2-Methyl-6-Nitro-1,3-Benzothiazole
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HS Code |
721284 |
| Chemical Formula | C8H6N2O2S |
| Molecular Weight | 194.21 g/mol |
| Appearance | Solid |
| Color | Typically yellowish |
| Odor | Characteristic organic odor |
| Melting Point | Specific value would need lab determination |
| Boiling Point | Specific value would need lab determination |
| Solubility In Water | Low solubility |
| Solubility In Organic Solvents | Soluble in some common organic solvents like ethanol, acetone |
| Density | Specific value would need lab determination |
| Stability | Stable under normal conditions but may react with strong oxidizing agents |
As an accredited 2-Methyl-6-Nitro-1,3-Benzothiazole factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 500g of 2 - Methyl - 6 - Nitro - 1,3 - Benzothiazole packaged in airtight, chemical - resistant containers. |
| Shipping | 2 - Methyl - 6 - Nitro - 1,3 - Benzothiazole is shipped in accordance with strict chemical regulations. It's carefully packaged in suitable containers to prevent leakage, and transported by carriers experienced in handling hazardous chemicals. |
| Storage | 2 - Methyl - 6 - nitro - 1,3 - benzothiazole should be stored in a cool, dry, well - ventilated area. Keep it away from heat sources, flames, and oxidizing agents. Store in a tightly - sealed container to prevent moisture and air exposure, which could potentially affect its chemical stability. Use appropriate storage cabinets designated for hazardous chemicals. |
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The reductive conversion of 2-methyl-6-nitro-1,3-benzothiazole to its 6-amino analogue forms the backbone of azo dye and organic pigment syntheses serving the polyester, polyamide, and cellulose acetate fibre markets. Under typical hydrogenation conditions—Raney Ni catalyst slurry at 5–8 wt% loading relative to nitro substrate, 40–60°C, 3–5 bar H₂ partial pressure in a glass-lined or Hastelloy C-276 autoclave—the nitro group is selectively reduced without scission of the thiazole ring. Laboratory and pilot-plant observations indicate that exotherm overshoot beyond 65°C promotes desulphurisation, generating tarry by-products that foul catalyst pores and reduce batch-to-batch amine purity below the 98.5 area% threshold required for high-strength dye intermediates. The crude 6-amino intermediate is isolated as a hydrochloride salt to suppress aerial oxidation, then diazotised at 0–5°C with 1.05 molar equivalents of sodium nitrite in aqueous HCl. The resulting diazonium salt couples with N,N-diethylaniline, 2-naphthol, or pyrazolone derivatives to yield C.I. Disperse Yellow, C.I. Solvent Orange, and C.I. Acid Red chromophores with tinctorial strength tested against ISO 105-B02:2014 and wash fastness per ISO 105-C06:2010. Processing bottlenecks at full production scale include the need for tight pH control during coupling—deviations beyond ±0.3 units from the optimised value (typically 4.5–5.5 for naphthol coupling) cause premature precipitation of amorphous dye particles that resist standard milling and reduce filtration rates on Nutsche filter-dryers below design throughput. REACH registration under EC 1907/2006 and compliance with ETAD code of practice are preconditions for shipment into EU dye houses. What Makes This Intermediate Suitable for High-Reliability Electroplating Brighteners?In zinc and zinc-alloy electroplating, the 6-amino derivative obtained by catalytic reduction is sulphonated with chlorosulphonic acid in dichloromethane at 10–20°C to produce 2-methyl-6-sulphoamino-benzothiazole, which is then quaternised with dimethyl sulphate or benzyl chloride. The resulting quaternary salt functions as a leveling and brightening agent in acid zinc baths processed per ASTM B633-19. Bath concentrations are held within 0.02–0.10 g/L, with optimal brightness at cathodic current densities of 2–5 A/dm² examined by Hull cell panels ( 267 mL, 5 minutes at 1 A). Below 0.015 g/L, burn marks appear in high-current-density zones; above 0.12 g/L, competitive adsorption shifts the deposit morphology from semi-bright laminar to brittle columnar growth, reducing elongation in mandrel bend tests. The purified intermediate must contain less than 0.3 wt% unsulphonated amine, which precipitates as an insoluble scum on the electrolyte surface and creates pit defects confirmed by SEM cross-sections. Production-scale electrolyte life-extension trials have demonstrated that continuous carbon treatment ( 0.5 kg activated carbon per 1000 L bath per week) maintains Hull cell appearance rating above 8 out of 10 for over 40 ampere-hours per litre. REACH Annex XVII restrictions on dimethyl sulphate necessitate closed-loop quaternisation with vapour recovery exceeding 99.5% efficiency. Corrosion Inhibitor Formulations for Hydrochloric Acid Pickling BathsBlends of 2-methyl-6-nitro-1,3-benzothiazole and its partially hydrogenated derivatives are deployed as mixed-type inhibitors in 10–20 wt% HCl pickling solutions for carbon steel at 40–80°C. The nitro compound itself provides anodic polarisation through chemisorption of the thiazole nitrogen lone pair onto the ferrite surface, while the amine derivative reinforces cathodic inhibition. Weight-loss immersion tests following ASTM G31-21 with SAE 1010 coupons yield the following pilot-plant dataset at 60°C after 6 hours:
Below 0.25 wt%, localised attack persists at grain boundaries; above 1.0 wt%, marginal gain in protection is offset by oiling-out of unadsorbed inhibitor, which fouls downstream solvent-extraction recovery units. Potentiodynamic polarisation scans (ASTM G5-14e1, scan rate 0.166 mV/s) confirm mixed inhibition with a shift of corrosion potential by less than ±30 mV relative to the uninhibited couple. Field experience in continuous strip-pickling lines shows that pre-dissolving the inhibitor in a 1:4 (w/w) mixture of isopropanol and ethylene glycol monobutyl ether before metering into the acid circuit eliminates agglomerates that otherwise clog 100-mesh inline filters. Compliance with the U.S. EPA’s Effluent Limitation Guidelines for iron and steel manufacturing ( 40 CFR Part 420) requires inhibitor breakdown products to exhibit LC50 values above 100 mg/L in fathead minnow 96-hour acute tests. When Pre-Coated onto Photographic Paper as a Silver-Halide StabiliserSubstituted benzothiazoles bearing a nitro group function as antifoggants and stabilisers in silver chloride and silver chlorobromide emulsions coated onto resin-coated photographic paper for colour-negative printing. The compound is dissolved in a 1:1 mixture of methanol and ethyl acetate and added to the emulsion melt at 0.5–2.0 mg per mole of silver halide, immediately before coating onto the paper support at 35–40°C. Under the alkaline developer conditions (pH 10.2–10.5), the nitro group is partially reduced in situ, generating low concentrations of the amine that interact with gold(I) sulphide sensitiser clusters and raise minimum density (Dmin) stability over 28-day accelerated ageing at 50°C/80% RH as prescribed by ISO 18936:2020. Over-dosage beyond 3.0 mg/mol Ag causes desensitisation of the toe of the characteristic curve, reducing ISO speed by 2–3 stops. The stabiliser must be free from residual reducing agents heavier than 0.1% sulphated ash, because particulates produce visible pepper fog spots on minilab RA-4 prints detected by densitometry at D=0.01 above Dmin. Roller-transport processing machines (e.g., Fujifilm Frontier series) operating at 35 seconds dry-to-dry impose additional constraints: the stabiliser must not crystallise in the developer recirculation loop, requiring solubility above 1.0 g/L at pH 10.5. Cyclocondensation of 2-methyl-6-nitro-1,3-benzothiazole with thiourea followed by alkaline hydrolysis opens a route to 2-mercapto-6-nitrobenzothiazole, a vulcanisation retarder for highly unsaturated diene elastomers. In natural rubber and polybutadiene compounds, this retarder is dosed at 0.2–0.5 phr together with sulphenamide accelerators to delay scorch without compromising the T90 cure time by more than 10% on a Moving-Die Rheometer at 160°C (ISO 6502-3:2023). Plant-floor records from a two-roll mill (18-inch roll diameter, 1:1.2 friction ratio) indicate that when the retarder is added as a fine powder pre-dispersed in dioctyl phthalate (50% paste), Mooney scorch time at 130°C extends from 12 to 24 minutes, providing a wider processing window for thick-section injection-molded mounts. The nitro group must remain intact throughout compounding, as premature reduction by mercaptosilane coupling agents (present in silica-filled tread compounds) generates amine species that accelerate cure and negate the retarding effect. Hence, silane addition is staged downstream of the retarder masterbatch drop temperature, kept below 120°C. |
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2-Methyl-6-nitro-1,3-benzothiazole (CAS 2942-07-6) is supplied as a crystalline yellow powder with a molecular weight of 194.21 g·mol⁻¹ and a melting transition in the range 91–95 °C by differential scanning calorimetry at 10 K·min⁻¹. Lot-to-lot purity as determined by HPLC equipped with a C18 reversed-phase column (250 × 4.6 mm, 5 µm) using a mobile phase of methanol/water (70:30 v/v) at 1.0 mL·min⁻¹ and UV detection at 254 nm consistently exceeds 98.0% area. The principal impurity, when present, is the 5-nitro isomer, arising from the electrophilic nitration pathway. Karl Fischer titration indicates water content <0.3 wt%, and residue on ignition is below 0.1 wt%. The compound exhibits good solubility in dimethylformamide (> 20 g·L⁻¹ at 20 °C) and acetone, moderate solubility in ethanol (~8 g·L⁻¹), and negligible aqueous solubility (<0.05 g·L⁻¹).
Identity confirmation and batch-to-batch consistency are further assured by spectroscopic fingerprinting. 1H NMR (DMSO-d6, 400 MHz) displays the diagnostic singlet for the 2-methyl group at δ 2.65 (3H) and three aromatic protons: H-4 as a doublet at δ 7.59 (J = 8.8 Hz), H-5 as a doublet of doublets at δ 8.15 (J = 8.8, 2.2 Hz), and H-7 as a meta-coupled doublet at δ 8.68 (J = 2.2 Hz). The FT-IR spectrum (KBr disc) records the asymmetric and symmetric NO₂ stretching bands at 1520 cm⁻¹ and 1345 cm⁻¹, respectively, along with the thiazole C=N vibration near 1595 cm⁻¹. These spectral data form the basis of a validated identity test aligned with United States Pharmacopeia general chapter <197> for spectroscopic identification.
The transformation of the 6-nitro substituent into a primary amine unlocks a wide array of synthetic downstream chemistries. On a laboratory scale, the reduction proceeds cleanly with stannous chloride in hydrochloric acid. A representative procedure charges 10.0 g (51.5 mmol) of 2-methyl-6-nitrobenzothiazole into 50 mL of concentrated HCl; 34.8 g (154 mmol) of SnCl₂·2H₂O is added portionwise while maintaining an internal temperature below 10 °C. The reaction mixture is then heated to 80 °C for 2 h. After cooling, dilution, and basification to pH 9–10 with 20% aqueous NaOH, the precipitated solid is extracted with ethyl acetate and recrystallised from ethanol/water to afford 6.5–7.1 g (77–84%) of 6-amino-2-methylbenzothiazole as an off-white crystalline powder (mp 132–135 °C).
For multi-kilogram campaigns, catalytic hydrogenation is preferred to avoid heavy-metal waste streams. In a 50 L Hastelloy C-276 autoclave, 5.0 kg of substrate is dissolved in 20 L of tetrahydrofuran, charged with 0.5 kg of water-wet Raney nickel catalyst, and stirred under hydrogen at 30 bar and 60 °C for 8 h. Headspace gas analysis by micro-GC tracks hydrogen consumption; conversion exceeds 99% when the theoretical uptake is reached. After catalyst filtration through a 5 µm sintered-metal candle and solvent distillation under vacuum, the amine is isolated in 85–88% yield with a purity by GC-FID of 99.2%. This amine serves as a diazotisable intermediate for azo colorants, a building block for polybenzothiazole polymers, and a precursor to biologically active fused heterocycles.
Diazotisation of the 6-amino derivative with sodium nitrite in aqueous HCl at 0–5 °C generates a diazonium salt that couples efficiently with electron-rich aromatics. Coupling with β-naphthol at pH 9–10 produces a red-orange azo colorant with λmax 480 nm (ε ≈ 2.5 × 10⁴ L·mol⁻¹·cm⁻¹ in DMF). When the coupling component is 2-naphthol-3,6-disulfonic acid (R acid), the resultant disulfonated dye exhibits improved water solubility and substantivity for nylon and cellulose acetate fibres. Lightfastness on nylon 6,6 assessed according to ISO 105-B02, reaches a Blue Wool scale rating of 4–5 after application from a neutral dyebath and after-treatment with a cationic fixative based on a quaternary ammonium polymer. Published migration fastness data under AATCC TM 15 conditions indicate a staining grade on multifibre witness fabric of 4–5 for acetate and 4 for nylon, with somewhat lower performance on cotton (3). This application domain distinguishes the title compound from non-nitrated benzothiazoles, which lack the chromophoric and reactive handle required for azo dye synthesis.
The compound is most economically produced by direct nitration of 2-methylbenzothiazole. In a jacketed glass-lined reactor of 500 L capacity, 150 kg of molten 2-methylbenzothiazole is dissolved in 300 kg of 96 wt% sulfuric acid with jacket circulation at −5 °C. A precooled mixed acid consisting of 70 kg of 65 wt% nitric acid and 50 kg of sulfuric acid is metered in over 6 h, keeping the bulk temperature at 0–5 °C. The para-directing influence of the thiazole sulfur atom and the meta-directing effect of the protonated thiazole nitrogen favour electrophilic attack at the 6-position, giving a typical isomer ratio of 85:15 (6-nitro : 5-nitro) as determined by calibrated GC-MS. When the nitrating medium is replaced with 70% nitric acid in acetic anhydride at −10 to 0 °C, the selectivity improves to 95:5 in favour of the 6-nitro isomer, albeit with a slight penalty in isolated yield. After drowning onto crushed ice, the crude cake is washed to neutral pH and recrystallised from 95% ethanol to deliver 105–110 kg of product with isomer purity > 99% and residual ethanol below 500 ppm after vacuum tray drying at 45 °C and 20 mbar. Batch processing records over 12 consecutive campaigns show an isolated yield of 68–71% and an overall cycle time of 22 h from raw material charge to dry product.
| Compound | CAS | Melting Point (°C) | Characteristic Spectroscopic Marker | Primary Industrial Use / Differentiation |
|---|---|---|---|---|
| 2-Methyl-6-nitrobenzothiazole | 2942-07-6 | 91–95 | NO₂ asym/sym stretch 1520/1345 cm⁻¹ | Azo dye intermediate; precursor to 6-amino derivative |
| 2-Methyl-5-nitrobenzothiazole | 2942-06-5 | 126–128 | H-4 singlet downfield shift (>δ 8.5) | Less reactive amine; limited commercial availability |
| 6-Nitrobenzothiazole | 17347-46-9 | 177–179 | No methyl singlet in ¹H NMR | Laboratory reagent; higher melting point limits melt processing |
| 2-Mercaptobenzothiazole (MBT) | 149-30-4 | 177–181 | SH stretch 2560 cm⁻¹ | Primary rubber vulcanisation accelerator; no nitro-function chemistry |
The isomeric 2-methyl-5-nitrobenzothiazole (CAS 2942-06-5) is formed as a minor coproduct in the mixed-acid nitration described above. Its melting point is significantly higher at 126–128 °C, reflecting differences in crystal packing imparted by the proximity of the nitro group to the thiazole nitrogen. Under identical catalytic hydrogenation conditions, the 5-nitro isomer reduces approximately 1.5 times more slowly, a kinetic effect attributed to steric shielding by the adjacent annular nitrogen. The resulting 5-amino-2-methylbenzothiazole is a weaker diazonium component: Hammett σm constants predict a lower electrophilicity for the diazonium group conjugated at the 5-position, and coupling yields with phenols are typically 15–20% lower on a molar basis than those of the 6-amino isomer. These performance disparities underline the importance of isomeric purity specifications for quality-critical applications such as certified reference dyes and pharmaceutical intermediates.
Condensation of 6-amino-2-methylbenzothiazole with α-halocarbonyl compounds provides an entry into the imidazo[2,1-b][1,3]benzothiazole scaffold, which is under investigation for antimicrobial and antitumour activities. A well-established protocol heats 1.0 equiv of the amine with 1.05 equiv of a 2-bromo-4′-substituted acetophenone in absolute ethanol containing 2.0 equiv of anhydrous sodium acetate. After 6 h under reflux and slow cooling, the cyclised product crystallises as a tan solid, typically in 68–72% yield without additional chromatographic purification. Characterisation by 1H NMR shows the disappearance of the amine proton signal and the emergence of the imidazole C-H singlet near δ 8.2. In vitro screening against Staphylococcus aureus ATCC 29213 conducted in accordance with CLSI guideline M07-A10 yielded minimum inhibitory concentration values between 4 and 16 µg·mL⁻¹ for halogen-substituted aryl analogues, with the 4-chlorophenyl derivative exhibiting the highest potency. Cytotoxicity against HeLa cells (ATCC CCL-2) assessed by MTT assay per ISO 10993-5 demonstrates an IC₅₀ of 28 µM for the same compound, providing a selectivity index of approximately 7 relative to the MIC. This synthetic route is not available for 2-mercaptobenzothiazole or unsubstituted 2-methylbenzothiazole, which lack the requisite aromatic amine handle—a clear differentiator for the 6-nitro intermediate.
Storage under dry nitrogen at 2–8 °C is recommended when the product will be held beyond six months. Although the compound is not hygroscopic, pre-drying over phosphorus pentoxide in a vacuum desiccator for 24 h is advised prior to moisture-sensitive operations such as Grignard reagent additions or lithium diisopropylamide deprotonations. The solid is classified as Acute Toxicity Category 4 (H302), Skin Irritation Category 2 (H315), Eye Irritation Category 2A (H319), and STOT SE 3 (H335). Engineering controls for dust containment and nitrile gloves with a breakthrough time exceeding 480 min per EN 374 are mandatory on production lines. Avoid contact with strong alkalis; a runaway exotherm with onset at 245 °C (DSC, 5 K·min⁻¹, energy release 1.2 kJ·g⁻¹) places the neat material in Hazard Class 4.1 under UN Test N.1. Process safety evaluations for operations above 200 °C must therefore incorporate adiabatic calorimetry data derived from an APTAC or ARC instrument.
