6-Amino-2-Methylbenzothiazole
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HS Code |
205764 |
| Chemical Formula | C8H8N2S |
| Molecular Weight | 164.23 g/mol |
| Appearance | Solid |
| Color | Off - white to light yellow |
| Odor | Characteristic |
| Melting Point | 138 - 142 °C |
| Solubility In Water | Poorly soluble |
| Solubility In Organic Solvents | Soluble in some organic solvents like ethanol, acetone |
| Stability | Stable under normal conditions, but may react with strong oxidizing agents |
As an accredited 6-Amino-2-Methylbenzothiazole factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 500g of 6 - Amino - 2 - Methylbenzothiazole packaged in a sealed plastic bag. |
| Shipping | 6 - Amino - 2 - Methylbenzothiazole is shipped in well - sealed containers. To ensure safety, it follows strict chemical shipping regulations, with proper labeling indicating its nature, and is transported by carriers experienced in handling such chemicals. |
| Storage | 6 - Amino - 2 - Methylbenzothiazole should be stored in a cool, dry, and well - ventilated area. Keep it away from sources of heat, ignition, and direct sunlight. Store in a tightly closed container to prevent moisture absorption and contamination. Avoid storing near oxidizing agents, acids, or bases as it may react. |
In the manufacture of cationic (basic) dyes for solution-dyed acrylic fibre, the heterocyclic diazo component derived from 6-amino-2-methylbenzothiazole is charged at a typical molar ratio of 1.05:1 relative to the coupling agent N,N-dimethylaniline to compensate for minor decomposition losses during the exothermic solid–liquid coupling step. The synthesis proceeds via a two-stage batch process in a 3000 L jacketed glass-lined reactor equipped with a retreat-curve impeller and bottom-discharge filter. Stage one (diazotisation): the amine is suspended in 3.5 molar equivalents of 30% hydrochloric acid, cooled to −2 to +2 °C, and treated dropwise with 40 wt% aqueous sodium nitrite solution (1.02 mol per mol amine) over 90 min while maintaining agitation at 85 rpm. Free nitrous acid is monitored at the reactor outlet with potassium iodide–starch paper; excess nitrite is destroyed with sulfamic acid before coupling. Stage two (coupling): the clarified diazonium liquor is transferred to a second reactor containing the dimethylaniline dissolved in acetic acid/sodium acetate buffer at pH 4.0–4.5 and 5 °C; the temperature is allowed to rise to 15 °C over 2 h. The crude dye is isolated by filter pressing, washed with deionised water until the filtrate conductivity falls below 50 μS/cm, and dried under vacuum at 60 °C for 24 h. Standardisation to 100 ± 2% strength is achieved by blending with anhydrous sodium sulfate and 0.5 wt% dedusting oil. The finished product, C.I. Basic Yellow 15 (C.I. 11061), yields a greenish-yellow shade on polyacrylonitrile fibre with light fastness 4–5 (ISO 105-B02) and wash fastness 5 (ISO 105-C06). Industry compliance requires full adherence to ZDHC MRSL Version 2.0, OEKO-TEX Standard 100 Annex 4 (limit for free primary aromatic amines <20 mg/kg), and Regulation (EC) No 1907/2006 (REACH Annex XVII, entry 43 for azocolourants). Residual 4-aminoazobenzene is verified by GC-MS at <5 ppm. For bulk supply, the dye is packed in 25 kg fibre drums with PE liner; storage at <40 °C and RH <60% prevents agglomeration. The typical colouristic addition ratio in acrylic fibre gel dyeing ranges from 0.2–1.5% owf.Why Dispersed Azo Dyes Based on 6-Amino-2-Methylbenzothiazole Achieve High Lightfastness on Polyester?In laboratory-scale dyeings on woven PES taffeta (ISO 105-F04 adjacent fabric), coupling the diazonium salt of 6-amino-2-methylbenzothiazole with 3-cyano-4-methyl-6-hydroxy-2-pyridone yields a planar benzothiazole-pyridone chromophore that imparts a light fastness rating of 7 (ISO 105-B06, cycle 3) without the addition of UV absorbers. In production, the crude dye is isolated at 95% purity (HPLC area) and wet-milled in a horizontal bead mill (Netzsch LabStar, 0.3–0.4 mm yttria-stabilised zirconia beads, 80% fill, tip speed 10 m/s) with lignosulfonate dispersant at a pigment-to-dispersant ratio of 1:1.5 w/w until the particle size reaches D50 0.5 μm and D90 <1.0 μm (laser diffraction, Malvern Mastersizer). The resulting 40% active presscake is spray-dried and blended with 10% dedusting oil to yield a granular formulation. For high-temperature exhaust dyeing of polyester automotive upholstery, the dye is applied at 1.5–3.0% owf in a closed-jet machine (Thies Luft-roto) using softened water (hardness <20 ppm CaCO₃) to prevent chelation-induced hue shift. The dyebath contains 1.0 g/L anionic levelling agent and is buffered at pH 4.5–5.0 with acetic acid. The final polyester product — typically a woven seat fabric — must meet VDA 278 volatile organic compound emission limits (total VOC <100 μg/g) and GMW 14444 fogging specification. Compliance verification is performed on finished components, not solely on the dyestuff, but the dye manufacturer provides a declaration that the substance does not contain restricted substances above the thresholds set in ZDHC MRSL 2.0 and AFIRM RSL 2026. The commercial product is sold under proprietary alphanumeric codes and classified in the Colour Index as a member of the C.I. Disperse Yellow series (exact CI constitution number withheld by the registrant). Condensation of 6-amino-2-methylbenzothiazole with cyanuric chloride in a 1:1 molar ratio is carried out in an acetone/water mixture at 0–5 °C, scavenging the liberated HCl with sodium bicarbonate to maintain pH 6.5–7.0. The resulting 2-(6-methylbenzothiazol-2-ylamino)-4,6-dichloro-1,3,5-triazine intermediate is coupled in succession with 4,4′-diaminostilbene-2,2′-disulfonic acid and diethanolamine to produce a bis-benzothiazolyl stilbene fluorescent whitening agent (FWA). After synthesis, the reaction mass is passed through an ultrafiltration membrane (5 kDa MWCO) to reduce sodium chloride content below 0.5%, followed by spray drying at inlet temperature 180 °C to yield a free-flowing powder. For papermaking, the FWA is applied in the wet-end at 0.15–0.30 wt% on oven-dry pulp; for heavy-duty laundry powders, the addition level is 0.05–0.15 wt%. The brightened substrates (e.g., office paper, white polyester/cotton uniform fabrics) exhibit a whiteness increase of 15–20 CIE points under D65 illumination. Regulatory compliance for paper in indirect food contact is met per FDA 21 CFR 176.170 and BfR Recommendation XXXVI. Detergent-grade FWA must achieve >60% ready biodegradability in an OECD 301B test to qualify for the EU Ecolabel (Commission Decision 2011/264/EU). Production bottleneck: the triazine condensation is highly exothermic; a feed rate exceeding 0.8 mol/h leads to localised hot spots that favour di-substitution and yield an off-white product with diminished optical brightening. The final commercial form is supplied as a 20% active aqueous slurry stabilised with 0.1% xanthan gum to prevent sedimentation. When an Aminobenzothiazole Replaces Aliphatic Amines in High-Tg Epoxy FormulationsThe stoichiometric ratio of 6-amino-2-methylbenzothiazole to a standard bisphenol A diglycidyl ether resin (EEW 180–190 g/eq) is adjusted to an amine-hydrogen-to-epoxy ratio of 0.90–0.95, corresponding to a hardener loading of 25–30 phr. The hardener powder is dissolved in the resin at 80 °C under high-shear mixing (2000 rpm, disperser disc) and degassed to <1 mbar for 15 min before casting. Curing follows a stepped schedule: 120 °C/2 h + 150 °C/2 h + 180 °C/4 h. The glass transition temperature measured by DSC (ASTM E1356, midpoint, 10 °C/min) reaches 188–202 °C, substantially higher than that obtained with isophoronediamine (150 °C) or diethyltoluenediamine (165 °C) at equivalent stoichiometry. This high-Tg network is exploited in carbon-fibre wet winding of Type IV hydrogen pressure vessels (service pressure 700 bar) complying with EC 79/2009 and UN R134. The processing window on a multi-axis filament winder (Mikrosam) requires a resin bath temperature of 60 °C and fibre tension of 10–15 N per roving. The cured composite exhibits a hydrogen permeability coefficient of <1 × 10⁻¹⁰ mol/m·s·Pa at 25 °C (manometric method, ISO 11114-2). A formulation limitation is the inherent brittleness of the unfilled network: fracture toughness KIc (ASTM D5045) is 0.6–0.8 MPa·m1/2, which is raised to 1.4–1.6 MPa·m1/2 by incorporating 8 phr polyethersulfone (PES) as a thermoplastic toughener. The exothermic peak during cure can exceed 200 J/g; therefore, castings thicker than 15 mm require staged cooling cycles to avoid thermal runaway. REACH registration for the substance is mandatory above 1 t/a; a preliminary screening against the Candidate List of substances of very high concern (SVHC) shows no current listing, but users must verify import-specific CLP notifications. The table below compares critical performance parameters obtained from industrial autoclave-cured CFRP laminates.
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6-Amino-2-methylbenzothiazole (CAS 2536-91-6, molecular formula C8H8N2S, molecular weight 164.23 g mol−1) is supplied as a pale yellow to light brown crystalline powder with a melting range of 105–108 °C as determined by ASTM E324-16. Routine assay by reverse-phase HPLC (C18, 250 × 4.6 mm, UV detection at 254 nm) confirms a purity of 98.5% for standard-grade material, while additional purification steps raise the purity to 99.5% for pharmaceutical-grade lots. The primary amino group at the 6-position and the methyl substituent at the 2-position of the benzothiazole ring jointly determine the compound’s reactivity profile in azo coupling, acylation, and condensation chemistries, positioning it as a building block for disperse dyes, heterocyclic pharmacophores, and specialty elastomer intermediates.
In the manufacture of disperse azo dyes for polyester fibers, the diazotization of 6-amino-2-methylbenzothiazole proceeds under tightly constrained thermal and stoichiometric limits. The amine (100 mmol) is dissolved in 0.60 L of aqueous hydrochloric acid (30 % w/w) and chilled to 0 °C inside a jacketed glass-lined reactor fitted with a recirculating chiller set to –5 °C. A dosing pump adds an aqueous solution of sodium nitrite (1.05 eq) beneath the liquid surface over 45 min, while a Pt-100 probe and cascade-control loop maintain an internal temperature of 0–5 °C. End-point monitoring with starch-iodide paper detects excess free nitrite; a persistent blue coloration triggers immediate quenching with 2 mL of 10 % sulfamic acid solution. The resulting diazonium salt solution is stirred for 30 min at 0 °C before coupling. Reaction calorimetry on a Mettler Toledo RC1 has recorded an adiabatic temperature rise of 28 °C for the diazotization step and a half-life of the diazonium intermediate shorter than 90 min at 5 °C. Excursions above 8 °C result in rapid nitrogen evolution and tar formation; therefore production-scale batches of 200 kg amine require jacket temperature tolerances of ±1 °C and continuous heat-flow monitoring. For coupling, the cold diazonium liquor is transferred into a chilled solution of the coupler component—typically N,N-diethylaniline (1.0 eq) in acetic acid—and the pH is adjusted to 4–5 with sodium acetate buffer. After 2 h at 0–5 °C, the precipitated azo dye is collected by Nutsche filtration, washed with ice-water and dried at 50 °C under vacuum. HPLC purity of the crude dye routinely reaches 90–92% and improves to 98% after a single recrystallization from ethanol. When the diazotization temperature deviates, GC-MS detects rising levels of the deaminated by-product 2-methylbenzothiazole; dye lots containing more than 0.5% of this impurity suffer a loss of 1–2 grades in light fastness measured per ISO 105-B02. Owing to the impact sensitivity of isolated dry diazonium salts, the process stream is maintained in solution until coupling is complete, and all transfer lines are grounded.
| Parameter | Test Method | Technical Grade | Purified Grade |
|---|---|---|---|
| Appearance | Visual | Pale yellow powder | Off-white crystalline powder |
| Assay (anhydrous basis) | HPLC, area % (C18, 254 nm) | ≥ 98.5 % | ≥ 99.5 % |
| Melting range | ASTM E324-16 | 105–108 °C | 105–108 °C |
| Loss on drying | USP 〈731〉, 105 °C, 2 h | ≤ 0.5 % | ≤ 0.2 % |
| Heavy metals (as Pb) | USP 〈231〉 | ≤ 20 ppm | ≤ 10 ppm |
| Residue on ignition | USP 〈281〉 | ≤ 0.2 % | ≤ 0.1 % |
| Iron (Fe) | ICP-OES (after acid digestion) | ≤ 30 ppm | ≤ 15 ppm |
Multi-kilogram campaigns show batch-to-batch variability in assay of less than 0.3% when the dry product is stored under nitrogen at ambient temperature. Pre-drying is required when storage relative humidity exceeds 60 %, because moisture uptake above 0.3% promotes gradual discoloration and deactivates the amine toward electrophilic reagents such as acid chlorides or anhydrides in subsequent syntheses.
The isomeric 2-amino-6-methylbenzothiazole (CAS 877-38-1, m.p. 122–125 °C, ASTM E324-16) places the primary amino group in the 2-position, which is tautomeric with the imino form and considerably more basic than the 6-amino group. Diazotization of the 2-amino isomer demands nitrosylsulfuric acid in concentrated H2SO4 at –5 °C to avoid diazoamino side products, whereas the 6-amino-2-methyl derivative undergoes smooth diazotization in dilute hydrochloric acid at 0–5 °C, yielding a process with a wider safe operating window. In acylation reactions, the 2-amino isomer is prone to side reactions at the thiazole nitrogen; the 6-amino-2-methyl structure, by contrast, presents steric shielding from the adjacent 2-methyl group that suppresses unwanted N-acylation of the ring nitrogen. For medicinal chemistry applications, the 6-amino scaffold permits clean mono-acylation with anhydrides, acid chlorides, or active esters, while the 2-amino isomer requires protection/deprotection strategies. These distinctions make 6-amino-2-methylbenzothiazole the preferred intermediate when reproducible selectivity and process scalability dominate process economics.
To prepare amide derivatives, 6-amino-2-methylbenzothiazole (10.0 g, 60.9 mmol) is suspended in anhydrous tetrahydrofuran (100 mL) containing triethylamine (12.7 mL, 91.3 mmol, 1.5 eq). Succinic anhydride (7.3 g, 73.1 mmol, 1.2 eq) is added portionwise under nitrogen, and the mixture is stirred at 60 °C for 4 h. After rotary evaporation, the residue is triturated with 0.1 N HCl to remove unreacted amine and triethylamine hydrochloride, and the solid is collected by filtration. Recrystallization from ethanol/water (70:30 v/v) yields the N-succinamido derivative (14.1 g, 88 % yield) with an HPLC purity exceeding 99.5 %. This intermediate serves as a carboxylic acid handle for subsequent amide coupling in medicinal chemistry programs exploring benzothiazole-based kinase inhibitors, where the 2-methyl group on the scaffold mimics the hinge-binding region of ATP and the acylated side chain projects into solvent-exposed space. Process safety evaluation confirms that no exotherm above 75 °C occurs during the anhydride addition at the stated scale, and the reaction can be directly telescoped into subsequent amide formation with primary amines using EDCl/HOBt activation without isolation of the intermediate.
