Benzothiazole,96%

What Specific Molar Ratio Governs the Formation of 4,4′-Bis(benzothiazole-2-yl)stilbene from Terephthaldehyde?

Synthesis of the di-styrylbenzene-type optical brightener 4,4′-bis(benzothiazole-2-yl)stilbene (CAS 63579-02-0) from benzothiazole 96% proceeds via a high-temperature condensation with dimethyl terephthalate in a 1:0.48 molar stoichiometry, typically in a high-boiling aromatic solvent such as 1,2,4-trichlorobenzene at 210–215 °C under nitrogen blanket with 0.3–0.5 mol% antimony trioxide catalyst. This chemistry yields a bis-benzothiazole adduct with a λ_max absorption at 370–375 nm and blue-violet fluorescence peaking at 435–440 nm, measured in dimethylformamide solution per ISO 2470-1:2016. Inclusion levels in polycarbonate, rigid PVC, and polystyrene range from 0.008–0.035 wt%, standardized by CIELAB b* value reduction to ≤ -6.0 at 0.02% loading in a 3 mm injection-molded plaque, evaluated under D65 illumination. Post-extrusion sheet intended for food-contact packaging must comply with EU Regulation 10/2011 Annex I and the specific migration limit for benzothiazole itself set at 0.05 mg/kg food simulant, while U.S. indirect additive clearance falls under FDA 21 CFR 178.3297 (colorants for polymers). The downstream manufacturing process involves a wiped-film evaporator to strip solvent to <150 ppm residual, followed by a pin mill micronization step to a particle size D₉₀ < 5 µm, which is critical for uniform dispersion in polyester masterbatch. Typical terminal articles include blow-molded PET water bottles, polyolefin nonwoven fibers for hygiene products, and extruded PMMA light-diffusing panels where ultraviolet-induced yellowing index increase must remain below 2.0 after 500 hours Xenon-arc exposure per ISO 4892-2:2013.

The largest-volume application of benzothiazole 96% globally remains its conversion to 2-mercaptobenzothiazole (MBT, CAS 149-30-4), which serves as the primary accelerator in sulfur-vulcanized diene rubber goods. Production is conducted in a 316L stainless steel high-pressure autoclave rated for PN 100, charged with benzothiazole, carbon disulfide, and sulfur in a typical molar feed ratio of 1:1.08:1.25, alongside a tertiary amine catalyst at 0.8–1.2 wt% of the total organic charge. The vessel is brought to 230–240 °C under a sustained pressure of 55–68 bar for a hold time of 5–7 hours, after which hydrogen sulfide off-gas is scrubbed in a 15% sodium hydroxide packed column and the crude MBT slurry is purified via acidification to pH 3.0–3.5 with sulfuric acid, crystallized, and dried in a rotary vacuum dryer at < 80 °C to a residual moisture of < 0.3 wt%. Conforming to GB/T 11407-2013 and ISO 10398:1998, the resulting MBT powder exhibits an initial melting point of 180–182 °C and a methanol-insoluble matter below 0.15%. In a typical natural rubber passenger tire tread formulation (NR 100 phr, N330 carbon black 50 phr, zinc oxide 5 phr, stearic acid 2 phr, sulfur 2.5 phr), MBT is dosed at 0.8–1.5 phr to achieve a Mooney scorch time (t₅ at 121 °C) of 18–24 minutes per ASTM D1646 and a rheometer cure time (t₉₀ at 160 °C) of 4–6 minutes on an MDR 2000 instrument per ASTM D5289. End products include steel-belted radial tire treads, conveyor belt covers, and vibration-damping engine mounts, all subject to REACH Annex XVII entry 50 restrictions on residual free benzothiazole in the vulcanizate.

A niche but pharmacologically critical downstream route involves the N-alkylation of benzothiazole to yield intermediates for topical imidazole antifungals such as eberconazole nitrate. In a 500-L glass-lined reactor under nitrogen, benzothiazole 96% is reacted with 1-(2,4-dichlorophenyl)-2-(chloromethyl)-1H-imidazole in anhydrous dimethylformamide at 50–55 °C in the presence of finely ground potassium carbonate (1.4 equivalents), with the benzothiazole-to-alkylating agent molar ratio maintained at 1:0.98 to limit dialkylation impurities detected by UPLC at 0.10% area threshold. After 18 hours, the mixture is drowned into purified water, extracted with toluene, and the organic layer washed to a conductivity < 5 µS/cm, then concentrated in a wiped-film evaporator at 60 °C/20 mbar to a non-volatile residue suitable for salt formation. The resulting intermediate must exhibit a purity of ≥ 99.5% by area normalization and contain benzothiazole at ≤ 0.05%, meeting the organic impurity criteria of European Pharmacopoeia monograph 2.2.46 for the final active pharmaceutical ingredient. This synthesis is executed within an ISO 14644-1 Class 8 cleanroom with differential pressure cascade maintaining −15 Pa in the reactor room relative to surrounding corridors, and all solvents used comply with ICH Q3C residual solvent class 2 limits. The final formulation, a 1% w/w eberconazole nitrate cream, incorporates the intermediate after nitrate salt precipitation and jet-milling to D₉₀ < 10 µm for consistent topical bioavailability.

Metal Passivation in Glycol-Based Engine Coolants: Benzothiazole Concentration Thresholds

Benzothiazole 96% is directly incorporated into heavy-duty engine coolant concentrates as a copper-corrosion inhibitor, typically at 0.15–0.40 wt% active substance in the ready-to-use fluid, representing a 3.0–8.0 g/L as-sold concentrate based on 33 vol% coolant-to-water dilution per SAE J1034. The inhibition mechanism relies on the chemisorption of the thiazole ring onto cuprous oxide surfaces, with electrochemical potentiodynamic polarization scans (ASTM G59) in 30 vol% ethylene glycol solution containing 200 ppm chloride showing a shift in corrosion potential (E_corr) from −220 mV vs. SCE to +45 mV when 25 mg/L benzothiazole is present, accompanied by a decline in corrosion current density (i_corr) from 8.5 µA/cm² to below 0.3 µA/cm². Compatibility with other inhibitors is mandatory: benzothiazole must be blended with sebacate or azelaic acid (0.5–1.5%), a carboxylate base, and a small amount of tolyltriazole (0.05–0.10%) to protect aluminum cylinder heads; the entire formulation passes ASTM D1384 (glassware corrosion test) when mass loss for copper coupons remains under 5 mg and for aluminum under 10 mg after 336 hours at 88 °C, aerated. During coolant manufacturing, benzothiazole is pre-dissolved in a 50% aqueous caustic potash solution to form its potassium salt, ensuring rapid dissolution in the glycol matrix and preventing filter-plugging crystal formation at storage temperatures as low as −25 °C. The final coolant concentrate is subject to ASTM D3147 foam tendency testing and ASTM D4340 hot-surface aluminum corrosion rate assessment, where the maximum allowable rate is 1.0 mg/cm²/week. Heavy trucks, off-highway earthmovers, and stationary natural-gas engines are typical end-use environments, reflecting an operational life of 6,000–8,000 service hours.

When Benthiavalicarb-isopropyl Production Requires Benzothiazole 96% with Nitrile Byproduct Management

Benzothiazole 96% supplies the heterocyclic core for the CAA fungicide benthiavalicarb-isopropyl (CAS 177406-68-7), specifically through an early-stage synthesis of 2-benzothiazol-2-yl-acetonitrile. The route in a cGMP pilot plant reacts benzothiazole with chloroacetonitrile in anhydrous tetrahydrofuran under sodium hydride dispersion (60% in mineral oil) at −5 to 0 °C, using a molar charge of benzothiazole to chloroacetonitrile of 1:1.05 to drive complete alkylation. The resulting nitrile is reduced via catalytic hydrogenation over Raney nickel at 40 psi H₂ and 45 °C to the corresponding amine, which is subsequently acylated with isopropyl chloroformate in the presence of aqueous sodium bicarbonate at pH 7.5–8.0 to give the active substance. Formulators of benthiavalicarb-isopropyl 15% suspension concentrate (SC) register the product under FAO specification 595/SC (November 2014), and quality control involves CIPAC method 456 for HPLC assay with a permitted tolerance of ±2.5% of the declared active ingredient. The formulated SC must pass wet sieve analysis through a 75 µm sieve with less than 0.5% retained, and a pourability residue below 5% per CIPAC MT 148.1. Late blight (Phytophthora infestans) control on potatoes and downy mildew (Plasmopara viticola) on grapes represent the primary terminal use patterns, with a typical field application rate of 1.2–1.5 L/ha of the 15% SC. The bulk active ingredient manufacturing step itself is subject to China’s GB 9553-2016 effluent discharge limits for heterocyclic pesticide intermediates, specifically a total nitrogen cap of 15 mg/L after plant wastewater treatment.

Pressure-treated utility pole and rail tie preservation formulations increasingly utilize benzothiazole-derived 2-(thiocyanomethylthio)benzothiazole (TCMTB, CAS 21564-17-0) to replace copper naphthenate in ground-contact applications where copper tolerance of soil microorganisms has become problematic. Synthesis of TCMTB from benzothiazole 96% proceeds in a jacketed glass-lined reactor by dropwise addition of 37% formalin (1.03 molar equivalents relative to benzothiazole) and sodium thiocyanate solution (1.05 equivalents) into a pre-formed chloromethylation mixture of benzothiazole, hydrochloric acid, and paraformaldehyde at 10–15 °C over 4 hours, then holding for an additional 2 hours at 25 °C to reach a product assay of 94–96% after phase separation and vacuum dehydration. The resulting amber oil is formulated as a 30% emulsifiable concentrate using a nonionic/anionic surfactant blend (HLB 12.5–13.0) and diluted to 0.8–2.5% active ingredient in the treating solution for vacuum-pressure impregnation of radiata pine or Southern yellow pine sapwood in a full-cell process at 1200 kPa for 60–90 minutes. Retention targets per AWPA P5-14 Use Category 4A require 0.40 kg/m³ TCMTB on an oxide basis, verified by HPLC quantification of benzothiazole derivative residues per AWPA A28-14. Treated timber in cooling tower fills and agricultural fence posts must release less than 15 mg/L total benzothiazole species in the standardized EN 84 leaching test to satisfy the EU Biocidal Products Regulation 528/2012 Annex VI common principles. End-product durability in accelerated soil-block testing (AWPA E10-16) shows mass loss below 5% after 16 weeks exposure to Gloeophyllum trabeum, a drastic improvement over untreated controls that typically lose over 45% of their dry mass in the same period.