Toluene

Toluene

Names
IUPAC name Methylbenzene
Other names toluene phenylmethane toluol Anisen
Identifiers
CAS Number	108-88-3
Abbreviations	PhMe MePh BnH
ChEBI	CHEBI:17578
ChEMBL	ChEMBL9113
ChemSpider	1108
DrugBank	DB01900
IUPHAR/BPS	5481
Jmol 3D model	Interactive image
KEGG	C01455
PubChem	1140
RTECS number	XS5250000
UNII	3FPU23BG52
InChI InChI=1S/C7H8/c1-7-5-3-2-4-6-7/h2-6H,1H3 Key: YXFVVABEGXRONW-UHFFFAOYSA-N 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[1]
Odor	sweet, pungent, benzene-like[2]
Density	0.87 g/mL (20 °C)[1]
Melting point	−95 °C (−139 °F; 178 K)[1]
Boiling point	111 °C (232 °F; 384 K)[1]
Solubility in water	0.52 g/L (20 °C)[1]
Vapor pressure	2.8 kPa (20°C)[2]
Refractive index (nD)	1.497 (20 °C)
Viscosity	0.590 cP (20 °C)
Structure
Dipole moment	0.36 D
Hazards
Main hazards	highly flammable
Safety data sheet	See: data page SIRI.org
R-phrases	R11, R38, R48/20, R63, R65, R67
S-phrases	(S2), S36/37, S29, S46, S62
NFPA 704	3 2 0
Flash point	6 °C (43 °F; 279 K)[1]
Explosive limits	1.1%-7.1%[2]
Threshold Limit Value	50 mL m^−3, 190 mg m^−3
Lethal dose or concentration (LD, LC):
LC50 (Median concentration)	>26700 ppm (rat, 1 hr) 400 ppm (mouse, 24 hr)[3]
LCLo (Lowest published)	55,000 ppm (rabbit, 40 min)[3]
US health exposure limits (NIOSH):
PEL (Permissible)	TWA 200 ppm C 300 ppm 500 ppm (10-minute maximum peak)[2]
REL (Recommended)	TWA 100 ppm (375 mg/m^3) ST 150 ppm (560 mg/m^3)[2]
IDLH (Immediate danger)	500 ppm[2]
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
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Infobox references

Toluene /ˈtɒljuːiːn/, formerly known as toluol /ˈtɒljuːɒl/, is a colorless, 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 a solvent.^[4] In 2013, worldwide sales of toluene amounted to about 24.5 billion US-dollars.^[5]

As the solvent in a common glue, toluene is sometimes used as a recreational inhalant ("glue sniffing"^[6]) and has the potential of causing severe neurological harm.^[7][8]

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.^[9] 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.^[10] In 1843, Jöns Jacob Berzelius recommended the name toluin.^[11] 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.^[12]

Chemical properties

Toluene reacts as a normal aromatic hydrocarbon in electrophilic aromatic substitution.^[13][14][15] Because the methyl group has greater electron-releasing properties that a hydrogen atom in the same position, 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. Toluene reacts with Potassium permanganate to yield benzoic acid, and with chromyl chloride to yield toluene benzaldehyde (Étard reaction).

The methyl group undergoes halogenation 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.^[16]

C₆H₅CH₃ + Br₂ → C₆H₅CH₂Br + HBr

C₆H₅CH₂Br + Br₂ → C₆H₅CHBr₂ + HBr

The methyl group in toluene undergoes deprotonation only with very strong bases, its pK_a is estimated to be approximately 41.^[17] 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 a byproduct in the production of gasoline by a catalytic reformer or ethylene cracker; It is also a byproduct of the production of coke from coal. Final separation and purification is done by any of the by distillation or solvent extraction processes used for 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.^[18]

Precursor to other chemicals

In addition to the synthesis of benzene and xylene, toluene feedstock for toluene diisocyanate (used in the manufacture of polyurethane foam), trinitrotoluene (the explosive, TNT), and a number of synthetic drugs.

Solvent

Toluene is a common solvent, e.g. for paints, paint thinners, silicone sealants,^[19] 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 for internal combustion engines. Toluene at 86% by volume fueled all the turbo Formula One 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 One 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 °C (158 °F). Honda solved this problem in their Formula One 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 incurs no fuel excise tax, while other fuels are taxed at more than 40%, providing a greater profit margin for fuel suppliers. The extent of toluene substitution has not been determined.^[20][21]

Toluene is one of a group of fuels that have recently included in jet fuel surrogate blends.^[22] 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 color of the toluene solution of C₆₀ is bright purple.

Toluene is 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 hemoglobin 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.^[23]

Toxicology and metabolism

Inhalation of toluene in low to moderate levels can cause tiredness, confusion, weakness, drunken-type actions, memory loss, nausea, loss of appetite, hearing loss, 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.^[24][25] Toluene is, however, much less toxic than benzene, and has as a consequence, largely replaced it as an aromatic solvent in chemical preparation. The US Environmental Protection Agency (EPA) states that the carcinogenic potential of toluene cannot be evaluated due to insufficient information.^[26]

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.^[27] Additionally, toluene has been shown to display antidepressant-like effects in rodents in the forced swim test (FST) and the tail suspension test (TST).^[27]

Toluene is sometimes used as a recreational inhalant ("glue sniffing"), likely on account of its euphoric and dissociative effects.^[27]

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.^[28]

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 such inhalants.^[29]

References

1. Record in the GESTIS Substance Database of the IFA
2. "NIOSH Pocket Guide to Chemical Hazards #0619". National Institute for Occupational Safety and Health (NIOSH).
3. "Toluene". Immediately Dangerous to Life and Health. National Institute for Occupational Safety and Health (NIOSH).
4. Hogan, C. Michael (2011), "Sulfur", in Jorgensen, A.; Cleveland, C. J., Encyclopedia of Earth, Washington DC: National Council for Science and the Environment, retrieved 26 October 2012, Sulfur is insoluble in water, but soluble in carbon disulfide, somewhat soluble in other non-polar organic solvents such as the aromatics benzene and toluene.
5. Ceresana. "Toluene – Study: Market, Analysis, Trends - Ceresana".
6. McKeown, Nathanael J (Feb 01, 2015). Tarabar, Asim, ed. "Toluene Toxicity: Background, Pathophysiology, Epidemiology". WebMD Health Professional Network. Check date values in: |date= (help)
7. Streicher, H. Z.; Gabow, P. A.; Moss, A.H.; Kono, D.; Kaehny, W. D. (1981). "Syndromes of toluene sniffing in adults". Annals of Internal Medicine 94 (6): 758–62. doi:10.7326/0003-4819-94-6-758. PMID 7235417.
8. Devathasan, G.; Low, D.; Teoh, P. C.; Wan, S. H.; Wong, P. K. (1984). "Complications of chronic glue (toluene) abuse in adolescents". Aust N Z J Med 14 (1): 39–43. doi:10.1111/j.1445-5994.1984.tb03583.x. PMID 6087782.
9. See:
   • Pelletier and Walter (1837) "Examen des produits provenant du traitement de la résine dans la fabrication du gaz pour l'éclairage" (Examination of products arising from the treatment of resin during the production of illuminating gas), Comptes rendus, 4 : 898–899.
   • Pelletier and Philippe Walter (1838) "Examen des produits provenant du traitement de la résine dans la fabrication du gaz pour l'éclairage," Annales de Chimie et de Physique, 2nd series, 67 : 269-303. Toluene is named on pp. 278-279: "Nous désignerons la substance qui nous occupe par le nom de rétinnaphte, qui rappelle son origine et ses propriétés physiques (ρητίνη-νάφτα)." (We will designate the substance that occupies us by the name of rétinnaphte, which recalls its origin and its physical properties (ρητίνη-νάφτα [resin-naphtha]).
10. See:
    • Deville (1841) "Recherches sur les résines. Étude du baume de Tolu" (Investigations of resins. Study of Tolu balsam), Comptes rendus, 13 : 476–478.
    • H. Deville (1841) "Recherches chimiques sur les résines; Premier mémoire" (Chemical investigations of resins; first memoir), Annales de Chimie et de Physique, 3rd series, 3 : 151-195. Deville names toluene on p. 170: "J'ai adopté, pour le corps qui m'occupe dans ce moment, le nom de benzoène, qui rappelle, dans les baumes dont il provient, ce caractère presque générique qui est de contenir de l'acide benzoïque." (I've adopted, for this substance that occupies me at the moment, the name benzoène, which recalls, in the balsams from which it comes, that character which is contained in benzoic acid.)
    • Wisniak, Jaime (2004). "Henri Étienne Sainte-Claire Deville: A physician turned metallurgist". Journal of Materials Engineering and Performance 13 (2): 117–118. doi:10.1361/10599490418271.
11. Jacob Berzelius (1843) Jahres Berichte, 22 : 353-354..
12. See:
    • Cahours, Auguste (1850) "Recherches sur les huiles légéres obtenues dans la distillation du bois" (Investigations of light oils obtained by the distillation of wood), Compte rendus, 30 : 319-323 ; see page 320.
    • Jaime Wisniak (October 2013) "Auguste André Thomas Cahours," Educación Química, 24 (4) : 451–460.
13. B. S. Furniss et al., Vogel's Textbook of Practical Organic Chemistry, 5th edition, Longman/Wiley, New York, 1989
14. L. G. Wade, Organic Chemistry, 5th ed., p. 871, Prentice Hall, Upper Saddle RIver, New Jersey, 2003
15. J. March, Advanced Organic Chemistry, 4th ed., p. 723, Wiley, New York, 1992
16. Podgoršek, Ajda; Stavber, Stojan; Zupan, Marko; Iskra, Jernej (2006). "Free radical bromination by the H2O2–HBr system on water". Tetrahedron Letters 47 (40): 7245. doi:10.1016/j.tetlet.2006.07.109.
17. Henry Hsieh, Roderic P. Quirk. Anionic Polymerization: Principles and Practical Applications. p. 41.
18. Jörg Fabri, Ulrich Graeser, Thomas A. Simo "Toluene" in Ullmann's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH, Weinheim. doi:10.1002/14356007.a27_147.pub2
19. "Dual cure, low-solvent silicone pressure sensitive adhesives - General Electric Company".
20. "Scam on petrol sparks spot tests - Liberty Oil".
21. "The World Today Archive - Authorities yet to acknowledge petrol scam problem".
22. Ji, C.; Egolfopoulos, F. N. (2011). "Hydrogen Flame propagation of mixtures of air with binary liquid fuel mixtures". Proc. Comb. Inst. 33: 955–961. doi:10.1016/j.proci.2010.06.085.
23. Merory, Joseph (1968). Food Flavorings: Composition, Manufacture and Use (2nd ed.). Westport, CT: AVI Publishing Company, Inc..
24. "Health Effects of Toluene", Canadian Centre for Occupational Health and Safety.
25. "Toluene Toxicity Physiologic Effects", Agency for Toxic Substances and Disease Registry.
26. , EPA
27. Cruz, S. L.; Soberanes-Chávez, P.; Páez-Martinez, N.; López-Rubalcava, C. (June 2009). "Toluene has antidepressant-like actions in two animal models used for the screening of antidepressant drugs". Psychopharmacology 204 (2): 279–86. doi:10.1007/s00213-009-1462-2. PMID 19151967.
28. Prenafeta-Boldu, Francesc X.; Kuhn, Andrea; Luykx, Dion M. A. M.; Anke, Heidrun; van Groenestijn, Johan W.; de Bont, Jan A. M. (April 2001). "Isolation and characterisation of fungi growing on volatile aromatic hydrocarbons as their sole carbon and energy source". Mycological Research (Elsevier) 105 (4): 477–484. doi:10.1017/S0953756201003719.
29. "State Laws on Inhalant Use".

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)