Toluene

Toluene (/ˈtɒljuiːn/), also known as toluol (/ˈtɒljuɒl/), is an aromatic hydrocarbon. It 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. Toluene is predominantly used as an industrial feedstock and a solvent. Toluene (/ˈtɒljuiːn/), also known as toluol (/ˈtɒljuɒl/), is an aromatic hydrocarbon. It 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. Toluene is predominantly used as an industrial feedstock and a solvent. As the solvent in some types of paint thinner, contact cement and model airplane glue, toluene is sometimes used as a recreational inhalant and has the potential of causing severe neurological harm. The compound was first isolated in 1837 through a distillation of pine oil by a Polish chemist named Filip Walter, who named it rétinnaphte. 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. In 1843, Jöns Jacob Berzelius recommended the name toluin. 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. 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 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. The methyl group in toluene undergoes deprotonation only with very strong bases, its pKa is estimated to be approximately 41. Hydrogenation of toluene gives methylcyclohexane. The reaction requires a high pressure of hydrogen and a catalyst. 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). Toluene is inexpensively produced industrially. 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: