Toluene
[CAS# 108-88-3]

Identification

• Classification: Organic raw materials >> Hydrocarbon compounds and their derivatives >> Aromatic hydrocarbon
• Name: Toluene
• Synonyms: Tol; Toluol; Methylbenzene
• Molecular Formula: C₇H₈
• Molecular Weight: 92.14
• CAS Registry Number: 108-88-3
• EC Number: 203-625-9
• SMILES: CC1=CC=CC=C1

Properties

• Density: 0.9±0.1 g/cm³ Calc.^*, 0.867 g/mL (Expl.)
• Melting point: -93 °C (Expl.)
• Boiling point: 110.6±3.0 °C 760 mmHg (Calc.)^*, 110.6 - 111.7 °C (Expl.)
• Flash point: 4.4 °C (Calc.)^*, 3.9 - 5 °C (Expl.)
• Solubility: water: 0.07 g/100g (Expl.)
• Index of refraction: 1.5 (Calc.)^*, 1.497 (Expl.)

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software.

Safety Data

• Hazard Symbols: GHS02;GHS07;GHS08 Danger
• Risk Statements: H225-H304-H315-H336-H361d-H373
• Safety Statements: P203-P210-P233-P240-P241-P242-P243-P260-P261-P264-P271-P280-P301+P316-P302+P352-P303+P361+P353-P304+P340-P318-P319-P321-P331-P332+P317-P362+P364-P370+P378-P403+P233-P403+P235-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Aspiration hazard	Asp. Tox.	1	H304
Flammable liquids	Flam. Liq.	2	H225
Skin irritation	Skin Irrit.	2	H315
Specific target organ toxicity - repeated exposure	STOT RE	2	H373
Specific target organ toxicity - single exposure	STOT SE	3	H336
Reproductive toxicity	Repr.	2	H361
Chronic hazardous to the aquatic environment	Aquatic Chronic	3	H412
Reproductive toxicity	Repr.	2	H361d
Eye irritation	Eye Irrit.	2	H319
Chronic hazardous to the aquatic environment	Aquatic Chronic	2	H411
Flammable liquids	Flam. Liq.	3	H226
Specific target organ toxicity - single exposure	STOT SE	3	H335
Aspiration hazard	Asp. Tox.	1	H305
Reproductive toxicity	Repr.	1A	H360
Acute toxicity	Acute Tox.	4	H302
Specific target organ toxicity - repeated exposure	STOT RE	1	H372
Reproductive toxicity	Repr.	2	H361fd
Acute toxicity	Acute Tox.	4	H332
Specific target organ toxicity - single exposure	STOT SE	1	H370
Carcinogenicity	Carc.	1A	H350
Germ cell mutagenicity	Muta.	1B	H340
Skin sensitization	Skin Sens.	1	H317
Reproductive toxicity	Repr.	1A	H361
Reproductive toxicity	Repr.	2	H361d

• Transport Information: UN 1294

Discovery and Applications

Toluene is an aromatic hydrocarbon with the molecular formula C₇H₈. It was first isolated in the 1830s by distilling pine oil, and later identified as a component of tolu balsam. The compound’s name is derived from this natural resin. In 1843, the French chemist Henri Étienne Sainte-Claire Deville successfully obtained pure toluene by distilling tolu balsam, and its chemical nature was clarified over the following decades through the development of structural organic chemistry.

Toluene consists of a benzene ring substituted with a single methyl group. It is a colorless, water-insoluble liquid with a characteristic sweet odor, and is one of the simplest and most widely used mono-substituted benzenes. Due to its chemical properties, toluene serves as an essential industrial feedstock and solvent.

One of the primary applications of toluene is in the production of benzene and xylene via catalytic reforming and transalkylation. Toluene is also extensively used as a solvent for paints, coatings, adhesives, inks, and cleaning agents. Its nonpolar character makes it particularly useful for dissolving organic compounds that are poorly soluble in water.

In the chemical industry, toluene undergoes a variety of transformations. Nitration of toluene yields mono-, di-, and trinitrotoluene (TNT), with TNT being a major explosive compound. Through halogenation, sulfonation, and oxidation, toluene can be converted into a variety of other derivatives, such as benzaldehyde, benzoic acid, and chlorotoluene. Another significant derivative is toluene diisocyanate (TDI), which is a precursor for polyurethane foam production.

Toluene is also used in the synthesis of phenol via the cumene process and as a feedstock for making styrene by alkylation with ethylene to form ethylbenzene, followed by dehydrogenation. Furthermore, it can be methylated to produce xylenes, which are important petrochemicals.

The compound is naturally present in crude oil and is also generated during the catalytic reforming of naphtha in petroleum refineries. In addition, it is produced during the combustion of organic materials and is found in vehicle emissions and cigarette smoke.

Due to its volatility and widespread use, exposure to toluene is a concern in occupational and environmental health. Inhalation of toluene vapors can affect the central nervous system and, at high concentrations, may lead to dizziness, headaches, or even loss of coordination. Chronic exposure can have more severe neurological and systemic effects. Consequently, regulatory agencies have established permissible exposure limits for toluene in industrial environments.

Nevertheless, toluene remains a vital raw material in organic synthesis and industrial chemistry, playing a critical role in the production of polymers, dyes, pharmaceuticals, and agrochemicals. Its combination of chemical stability, solubility characteristics, and reactivity under controlled conditions make it a valuable and versatile compound in both research and manufacturing contexts.

References

1979. Toxic effects of toluene. JAMA: The Journal of the American Medical Association, 242(14).
DOI: 10.1001/jama.1979.03300140013014

1979. Conjugation and urinary excretion of toluene and m-xylene metabolites in a man. Scandinavian Journal of Work, Environment & Health, 5(2).
DOI: 10.5271/sjweh.2659

1996. Solid acid (superacid) catalyzed regioselective adamantylation of substituted benzenes. Catalysis Letters, 38(1-2).
DOI: 10.1007/bf00814460