Benzene
DETAIL
As the solvent in some types of paint thinner, permanent markers, contact cement and certain types of glue, toluene is sometimes used as a recreational inhalant and has the potential of causing severe neurological harm.
Chemical properties
Toluene reacts as a normal aromatic hydrocarbon in electrophilic aromatic substitution. Because the methyl group has greater electron-releasing properties than a hydrogen atom in the same position, toluene is more reactive than benzene toward 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 benzaldehyde (Étard reaction).
The C-H bonds of the methyl group in toluene are benzylic, which means that they are weaker than C-H bonds in simpler alkanes. Reflecting this weakness, the methyl group in toluene undergoes halogenation under free radical conditions. For example, when heated with N-bromosuccinimide (NBS) in the presence of AIBN, toluene converts to benzyl bromide. The same conversion can be effected with elemental bromine in the presence of UV light or even sunlight.
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 distillation or solvent extraction processes used for BTX aromatics (benzene, toluene, and xylene isomers).
Other preparative routes
Toluene can be prepared by a variety of methods. For example, benzene reacts with methanol in presence of a solid acid to give toluene.
Uses
Precursor to benzene and xylene
Toluene is mainly used as a precursor to benzene via hydrodealkylation:
Nitration
Nitration of toluene give mono-, di-, and trinitrotoluene, all of which are widely used. Dinitrotoluene is the precursor to toluene diisocyanate, which used in the manufacture of polyurethane foam. Trinitrotoluene is the explosive typically abbreviated TNT.
Oxidation
Benzoic acid and benzaldehyde are produced commercially by partial oxidation of toluene with oxygen. Typical catalysts include cobalt or manganese naphthenates.
toluene oxidation
Solvent
Toluene is a common solvent, e.g. for paints, paint thinners, silicone sealants, 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 as well as jet fuel.