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Benzene

Benzene
Benzene structure
CAS No.
71-43-2
Chemical Name:
Benzene
Synonyms
PHENE;BENZOL;Benzen;Fenzen;BENZENE;Benzeen;Benzole;Benzolo;Annulene;BenzeneI
CBNumber:
CB6854153
Molecular Formula:
C6H6
Formula Weight:
78.11
MOL File:
71-43-2.mol

Benzene Properties

Melting point:
5.5 °C(lit.)
Boiling point:
80 °C(lit.)
Density 
0.874 g/mL at 25 °C(lit.)
vapor density 
2.77 (vs air)
vapor pressure 
166 mm Hg ( 37.7 °C)
refractive index 
n20/D 1.501(lit.)
Flash point:
12 °F
storage temp. 
0-6°C
solubility 
Miscible with alcohol, chloroform, dichloromethane, diethyl ether, acetone and acetic acid.
pka
43(at 25℃)
form 
Liquid
color 
APHA: ≤10
Relative polarity
0.111
Odor
Paint-thinner-like odor detectable at 12 ppm
explosive limit
1.4-8.0%(V)
Water Solubility 
0.18 g/100 mL
λmax
λ: 280 nm Amax: 1.0
λ: 290 nm Amax: 0.15
λ: 300 nm Amax: 0.06
λ: 330 nm Amax: 0.02
λ: 350-400 nm Amax: 0.01
Merck 
14,1066
BRN 
969212
Exposure limits
TLV-TWA 10 ppm (~32 mg/m3) (ACGIH and OSHA); ceiling 25 ppm (~80 mg/m3) (OSHA and MSHA); peak 50 ppm (~160 mg/m3)/10 min/8 h (OSHA); carcinogenicity: Suspected Human Carcinogen (ACGIH), Human Sufficient Evidence (IARC).
Stability:
Stable. Substances to be avoided include strong oxidizing agents, sulfuric acid, nitric acid, halogens. Highly flammable.
CAS DataBase Reference
71-43-2(CAS DataBase Reference)
NIST Chemistry Reference
Benzene(71-43-2)
EPA Substance Registry System
Benzene(71-43-2)
SAFETY
  • Risk and Safety Statements
  • Hazard and Precautionary Statements (GHS)
  • NFPA
Hazard Codes  F,T
Risk Statements  45-46-11-36/38-48/23/24/25-65-39/23/24/25-23/24/25
Safety Statements  53-45-36/37-16-7
RIDADR  UN 1114 3/PG 2
WGK Germany  3
RTECS  CY1400000
3-10
Autoignition Temperature 560 °C
TSCA  Yes
HS Code  2902 20 00
HazardClass  3
PackingGroup  II
Hazardous Substances Data 71-43-2(Hazardous Substances Data)
Toxicity LD50 orally in young adult rats: 3.8 ml/kg (Kimura)
Symbol(GHS):
Signal word: Danger
Hazard statements:
Code Hazard statements Hazard class Category Signal word Pictogram P-Codes
H225 Highly Flammable liquid and vapour Flammable liquids Category 2 Danger P210,P233, P240, P241, P242, P243,P280, P303+ P361+P353, P370+P378,P403+P235, P501
H302 Harmful if swallowed Acute toxicity,oral Category 4 Warning P264, P270, P301+P312, P330, P501
H304 May be fatal if swallowed and enters airways Aspiration hazard Category 1 Danger
H315 Causes skin irritation Skin corrosion/irritation Category 2 Warning P264, P280, P302+P352, P321,P332+P313, P362
H319 Causes serious eye irritation Serious eye damage/eye irritation Category 2A Warning P264, P280, P305+P351+P338,P337+P313P
H336 May cause drowsiness or dizziness Specific target organ toxicity,single exposure; Narcotic effects Category 3 Warning P261, P271, P304+P340, P312,P403+P233, P405, P501
H340 May cause genetic defects Germ cell mutagenicity Category 1A, 1B Danger
H350 May cause cancer Carcinogenicity Category 1A, 1B Danger
H361 Suspected of damaging fertility or the unborn child Reproductive toxicity Category 2 Warning P201, P202, P281, P308+P313, P405,P501
H370 Causes damage to organs Specific target organ toxicity, single exposure Category 1 Danger P260, P264, P270, P307+P311, P321,P405, P501
H372 Causes damage to organs through prolonged or repeated exposure Specific target organ toxicity, repeated exposure Category 1 Danger P260, P264, P270, P314, P501
H373 May cause damage to organs through prolonged or repeated exposure Specific target organ toxicity, repeated exposure Category 2 Warning P260, P314, P501
H411 Toxic to aquatic life with long lasting effects Hazardous to the aquatic environment, long-term hazard Category 2
H412 Harmful to aquatic life with long lasting effects Hazardous to the aquatic environment, long-term hazard Category 3 P273, P501
Precautionary statements:
P201 Obtain special instructions before use.
P202 Do not handle until all safety precautions have been read and understood.
P210 Keep away from heat/sparks/open flames/hot surfaces. — No smoking.
P233 Keep container tightly closed.
P240 Ground/bond container and receiving equipment.
P260 Do not breathe dust/fume/gas/mist/vapours/spray.
P264 Wash hands thoroughly after handling.
P264 Wash skin thouroughly after handling.
P270 Do not eat, drink or smoke when using this product.
P271 Use only outdoors or in a well-ventilated area.
P273 Avoid release to the environment.
P280 Wear protective gloves/protective clothing/eye protection/face protection.
P311 Call a POISON CENTER or doctor/physician.
P331 Do NOT induce vomiting.
P391 Collect spillage. Hazardous to the aquatic environment
P301+P310 IF SWALLOWED: Immediately call a POISON CENTER or doctor/physician.
P303+P361+P353 IF ON SKIN (or hair): Remove/Take off Immediately all contaminated clothing. Rinse SKIN with water/shower.
P305+P351+P338 IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continuerinsing.
P307+P311 IF exposed: call a POISON CENTER or doctor/physician.
P308+P313 IF exposed or concerned: Get medical advice/attention.
P370+P378 In case of fire: Use … for extinction.
P405 Store locked up.
P403+P235 Store in a well-ventilated place. Keep cool.

NFPA 704

Diamond Hazard Value Description
3
2 0
Health   2 Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury (e.g. diethyl ether, ammonium phosphate, iodine)
Flammability   3 Liquids and solids (including finely divided suspended solids) that can be ignited under almost all ambient temperature conditions . Liquids having a flash point below 22.8 °C (73 °F) and having a boiling point at or above 37.8 °C (100 °F) or having a flash point between 22.8 and 37.8 °C (73 and 100 °F). (e.g. gasoline, acetone)
Instability   0 Normally stable, even under fire exposure conditions, and is not reactive with water (e.g. helium,N2)
Special  

(NFPA, 2010)

Benzene price More Price(32)

Manufacturer Product number Product description CAS number Packaging Price Updated Buy
Sigma-Aldrich 12540 Benzene analytical standard 71-43-2 5ml-f $47.4 2018-11-13 Buy
Sigma-Aldrich 12540 Benzene analytical standard 71-43-2 50ml-f $330 2018-11-13 Buy
TCI Chemical B0020 Benzene [for Spectrophotometry] >99.5%(GC) 71-43-2 500mL $46 2018-11-22 Buy
Sigma-Aldrich 401765 Benzene anhydrous, 99.8% 71-43-2 100ml $46.9 2018-11-13 Buy
Sigma-Aldrich CRM48617 Benzene solution certified reference material, TraceCERT , 200 μg/mL in methanol 71-43-2 crm48617 $16 2018-11-23 Buy

Benzene Chemical Properties,Uses,Production

Description

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 its structure, benzene is a very stable organic compound. It 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).

Chemical Properties

Benzene,C6H6, also known as benzol, phenyl hydride, phene, cyclohexatriene and coal naptha,is a colorless,flammable liquid. It is an aromatic hydrocarbon that boils at 80.1 DC. It is used as a solvent and an intermediate in manufacturing organic compounds such as styrene and phenol.

Chemical Properties

Benzene is a colorless, flammable liquid with a pleasant odor. It 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. It is essential in the manufacture of detergents, pesticides, solvents, and paint removers. It is present in fuels such as gasoline up to the level of 5%.

Chemical Properties

Benzene is a clear, volatile, colorless, highly flammable liquid with a pleasant, characteristic odor.

History

Benzene was discovered in 1825 by Michael Faraday (1791–1867), who identified it in a liquid residue from heated whale oil. Faraday called the compound bicarburet of hydrogen, and its name was later changed to benzin by Eilhardt Mitscherlich (1794–1863), who isolated the compound from benzoin (C14H12O2).

Uses

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

Uses

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 it 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. It 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.

Uses

Benzene occurs in coal and coal-tar distillationproducts and in petroleum products suchas gasoline. It is also found in the gases andleachates of landfills for industrial wastes,construction debris, and landscaping refuse(Oak Ridge National Laboratory 1989). Traceamounts of benzene, toluene, xylenes, andother volatile organics have been found inthe soils and groundwaters near many sanitarylandfills (U.S. EPA 1989a,b). Kramer(1989) 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 (Hoffmann et al. 1989); thus the riskof its 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.

Uses

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.

Definition

ChEBI: A six-carbon aromatic annulene in which each carbon atom donates one of its two 2p electrons into a delocalised pi system. A toxic, flammable liquid byproduct of coal distillation, it is used as an industrial solvent. Benzene is a carcinogen that also damages bone marrow and the central nervous system.

Definition

A colorless liquid hydrocarbon with a characteristic odor. Benzene is a highly toxic compound and continued inhalation of the vapor is harmful. It was originally isolated from coal tar and for many years this was the principal source of the compound.Contemporary manufacture is from hexane; petroleum vapor is passed over platinum at 500°C and at 10 atmospheres pressure: C6H14 → C6H6 + 4H2 Benzene is the simplest aromatic hydrocarbon. It shows characteristic electrophilic substitution reactions, which are difficult to explain assuming a simple unsaturated structure (such as Kekulé’s (1865) or Dewar’s (1867) formulae). This anomolous behavior can now be explained by assuming that the six pi electrons are delocalized and that benzene is, therefore, a resonance hybrid. It consists of two Kekulé structures and three Dewar structures, the former contributing 80% and the latter 20% to the hybrid. Benzene is usually represented by either a Kekulé structure or a hexagon containing a circle (which denotes the delocalized electrons).

Definition

benzene: A colourless liquid hydrocarbon,C6H6; r.d. 0.88; m.p. 5.5°C;b.p. 80.1°C. It is now made fromgasoline from petroleum by catalyticreforming (formerly obtained fromcoal tar). Benzene is the archetypalaromatic compound. It has an un-saturated molecule, yet will not readilyundergo addition reactions. Onthe other hand, it does undergo substitutionreactions in which hydrogenatoms are replaced by otheratoms or groups. This behaviour occursbecause of delocalization of pelectronsover the benzene ring, andall the C–C bonds in benzene areequivalent and intermediate inlength between single and doublebonds. It can be regarded as a resonancehybrid of Kekulé and Dewarstructures. In formulaeit can be represented by a hexagonwith a ring inside it.

Production Methods

Today benzene, which is a natural component of petroleum, is obtained from petroleum by several processes. Toluene hydrodealkylation involves mixing toluene (C6H5CH3) and hydrogen in the presence of catalysts and temperatures of approximately 500°C and pressures of about 50 atmospheres to produce benzene and methane: C6H5CH3 + H2 → C6H6 + CH4. Hydrodealkylation strips the methyl group from toluene to produce benzene. Toluene disproportionation involves combining toluene so that the methyl groups bond to one aromatic ring, producing benzene and xylene. Benzene can also be obtained from petroleum reforming in which temperature, pressure, and catalysts are used to convert petroleum components to benzene, which can then be extracted using solvents and distillation processes. Another source of benzene is pyrolysis gasoline or pygas.

General Description

A clear colorless liquid with a petroleum-like odor. Flash point less than 0°F. Less dense than water and slightly soluble in water. Hence floats on water. Vapors are heavier than air.

Air & Water Reactions

Highly flammable. Slightly soluble in water.

Reactivity Profile

Benzene reacts vigorously with allyl chloride or other alkyl halides even at minus 70°C in the presence of ethyl aluminum dichloride or ethyl aluminum sesquichloride. Explosions have been reported [NFPA 491M 1991]. Ignites in contact with powdered chromic anhydride [Mellor 11:235 1946-47]. Incompatible with oxidizing agents such as nitric acid. Mixtures with bromine trifluoride, bromine pentafluoride, iodine pentafluoride, iodine heptafluoride and other interhalogens can ignite upon heating [Bretherick 5th ed. 1995]. Benzene and cyanogen halides yield HCl as a byproduct (Hagedorn, F. H. Gelbke, and Federal Republic of Germany. 2002. Nitriles. In Ullman Encyclopedia of Industrial Chemistry. Wiley-VCH Verlag GmbH & Co. KGaA.). The reaction of Benzene and trichloroacetonitrile evolves toxic chloroform and HCl gasses. (Hagedorn, F., H.-P. Gelbke, and Federal Republic of Germany. 2002. Nitriles. In Ullman Encyclopedia of Industrial Chemistry. Wiley-VCH Verlag GmbH & Co. KGaA.).

Hazard

A confirmed carcinogen. Highly toxic. Flammable, dangerous fire risk. Explosive limits in air 1.5 to 8% by volume.

Health Hazard

The acute toxicity of benzene is low. Inhalation of benzene can cause dizziness, euphoria, giddiness, headache, nausea, drowsiness, and weakness. Benzene can cause moderate irritation to skin and severe irritation to eyes and mucous membranes. Benzene readily penetrates the skin to cause the same toxic effects as inhalation or ingestion. The chronic toxicity of benzene is significant. Exposure to benzene affects the blood and blood-forming organs such as the bone marrow, causing irreversible injury; blood disorders including anemia and leukemia may result. The symptoms of chronic benzene exposure may include fatigue, nervousness, irritability, blurred vision, and labored breathing. Benzene is regulated by OSHA as a carcinogen (Standard 1910.1028) and is listed in IARC Group 1 ("carcinogenic to humans"). This substance is classified as a "select carcinogen" under the criteria of the OSHA Laboratory Standard.

Health Hazard

Dizziness, excitation, pallor, followed by flushing, weakness, headache, breathlessness, chest constriction, nausea, and vomiting. Coma and possible death.

Health Hazard

Exposure to low concentrations of benzene vapor or liquid causes dizziness, lightheadedness, headache, loss of appetite, stomach upset, and irritation to the nose and throat. Prolonged exposure to high concentrations of benzene leads to functional irregularities in the heart beat and in severe cases to death. Benzene is a known carcinogen to humans. It causes leukemia and blood disorders such as aplastic anemia. The major types of leukemia related to benzene exposure are (i) acute myelogenous leukemia (AML); (ii) acute lymphocytic leukemia (ALL); (iii) chronic myelogenous leukemia, also called chronic myeloid leukemia (CML); (iv) chronic lymphocytic leukemia (CLL), and hairy cell leukemia (HCL). Occupational exposure to benzene is frequent, such as in road-tanker drivers and Chinese glueand shoe-making factory workers. Exposure to benzene has been linked with the development of rarer forms of leukemia, such as AML and ALL. It has also been linked to lymphoma and rare blood diseases

Health Hazard

Benzene is an acute as well as a chronictoxicant. The acute toxic effects from inhalation,ingestion, and skin contact are low tomoderate. The symptoms in humans are hallucination,distorted perception, euphoria, somnolence,nausea, vomiting, and headache. Thenarcotic effects in humans may occur frominhaling benzene in air at a concentrationof 200 ppm. High concentrations may cause convulsions. A 5- to 10-minute exposure to2% benzene in air may be fatal. Death mayresult from respiratory failure.
Benzene is an irritant to the eyes, nose,and respiratory tract. The chronic poisoningfrom benzene is much more severe than itsacute toxicity. The target organs to acuteand chronic poisoning are the blood, bonemarrow, central nervous system, respiratorysystem, eyes, and skin. Heavy occupationalexposures to benzene can cause bone marrowdepression and anemia, and in rare cases,leukemia. Leukemia may develop severalyears after the exposure ceases. Deaths fromleukemia, attributed to occupational exposureto benzene in the workplace, which may beon the order of 200 ppm concentration, havebeen documented (ACGIH 1986). Benzene islisted as a suspected human carcinogen. Inaddition to leukemia, malignant lymphoma,and myeloma, lung cancer in subjects exposedto benzene has been reported (Aksoy 1989).
Absorption of liquid benzene through theskin may be harmful. The main eliminationpathway for benzene absorbed throughinhalation or skin contact is metabolism.Hydroxyl radicals play an important role inthe process of metabolism. Khan and coworkers(1990) have reported the formationof formaldehyde and degradation of deoxyribose,suggesting the generation of hydroxylradicals during benzene toxicity to the bonemarrow S-9 fraction. The hydroxyl radicalsreact with benzene to form phenols and dihydroxyphenols,which are excreted rapidly inurine. About one-third of the retained benzeneis excreted as phenols in the urine. Theremaining two-thirds may be further degradedand attached onto the tissue or oxidized andexhaled as CO2.
Kalf and associates (1989) have investigatedthe action of prostaglandin H synthasein benzene toxicity and preventionof benzene-induced myelo- and genotoxicityby nonsteroidal anti-inflammatory drugs(NSAIDs). Indomethacin, a prostaglandin Hsynthase inhibitor prevented the dose- dependentbone marrow depression and increase in marrow prostaglandin E level in mice intravenouslydosed with benzene. Indomethacin,aspirin, or meclofenamate prevented thedecrease in cellularity and increase in micronucleatedpolychromatic erythrocytes in peripheralblood, caused by intravenous injectionof benzene (100–1000 mg/kg) in mice.

Fire Hazard

Flash Point (°F): 12 ℃; Flammable Limits in Air (%): 1.3-7.9; Fire Extinguishing Agents: Dry chemical, foam and carbon dioxide; Fire Extinguishing Agents Not To Be Used: Water may be ineffective; Special Hazards of Combustion Products: Not pertinent; Behavior in Fire: Vapor is heavier than air and can travel considerable distance to source of ignition and flash back; Ignition Temperature (°F): 1,097; Electrical Hazard: Class I, Group D; Burning Rate: 6.0 mm/min.

Fire Hazard

Benzene is a highly flammable liquid (NFPA rating = 3), and its vapors may travel a considerable distance to a source of ignition and "flash back." Vapor-air mixtures are explosive above the flash point. Carbon dioxide and dry chemical extinguishers should be used to fight benzene fires.

Fire Hazard

Behavior in Fire: Vapor is heavier than air and may travel considerable distance to a source of ignition and flash back.

Flammability and Explosibility

Benzene is a highly flammable liquid (NFPA rating = 3), and its vapors may travel a considerable distance to a source of ignition and "flash back." Vapor-air mixtures are explosive above the flash point. Carbon dioxide and dry chemical extinguishers should be used to fight benzene fires.

Chemical Reactivity

Reactivity with Water No reaction; Reactivity with Common Materials: No reactions; Stability During Transport: Stable; Neutralizing Agents for Acids and Caustics: Not pertinent; Polymerization: Not pertinent; Inhibitor of Polymerization: Not pertinent.

Industrial uses

A colorless, liquid, inflammable, aromatichydrocarbon which boils at 80.1°C and freezesat 5.4 to 5.5°C. Benzene is used as a solventand particularly in Europe as a constituent ofmotor fuel. In the United States the largest usesof benzene are for the manufacture of styreneand phenol. Other important outlets are in theproduction of chlorinated benzenes (used inDDT and moth flakes), and benzene hexachloride,an insecticide.

Safety Profile

Confirmed human carcinogen producing myeloid leukemia, Hodgkin's dsease, and lymphomas by inhalation. Experimental carcinogenic, neoplastigenic, and tumorigenic data. A human poison by inhalation. An experimental poison by skin contact, intraperitoneal, intravenous, and possibly other routes. Moderately toxic by ingestion and subcutaneous routes. A severe eye and moderate sktn irritant. Human systemic effects by inhalation and ingestion: blood changes, increased body temperature. Experimental teratogenic and reproductive effects. Human mutation data reported. A narcotic. In industry, inhalation is the primary route of chronic benzene poisoning. Poisoning by skin contact has been reported. Recent (1 987) research indicates that effects are seen at less than 1 ppm. Exposures needed to be reduced to 0.1 ppm before no toxic effects were observed. Elimination is chiefly through the lungs. A common air contaminant. heat or flame. Explodes on contact with diborane, bromine pentafluoride, permanganic acid, peroxornonosulfuric acid, and peroxodisulfuric acid. Forms sensitive, explosive mixtures with iodine pentafluoride, silver perchlorate, nitryl perchlorate, nitric acid, liquid oxygen, ozone, and arsenic pentafluoride + potassium methoxide (explodes above 30℃). Ignites on contact with sodium peroxide + water, dioxygenyl tetrafluoroborate, iodine heptafluoride, and dioxygen difluoride. Vigorous or incandescent reaction with hydrogen + Raney nickel (above 210℃), uranium hexafluoride, and bromine trifluoride. Can react vigorously with oxidzing materials, such as Cla, Cr03,02, NClO4,03, perchlorates, (ACl3 + FClO4), (H2SO4 + permanganates), K2O2(, NH4OH + acetic acid), Na2O2. Moderate explosion hazard A dangerous fire hazard when when exposed to heat or flame. Use with adequate venulation. To fight fire, use foam, CO2, dry chemical. Poisoning occurs most commonly via inhalation of the vapor, although benzene can penetrate the skin and cause poisoning. Locally, benzene has a comparatively strong irritating effect, producing erythema and burning, and, in more severe cases, edema and even blistering. Exposure to high concentrations of the vapor (3000 ppm or higher) may result from failure of equipment or spillage. Such exposure, while rare in industry, may cause acute poisoning, characterized by the narcotic action of benzene on the central nervous system. The anesthetic action of benzene is sirmlar to that of other anesthetic gases, consisting of a preluninary stage of excitation followed by depression and, if exposure is continued, death through respiratory failure. The chronic, rather than the acute, form of benzene poisoning is important in industry. It is a recognized leukemogen. There is no specific blood picture occurring in cases of chronic benzol poisoning. The bone marrow may be hypoplastic, normal, or hyperplastic, the changes reflected in the peripheral blood. Anemia, leucopenia, macrocytosis, reticulocytosis, thrombocytopenia, hgh color index, and prolonged bleeding time may be present. Cases of myeloid leukemia have been reported. For the worker, repeated blood examinations are necessary, inclulng hemoglobin determinations, white and red cell counts, and dlfferential smears. Where a worker shows a progressive drop in either red or white cells, or where the white count remains below <5000/mm3 or the red count remains below 4.0 d o n / m m 3 , on two successive monthly examinations, the worker should be immediately removed from benzene exposure. Elimination is chefly through the lungs, when fresh air is breathed. The portion that is absorbed is oxidized, and the oxidation products are combined with sulfuric and glycuronic acids and eliminated in the urine. This may be used as a lagnostic sign. Benzene has a definite cumulative action, and exposure to a relatively hgh concentration is not serious from the point of view of causing damage to the blood-forming system, provided the exposure is not repeated. In acute poisoning, the worker becomes confused and dizzy, complains of tightening of the leg muscles and of pressure over the forehead, then passes into a stage of excitement. If allowed to remain exposed, he quickly becomes stupefied and lapses into coma. In nonfatal cases, recovery is usually complete with no permanent disabhty. In chronic poisoning the onset is slow, with the symptoms vague; fatigue, headache, dizziness, nausea and loss of appetite, loss of weight, and weakness are common complaints in early cases. Later, pallor, nosebleeds, bleeding gums, menorrhagia, petechiae, and purpura may develop. There is great inlvidual variation in the signs and symptoms of chronic benzene poisoning.

Potential Exposure

Benzene is used as a constituent in motor fuels; as a solvent for fats; inks, oils, paints, plastics, and rubber, in the extraction of oils from seeds and nuts; in photogravure printing. It is also used as a chemical intermediate. By alkylation, chlorination, nitration, and sulfonation, chemicals, such as styrene, phenols, and malefic anhydride are produced. Benzene is also used in the manufacture of detergents, explosives, pharmaceuticals; in the manufacture of cyclohexane and ethylbenzene; and dye-stuffs. Increased concern for benzene as a significant environmental pollutant arises from public exposure to the presence of benzene in gasoline and the increased content in gasoline due to requirements for unleaded fuels for automobiles equipped with catalytic exhaust converters.

First aid

If this chemical gets into the eyes, remove any contact lenses at once and irrigate immediately for at least 15 minutes, occasionally lifting upper and lower lids. Seek medical attention immediately. If this chemical contacts the skin, remove contaminated clothing and wash immediately with soap and water. Seek medical attention immediately. If this chemical has been inhaled, remove from exposure, begin rescue breathing (using universal precautions, including resuscitation mask) if breathing has stopped and CPR if heart action has stopped. Transfer promptly to a medical facility. When this chemical has been swallowed, rinse mouth, get medical attention. Do not induce vomiting.

storage

work with benzene should be conducted in a fume hood to prevent exposure by inhalation, and splash goggles and impermeable gloves should be worn at all times to prevent eye and skin contact. Benzene should be used only in areas free of ignition sources.

Shipping

UN1114 Benzene, Hazard Class: 3; Labels: 3— Flammable liquid

Purification Methods

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.) [Schwartz & Parker Anal Chem 33 1396 1961.] *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. [Holmes & Beeman Ind Eng Chem 26 172 1934.] 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. (This low-boiling distillation leaves any non-azeotrope-forming impurities behind.) 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. [Peebles et al. J Am Chem Soc 82 2780 1960.] *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. [Beilstein 5 H 175, 5 I 95, 5 II 119, 5 III 469.] 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.

Incompatibilities

Incompatible with oxidizers (chlorates, nitrates, peroxides, permanganates, perchlorates, chlorine, bromine, fluorine, etc.); contact may cause fires or explosions. Keep away from alkaline materials, strong bases, strong acids, oxoacids, epoxides, many fluorides and perchlorates, nitric acid.

Waste Disposal

Dissolve or mix the material with a combustible solvent and burn in a chemical incinerator equipped with an afterburner and scrubber. All federal, state, and local environmental regulations must be observed. Dilution with alcohol or acetone to minimize smoke is recommended. Bacterial degradation is also possible.

Benzene Preparation Products And Raw materials

Raw materials

Preparation Products


Benzene Suppliers

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Benzene Spectrum


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