TOLUENE: STRUCTURE, PROPERTIES, USES, OBTAINING - CHEMISTRY - 2024

The toluene is a condensed aromatic hydrocarbon whose formula is C ₆ H ₅ CH ₃ or PhCH ₃ and consisting of a methyl group (CH ₃) attached to a benzene ring or phenyl group (Ph). It is found naturally in crude oil, in coal, in volcanic fumes, and in some trees, such as the tolu tree of South America.

This solvent with a characteristic odor is used mainly as an industrial raw material, and as a paint thinner. It is also used in the elimination of parasites present in cats and dogs, such as ascarids and hookworms.

Structural formula of toluene. Source: Neurotiker via Wikipedia.

Toluene was first isolated by Pierre-Joseph Pelletier and Philippe Walter, in 1837, from pine oil. Later, Henri Étienne Sainte-Claire Deville, in 1841, isolated it from tolu balsam and pointed out that his product was similar to the one previously isolated. In 1843, Berzelius christened it Toluin.

Most of the toluene is obtained as a side or secondary product in the gasoline production processes and the conversion of coal into coke. It is also produced by reactions carried out in the laboratory, for example, the reaction of benzene with methyl chloride.

Structure

Toluene molecular structure. Source: Ben Mills via Wikipedia.

In the upper image we have the molecular structure of toluene represented by a model of spheres and bars. Note that it looks exactly the same as the structural formula indicated, with the difference that it is not a completely flat molecule.

In the center of the benzene ring, which in this case can be seen as a phenyl group, Ph, its aromatic character is highlighted by the dotted lines. All carbon atoms have sp ² hybridization, except for the CH ₃ group, whose hybridization is sp ³.

It is for this reason that the molecule is not completely flat: the hydrogens of CH ₃ are located at different angles to the plane of the benzene ring.

Toluene is an apolar, hydrophobic and aromatic molecule. Their intermolecular interactions are based on London's dispersive forces, and on dipole-dipole interactions, since the center of the ring is "charged" with the electron density provided by CH ₃; while hydrogen atoms have low electron density.

Therefore, toluene has several types of intermolecular interactions that hold the molecules of its liquid together. This is reflected in its boiling point, 111 ° C, which is high considering that it is an apolar solvent.

Properties

Physical appearance

Colorless and transparent liquid

Molar mass

92.141 g / mol

Odor

Sweet, pungent and similar to benzene

Density

0.87 g / mL at 20 ºC

Melting point

-95 ºC

Boiling point

111 ºC

Solubility

Toluene has negligible solubility in water: 0.52 g / L at 20 ° C. This is due to the difference in polarities between toluene and water.

On the other hand, toluene is soluble, or in this case miscible, with ethanol, benzene, ethyl ether, acetone, chloroform, glacial acetic acid and carbon disulfide; that is, it solubilizes better in less polar solvents.

Refractive index (n

1,497

Viscosity

0.590 cP (20 ° C)

ignition point

6 ºC. Toluene should be handled in fume hoods and as far away as possible from any flame.

Vapor density

3.14 in relation to air = 1. That is, its vapors are three times as dense as air.

Vapor pressure

2.8 kPa at 20 ° C (about 0.27 atm).

Auto ignition temperature

480 ° C

Decomposition

May react vigorously with oxidizing materials. When heated to decomposition, it emits acrid and irritating smoke.

Surface tension

29.46 mN at 10 ºC

Dipole moment

0.36 D

Reactivity

Toluene is prone to chlorination to produce ortho-chlorotoluene and para-chlorotoluene. It is also easy to nitrify to produce nitrotoluene, which is the raw material for dyes.

One part toluene combines with three parts nitric acid to form trinitrotoluene (TNT): one of the best known explosives.

Likewise, toluene undergoes sulfonation to generate o-toluene-sulfonic and p-toluene-sulfonic acids, which are the raw material for the manufacture of dyes and saccharin.

The methyl group of toluene undergoes hydrogen loss due to the action of a strong base. Also the methyl group is susceptible to oxidation, so it reacts with potassium permanganate to produce benzoic acid and benzaldehyde.

Applications

Industrial

TNT, the most symbolic explosive of all, is produced using toluene as the main raw material. Source: Pixabay.

Toluene is used in the manufacture of paints, paint thinners, nail polishes, adhesives or glue, lacquers, inks, nylon, plastic, polyurethane foam, most oils, vinyl organosols, medicines, colorants, perfumes, explosives (TNT).

In the same way, toluene is used in the form of sulfonated toluenes in the manufacture of detergent. Toluene is also of great importance in the manufacture of plastic cements, cosmetic stain removers, antifreezes, inks, asphalt, permanent markers, contact cements, etc.

Solvent and thinner

Toluene is used in the dilution of paints, which facilitates its application. It is used to dissolve the edges of polystyrene kits, thus allowing the joining of parts that make up scale model airplanes. In addition, it is used in the extraction of natural products from plants.

Toluene is a solvent in inks used in etching. Cements mixed with rubber and toluene are used to cover a large number of products. Toluene is also used as a solvent in printing inks, lacquers, leather tanners, glues, and disinfectants.

Even more interesting, toluene is used as a solvent for carbon nanomaterials (such as nanotubes) and fullerenes.

Others

A mixture of benzene, toluene, and xylene (BTX) is added to gasoline to increase its octane number. Toluene is a high octane reserve and jet gasoline additive. It is also used in the manufacture of naphtha.

Toluene helps in the elimination of some species of roundworms and hookworms, as well as tapeworms that are parasites of cats and dogs.

Obtaining

Most of the toluene is obtained from crude oil distillates, generated during the pyrolysis of hydrocarbons (steam cracking). The catalytic reform of the oil vapors represents 87% of the toluene produced.

An additional 9% toluene is removed from the pyrolysis gasoline produced during the manufacture of ethylene and propylene.

Coal tar from coke ovens contributes 1% of the toluene produced, while the remaining 2% is obtained as a by-product of styrene manufacture.

Damaging effects

Toluene is a solvent that is inhaled to get high, since it has a narcotic action that affects the functioning of the central nervous system. Toluene enters the body by ingestion, inhalation, and absorption through the skin.

At an exposure level of 200 ppm, excitement, euphoria, hallucinations, distorted perceptions, headache, and dizziness can occur. While higher levels of exposure to toluene can cause depression, drowsiness and stupor.

When inhalation exceeds a concentration of 10,000 ppm, it is capable of causing the death of the individual due to respiratory failure.

References

1. Graham Solomons TW, Craig B. Fryhle. (2011). Organic Chemistry. (10 ^th edition.). Wiley Plus.
2. Carey F. (2008). Organic Chemistry. (Sixth edition). Mc Graw Hill.
3. Morrison and Boyd. (1987). Organic chemistry. (Fifth edition). Addison-Wesley Iberoamericana.
4. National Center for Biotechnology Information. (2020). Toluene. PubChem Database., CID = 1140. Recovered from: pubchem.ncbi.nlm.nih.gov
5. Wikipedia. (2020). Toluene. Recovered from: en.wikipedia.org
6. Engineering ToolBox, (2018). Toluene - Thermophysical Properties. Recovered from: engineeringtoolbox.com
7. Vedantu. (sf). Toluene. Recovered from: vedantu.com