Chemical Properties
Toluene is a clear, colorless, flammable liquid with a sweet/pungent odor. It is extensively used as a solvent in different industries, i.e., rubber chemical manufacturing, drugs and pharmaceuticals, thinner for inks, paints dyes, and perfume manufacturing. It is a natural constituent of crude oil and is produced from petroleum refi ning and coke-oven operations. Toluene occurs naturally as a component of crude oil and occurs in petroleum refi ning and coke oven operations. Occupational workers associated with several kinds of activities, such as manufacturing of dyes, printing inks, painting automobile mechanics, gasoline manufacturers, shippers, and retailers, adhesives and coatings manufacturers and applicators, audio-equipment product workers, chemical industry workers, coke-oven workers, fabric manufacturers (fabric coating), sites of hazardous wastes, linoleum manufacturers, in pharmaceutical manufacturing, printing works, shoe manufacturing industry, become exposed to toluene.
General Description
A clear colorless liquid with a characteristic aromatic odor. Flash point 40°F. Less dense than water (7.2 lb/gal) and insoluble in water. Hence floats on water. Vapors heavier than air. May be toxic by inhalation, ingestion or skin contact. Used in aviation and automotive fuels, as a solvent, and to make other chemicals.
Reactivity Profile
TOLUENE(108-88-3) 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]. Incompatible with strong oxidizing agents. When added to a tank of sulfur dichloride, the tank over pressurized and ruptured in a reaction thought to be catalyzed by iron or iron(III) chloride [Chem. Eng. News, 1988, 66(32), 2].
Air & Water Reactions
Highly flammable. Insoluble in water.
Health Hazard
Exposures to toluene cause adverse health effects to animals and humans. The symptoms of toxicity and poisoning include, but are not limited to, mild irritation to the skin, headache, nausea, and effects on the CNS. Prolonged exposure to high concentrations of toluene causes disturbances in vision, dizziness, nausea, CNS depression, paresthesia, and sudden collapse. The acute oral LD50 value of toluene in laboratory rats has been reported as 636–7300 mg/kg. Exposure to toluene has been reported to cause rapid and severe corneal damage and conjunctiva infl ammation. The acute dermal LD50 in rabbits was found to be between 1200 and 1400 mg/kg.
Health Hazard
Vapors irritate eyes and upper respiratory tract; cause dizziness, headache, anesthesia, respiratory arrest. Liquid irritates eyes and causes drying of skin. If aspirated, causes coughing, gagging, distress, and rapidly developing pulmonary edema. If ingested causes vomiting, griping, diarrhea, depressed respiration.
Potential Exposure
Toluene is used as an industrial chemical, chemical intermediate; solvent, and emulsifier; may be encountered in the manufacture of benzene. It is also used as a chemical feed for toluene diisocyanate, phenol, benzyl and benzoyl derivatives; benzoic acid; toluene sulfonates; nitrotoluenes, vinyltoluene, and saccharin; as a solvent for paints and coatings; or as a component of automobile and aviation fuels.
Fire Hazard
Behavior in Fire: Vapor is heavier than air and may travel a considerable distance to a source of ignition and flash back.
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, get medical attention. Give large quantities of water and induce vomiting. Do not make an unconscious person vomit.
Shipping
UN1294 Toluene, Hazard Class: 3; Labels: 3-Flammable liquid.
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. Violent reaction with mixtures of nitric and sulfuric acid.
Waste Disposal
Consult with environmental regulatory agencies for guidance on acceptable disposal practices. Generators of waste containing this contaminant (≥100 kg/mo) must conform with EPA regulations governing storage, transportation, treatment, and waste disposal.
Physical properties
Colorless, clear, flammable liquid with a pleasant, sweet or paint-like odor similar to benzene. At
40 °C, the lowest concentration at which an odor was detected were 960 μg/L. Similarly at 25 °C,
the lowest concentration at which a taste was detected was 960 μg/L (Young et al., 1996).
Experimentally determined detection and recognition odor threshold concentrations were 600
μg/m3 (160 ppbv) and 7.0 mg/m3 (1.9 ppmv), respectively (Hellman and Small, 1974). Leonardos
et al. (1969) reported higher odor threshold concentrations for toluene derived from coke (4.68
ppmv) and petroleum (2.14 ppmv). The average least detectable odor threshold concentrations in
water at 60 °C and in air at 40 °C were 24 and 140 μg/L, respectively (Alexander et al., 1982). An
odor threshold concentration of 330 ppbv was determined by a triangular odor bag method (Nagata
and Takeuchi, 1990). Cometto-Mu?iz and Cain (1994) reported an average nasal pungency
threshold concentration of 29,574 ppmv.
History
Toluene is a clear, flammable, aromatic hydrocarbon liquid with a smell similar to benzene.
It is also called methylbenzene, indicating that a methyl group has been added to one of
benzene’s carbon atoms. Toluene was first isolated by Pierre-Joseph Pelletier (1788–1842) and
Philippe Walter (1810–1847) in 1837. The name toluene comes from the South American
tree Toluifera balsamum. Henri-Etienne Sainte-Claire Deville (1818–1881) isolated toluene
from the tree’s gum, Tolu balsam, in 1841.
The main source of toluene is from the catalytic reforming of naphthas during petroleum
processing. During this process cycloalkanes are dehydrated, forming aromatics such as
toluene and xylene along with hydrogen. Toluene can also be obtained from the pyrolysis of
gasoline. It is a by-product when styrene is produced and can also be produced from coal tar,
which was its main source in the first half of the 20th century.
Definition
ChEBI: The simplest member of the class toluenes consisting of a benzene core which bears a single methyl substituent.
Preparation
Toluene is the starting material for the production of tolylene diisocyanate
(TDI)，the process may be varied to give
products of differing isomer contents. The nitration of toluene (with a nitrating mixture containing 20% nitric acid, 60% sulphuric acid and 20%
water at 30-45°C) gives a mixture of 2-nitrotoluene (about 60%) and 4-
nitrotoluene (40%). If this mixture is nitrated further (with a mixture of 35%
nitric acid and 65% sulphuric acid at 65-80°C) without separation, the product is a mixture of2,4-dinitrotoluene (about 80%) and 2,6-dinitrotoluene
(20%). If, on the other hand, the mixed mononitrates are separated (by
distillation), then further nitration of the 2-nitrotoluene yields a mixture of
2,4-dinitrotoluene (about 65%) and 2,6-dinitrotoluene (35%) whilst further
nitration of the 4-nitrotoluene gives only 2,4-dinitrotoluene.
Production Methods
Benzene is produced from toluene through a process called hydrodealkylation. In thisprocess, toluene reacts with hydrogen in the presence of a chromium, platinum, or molybdenumcatalysts at temperatures of several hundred degrees Celsius and pressures of about50 atmospheres: C6H5CH3 + H2 → C6H6 + CH4. Toluene can also be used to producephenol, (C6H5OH), benzoic acid (C6H5COOH), and benzaldehyde (C6H5CHO). Nitratedforms of toluene produce explosive compounds; the most common of these is TNT (SeeTrinitrotoluene).
Synthesis Reference(s)
Canadian Journal of Chemistry, 55, p. 3755, 1977
DOI: 10.1139/v77-529Chemistry Letters, 11, p. 1707, 1982
Tetrahedron Letters, 17, p. 2689, 1976
Hazard
Flammable, dangerous fire risk. Explosive
limits in air 1.27–7%. Toxic by ingestion,
inhalation, and skin absorption. Visual impairment,
female reproductive effects, and pregnancy loss.
Questionable carcinogen.
Flammability and Explosibility
Toluene is a flammable liquid (NFPA rating = 3), and its vapor can travel a
considerable distance to an ignition source and "flash back." Toluene vapor forms
explosive mixtures with air at concentrations of 1.4 to 6.7% (by volume). Hazardous
gases produced in fire include carbon monoxide and carbon dioxide. Carbon dioxide
and dry chemical extinguishers should be used to fight toluene 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.
Carcinogenicity
The IARC has determined that there is
evidence for the lack of carcinogenicity of
toluene in experimental animals and that there
is inadequate evidence for carcinogenicity in
humans. Results of in vitro assays generally
indicate that toluene is not genotoxic. Reports
of increased incidences of sister chromatid
exchanges and chromatid breaks in exposed
workers are confounded by concurrent exposure
to other organic chemicals.
Source
Detected in distilled water-soluble fractions of 87 octane gasoline (25.9 mg/L), 94 octane
gasoline (86.9 mg/L), Gasohol (60.8 mg/L), No. 2 fuel oil (1.54 mg/L), jet fuel A (1.05 mg/L),
diesel fuel (0.86 mg/L), military jet fuel (JP-4 (32.0 mg/L) (Potter, 1996), new motor oil (16.3 to
16.9 8 μg/L), and used motor oil (781–814 μg/L) (Chen et al., 1994). The average volume percent
and estimated mole fraction in American Petroleum Institute PS-6 gasoline are 3.519 and 0.04392,
respectively (Poulsen et al., 1992). Schauer et al. (1999) reported toluene in a diesel-powered
medium-duty truck exhaust at an emission rate of 3,980 μg/km. Diesel fuel obtained from a
service station in Schlieren, Switzerland contained toluene at an estimated concentration of 374
mg/L (Schluep et al., 2001).
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 toluene concentrations reported in water-soluble fractions of unleaded gasoline,
kerosene, and diesel fuel were 23.676, 1.065, and 0.552 mg/L, respectively. When the authors
analyzed the aqueous-phase via U.S. EPA approved test method 610, average toluene
concentrations in water-soluble fractions of unleaded gasoline, kerosene, and diesel fuel were
lower, i.e., 12.969, 0.448, and 0.030 mg/L, respectively.
Kaplan et al. (1996) determined toluene concentrations in four different grades of gasolines.
Average toluene concentrations were 32.6 g/L in regular unleaded gasoline, 28.7 g/L in leaded
gasoline, 36.7 g/L in unleaded plus gasoline, and 40.9 g/L in Super unleaded gasoline.
Harley et al. (2000) analyzed the headspace vapors of three grades of unleaded gasoline where
ethanol was added to replace methyl tert-butyl ether. The gasoline vapor concentrations of toluene
in the headspace were 1.9 wt % for regular grade, 1.8 wt % for mid-grade, and 2.0 wt % for
premium grade.
In 7 coal tar samples, toluene concentrations ranged from ND to 7,000 ppm (EPRI, 1990).
Detected in 1-yr aged coal tar film and bulk coal tar at concentrations of <75 and 220 mg/kg, respectively (Nelson et al., 1996). A high-temperature coal tar contained toluene at an average
concentration of 0.25 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 toluene was 158 mg/kg of pine burned. Emission rates of toluene were not measured during
the combustion of oak and eucalyptus.
Reported as an impurity (≤ 0.8 wt %) in 98.5 wt % benzyl mercpatan (Chevron Phillips, April
2005).
Drinking water standard (final): MCLG: 1 mg/L; MCL: 1 mg/L. In addition, a DWEL of 7 μg/L
was recommended (U.S. EPA, 2000).
Environmental Fate
Biological. Toluene can undergo two types of microbial attack. The first type proceeds via immediate hydroxylation of the benzene ring, followed by ring cleavage. The second type of
attack proceeds via oxidation of the methyl group followed by hydroxylation and ring cleavage
(Fewson, 1981). A mutant of Pseudomonas putida oxidized toluene to (+)-cis-2,3-dihydroxy-1-
methylcyclohexa-1,4-diene (Dagley, 1972). Claus and Waker (1964) reported that Pseudomonas
sp. and an Achromobacter sp. oxidized toluene to 3-methylcatechol. Other metabolites identified
in the microbial degradation of toluene include cis-2,3-dihydroxy-2,3-dihydrotoluene, 3-
methylcatechol, benzyl alcohol, benzaldehyde, benzoic acid, catechol (quoted, Verschueren,
1983), and 1-hydroxy-2-naphthoic acid (Claus and Walker, 1964). In a methanogenic aquifer
material, toluene degraded completely to carbon dioxide (Wilson et al., 1986). In activated sludge,
26.3% of the applied toluene mineralized to carbon dioxide after 5 d (Freitag et al., 1985). Based
on a first-order degradation rate constant of 0.07/yr, the half-life of toluene is 39 d (Zoeteman et
al., 1981).
Photolytic. Cox et al. (1980) reported a rate constant of 7.2 x 10-12 cm3/molecule?sec for the
reaction of gaseous toluene with OH radicals based on a value of 8 x 10-12 cm3/molecule?sec for
the reaction of ethylene with OH radicals.
Surface Water. Mackay and Wolkoff (1973) estimated an evaporation half-life of 30.6 min from
a surface water body that is 25 °C and 1 m deep.
Groundwater. Nielsen et al. (1996) studied the degradation of toluene in a shallow,
glaciofluvial, unconfined sandy aquifer in Jutland, Denmark. As part of the in situ microcosm
study, a cylinder that was open at the bottom and screened at the top was installed through a cased
borehole approximately 5 m below grade. Five liters of water was aerated with atmospheric air to
ensure aerobic conditions were maintained. Groundwater was analyzed weekly for approximately
3 months to determine toluene concentrations with time. The experimentally determined firstorder
biodegradation rate constant and corresponding half-life following a 5-d lag phase were
0.4/d and 1.73 d, respectively.
Photolytic. Synthetic air containing gaseous nitrous acid and toluene exposed to artificial
sunlight (λ = 300–450 nm) yielded methyl nitrate, peroxyacetal nitrate, and a nitro aromatic
compound tentatively identified as a nitrophenol or nitrocresol (Cox et al., 1980). A n-hexane
solution containing toluene and spread as a thin film (4 mm) on cold water (10 °C) was irradiated
by a mercury medium pressure lamp. In 3 h, 26% of the toluene photooxidized into benzaldehyde, benzyl alcohol, benzoic acid, and m-cresol (Moza and Feicht, 1989). Methane and ethane were
reported as products of the gas-phase photolysis of toluene at 2537 ? (Calvert and Pitts, 1966).
Chemical/Physical. Products identified from the reaction of toluene with nitric oxide and OH
radicals include benzaldehyde, benzyl alcohol, 3-nitrotoluene, p-methylbenzoquinone, and o-, m-,
and p-cresol (Kenley et al., 1978). Gaseous toluene reacted with nitrate radicals in purified air
forming the following products: benzaldehyde, benzyl alcohol, benzyl nitrate, and 2-, 3-, and 4-
nitro-toluene (Chiodini et al., 1993). Under atmospheric conditions, the gas-phase reaction with
OH radicals and nitrogen oxides resulted in the formation of benzaldehyde, benzyl nitrate, 3-
nitrotoluene, and o-, m-, and p-cresol (Finlayson-Pitts and Pitts, 1986; Atkinson, 1990).
Solubility in organics
Soluble in acetone, carbon disulfide, and ligroin; miscible with acetic acid, ethanol, benzene,
ether, chloroform (U.S. EPA, 1985), and other organic solvents including xylenes, toluene, and
ethylbenzene.
storage
toluene should be
used only in areas free of ignition sources, and quantities greater than 1 liter should
be stored in tightly sealed metal containers in areas separate from oxidizers.
Purification Methods
Dry toluene with CaCl2, CaH2 or CaSO4, and dry further by standing with sodium, P2O5 or CaH2. It can be fractionally distilled from sodium or P2O5. Unless specially purified, toluene is likely to be contaminated with methylthiophenes and other sulfur-containing impurities. These can be removed by shaking with conc H2SO4, but the temperature must be kept below 30o if sulfonation of toluene is to be avoided. A typical procedure consists of shaking toluene twice with cold conc H2SO4 (100mL of acid per L), once with water, once with aqueous 5% NaHCO3 or NaOH, again with H2O, then drying successively with CaSO4 and P2O5, with final distillation from P2O5 or over LiAlH4 after refluxing for 30minutes. Alternatively, the treatment with NaHCO3 can be replaced by boiling under reflux with 1% sodium amalgam. Sulfur compounds can also be removed by prolonged shaking of the toluene with mercury, or by two distillations from AlCl3, the distillate then being washed with water, dried with K2CO3 and stored with sodium wire. Other purification procedures include refluxing and distillation of sodium dried toluene from diphenylpicrylhydrazyl, and from SnCl2 (to ensure freedom from peroxides). It has also been co-distilled with 10% by volume of ethyl methyl ketone, and again fractionally distilled. [Brown & Pearsall J Am Chem Soc 74 191 1952.] For removal of carbonyl impurities see *benzene. Toluene has been purified by distillation under nitrogen in the presence of sodium benzophenone ketyl. Toluene has also been dried with MgSO4, after the sulfur impurities have been removed, and then fractionally distilled from P2O5 and stored in the dark [Tabushi et al. J Am Chem Soc 107 4465 1985]. Toluene can be purified by passage through a tightly packed column of Fuller's earth. Rapid purification: Alumina, CaH2 and 4A molecular sieves (3% w/v) may be used to dry toluene (6hours stirring and standing). Then the toluene is distilled, discarding the first 5% of distillate, and is stored over molecular sieves (3A, 4A) or Na wire. [Beilstein 5 H 280, 5 I 144, 5 II 209, 5 III 651, 5 IV 766.]
Toxicity evaluation
The mechanism of toxicity is suspected to be similar to other
solvents that rapidly induce anesthesia-like effects, i.e.,
a ‘nonspecific narcosis’ due to disruption (solvation) of the
integrity of the cellular membranes of the central nervous
system (CNS). The effect is similar to the ‘high’ experienced
upon exposure to other hydrocarbon solvents.
As seen with exposure to other hydrocarbon solvents, upon
inhalation, toluene is moderately toxic and may cause irritation
of the respiratory tract and narcosis. Toluene appears to
produce reversible effects on the liver, renal, and nervous
systems. The nervous system appears to be the most sensitive to
the effects of toluene. High-level toluene exposures produced
incoordination, ataxia, unconsciousness, and, eventually,
death. Lower level acute exposures in man produce dizziness,
exhilaration, and confusion. Although the actual biochemical
mechanism of toxicity has not been discerned, the narcotic
effects seen are most likely related to its physical solvent
properties.
