S S Chemicals

Toluene (/ˈtɒl.juiːn/), also known as toluol (/ˈtɒl.ju.ɒl, -ɔːl, -oʊl/), is a substituted aromatic hydrocarbon^[15] with the chemical formula C6H5CH3, often abbreviated as PhCH3, where Ph stands for the phenyl group. It is a colorless, water-insoluble liquid with the odor associated with paint thinners. It is a mono-substituted benzene derivative, consisting of a methyl group (CH₃) attached to a phenyl group by a single bond. As such, its systematic IUPAC name is methylbenzene. Toluene is predominantly used as an industrial feedstock and a solvent.

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^[16] and has the potential of causing severe neurological harm.^[17][18]

History

The compound was first isolated in 1837 through a distillation of pine oil by Pierre Joseph Pelletier and Filip Neriusz Walter, who named it rétinnaphte.^[19][20] In 1841, 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.^[21][22][23] In 1843, Jöns Jacob Berzelius recommended the name toluin.^[24] 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.^[25][26]

Chemical properties

The distance between carbon atoms in the toluene ring is 0.1399 nm. The C-CH₃ bond is longer at 0.1524 nm, while the average C-H bond length is 0.111 nm.^[27]

Ring reactions

Toluene reacts as a normal aromatic hydrocarbon in electrophilic aromatic substitution.^[28][29][30] 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.

Nitration of toluene gives mono-, di-, and trinitrotoluene, all of which are widely used. Dinitrotoluene is the precursor to toluene diisocyanate, a precursor to polyurethane foam. Trinitrotoluene (TNT) is an explosive.

Complete hydrogenation of toluene gives methylcyclohexane. The reaction requires a high pressure of hydrogen and a catalyst.

Side chain reactions

The C-H bonds of the methyl group in toluene are benzylic, therefore they are weaker than C-H bonds in simpler alkanes. Reflecting this weakness, the methyl group in toluene undergoes a variety of free radical reactions. 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 ev