Toluene

Toluene, also known as '''methylbenzene''' or '''phenylmethane''' is a clear, Water -insoluble liquid with the typical smell of Paint Thinner s, 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 Isomer s 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 a common s, paint thinners, many Chemical Reactant s, Rubber , Printing ink, Adhesive s, Lacquer s, Leather Tanners , Disinfectant s, Glue s. It can also be used as a Fullerene indicator, and is a raw material for Toluene Diisocyanate (used in the manufacture of Polyurethane foam), Phenol and TNT . Toluene can be used as an Octane booster in Gasoline fuels used in Internal Combustion Engine s. Industrial uses of toluene include dealkylation to Benzene and disproportionation to a mixture of Benzene and Xylene .

TOXICOLOGY AND METABOLISM

See Also: 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

SEE ALSO

# External solubility data
# NIST WebBook
# Computational Chemistry Wiki

REFERENCES

# B. S. Furnell et al., ''Vogel's Textbook of Practical Organic Chemistry'', 5th edition, Longman/Wiley, New York, 1989.
# (a) L. G. Wade, ''Organic Chemistry'', 5th ed., p. 871, Prentice Hall, Upper Saddle RIver, New Jersey, 2003.
# J. March, ''Advanced Organic Chemistry'', 4th ed., p. 723, Wiley, New York, 1992.
# Miyagi, Y., Shima, F., Ishido, K. et al. Tremor induced by toluene misuse successfully treated by a Vim thalamotomy. ''Journal of Neurology Neurosurgery and Psychiatry'' 66(6):794-6, (1999).
# Urban, P., Lukáš, E., Pelclová, D. et al. Neurological and Neurophysiological Follow-up on Workers With Severe Chronic Exposure to Toluene. ''Neurotoxicity'' P25:s130, (2003).
# Yamaguchi, H., Kidachi, Y. and Ryoyama, K. Toluene at Environmentally Relevant Low Levels Disrupts Differentiation of Astrocyte Precursor Cells. ''Archives of Environmental Health'' 57(3):232-8, (2002).

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Toluene