BENZENE

CAS Number: 71-43-2
EC Number: 200-753-7
Chemical formula: C6H6
Molar mass: 78.114 g·mol−1

Benzene is an organic chemical compound with the molecular formula C6H6. 
The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. 
Because Benzene contains only carbon and hydrogen atoms, benzene is classed as a hydrocarbon.

Benzene is primarily used as a feedstock, or raw material, to make other industrial chemicals, such as ethylbenzene, cumene and cyclohexane. 
Benzene is also used as a solvent in the chemical and pharmaceutical industries.

Most benzene exposure comes from the air from a number of sources, including forest fires, auto exhaust and gasoline from fueling stations. 
Benzene in cigarette smoke is a major source of exposure. 
Very low levels of benzene have been detected in fruits, vegetables, nuts, dairy products, eggs and fish. 
Most people are exposed to only very tiny amounts of benzene from water and food.

Benzene is a colorless, volatile, highly flammable liquid that is used extensively in the chemical industry and received wide interest in the early days of organic chemistry.
Because of Benzene structure, benzene is a very stable organic compound. 
Benzene does not readily undergo addition reactions. 
Addition reactions involving benzene require high temperature, pressure, and special catalysts. 

The most common reactions involving benzene involve substitution reactions. 
Numerous atoms and groups of atoms may replace a hydrogen atom or several hydrogen atoms in benzene. 
Th ree important types of substitution reactions involving benzene are alkylation, halogenation, and nitration. 
In alkylation, an alkyl group or groups substitute for hydrogen(s).

Benzene is registered under the REACH Regulation and is manufactured in and / or imported to the European Economic Area, at ≥ 1 000 000 tonnes per annum.
Benzene is used in articles, by professional workers (widespread uses), in formulation or re-packing, at industrial sites and in manufacturing.

Benzene is an organic chemical compound with the molecular formula C6H6 . 
Benzene molecule is composed of 6 atoms joined in a ring, with 1 hydrogen atom attached to each carbon atom. 
Because Benzene molecules contain only carbon and hydrogen atoms, benzene is classed as a hydrocarbon.

Benzene is a natural constituent of crude oil and is one of the most elementary petrochemicals. 
Benzene is a colorless and highly flammable liquid with a sweet smell. 
Benzene is mainly used as a precursor to heavy chemicals. 
About 80% of benzene is consumed in the production of three chemicals, ethylbenzene, cumene and cyclohexane. 
Most non-industrial applications have been limited due to benzene's carcinogenity.

Benzene is a chemical that is released into the air from emissions from automobiles and burning coal and oil. 
Benzene is also used in the manufacture of a wide range of industrial products, including chemicals, dyes, detergents, and some plastics.

Benzene is a component of products derived from coal and petroleum and is found in gasoline and other fuels. 
Benzene is used in the manufacture of plastics, detergents, pesticides, and other chemicals. 
With exposures from less than five years to more than 30 years, individuals have developed, and died from, leukemia. 
Long-term exposure may affect bone marrow and blood production. 
Short-term exposure to high levels of benzene can cause drowsiness, dizziness, unconsciousness, and death.

Benzene is the simplest organic, aromatic hydrocarbon. 
Benzene is one of the elementary petrochemicals and a natural constituent of crude oil. 
Benzene has a gasoline-like odour and is a colourless liquid. 
Benzene is highly toxic and carcinogenic in nature. 
Benzene is primarily used in the production of polystyrene.

Benzene is a colourless, volatile and flammable liquid with a distinctive odour. 
Benzene evaporates into the air very quickly and is a dangerous fire hazard when exposed to heat or flame. 
Benzene is only slightly soluble in water, but will mix with most organic solvents.
Benzene is one of the simplest organic chemicals known as 'aromatic' compounds - their carbon atoms are arranged in rings rather than chains.

Benzene is a six membered aromatic compound. 
The capability of superhalogen induced ionization of benzene molecules has been reported based on ab initio calculations. 
Benzene, a commonly used industrial solvent is also an air pollutant and a potent carcinogen.

Benzene is a naturally occurring substance produced by volcanoes and forest fires and present in many plants and animals, but benzene is also a major industrial chemical made from coal and oil. 
As a pure chemical, benzene is a clear, colourless liquid. 
In industry, benzene is used to make other chemicals as well as some types of plastics, detergents, and pesticides. 
Benzene is also a component of gasoline.

Benzene is a natural constituent of crude oil and is one of the elementary petrochemicals. 
Due to the cyclic continuous pi bonds between the carbon atoms, benzene is classed as an aromatic hydrocarbon. 
Benzene is sometimes abbreviated PhH. 

Benzene is a colorless and highly flammable liquid with a sweet smell, and is partially responsible for the aroma around petrol (gasoline) stations. 
Benzene is used primarily as a precursor to the manufacture of chemicals with more complex structure, such as ethylbenzene and cumene, of which billions of kilograms are produced annually. 
Although a major industrial chemical, benzene finds limited use in consumer items because of Benzene toxicity.

Benzene is a colorless or light-yellow liquid chemical at room temperature. 
Benzene is used primarily as a solvent in the chemical and pharmaceutical industries, as a starting material and an intermediate in the synthesis of numerous chemicals, and in gasoline. 
Benzene is produced by both natural and man-made processes. 
Benzene is a natural component of crude oil, which is the main source of benzene produced today. 
Other natural sources include gas emissions from volcanoes and forest fires.

Benzene is a colorless, flammable liquid with a sweet odor. 
Benzene evaporates quickly when exposed to air. 
Benzene is formed from natural processes, such as volcanoes and forest fires, but most exposure to benzene results from human activities.

Benzene is among the 20 most widely used chemicals in the United States. 
Benzene is used mainly as a starting material in making other chemicals, including plastics, lubricants, rubbers, dyes, detergents, drugs, and pesticides. 
In the past Benzene was also commonly used as an industrial solvent (a substance that can dissolve or extract other substances) and as a gasoline additive, but these uses have been greatly reduced in recent decades.

Benzene is also a natural part of crude oil and gasoline (and therefore motor vehicle exhaust), as well as cigarette smoke.

Benzene (C6H6), simplest organic, aromatic hydrocarbon and parent compound of numerous important aromatic compounds. 
Benzene is a colourless liquid with a characteristic odour and is primarily used in the production of polystyrene. 
Benzene is highly toxic and is a known carcinogen; exposure to Benzene may cause leukemia. 
As a result, there are strict controls on benzene emissions.

Benzene is a chemical that is a colorless or light yellow liquid at room temperature. 
Benzene has a sweet odor and is highly flammable.
Benzene evaporates into the air very quickly. 
It vapor is heavier than air and may sink into low-lying areas.
Benzene dissolves only slightly in water and will float on top of water.

Benzene is formed from both natural processes and human activities.
Natural sources of benzene include volcanoes and forest fires. 
Benzene is also a natural part of crude oil, gasoline, and cigarette smoke.

Benzene is widely used in the United States. 
Benzene ranks in the top 20 chemicals for production volume.
Some industries use benzene to make other chemicals that are used to make plastics, resins, and nylon and synthetic fibers. 
Benzene is also used to make some types of lubricants, rubbers, dyes, detergents, drugs, and pesticides.

Benzene derivatives
Many important chemical compounds are derived from benzene by replacing one or more of Benzene hydrogen atoms with another functional group. 
Examples of simple benzene derivatives are phenol, toluene, and aniline, abbreviated PhOH, PhMe, and PhNH2, respectively. 

Linking benzene rings gives biphenyl, C6H5–C6H5. 
Further loss of hydrogen gives "fused" aromatic hydrocarbons, such as naphthalene, anthracene, phenanthrene, and pyrene. 
The limit of the fusion process is the hydrogen-free allotrope of carbon, graphite.

In heterocycles, carbon atoms in the benzene ring are replaced with other elements. 
The most important variations contain nitrogen. 
Replacing one CH with N gives the compound pyridine, C5H5N. 
Although benzene and pyridine are structurally related, benzene cannot be converted into pyridine. 
Replacement of a second CH bond with N gives, depending on the location of the second N, pyridazine, pyrimidine, or pyrazine.

Household Products of Benzene:    
Information on 72 consumer products that contain Benzene in the following categories is provided:
Auto Products
Commercial / Institutional
Home Maintenance
Inside the Home
Pet Care

Characteristics of Benzene:
Modern bonding models (valence-bond and molecular orbital theories) explain the structure and stability of benzene in terms of delocalization of six of Benzene electrons, where delocalization in this case refers to the attraction of an electron by all six carbons of the ring instead of just one or two of them. 
This delocalization causes the electrons to be more strongly held, making benzene more stable and less reactive than expected for an unsaturated hydrocarbon. 

As a result, the hydrogenation of benzene occurs somewhat more slowly than the hydrogenation of alkenes (other organic compounds that contain carbon-carbon double bonds), and benzene is much more difficult to oxidize than alkenes. 
Most of the reactions of benzene belong to a class called electrophilic aromatic substitution that leave the ring itself intact but replace one of the attached hydrogens. 
These reactions are versatile and widely used to prepare derivatives of benzene.

Experimental studies, especially those employing X-ray diffraction, show benzene to have a planar structure with each carbon-carbon bond distance equal to 1.40 angstroms (Å). 
This value is exactly halfway between the C=C distance (1.34 Å) and C—C distance (1.46 Å) of a C=C—C=C unit, suggesting a bond type midway between a double bond and a single bond (all bond angles are 120°). 
Benzene has a boiling point of 80.1 °C (176.2 °F) and a melting point of 5.5 °C (41.9 °F), and Benzene is freely soluble in organic solvents, but only slightly soluble in water.

Benzene was discovered in 1825 by the English physicist Michael Faraday and was made available in large quantities in 1842 after Benzene was found to contain benzene. 
Large amounts of benzene are now extracted from petroleum.
Benzene is a colourless liquid with a characteristic odour of formula C6H6. 

Benzene is a closed ring of six carbon atoms linked by bonds that alternate between single and double bonds. 
Each carbon atom is bound by a single hydrogen atom.
Benzene melts at a temperature of 5.5 ° C, boils at 80.1°C. 
Benzene and Benzene derivatives are part of an essential chemical community known as aromatic compounds. 

Benzene is a precursor in the production of medicines, plastics, oil, synthetic rubber, and dyes.
As a result, the hydrogenation of benzene happens much more slowly than the hydrogenation of other organic compounds containing carbon-carbon double bonds, and benzene is much more difficult to oxidize than alkenes. 
Most of the reactions of benzene belong to a class called electrophilic aromatic substitution, which leaves the ring intact but replaces one of the hydrogens attached to Benzene. 
These reactions are versatile and commonly used for the preparation of benzene derivatives.

Methods of Manufacturing of Benzene:    
Worldwide, ~30% of commercial benzene is produced by catalytic reforming, a process in which aromatic molecules are produced from the dehydrogenation of cycloparaffins, dehydroisomerization of alkyl cyclopentanes, and the cyclization and subsequent dehydrogenation of paraffins. 
The feed to the catalytic reformer may be a straight-run, hydrocracked, or thermally cracked naphtha fraction in the C6 to 200 °C range. 
If benzene is the main product desired, a narrow naphtha cut of 71-104 °C is fed to the reformer. 

The reforming catalyst most frequently consists of platinum-rhenium on a high surface area alumina support. 
The reformer operating conditions and type of feedstock largely determine the amount of benzene that can be produced. 
The benzene product is most often recovered from the reformate by solvent extraction techniques.

Benzene is produced from the hydrodemethylation of toluene under catalytic or thermal conditions. 
The main catalytic hydrodealkylation processes are Hydeal and DETOL. 
Two widely used thermal processes are HDA and THD. 
These processes contribute 25-30% of the world's total benzene supply. 

In catalytic toluene hydrodealkylation, toluene is mixed with a hydrogen stream and passed through a vessel packed with a catalyst, usually supported chromium or molybdenum oxides, platinum or platinum oxides, on silica or alumina. 
The operating temperatures range from 500 to 595 °C and pressures are usually 4-6 MPa (40-60 atm). 
The reaction is highly exothermic and the temperature is controlled by injection of quench hydrogen at several places along the reaction. 

Conversions per pass typically reach 90% and selectivity to benzene is often >95%. 
The catalytic process occurs at lower temperatures and offers higher selectivities but requires frequent regeneration of the catalyst. 
Products leaving the reactor pass through a separator where unreacted hydrogen is removed and recycled to the feed. 
Further fractionation separates methane from the benzene product.

The steam cracking of heavy naphthas or light hydrocarbons such as propane or butane to produce ethylene yields a liquid by-product rich in aromatic content called pyrolysis gasoline, dripolene, or drip oil. 
A typical pyrolysis gasoline contains up to 65% aromatics, 50% of which is benzene. 
Approximately 30-35% of benzene produced worldwide is derived from pyrolysis gasoline. 

The remainder of the product is composed of mono- and diolefins. 
These olefinic substances are removed by a mild hydrogenation step. 
Following hydrogenation, the resulting pyrolysis gasoline is used in motor gasoline. 
Alternatively, pure benzene could be recovered from the pyrolysis gasoline by solvent extraction and subsequent distillation.

Two molecules of toluene are converted into one molecule of benzene and one molecule of mixed-xylene isomers in a sequence called transalkylation or disproportionation. 
Economic feasibility of the process strongly depends on the relative prices of benzene, toluene, and xylene. 
Operation of a transalkylation unit is practical only when there is an excess of toluene and a strong demand for benzene. 
In recent years, xylene and benzene prices have generally been higher than toluene prices so transalkylation is presently an attractive alternative to hydrodealkylation.

Benzene has been recovered from coal tar. 
The lowest boiling fraction is extracted with caustic soda to remove tar acids. 
The base washed oil is then distilled and further purified by hydrodealkylation.

Clinical Laboratory Methods of Benzene:
Volatile cmpd such as benzene are separated from blood or tissue homogenate directly on gas-chromatographic column & detected using a flame ionization detector. 
High volatility permits gas chromatograph to be operated at relatively low temp. 
The nonvolatile & high boiling components of the biological matrix are left behind in the injection port. 
This insures long column life & requires only occasional cleaning of the injection chamber.

GLC & colorimetric (phenol metabolite) methods are used to determine benzene in serum, urine, & breath. 
Conventional reference range: >1.0 mg/L (toxic concn) for serum; <10.0 mg/L as phenol, >75.0 mg/L (toxic concn) as phenol for urine. 
Internationally recommended conc reference range is: >13 umol/L (toxic concn) for serum; <106 umol/L as phenol, >795 umol/L (toxic concn) as phenol for urine. 
Substances producing phenol as a metabolite can interfere with color assay.

General Manufacturing Information of Benzene:

Manufacture of Benzene:
Release to the environment of this substance can occur from industrial use: manufacturing of the substance, formulation of mixtures and as an intermediate step in further manufacturing of another substance (use of intermediates).

Industry Processing Sectors
Adhesive manufacturing
All other basic organic chemical manufacturing
All other chemical product and preparation manufacturing
All other petroleum and coal products manufacturing
Cyclic crude and intermediate manufacturing
Electrical equipment, appliance, and component manufacturing
Petrochemical manufacturing
Petroleum lubricating oil and grease manufacturing
Petroleum refineries
Plastic material and resin manufacturing
Plastics product manufacturing
Rubber product manufacturing
Soap, cleaning compound, and toilet preparation manufacturing
Synthetic rubber manufacturing
Wholesale and retail trade
fuels blending

The term benzene denotes the pure compound; benzol is still used to a small degree in some countries to represent the compound or a material having benzene as Benzene main component. 
Benzine, on the other hand, is a low-boiling hydrocarbon mixture or naphtha, often nonaromatic in composition.

Benzene was first isolated by Michael Faraday in 1825 from the liquid condensed by compressing oil gas. 
He proposed the name bicarburet of hydrogen for the new compound. 
In 1833, Eilhard Mischerlich synthesized bicarburet of hydrogen by distilling benzoic acid, obtained from gum benzoin, with lime and suggested the name benzin for the compound. 
In 1845, A.W. Hoffman and C. Mansfield found benzene in light oil derived from coal tar. 

The first practical industrial process for recovery of benzene from coal tar was reported by Mansfield in 1849. 
Coal tar soon became the largest source of benzene. 
Soon afterward, benzene was discovered in coal gas and this initiated the recovery of coal gas light oil as a source of benzene. 
Until the 1940's, light oil obtained from the destructive distillation of coal was the principal source of benzene.

Health Effects of Benzene:
Acute exposure to benzene produces toxic effects on the central nervous system; however, in order to evaluate the chronic effects, consideration must be given to the myelotoxic and possible chromosome damaging and leukemogenic effects of benzene. 
The time required for expression of chlorine benzene toxicity indicates a vast difference in individual sensitivity.

Most cases of severe benzene intoxication have been reported in workers exposed to rather high concentrations of benzene under somewhat unhygienic working conditions. 
Benzene is probable that all cases reported as “Leukemia associated with benzene exposure” have resulted from exposure rather high concentrations of benzene and other chemicals.

Aromaticity of Benzene:
Benzene is an aromatic compound, as the C-C bonds formed in the ring are not exactly single or double, rather they are of intermediate length. 
Aromatic compounds are divided into two categories: benzenoids (one containing benzene ring) and non-benzenoids (those not containing benzene ring), provided they follow Huckel rule. 
According to Huckel rule, for a ring to be aromatic Benzene should have the following property:

Planarity of Benzene:
Complete delocalization of the π electrons in the ring
Presence of (4n + 2) π electrons in the ring where n is an integer (n = 0, 1, 2, . . .)

Resonance of Benzene:
The oscillating double bonds in the benzene ring are explained with the help of resonance structures as per valence bond theory. 
All the carbon atoms in the benzene ring are sp2 hybridized. 

One of the two sp2 hybridized orbitals of one atom overlaps with the sp2 orbital of adjacent carbon atom forming six C-C sigma bonds. 
Other left sp2 hybridized orbitals combine with s orbital of hydrogen to form six C-H sigma bonds. 
Remaining unhybridized p orbitals of carbon atoms form π bonds with adjacent carbon atoms by lateral overlap.

This explains an equal possibility for the formation of C1 –C2, C3 – C4, C5 – C6 π bonds or C2 – C3, C4 – C5, C6-C1 π bonds. 
Hence, Benzene explains the formation of two resonance structures proposed by Kekule.

Properties of Benzene:
The various properties of benzene are mentioned below:

Benzene is immiscible in water but soluble in organic solvents.
Benzene is a colourless liquid and has an aromatic odour.
Benzene has a density of 0.87g cm-3. 
Benzene is lighter than water.

Benzene has a moderate boiling point and a high melting point. 
(Boiling point: 80.5°C, Melting point: 5.5°C)
Benzene shows resonance.
Benzene is highly inflammable and burns with a sooty flame.

Chemical Properties of Benzene:
Benzene is a clear, volatile, colorless, highly flammable liquid with a pleasant, characteristic odor. 
Benzene is an aromatic hydrocarbon that boils at 80.1 DC. 

Benzene is used as a solvent in many areas of industries, such as rubber and shoe manufacturing, and in the production of other important substances, such as styrene, phenol, and cyclohexane. 
Benzene is essential in the manufacture of detergents, pesticides, solvents, and paint removers. 
Benzene is present in fuels such as gasoline up to the level of 5%.

Physical properties of Benzene:
Clear, colorless to light yellow watery liquid with an aromatic, musty, phenolics or gasoline-like odor. 
At 40 °C, an odor threshold concentration of 190 μg/L in air was determined by Young et al.

An odor threshold of 4.68 ppmv was determined by Leonardos et al. 
A detection odor threshold concentration of 108 mg/m3 (34 ppmv). 
The average least detectable odor threshold concentrations in water at 60 °C and in air at 40 °C were 0.072 and 0.5 mg/L, respectively.

Formulation or re-packing of Benzene:
Benzene is used in the following products: laboratory chemicals, coating products, fillers, putties, plasters, modelling clay and non-metal-surface treatment products.
Benzene has an industrial use resulting in manufacture of another substance (use of intermediates).
Release to the environment of this substance can occur from industrial use: formulation of mixtures, manufacturing of the substance and as an intermediate step in further manufacturing of another substance (use of intermediates).

Purification Methods of Benzene:
For most purposes, benzene can be purified sufficiently by shaking with conc H2SO4 until free from thiophene, then with H2O, dilute NaOH and water, followed by drying (with P2O5, sodium, LiAlH4, CaH2, 4X Linde molecular sieve, or CaSO4, or by passage through a column of silica gel, and for a preliminary drying, CaCl2 is suitable), and distillation. 
A further purification step to remove thiophene, acetic acid and propionic acid, is crystallisation by partial freezing. 
The usual contaminants in dry thiophene-free benzene are non-benzenoid hydrocarbons such as cyclohexane, methylcyclohexane, and heptanes, together with naphthenic hydrocarbons and traces of toluene. 

Carbonyl-containing impurities can be removed by percolation through a Celite column impregnated with 2,4-dinitrophenylhydrazine, phosphoric acid and H2O. 
(Prepared by dissolving 0.5g DNPH in 6mL of 85% H3PO4 by grinding together, then adding and mixing 4mL of distilled H2O and 10g Celite.)
Benzene has been freed from thiophene by refluxing with 10% (w/v) of Raney nickel for 15minutes, after which the nickel is removed by filtration or centrifugation. 
Dry benzene is obtained by doubly distilling high purity benzene from a solution containing the blue ketyl formed by the reaction of sodium-potassium alloy with a small amount of benzophenone. 
Thiophene has been removed from benzene (absence of bluish-green coloration when 3mL of benzene is shaken with a solution of 10mg of isatin in 10mL of conc H2SO4) by refluxing the *benzene (1.25L) for several hours with 40g HgO (freshly precipitated) dissolved in 40mL glacial acetic acid and 300mL of water. 

The precipitate is filtered off, the aqueous phase is removed and the benzene is washed twice with H2O, dried and distilled. 
Alternatively, benzene dried with CaCl2 has been shaken vigorously for 0.5hour with anhydrous AlCl3 (12g/L) at 25-35o, then decanted, washed with 10% NaOH, and water, dried and distilled. 
The process is repeated, giving thiophene-free benzene.

After shaking successively for about an hour with conc H2SO4, distilled water (twice), 6M NaOH, and distilled water (twice), benzene is distilled through a 3-ft glass column to remove most of the water. 
Absolute EtOH is added and the benzene-alcohol azeotrope is distilled. 
The middle fraction is shaken with distilled water to remove EtOH, and again redistilled. 

Final slow and very careful fractional distillation from sodium, then LiAlH4 under N2, removed traces of water and peroxides. 
Benzene liquid and vapour are very TOXIC and HIGHLY FLAMMABLE, and all operations should be carried out in an efficient fume cupboard and in the absence of naked flames in the vicinity. 
Rapid purification: To dry benzene, alumina, CaH2 or 4A molecular sieves (3% w/v) may be used (dry for 6hours). 
Then benzene is distilled, discarding the first 5% of distillate, and stored over molecular sieves (3A, 4A) or Na wire.

Application of Benzene:
Benzene is an important chemical; Benzene is used a starting material for a wide range of chemicals which feed into major industrial manufacturing processes. 
End products from processes requiring benzene include plastics, foams, dyes, detergents, solvents, and insecticides.

Before Benzene toxic nature was realised, benzene was previously used in cosmetics (for example aftershaves), domestic (cleaning) solvents and in the process of decaffeinating coffee. 
Benzene use in such consumer products or processes is no longer permitted.

Benzene may be used in the following processes:
Formation of phenyl acetate by aerobic oxidation using Pd catalyst and acetic acid as solvent.
Formation of phenol by hydroxylation in the presence of mesoporous carbon nitride supported on vanadium catalyst.
As a solvent to prepare nanoparticles of gallium nitride (GaN) by reacting Li3N and GaCl3 at 280°C.

Uses of Benzene:
Benzene is also converted to cyclohexane, which is used to produce nylon and synthetic fibers.

Benzene occurs in coal and coal-tar distillationproducts and in petroleum products suchas gasoline. 
Benzene is also found in the gases andleachates of landfills for industrial wastes,construction debris, and landscaping refuse. 
Traceamounts of benzene, toluene, xylenes, andother volatile organics have been found inthe soils and groundwaters near many sanitarylandfills. 
Kramer has assessed the level of exposuresto benzene during removal, cleaning, pumping,and testing of underground gasoline storagetanks. 

The average human exposureswere 0.43–3.84 ppm (in 1.5–6 hours) and thehighest short-term (15–minute) exposure was9.14 ppm. 
Benzene also occurs in the tobaccosmoke; thus the riskof Benzene exposure may enhance from inhalingsuch smoke.
Benzene is used as a solvent for waxes,resins, and oils; as a paint remover; as a diluentfor lacquers; in the manufacture of dyes,pharmaceuticals, varnishes, and linoleum;and as a raw material to produce a numberof organic compounds.

Manufacturing of ethylbenzene (for styrene monomer), dodecylbenzene (for detergents), cyclo- hexane (for nylon), phenol, nitrobenzene (for ani- line), maleic anhydride, chlorobenzene, diphenyl, benzene hexachloride, benzene-sulfonic acid, and as a solvent.

Benzene is also known as benzol, benzole, coal tar naphtha, and phenyl hydride, benzene is a clear, colorless, flammable liquid made by passing coke gas through oil, which is then distilled to produce benzene and toluol. 
The benzene is separated from the toluol by fractional distillation. 
Benzene is soluble in alcohol, ether, chloroform, and glacial acetic acid, but Benzene is insoluble in water. 
Benzene was used as a solvent for many photographic operations in the 19th century. 

In the collodion process, benzene was used to dissolve rubber to both subcoat and supercoat negatives. 
Benzene was also used as a solvent for Canada balsam in the Cutting method of sealing ambrotypes and cementing lens elements. 
Benzene was also used as a solvent for wax, gums, resins, and amber and in particular for retouching varnishes applied to silver bromide gelatin negatives.

Benzene is used in various industrial processes such as in the manufacture of lubricants, plastics, rubbers, dyes, synthetic fibres, etc. 
However, Benzene has non-industrial uses too which are limited due to the reason benzene is toxic and carcinogenic. 
The different uses of Benzene are mentioned below.

Benzene is used in the preparation of phenol. 
Benzene is also used to prepare aniline used in dyes and in dodecylbenzene used for the detergents.
In early times, benzene was used in degreasing of metal.
Benzene is used for manufacturing of nylon fibres.
The main use of benzene is that Benzene is used in the manufacture of other chemicals such as ethylbenzene, cyclohexane, cumene, nitrobenzene, alkylbenzene, etc.

At one time, benzene was obtained almost entirely from coal tar; however, since about 1950, these methods have been replaced by petroleum-based processes. 
More than half of the benzene produced each year is converted to ethylbenzene, then to styrene, and then to polystyrene. 
The next largest use of benzene is in the preparation of phenol. 
Other uses include the preparation of aniline (for dyes) and dodecylbenzene (for detergents).

Benzene is used as a constituent in motor fuels; as a solvent for fats, waxes, resins, oils, inks, paints, plastics, and rubber; in the extraction of oils from seeds and nuts; and in photogravure printing. 
Benzene is also used as a chemical intermediate. 
Benzene is also used in the manufacture of detergents, explosives, pharmaceuticals, and dyestuffs.

Benzene is used to make chemicals used in the manufacture of industrial products such as dyes, detergents, explosives, pesticides, synthetic rubber, plastics, and pharmaceuticals. 
Benzene is found in gasoline and trace amounts are found in cigarette smoke. 
Benzene has been banned as an ingredient in products intended for use in the home, including toys. 

Benzene has a sweet, aromatic, gasoline-like odor. 
Most individuals can begin to smell benzene in air at 1.5 to 4.7 ppm. 
The odor threshold generally provides adequate warning for acutely hazardous exposure concentrations but is inadequate for more chronic exposures.

Benzene was used in the past as a solvent in inks, rubber, lacquers, and paint removers. 
Today, Benzene is used mainly in closed processes to synthesize organic chemicals. 
Gasoline in some countries contains a high concentration of benzene (as high as 30%); the U.S. average is 1-3%. 
Workers who remove or clean underground storage tanks may be exposed to significant levels. 

Gasoline in North America now contains about 1% benzene.
The European Union (EU) reduced in 2000 the maximum allowed benzene content in gasoline from 5% to 1% by volume. 
Mean exposures in the Swedish petroleum industry are well below the Swedish occupational exposure limits. 

Benzene is used mainly as an intermediate to make other chemicals, above all ethylbenzene (and other alkylbenzenes), cumene, cyclohexane, and nitrobenzene. 
In 1988 Benzene was reported that two-thirds of all chemicals on the American Chemical Society's lists contained at least one benzene ring.
More than half of the entire benzene production is processed into ethylbenzene, a precursor to styrene, which is used to make polymers and plastics like polystyrene. 
Some 20% of the benzene production is used to manufacture cumene, which is needed to produce phenol and acetone for resins and adhesives. 

Cyclohexane consumes around 10% of the world's benzene production; Benzene is primarily used in the manufacture of nylon fibers, which are processed into textiles and engineering plastics. 
Smaller amounts of benzene are used to make some types of rubbers, lubricants, dyes, detergents, drugs, explosives, and pesticides. 
In 2013, the biggest consumer country of benzene was China, followed by the USA. 
Benzene production is currently expanding in the Middle East and in Africa, whereas production capacities in Western Europe and North America are stagnating.

Toluene is now often used as a substitute for benzene, for instance as a fuel additive. 
The solvent-properties of the two are similar, but toluene is less toxic and has a wider liquid range. 
Toluene is also processed into benzene.

Plastics
synthetic rubber
glues
paints
furniture wax
lubricants
dyes
detergents
pesticides
pharmaceuticals.

Widespread uses by professional workers:

Benzene is used in the following products: laboratory chemicals and pH regulators and water treatment products.
Benzene is used in the following areas: health services and scientific research and development.
Benzene is used for the manufacture of: chemicals.
Release to the environment of this substance can occur from industrial use: formulation of mixtures, as an intermediate step in further manufacturing of another substance (use of intermediates) and as processing aid.
Other release to the environment of this substance is likely to occur from: indoor use (e.g. machine wash liquids/detergents, automotive care products, paints and coating or adhesives, fragrances and air fresheners).

Uses at industrial sites of Benzene:
Benzene is used in the following products: coating products, fillers, putties, plasters, modelling clay, laboratory chemicals and polymers.
Benzene has an industrial use resulting in manufacture of another substance (use of intermediates).
Benzene is used for the manufacture of: chemicals.
Release to the environment of this substance can occur from industrial use: as an intermediate step in further manufacturing of another substance (use of intermediates), formulation of mixtures, in the production of articles and manufacturing of the substance.

Adhesives and sealant chemicals
Fuels and fuel additives
Intermediates
Laboratory chemicals
Plasticizers
Processing aids, not otherwise listed
Processing aids, specific to petroleum production
Rubber Vehicle Tires
Sold to re-sellers for petroleum fuel and petrochemical industry
Solvents (for cleaning and degreasing)
Solvents (which become part of product formulation or mixture)

Consumer Uses of Benzene:    
Adhesives and sealants
Automotive care products
Chemical Feed Stock
Cleaning and furnishing care products
Food packaging
Fuels and related products
Intermediate
Intermediates
Lubricants and greases
Metal products not covered elsewhere
Paper products
Plastic and rubber products not covered elsewhere
Sold to re-sellers for petroleum fuel and petrochemical industry
petrochemicals

Component of gasoline of Benzene:
As a gasoline (petrol) additive, benzene increases the octane rating and reduces knocking. 
As a consequence, gasoline often contained several percent benzene before the 1950s, when tetraethyl lead replaced Benzene as the most widely used antiknock additive. 
With the global phaseout of leaded gasoline, benzene has made a comeback as a gasoline additive in some nations. 

In the United States, concern over Benzene negative health effects and the possibility of benzene's entering the groundwater have led to stringent regulation of gasoline's benzene content, with limits typically around 1%.
European petrol specifications now contain the same 1% limit on benzene content. 
The United States Environmental Protection Agency introduced new regulations in 2011 that lowered the benzene content in gasoline to 0.62%.
In many European languages, the word for petroleum or gasoline is an exact cognate of "benzene".

Reactions of Benzene:
The most common reactions of benzene involve substitution of a proton by other groups. 
Electrophilic aromatic substitution is a general method of derivatizing benzene. 
Benzene is sufficiently nucleophilic that Benzene undergoes substitution by acylium ions and alkyl carbocations to give substituted derivatives.

The most widely practiced example of this reaction is the ethylation of benzene.

Approximately 24,700,000 tons were produced in 1999. 
Highly instructive but of far less industrial significance is the Friedel-Crafts alkylation of benzene (and many other aromatic rings) using an alkyl halide in the presence of a strong Lewis acid catalyst.
Similarly, the Friedel-Crafts acylation is a related example of electrophilic aromatic substitution. 
The reaction involves the acylation of benzene (or many other aromatic rings) with an acyl chloride using a strong Lewis acid catalyst such as aluminium chloride or Iron(III) chloride.

Sulfonation, chlorination, nitration of Benzene:
Using electrophilic aromatic substitution, many functional groups are introduced onto the benzene framework. 
Sulfonation of benzene involves the use of oleum, a mixture of sulfuric acid with sulfur trioxide. 

Sulfonated benzene derivatives are useful detergents. 
In nitration, benzene reacts with nitronium ions (NO2+), which is a strong electrophile produced by combining sulfuric and nitric acids. 
Nitrobenzene is the precursor to aniline. 
Chlorination is achieved with chlorine to give chlorobenzene in the presence of a Lewis acid catalyst such as aluminium tri-chloride.

Hydrogenation of Benzene:
Via hydrogenation, benzene and Benzene derivatives convert to cyclohexane and derivatives. 
This reaction is achieved by the use of high pressures of hydrogen in the presence of heterogeneous catalysts, such as finely divided nickel. 
Whereas alkenes can be hydrogenated near room temperatures, benzene and related compounds are more reluctant substrates, requiring temperatures >100 °C. 

This reaction is practiced on a large scale industrially. 
In the absence of the catalyst, benzene is impervious to hydrogen. 
Hydrogenation cannot be stopped to give cyclohexene or cyclohexadienes as these are superior substrates. 
Birch reduction, a non catalytic process, however selectively hydrogenates benzene to the diene.

Metal complexes of Benzene:
Benzene is an excellent ligand in the organometallic chemistry of low-valent metals. 
Important examples include the sandwich and half-sandwich complexes, respectively, Cr(C6H6)2 and [RuCl2(C6H6)]2.

Production of Benzene:
Four chemical processes contribute to industrial benzene production: catalytic reforming, toluene hydrodealkylation, toluene disproportionation, and steam cracking. 
According to the ATSDR Toxicological Profile for benzene, between 1978 and 1981, catalytic reformates accounted for approximately 44–50% of the total U.S benzene production.

Catalytic reforming of Benzene:
In catalytic reforming, a mixture of hydrocarbons with boiling points between 60 and 200 °C is blended with hydrogen gas and then exposed to a bifunctional platinum chloride or rhenium chloride catalyst at 500–525 °C and pressures ranging from 8–50 atm. 
Under these conditions, aliphatic hydrocarbons form rings and lose hydrogen to become aromatic hydrocarbons. 

The aromatic products of the reaction are then separated from the reaction mixture (or reformate) by extraction with any one of a number of solvents, including diethylene glycol or sulfolane, and benzene is then separated from the other aromatics by distillation. 
The extraction step of aromatics from the reformate is designed to produce aromatics with lowest non-aromatic components. 
Recovery of the aromatics, commonly referred to as BTX (benzene, toluene and xylene isomers), involves such extraction and distillation steps.

In similar fashion to this catalytic reforming, UOP and BP commercialized a method from LPG (mainly propane and butane) to aromatics.

Toluene hydrodealkylation of Benzene:
Toluene hydrodealkylation converts toluene to benzene. 
In this hydrogen-intensive process, toluene is mixed with hydrogen, then passed over a chromium, molybdenum, or platinum oxide catalyst at 500–650 °C and 20–60 atm pressure. 
Sometimes, higher temperatures are used instead of a catalyst (at the similar reaction condition). 

Under these conditions, toluene undergoes dealkylation to benzene and methane:
C6H5CH3 + H2 -> C6H6 + CH4

This irreversible reaction is accompanied by an equilibrium side reaction that produces biphenyl (aka diphenyl) at higher temperature:
2C6H6 ⇌ H2 + C6H5–C6H5

If the raw material stream contains much non-aromatic components (paraffins or naphthenes), those are likely decomposed to lower hydrocarbons such as methane, which increases the consumption of hydrogen.

A typical reaction yield exceeds 95%. 
Sometimes, xylenes and heavier aromatics are used in place of toluene, with similar efficiency.

This is often called "on-purpose" methodology to produce benzene, compared to conventional BTX (benzene-toluene-xylene) extraction processes.

Toluene disproportionation of Benzene:
Toluene disproportionation (TDP) is the conversion of toluene to benzene and xylene.

Given that demand for para-xylene (p-xylene) substantially exceeds demand for other xylene isomers, a refinement of the TDP process called Selective TDP (STDP) may be used. 
In this process, the xylene stream exiting the TDP unit is approximately 90% p-xylene. 
In some systems, even the benzene-to-xylenes ratio is modified to favor xylenes.

Steam cracking of Benzene:
Steam cracking is the process for producing ethylene and other alkenes from aliphatic hydrocarbons. 
Depending on the feedstock used to produce the olefins, steam cracking can produce a benzene-rich liquid by-product called pyrolysis gasoline. 
Pyrolysis gasoline can be blended with other hydrocarbons as a gasoline additive, or routed through an extraction process to recover BTX aromatics (benzene, toluene and xylenes).

Other methods of Benzene:
Although of no commercial significance, many other routes to benzene exist. 
Phenol and halobenzenes can be reduced with metals. 

Benzoic acid and Benzene salts undergo decarboxylation to benzene. 
The reaction of the diazonium compound derived from aniline with hypophosphorus acid gives benzene. 
Alkyne trimerisation of acetylene gives benzene.

Health effects of Benzene:
Benzene is classified as a carcinogen, which increases the risk of cancer and other illnesses, and is also a notorious cause of bone marrow failure. 
Substantial quantities of epidemiologic, clinical, and laboratory data link benzene to aplastic anemia, acute leukemia, bone marrow abnormalities and cardiovascular disease.
The specific hematologic malignancies that benzene is associated with include: acute myeloid leukemia (AML), aplastic anemia, myelodysplastic syndrome (MDS), acute lymphoblastic leukemia (ALL), and chronic myeloid leukemia (CML).

The American Petroleum Institute (API) stated in 1948 that "Benzene is generally considered that the only absolutely safe concentration for benzene is zero".
There is no safe exposure level; even tiny amounts can cause harm.
The US Department of Health and Human Services (DHHS) classifies benzene as a human carcinogen. 

Long-term exposure to excessive levels of benzene in the air causes leukemia, a potentially fatal cancer of the blood-forming organs. 
In particular, acute myeloid leukemia or acute nonlymphocytic leukemia (AML & ANLL) is caused by benzene.
IARC rated benzene as "known to be carcinogenic to humans".

As benzene is ubiquitous in gasoline and hydrocarbon fuels that are in use everywhere, human exposure to benzene is a global health problem.
Benzene targets the liver, kidney, lung, heart and brain and can cause DNA strand breaks and chromosomal damage. 
Benzene causes cancer in animals including humans. 
Benzene has been shown to cause cancer in both sexes of multiple species of laboratory animals exposed via various routes.

Structure of Benzene:
The structure of benzene has been of interest since Benzene discovery. 
Benzene is a cyclic hydrocarbon (chemical formula: C6H6), i.e., each carbon atom in benzene is arranged in a six-membered ring and is bonded to only one hydrogen atom. 
According to molecular orbital theory, benzene ring involves the formation of three delocalized π – orbitals spanning all six carbon atoms, while the valence bond theory describes two stable resonance structures for the ring.

X-ray diffraction shows that all six carbon-carbon bonds in benzene are of the same length, at 140 picometres (pm).
The C–C bond lengths are greater than a double bond (135 pm) but shorter than a single bond (147 pm). 
This intermediate distance is caused by electron delocalization: the electrons for C=C bonding are distributed equally between each of the six carbon atoms. 
Benzene has 6 hydrogen atoms, fewer than the corresponding parent alkane, hexane, which has 14. 

Benzene and cyclohexane have a similar structure, only the ring of delocalized electrons and the loss of one hydrogen per carbon distinguishes Benzene from cyclohexane. 
The molecule is planar.
The molecular orbital description involves the formation of three delocalized π orbitals spanning all six carbon atoms, while the valence bond description involves a superposition of resonance structures.
Benzene is likely that this stability contributes to the peculiar molecular and chemical properties known as aromaticity. 
To accurately reflect the nature of the bonding, benzene is often depicted with a circle inside a hexagonal arrangement of carbon atoms.

Derivatives of benzene occur sufficiently often as a component of organic molecules that the Unicode Consortium has allocated a symbol in the Miscellaneous Technical block with the code U+232C (⌬) to represent Benzene with three double bonds, and U+23E3 (⏣) for a delocalized version.

Handling and Storage of Benzene:

Nonfire Spill Response of Benzene:
ELIMINATE all ignition sources (no smoking, flares, sparks or flames in immediate area). 
All equipment used when handling the product must be grounded. 
Do not touch or walk through spilled material. 

Stop leak if you can do Benzene without risk. 
Prevent entry into waterways, sewers, basements or confined areas. 
A vapor-suppressing foam may be used to reduce vapors. 
Absorb or cover with dry earth, sand or other non-combustible material and transfer to containers. 

Use clean, non-sparking tools to collect absorbed material. 
LARGE SPILL: Dike far ahead of liquid spill for later disposal. 
Water spray may reduce vapor, but may not prevent ignition in closed spaces.

Safe Storage of Benzene:
Fireproof. 
Separated from food and feedstuffs, oxidants and halogens. 
Store in an area without drain or sewer access.

History of Benzene:

Discovery of Benzene:
The word "benzene" derives from "gum benzoin" (benzoin resin), an aromatic resin known to European pharmacists and perfumers since the 16th century as a product of southeast Asia.
An acidic material was derived from benzoin by sublimation, and named "flowers of benzoin", or benzoic acid. 
The hydrocarbon derived from benzoic acid thus acquired the name benzin, benzol, or benzene.

Michael Faraday first isolated and identified benzene in 1825 from the oily residue derived from the production of illuminating gas, giving Benzene the name bicarburet of hydrogen.
In 1833, Eilhard Mitscherlich produced Benzene by distilling benzoic acid (from gum benzoin) and lime. 
He gave the compound the name benzin.
In 1836, the French chemist Auguste Laurent named the substance "phène"; this word has become the root of the English word "phenol", which is hydroxylated benzene, and "phenyl", the radical formed by abstraction of a hydrogen atom (free radical H•) from benzene.

In 1845, Charles Mansfield, working under August Wilhelm von Hofmann, isolated benzene from coal tar.
Four years later, Mansfield began the first industrial-scale production of benzene, based on the coal-tar method.

Gradually, the sense developed among chemists that a number of substances were chemically related to benzene, comprising a diverse chemical family. 
In 1855, Hofmann used the word "aromatic" to designate this family relationship, after a characteristic property of many of Benzene members.
In 1997, benzene was detected in deep space.

Ring formula of Benzene:
The empirical formula for benzene was long known, but Benzene highly polyunsaturated structure, with just one hydrogen atom for each carbon atom, was challenging to determine. 
Archibald Scott Couper in 1858 and Johann Josef Loschmidt in 1861 suggested possible structures that contained multiple double bonds or multiple rings, but too little evidence was then available to help chemists decide on any particular structure.

In 1865, the German chemist Friedrich August Kekulé published a paper in French (for he was then teaching in Francophone Belgium) suggesting that the structure contained a ring of six carbon atoms with alternating single and double bonds. 
The next year he published a much longer paper in German on the same subject.
Kekulé used evidence that had accumulated in the intervening years—namely, that there always appeared to be only one isomer of any monoderivative of benzene, and that there always appeared to be exactly three isomers of every disubstituted derivative—now understood to correspond to the ortho, meta, and para patterns of arene substitution—to argue in support of his proposed structure.
Kekulé's symmetrical ring could explain these curious facts, as well as benzene's 1:1 carbon-hydrogen ratio.

The new understanding of benzene, and hence of all aromatic compounds, proved to be so important for both pure and applied chemistry that in 1890 the German Chemical Society organized an elaborate appreciation in Kekulé's honor, celebrating the twenty-fifth anniversary of his first benzene paper. 
Here Kekulé spoke of the creation of the theory. 
He said that he had discovered the ring shape of the benzene molecule after having a reverie or day-dream of a snake seizing Benzene own tail (this is a common symbol in many ancient cultures known as the Ouroboros or Endless knot).

This vision, he said, came to him after years of studying the nature of carbon-carbon bonds. 
This was 7 years after he had solved the problem of how carbon atoms could bond to up to four other atoms at the same time. 
Curiously, a similar, humorous depiction of benzene had appeared in 1886 in a pamphlet entitled Berichte der Durstigen Chemischen Gesellschaft (Journal of the Thirsty Chemical Society), a parody of the Berichte der Deutschen Chemischen Gesellschaft, only the parody had monkeys seizing each other in a circle, rather than snakes as in Kekulé's anecdote.

Some historians have suggested that the parody was a lampoon of the snake anecdote, possibly already well known through oral transmission even if Benzene had not yet appeared in print.
Kekulé's 1890 speech in which this anecdote appeared has been translated into English.
If the anecdote is the memory of a real event, circumstances mentioned in the story suggest that Benzene must have happened early in 1862.

In 1929, the cyclic nature of benzene was finally confirmed by the crystallographer Kathleen Lonsdale using X-ray diffraction methods.
Using large crystals of hexamethylbenzene, a benzene derivative with the same core of six carbon atoms, Lonsdale obtained diffraction patterns. 
Through calculating more than thirty parameters, Lonsdale demonstrated that the benzene ring could not be anything but a flat hexagon, and provided accurate distances for all carbon-carbon bonds in the molecule.

Nomenclature of Benzene:
The German chemist Wilhelm Körner suggested the prefixes ortho-, meta-, para- to distinguish di-substituted benzene derivatives in 1867; however, he did not use the prefixes to distinguish the relative positions of the substituents on a benzene ring.
Benzene was the German chemist Karl Gräbe who, in 1869, first used the prefixes ortho-, meta-, para- to denote specific relative locations of the substituents on a di-substituted aromatic ring (viz, naphthalene).
In 1870, the German chemist Viktor Meyer first applied Gräbe's nomenclature to benzene.

Early applications of Benzene:
In the 19th and early 20th centuries, benzene was used as an after-shave lotion because of Benzene pleasant smell. 
Prior to the 1920s, benzene was frequently used as an industrial solvent, especially for degreasing metal. 
As Benzene toxicity became obvious, benzene was supplanted by other solvents, especially toluene (methylbenzene), which has similar physical properties but is not as carcinogenic.

In 1903, Ludwig Roselius popularized the use of benzene to decaffeinate coffee. 
This discovery led to the production of Sanka. 
This process was later discontinued. 
Benzene was historically used as a significant component in many consumer products such as Liquid Wrench, several paint strippers, rubber cements, spot removers, and other products. 
Manufacture of some of these benzene-containing formulations ceased in about 1950, although Liquid Wrench continued to contain significant amounts of benzene until the late 1970s.

Occurrence of Benzene:
Trace amounts of benzene are found in petroleum and coal. 
Benzene is a byproduct of the incomplete combustion of many materials. 
For commercial use, until World War II, most benzene was obtained as a by-product of coke production (or "coke-oven light oil") for the steel industry. 

However, in the 1950s, increased demand for benzene, especially from the growing polymers industry, necessitated the production of benzene from petroleum. 
Today, most benzene comes from the petrochemical industry, with only a small fraction being produced from coal.
Benzene molecules have been detected on Mars.

Detectable levels of benzene have been found in a number of soft drinks that contain either a sodium or potassium benzoate preservative and ascorbic acid, and 'diet' type products containing no added sugar are reported to be particularly likely to contain benzene at detectable levels. 
Surveys carried out in the USA, the UK and Canada have all confirmed that a small proportion of these products may contain low levels of benzene. 
For example, in a survey of 86 samples analysed by the FDA between April 2006 and March 2007, only five products were found to contain benzene at concentrations above 5 ug kg-1. 

The levels found were in a range from approximately 10–90 ug kg-1. 
A survey of 150 UK-produced soft drinks by the Food Standards Agency (FSA) published in 2006 showed that four products contained benzene at levels above 10 ug kg-1, and the highest level recorded was 28 ug kg-1. 
However, Benzene has been reported that higher levels may develop in these products during prolonged storage, especially if they are exposed to daylight.
Benzene may also be formed in some mango and cranberry drinks in the absence of added preservatives, because these fruits contain natural benzoates.

Exposure of Benzene:
According to the Agency for Toxic Substances and Disease Registry (ATSDR) (2007), benzene is both a synthetically-made and naturally occurring chemical from processes that include: volcanic eruptions, wild fires, synthesis of chemicals such as phenol, production of synthetic fibers, and fabrication of rubbers, lubricants, pesticides, medications, and dyes. 
The major sources of benzene exposure are tobacco smoke, automobile service stations, exhaust from motor vehicles, and industrial emissions; however, ingestion and dermal absorption of benzene can also occur through contact with contaminated water. 

Benzene is hepatically metabolized and excreted in the urine. 
Measurement of air and water levels of benzene is accomplished through collection via activated charcoal tubes, which are then analyzed with a gas chromatograph. 
The measurement of benzene in humans can be accomplished via urine, blood, and breath tests; however, all of these have their limitations because benzene is rapidly metabolized in the human body.

Exposure to benzene may lead progressively to aplastic anemia, leukaemia, and multiple myeloma.

OSHA regulates levels of benzene in the workplace.
The maximum allowable amount of benzene in workroom air during an 8-hour workday, 40-hour workweek is 1 ppm. 
As benzene can cause cancer, NIOSH recommends that all workers wear special breathing equipment when they are likely to be exposed to benzene at levels exceeding the recommended (8-hour) exposure limit of 0.1 ppm.

Benzene exposure limits
The United States Environmental Protection Agency has set a maximum contaminant level (MCL) for benzene in drinking water at 0.005 mg/L (5 ppb), as promulgated via the U.S. National Primary Drinking Water Regulations.
This regulation is based on preventing benzene leukemogenesis. 
The maximum contaminant level goal (MCLG), a nonenforceable health goal that would allow an adequate margin of safety for the prevention of adverse effects, is zero benzene concentration in drinking water. 
The EPA requires that spills or accidental releases into the environment of 10 pounds (4.5 kg) or more of benzene be reported.

The U.S. Occupational Safety and Health Administration (OSHA) has set a permissible exposure limit of 1 part of benzene per million parts of air (1 ppm) in the workplace during an 8-hour workday, 40-hour workweek. 
The short term exposure limit for airborne benzene is 5 ppm for 15 minutes.
These legal limits were based on studies demonstrating compelling evidence of health risk to workers exposed to benzene. 
The risk from exposure to 1 ppm for a working lifetime has been estimated as 5 excess leukemia deaths per 1,000 employees exposed. 
(This estimate assumes no threshold for benzene's carcinogenic effects.) OSHA has also established an action level of 0.5 ppm to encourage even lower exposures in the workplace.

The U.S. National Institute for Occupational Safety and Health (NIOSH) revised the Immediately Dangerous to Life and Health (IDLH) concentration for benzene to 500 ppm. 
The current NIOSH definition for an IDLH condition, as given in the NIOSH Respirator Selection Logic, is one that poses a threat of exposure to airborne contaminants when that exposure is likely to cause death or immediate or delayed permanent adverse health effects or prevent escape from such an environment. 
The purpose of establishing an IDLH value is (1) to ensure that the worker can escape from a given contaminated environment in the event of failure of the respiratory protection equipment and (2) is considered a maximum level above which only a highly reliable breathing apparatus providing maximum worker protection is permitted.

In September 1995, NIOSH issued a new policy for developing recommended exposure limits (RELs) for substances, including carcinogens. 
As benzene can cause cancer, NIOSH recommends that all workers wear special breathing equipment when they are likely to be exposed to benzene at levels exceeding the REL (10-hour) of 0.1 ppm.
The NIOSH short-term exposure limit (STEL – 15 min) is 1 ppm.

American Conference of Governmental Industrial Hygienists (ACGIH) adopted Threshold Limit Values (TLVs) for benzene at 0.5 ppm TWA and 2.5 ppm STEL.

First Aid of Benzene:    

EYES: First check the victim for contact lenses and remove if present. 
Flush victim's eyes with water or normal saline solution for 20 to 30 minutes while simultaneously calling a hospital or poison control center. 
Do not put any ointments, oils, or medication in the victim's eyes without specific instructions from a physician. 
IMMEDIATELY transport the victim after flushing eyes to a hospital even if no symptoms (such as redness or irritation) develop. 

SKIN: IMMEDIATELY flood affected skin with water while removing and isolating all contaminated clothing. 
Gently wash all affected skin areas thoroughly with soap and water. 
IMMEDIATELY call a hospital or poison control center even if no symptoms (such as redness or irritation) develop. 
IMMEDIATELY transport the victim to a hospital for treatment after washing the affected areas. 

INHALATION: IMMEDIATELY leave the contaminated area; take deep breaths of fresh air. 
IMMEDIATELY call a physician and be prepared to transport the victim to a hospital even if no symptoms (such as wheezing, coughing, shortness of breath, or burning in the mouth, throat, or chest) develop. 
Provide proper respiratory protection to rescuers entering an unknown atmosphere. 
Whenever possible, Self-Contained Breathing Apparatus (SCBA) should be used; if not available, use a level of protection greater than or equal to that advised under Protective Clothing. 

INGESTION: DO NOT INDUCE VOMITING. 
Volatile chemicals have a high risk of being aspirated into the victim's lungs during vomiting which increases the medical problems. 
If the victim is conscious and not convulsing, give 1 or 2 glasses of water to dilute the chemical and IMMEDIATELY call a hospital or poison control center. 
IMMEDIATELY transport the victim to a hospital. 

If the victim is convulsing or unconscious, do not give anything by mouth, ensure that the victim's airway is open and lay the victim on his/her side with the head lower than the body. 
DO NOT INDUCE VOMITING. 
IMMEDIATELY transport the victim to a hospital. 

OTHER: Since this chemical is a known or suspected carcinogen you should contact a physician for advice regarding the possible long term health effects and potential recommendation for medical monitoring. 
Recommendations from the physician will depend upon the specific compound, Benzene chemical, physical and toxicity properties, the exposure level, length of exposure, and the route of exposure. 

Fire Fighting of Benzene:
CAUTION: All these products have a very low flash point: Use of water spray when fighting fire may be inefficient. 
SMALL FIRE: Dry chemical, CO2, water spray or regular foam. 
LARGE FIRE: Water spray, fog or regular foam. 

Do not use straight streams. 
Move containers from fire area if you can do Benzene without risk. 
FIRE INVOLVING TANKS OR CAR/TRAILER LOADS: Fight fire from maximum distance or use unmanned hose holders or monitor nozzles. 

Cool containers with flooding quantities of water until well after fire is out. 
Withdraw immediately in case of rising sound from venting safety devices or discoloration of tank. 
ALWAYS stay away from tanks engulfed in fire. 
For massive fire, use unmanned hose holders or monitor nozzles; if this is impossible, withdraw from area and let fire burn. 

Cleanup Methods of Benzene:    
For spills on water, contain with booms or barriers, use surface acting agents to thicken spilled materials. 
Remove trapped materials with suction hoses.

A high-efficiency particulate arrestor (HEPA) or charcoal filters can be used to minimize amt of carcinogen in exhausted air ventilated safety cabinets, lab hoods, glove boxes or animal rooms.
Filter housing that is designed so that used filters can be transferred into plastic bag without contaminating maintenance staff is avail commercially. 
Filters should be placed in plastic bags immediately after removal.

The plastic bag should be sealed immediately.
The sealed bag should be labelled properly.
Waste liquids should be placed or collected in proper containers for disposal. 

The lid should be secured & the bottles properly labelled. 
Once filled, bottles should be placed in plastic bag, so that outer surface is not contaminated.
The plastic bag should also be sealed & labelled.
Broken glassware should be decontaminated by solvent extraction, by chemical destruction, or in specially designed incinerators. 

Eliminate all ignition sources. 
Stop or control the leak, if this can be done without undue risk. 
Use water spray to cool and disperse vapors, protect personnel, and dilute spills to form nonflammable mixtures. 
Absorb in noncombustible material for proper disposal. 
Control runoff and isolate discharged material for proper disposal.

Disposal Methods of Benzene:
Generators of waste (equal to or greater than 100 kg/mo) containing this contaminant, EPA hazardous waste number F005, U019, D018, must conform with USEPA regulations in storage, transportation, treatment and disposal of waste.

SRP: Wastewater from contaminant suppression, cleaning of protective clothing/equipment, or contaminated sites should be contained and evaluated for subject chemical or decomposition product concentrations. 
Concentrations shall be lower than applicable environmental discharge or disposal criteria. 
Alternatively, pretreatment and/or discharge to a permitted wastewater treatment facility is acceptable only after review by the governing authority and assurance that "pass through" violations will not occur. 
Due consideration shall be given to remediation worker exposure (inhalation, dermal and ingestion) as well as fate during treatment, transfer and disposal. 

Biodegradation, incineration: Benzene is biodegradable. 
Diluted aqueous soln, therefore, are drained into sewage treatment plants and decomposed there by anaerobic bacteria. 
Solvent mixtures and sludges of higher concn are burnt in special waste incinerators if a recovery process is uneconomical.

Identifiers of Benzene:
CAS Number: 71-43-2
ChEBI: CHEBI:16716 
ChEMBL: ChEMBL277500 
ChemSpider: 236 
ECHA InfoCard: 100.000.685 
EC Number: 200-753-7
KEGG: C01407 
PubChem CID: 241
RTECS number: CY1400000
UNII: J64922108F
CompTox Dashboard (EPA): DTXSID3039242 
InChI: InChI=1S/C6H6/c1-2-4-6-5-3-1/h1-6H 
Key: UHOVQNZJYSORNB-UHFFFAOYSA-N 
SMILES: c1ccccc1

Properties of Benzene:
Chemical formula: C6H6
Molar mass: 78.114 g·mol−1
Appearance: Colorless liquid
Odor: sweet aromatic
Density: 0.8765(20) g/cm3[2]
Melting point: 5.53 °C (41.95 °F; 278.68 K)
Boiling point: 80.1 °C (176.2 °F; 353.2 K)
Solubility in water: 
1.53 g/L (0 °C)
1.81 g/L (9 °C)
1.79 g/L (15 °C)
1.84 g/L (30 °C)
2.26 g/L (61 °C)
3.94 g/L (100 °C)
21.7 g/kg (200 °C, 6.5 MPa)
17.8 g/kg (200 °C, 40 MPa)
Solubility: Soluble in alcohol, CHCl3, CCl4, diethyl ether, acetone, acetic acid
Solubility in ethanediol: 
5.83 g/100 g (20 °C)
6.61 g/100 g (40 °C)
7.61 g/100 g (60 °C)
Solubility in ethanol: 
20 °C, solution in water:
1.2 mL/L (20% v/v)
Solubility in acetone: 
20 °C, solution in water:
7.69 mL/L (38.46% v/v)
49.4 mL/L (62.5% v/v)
Solubility in diethylene glycol: 52 g/100 g (20 °C)
log P: 2.13
Vapor pressure: 
12.7 kPa (25 °C)
24.4 kPa (40 °C)
181 kPa (100 °C)
Conjugate acid: Benzenium
UV-vis (λmax): 255 nm
Magnetic susceptibility (χ): −54.8·10−6 cm3/mol
Refractive index (nD): 
1.5011 (20 °C)
1.4948 (30 °C)
Viscosity: 
0.7528 cP (10 °C)
0.6076 cP (25 °C)
0.4965 cP (40 °C)
0.3075 cP (80 °C)

Molecular Weight: 78.11
XLogP3: 2.1
Hydrogen Bond Donor Count: 0    
Hydrogen Bond Acceptor Count: 0    
Rotatable Bond Count: 0    
Exact Mass: 78.0469501914    
Monoisotopic Mass: 78.0469501914
Topological Polar Surface Area: 0 Ų
Heavy Atom Count: 6    
Formal Charge: 0    
Complexity: 15.5    
Isotope Atom Count: 0    
Defined Atom Stereocenter Count: 0    
Undefined Atom Stereocenter Count: 0    
Defined Bond Stereocenter Count: 0    
Undefined Bond Stereocenter Count: 0    
Covalently-Bonded Unit Count: 1    
Compound Is Canonicalized: Yes

Boiling point: 79 °C (1013 hPa)
Density: 0.95 g/cm3 (20 °C)
Explosion limit: 1.4 - 8.0 %(V)
Flash point: -11 °C
Ignition temperature: 555 °C
Melting Point: 6.7 °C
Vapor pressure: 101 hPa (20 °C)
Viscosity kinematic: 0.78 mm2/s (20 °C)
Solubility: 1.8 g/l

Structure of Benzene:
Molecular shape: Trigonal planar
Dipole moment: 0 D

Thermochemistry of Benzene:
Heat capacity (C): 134.8 J/mol·K
Std molar entropy (So298): 173.26 J/mol·K
Std enthalpy of formation (ΔfH⦵298): 48.7 kJ/mol
Std enthalpy of combustion (ΔcH⦵298): -3267.6 kJ/mol

Related compounds of Benzene:    
Toluene
Borazine

Names of Benzene:

Translated names of Benzene:
benceno (es)
Benseen (et)
Bentseeni (fi)
benzeen (nl)
benzen (cs)
benzen (da)
benzen (hr)
benzen (no)
benzen (pl)
benzen (ro)
benzen (sl)
benzen (sv)
benzenas (lt)
benzene (it)
benzeno (pt)
Benzol (de)
benzol (hu)
benzols (lv)
benzène (fr)
benzén (sk)
βενζόλιο (el)
бензен (bg)

CAS names of Benzene:
Benzene

IUPAC names of Benzene:
BENZENE
Benzene
benzene
BENZENE
Benzene
benzene
Benzene-1,3-diamine
Benzol
Benzol
Petroleum benzene

Trade names of Benzene:
Annülene
Benceno
Benzen ropný
Benzene
benzene
Benzene (8CI, 9CI)
Benzene - E
Benzene SP
Benzol
Benzole
Coal naphtha
Cyclohexatriene
Petrobenzene
Petroleum benzene
Phene
Phenyl hydride
Pur Benzene
Pure benzene
Pyrobenzol
Pyrobenzole
Reinbenzol

Preferred IUPAC name of Benzene:
Benzene

Other names of Benzene:
Benzol (historic/German)
Cyclohexa-1,3,5-triene; 1,3,5-Cyclohexatriene
Annulene (not recommended)

Synonyms of Benzene:    
benzene
benzol
71-43-2
Cyclohexatriene
benzole
Pyrobenzole
Benzine
Benzen
Phenyl hydride
Pyrobenzol
Phene
Mineral naphtha
Coal naphtha
Bicarburet of hydrogen
Benzolene
Benzin
[6]Annulene
Motor benzol
Carbon oil
Benzeen
Benzolo
Fenzen
Nitration benzene
(6)Annulene
Benzol 90
Rcra waste number U019
NCI-C55276
NSC 67315
UN 1114
CHEBI:16716
UNII-J64922108F
CHEMBL277500
MFCD00003009
Hydrocarbons, C4-8
J64922108F
Benzeen 
Benzen
Fenzen
Benzolo 
BNZ
Benzine (Obs.)
Benzin (Obs.)
Caswell No. 077
Benzol diluent
Benzene 100 microg/mL in Methanol
Benzene, ACS reagent, >=99.0%
Benzene, pure
CCRIS 70
54682-86-9
HSDB 35
1,3,5-cyclohexatriene
EINECS 200-753-7
UN1114
EPA Pesticide Chemical Code 008801
Annulene
Benzinum
Benzolum
Aromatic alkane
Benzene (including benzene from gasoline)
p-benzene
benzene solution
benzene-
AI3-00808
1hyz
1swi
[6]-annulene
68956-52-5
Benzene ACS Grade
Benzene, for HPLC
{[6]Annulene}
Ph-H
Phenyl; Phenyl Radical
2z9g
4i7j
Benzene + aniline combo
DSSTox_CID_135
Benzene, labeled with carbon-14 and tritium
WLN: RH
Epitope ID:116867
Benzene, purification grade
EC 200-753-7
Benzene, analytical standard
DSSTox_RID_79433
Benzene, LR, >=99%
DSSTox_GSID_39242
ghl.PD_Mitscher_leg0.503
26181-88-4
Benzene, anhydrous, 99.8%
Benzene, AR, >=99.5%
DTXSID3039242
3,4-DNH
1l83
220l
223l
Benzene 10 microg/mL in Methanol
ZINC967532
trans-N-Methylphenylcyclopropylamine
ACT02832
BCP26158
Benzene, for HPLC, >=99.8%
Benzene, for HPLC, >=99.9%
NSC67315
Tox21_202487
1,3-Cyclohexadiene-5,6-diylradical
BDBM50167939
BM 613
NSC-67315
STL264205
Benzene 5000 microg/mL in Methanol
Benzene, purum, >=99.0% (GC)
AKOS008967253
MCULE-4899719484
Benzene, SAJ first grade, >=99.0%
CAS-71-43-2
Benzene [UN1114] [Flammable liquid]
Benzene, JIS special grade, >=99.5%
erythro-Phenyl-2-piperidyl-carbinol,(-)
NCGC00090744-01
NCGC00090744-02
NCGC00163890-01
NCGC00163890-02
NCGC00260036-01
trans-N, N-Dimethylphenylcyclopropylamine
Cc-34,(+/-)
RNG
DS-002542
B0020
FT-0622636
FT-0622637
FT-0622667
FT-0627856
FT-0657604
Q0038
Q2270
Benzene, ACS spectrophotometric grade, >=99%
C01407
Benzene, ReagentPlus(R), thiophene free, >=99%
Benzene, puriss. p.a., Reag. Ph. Eur., >=99.7%
Q26841227
Z57120059
Benzene, for residue analysis, suitable for 5000 per JIS
Benzene, suitable for 300 per JIS, >=99.5%, for residue analysis
Benzene, Pharmaceutical Secondary Standard; Certified Reference Material
Benzene, suitable for 1000 per JIS, >=99.5%, for residue analysis
Benzene, puriss., absolute, over molecular sieve (H2O <=0.005%), >=99.5% (GC)
200-753-7 
71-43-2 
benzeen
Benzen
Benzen 
Benzen 
Benzene
Benzène 
Benzeno 
Benzine
Benzol 
Benzolo 
MFCD00003009 
MFCD00198116 
Βενζόλιο
Бензол
ベンゼン
Annulene
Benceno
Benzinum
Benzolum
Bnz
(1,2,3,5-2H4)Benzene 
(2H)Benzene
(6)annulene
1,2,3-Trideuteriobenzene
1,2,4-Trideuteriobenzene
1,2-Dideuteriobenzene
1,4-Dideuteriobenzene
14941-52-7 
14941-53-8
1684-46-4
19467-24-4 
200-753-7MFCD00003009
462-80-6 
BENZENE (1,3,5-D3)
Benzene, anhydrous, ACS
Benzene-1,2,4,5-d4
Benzene-1,2,4-d3
Benzene-1,2-d2
Benzene-1,3-d2
Benzene-1,4-d2
Benzene-d2-1
Benzin
benzole
Benzolene
Phene
phenyl hydride
Pyrobenzol
Pyrobenzole
WLN: RH