| HS Code | 948966 |
| Product Name | Anhydrous Toluene |
| Chemical Formula | C7H8 |
| Molecular Weight | 92.14 g/mol |
| Cas Number | 108-88-3 |
| Appearance | Colorless liquid |
| Odor | Aromatic, benzene-like |
| Density | 0.8669 g/mL at 25 °C |
| Boiling Point | 110.6 °C |
| Melting Point | -95 °C |
| Flash Point | 4.4 °C (closed cup) |
| Autoignition Temperature | 480 °C |
| Solubility In Water | 0.52 g/L at 20 °C |
| Vapor Pressure | 28.4 mmHg at 25 °C |
| Refractive Index | 1.4961 at 20 °C |
| Water Content | ≤ 0.005% |
| Purity | ≥ 99.8% |
As an accredited Anhydrous Toluene factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Anhydrous Toluene packaged in 1 L amber glass bottles with PTFE-lined caps, securely sealed and labeled flammable/moisture-sensitive for safe transport. |
| Container Loading (20′ FCL) | Anhydrous Toluene, hazardous flammable liquid, is loaded into a 20′ FCL container in sealed drums, properly secured, labeled, and placarded. |
| Shipping | Anhydrous Toluene is typically shipped as UN1294, Toluene, Class 3 flammable liquid, Packing Group II. Use approved, sealed steel or glass containers under inert gas to prevent moisture. Label flammable, mark UN1294, and provide SDS/shipping papers. Store away from heat, sparks, oxidizers, and moisture. |
| Storage | Store anhydrous toluene in a cool, dry, well-ventilated, fire-resistant area away from heat, sparks, open flames, and oxidizers. Keep containers tightly closed, labeled, grounded, and bonded; protect from moisture, preferably under dry nitrogen. Use approved flammable-liquid cabinets and explosion-proof equipment. Separate from acids, bases, and incompatible materials. Avoid static discharge and inhalation. Ensure secondary containment where required. Follow local regulations. |
| Shelf Life | Anhydrous toluene generally has a shelf life of about two years when stored sealed, dry, cool, and protected from moisture. |
Anhydrous toluene enters the toluene diisocyanate chain as the substrate for mixed-acid nitration, not as a diluent. Plants converting toluene to dinitrotoluene typically specify nitration-grade material under ASTM D841-21 and control feed water below 0.02 wt% by ASTM E1064 coulometric Karl Fischer titration. The first nitration stage operates as a continuous two-phase reaction in a CSTR cascade or loop nitrator with a mixed acid containing 30–35 wt% nitric acid, 55–60 wt% sulfuric acid, and a water balance below 10 wt%. The nitric acid-to-toluene molar feed is held between 1.05:1 and 1.15:1 in the first stage to avoid excessive dinitration, while total acid feed after the second stage approaches 2.05–2.20 mol HNO₃ per mol toluene. Mononitration temperature is controlled at 35–45 °C with jacket and coil cooling; second-stage dinitration is elevated to 60–75 °C because the deactivated nitrotoluene ring requires higher nitronium ion activity. Water entering with the toluene reduces sulfuric acid strength, decreases nitronium ion concentration, and increases organic solubility in the acid phase; production-scale effects include slower phase separation, emulsion formation at the nitrator overflow, and higher spent acid recovery load in the downstream vacuum reconcentration unit. The isomer distribution after dinitration is approximately 76–80% 2,4-dinitrotoluene, 19–21% 2,6-dinitrotoluene, and the remainder mixed isomers; this ratio is governed by acid strength, temperature profile, and residence time rather than by toluene feedstock alone. The dinitrotoluene mixture is subsequently hydrogenated over nickel or palladium catalysts to toluene diamine and phosgenated to TDI for flexible polyurethane slabstock foam, elastomers, coatings, and sealants. Nitration units and spent acid handling are covered by major hazard legislation including Seveso III Directive 2012/18/EU in the European Union, and the exothermic nitration heat must be removed through external coolers or loop-reactor heat exchangers because dinitrotoluene thermal instability becomes critical above 250 °C in confined storage.
Fixed-bed hydrodealkylation of anhydrous toluene to benzene is another high-temperature aromatic conversion route where feed water is controlled not for phase separation but for catalyst life and selectivity. In a typical catalytic HDA unit, toluene is mixed with hydrogen-rich make-up and recycle gas at a hydrogen-to-aromatic molar ratio between 4:1 and 6:1, preheated through feed-effluent heat exchange, and brought to reaction temperature in a fired heater. The catalyst bed operates over chromium-promoted alumina at 550–650 °C and reactor pressures between 3.0 MPa and 5.0 MPa; thermal HDA variants operate above 650 °C without a catalyst. The primary reaction C6H5CH3 + H2 → C6H6 + CH4 is net exothermic, so staged quench hydrogen or inter-bed cooling is required to prevent temperature runaway. Water entering with the toluene or recycled hydrogen competes for adsorption on alumina Lewis acid sites, promotes sintered catalyst surface loss, and shifts the product distribution toward polyalkylbenzenes and polynuclear aromatics that accelerate coke deposition. Sulfur compounds are a more severe catalyst poison; therefore catalytic HDA units frequently require a hydrotreated or extractive-distilled toluene fraction with sulfur below 1 mg/kg and water below 10 mg/kg to maintain cycle lengths beyond 12 months. Published engineering data describe benzene yields above 95 mol% in optimized catalytic HDA when conversion is limited to avoid excessive toluene cracking to methane and coke. The benzene produced is routed directly to phenol via cumene oxidation, ethylbenzene/styrene, cyclohexane, or linear alkylbenzene processes. Because the unit operates above the autoignition temperature of toluene, piping and reactor metallurgy are governed by pressure equipment codes, and the plant flare system must handle high-temperature hydrogen-methane vapours during depressurization.
Anhydrous toluene functions as a low-moisture aromatic carrier in industrial coatings and contact adhesives where chlorinated rubber or polychloroprene resins are not fully soluble in aliphatic or oxygenated solvents alone. Chlorinated rubber maintenance primers use toluene in combination with methyl ethyl ketone, acetone, or xylene at total solids between 30 wt% and 40 wt%; a high-build topcoat may contain toluene at 20–30 wt% of the liquid formulation, adjusted by rotational viscometer to 200–500 mPa·s at 23 °C in accordance with ASTM D2196 or ISO 2884-1. Hansen solubility parameters for toluene are approximately 18.0 MPa1/2 dispersion, 1.4 MPa1/2 polar, and 2.0 MPa1/2 hydrogen bonding; these values place toluene inside the miscibility window for many chlorinated rubber and polychloroprene resin binders. In polychloroprene contact adhesives, toluene is blended with n-hexane or cyclohexane to adjust open time and wet tack; solvent blend ratio is determined by evaporation profile tests such as ASTM D3539 and by comparative brush-out or roll-coat trials under controlled temperature and humidity. Water in anhydrous toluene is controlled below 0.02 wt% because free water can promote flash rust on sand-blasted steel beneath chlorinated primers, with adhesion loss measurable by ASTM D3359 cross-cut tape testing after conditioning above 60% relative humidity. Toluene is classified under EU CLP Regulation 1272/2008 as Flam. Liq. 2 H225, Asp. Tox. 1 H304, STOT RE 2 H373, and Repr. 2 H361d; therefore maintenance coating operations are confined to industrial spray booths, enclosed coating lines, or automated curtain coaters with activated carbon recovery or regenerative thermal oxidation achieving 95–99% destruction efficiency. Directive 2004/42/EC is primarily aimed at decorative paints and does not govern most industrial maintenance finishes used on ships, cranes, or chemical plant steel, but national VOC emissions rules still require solvent mass balance records. Finished products include chlorinated rubber pool coatings, marine ballast tank linings, polychloroprene rubber-to-metal adhesives, and heat-seal coatings on flexible packaging where solvent release is controlled by oven temperature and residence time.
Pharmaceutical syntheses use anhydrous toluene as a solvent carrier in reactions where water terminates the active species or alters crystal morphology during isolation. For Grignard and organolithium chemistry, toluene is blended with tetrahydrofuran or 2-methyltetrahydrofuran to maintain solubility of the organometallic complex while suppressing the exotherm and improving phase separation during aqueous quench. The water specification for organometallic processing is tighter than nitration-grade material: operators commonly require ASTM E1064 Karl Fischer results below 0.005 wt%, with molecular sieve drying or azeotropic distillation used immediately before charging. In API final intermediate processing, toluene also removes water via a heterogeneous azeotrope at 84.1 °C; the condensed distillate separates in a Dean-Stark trap and water is withdrawn while toluene reflux returns to the reactor. The central regulatory boundary is residual solvent content in the final active pharmaceutical ingredient. Under ICH Q3C, toluene is Class 2 with a permitted daily exposure of 8.9 mg/day and a concentration limit of 890 ppm in the final drug substance; this limit drives terminal crystallization solvent selection and drying conditions. The compliance matrix below summarises the ICH Q3C classifications most often considered when toluene is used alongside other processing solvents.
| Solvent | ICH Q3C Class | PDE (mg/day) | Concentration Limit (ppm) |
|---|---|---|---|
| Toluene | Class 2 | 8.9 | 890 |
| Benzene | Class 1 | 0.02 | 2 |
| Methanol | Class 2 | 30.0 | 3000 |
| Dichloromethane | Class 2 | 6.0 | 600 |
Final isolation equipment includes agitated filter dryers, rotary vacuum dryers, and nitrogen-blanketed crystallizers in which residual toluene is removed until headspace gas chromatography or loss on drying meets the 890 ppm limit under USP 467; finished dosage form suppliers document the control as part of current good manufacturing practice under 21 CFR Part 211. Because toluene is not classified as a peroxide-forming solvent, it can be stored in stainless steel or carbon steel tanks; however, it is incompatible with strong oxidizers and must be segregated from nitric acid and chlorine service. Process analytical technology in larger API plants monitors water concentration in toluene before organometallic additions, because batch-to-batch variation from 0.005 wt% to 0.02 wt% water consumes the organometallic reagent and produces quenched byproducts that are difficult to purge in the downstream crystallization. Published data for optimal solvent volumes are limited because the ratio is tied to reaction heat and substrate solubility; typical laboratory-scale syntheses use 5–15 mL toluene per gram of limiting reagent, but this range is not a universal process parameter.
Liquid-phase air oxidation of anhydrous toluene to benzoic acid is a bubble-column or continuous stirred-tank process in which cobalt and manganese acetate catalysts and a bromide promoter are maintained in a recycled benzoic acid phase. The reactor operates at 150–170 °C and 0.6–1.0 MPa air pressure, with cobalt loadings often in the range 100–500 mg/kg, manganese loadings 200–800 mg/kg, and ionic bromide promoter 300–1,000 mg/kg relative to toluene feed. Conversion per pass is typically limited to 30–50% to preserve selectivity; unreacted toluene is recovered by flash evaporation and returned to the reaction loop. Water in the toluene feed is controlled below 200 mg/kg because elevated water activity hydrolyses hydrogen bromide at the gas-liquid interface, slows cobalt-catalysed chain initiation, and increases the formation of benzyl alcohol and benzyl benzoate intermediates that must be recycled or separated. Off-gas from the reactor is sent through a chilled condenser and thermal oxidizer because carbon monoxide and carbon dioxide are formed by oxidative decarboxylation side reactions. The crude benzoic acid is purified by distillation, sublimation, or melt crystallization; product quality is commonly specified by USP/FCC monographs or internal polymer-grade limits for phenol manufacture. Downstream, benzoic acid is converted to sodium benzoate food preservative, benzoyl chloride, phenol via copper-catalysed oxidative decarboxylation, and benzoate plasticizers. Anhydrous toluene is preferred because water removal downstream would otherwise require additional distillation energy and would reduce benzoic acid crystallizer yield. Published data for plant-specific water thresholds are limited; however, continuous oxidation units consistently list feed water, bromine recovery, and off-gas oxygen concentration as the three high-impact variables for reactor control. The air compressor, sparger arrangement, and reactor liquid height are designed so that oxygen mass transfer is sufficient while headspace oxygen remains below the limiting oxygen concentration for toluene vapour at the operating temperature and pressure.
Anhydrous toluene is the base feedstock for benzyl chloride production by free-radical side-chain chlorination in a photochlorination or thermally initiated continuous reactor. The chlorination is conducted at 100–120 °C with chlorine gas introduced through a porous sparger under ultraviolet illumination; the reactor is fabricated from nickel or glass-lined steel because wet chlorine generates hydrochloric acid and hypochlorous acid that attack stainless steel. Chlorine-to-toluene molar feed is held between 0.9:1 and 1.0:1 to keep the product distribution weighted toward benzyl chloride and to limit sequential chlorination to benzal chloride and benzotrichloride. The boiling points of the three side-chain chlorides are approximately 179 °C, 205 °C, and 220 °C respectively; vacuum distillation separates them, with heavier fractions recycled or sold as intermediates for benzaldehyde and benzotrichloride derivatives. Water in the feed has two direct effects: it hydrolyses benzyl chloride to benzyl alcohol and dibenzyl ether in the presence of metal chlorides, and it converts chlorine to HCl and HOCl, reducing effective chlorine concentration and promoting ring chlorination products that are difficult to separate. The toluene charge is therefore dried to below 50 mg/kg water and stored under dry nitrogen; benzyl chloride product is also kept below 100 mg/kg water to avoid storage corrosion. Terminal products from benzyl chloride include benzyl alcohol for coatings and fragrances, benzyl quaternary ammonium disinfectants, phenylacetic acid for pharmaceutical intermediates, and benzyl esters used as plasticizers or textile auxiliaries. This reaction route is incompatible with amines and other nucleophiles because benzyl chloride is a reactive alkylating agent; plant piping and tank vent scrubbers are dedicated to chlorinated organic service. The process is covered by major accident hazard obligations in the European Union where chlorine inventory exceeds Seveso III Directive 2012/18/EU thresholds.
Competitive Anhydrous Toluene prices that fit your budget—flexible terms and customized quotes for every order.
For samples, pricing, or more information, please contact us at +8615365186327 or mail to sales3@ascent-chem.com.
We will respond to you as soon as possible.
Tel: +8615365186327
Email: sales3@ascent-chem.com
Flexible payment, competitive price, premium service - Inquire now!
Anhydrous toluene is the moisture-controlled aromatic hydrocarbon solvent supplied under CAS 108-88-3, molecular formula C₇H₈, molar mass 92.14 g/mol, and EC number 203-625-9. Suppliers typically designate the material as “Anhydrous Toluene 99.8%,” “Extra Dry Toluene,” or “Toluene Anhydrous” without a universal model number; the descriptor rather than the code defines the product because the key differentiator is a Karl Fischer water limit of ≤0.005 wt% (50 ppm). Some distributor product lists use a shorthand such as TOL-ANH-50, where the suffix denotes the maximum water content in parts per million. The boiling point at 101.3 kPa is 110.6 °C, density at 20 °C is 0.865–0.867 g/cm³ by ASTM D4052-22, and the closed-cup flash point is 4 °C by ASTM D3828. Transport classification is UN 1294, hazard class 3, packing group II. The solvent is packed under dry nitrogen or argon in 1 L, 2.5 L, 4 L, 20 L, and 200 L containers; moisture-sensitive applications should treat the material as a reactive solvent even though it is not classified as a catalyst or reagent itself.
The primary specification is not purity alone; technical-grade toluene may also assay above 99% by gas chromatography yet contain dissolved water at 300–500 ppm. The anhydrous grade closes this gap by specifying water at ≤0.005 wt% (50 ppm) by ASTM E203-16 coulometric Karl Fischer titration, residue after evaporation ≤0.0005 wt% (5 ppm) by ASTM D1353-13, color ≤10 Pt-Co by ASTM D1209-00, distillation range 110.0–110.8 °C at 101.3 kPa by ASTM D850-18, total sulfur ≤0.0001 wt% (1 ppm) by ASTM D5453-19, and benzene ≤0.01 wt% (100 ppm) by gas chromatographic analysis. The benzene limit is relevant in pharmaceutical process solvents because benzene is an ICH Q3C Class 1 impurity with a concentration limit of 2 ppm in drug products; toluene itself is an ICH Q3C Class 2 solvent with a permitted daily exposure of 8.9 mg/day. A representative certificate of analysis may show water at 9–18 ppm, assay at 99.85–99.95%, and residue at 2–5 ppm; these values should be verified against the supplier lot because package size and storage conditions shift the final water content.
Residue after evaporation is controlling in microelectronic and pharmaceutical isolation steps because nonvolatile residues from plasticizers, hydrolysis products, or stabilizers remain in the final product after solvent evaporation. A residue level of 5 ppm in 1 L of toluene deposits approximately 4.3 mg of nonvolatile material; at a 100 L process scale, the potential residue becomes approximately 0.43 g. If the downstream product is a high-potency active pharmaceutical ingredient or a polymer with residual monomer limits, this residue may be analytically significant. For that reason, the solvent is not only dried but also filtered through 0.2 µm membrane filters into clean-in-place vessels before use in regulated processes.
| Property | Limit | Method |
|---|---|---|
| Assay as toluene | ≥99.8% area normalized | ASTM D7504-20, GC-FID |
| Water | ≤0.005 wt% (50 ppm) | ASTM E203-16, coulometric Karl Fischer |
| Distillation range | 110.0–110.8 °C at 101.3 kPa | ASTM D850-18 |
| Color | ≤10 Pt-Co | ASTM D1209-00 |
| Non-volatile residue | ≤0.0005 wt% (5 ppm) | ASTM D1353-13 |
| Total sulfur | ≤0.0001 wt% (1 ppm) | ASTM D5453-19 |
| Benzene | ≤0.01 wt% (100 ppm) | ASTM D7504-20, internal standard |
| Density at 20 °C | 0.865–0.867 g/cm³ | ASTM D4052-22 |
Certificate of analysis data should be evaluated with attention to the method detection limit. A coulometric Karl Fischer apparatus with a detection limit of 0.1 µg water can quantify water in anhydrous toluene at 1 ppm, but sampling error from syringe transfer through humid air can add 5–15 ppm to the reported value if the sample vial is not sealed under dry nitrogen. In routine quality control, a 20 µL sample injected into a diaphragm-free coulometric cell equipped with a fritted generator electrode gives repeatability of ±2 ppm at the 20 ppm level; values below 10 ppm require glass vials with PTFE-lined septa and a dry nitrogen glove bag.
High-purity anhydrous toluene is not necessarily low in benzene; if the intended use is a pharmaceutical or food-contact application, benzene should be specified separately at ≤0.001 wt% (10 ppm) or lower. Some suppliers provide a low-benzene anhydrous grade, but a universal model designation does not exist; the purchaser must specify both water and benzene limits because the two properties are independently controlled.
Because 1 L of anhydrous toluene at 50 ppm water contains 2.78 mmol H₂O, the solvent is not automatically dry enough for organolithium, Grignard, or anionic polymerization work; many preparative procedures require the final solvent to be dried to ≤10 ppm, equivalent to 0.56 mmol water per liter. This distinction is critical in anionic styrene polymerization, where each water molecule terminates one growing polymer chain. At a 1.0 mmol initiator charge, residual water at 10 ppm in 1 L consumes 56% of the active centers before propagation begins; at 50 ppm, water exceeds the initiator charge by a factor of 2.8. For this reason, standard laboratory preparation of anhydrous toluene for anionic polymerizations combines a preliminary molecular sieve drying step with distillation from sodium–benzophenone ketyl under inert gas, typically in a 5 L Schlenk flask fitted with a 30 cm Vigreux column and a mineral oil bubbler.
In pilot-plant organometallic reactions, the same stoichiometric sensitivity translates into stricter transfer controls. A 200 L stainless steel drum previously opened for sampling can show water levels rising from 12 ppm to 40–80 ppm after repeated extraction through un-dried fluoropolymer dip tubes. Production-scale equipment such as 1,000 L glass-lined reactors with double mechanical seals and nitrogen pads at 5–10 kPa gauge are used to maintain water conditions during organometallic reagent formation. Mechanical seal flush lines should be supplied with dry nitrogen rather than city water; ingress of 10 mL water into 1,000 L toluene raises water concentration by approximately 12 ppm, enough to alter stoichiometric performance in low-initiator processes.
Distillation from sodium–benzophenone ketyl remains the standard for stringent water and oxygen removal, but it introduces benzophenone decomposition products that are detectable by GC at 0.01–0.1 wt% unless a middle cut is taken. For large-scale processes where such residues are unacceptable, in-line molecular sieve drying is preferred because it does not add a scavenger-derived residue. However, molecular sieve drying does not remove dissolved oxygen; oxygen-sensitive organometallic processes must therefore combine water removal with argon or nitrogen sparging at 0.1–0.3 L/min and monitor dissolved oxygen below 5 ppm.
Anhydrous toluene that is received at 50 ppm is routinely polished before catalyst-sensitive processing using columns packed with 3A molecular sieves of 1.6 mm or 3.2 mm extrudate diameter. The 0.3 nm pore aperture of 3A sieves excludes the toluene molecule, which has a kinetic diameter near 0.61 nm, while allowing water to diffuse into the aluminosilicate cage. A vertical column of 30 cm internal diameter and 120 cm bed height can polish water from 30 ppm to below 5 ppm at linear velocities of 0.02–0.04 m/s, but capacity is strongly dependent on feed moisture and regeneration. Molecular sieves regenerated at 250 °C for 4 h under 0.2 m/s nitrogen flow remove water effectively; incomplete regeneration at 180 °C has been associated with early breakthrough in 200 L batch dryers, where Karl Fischer readings increase from 4 ppm to 85 ppm within 6 h.
For packaging, glass containers with PTFE-lined caps reduce water permeation; polyethylene containers are not suitable for long-term storage of ≤10 ppm toluene because water vapor permeation through polyethylene can raise water content by 0.5–2 ppm/day depending on wall thickness and ambient humidity. Steel drums with phenolic or epoxy-phenolic linings are preferred for 200 L quantities. Transfer lines should be stainless steel or fluoropolymer, purged with dry nitrogen at 0.5–1.0 L/min and verified by dew-point meter or Karl Fischer before charging. In a closed 1,000 L reactor maintained under a 5–10 kPa nitrogen pad, water content can be held at ≤10 ppm for 14 days; without a pad, atmospheric moisture ingress through pump seals and manway gaskets can increase water at 1–3 ppm/day.
Commercial columns for toluene polishing are often specified with length-to-diameter ratios above 4:1 and pressure drop below 0.7 bar at 30 L/min flow. A 50 L bed of 3A molecular sieves can reduce water from 50 ppm to ≤5 ppm for 500–800 L toluene, but breakthrough is gradual; operators use Karl Fischer sampling at intervals of 30 min or online near-infrared water analyzers. Spent sieve beds are not reliably judged by color; only Karl Fischer or an in-line moisture analyzer can confirm breakthrough, because the water adsorption front moves through the bed before visible wetting occurs.
Technical-grade toluene is not interchangeable with anhydrous toluene in catalyst systems involving titanium tetrachloride, trimethylaluminum, methylaluminoxane, or organolithium reagents. Technical grades are typically supplied with water up to 0.05 wt% (500 ppm), which is one order of magnitude above the 50 ppm anhydrous limit and enough to hydrolyze organometallic co-catalysts. For example, water reacts irreversibly with trimethylaluminum to form methane and aluminum hydroxide/oxide species; 1 L of toluene at 500 ppm water introduces 27.8 mmol H₂O, which can deplete 27.8 mmol of trimethylaluminum and alter cocatalyst-to-catalyst ratios in metallocene polymerization. ACS reagent toluene allows water at 0.03 wt% (300 ppm), which is still six times higher than the anhydrous limit; therefore, ACS material is acceptable for non-aqueous titrations and general laboratory extraction but is not a substitute for anhydrous grade in organometallic synthesis. HPLC toluene is optimized for UV transmittance and low particulates rather than water control, and its water content often overlaps with technical or ACS grade. Thus grade selection is a chemical compatibility decision, not solely a purity decision.
| Grade | Typical water limit | Typical assay | Primary control target | Compatibility with organometallic chemistry |
|---|---|---|---|---|
| Anhydrous | ≤0.005 wt% (50 ppm) | ≥99.8% | Water and residue | Suitable only with controlled transfer and further drying where required |
| ACS reagent | ≤0.03 wt% (300 ppm) | ≥99.5% | General laboratory purity | Not recommended without subsequent drying |
| Technical | ≤0.05 wt% (500 ppm) | 99.0–99.7% | Broad industrial use | Unsuitable for organometallic or anionic processes |
| HPLC | 0.02–0.05 wt% | ≥99.9% | UV transmission and particulates | Not specified for moisture control; verify lot water before use |
Across fine-chemical manufacturing, anhydrous toluene functions as a process solvent for magnesium-based Grignard reactions, for lithium–halogen exchange in substituted arenes, and for catalytic hydrogenation of benzyl ethers or nitro groups at 60–100 °C and 3–10 bar hydrogen over palladium or Raney nickel. The solvent must be low in water, but also low in sulfur because sulfur compounds poison precious-metal catalysts; a sulfur limit of 1 ppm is therefore more than a purity marker. In hydrogenation of a nitroarene at 80 °C on 5% Pd/C, use of toluene containing 10 ppm thiophene or benzothiophene has been associated with catalyst-cycle shortening and higher palladium attrition, although published data for this specific configuration is limited. For this reason, plant operators typically specify both total sulfur and water on the purchase order and verify retained samples by ASTM D5453-19 and ASTM E203-16 before charging.
In batch hydrogenation at 4 bar hydrogen on 5% Pd/C, water in toluene at 200–500 ppm is generally tolerated because the catalyst surface is not hydrolytically sensitive. However, the same solvent lot may be reused after a distillation recovery step, and water removal from recovered toluene requires a separate drying operation; therefore, starting with anhydrous grade avoids mixed-lot moisture and accelerates batch turnaround. Published data for this specific configuration is limited, but plant practice is to set a water limit of 100 ppm for hydrogenation and lower than 10 ppm for organometallic reactions.
Storage before use requires exclusion of atmospheric oxygen and moisture; the solvent is flammable with a lower explosive limit of 1.1 vol% and an upper explosive limit of 7.1 vol%, so tank and drum operations are performed under inert gas. Toluene may form hazardous oxidation products such as benzaldehyde and benzoic acid during prolonged air exposure, and anhydrous grade is not oxygen-free unless sparged. Incompatibilities include strong exothermic reactions with concentrated nitric acid, sulfuric acid, and oxidizing agents; mixtures with nitric acid can form nitrotoluenes and should be avoided. Contact with amine-based additives or water-based quench lines should be avoided if the solvent is to be reused in moisture-sensitive organometallic batches. Because water saturation in toluene at 25 °C is approximately 520 ppm, the 50 ppm limit is not close to saturation, but it is still too high for anionic chain-growth polymerizations; for such processes, final water should be below 10 ppm and verified immediately before use.
Dedicated to excellence in chemistry — serving industries worldwide with integrity and innovation.
