toluene can be used to break openred blood cells in order to extracthemoglobin in biochemistry experiments. Toluene has also been used as a coolant for its good heat transfer capabilities in sodium cold traps used in nuclear reactor system loops. Toluene had also been used in the process ofremoving the cocaine from coca leaves in the production of Coca-Cola syrup.^[44]

The environmental and toxicological effects of toluene have been extensively studied.^[45]

Toluene is irritating to the eyes, skin, and respiratory tract. It is absorbed slowly through the skin. It can cause systemic toxicity by inhalation or ingestion. Inhalation is the most common route of exposure. Symptoms of toluene poisoning includecentral nervous system effects (headache, dizziness, drowsiness,ataxia,euphoria,tremors,hallucinations,seizures, and coma), chemicalpneumonitis, respiratory depression,ventricular arrhythmias, nausea, vomiting, andelectrolyte imbalances.^[38]

Inhalation of toluene in low to moderate levels can cause tiredness, confusion, weakness, drunken-type actions, memory loss, nausea, loss of appetite,hearing loss,^[46][47][48] and colour vision loss.^[49] Some of these symptoms usually disappear when exposure is stopped. Inhaling high levels of toluene in a short time may cause light-headedness, nausea, or sleepiness, unconsciousness, and evendeath.^[50][51] Toluene is, however, much less toxic thanbenzene, and as a consequence, largely replaced it as an aromatic solvent in chemical preparation. TheUS Environmental Protection Agency (EPA) states that thecarcinogenic potential of toluene cannot be evaluated due to insufficient information.^[52] In 2013, worldwide sales of toluene amounted to about 24.5 billion US dollars.^[53]

Toluene occurs as anindoor air pollutant in a number of processes including electrosurgery, and can be removed from the air with anactivated carbon filter.^[54]

Similarly to many other solvents such as1,1,1-trichloroethane and somealkylbenzenes, toluene has been shown to act as anon-competitiveNMDA receptor antagonist andGABA_A receptorpositive allosteric modulator.^[55] Additionally, toluene has been shown to displayantidepressant-like effects in rodents in theforced swim test (FST) and thetail suspension test (TST),^[55] likely due to its NMDA antagonist properties.

Toluene is sometimes used as a recreationalinhalant ("glue sniffing"), likely on account of itseuphoric anddissociative effects.^[55]

Toluene inhibits excitatory ion channels such as theNMDA receptor,nicotinic acetylcholine receptor, and theserotonin 5-HT₃ receptor. It also potentiates the function of inhibitory ion channels, such as theGABA_A andglycine receptors. In addition, toluene disruptsvoltage-gated calcium channels and ATP-gated ion channels.^[56]

Toluene is used as anintoxicative inhalant in a manner unintended by manufacturers. People inhale toluene-containing products (e.g.,paint thinner,contact cement, correction pens, model glue, etc.) for itsintoxicating effect. The possession and use of toluene and products containing it are regulated in many jurisdictions, for the supposed reason of preventing minors from obtaining these products forrecreational drug purposes. As of 2007, 24 US states had laws penalizing use, possession with intent to use, and/or distribution of such inhalants.^[57] In 2005 theEuropean Union banned the general sale of products consisting of greater than 0.5% toluene.^[58]

Several types of fungi includingCladophialophora,Exophiala,Leptodontidium (syn.Leptodontium),Pseudeurotium zonatum, andCladosporium sphaerospermum, and certain species of bacteria can degrade toluene using it as a source of carbon and energy.^[59]

• Haynes, William M., ed. (2016).CRC Handbook of Chemistry and Physics (97th ed.).CRC Press.ISBN 978-1-4987-5429-3.

• ATSDR – Case Studies in Environmental Medicine: Toluene Toxicity U.S. Department of Health and Human Services (public domain)
• American Industrial Hygiene Association,The Ear Poisons, The Synergist, November 2018.
• Toluene CDC – NIOSH Workplace Safety and Health Topic (DHHS)
• OSHA-NIOSH 2018.Preventing Hearing Loss Caused by Chemical (Ototoxicity) and Noise Exposure Safety and Health Information Bulletin (SHIB), Occupational Safety and Health Administration and the National Institute for Occupational Safety and Health. SHIB August 3, 2018. DHHS (NIOSH) Publication No. 2018-124.
• Toxic trouble: Chinese children fall ill after inhaling fumes from newly laid school running tracks, South China Morning Post, 2015