Toluene
- Retinaphtha
- Methylbenzene
- Methyl benzene
- Anisen
- Toluene
- Nylmethane
Colorless liquid with a characteristic odor
Liquid
0.87 g · cm -3
-95 ° C
111 ° C.
29.1 hPa ( 20 ° C)
Poorly in water ( 470 mg · l-1 at 20 ° C)
0.375 (10 ) D ( 1.3 × 10-30 C · m)
1,4969
Risk
50 ml · m-3, 190 mg · m-3
636 mg · kg -1 ( LD50, rat, oral)
Template: Infobox chemical / molecular formula search available
Toluene, common name according to IUPAC and toluene, methyl benzene, phenylmethane, according to IUPAC nomenclature called methyl benzene, is a colorless, characteristic smelling, volatile liquid that is similar to benzene in many of their properties. Toluene is an aromatic hydrocarbon, often replaced it as the toxic solvent benzene. It is included among other things, in the gasoline.
History of the name
When Henri Etienne Sainte -Claire Deville won toluene from Tolu, he had the name Benzoën accepted for this body, which reminds at the balsams, of which he comes to the almost generic character, the fact to keep benzoic acid. Berzelius suggested then in its annual reports the name Toluin ago. The modification in toluene first appears in a paper by Muspratt and Hoffmann, who, however - probably by mistake - relying about the name on the above point of Berzelius.
History
1844 toluene was won for the first time by Henri Etienne Sainte -Claire Deville by dry distillation of tolu balsam; This is what has it got its name. By nitration of toluene using nitrating acid (mixture of nitric acid and sulfuric acid) was produced in 1863 by the chemist Julius Wilbrand for the first time TNT. The large-scale production was finally taken up in Germany in 1891; this procedure is still used today.
Deposits and emissions
Toluene is in the oil and the light oil, which is obtained in the distillation of coal tar, present in minor amounts. Toluene is released among others by motor vehicle traffic, because it is included in gasoline, and is produced in small quantities by the incomplete combustion of organic matter, such as when smoking. In recent years, a decline in toluene emissions can be observed, the annual mean is, for example, in Rhineland -Palatinate 30 ľg/m3, depending on the site but it can cause major fluctuations of this value. Main emission factor is the motor vehicle traffic with approximately 65 %, 33% are due to the use of Toluolprodukten and 2% on the Toluolherstellung. Liberated toluene is degraded in the atmosphere, as in benzene, after several days by reactions with hydroxyl radicals ( OH radicals ).
Production and representation
A direct recovery of petroleum or by dry distillation of bituminous coal is not economically in the current (2006) crude oil prices.
In the industry, it is mainly obtained in the processing of crude oil, by the ( produced by cracking ) of n- heptane is reformed into methylcyclohexane and then dehydrogenated to toluene. This process is called also dehydrocyclisation.
During the Second World War took place in Germany due to lack of oil shortages in the Toluolherstellung, so it was also prepared from benzene and methanol by means of the Friedel -Crafts alkylation. The Friedel -Crafts alkylation has limiting factors that significantly reduce the yield and thus the economic importance of alkylbenzenes are more reactive than benzene itself in the electrophilic substitution of aromatics; Therefore, the alkylbenzene just created tends to react to two and multiply alkylated products. The yield of toluene is lower:
In fact, one uses enormous amounts of the starting materials because they are inexpensive, and the resulting toluene continuously isolated. Because the chemical processes all run in the form of equilibrium reactions and are thus displaced in the direction of toluene.
Toluene also apply in the preparation of ethene and propene. World production is annually between 5.00001 million million tons. Photochemically it is accessible by isomerization of cycloheptatriene.
Properties
Physical Properties
Toluene is the simplest representative of the alkylbenzenes. In air, it burns incompletely with yellow, heavily sooting flame. The liquid smells characteristic, pungent pleasant ( like benzene ) and has an odor threshold of 0.6 to 263 mg/m3. Toluene melts at -95 ° C, boils at 111 ° C and under atmospheric conditions, a colorless, clear, water-white liquid that is highly refractile (refractive index: 1.4969 ). In water it is almost insoluble ( 0.47 g / l); with carbon disulfide, ethanol and diethyl ether is miscible in all proportions. Also in chloroform, acetone and most other organic solvents, toluene is readily soluble. The compound forms a variety of solvents azeotropically boiling mixtures. The azeotropic compositions and boiling points are given in the following table. No azeotropes are formed with n-hexane, n-heptane, n-octane, benzene, ethyl benzene, cyclohexanol, chloroform, carbon tetrachloride, acetone, methyl ethyl ketone, diethyl ether, ethyl acetate, dimethylformamide, dimethyl sulfoxide, carbon disulfide and phenol.
The dynamic viscosity is 0.6 mPa · s, toluene is therefore less viscous than water. The calorific value of 40 940 kJ / kg.
Chemical Properties
Toluene is stable and relatively unreactive under normal conditions, with oxidants and acids it reacts violently, however. It is similar reactions such as phenol and benzene; the reactivity of toluene is between these two compounds. Toluene attacks many plastics and is therefore usually stored in glass or metal containers. By the oxidation (for example with potassium permanganate solution acidic ) benzyl alcohol and toluene can be converted to benzaldehyde benzoic acid. Toluene is a particularly radical substitution reactions and electrophilic substitution reactions. Nucleophilic substitution reactions are rare.
Especially in the heat or under irradiation with light can toluene with suitable reactants (eg, bromine) radical substitution reactions at the methyl group received (see SSS rule):
Since toluene is relatively inert, run electrophilic substitution reactions at him from only relatively slowly. In the presence of a suitable catalyst, the reaction speed can be increased considerably (see KKK rule). There are preferentially formed para- and ortho- substituted products:
Toluene reacts with nitric acid to 4- nitrotoluene and water, besides also arises the isomeric 2 -nitrotoluene. The actual nitrating agent (NO2 ) is formed in the presence of sulfuric acid from nitric acid:
Over multiple nitration TNT ( trinitrotoluene ) can be obtained.
Another important reaction is the oxidation of toluene to benzoic acid.
Safety characteristics
Toluene forms flammable vapor - air mixtures. The compound has a flash point at 6 ° C. The explosion range is between 1.1 Vol % (42 g/m3) as the lower explosive limit ( LEL) and 7.8 % by volume (300 g/m3 ) and upper explosive limit (UEL ). A correlation of the explosion limits of the vapor pressure of function results in a lower explosion point of 3 ° C and an upper explosion point of 40 ° C. The limiting oxygen concentration is about 9.6 % by volume (at 100 ° C). The marginal gap width was determined to be 1.06 mm. The result is thus a mapping in the explosion group IIA. The ignition temperature is 535 ° C. The fabric falls within the temperature class T1. The electrical conductivity is very low with 8:10 -14 S · m -1, so that difficulties can arise when handling electrostatic charges.
Safety
Toluene is harmful (Xn ) and highly flammable (F). Toluene itself does not mutagenic, however, is often contaminated with benzene. The lower toxicity of toluene to benzene can be explained by its other metabolism. Toluene is metabolized by oxidation hardly the ring, but mainly by oxidation of the side chain for benzoic acid, in contrast to benzene. The reason for this is the high selectivity of the Monooxygenasesystems P450 for the methyl group of toluene. For this reason, results in hardly any carcinogenic epoxide as in the case of benzene. The small amount of epoxide can be reduced to the diol by conjugation of glutathione, spontaneous intramolecular rearrangement to the phenol, or by enzymatic hydrolysis.
In the form of benzoic acid and hippuric acid is toluene, in addition to small amounts of o- cresol, excreted in the urine.
Toluene causes nerve, kidney, and possibly liver damage. Toluene is toxic for reproduction and teratogenic. Inhalation of toluene vapors can cause non-specific symptoms such as fatigue, malaise, sensory disturbances, disturbances of motor coordination and loss of consciousness. In regular contact may cause a Toluolsucht that goes along with Mirth and Erregungsräuschen. Toluene vapors have a narcotic effect and irritate the eyes and respiratory system difficult, allergic reactions to toluene are possible. Toluene should be stored in well-ventilated places.
Toluene, even in small quantities, although it is not water soluble, water pollutant ( WGK 2). It is readily biodegradable. Toluene may, as well as benzene, in the EU no longer be used as a substance or constituent of preparations in adhesives and spray paints or placed on the market.