Toluene

Toluene

Names
IUPAC name Methylbenzene
Other names toluene phenylmethane toluol Anisen
Identifiers
CAS Number	108-88-3 Y
Abbreviations	PhMe MePh BnH
ChEBI	CHEBI:17578 N
ChEMBL	ChEMBL9113 Y
ChemSpider	1108 Y
DrugBank	DB01900 N
IUPHAR/BPS	5481
Jmol 3D model	Interactive image
KEGG	C01455 Y
PubChem	1140
RTECS number	XS5250000
UNII	3FPU23BG52 Y
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	C7H8
Molar mass	92.14 g·mol−1
Appearance	Colorless liquid
Odor	sweet, pungent, benzene-like
Density	0.87 g/mL (20 °C)
Melting point	−95 °C (−139 °F; 178 K)
Boiling point	111 °C (232 °F; 384 K)
Solubility in water	0.52 g/L (20 °C)
Vapor pressure	21 mmHg (20°C)
Refractive index (nD)	1.497 (20 °C)
Viscosity	0.590 cP (20 °C)
Structure
Dipole moment	0.36 D
Vapor pressure	{{{value}}}
Related compounds
Related aromatic hydrocarbons	benzene xylene naphthalene
Related compounds	methylcyclohexane
Supplementary data page
Structure and properties	Refractive index (n), Dielectric constant (εr), etc.
Thermodynamic data	Phase behaviour solid–liquid–gas
Spectral data	UV, IR, NMR, MS
N verify (what is YN ?)
Infobox references

Toluene /ˈtɒljuːiːn/, formerly known as toluol /ˈtɒljuːɒl/, is a colourless, 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. Its economic significance is considerable: In 2013, worldwide about 24.5 billion US-dollars were generated with the sale of toluene.

History

The compound was first isolated in 1837 through a distillation of pine oil by a Polish chemist named Filip Walter, who named it rétinnaphte. In 1841, French chemist Henri Étienne Sainte-Claire Deville isolated a hydrocarbon from balsam of Tolu (an aromatic extract from the tropical Colombian tree Myroxylon balsamum), which Deville recognized as similar to Walter's rétinnaphte and to benzene; hence he called the new hydrocarbon benzoène. In 1843, Jöns Jacob Berzelius recommended the name toluin. In 1850, French chemist Auguste Cahours isolated from a distillate of wood a hydrocarbon which he recognized as similar to Deville's benzoène and which Cahours named toluène.

Chemical properties

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 pK_a is approximately 45. Catalytic hydrogenation of toluene gives methylcyclohexane. The reaction requires a high pressure of hydrogen and a catalyst.

Production

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 of 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).

Laboratory preparation

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.

Uses

Toluene is mainly used as a precursor to benzene. The process involves hydrodealkylation:

C₆H₅CH₃ + H₂ → C₆H₆ + CH₄

The second ranked application involves its disproportionation to a mixture of benzene and xylene. When oxidized it yields benzaldehyde and benzoic acid, two important intermediates in chemistry.

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.

Solvent

Toluene is a common solvent, e.g. for paints, paint thinners, silicone sealants, many chemical reactants, rubber, printing ink, adhesives (glues), lacquers, leather tanners, and disinfectants.

Fuel

Toluene can be used as an octane booster in gasoline fuels used in internal combustion engines. Toluene at 86% by volume fuelled 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 vaporise easily unless preheated to 70 degrees Celsius (Honda accomplished this in their Formula 1 cars by routing the fuel lines through the exhaust system to heat the fuel).

In Australia, in 2003, toluene was 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.

Toluene is another in a group of fuels that have recently been used as components for jet fuel surrogate blends. Toluene is used as a jet fuel surrogate for its content of aromatic compounds.

Niche applications

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 colour 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 haemoglobin 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 of removing the cocaine from coca leaves in the production of Coca-Cola syrup.

Toxicology and metabolism

Main article: Toluene (toxicology)

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, 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. The EPA considers that there is inadequate information to assess the carcinogenic potential of toluene.

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 GABA_A receptor positive allosteric modulator. Additionally, toluene has been shown to display antidepressant-like effects in rodents in the forced swim test (FST) and the tail suspension test (TST).

It is sometimes used as an inhalant, likely on account of its euphoric and dissociative effects.

Bioremediation

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.

Legal status

Toluene is an intoxicative inhalant and its possession and use are regulated in many jurisdictions. As of 2007, 24 U.S. states had laws penalizing use, possession with intent to use, and/or distribution of inhalants such as toluene.

External links

• 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)