Ethylbenzene

Chemical Properties

Ethylbenzene is a colorless, volatile, highly flammable liquid having a gasoline-like odor. Less dense than water and insoluble in water. Hence floats on water. Vapors are heavier than air. Ethylbenzene is a member of the family of chemicals called alkylbenzenes. These are aromatic compounds containing a benzene substituted at one or more positions. It is found in natural products such as coal tar and petroleum and is also found in manufactured products such as inks, insecticides, and paints. Ethylbenzene is used primarily to make another chemical, styrene. Other uses include as a solvent, in fuels, and to make other chemicals. It is manufactured commercially from benzene and ethylene.

Uses

Ethylbenzene is used primarily to make styrene monomer (SM) [1]counting greater than 99%. At less than 1%, it is used as a solvent[2], in fuels[3], or as a starting material[4] to make other chemicals.
[1] Ethylbenzene is mainly used in the manufacture of styrene, which is the raw material of producing styrene-based polymers that are widely used in products such as packaging, kitchen utensils and electronic equipment housing.2
[2] Solvents in a variety of Industries

[3] Ethyl benzene (C6H5C2H5) is the smallest aromatic hydrocarbon molecule with C C key chain structure, and the C C single bond adjacent to benzene ring is far more weaker than those of other chemical bonds thus it is the most easily broken key. It is the characteristic structure of single chain alternative fuels such as n-propylbenzene n-butylbenzene in diesel oil and aviation kerosene.
[4] Ethylbenzene may be used as a starting material to synthesize: (1) Acetophenone via selection oxidation in the presence of potassium dichromate supported on neutral alumina and using air as the oxidizing agent. (2) Styrene via dehydrogenation over nanodiamonds in an oxygen-lean environment.

Preparation

Preparation of Ethylbenzene from Acetophenone.
Principle: The carbonyl function can be completely reduced to methylene under acidic, basic or neutral conditions. Amongst these the most common methods are Clemmensen's reduction, Wolf Kishner reduction and Mozingo reduction. The reduction of carbonyl group using hydrazine in basic medium using KOH is called as Wolf-Kishner reduction.
Reaction:

Procedure: Place 0.5 ml acetophenone, 5.0 ml ethylene glycol and 1.0 ml of 90% hydrazine hydrate solution and 1.1 g KOH pellets in a round bottom flask fitted with water condenser. Warm the reaction mixture of boiling water bath till KOH dissolves and then reflux for 1 h on wire gauze. Distill using Hickmann head till the temperature is 175oC. Keep the distillate and again reflux for 2 h. Cool this and extract twice with 10 ml ether. Combine the ether extracts with the distillate removed earlier and dry over sodium sulphate, decant and evaporate the ether.

Ethylbenzene Production

Ethylbenzene is currently used on a large scale industrially for the production of styrene monomer. Ethylbenzene may be produced by a number of chemical processes but one process which has achieved a significant degree of commercial success is the alkylation of benzene with ethylene in the presence of a solid, acidic zeolite catalyst.
A preferred catalyst includes the synthetic zeolite identified in this specification as MCM-22.In the production of ethylbenzene by this process; ethylene is used as the alkylating agent and is reacted with benzene in the presence of the catalyst at certain temperatures.

Production of ethylbenzene involves the liquid-phase reaction of ethylene with benzene
C2H4 + C6H6 C8H10
Undesirable reaction occurred by the formation of Di-ethyl benzene from reaction of ethylbenzene with ethylene.
C8H10 + C2H4 C10H14
A third reaction also occurs, in which Di-ethyl benzene reacts with benzene to form ethylbenzene.
C10H14 + C6H6 2C8H10

Health Effects

Ethylbenzene has low acute and chronic toxicity for humans. It is toxic to the central nervous system and is an irritant of mucous membranes and the eyes. Ethylbenzene exposure might be associated with hearing loss, neurobehavioral function impairment, and imbalance of neurotransmitters, and it is an inducer of liver microsomal enzymes. The toxicity is stronger along with the rise of exposure volume, see the table below:
 
Carcinogenicity
CLASSIFICATION: D; not classifiable as to human carcinogenicity.
BASIS FOR CLASSIFICATION: nonclassifiable due to lack of animal bioassays and human studies.

Description

Ethylbenzene is a colorless liquid with a pungent aromaticodor. The odor threshold is 0.092- 0.60 ppm.Molecular weight = 106.18; Specific gravity (H2O:1) =0.87; Boiling point = 136℃; Freezing/Meltingpoint = - 95℃; Vapor pressure = 7% mmHg at 20℃;Flash point = 12.8℃; Autoignition temperature = 432℃.Explosive limits: LEL = 0.8%; UEL = 6.7%. HazardIdentification (based on NFPA-704 M Rating System):Health 2, Flammability 3, Reactivity 0. Practically insolublein water; solubility = 0.7%.

Chemical Properties

Ethylbenzene is a colorless liquid. Pungent aromatic odor. The Odor Threshold is 0.092
0.60 ppm

Physical properties

Clear, colorless liquid with a sweet, gasoline-like odor. At 40 °C, the average odor threshold concentration and the lowest concentration at which an odor was detected were 550 and 150 μg/L, respectively. Similarly, at 25 °C, the average taste threshold concentration and the lowest concentration at which a taste was detected were 780 and 390 μg/L, respectively (Young et al., 1996). The average least detectable odor threshold concentrations in water at 60 °C and in air at 40 °C were 2.4 and 72 μg/L, respectively (Alexander et al., 1982). Cometto-Muiz and Cain (1994) reported an average nasal pungency threshold concentration of 10,100 ppm_v.

Occurrence

Has apparently not been reported to occur in nature.

Uses

Primarily used in the production of styrene; also used as an industrial solvent, as a constituent of asphalt and naptha, and as an antiknock agent in aviation and motor fuels

Uses

Ethylbenzene is used as a solvent and as anintermediate to produce styrene monomer.

Uses

Anesthetic.
Ethylbenzene is almost exclusively (> 99%) used as an intermediate for the production of styrene monomer. Less than 1 % of the ethylbenzene produced is used as a paint solvent or as an intermediate for the production of diethylbenzene and acetophenone (IARC 2000).
Ethylbenzene is a constituent (15-20%) of commercial xylene (“mixed xylenes”), and hence used as a component of solvents, as a diluent in paints and lacquers, and as a solvent in the rubber and chemical manufacturing industries (WHO 1996).
Ethylbenzene has been added to motor and aviation fuels because of its anti-knock properties. Estimates of ethylbenzene in gasoline have ranged from <1-2.7%. (IARC 2000).

Preparation

By Friedel-Crafts reaction on benzene, ethylbromide and aluminium chloride (Arc tander, 1969).
Ethylbenzene is manufactured by alkylation from benzene and ethylene.

Production Methods

Ethylbenzene is produced by alkylation of benzene with ethylene, except for a very small fraction that is recovered from mixed C8 aromatics by superfractionation. The reaction takes place on acidic catalysts and can be carried out either in the liquid or vapor phase.

Definition

ethylbenzene: A colourless flammableliquid, C₆H₅C₂H₅; r.d. 0.867;m.p. –95°C; b.p. 136°C. It is madefrom ethene and ethybenzene by aFriedel–Crafts reaction and is usedin making phenylethene (for polystyrene).

Synthesis Reference(s)

Chemistry Letters, 12, p. 909, 1983
Journal of the American Chemical Society, 85, p. 2768, 1963 DOI: 10.1021/ja00901a021
Tetrahedron Letters, 11, p. 4401, 1970

General Description

A clear colorless liquid. Flash point 59°F. Less dense than water (at 7.2 lb / gal) and insoluble in water. Hence floats on water. Vapors heavier than air. Used as a solvent and to make other chemicals.
Sweet. but somewhat "gassy" odor. If at all reminiscent of any natural material, it would be a Hyacinth-type of gassy sweetness.

Air & Water Reactions

Highly flammable. Insoluble in water.

Reactivity Profile

Ethylenzene can react vigorously with strong oxidizing materials .

Hazard

Toxic by ingestion, inhalation, and skin absorption; irritant to skin and eyes. Flammable, dangerous fire risk. Possible carcinogen.

Health Hazard

The acute toxicity of Ethylbenzene is low.At high concentrations its exposure producesnarcotic effects similar to benzene andtoluene. A 4-hour exposure to a concentrationof 4000 ppm proved fatal to rats. The lethaldose varies with species. Deaths resulted fromintense congestion and edema of the lungs.
Other than the narcotic effects, Ethylbenzeneexhibits irritant properties that are somewhatgreater than those of benzene or toluene.It is an irritant to the skin, eyes, and nose.Repeated contact with the liquid may causereddening of the skin and blistering. Thevapors at 200 ppm may cause mild irritationof the eyes in humans, which may becomesevere and lacrimating at 2000–3000 ppm.
The oral toxicity in animals was foundto be low to very low. An LD50 value of3500 mg/kg for rats has been documented(NIOSH 1986). No adverse effects werenoted in animals subjected to chronic inhalationexposure at below 400 ppm. At higherdosages only the liver was affected (ACGIH1986). Ethylbenzene is eliminated from thebody by metabolic excretion. The urinarymetabolites in humans are mainly mandelicacid, C6H5CH(OH)COOH, and benzoylformicacid, C6H5COCOOH.

Flammability and Explosibility

Highly flammable

Chemical Reactivity

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

Safety Profile

Moderately toxic by ingestion and intraperitoneal routes. Mildly toxic by inhalation and skin contact. An experimental teratogen. Other experimental reproductive effects. Human systemic effects by inhalation: eye, sleep, and pulmonary changes. An eye and skin irritant. Human mutation data reported. The liquid is an irritant to the skin and mucous membranes. A concentration of 0.1% of the vapor in air is an irritant to human eyes, and a concentration of 0.2% is extremely irritating at first, then causes dizziness, irritation of the nose and throat, and a sense of constriction in the chest. Exposure of guinea pigs to 1% concentration has been reported as causing ataxia, loss of consciousness, tremor of the extremities, and finally death through respiratory failure. The pathological findings were congestion of the brain and lungs with edema. A very dangerous fire and explosion hazard when exposed to heat or flame; can react vigorously with oxidizing materials. To fight fire, use foam, CO2, dry chemical. Emitted from modern budding materials (CENEAR 69,22,91). When heated to decomposition it emits acrid smoke and irritating fumes.

Potential Exposure

Ethylbenzene is used in styrene manufacture and in synthesis of p-nitroacetophenone; in the manufacture of cellulose acetate, and synthetic rubber. It is also used as a solvent or diluent; and as a component of automotive and aviation gasoline. Significant quantities of EB are present in mixed xylenes. These are used as dilatants in the paint industry, in agricultural sprays for insecticides and in gasoline blends (which may contain as much as 20% EB). In light of the large quantities of EB produced and the diversity of products in which it is found, there may exist environmental sources for ethylbenzene, e.g., vaporization during solvent use; pyrolysis of gasoline and emitted vapors at filling stations. Groups of individuals who are exposed to EB to the greatest extent and could represent potential pools for the expression of EB toxicity include: (1) individuals in commercial situations where petroleum products or by-products are manufactured e.g., rubber or plastics industry); (2) individuals residing in areas with high atmospheric smog generated by motor vehicle emissions

First aid

If this chemical gets into the eyes, remove anycontact lenses at once and irrigate immediately for at least15 min, occasionally lifting upper and lower lids. Seek medical attention immediately. If this chemical contacts theskin, remove contaminated clothing and wash immediatelywith soap and water. Seek medical attention immediately. Ifthis chemical has been inhaled, remove from exposure,begin rescue breathing (using universal precautions, including resuscitation mask) if breathing has stopped and CPR ifheart action has stopped. Transfer promptly to a medicalfacility. When this chemical has been swallowed, get medical attention. Give large quantities of water and inducevomiting. Do not make an unconscious person vomit

Source

Detected in distilled water-soluble fractions of 87 octane gasoline (2.38 mg/L), 94 octane gasoline (7.42 mg/L), Gasohol (3.54 mg/L), No. 2 fuel oil (0.21 mg/L), jet fuel A (0.41 mg/L), diesel fuel (0.17 mg/L), military jet fuel JP-4 (1.57 mg/L) (Potter, 1996), new motor oil (0.15 to 0.17 μg/L), and used motor oil (117 to 124 μg/L) (Chen et al., 1994). The average volume percent and estimated mole fraction in American Petroleum Institute PS-6 gasoline are 1.570 and 0.017, respectively (Poulsen et al., 1992). Diesel fuel obtained from a service station in Schlieren, Switzerland contained ethylbenzene at a concentration of 690 mg/L (Schluep et al., 2001). Kaplan et al. (1996) determined ethylbenzene concentrations in four different grades of gasolines. Average ethylbenzene concentrations were 9.1 g/L in regular unleaded gasoline, 8.0 g/L in leaded gasoline, 9.3 g/L in unleaded plus gasoline, and 10.1 g/L in Super unleaded gasoline. Thomas and Delfino (1991) equilibrated contaminant-free groundwater collected from Gainesville, FL with individual fractions of three individual petroleum products at 24–25 °C for 24 h. The aqueous phase was analyzed for organic compounds via U.S. EPA approved test method 602. Average ethylbenzene concentrations reported in water-soluble fractions of unleaded gasoline, kerosene, and diesel fuel were 2.025, 0.314, and 0.104 mg/L, respectively. When the authors analyzed the aqueous-phase via U.S. EPA approved test method 610, average ethylbenzene concentrations in water-soluble fractions of unleaded gasoline, kerosene, and diesel fuel were lower, i.e., 1.423, 0.171, and 0.079 mg/L, respectively.
Schauer et al. (1999) reported ethylbenzene in a diesel-powered medium-duty truck exhaust at an emission rate of 470 μg/km. California Phase II reformulated gasoline contained ethylbenzene at a concentration of 12,800 mg/kg. Gas-phase tailpipe emission rates from gasoline-powered automobiles with and without catalytic converters were 4.18 and 434.0 mg/km, respectively (Schauer et al., 2002).
Detected in 1-yr aged coal tar film and bulk coal tar at concentrations of 350 and 2,100 mg/kg, respectively (Nelson et al., 1996). A high-temperature coal tar contained ethylbenzene at an average concentration of 0.02 wt % (McNeil, 1983).
Identified as one of 140 volatile constituents in used soybean oils collected from a processing plant that fried various beef, chicken, and veal products (Takeoka et al., 1996).
Schauer et al. (2001) measured organic compound emission rates for volatile organic compounds, gas-phase semi-volatile organic compounds, and particle-phase organic compounds from the residential (fireplace) combustion of pine, oak, and eucalyptus. The gas-phase emission rate of ethylbenzene was 22.9 mg/kg of pine burned. Emission rates of ethylbenzene were not measured during the combustion of oak and eucalyptus.

Environmental Fate

Biological. Phenylacetic acid was reported to be the biooxidation product of ethylbenzene by Nocardia sp. in soil using n-hexadecane or n-octadecane as the substrate. In addition, Methylosinus trichosporium OB3b was reported to metabolize ethylbenzene to 2- and 3- hydroxybenzaldehyde with methane as the substrate (Keck et al., 1989). Ethylbenzene was oxidized by a strain of Micrococcus cerificans to phenylacetic acid (Pitter and Chudoba, 1990). A culture of Nocardia tartaricans ATCC 31190, growing in a hexadecane medium, oxidized ethylbenzene to 1-phenethanol, which oxidized to acetophenone (Cox and Goldsmith, 1979). When ethylbenzene (5 mg/L) was statically incubated in the dark at 25 °C with yeast extract and settled domestic wastewater inoculum, complete biodegradation with rapid acclimation was observed after 7 d. At a concentration of 10 mg/L, significant degradation occurred with gradual adaptation. Percent losses of 69, 78, 87, and 100 were obtained after 7, 14, 21, and 28-d incubation periods, respectively (Tabak et al., 1981). Olsen and Davis (1990) reported a first-order degradation rate constant of 0.07/yr and a half-life of 37 d.
Surface Water. The evaporation half-life of ethylbenzene in surface water (1 m depth) at 25 °C is estimated to be from 5 to 6 h (Mackay and Leinonen, 1975). Estimated half-lives of ethylbenzene (3.3 μg/L) from an experimental marine mesocosm during the spring (8–16 °C), summer (20–22 °C), and winter (3–7 °C) were 20, 2.1, and 13 d, respectively (Wakeham et al., 1983).
Photolytic. Irradiation of ethylbenzene (λ <2537 ) at low temperatures will form hydrogen, styrene, and free radicals (Calvert and Pitts, 1966).
Chemical/Physical. Complete combustion in air yields carbon dioxide and water vapor. Ethylbenzene will not hydrolyze in water (Kollig, 1993).

Metabolism

The main oxidation of ethyl benzene occurs at the activated α-methylene group to yield methylphenylcarbinol which is also the precursor of hippuric and mandelic acids. Both optical isomers of methylphenylcarbinol are formed, probably in equal amounts, and these have been isolated from the urine of rabbits as the corresponding glucuronides. The two optical forms of mandelic acid have also been found (Williams, 1959).

storage

Color Code—Red: Flammability Hazard: Store ina flammable liquid storage area or approved cabinet awayfrom ignition sources and corrosive and reactive materials.Prior to working with this chemical you should be trainedon its proper handling and storage. Before entering confinedspace where this chemical may be present, check to makesure that an explosive concentration does not exist. Protectagainst physical damage. Outside or detached storage ispreferable. Inside storage should be in a standard flammableliquids storage room or cabinet. Isolate from acute firehazards and oxidizing agents. Store in tightly closed containers in a cool, well-ventilated area away from heat.Sources of ignition, such as smoking and open flames, areprohibited where this chemical is used, handled, or stored ina manner that could create a potential fire or explosion hazard. Metal containers involving the transfer of 5 gallons ormore of this chemical should be grounded and bonded.Drums must be equipped with self-closing valves, pressurevacuum bungs, and flame arresters. Use only nonsparkingtools and equipment, especially when opening and closingcontainers of this chemical.

Shipping

UN1175 Ethylbenzene, Hazard Class: 3; Labels: 3-Flammable liquid

Toxicity evaluation

Ethylbenzene acts by a variety of toxic mechanisms in affected tissues/organs. Acute CNS depressive or narcotic effects occur nonspecifically and likely result from unmetabolized ethylbenzene’s disruption of neuronal membranes. Ototoxicity also appears to result from unmetabolized ethylbenzene damage to hair cells of the cochlea. Both of these toxicities are relevant to humans. Other ethylbenzene toxicities appear to be linked to metabolism or metabolites, and hence, differences are expected between laboratory animals and humans. Induction of cytochrome P450E1 is postulated to contribute to liver changes in mice and kidney changes in rats. Rat kidney toxicity is demonstrated to be associated with alpha-2u-globulin nephropathy and exacerbation of chronic progressive nephropathy, conditions that are not relevant to human health. Lung toxicity is postulated to arise from mouse specific lung enzyme (cytochrome P450F2) metabolism to cytotoxic metabolite(s) and associated chronic cell proliferation in lung target cells.

Incompatibilities

Vapors may form explosive mixture with air. 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, and epoxides. Attacks plastics and rubber. May accumulate static electrical charges, and may cause ignition of its vapors.

Toxics Screening Level

The Initial Risk Screening Level (IRSL) for ethylbenzene is 0.4 μg/m3 with annual averaging time.

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