2-Methyl-6-Nitrobenzothiazole

Reduction of 2-methyl-6-nitrobenzothiazole over 5% Pd/C (0.5% w/w loading) in methanol at 45°C and 0.3 MPa H₂ proceeds with >99% conversion within 4 hours, monitored by TLC on silica gel with hexane/ethyl acetate 3:1. After filtration through a Celite pad to remove the catalyst, the filtrate is concentrated under reduced pressure and the residue recrystallized from toluene/hexane to afford 2-methylbenzothiazol-6-amine as off-white crystals, purity 99.7% by HPLC at 254 nm. Residual palladium meets the 10 µg·g⁻¹ requirement of ICH Q3D for oral drug substances. This amine serves as a versatile nucleophile for CNS-targeted compound libraries. Acylation with 4-(4-fluorophenyl)butanoic acid using HATU (1.1 eq) and DIPEA (3.0 eq) in DMF at 0°C to room temperature over 16 h yields the corresponding amide, isolated by flash chromatography and dried at 45°C under vacuum for 24 h. A representative lot showed a melting point of 178–180°C by DSC at 10 K·min⁻¹ under N₂. In vitro CYP450 inhibition screening (CYP3A4, 2D6, 2C9) at 10 µM indicated less than 15% inhibition, suggesting a low drug–drug interaction risk for downstream candidates. The intermediate is shipped in 25 kg HDPE drums under inert atmosphere, classified as non-dangerous goods under IMDG Code, and requires storage at 2–8°C to maintain stability beyond 12 months. Analytical release includes assay by non-aqueous titration with perchloric acid and residual ethanol by headspace GC (<5000 ppm).

From Nitro Reduction to Azo Chromophore: A High-Washfastness Disperse Red Route

In a 500 L glass-lined reactor, 100 kg of 2-methyl-6-nitrobenzothiazole is charged with 95 kg of iron powder (200 mesh) and 450 L of 8% aqueous HCl. The mixture is heated to 95°C for 6 hours with vigorous stirring until HPLC (C18, MeOH/water 70:30, 254 nm) confirms <0.3% remaining nitro compound. After cooling to 50°C, the slurry is neutralized with 30% NaOH to pH 8.5, extracted with toluene (3 × 150 L), and the combined organic phase is dried over anhydrous MgSO₄ and stripped to yield crude 2-methylbenzothiazol-6-amine, which is vacuum-distilled at 145–148°C (2 mmHg) for use in diazotization. The amine (82 kg) is dissolved in 250 L of 30% HCl and cooled to −5°C. A 40% aqueous NaNO₂ solution (37 kg NaNO₂ in 92 L water) is added below the liquid surface at −5 to 0°C over 60 min, maintaining a positive nitrite test on starch-iodide paper. Excess nitrous acid is quenched with sulfamic acid and the diazonium salt solution is clarified by filtration. For the coupling component, 98 kg of N-ethyl-N-(2-cyanoethyl)aniline is dissolved in 300 L water containing 35 L HCl and 50 kg ice, then the clarified diazo liquor is pumped in over 90 min at 0–5°C, while pH is maintained at 3.8–4.2 by simultaneous addition of 20% sodium acetate solution. After stirring for a further 2 h and warming to 25°C, the precipitated dye is filtered on a plate-and-frame filter press, washed with demineralized water to a conductivity <200 µS·cm⁻¹, and dried in a vacuum tray dryer at 75°C for 16 h until moisture <0.5% (Karl Fischer). The final dark red powder exhibits dispersibility ≥4 (AATCC Test Method 146-2006, grade). Exhaust dyeing on knitted polyester fabric (plain jersey, 150 g·m⁻²) is performed in a Mathis Labomat at 130°C with a liquor ratio of 1:10, using 1.0% owf dye, 0.5 g·L⁻¹ Dispersogen P, and acetic acid to pH 4.5. Reduction clearing with 2 g·L⁻¹ sodium hydrosulfite and 2 g·L⁻¹ NaOH at 80°C for 20 min removes surface dye. The dye is registered under REACH and conforms to Oeko-Tex Standard 100 class I requirements, with a 4,4’-diaminodiphenylmethane content below 20 mg·kg⁻¹ (DIN 54231:2005).

Can a Simple Pyridyl Imine Derivative Achieve Sub-10 nM Zn²⁺ Detection Limit?

Condensation of 10 mmol 2-methylbenzothiazol-6-amine with 10.5 mmol pyridine-2-carboxaldehyde in 30 mL absolute ethanol containing 0.1 mL glacial acetic acid is refluxed under nitrogen for 5 h. On cooling, a yellow Schiff base precipitates; it is collected by filtration, washed with cold ethanol, and recrystallized from toluene to give needle-shaped crystals in 82% yield, mp 192–193°C. ¹H NMR (DMSO-d₆, 400 MHz) δ 2.82 (s, 3H, CH₃), 7.48 (dd, 1H, J = 8.4, 2.2 Hz), 7.54 (d, 1H, J = 8.4 Hz), 7.72 (d, 1H, J = 2.2 Hz), 7.95 (d, 1H, J = 7.8 Hz), 8.06 (m, 2H), 8.72 (dd, 1H, J = 4.8, 1.7 Hz), 9.05 (s, 1H, CH=N). In HEPES buffer (10 mM, pH 7.4, 1% DMSO), the probe exhibits weak fluorescence (Φ = 0.03) due to C=N isomerization and PET from the imine nitrogen. Addition of Zn²⁺ (1.0 eq) triggers a 22-fold emission enhancement at 488 nm (λex 405 nm) and a colorimetric shift from pale yellow to intense green under 365 nm UV. The detection limit (S/N = 3) is 7.2 nM, well below the WHO guideline for zinc in drinking water (76 µM). Selectivity against Cd²⁺ is achieved by a fluorescence ratio F₄₈₈/F₅₅₀ (> 12 for Zn²⁺, < 0.5 for Cd²⁺). MTT assays on HeLa cells after 24 h show 95% survival at 20 µM probe, supporting intracellular imaging applications. The ligand is supplied in amber glass vials under argon, lot size 1 g or 5 g, and stored at −20°C to prevent imine hydrolysis.

Q235 mild steel specimens (composition wt%: C 0.17, Si 0.25, Mn 0.55, P 0.02, S 0.02, balance Fe) with dimensions 50 mm × 25 mm × 2 mm were polished to 800 grit, degreased in acetone, and immersed in 1 M HCl blank and inhibited solutions at 30±1°C for 6 h according to ASTM G31-72. Weight loss data gave a corrosion rate of 31.2 mm·y⁻¹ in the blank. Addition of 100 mg·L⁻¹ 2-methyl-6-nitrobenzothiazole reduced the rate to 6.8 mm·y⁻¹ (efficiency 78.2%); at 300 mg·L⁻¹ the rate was 1.9 mm·y⁻¹ (93.9%). A synergistic blend of 200 mg·L⁻¹ of the compound plus 50 mg·L⁻¹ KI gave an efficiency of 97.4%, outperforming the individual inhibitor. Potentiodynamic polarization (scan rate 0.5 mV·s⁻¹, from −250 to +250 mV vs. OCP, three-electrode cell with SCE) classified the compound as a mixed-type inhibitor with strong anodic control; corrosion current density decreased from 580 µA·cm⁻² (blank) to 35 µA·cm⁻² at 300 mg·L⁻¹. Electrochemical impedance spectra (EIS) at OCP from 100 kHz to 10 mHz exhibited a single capacitive loop whose diameter increased with inhibitor concentration, modeled by an R(Q(RW)) equivalent circuit. The charge transfer resistance Rct rose from 12.7 Ω·cm² to 452 Ω·cm² at 300 mg·L⁻¹. Langmuir adsorption isotherm analysis returned an adsorption equilibrium constant Kads of 1.6×10⁴ L·mol⁻¹ and ΔG°ads of −34.8 kJ·mol⁻¹, indicating spontaneous chemisorption. The inhibitor stock solution is supplied as a 25% concentrate in diethylene glycol monobutyl ether, diluted to use concentration with HCl pickling baths. It complies with the biodegradability requirement (OECD 301F, >60% in 28 days) of EU Ecolabel for industrial cleaning products.

If an Extended Mooney Scorch Plateau Is Required for High-Speed Extrusion Compounding

The synthesis route converts the nitro precursor to 2-methyl-6-mercaptobenzothiazole (2M-6MBT) via a three-step sequence: reduction, diazotization, and thiolation. 164 g (1 mol) of 2-methylbenzothiazol-6-amine (obtained by catalytic hydrogenation of 2-methyl-6-nitrobenzothiazole) is dissolved in 400 mL water and 220 mL concentrated HCl, cooled to 0°C. A solution of 72 g sodium nitrite in 180 mL water is added dropwise at −2 to 0°C, giving a clear diazonium solution. Separately, sodium disulfide is prepared by heating 48 g sulfur and 180 g Na₂S·9H₂O in 300 mL water at 80°C for 30 min. The diazonium liquor is drained into the disulfide solution at 15–20°C over 45 min with vigorous stirring. After 2 h, the mixture is acidified with HCl to pH 2, and the precipitated crude bis(2-methylbenzothiazol-6-yl) disulfide is filtered, washed, and reslurried in hot sodium sulfite solution with 5% NaBH₄ to cleave the disulfide bond, yielding the free thiol 2M-6MBT after acidification. The thiol is recrystallized from isopropanol, white powder, mp 128–130°C. For sulfenamide synthesis, 20.0 g (0.11 mol) 2M-6MBT is suspended in 150 mL water, and 11.5 g (0.116 mol) cyclohexylamine is added. The slurry is cooled to 5°C and 12.8 g of 10% NaOCl solution is metered in over 90 min while maintaining pH 9.5 with carbonate buffer. The solid N-cyclohexyl-2-methyl-6-mercaptobenzothiazole sulfenamide (CMMS) is filtered, washed until chlorine-free, and dried at 40°C under vacuum. HPLC assay gives 98.2% purity. This sulfenamide was evaluated in a standard truck-tire sidewall compound: SMR 20 natural rubber 60 phr, BR 1203 40 phr, N330 carbon black 50 phr, processing oil 8 phr, zinc oxide 4 phr, stearic acid 2 phr, sulfur 1.8 phr, and CMMS 1.0 phr. Using a MDR at 150°C (ASTM D5289), the compound showed a minimum torque ML of 2.1 dN·m, maximum torque MH of 14.6 dN·m, and scorch times t_s1 and t_c10 of 8.2 min and 7.5 min, respectively. Mooney scorch at 130°C (ISO 289-1:2015) gave MS t₅ of 34.6 min, which is 55% longer than a CBS-accelerated control. The tensile sheet cured at 150°C for t₉₀+3 min showed tensile strength 22.3 MPa and elongation at break 480% (ISO 37:2017, type 2 dumbbell). CMMS is classified under HS code 2934.20, packed in 25 kg net weight paper bags with PE liner, and requires storage below 30°C in low-humidity conditions to prevent hydrolytic degradation. It does not form N-nitrosamine upon vulcanization, as the secondary amine is sterically hindered; nitrosamine content measured by GC-TEA is below 2 µg·kg⁻¹, complying with EU Directive 93/11/EEC.

Benzothiazole-Thiadiazole Fungicidal Conjugates

The 6-amino derivative of 2-methylbenzothiazole is coupled with 5-chloromethyl-1,3,4-thiadiazole-2-thiol via a thioether bridge. In a 2 L three-neck flask, 0.15 mol (24.6 g) of 2-methylbenzothiazol-6-amine is dissolved in 300 mL DMF with 0.33 mol potassium carbonate. 0.15 mol 2-chloromethyl-5-mercapto-1,3,4-thiadiazole (prepared from thiosemicarbazide and CS₂) in 100 mL DMF is added dropwise at 25°C, and the batch is heated to 70°C for 8 h. Progress is tracked by TLC (ethyl acetate/petroleum ether 1:1). The reaction mass is poured into 1.5 L ice water; the precipitated crude product is filtered, washed, and recrystallized from ethanol-DMF (8:2) to yield a white crystalline solid with a melting point of 161–163°C. Yield: 78%. The active ingredient is formulated as a 25% wettable powder (WP) with kaolin carrier, sodium lignosulfonate dispersant (3%), and alkylnaphthalene sulfonate wetting agent (1.5%). In greenhouse trials against rice sheath blight (Rhizoctonia solani), conducted according to EPPO PP 1/28(3), foliar application at 150 g a.i./ha achieved 87% control efficacy 14 days after inoculation, comparable to validamycin at 50 g/ha. The product has an acute oral LD₅₀ (rat) > 2000 mg·kg⁻¹ (OECD 423) and is classified as GHS Category 5 or unclassified. A 24-month storage stability study at 25±2°C showed less than 1.5% degradation of the active ingredient, meeting FAO specification. The technical material is shipped in 50 kg fibre drums with a UN-approved inner liner and requires the label ‘Keep away from foodstuffs’. It is not listed in the Stockholm Convention on Persistent Organic Pollutants and has a half-life in soil (aerobic, OECD 307) of 18 days, indicating moderate persistence.