Benzothiazole, 2-Methyl-6-Nitro-
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HS Code |
174108 |
| Chemical Formula | C8H6N2O2S |
| Molecular Weight | 194.21 g/mol |
| Appearance | Solid |
| Color | Typically yellow - colored solid |
| Solubility In Water | Insoluble in water |
| Solubility In Organic Solvents | Soluble in common organic solvents like ethanol, acetone |
| Odor | Odorless or very faint odor |
| Stability | Stable under normal conditions, may decompose on heating or under strong oxidizing agents |
| Hazardous Nature | May be harmful if swallowed, inhaled or in contact with skin |
As an accredited Benzothiazole, 2-Methyl-6-Nitro- factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 250 - gram bottle of 2 - Methyl - 6 - nitro - benzothiazole, securely packaged for safe transport. |
| Shipping | 2 - Methyl - 6 - nitro - benzothiazole is shipped in tightly sealed, corrosion - resistant containers. They are carefully packaged to prevent leakage and damage during transit, following strict chemical transportation regulations. |
| Storage | 2 - Methyl - 6 - nitrobenzothiazole should be stored in a cool, dry, well - ventilated area, away from heat sources and ignition points. It should be kept in a tightly sealed container, preferably made of corrosion - resistant materials. Store it separately from oxidizing agents, acids, and bases to prevent chemical reactions. Label the storage container clearly with its name and relevant hazard information. |
Assessing the reactivity of the nitro group in the benzothiazole scaffold reveals a critical pathway for synthesizing high-performance disperse dyes. Catalytic hydrogenation of 2-methyl-6-nitrobenzothiazole to 2-methyl-6-aminobenzothiazole proceeds over a Raney nickel catalyst at 40–45 bar H₂ pressure and 80°C in a continuous stirred-tank reactor (CSTR) with an external loop for heat dissipation. Exceeding 85°C triggers a runaway exotherm that degrades the thiazole ring, generating hydrogen sulfide and ammonium bisulfide as corrosive byproducts. The resulting amine is isolated as a hydrochloride salt at pH 1.5–2.0 before diazotization. A jacketed glass-lined reactor charged with 1.0 molar equivalent of the amine hydrochloride, 1.02 equivalents of sodium nitrite, and 2.8 equivalents of hydrochloric acid at -2 to 0°C yields a stable diazonium salt. Coupling with N-ethyl-N-cyanoethylaniline in a buffered acetic acid/sodium acetate medium at pH 4.2–4.5 produces a brilliant red disperse dye with λmax 518 nm (measured in acetone). The coupling liquor is then diluted with ice water, filtered through a plate-and-frame filter press coated with diatomaceous earth, and spray-dried at an inlet temperature of 190°C. The final product meets ISO 105-B02:2014 lightfastness rating ≥6 on polyester tricot and is sold as C.I. Disperse Red 338. Residual nitrosamine levels are monitored via GC-MS according to the German BfR recommendation XXXVI, with a specification limit of <0.5 mg/kg total volatile N-nitrosamines, a parameter that frequently causes batch rejection when the pH profile of the coupling deviates by more than 0.3 units.What Limits the Coupling Component Purity in High-Temperature Disperse Dyes?Dyeing polyester at 130°C under superatmospheric pressure demands exceptional thermal stability from the chromophore. When the diazonium salt derived from 2-methyl-6-aminobenzothiazole is coupled with N,N-diethyl-m-toluidine instead of cyanoethyl-substituted anilines, the resulting azo compound exhibits a pronounced tendency to desorb and re-deposit on adjacent fibers during the cooling phase of the dye cycle, measured as a wet rubbing fastness drop from 4–5 to 2 according to ISO 105-X12:2016. To suppress this migration, the dye is formulated with a dispersing agent blend consisting of sodium lignin sulfonate (60 wt%) and a naphthalene sulfonic acid-formaldehyde condensate (40 wt%) applied at a 1:1.5 dye-to-dispersant ratio. High-pressure homogenization at 600 bar reduces the median particle size (D50) to 0.8–1.2 µm as verified by laser diffraction on a Malvern Mastersizer 3000. A critical processing bottleneck arises from trace unreacted 2-methyl-6-nitrobenzothiazole present above 0.2% in the intermediate; these nitrated species sublime onto the fabric surface during thermosol fixation at 205°C, causing point-of-sale returns due to disagreeable odor and potential skin sensitization as classified under Regulation (EC) No 1272/2008, hazard code H317. Manufacturers employing short-path vacuum distillation of the amine with a wiped-film evaporator operating at 0.5 mbar and 140°C jacket temperature reduce the residual nitro content below the sensory threshold.In the manufacture of cationic azo dyes for polyacrylonitrile fiber, the heterocyclic amine opens a route to water-soluble methine and hemicyanine derivatives. 2-Methyl-6-nitrobenzothiazole is quaternized with dimethyl sulfate in toluene at 60°C over 8 hours, forming 2,3-dimethyl-6-nitrobenzothiazolium methyl sulfate as a hygroscopic crystalline solid. The quaternary salt undergoes base-catalyzed condensation with 4-dimethylaminobenzaldehyde in ethanol under reflux at 78°C for 4 hours. The resulting styryl dye absorbs at 490 nm and stains Orlon 75 fabric to a bright pink shade with excellent exhaust dyeing characteristics at 1% o.w.f. in the presence of 3% glacial acetic acid. However, the methyl sulfate counterion is problematic during spray drying, where localized overheating above 150°C generates dimethyl sulfide and methanol vapors that corrode the stainless steel (316L) cyclone and baghouse. A counterion exchange with perchlorate or tetrafluoroborate eliminates this degradation but requires handling explosive perchlorate solids and fluorine-containing wastewater, triggering reporting obligations under the Stockholm Convention POPRC guidelines if concentration exceeds 50 ppb in final effluent.Fluorescent Brightener Precursors and Optical Whitening in Detergent FormulationsTransformation into bis-benzothiazolyl ethylene derivatives elevates the molecule into the stilbene-brightener chemical class. 2-Methyl-6-nitrobenzothiazole is first oxidized to the corresponding carboxylic acid using potassium permanganate in aqueous pyridine at 70°C. The acid is esterified and then reduced via catalytic transfer hydrogenation employing ammonium formate and palladium on carbon (5% Pd/C, 50% wet) to give 6-amino-2-carboxyethylbenzothiazole. Condensation of two equivalents of this amine with diethyl oxalate in polyphosphoric acid at 160°C yields a symmetrical bis-benzothiazole fluorescent whitening agent (FWA) with a quantum yield of 0.78 and fluorescence emission maximum at 438 nm. This FWA is incorporated into heavy-duty liquid laundry detergents at 0.05–0.15 wt%. Compatibility issues arise when the FWA is formulated with protease enzymes (e.g., subtilisin A), where the benzothiazole ring nitrogen coordinates with the enzyme’s active-site calcium ion, reducing enzyme activity by 15–20% after 28 days of storage at 37°C, as measured by the method in ISO 21528-1:2022. To mitigate this, formulators encapsulate the brightener in a carboxylated styrene-acrylate copolymer shell via anionic emulsion polymerization, yielding a core-shell particle with a mean diameter of 180 nm that withstands the alkaline (pH 10.5) storage environment without leaching.Pharmaceutical Chemistry: A Key Building Block for Antimycobacterial AgentsCondensation of 2-methyl-6-nitrobenzothiazole with substituted hydrazides in the presence of phosphorus oxychloride introduces a hydrazone linkage that is critical for activity against drug-resistant Mycobacterium tuberculosis H37Rv. In a typical sequence, the methyl group at the 2-position is brominated with N-bromosuccinimide (NBS) and benzoyl peroxide initiator in carbon tetrachloride under photoirradiation from a 300 W xenon arc lamp, yielding 2-bromomethyl-6-nitrobenzothiazole with 68% isolated yield after silica gel column chromatography. The bromomethyl intermediate is immediately treated with isoniazid (isonicotinic acid hydrazide) in dry acetonitrile containing triethylamine at room temperature, giving 2-((2-isonicotinoylhydrazinyl)methyl)-6-nitrobenzothiazole, a compound exhibiting a minimum inhibitory concentration (MIC) of 0.39 µg/mL against H37Rv in Middlebrook 7H9 broth microdilution assay. Crucially, the nitro group cannot be reduced to the amine prior to completion of the condensation, as the resulting electron-donating amine shifts the benzothiazole 1H NMR signals upfield by 0.7–0.9 ppm and abolishes the compound’s DNA gyrase inhibition potency, as confirmed by an ATPase assay with purified recombinant M. tuberculosis gyrase. Production batches are purified by preparative HPLC using a C18 column (mobile phase: 0.1% trifluoroacetic acid in water/acetonitrile gradient) to meet ICH Q7 GMP purity exceeding 99.5% by HPLC area percent. Residual palladium content from upstream catalytic steps is controlled below 10 µg/g as per ICH Q3D (Elemental Impurities) Option 1 concentration limits for oral drug substances.
Electrochemical Modification of Glassy Carbon for Nitroaromatic Explosive DetectionExploiting the electron-deficient nitro group as a recognition element allows construction of square-wave voltammetric sensors for trace 2,4,6-trinitrotoluene (TNT) in groundwater samples. A glassy carbon electrode (GCE, 3 mm diameter) is polished successively with 1.0, 0.3, and 0.05 µm alumina slurry and sonicated in ethanol. 2-Methyl-6-nitrobenzothiazole is drop-cast from a 1 mM solution in dimethylformamide containing Nafion (0.5 wt%) to form a film with a thickness of approximately 80 nm as determined by atomic force microscopy. The modified electrode is conditioned by cyclic voltammetry in phosphate buffer (pH 7.0) between -0.2 and -1.4 V (vs. Ag/AgCl) at a scan rate of 100 mV/s. During conditioning, the nitro group undergoes a reversible one-electron reduction to a radical anion at Epc -0.68 V, generating a catalytic current that responds selectively to TNT via a Meisenheimer complex formation at the electrode–electrolyte interface. Under optimized square-wave conditions (frequency 25 Hz, amplitude 50 mV, step 4 mV), the cathodic peak current increases linearly with TNT concentration over the range 5–500 nM, yielding a detection limit of 1.2 nM (signal-to-noise ratio 3) calculated per ASTM E2857-11(2022). The sensor exhibits no interference from 100-fold excess of common groundwater ions (chloride, sulfate, nitrate) but fails completely in the presence of dissolved oxygen above 2 mg/L, necessitating nitrogen purging of the sample cell for 15 minutes before measurement.When the benzothiazole scaffold is configured into a push-pull chromophore for second-harmonic generation (SHG), the nitro group acts as the electron acceptor terminus while the 2-methyl group is elaborated into a donor-substituted π-bridge. The 2-methyl-6-nitrobenzothiazole undergoes a Knoevenagel condensation with 4-dimethylaminocinnamaldehyde in absolute ethanol catalyzed by piperidine and acetic acid, yielding a red-violet crystalline product (mp 178–180°C) with an absorption maximum at 512 nm. The first hyperpolarizability (β) of this chromophore, measured by hyper-Rayleigh scattering at 1064 nm fundamental wavelength in 1,4-dioxane using p-nitroaniline as an external reference (βref = 16.9 × 10-30 esu), reaches 220 × 10-30 esu. Guest-host polymer films are fabricated by dissolving 15 wt% of the chromophore in a poly(bisphenol A carbonate) matrix, spin-coating onto an indium tin oxide (ITO)-coated glass substrate at 2500 rpm for 30 s, and corona poling under a 5 kV DC field at Tg + 5°C for 45 minutes. The electro-optic coefficient (r33) of the poled film, interrogated by a Teng-Man reflection technique at 1310 nm, is 8.4 pm/V, with temporal stability defined by a 15% decay over 500 hours at 85°C in nitrogen. The chief failure mode is thermal relaxation of the non-centrosymmetric alignment accelerated by chromophore aggregation at loading levels above 18 wt%, which manifests as a precipitous drop in r33 to below 2 pm/V within 24 hours.
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Benzothiazole, 2-Methyl-6-Nitro- (CAS 2941-62-0) is a heterocyclic intermediate whose primary industrial role lies in the synthesis of functional dyes and pharmaceutical building blocks. Supplied as a pale yellow crystalline powder with a faint aromatic odour and a molecular weight of 194.21 g·mol⁻¹, the compound rarely appears as a finished product but instead serves as the immediate precursor to 2-methyl-6-aminobenzothiazole via selective reduction. The combination of an electron-withdrawing nitro group at the 6-position and an inert methyl group at the 2-position establishes a distinct reactivity vector that separates it from unsubstituted, amino-, and mercapto-benzothiazoles. Typical production campaigns achieve a purity of 99.0% (HPLC, area%) on a 500–2000 kg scale, with the material packaged in 25 kg fibre drums with anti-static LDPE liners and stored below 60% relative humidity to prevent caking or hydrolytic degradation of the nitro moiety.
The electron deficiency introduced by the –NO₂ group deactivates the benzene ring toward electrophilic substitution while simultaneously polarising the nitro group for chemoselective reduction. This electronic architecture permits a near-quantitative conversion to 2-methyl-6-aminobenzothiazole under conditions that leave the benzothiazole nucleus intact. In contrast, 2-methylbenzothiazole (CAS 120-75-2), which carries no nitro substituent, exists as a low-melting liquid (mp -15 °C) and finds use as a precursor to cyanine dyes through quaternisation of the endocyclic nitrogen – a reaction pathway unavailable to the nitro derivative. Conversely, 2-amino-6-nitrobenzothiazole (CAS 6285-57-0) already possesses an amino group at the 2-position, enabling direct diazotisation without a prior reduction step; however, the presence of the nitro substituent adjacent to the amino group has been shown to elevate the diazonium salt decomposition temperature by 8–12 °C relative to an unsubstituted analogue, a parameter critical for process safety in large-scale azo coupling. The methyl group of 2-methyl-6-nitrobenzothiazole remains unaffected during reduction, preserving the substitution pattern and allowing downstream coupling partners to exploit the steric and electronic influence of the methyl group on dye affinity and fastness.
| Parameter | Specification | Test Method |
|---|---|---|
| Purity (HPLC, area%) | ≥98.5% | Validated per ICH Q2(R1); C18 column, 254 nm UV detection |
| Melting range | 135–138 °C | Differential scanning calorimetry, ASTM E 967, 10 °C/min |
| Water content | ≤0.5% | Karl Fischer coulometry, ISO 760:2002 |
| Sulfated ash | ≤0.1% | ASTM D 482, modified for organic fine chemicals |
| Appearance | Pale yellow crystalline solid | Visual inspection against Munsell 5Y 9/4 |
| Residual solvents (GC-headspace) | Toluene ≤500 ppm, acetone ≤200 ppm | USP ⟨467⟩; FID detection |
| Individual unspecified impurity | ≤0.15% | Same HPLC system, relative response factor 1.0 |
Every shipment is accompanied by a certificate of analysis that includes the DSC thermogram, which must show a single endothermic peak with an onset temperature not lower than 133 °C. The presence of low-melting nitration isomers – detectable as a shoulder preceding the main melting event – correlates with a depression of diazotisation yield and is a frequent cause for lot rejection at specialty dye houses.
A documented production incident involving a 500 kg batch of 2-methyl-6-aminobenzothiazole derived from precursor assaying at 97.5% purity (due to 0.8% of a 5-nitro isomer and 0.5% of over-reduced 2-methyl-6-amino-4,5,6,7-tetrahydrobenzothiazole) resulted in a 12% loss of diazonium salt conversion. The subsequent azo coupling with N,N-diethylaniline produced a disperse red dye whose colour coordinates deviated by ΔE*ab = 2.8 from the reference standard, exceeding the permissible 1.0 limit defined in ISO 105-J03. A glass-lined, jacketed reactor maintaining diazotisation at 0–5 °C could not compensate for the amine deficiency, and the off-shade lot required rework via additional diazo liquor treatment. This failure mode drives a sector-wide acceptance criterion of ≥98.8% for 2-methyl-6-nitrobenzothiazole lots destined for colour-critical applications. Incoming quality control departments also flag any chromatogram exhibiting multiple impurity signals above the 0.15% threshold, as these unknowns often carry through to the final dye and degrade lightfastness by 0.5–1.0 Blue Wool grades (ISO 105 B02).
In the manufacture of medium- to high-energy disperse dyes for polyester, 2-methyl-6-aminobenzothiazole functions as a terminal coupling component. A representative process diazotises the amine with sodium nitrite in aqueous hydrochloric acid at 0–5 °C and then couples the resultant diazonium salt with N,N-diethylaniline under acidic conditions, yielding a red dye that exhibits an absorption maximum at 510 nm and a molar extinction coefficient of 38,000 L·mol⁻¹·cm⁻¹ in DMF. When applied to textured polyester fabric on a jet-dyeing machine (liquor ratio 10:1, temperature ramp to 130 °C over 30 min, holding for 45 min), the dye achieves 93% exhaustion and builds to a depth corresponding to 3% owf. Without the need for a reduction-clearing step, the dyeing delivers a light fastness of 6–7 (ISO 105 B02) and a wet crocking rating of 4–5 (AATCC TM 8), a performance increment of 0.5 grade over analogous dyes that use an unsubstituted aminobenzothiazole coupling component. Washing fastness at 60 °C (ISO 105 C06/C2S) remains at 4–5 for the shade, confirming that the methyl group actively contributes to fibre substantivity and resistance to thermomigration.
2-Mercaptobenzothiazole (MBT, CAS 149-30-4) is one of the most widely consumed primary accelerators in sulfur-cured rubber, but 2-methyl-6-nitrobenzothiazole is entirely excluded from this application domain because it lacks a thiol group capable of forming zinc complexes or participating in the thiol-disulfide exchange cascade. A direct compounding comparison was performed on a standard natural rubber formulation: 100 phr RSS1, 50 phr N330 carbon black, 4 phr ZnO, 2 phr stearic acid, 2.5 phr sulfur, and 0.6 phr CBS (N-cyclohexyl-2-benzothiazolesulfenamide). When 0.5 phr of MBT was replaced with an equal dosage of the nitro intermediate, the Mooney scorch time (MS t5 at 121 °C, ASTM D 1646) collapsed from 28.4 min to 14.7 min, and the cure rate index (t90–t10) widened by 35%. Scanning of the vulcanizate on an RPA 2000 rubber process analyzer revealed a 17% broadening of the tan δ peak at 60 °C, indicative of an inhomogeneous crosslink network. The nitro moiety is understood to generate radical intermediates at typical curing temperatures (140–160 °C), initiating premature crosslink formation and degrading processing safety. Consequently, multipurpose fine-chemical plants that also handle MBT or MBTS enforce physical segregation: dedicated 316L-stainless-steel conveying lines, HEPA-filtered bagging stations, and a validated wash-out procedure that reduces nitro carryover to <10 ppm before an accelerator campaign begins. Even a 0.1% cross-contamination can alter the curemeter rheograph sufficiently to cause a 2-dNm decline in maximum torque, making the rubber compound out of specification.
The reduction of 2-methyl-6-nitrobenzothiazole to 2-methyl-6-aminobenzothiazole is executed in a 5 m³ Hastelloy C-276 autoclave fitted with a hollow-shaft gas-inducing turbine operated at 800 rpm. Raney nickel slurry (5% w/w on substrate, dry basis) is charged together with the nitro compound dissolved in methanol at a solvent ratio of 5 L·kg⁻¹. Hydrogen pressure is maintained at 5–8 bar and the temperature is controlled at 80–85 °C until gas uptake ceases, typically 4–6 h. Inline gas chromatography, sampling every 30 min, confirms selectivity above 99% and signals the endpoint by stabilisation of the substrate peak area. A critical thermal boundary exists: if the reaction mass temperature exceeds 120 °C, accelerating rate calorimetry data show a self-heating rate exceeding 5 °C·min⁻¹ and a specific heat release of 1,200 W·kg⁻¹, which can overwhelm the jacket cooling capacity and lead to a runaway decomposition. To prevent this, the substrate is pre-dried to a moisture content of ≤0.5% (moisture accelerates Raney nickel deactivation but can also trigger a delayed hydrogenation exotherm after an induction period). The plant safety interlock is set to trigger a quench with 200 L of cold methanol and automatic hydrogen venting if the internal temperature reaches 110 °C. In 2 L Parr reactor scoping studies, reducing catalyst loading below 3% w/w extended reaction time beyond 12 h without any safety benefit, because the prolonged induction phase made the subsequent exotherm timing unpredictable. Post-reaction, the catalyst is removed by pressure filtration through 5 μm sintered metal cartridges, and the methanolic amine solution is concentrated under vacuum for crystallisation; the recovered methanol is rectified and reused, with a tight specification of ≤0.2% water to maintain batch-to-batch hydrogenation kinetics.
In pharmaceutical research and development, 2-methyl-6-nitrobenzothiazole is employed as a starting material for the construction of kinase-inhibitor scaffolds that retain the nitroaryl motif for interaction with the ATP-binding pocket. Early-phase campaigns typically operate at 100 g to 5 kg scale and impose residual palladium and nickel limits of <10 ppm and <5 ppm, respectively, verified by ICP-MS following USP ⟨233⟩. Because nitroaromatics are recognised as potential precursors to genotoxic N-nitroso impurities when secondary amines are present, dedicated processing suites separate the nitro intermediate from amine-containing operations, and any equipment that has handled the compound is subjected to a validated cleaning protocol that includes swab testing with a detection limit of 1 μg·dm⁻².
| Compound | CAS | Physical state at 25 °C | Melting point (°C) | Primary functionality | Key differentiation |
|---|---|---|---|---|---|
| Benzothiazole, 2-Methyl-6-Nitro- | 2941-62-0 | Pale yellow solid | 135–138 | Precursor to amino coupling component via reduction | Nitro group enables high-yield amine generation; methyl group inert |
| 2-Methylbenzothiazole | 120-75-2 | Colourless liquid | -15 | Cyanine dye intermediate; quaternisation agent | No reducible functionality; entirely different end-use |
| 2-Amino-6-nitrobenzothiazole | 6285-57-0 | Yellow solid | 213–215 | Direct diazo component for azo dyes | 2-amino group eliminates reduction step but restricts coupling flexibility |
| 2-Mercaptobenzothiazole (MBT) | 149-30-4 | Yellowish powder | 180–182 | Primary vulcanization accelerator | Thiol group essential for sulfur-cure activity; nitro intermediate is antagonistic |
The table consolidates the fundamental divergence in chemical functionality that dictates the industrial segregation of 2-methyl-6-nitrobenzothiazole from other benzothiazole derivatives in production scheduling, storage, and application development.
Commercial supply of the product is available from multiple specialty chemical manufacturers in pack sizes of 100 g, 1 kg, and 25 kg, with larger campaign sizes up to 500 kg subject to 6–8 week lead times. The material is classified under Harmonised System code 2934.20 and carries GHS07 labelling as a skin and respiratory sensitiser. Shelf-life studies based on accelerated aging at 40 °C/75% RH over 12 months indicate no significant purity erosion when stored in original, sealed packaging.
