Toluene
| Toluene | |
|---|---|
 |
 |
| Other names | phenylmethane toluol methylbenzene |
| Identifiers | |
| CAS number | 108-88-3 |
| RTECS number | XS5250000 |
| SMILES |
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| ChemSpider ID | |
| Properties | |
| Molecular formula | C7H8 (C6H5CH3) |
| Molar mass | 92.14 g/mol |
| Appearance | Clear colorless, liquid |
| Density | 0.8669 g/mL, liquid |
| Melting point |
−93 °C |
| Boiling point |
110.6 °C |
| Solubility in water | 0.47 g/l (20-25°C) |
| Viscosity | 0.590 cP at 20°C |
| Structure | |
| Dipole moment | 0.36 D |
| Hazards | |
| MSDS | ScienceLab.com |
| Main hazards | highly flammable |
| NFPA 704 |
 3
2
0
|
| R-phrases | R11, R38, R48/20, R63, R65, R67 |
| S-phrases | (S2), S36/37, S29, S46, S62 |
| Flash point | 4 °C/ 39.2 °F |
| Related compounds | |
| Related aromatic hydrocarbon | 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 references |
|
Toluene, also known as methylbenzene or phenylmethane, is a clear, water-insoluble liquid with the typical smell of paint thinners, redolent 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. Like other solvents, toluene is also used as an inhalant drug for its intoxicating properties.[1][2]
Contents |
History
The name toluene was derived from the older name toluol, which refers to tolu balsam, an aromatic extract from the tropical Colombian 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.[3][4][5] 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 reaction with chromyl chloride leads to benzaldehyde (Étard reaction). 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.
Catalytic hydrogenation of toluene to methylcyclohexane requires a high pressure of hydrogen to go to completion, because of the stability of the aromatic system. pKa is approximately 45.
Production
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 solvent, able to dissolve: paints, paint thinners, silicone sealants,[6] many chemical reactants, rubber, printing ink, adhesives (glues), lacquers, leather tanners, and disinfectants. It can also be used as a fullerene indicator, and is a raw material for toluene diisocyanate (used in the manufacture of polyurethane foam) and TNT. It is also used as an adhesive 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.
Industrial uses of toluene include dealkylation to benzene, and the disproportionation to a mixture of benzene and xylene in the BTX process. When oxidized it yields benzaldehyde and benzoic acid, two important intermediates in chemistry. It is also used as a carbon source for making Multi-Wall Carbon Nanotubes. Toluene can be used to break open red blood cells in order to extract hemoglobin in biochemistry experiments.
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). Toluene also poses similar problems as alcohol fuels, as it eats through standard rubber fuel lines and has no lubricating properties as standard gasoline does, which can break down fuel pumps and cause upper cylinder bore wear.
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 has been abused by teenagers in the early to mid 1990's to get high, this was prominent in Dallas, Texas. This was known as "Tolly" in the streets, in which certain brands of octane booster that contained Toluene were used in small rags and "huffed". The effects caused mild to serious hallucinations.
Toluene has also been used in the process of removing the cocaine from coca leaves in the production of Coca-Cola syrup.[7]
Toxicology and metabolism
Inhalation of toluene fumes can be intoxicating, but in larger doses nausea-inducing. Toluene may enter the human system not only through vapour inhalation from the liquid evaporation, but also following soil contamination events, where human contact with soil, ingestion of contaminated groundwater or soil vapour off-gassing can occur.
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.[8] The toxic metabolites are created by the remaining 5% that are oxidized to benzaldehyde and cresols.[9][10] Most of the reactive products are detoxified by conjugation to glutathione but the remainder may severely damage cells.[11]
Toluene is mainly excreted as benzoic acid and hippuric acid, both formed by further metabolic oxidation of benzyl alcohol.
See also
- Organic chemistry
- Water pollution
- Isotoluenes are toluene isomers
Footnotes
- ↑ Streicher HZ, Gabow PA, Moss AH, Kono D, Kaehny WD (1981). "Syndromes of toluene sniffing in adults". Ann. Intern. Med. 94 (6): 758–62. PMID 7235417.
- ↑ Devathasan G, Low D, Teoh PC, Wan SH, Wong PK (1984). "Complications of chronic glue (toluene) abuse in adolescents". Aust N Z J Med 14 (1): 39–43. PMID 6087782.
- ↑ B. S. Furnell et al., Vogel's Textbook of Practical Organic Chemistry, 5th edition, Longman/Wiley, New York, 1989
- ↑ 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
- ↑ Dual cure, low-solvent silicone pressure sensitive adhesives - Patent 6387487
- ↑ Merory, Joseph (1968). Food Flavorings: Composition, Manufacture and Use (2nd ed.). Westport, CT: AVI Publishing Company, Inc...
- ↑ Nakajima T, Wang R, Elovaara E, Gonzalez F, Gelboin H, Raunio H, Pelkonen O, Vainio H, Aoyama T (1997). "Toluene metabolism by cDNA-expressed human hepatic cytochrome P450". Biochem Pharmacol 53 (3): 271–7. doi:. PMID 9065730.
- ↑ Chapman D, Moore T, Michener S, Powis G. "Metabolism and covalent binding of [14C]toluene by human and rat liver microsomal fractions and liver slices". Drug Metab Dispos 18 (6): 929–36. PMID 1981539.
- ↑ Hanioka H, Hamamura M, Kakino K, Ogata H, Jinno H, Takahashi A, Nishimura T, Ando M (1995). "Dog liver microsomal P450 enzyme-mediated toluene biotransformation". Xenobiotica 25 (11): 1207–17. PMID 8592870.
- ↑ van Doorn R, Leijdekkers C, Bos R, Brouns R, Henderson P (1981). "Alcohol and sulphate intermediates in the metabolism of toluene and xylenes to mercapturic acids". J Appl Toxicol 1 (4): 236–42. doi:. PMID 6764216.
External links
- ATSDR - Case Studies in Environmental Medicine: Toluene Toxicity U.S. Department of Health and Human Services (public domain)
- External solubility data
- Computational Chemistry Wiki