Arenas, which include toluene, can be considered as derivatives of the ancestor and the first member of the homologous series - benzene. The general formula of the compounds that belong to this class is C n H 2n – 6 . In the molecules of aromatic hydrocarbons contains a benzene ring (cycle, core). The toluene formula C 7 H 8 reflects the substance belonging to this large group of organic compounds. To many, toluene is known under a different name - methylbenzene. The substance is widely used in industry, is used as an organic solvent, stain remover and for other purposes.
What is toluene?
One of the most important arenas, toluene, is a methyl derivative of benzene. A water-insoluble, colorless liquid has a sweetish aroma, reminiscent of the smell of paints, varnishes, solvents.
The chemical formula of toluene - C 7 H 8 - can be written differently: C 6 H 5 –CH 3. In this case, the number of atoms remains the same, but there is a noticeable difference from benzene, which consists in the radical - methyl.
Using other principles of nomenclature, the compound is called methylbenzene and phenylmethane. This is the same toluene, the general formula of which is C 7 H 8. But in the first case, the emphasis is on the fact that one of the hydrogen atoms that are associated with the carbon of the benzene ring is replaced by a methyl radical. For the second name, a different approach was chosen. It is believed that in methane, one hydrogen is replaced by a phenyl radical. This is the particle into which benzene is converted, giving off a hydrogen atom.
Molecule structure
The composition of organic matter, consisting only of carbon and hydrogen atoms, is reflected in the toluene formula. Spherical and bulk models give an idea of the structure of the compound molecule, its difference from substances of the same homological series. There is a similarity between toluene and benzene, which consists in the presence of a ring of 6 carbon atoms in a state of sp
2 hybridization. Each of them forms three sigma bonds with neighboring particles (two carbon atoms and one hydrogen). Perpendicular to the ring, a single electronic system arises from the remaining non-hybrid p-orbitals (one for six carbon atoms). As a result, the entire cycle acquires considerable strength and stability, and hence the substance toluene. The structural formula of the compound includes the seventh carbon from the methyl group, which is in a state of sp
3 hybridization. It is bound to three hydrogen atoms, and the fourth bond is spent on a compound with one carbon in the benzene ring.
Structural formulas of methylbenzene
The electron density between the carbon atoms that form the aromatic nucleus is evenly distributed. The phenomenon is reflected in the formula of benzene, toluene and other arenes by the sign of aromaticity (circle in the ring). The presence of a methyl radical in one of the carbon atoms in the nucleus is also noted. The bonds between all particles are shown by dashes. The structural formula in this case reflects the composition and basic features of the structure of the molecule of matter.
The simplified toluene formula is a hexagon with a ring inside or dashes denoting a double bond. A methyl group can be present at any of the six atoms of the nucleus; they are equivalent to each other. The disadvantage of this image method is obvious. The record does not give an idea of the composition of the substance and the equivalence of all carbon-carbon bonds in the ring.
Obtaining methylbenzene in the laboratory and industry
In the laboratory, toluene was first obtained in 1835-1938 by P. Peltier and A. Deville. The first scientist distilled pine gum, and the second used toluan balsam, extracted from the South American Toluifera tree in Colombia. Thus arose the trivial name of the substance - toluene. Currently, a significant amount of methylbenzene gives distillation of oil and coal tar, followed by purification. In the process of coking, toluene is extracted from coke oven gas. In the synthesis of styrene, it stands out as a by-product of the reaction of benzene and ethylene. In the laboratory and industry, the production of toluene is carried out by different methods.
- Dehydrocyclization of acyclic hydrocarbons. Toluene is obtained from heptane in the presence of a catalyst at a temperature of 300 ° C.
- Alkylation of benzene, which is called the Friedel-Crafts reaction. It is carried out in the presence of an AlCl3 catalyst or other catalysts: C 6 H 5 –H + CH 3 Cl = C 6 H 5 –CH 3 + HCl.
- Interaction with bromobenzene: 6 5 –Br + 3 –Br + 2Na = 6 5 – 3 + 2NaBr.
- Mixing of zinc and cresol: C 6 H 4 CH 3 OH + Zn = C 6 H 5 CH 3 + ZnO.
- Treatment of toluenesulfonic acid.
Physical properties of methylbenzene
Toluene, whose structural formula contains a benzene core, exhibits physical properties typical of aromatic compounds.
- A clear, colorless liquid smells paint.
- Methylbenzene hardens at low temperatures and begins to melt at –93 ° C.
- The boiling point of toluene is 110.63 ° C. The density of the substance is 0.8669 g / ml.
- The solubility of methylbenzene in water at a temperature of 20 ° C is 0.47 g / l. The molar mass of the substance M (C 7 H 8 ) = 92.14 g / mol.
Chemical properties of toluene: oxidation
The features of all arenas are determined by a chemically stable cycle of six carbon atoms. The toluene formula is a benzene ring that is formally unsaturated and a methyl radical. Aromatic hydrocarbons are similar in properties to alkenes, which are characterized by addition reactions. But the hydrogen atoms in the molecules of benzene and its homologs can participate in substitution reactions, which brings together arenas and alkanes. Toluene is more reactive than benzene. The substance is characterized by oxidation reactions.
- Combustion, which is accompanied by the release of carbon dioxide and the formation of water: C 7 H 8 + 9O 2 = 7CO 2 + 4H 2 O.
- In the interaction of toluene with potassium permanganate , the methyl group in the side chain of the molecule of the substance is oxidized to carboxyl. The reaction produces benzoic acid.
Chemical reactions of the aromatic nucleus of toluene
- Bromination, which is carried out in the presence of catalysts. A halogenated substance is formed: C 7 H 8 + Br 2 = C 7 H 7 Br + HBr.
- Nitration of methylbenzene is carried out with a mixture consisting of concentrated nitric and sulfuric acids. The nitro group in toluene can occupy the ortho and para position. The reaction proceeds by the mechanism of electrophilic substitution. At high temperature, an explosive Trinitrotoluene (TNT) is formed.
- Hydrogenation with hydrogen on a catalyst leads to dearomatization and the production of methylcyclohexane: C 7 H 8 + 3H 2 = C 7 H 14.
- Chlorination with strong heating or under the action of UV radiation ends with the formation of hexachlorocyclohexane.
The use of methylbenzene
Toluene is widely used as a starting material in organic synthesis. It is an essential material in the production of many substances. The use of toluene:
- obtaining dyes;
- production of stain removers, detergents;
- production of TNT explosives;
- the use of adhesives, paints, synthetic fragrances and cleaning agents as a solvent;
- manufacture of paints for construction work;
- release of products for nails;
- pharmaceutical manufacturing;
- increase in octane number of fuel;
- organic synthesis of benzoic acid, benzaldehyde, benzyl chloride, saccharin, benzyl alcohol and other substances;
Toluene acts as an industrial solvent in dry cleaners and is used in the process of tanning leather. It is a precursor to a number of petroleum products, phenol, formaldehyde, pesticides and other compounds.
Toluene toxicity
Methylbenzene is a fire hazard. The vapor-air mixture explodes under certain conditions. Liquid toluene is highly flammable. The structural formula gives an idea of the composition and structure, but does not contain information about the effect of a substance on the human body. It has been established that toluene is toxic and has a carcinogenic effect. Vapors of methylbenzene freely penetrate the skin, respiratory system, cause changes in the central nervous system, irritation of integumentary tissues, dermatitis. Upon inhalation of toluene fumes, a person becomes inhibited, tremors, and the activity of the vestibular apparatus is disturbed. Work with toluene, paints, solvents in rubber gloves, thoroughly ventilate the room or use a range hood. Methylbenzene is a weak narcotic substance, causes toluene substance abuse. Other forms of negative effects of the substance:
- eye irritation and color vision impairment;
- prolonged exposure may cause hearing loss;
- high blood concentration causes liver damage, kidney necrosis;
- inhalation of a large amount of vapor leads to dizziness, drowsiness, headache.
Conclusion
Toluene is produced in large quantities at petrochemical plants or is obtained as a by-product at coke plants. The compound is a valuable raw material for large-scale organic synthesis, used in the pharmaceutical industry. Includes methylbenzene in the composition of many types of solvents that are used in work with paints and varnishes. Toluene belongs to the hazard class III in the classification of toxic compounds. When working with a substance, the concentration of its vapors in the air should not exceed the values determined by sanitary and hygienic standards. When handling toluene, open flames and sparks must not be allowed, this can lead to an explosion. There are also environmental problems associated with the release of toluene into the atmosphere:
- when burning oil, various types of fuel;
- in active volcanoes;
- in forest fires;
- when using solvents and paints.
The toxic properties of toluene, fire and explosion hazard require careful handling of the liquid substance and its vapors.