| HS Code | 435206 |
| Productname | Purified Toluene |
| Chemicalformula | C7H8 |
| Casnumber | 108-88-3 |
| Molecularweight | 92.14 g/mol |
| Appearance | Colorless clear liquid |
| Odor | Aromatic, benzene-like |
| Boilingpoint | 110.6 °C |
| Meltingpoint | -95 °C |
| Density | 0.8669 g/mL at 20 °C |
| Solubility | Insoluble in water; miscible with ethanol, ether, acetone, benzene |
| Purity | ≥99.5% |
| Flashpoint | 4.4 °C (closed cup) |
| Autoignitiontemperature | 480 °C |
| Vaporpressure | 22 mmHg at 20 °C |
| Viscosity | 0.59 cP at 20 °C |
| Refractiveindex | 1.4961 at 20 °C |
| Storageconditions | Store in cool, dry, well-ventilated area away from ignition sources |
| Hazardclass | Flammable liquid Category 2; skin irritation Category 2; reproductive toxicity Category 2; STOT SE Category 3 |
As an accredited Purified Toluene factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Purified Toluene is supplied in 20 L UN-approved steel drums, securely sealed with hazard labels and flammability warnings. |
| Container Loading (20′ FCL) | Purified Toluene loaded into a 20-foot FCL container with UN 1294 hazardous documentation, secure drums, and flammable liquid placards. |
| Shipping | Purified Toluene ships as a flammable liquid: UN 1294, Class 3, Packing Group II. Use UN-approved containers, flammable-liquid labels, and proper shipping papers. Follow DOT, IMDG, and IATA rules. Keep cool, ventilated, away from ignition sources, oxidizers, and static; ground equipment during handling. |
| Storage | Store Purified Toluene in a cool, dry, well-ventilated area away from heat, sparks, flames, and strong oxidizers. Keep containers tightly closed, upright, and grounded in an approved flammable-liquid storage cabinet or dedicated solvent store. Use secondary containment, avoid direct sunlight, and ensure proper labeling, ventilation, and spill kits. Segregate from acids, bases, and reactive chemicals. Follow local regulations. |
| Shelf Life | Purified toluene is stable; no specific shelf life if stored properly in sealed containers away from heat, light, and ignition sources. |
In flexible polyurethane slabstock production, purified toluene enters the diisocyanate value chain as the aromatic precursor for dinitrotoluene (DNT). Commercial nitration-grade toluene is specified under ASTM D841-18 with minimum purity of 99.9 wt%, non-aromatic hydrocarbon content below 0.10 wt%, and water below 0.02 wt% because olefinic and sulfur impurities participate in side reactions during mixed-acid nitration and poison downstream hydrogenation catalysts. In continuous nitration, toluene is dispersed in a mixed acid composed of 25–35 wt% nitric acid, 50–60 wt% sulfuric acid, and 10–20 wt% water; the HNO₃-to-toluene molar ratio is held between 2.02:1 and 2.10:1 to minimize oxidative degradation while achieving conversion above 98%. The exotherm is managed in loop reactors with external heat exchangers; temperature is kept between 55°C and 65°C because dinitrotoluene formation shifts toward higher 2,6-isomer content and nitrophenol impurities above 75°C, narrowing downstream TDA isomer split. The resulting dinitrotoluene stream, typically an 80:20 mixture of 2,4- and 2,6-isomers, is hydrogenated to toluene diamine in a fixed-bed or slurry-phase reactor over nickel or palladium catalysts at 2–5 MPa hydrogen pressure and 100–150°C. Phosgenation in a stirred-tank or falling-film reactor then converts TDA to toluene diisocyanate; the final TDI isomer ratio is controlled by the DNT isomer ratio, yielding TDI-80/20 or TDI-65/35 for flexible slabstock and molded foam systems. The overall consumption coefficient for purified toluene is between 0.58 and 0.65 kg per kg TDI, depending on nitration selectivity and distillation losses. Terminal products include flexible polyurethane foams for furniture, automotive seating, and bedding, where TDI is reacted with polyether polyols, water, catalysts, and silicone surfactants. Compliance obligations include REACH registration for toluene as an intermediate; the Annex XVII Entry 48 consumer restriction on toluene in adhesives and spray paints does not apply to industrial TDI synthesis. Worker exposure is governed by the EU indicative occupational exposure limit for toluene of 192 mg/m³ over an 8-hour reference period.
| Downstream process | Critical impurity or parameter | Limit or range | Test method / standard |
|---|---|---|---|
| Continuous mixed-acid nitration to dinitrotoluene | Non-aromatic hydrocarbons | <0.10 wt% | ASTM D841-18 |
| Fixed-bed hydrodealkylation | Total sulfur | <1 ppmw | ASTM D5453-19 |
| Benzoic acid liquid-phase oxidation | Water | <0.05 wt% | ASTM E203-21 |
| Chlorosulfonation to sulfonyl chloride | Water | <50 ppm | ASTM E203-21 |
| Analytical extraction | Evaporation residue | <0.0005 wt% | ISO 6353-2 |
Because hydrodealkylation is strongly endothermic and carbon-deposition sensitive, the purified toluene stream fed to a fixed-bed unit is usually blended with recycled hydrogen at a H₂-to-toluene molar ratio between 3:1 and 6:1 before entering a fired heater. The feedstock specification for this route is less demanding than nitration-grade material but still excludes sulfur compounds above 1 ppmw because sulfur accelerates coking on the chromium-promoted alumina-supported molybdenum catalyst. Reactor inlet temperature is maintained between 600°C and 680°C; pressure is typically 35–50 barg. Under these conditions single-pass toluene conversion is held at 65–80% to preserve benzene selectivity between 92 mol% and 96 mol%. The main side products are methane, ethane, and heavier aromatic condensation products that cause catalyst deactivation; regeneration intervals of 6–24 months are common depending on feed purity and H₂ partial pressure. Downstream, the reactor effluent is cooled, liquid product is separated from fuel gas, and the benzene is purified by a sequence of extractive distillation, clay treating, and final distillation to meet ASTM D2359-19 Refined Benzene-535 specifications: minimum purity 99.9 wt%, thiophene content below 0.5 mg/kg, and solidification point not lower than 5.35°C. The recovered unreacted toluene is recycled to the reactor feed; the benzene yield based on fresh toluene feed is typically 90–95% of stoichiometric. Terminal products from this benzene include styrene for polystyrene and ABS resins, cumene for phenol/acetone, cyclohexane for adipic acid and caprolactam, and nitrobenzene for aniline. The operation is subject to Seveso III thresholds for hydrogen and benzene, and benzene exposure limits under the EU Carcinogens and Mutagens Directive.
Liquid-phase air oxidation capacity for benzoic acid consumes a toluene stream with a defined benzaldehyde content below 0.05 wt% and iron below 0.5 ppm because aldehyde intermediates autoxidize to colored byproducts and iron promotes uncatalyzed peroxide decomposition. The oxidation is performed in a sparged bubble column or stirred gas-liquid reactor at 145–170°C and 0.8–1.2 MPa air pressure. Cobalt and manganese acetate catalysts are introduced as a hydrocarbon-soluble package at a combined metal concentration of 50–500 ppmw relative to toluene; the Co:Mn mass ratio is typically 1:1 to 3:1, depending on whether the target is benzoic acid or benzaldehyde-rich intermediate. Air is fed at 1.5–2.5 times the stoichiometric oxygen demand, but single-pass toluene conversion is deliberately limited to 20–35% to avoid over-oxidation to benzaldehyde benzoate and quinone-like tar. The crude benzoic acid is recovered by cooling, centrifugation, and vacuum distillation or melt crystallization. For food-grade sodium benzoate, the acid is reacted with sodium hydroxide to form sodium benzoate E211, which must comply with EU Regulation 231/2012, the Food Chemicals Codex monograph, and the Joint FAO/WHO Expert Committee on Food Additives specification. Terminal products include benzoate preservatives for carbonated beverages, acidified foods, and personal care, plus benzoyl chloride and phenol via decarboxylation for chemical intermediates. Process compliance includes REACH for the toluene feed and ISO 9001 lot release for food additive grade.
Across sulfonation plants producing p-toluenesulfonyl chloride, the moisture content of purified toluene is constrained below 50 ppm because water reacts exothermically with chlorosulfonic acid and shifts the chlorosulfonation reaction toward hydrolysis products, reducing the sulfonyl chloride assay below the 98% needed for downstream pharmaceutical intermediates. Toluene is fed to a glass-lined stirred reactor in a chlorosulfonic acid-to-toluene molar ratio of 2.0:1 to 2.5:1 at 5–20°C; the addition is rate-controlled to keep the exotherm within the jacket cooling capacity because localized temperature excursions above 35°C promote sulfone formation and charring. The reaction mass is quenched into ice-water, and the dense organic layer is separated, washed, and vacuum-distilled to separate p-toluenesulfonyl chloride from the less reactive ortho isomer and unreacted toluene. Terminal products include p-toluenesulfonyl chloride used as an intermediate for sulfonamide antibiotics, saccharin, and dyes, while p-toluenesulfonic acid monohydrate from hydrolysis serves as an acid catalyst in polyester resin curing and pharmaceutical salt formation. Compliance obligations include REACH registration, and residual toluene in the isolated sulfonyl chloride must meet pharmaceutical limits; the ICH Q3C residual solvent guideline classifies toluene as Class 2 with a permitted daily exposure of 8.9 mg/day and a concentration limit of 890 ppm in drug substances.
Regulatory pressure on solvent-borne inks has narrowed the legitimate downstream formulation window for purified toluene to industrial publication gravure and certain lamination adhesives where the film-forming resin system requires an aromatic solvency parameter close to 18.2 MPa0.5. In publication gravure inks, toluene is combined with ethyl acetate and methyl ethyl ketone at 40–60 wt% of the ink formulation, with nitrocellulose or polyamide resins dissolved at 15–25 wt% and pigments at 10–20 wt%. The solvent blend is adjusted on-press to a viscosity of 16–25 s on a Zahn cup #2 and a final ink film thickness of 0.5–1.5 µm after gravure cylinder doctoring. The downstream process involves high-velocity hot-air drying in long tunnel ovens; toluene evaporation at 60–90°C removes residual solvent below 5 mg/m² in printed film, which is then laminated or overcoated. For industrial adhesives, toluene may be used as a diluent for chloroprene rubber contact cements at 20–40 wt% of the wet adhesive, applied by roller coater and dried to a final bond line with less than 0.1 wt% residual toluene. Terminal products include high-definition magazine and catalog printing, flexible packaging lamination, and industrial contact adhesives. However, REACH Annex XVII Entry 48 prohibits placing toluene-containing adhesives or spray paints on the market for sale to the general public at or above 0.1 wt%; food-contact printing inks and adhesives are additionally subject to FDA 21 CFR 175.105 and EU Framework Regulation 1935/2004 migration and composition requirements.
Chromatographic baseline interference and detector contamination in gas chromatography–mass spectrometry methods for volatile organic compounds make analytical-grade purified toluene the default extraction solvent for selected soil and water methods, provided the reagent is certified to ACS specifications or ISO 6353-2 for purity of at least 99.8 wt%, evaporation residue below 0.0005 wt%, and water below 0.02 wt%. The solvent-to-sample ratio is method-defined: in liquid-liquid extraction of nonpolar semivolatiles from aqueous matrices, a typical ratio is 20 mL toluene per 1 L water, with a subsequent drying step over anhydrous sodium sulfate and concentration to 1 mL under a gentle nitrogen stream. The downstream process is analytical rather than chemical conversion; the extract is injected into a GC-MS system with a split/splitless injector at 250–280°C and separated on a phenyl-arylene stationary phase column. Terminal output is a quantitative data set for priority pollutants, pesticide residues, or pharmaceutical impurities in environmental and pharmaceutical laboratories. The reagent must be free of phthalate and bis(2-ethylhexyl) phthalate contamination because these plasticizer artifacts co-elute with target analytes at quantification limits below 0.1 µg/L. Compliance is maintained under ISO/IEC 17025 laboratory accreditation, and residual solvent issues in pharmaceutical samples are evaluated under ICH Q3C, where toluene is a Class 2 solvent with a concentration limit of 890 ppm.
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Purified toluene is supplied as a high-assay aromatic hydrocarbon in multiple release models—ACS reagent grade, HPLC grade, anhydrous packaging under inert gas, and low-carbonyl grade—where the controlled variables are benzene content, sulfur content, water content, oxidation byproducts, and non-volatile residue. The product is distinguished from technical-grade toluene not solely by assay but by the analytical burden of trace impurities that interfere with gas chromatography, UV spectroscopy, or organometallic catalysis. Normal physical constants include a boiling point of 110.6 °C, density of 0.865 g/mL at 20 °C, closed-cup flash point of 4.4 °C, lower explosive limit of 1.1 vol%, and water solubility in toluene near 0.033 wt% at 25 °C. The solvent is a nonpolar aprotic diluent with a Hildebrand solubility parameter near 18.2 MPa1/2. No single standard governs all purified toluene models; ACS Reagent Chemicals monograph limits for toluene are commonly referenced for reagent-grade material, while anhydrous and HPLC grades use additional in-house release criteria for water and UV absorbance.
Toluene produced by catalytic reforming of naphtha contains benzene, xylene, ethylbenzene, and sulfur compounds. Purification to low-benzene material requires fractional distillation; because benzene boils at 80.1 °C and toluene at 110.6 °C, separation is favorable, but the overhead benzene cut must be taken narrowly and reflux ratio controlled. In a batch column with 30 theoretical stages, a rapid draw can increase benzene carryover; batch-to-batch benzene variance is therefore minimized by using automated ratio control rather than manual cut points. Sulfur removal may require hydrodesulfurization or caustic extraction prior to distillation; release testing by ASTM D7183 total sulfur analysis at a quantification limit of 10 mg/kg is then used to verify sulfur control.
No single specification is uniform across supply chains. ACS Reagent Chemicals defines minimum assay and maximum impurity levels for general analytical use, while anhydrous HPLC-grade product typically tightens water and benzene limits. Table 1 shows representative release limits for two common purified toluene grades; exact values are batch-specific and method-defined.
| Parameter | Unit | ACS reagent limit | HPLC/anhydrous limit | Method |
|---|---|---|---|---|
| Assay by GC-FID | % | ≥99.5 | ≥99.8 | ASTM D7504 |
| Benzene | mg/kg | ≤50 | ≤10 | ASTM D7504 |
| Water | mg/kg | ≤300 | ≤50 | ASTM E1064 |
| Non-volatile residue | mg/kg | ≤10 | ≤5 | ASTM D1353 |
| Color, Pt-Co scale | — | ≤10 | ≤10 | ASTM D1209 |
| Total sulfur | mg/kg | ≤30 | ≤10 | ASTM D7183 |
These values are release criteria, not application warranties. For an extract intended for electron capture detection, a total sulfur result above 10 mg/kg can produce detector contamination and baseline instability after repeated injections. A solvent blank should be run under the same gas chromatographic conditions as the sample. Where benzene is a target analyte or a known interferent, the use of low-benzene purified toluene with benzene at or below 10 mg/kg is specified.
In headspace gas chromatography at equilibrium temperature 80 °C, purified toluene contributes a high vapor-phase solvent response that can saturate flame ionization detectors unless split injection or detector attenuation is used. The UV cutoff near 286 nm restricts absorbance detection below that wavelength; purified toluene is therefore a poor bulk mobile phase for reversed-phase HPLC with UV detection, while it remains suitable for dissolution and liquid-liquid extraction of nonpolar analytes. For gas chromatography/mass spectrometry, low non-volatile residue and low sulfur content reduce contamination of injection liners and ion source surfaces.
Purified toluene functions as an entrainer in Dean-Stark apparatus for removal of bulk water from reaction mixtures. The toluene-water heterogeneous azeotrope boils at 84.1 °C; the condensed vapor separates into a water-rich lower phase and a toluene-rich upper phase that returns to the pot. Anhydrous purified toluene with water at or below 50 mg/kg prevents the reflux return from adding water. On a 100 L glass-lined reactor with a jacketed overhead condenser, endpoint should be confirmed by Karl Fischer titration of the pot contents rather than by visual clearing of the distillate, because fine emulsions and bound water can persist after the last visible droplets are removed. Published data for exact drying rates in this specific configuration are limited because heat-transfer area, stirring, and condenser duty dominate the rate. The choice of toluene over higher-boiling xylene lowers pot temperature but carries a 4.4 °C flash point, so the headspace must remain nitrogen-inerted because the lower explosive limit is 1.1 vol%.
Toluene is not a peroxide-forming solvent in the manner of diethyl ether or tetrahydrofuran, but prolonged contact with air at elevated temperature produces benzaldehyde and benzoic acid via radical-chain autoxidation. Trace transition-metal residues can accelerate the process. The impact is most severe in low-carbonyl applications such as derivatization for aldehyde or ketone analysis, where even low benzaldehyde generation creates false positive responses. For anhydrous and low-carbonyl grades, the container is purged with inert gas and should be resealed under nitrogen after each use; opened containers exposed to air can show measurable benzoic acid within weeks when stored at temperatures above 35 °C. The ACS reagent monograph includes a test for substances darkened by sulfuric acid, which detects some oxidation and unsaturated impurities; it is not a kinetic limit for benzaldehyde generation. In production-scale solvent recovery, a wiped-film evaporator operated under vacuum reduces residence time at high temperature and limits oxidative byproduct accumulation compared with pot distillation.
Benzene has historically served as an aromatic reaction medium for organolithium and Grignard procedures, but its Class 1 residual solvent status under ICH Q3C imposes a permitted daily exposure of 0.02 mg/day, which drives replacement. Purified toluene is a Class 2 residual solvent with a permitted daily exposure of 8.9 mg/day and a concentration limit of 890 ppm. The substitution is not universally neutral. Toluene contains benzylic C–H bonds that are deprotonated by strong bases such as n-butyllithium; metalation at the methyl group can consume reagent and generate benzyl lithium species, altering reaction stoichiometry. For reactions requiring a non-basic aromatic diluent without acidic methyl hydrogens, high-purity benzene may be required on small scale, but the regulatory burden remains higher. In palladium-catalyzed cross-couplings conducted at 110 °C, purified toluene provides a higher reflux temperature than tetrahydrofuran and coordinates less strongly to palladium centers, but catalyst activation rates depend on ligand architecture and base solubility; comparative data for a given catalyst-substrate pair should be generated rather than assumed.
For liquid-liquid extraction of neutral organic molecules from aqueous process streams, purified toluene provides a nonpolar partition shift while maintaining a defined residual solvent limit under ICH Q3C. A toluene-rich extract is concentrated by vacuum distillation, often in a thin-film evaporator with jacket temperature 40–50 °C to prevent thermal degradation. Residual toluene in the final pharmaceutical intermediate must be reduced to 890 ppm or below unless process-specific justification is established; endpoint quantification is performed by headspace gas chromatography using a compendial method such as USP <467>.
In two-component polyurethane systems, purified toluene is used as a diluent for moisture-sensitive isocyanate prepolymers. Water in the solvent reacts with isocyanate groups to generate carbon dioxide and urea linkages, so anhydrous toluene with water at or below 50 mg/kg is required. The addition of 2.5 wt% purified toluene to a high-viscosity prepolymer can reduce viscosity for spray application; viscosity change is measurable by cone-and-plate rheometry under ASTM D2196 at 25 °C. Solvent dilution also changes open time and film formation; no single addition level is valid across all systems.
Material compatibility boundaries for purified toluene are defined by swelling and extraction. Long-term contact with low-density polyethylene or flexible polyvinyl chloride is unsuitable because plasticizers and antioxidants may leach into the solvent, increasing non-volatile residue and producing chromatographic artifacts. Polymer resistance can be screened by ASTM D543 immersion testing, which shows mass uptake and extractables generation. Equipment for closed transfer includes 316L stainless steel, borosilicate glass, and fluoropolymers such as PTFE or PFA. Elastomeric seals should be perfluoroelastomer rather than nitrile rubber, which can swell in aromatic solvents. At dispense points, a bonding and grounding clamp connected to a verified earth ground is required because toluene has a closed-cup flash point of 4.4 °C and static discharge can ignite a flammable headspace. Electrically conductive or static-dissipative components in pump diaphragms and transfer lines reduce accumulation; magnetically coupled sealless pumps eliminate mechanical seal leak points where ignition can occur.
The physical and regulatory property matrix across common aromatic solvents shows why purified toluene is selected as a compromise between benzene and xylene. Table 2 lists values from standard reference data.
| Parameter | Purified toluene | Benzene | Mixed xylene |
|---|---|---|---|
| Boiling point | 110.6 °C | 80.1 °C | 137–144 °C |
| Closed-cup flash point | 4.4 °C | −11.1 °C | 25–27 °C |
| UV cutoff | 286 nm | 280 nm | 290 nm |
| ICH Q3C class and PDE | Class 2, 8.9 mg/day | Class 1, 0.02 mg/day | Class 2, 21.7 mg/day |
These data show that purified toluene is not simply a substitute for either benzene or xylene. Its flash point is higher than benzene but lower than xylene; its boiling point is intermediate; UV cutoff is slightly red-shifted relative to benzene. For applications requiring lower toxicological burden and medium evaporation, purified toluene is selected when xylene’s higher boiling point slows recovery and benzene’s carcinogenicity is unacceptable.
A wiped-film evaporator used for solvent recovery from reaction mixtures preferentially removes toluene at low pressure; however, non-volatile residue limits in purified toluene should not be interpreted as absence of high-boiling reaction byproducts. A product contact test with a clean glass coupon after evaporation at 70 °C can reveal non-volatile residue far above the original solvent specification. For applications requiring residual solvent levels below 890 ppm in pharmaceutical intermediates, drying under vacuum with endpoint quantification by headspace gas chromatography is required.
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