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Benzene or benzol(another name for benzene) is one of the most important chemical in the world because of it wide variety of industrial uses. Benzene is widely uses on all the word spshaliy in The United States, Because of that benzene ranks in the top 20 in production volume for chemicals products .The major use of benzene is to make other chemicals like cyclohexane, cumene ,and styrene, also benzene use for manufacturing some types of lubricants, dyes, drugs, rubbers Pesticides and detergents.
The molecule formula of benzene is C6H6 . Each molecule of benzene is composed of a ring of six carbon atoms (each connected to a hydrogen atom).The first discovered of benzene was from coal tar in the 1800s by Michael Faraday. The structure molecule of benzene proved confusing and doubt for chemists for more than 40 years,becuse of there are few number of hydrogen atom for six single-bonded carbon atoms. Also the structure formula of benzene reveal to multiple double and/or triple carbon-carbon bonds.
There are two way for production of benzene :by natural processes, when wood is completely burned such as, during forest fires or during volcano eruptions ,or by people activates, from cigarette smock or car exhaust .Today benzene is manufacturing from petroleum.
Benzene consider as one of the most dangerous chemical. It is affect human health when they are exposure for long time. It result a lot of decease like: rapid heart rate,headaches,confusion,dizziness tremors and cancer. also benzene can cause death when they are breathing high amount of benzene.
Benzene enters to our environment due to many reason, for example :
1) Benzene exposure to the air from tobacco smoke, automobile service stations, exhaust from motor vehicles, and industrial emissions.
2) It is came from products that contain benzene, such as glues, paints, furniture wax, and detergents, can also be a source of exposure
3) Industrial waste or gases that containing high amount of benzene.
5) Working in industries that make or use benzene.
Physical Properties of benzene:
Benzene is a chemical that is a colorless or light yellow liquid at room temperature. It has a sweet odor and it is highly flammable (easy fair ).
Benzene is a volatile chemical it is evaporates to air very quickly. It is vapor is heavier than air.
. It has a freezing point of 41.9Â°F (5.5Â°C), the boiling point of Benzene is176.2Â°F (80.1Â°C), and a density of 0.8787 g/ml less than water density.
Benzene soluble only slightly in water and will float on top of water, but it is completely miscible with, carbons alcohols, chloroforms, disulfides, tetrachloride's, ethers, and other organic solvents.
The vapor pressure for benzene at standard T( 25Â°C) is 95.2 mm Hg and water partition coefficient (log Kow) of 2.13.
The chemical formula for benzene is C6H6, and it arrange in a ring structure with molecular weight of 78.11 g/mol.
Chemical properties of benzene
Benzene fits in the general form of C6H6. Benzene does not react with unsaturated hydrocarbons such as ethane, even though it has 6 electrons. On the other hand, benzene molecules are quite stable and give substitution reactions. Because of the density of electron is high on the ring, it gives substitution reactions
Chemical properties of benzene:
Benzene reacts with bromine or chlorine benzene undergoes addition reactions with bromine or chlorine.
Benzene undergoes nitration when heated with mixture
Benzene reacts with fuming sulphuric acid gives benzene sulphonicacil
Benzene and its homologues are highly inflammable liquids and burn with a sooty flame.
2C6H6 + 15O2 12CO2 + 6H2O Oxidation of alkyl sidechain
The alkyl sidechain in the molecule of an arene can be oxidized under different conditions.
With hot acidified KMnO4 or K2Cr2O7, the sidechain gets oxidized to COOH group irrespective of the length of the sidechain. For example,
Toluene Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â benzoic acid
phenylethane Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â benzoic acid
With weak oxidising agents such as acidic manganese dioxide (MnO2) or chromylchloride (CrO2Cl2), the side chain is oxidised to aldehyde (-CHO) group.
Benzene gives some addition reactions. Some typical reactions are:
Addition of hydrogen
Benzene on reduction with hydrogen under pressure in the presence of finely divided nickel at 200Â°C, gives an addition product hexahydrobenzene (cyclohexane).
Addition of chlorine
Chlorine adds on to benzene at its boiling point, in the presence of bright sunlight, to give hexachloride.
Addition of ozone
Benzene reacts slowly with ozone to form triozonide. Triozonide on hydrolysis with water gives glyoxal.
Benzene when passed through a red hot iron tube gives diphenyl.
Benzene uses and Application:
Benzene is used in industrial to manufacturing of many materials and products for example: some types of rubbers, lubricants, dyes, synthetic, insecticides, fumigants, styrene, gasoline, detergents, drugs, and paint removers. Benzene is also use in a cooking process.
Benzene also play as an important compound in a motor fuels, do to it is high octane number. It is also use as a solvent for, inks, resins, oils, , paints, fats, plastics, waxes and in an extraction process for taking out oils from seeds and nuts; and in photogravure paper printing. Benzene is also used as a chemical intermediate in some process . It is also used in the manufacture of explosives, detergents, dyestuffs and pharmaceuticals.
However from scientism said benzene used in a lot of research. Some manufacturers, especially in Europe, have used a gasoline additive (one application of benzene) to increase engine and machine efficiency and to improve starting qualities. The most important use of benzene, is in producing of other aromatic compounds
In general few amount of benzene results whenever carbon materials go under incomplete combustion. It comes out from volcanoes, forest fires and it is a component of cigarettes smoke. Benzene is a main material of combustion products that results from the burning of PVC (polyvinyl chloride).
In the past benzene was produced as a second component of coke production. In the 1950s the requests of benzene increases especially after the growing of plastic industry, so that made the necessary to produce the benzene from petrol. Now days most benzene comes from the petrochemical industry and small amount of benzene is produced from coke.
In Europe, benzene is produced primary from "pyrolysis gasoline coproduced in the steam cracking of naphtha, gasoil or condensates to make olefins", also in US the same thing happens, benzene is a product of catalytic reforming process. Where the Naphtha mixed with hydrogen and fed to a reactor that contains catalyst.
There are four chemical processes related to the production of benzene which are: catalytic reforming, toluene hydrodealkylation, toluene disproportionation, and steam cracking.
Toluene hydrodealkylation it is the process of converting the toluene to benzene by mixing the toluene with hydrogen. Then the mixture is passed through catalyst like a chromium, molybdenum, or platinum oxide under temperature of 500-600 Â°C and pressure of 40-60 atm. Instead of using catalyst sometimes they use high temperature at the same condition. At these conditions toluene goes under dealkylation to benzene and methane as shown in the reaction below:
C6H5CH3 + H2 â†’ C6H6 + CH4
This reaction produces a reaction companion that results biphenyl at higher temperature as the reaction below:
2 C6H6 H2 + C6H5-C6H5
If the raw material has high amount of non-aromatic components like paraffins or naphthenes those goes under decomposition process which convert them to a lower hydrocarbons like methane that increases the composition of hydrogen.
Sometimes there are another substances used in this process instead of toluene with the same efficiency like heavier aromatics or xylenes. This process named as "on-purpose".
It's the process that results ethylene and other alkenes from the reactions of the aliphatic hydrocarbons depending on the uses of raw material that produce olefins. Benzene can be produced by steam cracking as a rich liquid component called pyrolysis gasoline. That product can be mixed with other hydrocarbons like gasoline distilled and goes under BTX process that produced the gasoline component by separation method. That product contains benzene.
in this process number of hydrocarbons is mixed together with boiling point between 60-200 Â°C is mixed with the gas of hydrogen and the it goes through a bifunctional platinum chloride under conditions of 500-525 Â°C temperature and 8-50 atm pressure. Under the same conditions the aliphatic hydrocarbons lose hydrogen by forming rings and then they become aromatic hydrocarbons. After that the aromatic product should be separated from the product mixture. The separation process is done by the extraction of any component with number of solvents like diethylene glycol or sulfolane. At the end benzene will results and separated from the aromatic compounds by distillation
Toluene Hydroalkylation (HAD) is a name of the process that produced benzene and its main reaction:
Toluene + H2 Â® Benzene + CH4
Hydrogen and toluene are feed in to a reactor filled with catalyst to convert them to benzene and methane. This reaction is endothermic and goes under conditions of 500 C to 660 C, and 20 to 60 bar.
The (HAD) process starts with mixing fresh toluene with a stream of recycle unreacted toluene, mixing process is done in a storage tank. Then the toluene is pumped to gain it with stream of mixed hydrogen and fresh gas of hydrogen,