|Molar mass||92.14 g·mol−1|
|Density||0.87 g/mL (20 °C)|
|Melting point||−95 °C (−139 °F; 178 K)|
|Boiling point||111 °C (232 °F; 384 K)|
|0.52 g/L (20 °C) |
Refractive index (nD)
|1.497 (20 °C)|
|Viscosity||0.590 cP (20 °C)|
|Dipole moment||0.36 D|
|Main hazards||highly flammable|
|R-phrases||R11, R38, R48/20, R63, R65, R67|
|S-phrases||(S2), S36/37, S29, S46, S62|
|Flash point||6 °C (43 °F; 279 K)|
|50 mL m−3, 190 mg m−3|
Related aromatic hydrocarbons
|Supplementary data page|
|Refractive index (n),
Dielectric constant (εr), etc.
|UV, IR, NMR, MS|
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
|what is: / ?)(|
Toluene //, formerly known as toluol //, is a colorless, water-insoluble liquid with the smell associated with paint thinners. It is a mono-substituted benzene derivative, consisting of a CH3 group attached to a phenyl group. As such, its IUPAC systematic name is methylbenzene. It is an aromatic hydrocarbon.
Toluene is widely used as an industrial feedstock and as a solvent. Like other solvents, toluene is sometimes also used as an inhalant drug for its intoxicating properties; however, inhaling toluene has potential to cause severe neurological harm. Toluene is an important organic solvent.
The compound was first isolated in 1837 through a distillation of pine oil by a Polish chemist named Filip Walter, who named it retinaptha. This name was replaced shortly after by the word toluene derived from the older name toluol, which refers to tolu balsam, an aromatic extract from the tropical Colombian tree Myroxylon balsamum from which toluene was also isolated later. It was originally named by Jöns Jakob Berzelius.
Toluene reacts as a normal aromatic hydrocarbon towards electrophilic aromatic substitution. Owing to greater electron-releasing properties of the methyl group vs hydrogen, toluene is more reactive than benzene to electrophiles. It undergoes sulfonation to give p-toluenesulfonic acid, and chlorination by Cl2 in the presence of FeCl3 to give ortho and para isomers of chlorotoluene.
Importantly the methyl side chain in toluene is susceptible to oxidation. Potassium permanganate converts toluene to benzoic acid, whereas chromyl chloride leads to benzaldehyde (Étard reaction). The methyl group undergoes halogenation can be performed under free radical conditions. For example, N-bromosuccinimide (NBS) heated with toluene in the presence of AIBN leads to benzyl bromide. The same conversion can be effected with elemental bromine 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.
- C6H5CH3 + Br2 → C6H5CH2Br + HBr
- C6H5CH2Br + Br2 → C6H5CHBr2 + HBr
The methyl group in toluene undergoes deprotonation only with very strong bases, its pKa is approximately 45. Catalytic hydrogenation of toluene gives methylcyclohexane. The reaction requires a high pressure of hydrogen and a catalyst.
Toluene occurs naturally at low levels in crude oil and is usually produced in the production of gasoline via a catalytic reformer, in an ethylene cracker, or the production coke from coal. Final separation, either via distillation or solvent extraction, takes place in one of the many available processes for extraction of the BTX aromatics (benzene, toluene, and xylene isomers).
Toluene is so inexpensively produced industrially that it is not prepared in the laboratory. In principle it could be prepared by a variety of methods. For example, although only of didactical interest, benzene reacts with methyl chloride in presence of a Lewis acid such as aluminium chloride to give toluene:
- C6H5H + CH3Cl → C6H5CH3 + HCl
Such reactions are complicated by polymethylation because toluene is more susceptible to alkylation than is benzene.
Toluene is mainly used as a precursor to benzene. The process involves hydrodealkylation:
- C6H5CH3 + H2 → C6H6 + CH4
Precursor to other chemicals
Aside from being converted to benzene and xylene, toluene is a raw material for toluene diisocyanate (used in the manufacture of polyurethane foam) and TNT. Also an important precursor in the production of synthetic drugs.
Toluene can be used as an octane booster in gasoline fuels used in internal combustion engines. Toluene at 86% by volume fueled all the turbo Formula 1 teams in the 1980s, first pioneered by the Honda team. The remaining 14% was a "filler" of n-heptane, to reduce the octane to meet Formula 1 fuel restrictions. Toluene at 100% can be used as a fuel for both two-stroke and four-stroke engines; however, due to the density of the fuel and other factors, the fuel does not vaporize easily unless preheated to 70 degrees Celsius (Honda accomplished this in their Formula 1 cars by routing the fuel lines through the muffler system to heat the fuel).
In Australia, toluene has been found to have been illegally combined with petrol in fuel outlets for sale as standard vehicular fuel. Toluene attracts no fuel excise, whereas other fuels are taxed at over 40%, so fuel suppliers are able to profit from substituting the cheaper toluene for petrol. The extent of toluene substitution has not been determined.
In the laboratory, toluene is used as a solvent for carbon nanomaterials, including nanotubes and fullerenes, and it can also be used as a fullerene indicator. The color of the toluene solution of C60 is bright purple. It is also used as a cement for fine polystyrene kits (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 open red blood cells in order to extract hemoglobin 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.
Toxicology and metabolism
Inhalation of toluene in low to moderate levels can cause tiredness, confusion, weakness, drunken-type actions, memory loss, nausea, loss of appetite, and hearing and color vision loss. These symptoms usually disappear when exposure is stopped. Inhaling high levels of toluene in a short time may cause light-headedness, nausea, or sleepiness. It can also cause unconsciousness, and even death.
Toluene is, however, much less toxic than benzene, and has, as a consequence, largely replaced it as an aromatic solvent in chemical preparation. For example, benzene is a known carcinogen, whereas toluene has very little carcinogenic potential.
Similar to many other solvents such as 1,1,1-trichloroethane and some alkylbenzenes, toluene has been shown to act as a non-competitive NMDA receptor antagonist and GABAA receptor positive allosteric modulator. It is abused as an inhalant likely on account of the euphoric and dissociative effects these actions produce. Additionally, toluene has been shown to display antidepressant-like effects in rodents in the forced swim test (FST) and the tail suspension test (TST).
Several types of fungi including Cladophialophora, Exophiala, Leptodontium, Pseudeurotium zonatum, and Cladosporium sphaerospermum, and certain species of bacteria can degrade toluene using it as a source of carbon and energy.
- Record in the GESTIS Substance Database of the IFA
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|Wikimedia Commons has media related to toluene.|
|Wikiquote has quotations related to: Toluene|
- ATSDR – Case Studies in Environmental Medicine: Toluene Toxicity U.S. Department of Health and Human Services (public domain)
- Toluene CDC – NIOSH Workplace Safety and Health Topic (DHHS)