Toluene: Wikis

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Toluene
Identifiers
CAS number 108-88-3 Yes check.svgY
ChemSpider 1108
RTECS number XS5250000
SMILES
Properties
Molecular formula C7H8 or C6H5CH3
Molar mass 92.14 g/mol
Appearance colorless liquid
Density 0.8669 g/mL
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 External MSDS
R-phrases R11, R38, R48/20, R63, R65, R67
S-phrases (S2), S36/37, S29, S46, S62
NFPA 704
NFPA 704.svg
3
2
0
Flash point 4 °C (39 °F)
Threshold Limit Value 50 ml·m−3, 190 mg·m−3
Related compounds
Related aromatic hydrocarbons benzene
xylene
naphthalene
Related compounds methylcyclohexane
Supplementary data page
Structure and
properties
n, εr, etc.
Thermodynamic
data
Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
 Yes check.svgY (what is this?)  (verify)
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 Toluol, is a clear water-insoluble liquid with the typical smell of paint thinners. Chemically it is mono-substituted benzene derivative (benzene derivative in which one hydrogen atom from the benzene molecule has been replaced by a univalent group; in this case CH3).

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; however, this causes severe neurological harm.[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).

  • Toluene 3nitricacid.PNG

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. Toluene can also be treated with elemental bromine in the presence of UV light (direct sunlight) to yield 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.

Preparation

1. From Benzene(Friedel–Crafts_reaction)

Benzene reacts with methyl chloride in presence of anhydrous aluminium chloride to form toluene. The formation follows electrophilic substitution reaction mechanism

CH3Cl + AlCl3 → CH3+ + AlCl4-

C6H5H + CH3+ + AlCl4- → C6H5CH3 + HCl + AlCl3


The following catalysts can be used in place of AlCl3


AlCl3 > SbCl3 > SnCl4 > BF3 > ZnCl2 > HgCl2

Note that the reaction is not much useful as the mono-alkyl derivative formed readily undergoes further alkylation at a still greater speed to produce polysubstituted products.


2. From Bromobenzene(Wurtz-Fittig reaction) Wurtz-Fittig reaction implies that reaction of an aryl halide and alkyl halide in presence of sodium metal give substituted aromatic compound.

When bromobenzene and methyl bromide react with sodium metal in dry ether solution, toluene is obtained


C6H5Br + CH3Br + 2Na → C6H5CH3 + 2NaBr


3. From Toluic acid (decarboxylation)

When sodium salt of Toluic acid (o-, m-, p-) is heated with sodalime, toluene is obtained


C6H4CH3CooNa (sodium toluate) + NaOH → C6H5CH3 (Toluene) + Na2CO3


4. From Cresol


When cresol (o-, m-, p-) is distilled with zinc dust, toluene is obtained

C6H4CH3OH (Cresol) + Zn → C6H5CH3 (Toluene) + ZnO


5. From Toluene Sulphonic Acid

When toluene sulphonic acid is treated with superheated steam or boiled with HCl, toluene is obtained.


CH3C6H4SO3H (Toluene Sulphonic acid) + HOH (steam) → C6H5CH3 (Toluene) + H2SO4 (Sulfuric acid)


6. From Toluidine


Toluidine is first diazotized with sodium nitrite (NaNO2) and HCl at low temperature. The diazonium compound thus obtained is heated with alkaline stannous chloride (SnCl2). This reaction gives toluene.


7. From Grignard Reagent


When phenyl magnesium bromide (C6H5)MgBr) is reacted with methyl bromide, toluene is obtained.


8. From aromatic ketones


Using Friedel-Craft Reaction, when we react acid chloride with aromatic hydrocarbon in presence of anhydrous aluminium chloride (AlCl3), we obtain mixed aliphatic aromatic ketone. The ketone is then reduced with amalgamated zinc and conc. HCl

C6H6 + ClCoCH3 → C6H5COCH3 (Acetophenone) + HCl


C6H5COCH3 + 4H → C6H5CH2CH3 (Ethyl benzene)

This method is used to produce alkyl benzenes other than toluene

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 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.

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.

In Australia, toluene has been found to have been illegally combined with petrol in fuel outlets for sale as standard vehicular fuel. Toluene attracts no fuel excise, while other fuels are taxed at over 40%, so fuel suppliers are able to profit from substituting the cheaper toluene for petrol. This substitution is likely to affect engine performance and result in additional wear and tear. The extent of toluene substitution has not been determined.[7][8]

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 can be inhaled for its intoxicating effects. Low to moderate levels can cause tiredness, confusion, weakness, drunken-type actions, memory loss, nausea, loss of appetite, and hearing 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. It can also cause unconsciousness, and even death. Toluene may negatively affect kidney function.[9]

Toluene has also been used in the process of removing the cocaine from coca leaves in the production of Coca-Cola syrup.[10]

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.[11] The toxic metabolites are created by the remaining 5% that are oxidized to benzaldehyde and cresols.[12][13] Most of the reactive products are detoxified by conjugation to glutathione but the remainder may severely damage cells.[14]

The metabolism of toluene

Toluene is mainly excreted as benzoic acid and hippuric acid, both formed by further metabolic oxidation of benzyl alcohol.

The metabolism of benzyl alcohol

See also

Footnotes

  1. ^ 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. 
  2. ^ 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. 
  3. ^ B. S. Furnell et al., Vogel's Textbook of Practical Organic Chemistry, 5th edition, Longman/Wiley, New York, 1989
  4. ^ L. G. Wade, Organic Chemistry, 5th ed., p. 871, Prentice Hall, Upper Saddle RIver, New Jersey, 2003
  5. ^ J. March, Advanced Organic Chemistry, 4th ed., p. 723, Wiley, New York, 1992
  6. ^ Dual cure, low-solvent silicone pressure sensitive adhesives - Patent 6387487
  7. ^ http://www.libertyoil.com.au/www/230/1001164/displayarticle/1001248.html
  8. ^ http://www.abc.net.au/worldtoday/stories/s106466.htm
  9. ^ http://www.atsdr.cdc.gov/tfacts56.html
  10. ^ Merory, Joseph (1968). Food Flavorings: Composition, Manufacture and Use (2nd ed.). Westport, CT: AVI Publishing Company, Inc... 
  11. ^ 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:10.1016/S0006-2952(96)00652-1. PMID 9065730. 
  12. ^ Chapman D, Moore T, Michener S, Powis G (1990). "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. 
  13. ^ 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. 
  14. ^ 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:10.1002/jat.2550010411. PMID 6764216. 

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