Toluene
| Toluene | |
|---|---|
 |
|
| General | |
| Systematic name | toluene |
| Other names | methylbenzene phenylmethane toluol |
| Molecular formula | C7H8 |
| SMILES | CC1=CC=CC=C1 |
| Molar mass | 92.14 g/mol |
| Appearance | Clear, colourless liquid |
| CAS number | [108-88-3] |
| Properties | |
| Density and phase | 0.8669 g/cm3, liquid |
| Solubility in water | 0.053 g/100 mL (20-25°C) |
| In ethanol, acetone, hexane, dichloromethane |
Fully miscible |
| Melting point | -93 °C (180 K)/(-135.4°F) |
| Boiling point | 110.6 °C (383.8 K)/ 231.08°F |
| Critical Temperature | 320 °C (593 K)/ 608°F |
| Viscosity | 0.590 c P at 20°C/ 68°F |
| Dipole moment | 0.36 D |
| Hazards | |
| MSDS | External MSDS |
| Main hazards | highly flammable |
| NFPA 704 |
   |
| Flash point | 7 °C/ 44.6°F |
| R-phrases | R11, R20 |
| S-phrases | S16, S25, S29, S33 |
| RTECS number | XS5250000 |
| Supplementary data page | |
| Structure & properties | n, εr, etc. |
| Thermodynamic data | Phase
behaviour Solid, liquid, gas |
| Spectral data | UV, IR, NMR, MS |
| Related compounds | |
| Related
aromatic hydrocarbons |
benzene xylene naphthalene |
| Related compounds | methylcyclohexane |
| Except where noted otherwise, data are given
for materials in their standard state (at 25°C, 100 kPa) Infobox disclaimer and references |
|
This article is about the general properties of toluene, including its chemistry. For the toxicological effects, see Toluene (toxicology).
Toluene, also known as methylbenzene or phenylmethane is a clear, water-insoluble liquid with the typical smell of paint thinners, reminiscent of the sweet smell of the related compound benzene. It is an aromatic hydrocarbon that is widely used as an industrial feedstock and as a solvent.
History
The name toluene was derived from the older name toluol that refers to tolu balsam, an aromatic extract from the tropical American tree Myroxylon balsamum, from which it was first isolated. It was originally named by Jöns Jakob Berzelius.
Chemical properties
Toluene reacts as a normal aromatic hydrocarbon towards electrophilic aromatic substitution. The methyl group makes it around 25 times more reactive than benzene in such reactions. It undergoes smooth sulfonation to give p-toluenesulfonic acid, and chlorination by Cl2 in the presence of FeCl3 to give ortho and para isomers of chlorotoluene. It undergoes nitration to give ortho and para nitrotoluene isomers, but if heated it can give dinitrotoluene and ultimately the explosive trinitrotoluene (TNT).
With other reagents the methyl side chain in toluene may react, undergoing oxidation. Reaction with Potassium permanganate leads to benzoic acid, whereas chromyl chloride leads to benzaldehyde. Halogenation can be performed under free radical conditions. For example, NBS heated with toluene in the presence of AIBN leads to benzyl bromide.
Catalytic hydrogenation of toluene to methylcyclohexane requires a high pressure of hydrogen to go to completion, because of the stability of the aromatic system.
Preparation
Toluene occurs naturally at low levels in crude oil and is usually produced in the processes of making gasoline via a catalytic reformer, in an ethylene cracker or making coke from coal. Final separation (either via distillation or solvent extraction) takes place in a BTX plant.
Uses
Toluene is used as an octane booster in fuel, as a solvent in paints, paint thinners, chemical reactions, rubber, printing, adhesives, lacquers, leather tanning, disinfectants, and to produce phenol and TNT. It is also used as a raw material for toluene diisocyanate, which is used in the manufacture of polyurethane foam.
Precautions and metabolism
For the main article on this topic see Toluene (toxicology).
Inhalation of toluene fumes can be intoxicating, but in larger doses nausea-inducing. Chronic or frequent inhalation of toluene over long time periods leads to irreversible brain damage.
The toxicity of toluene can be explained mostly by its metabolism. As toluene has very low water solubility, it cannot exit the body via the normal routes (urine, feces, or sweat). It must be metabolized in order to be excreted. The methyl group of toluene is more easily oxidized by cytochrome P450 than the benzene ring. Therefore, in the metabolism of toluene, 95% is oxidized to become benzyl alcohol. The toxic metabolites are created by the remaining 5% that are ring oxidized to epoxides. Most of the epoxides become glutathione conjugated. However, the remainder will severely damage cells.
Toluene is mainly excreted as benzoic acid and hippuric acid, both formed by further metabolic oxidation of benzyl alcohol.
Behavioural Effects of Long Term Exposure
Serious adverse behavioural effects are often associated with toluene abuse related to the deliberate inhalation of solvents.4 Long term toluene exposure is often associated with effects such as: psychoorganic syndrome;5 visual evoked potential (VEP) abnormality;5 toxic polyneuropathy, cerebellar, cognitive, and pyramidal dysfunctions;5 optic atrophy; and brain lesions.4
Toluene causes postural tremors by increasing extracellular concentrations of γ-aminobutyric acid ( GABA) within the cerebellar cortex.4 Treatment with GABA agonists such as, benzodiazepines provide some relief from toluene induced tremor and ataxia.4 An alternative to drug treatment is vim thalamotomy.4 The tremors associated with toluene misuse do not seem to be a transient symptom, but an irreversible and progressive symptom which continues after solvent abuse has been discontinued.4
There is some evidence that low level toluene exposure may cause disruption in the differentiation of astrocyte precursor cells.6 This does not appear to be a major hazard to adults; however, exposure of pregnant women to toluene during critical stages of fetal development could cause serious disruption to neuronal development.6
Suppliers/manufacturers
- Lancaster (now part of Alfa)
- Fisher
- VWR
- Alfa
- Aldrich
- Aurora Fine Chemicals
- ScienceLab