| HS Code | 592302 |
| Product Name | Synthesis Grade Toluene |
| Chemical Formula | C7H8 |
| Cas Number | 108-88-3 |
| Ec Number | 203-625-9 |
| Molecular Weight | 92.14 g/mol |
| Appearance | Colorless liquid |
| Odor | Aromatic, benzene-like |
| Purity | ≥99.5% |
| Density | 0.866 g/cm³ at 20 °C |
| Boiling Point | 110.6 °C |
| Melting Point | -95 °C |
| Flash Point | 4 °C (closed cup) |
| Solubility | Slightly soluble in water; miscible with ethanol, ether, and acetone |
| Vapor Pressure | 3.8 kPa at 20 °C |
| Refractive Index | 1.496 at 20 °C |
| Autoignition Temperature | 480 °C |
As an accredited Synthesis Grade Toluene factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Synthesis Grade Toluene supplied in 2.5 L metal safety cans with flame-arresting caps, hazard labels, batch numbers, and secure outer cartons. |
| Container Loading (20′ FCL) | Synthesis Grade Toluene loaded into a 20′ FCL container, securely stowed, sealed, labeled, and documented for safe hazardous chemical transport. |
| Shipping | Synthesis Grade Toluene is shipped as a hazardous, flammable liquid (UN 1294, Class 3, Packing Group II) in UN-approved, tightly sealed containers. Packages bear flammable-liquid labels and UN markings. Transport requires proper shipping papers, emergency response information, placarding, segregation from oxidizers, and protection from ignition sources, heat, and sunlight. |
| Storage | Store Synthesis Grade Toluene in a cool, dry, well-ventilated, fire-resistant area away from heat, sparks, flames, and strong oxidizers. Keep containers tightly closed, clearly labeled, upright, and grounded. Use approved flammable-liquid cabinets or safety cans. Protect from direct sunlight, maintain secondary containment, and ensure spill kits and ventilation are available. Avoid inhalation and ignition sources. Store at moderate ambient temperature. |
| Shelf Life | Synthesis Grade Toluene shelf life is about five years when stored sealed in a cool, dry, well-ventilated area, away from ignition. |
Residual moisture in synthesis grade toluene supplied for organomagnesium and organolithium staging determines initiation reproducibility on production-scale cryogenic Grignard trains. A coulometric Karl Fischer result above 50 mg/kg (ASTM E1064-24) is routinely corrected by circulating the solvent through activated 4Å molecular sieves or passing it over alumina under a –40 °C nitrogen pad before metal addition. A typical synthesis-grade certificate meets the ASTM D841-22 nitration grade toluene specification for distillation range and sulfur, with additional internal limits on water and peroxide. The failure mode on a 2 m³ glass-lined reactor is not merely delayed induction; water-derived alkoxide films on magnesium turnings produce localized hot spots that raise tetrahydrofuran ring-opening impurities by several hundred milligrams per kilogram, which then complicate crystallization of the isolated API. Synthesis grade material with benzene above 500 mg/kg is rejected for organomagnesium staging because benzene coordinates to organolithium aggregates and alters reaction selectivity; this level is verified by ASTM D6526-12 capillary gas chromatography. Peroxide accumulation after drum exposure is checked with ASTM E298-17, and any lot exceeding 10 meq/kg active oxygen is pre-washed with sodium metabisulfite before distillation. Residual toluene remaining in the isolated pharmaceutical substance falls under the ICH Q3C(R8) Class 2 residual solvent limit of 890 ppm (PDE 8.9 mg/day), which governs the final solvent swap and drying curve rather than the initial feedstock specification.
In a continuous nitration train, toluene feed is contacted with mixed acid containing 30–35 wt% nitric acid and 50–60 wt% sulfuric acid in a cooled stirred reactor at 45–65 °C. Synthesis grade toluene with benzene above 500 mg/kg nitrates to nitrobenzene in parallel; nitrobenzene must be vacuum-distilled from the raw dinitrotoluene stream, and its accumulation raises the lower-boiling impurities fraction in the downstream hydrogenation feed. The dinitrotoluene isomer distribution is controlled at roughly 76–80 wt% 2,4-DNT and 20–24 wt% 2,6-DNT by spent acid strength and nitration residence time. The isomer mixture solidifies in transfer lines below 54–58 °C, so steam tracing is required from the nitrator to the hydrogenation battery.
| Feed impurity | Test method | Synthesis-grade threshold | Observed process consequence |
|---|---|---|---|
| Total sulfur | ASTM D7183-23 | ≤ 5 mg/kg | hydrogenation catalyst deactivation and higher reactor temperature |
| Water | ASTM E1064-24 | ≤ 50 mg/kg | urea oligomer deposits in phosgenation |
| Benzene | ASTM D6526-12 | ≤ 500 mg/kg | nitrobenzene byproduct load in DNT purification |
| Non-aromatic hydrocarbons | ASTM D6526-12 | ≤ 500 mg/kg | exothermic side products and spent acid fouling |
Hydrogenation of dinitrotoluene to toluene diamine is carried out over supported nickel or palladium catalysts in a slurry or fixed-bed autoclave at 100–200 °C and 20–50 bar hydrogen. Sulfur compounds entering with the original toluene concentrate on the catalyst surface; total sulfur exceeding 5 mg/kg in the synthesis grade feed produces a measurable loss in nitro group conversion within 300–500 h of continuous operation and forces an increase in catalyst loading or reactor temperature that shortens the cycle. The specification of sulfur below 5 mg/kg by ASTM D7183-23 is therefore a direct control on TDA quality, because unconverted dinitrotoluene and partially hydrogenated nitrotoluene intermediates become reactive impurities during phosgenation. Water above 50 mg/kg in the downstream TDA feed reacts with phosgene to form urea oligomers that deposit on the phosgene condenser and narrow the distillation cut for toluene diisocyanate monomer.
In catalytic hydrodealkylation, synthesis grade toluene is mixed with hydrogen at a molar ratio between 4:1 and 8:1, preheated to 600–700 °C, and passed over a chromia-alumina catalyst in a fixed-bed reactor at 40–60 bar. The desired reaction consumes toluene and hydrogen to produce benzene and methane; however, non-aromatic hydrocarbons in the feed are cracked in the same hot zone to lower molecular weight paraffins and olefins. A concentration above 0.02 wt% non-aromatics, determined by ASTM D6526-12, increases hydrogen consumption per ton of benzene and raises the inert gas load in the high-pressure separator. Sulfur compounds at even 1 mg/kg reduce the activity of the chromia-alumina surface and raise the reactor inlet temperature required to hold 60–70% toluene conversion per pass.
The hydrodealkylation section is not a purification unit for off-spec toluene. Fresh feed is combined with recycled toluene from the benzene fractionation column; if non-aromatic impurities accumulate in the recycle loop, they reach an equilibrium concentration that can exceed the fresh feed limit by 3–5 times. This forces a purge stream that removes valuable toluene and modifies the benzene product freeze point from the expected 5.5 °C specification of ASTM D852-20. Production-scale units therefore monitor the ratio of benzene to total non-aromatics in the recycle stream with online gas chromatography rather than relying on fresh feed certificates alone.
Oxidation of synthesis grade toluene to benzoic acid is operated in sparged titanium or Hastelloy C-276 reactors at 140–170 °C and 3–7 bar total pressure, using cobalt acetate and manganese acetate as homogeneous catalysts and air as the oxidant. The reaction proceeds through benzaldehyde as the principal intermediate; benzaldehyde then oxidizes to benzoic acid, while a side pathway forms benzyl alcohol and benzyl benzoate. The process window is narrow: at temperatures below 140 °C the benzaldehyde intermediate accumulates and must be recovered separately, while above 170 °C exothermic decarboxylation and ring-opening reactions produce color bodies and lower the acid yield by 2–5 percentage points. Trace sulfur, phenols, and olefins in the synthesis grade toluene poison the cobalt/manganese catalyst by forming insoluble coordination species that settle in the reactor loop and reduce oxygen uptake; total sulfur is therefore held below 5 mg/kg and water below 50 mg/kg.
The oxidation reaction is deliberately limited to 30–50% toluene conversion per pass to keep benzaldehyde and benzylic byproducts within a distilable range. Unconverted toluene is stripped and recycled, while crude benzoic acid is purified by melt crystallization or distillation to a purity above 99.5 wt%. For food-grade sodium benzoate, the resulting benzoic acid must meet the monograph requirements of the Food Chemicals Codex and the EU food additive specification E210/E211 regarding heavy metals, arsenic, and chlorinated organic impurities. Residual toluene in the benzoic acid after drying is controlled below 100 mg/kg using ASTM D6526-12, because downstream sodium benzoate production cannot remove a solvent residue once the acid is neutralized.
Oleum sulfonation of synthesis grade toluene in a stirred steel reactor with a glass-lined or PTFE-lined interior is initiated with 20–30% free sulfur trioxide at jacket temperatures between -5 °C and 10 °C. Under these kinetically controlled conditions, sulfonation occurs primarily at the ortho position; the para-isomer content rises as the reaction mass is held at 60–100 °C for the thermodynamic equilibration stage. The exothermic heat of dilution when toluene is fed into oleum is sufficient to raise the internal temperature by 20–30 °C within minutes if the addition rate is not restrained; runaway sulfonation produces sulfone crosslinks and dark polymeric byproducts that are difficult to remove from p-toluenesulfonic acid downstream. Published isomer distributions for continuous oleum sulfonation under these exact jacket conditions are limited; industrial control relies on in-line Raman spectroscopy or quench-and-titrate acidity rather than fixed recipes.
The resulting p-toluenesulfonic acid is used as an esterification catalyst and as a counterion in pharmaceutical salts where residual free toluene in the final dried acid must be below the ICH Q3C(R8) limit of 890 ppm in the drug substance. Synthesis grade toluene with non-aromatic impurities above 0.02 wt% produces odor-bearing alkylbenzenesulfonic acids that carry through to final formulations, so the feedstock is verified by ASTM D6526-12 before charging. For esterification reactors, p-toluenesulfonic acid loading is governed by the acid value titration of the finished ester; the sulfuric acid impurities from oleum sulfonation are removed by washing the crystalline p-toluenesulfonic acid with dichloromethane or toluene, followed by vacuum drying at 60–80 °C and 10–20 kPa.
When chlorine is injected below the liquid surface in a glass or fluoropolymer-lined column maintained at 80–100 °C under a 350–400 nm ultraviolet lamp, side-chain chlorination of synthesis grade toluene proceeds by a radical chain mechanism. Trace iron salts in the feedstock or reactor must be excluded because dissolved iron promotes electrophilic ring chlorination instead of benzylic substitution, producing chlorotoluene isomers that shift the boiling range of the crude benzyl chloride and make it unsuitable for quaternary ammonium biocide manufacture. The conversion is limited to 20–30% per pass to keep benzal chloride below 1–2 wt% in the crude distillate; unconverted toluene is recovered and recycled, while the raw benzyl chloride is fractionated under vacuum at 20–30 kPa to minimize thermal dehydrochlorination. Water in the toluene feed above 50 mg/kg hydrolyzes benzyl chloride during distillation to benzyl alcohol and generates hydrochloric acid corrosion in the overhead condenser; the feed is therefore dried over molecular sieves and checked by ASTM E1064-24. Benzyl chloride produced from synthesis grade toluene is subsequently hydrolyzed with aqueous sodium hydroxide at 100–110 °C to benzyl alcohol or reacted with tertiary amines to form benzalkonium-type biocides, both of which require residual toluene below 100 mg/kg in the isolated product to satisfy the harmonised classification of the EU CLP Regulation (Annex VI) for acute inhalation toxicity and skin sensitisation.
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Synthesis grade toluene is a high-purity aromatic hydrocarbon solvent identified by CAS 108-88-3, formula C₇H₈, and molar mass 92.14 g·mol⁻¹. Commercial part numbers are supplier-specific; standard, anhydrous, and high-purity variants may be assigned different product codes, and no universal model designation applies across the supply base. At 20 °C the liquid density is 0.8669 g·cm⁻³, the refractive index is 1.4961, and the normal boiling point is 110.6 °C. The freezing point is −95 °C. The closed-cup flash point is 4.4 °C, vapour pressure is 2.8 kPa at 20 °C, and the autoignition temperature is 480 °C. Because no single public standard currently defines “synthesis grade” toluene, supplier certificates of analysis control the grade. A representative certificate of analysis includes the parameters shown in Table 1; the ranges are common supply-base targets, not a universal ASTM specification. The closest public aromatic specification, ASTM D841, covers nitration-grade toluene and does not impose the tighter benzene, sulfur, and water limits often specified for synthesis use.
| Parameter | Common synthesis-grade target | Test method |
|---|---|---|
| Purity | 99.5–99.9 wt% | ASTM D2360 |
| Benzene | ≤0.01–0.05 wt% | ASTM D2360 |
| Water | ≤0.01–0.02 wt%; anhydrous variants may be lower | ASTM E1064 |
| Non-volatile residue | ≤0.0005 wt% | ASTM D1353 |
| Colour | ≤10 Pt-Co | ASTM D1209 |
| Sulfur | ≤1–5 mg/kg | ASTM D5453 |
Compared with nitration grade, synthesis grade is differentiated less by total aromatic purity than by the exclusion thresholds applied to benzene, non-aromatic hydrocarbons, sulfur-containing thiophenes, and water. Nitration grade toluene under ASTM D841 permits ≥98.5 wt% toluene and a maximum benzene content of 0.5 wt%; this impurity load is acceptable in exothermic nitration but can deactivate Ziegler-Natta catalysts or interfere with polar organometallic intermediates. ACS reagent-grade toluene, defined by the ACS Committee on Analytical Reagents, requires ≥99.5% assay and restricts water to ≤0.03 wt%, but it is not always characterised for process-specific species such as trace halides, oxygenates, or thiophene sulfur that synthesis-grade suppliers may report on request. Technical or commercial-grade streams may range from 90–98 wt% toluene and are generally unsuitable for synthesis use without prior distillation and purification because of olefinic and sulfur-bearing contaminants.
| Grade | Total toluene | Benzene control | Water control | Process consequence |
|---|---|---|---|---|
| Synthesis grade | 99.5–99.9 wt% | ≤0.05 wt% | ≤0.02 wt% | Must still be validated for anhydrous reaction classes |
| Nitration grade | ≥98.5 wt% | ≤0.5 wt% | Not tightly controlled | Acceptable for nitration; risk of catalyst deactivation elsewhere |
| ACS reagent | ≥99.5 wt% | Not always reported | ≤0.03 wt% | Laboratory analytical use; process-specific impurity profile may be incomplete |
| Technical | 90–98 wt% | Variable | Variable | Requires purification before synthesis |
Water content is not an isolated quality parameter; it defines the boundary between a process solvent and a catalyst poison in several reaction classes. A synthesis-grade lot with a certificate value of 0.01 wt% water contains approximately 100 mg·kg⁻¹ water, which is one order of magnitude higher than the <10 mg·kg⁻¹ target required in many metallocene-catalysed polymerisation systems. The toluene–water azeotrope boils at 84.1 °C and contains 19.6 wt% water, allowing azeotropic water removal in esterification, acetalisation, and condensation polymerisation. In a 1000 kg reactor charge of toluene containing 0.02 wt% water, the total water load is 0.2 kg, which forms roughly 1.05 kg of azeotrope at the azeotropic composition. On production-scale equipment, azeotropic drying is conducted in glass-lined reactors with external reflux condensers; batch-to-batch variability is monitored by ASTM E1064 Karl Fischer titration at the feed tank and after distillation. Toluene’s water solubility at 25 °C is approximately 0.52 g·L⁻¹; therefore a reflux splitter that returns water-saturated organic phase to the reactor can reintroduce moisture if the decanter is not maintained at the correct interface level.
For organolithium chemistry, toluene is frequently selected because its low Lewis basicity does not competitively coordinate the lithium centre to the same extent as tetrahydrofuran. Toluene has a dielectric constant of 2.38 at 25 °C and a dipole moment of 0.36 D; this weakly coordinating environment can change lithium reagent aggregation and may alter enantioselectivity in asymmetric deprotonation. However, synthesis grade toluene with ≤0.02 wt% water is generally not anhydrous enough for sec-butyllithium or tert-butyllithium at −78 °C; distillation from sodium-benzophenone ketyl or passage through activated 3A or 4A molecular sieve columns is performed immediately before use. Production-scale transfer requires nitrogen or argon blanketing with oxygen intrusion maintained below 0.5 ppm in the headspace; stainless-steel or glass-lined transfer lines with PTFE seals are used because toluene can extract plasticisers from flexible PVC tubing. In Ziegler-Natta polyolefin catalyst preparation, water and oxygen are catalyst poisons; methylaluminoxane-activated metallocene catalysts are routinely prepared in dry toluene containing <10 mg·kg⁻¹ water. Published data for the specific loss of catalyst activity as a function of water in synthesis grade toluene is limited, but catalyst suppliers commonly specify dry solvent as part of the catalyst handling procedure.
Synthesis grade toluene used in pharmaceutical synthesis is evaluated under ICH Q3C residual solvent guidance. Toluene is a Class 2 solvent with a permitted daily exposure of 8.9 mg·day⁻¹ and a concentration limit of 890 ppm in the drug substance, unless process-specific toxicological justification allows a higher limit. The use of synthesis grade rather than technical toluene does not eliminate the need for residual solvent analysis; it reduces the co-introduction of benzene and non-volatile residue that would otherwise complicate downstream crystallisation. Under EU CLP, toluene is classified as Flam. Liq. 2 (H225), Asp. Tox. 1 (H304), Repr. 2 (H361d), STOT RE 2 (H373), and Skin Irrit. 2 (H315); these classifications apply irrespective of purity grade. Occupational exposure limits include the OSHA permissible exposure limit of 200 ppm as an 8-hour time-weighted average and the ACGIH threshold limit value of 20 ppm; engineering controls must account for both.
Toluene’s vapour pressure of 2.8 kPa at 20 °C places the closed vessel above the lower explosive limit at ambient temperature. The flammability range in air is 1.1–7.1 vol%, and the closed-cup flash point is 4.4 °C; therefore, centrifuges, mixers, and pumps must be inerted, grounded, and interlocked to shut down on nitrogen failure. Magnetic-drive sealless pumps or double mechanical seals with quench systems are preferred; packed centrifugal pumps are inappropriate for continuous toluene transfer because gland leakage creates a flammable vapour zone. Storage tanks should incorporate pressure-vacuum breathing valves and nitrogen blanketing; all metal transfer components should have resistance to earth below 10 Ω under IEC 61340-5-1 static-control practices. The autoignition temperature of 480 °C requires hot surfaces such as steam coils and heat tracing to be classified and controlled below the temperature class limit of the area’s electrical classification.
Toluene is incompatible with strong oxidisers; contact with concentrated nitric acid, sulfur trioxide, or permanganate can initiate exothermic oxidation. Storage should be at 15–25 °C in a flammable-liquid store with secondary containment capacity of 110% of the largest vessel. Opened containers should be resealed under inert gas; repeated opening in high-humidity environments above 60% RH increases water uptake, making previously opened containers unsuitable for critical anhydrous applications without re-drying. Synthesis grade certificates of analysis do not automatically include halide content; when the material is intended for transition-metal catalysis, chloride and total halides should be added to the purchase specification. Drying over activated 3A or 4A molecular sieves is common; sieves should be activated at 300 °C under vacuum for at least 12 h and added to the vessel under inert gas.
Synthesis grade toluene is selected over benzene and mixed xylene when the process requires a balance of moderate boiling point, low polarity, and azeotropic water removal. Benzene has a normal boiling point of 80.1 °C but is classified as a known human carcinogen under IARC Group 1; mixed xylene has a boiling range of 138–144 °C and lower vapour pressure, which is advantageous for high-temperature dissolution but harder to remove by distillation. Toluene’s Hildebrand solubility parameter is approximately 18.2 MPa^0.5, with Hansen parameters δD 18.0 MPa^0.5, δP 1.4 MPa^0.5, and δH 2.0 MPa^0.5; these values guide polymer dissolution and non-covalent interaction screening. In electrophilic aromatic substitution, synthesis grade toluene can serve as both solvent and alkylbenzene substrate, but low benzene and sulfur content are critical to prevent competitive impurities. Published data for every specialty application cannot be transferred from generic solvent tables; process-specific compatibility and impurity tolerance must be verified by the certificate of analysis and site qualification runs.
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