5-Amino-2-Methylbenzothiazole
|
HS Code |
651824 |
| Chemical Formula | C8H8N2S |
| Molecular Weight | 164.23 g/mol |
| Appearance | Solid |
| Color | Typically off - white to light yellow |
| Odor | May have a characteristic, somewhat pungent odor |
| Melting Point | 147 - 151 °C |
| Solubility In Water | Poorly soluble in water |
| Solubility In Organic Solvents | Soluble in some organic solvents like ethanol, chloroform |
| Stability | Stable under normal conditions, but may react with strong oxidizing agents |
As an accredited 5-Amino-2-Methylbenzothiazole factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 1 kg of 605 - Amino - 2 - Methylbenzothiazole packaged in a sealed plastic bag. |
| Shipping | 5 - Amino - 2 - Methylbenzothiazole is shipped in properly sealed containers, adhering to chemical transportation regulations. Packed to prevent damage and leakage, ensuring safe transit to the destination. |
| Storage | 5 - 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. It should be separated from oxidizing agents and incompatible substances to avoid potential chemical reactions. |
Disperse Dye Intermediate Chemistry Under High-Temperature Exhaustion ConditionsThe condensation of diazotized 5-amino-2-methylbenzothiazole with N,N-disubstituted aniline coupling components yields azo disperse dyes exhibiting pronounced bathochromic shifts relative to aniline-derived analogues. Substituting the benzothiazole heterocycle for a standard phenyl diazo component increases molar extinction coefficients into the range of 45,000–62,000 L·mol⁻¹·cm⁻¹ depending on the electron-withdrawing character of substituents ortho to the azo linkage on the coupler fragment. This shift is attributable to the extended π-conjugation across the thiazole sulfur atom and the quinoidal resonance contribution from the electron-deficient heterocycle. Dye uptake on polyester fiber measured per ISO 105-B02:2014 consistently demonstrates lightfastness ratings of 6–7 on blue wool scale for medium-depth shades at 2.0% owf applied depth, a performance tier that unmodified aniline-based disperse dyes rarely achieve without co-formulation with UV absorbers.Manufacture of the diazo component itself requires careful control of nitrosylsulfuric acid stoichiometry during diazotization, as the amino group on the benzothiazole ring is significantly less basic (pKa of conjugate acid ≈ 2.1–2.4) than aniline derivatives due to the electron-withdrawing effect of the thiazole ring and the methyl substituent at the 2-position. Incomplete diazotization leaves residual free amine that competes as a coupling site, generating colored byproducts that shift the final dye hue and reduce batch-to-batch shade consistency on commercial dyeing machinery. Production-scale observations on Mathis Labomat or Thies mini-soft dyeing units operating at a 10:1 liquor ratio indicate that indirect coupling methods—where the diazonium salt solution is added to a buffered coupling component suspension maintained at 0–5°C and pH 4.0–4.5—suppress decomposition side reactions that otherwise manifest as filtration pressure increases during post-synthesis clarification through 0.5 µm absolute-rated bag filters.The finished disperse dye formulated from this intermediate is processed into aqueous dispersions through wet milling in horizontal bead mills charged with 0.3–0.6 mm yttria-stabilized zirconia grinding media. Milling residence time curves generated on Netzsch MiniCer or WAB Dyno-Mill units plateau at particle size distributions (D₉₀) below 1.0 µm after 4–6 passes, but over-milling beyond 8 passes induces Ostwald ripening in storage due to polydispersity broadening, with measurable crystal growth exceeding 2.5 µm D₉₀ within 14 days at 40°C accelerated storage per ISO 105-A05:1996. Dispersant selection—typically lignosulfonates or naphthalene sulfonate-formaldehyde condensates at 30–50 wt% relative to dye solids—determines high-temperature dispersion stability under exhaust dyeing conditions at 130–135°C where dispersion breakdown yields filter-clogging agglomerates on package dyeing machines operating at 2–3 bar differential pressure. Terminal consumer articles include deep navy, black, and rubine shades on polyester sportswear, automotive upholstery subjected to ISO 105-B06:1998 high-temperature lightfastness testing, and polyester microfiber cleaning textiles where high color strength at low denier is commercially mandatory.Benzoisothiazole pharmacophore construction via cyclocondensation5-Amino-2-methylbenzothiazole serves as a strategic starting material for constructing the 2-aminobenzothiazole pharmacophore embedded within numerous kinase inhibitor scaffolds and antimicrobial development candidates. The primary synthetic manipulation involves functionalization at the 5-amino position to install acrylamide, urea, or sulfonamide warheads without disturbing the methyl group at C-2, which modulates target selectivity through steric interactions with hydrophobic enzyme pockets. Published structure-activity relationship data for benzothiazole-based inhibitors of interleukin-1 receptor-associated kinase 4 indicate that the 2-methyl substituent reduces off-target binding to JAK2 kinase by a factor of approximately 12-fold compared to the des-methyl analogue at 1 µM screening concentration. Industrial synthetic routes operating under current Good Manufacturing Practice conditions couple the amino group with activated carboxylic acid derivatives in anhydrous tetrahydrofuran or dimethylformamide at −10 to 0°C using HATU or EDCI·HCl with N-methylmorpholine as auxiliary base, achieving HPLC purities exceeding 99.0 area% after silica gel chromatography monitored at 254 nm.The free amino group introduces a critical purification challenge: the compound partitions unpredictably between organic and aqueous phases depending on the protonation state of both the heterocyclic ring nitrogen and the exocyclic amine. Extraction efficiency for the free base form remains acceptable at pH >8.5 using ethyl acetate or dichloromethane, but emulsions form persistently at intermediate pH values in production-scale extraction vessels equipped with 200–500 L capacity and pitched-blade turbine agitators operating below 100 rpm. Process chemists on kilogram-scale campaigns routinely add sodium chloride to 15–20 wt% saturation in the aqueous layer to break these emulsions. Residual solvent analysis per USP <467> on the isolated intermediate dried in a double-cone rotary dryer at 40°C and <50 mbar typically reports dimethylformamide levels below 880 ppm, compliant with ICH Q3C Option 2 limits for class 2 solvents in active pharmaceutical ingredient manufacture.Formulation into drug product intermediates proceeds through telescoped processes where the benzothiazole intermediate is immediately dissolved in acetic acid and treated with potassium thiocyanate and bromine to generate a thiocyanato intermediate that spontaneously cyclizes to the thiazolo[5,4-b]pyridine ring system. Exothermic heat output during bromine addition must be controlled to keep the internal reaction temperature below 5°C to prevent runaway bromination at the activated 4-position of the benzothiazole ring, a side reaction that drops isolated yield by 15–25% within 2°C overshoot. Terminal drug candidates incorporating this core have advanced into phase I oncology trials as selective tropomyosin receptor kinase inhibitors, with the corresponding finished dosage forms being immediate-release capsules containing micronized drug substance blended with lactose monohydrate and croscarmellose sodium processed through roller compaction to eliminate solvent residues.When the sulfur atom of the thiazole ring participates in vulcanization cure rate modificationReplacement of conventional 2-mercaptobenzothiazole with 5-amino-2-methylbenzothiazole as a secondary accelerator in sulfur-cured natural rubber compounds shifts the scorch safety profile and the crosslink density distribution. Moving-belt rheometer data acquired per ASTM D5289-19a on formulations using 2.0 phr sulfur combined with 0.8 phr N-cyclohexyl-2-benzothiazolesulfenamide as primary accelerator and 0.2–0.5 phr 5-amino-2-methylbenzothiazole as secondary accelerator reveal a delayed onset of vulcanization reflected in ts2 values that increase by approximately 0.7–1.3 minutes at 160°C relative to diphenylguanidine-containing controls at equivalent molar loading. The cure rate index (tc90 − ts2) narrows by 15–22%, indicating a more efficient transition from the induction period to the fully cured plateau without the characteristic marching-modulus behavior observed with amine-only acceleration systems.The underlying mechanism involves coordination of the benzothiazole ring nitrogen and the exocyclic amino group to zinc ions present in the zinc oxide/stearic acid activator complex, forming a less nucleophilic sulfurating species compared to the zinc-accelerator complex derived from 2-mercaptobenzothiazole. This moderated reactivity suppresses premature crosslinking during calendering operations on 84-inch four-roll inclined Z-calenders processing rubber compounds at 85–95°C stock temperatures through 0.8–1.2 mm nip gaps. Tension control between calender rolls must be maintained within ±5 N per centimeter of web width to prevent gauge variation that translates to visible fabric texture on subsequent fabric-reinforced rubber sheeting.The amino group participates in post-vulcanization network maturation: residual free amine reacts with polysulfidic crosslinks over extended service life at operating temperatures above 70°C, shortening sulfur rank distribution from predominantly hexa- and pentasulfidic bridges toward more thermally stable di- and monosulfidic linkages. Dynamic mechanical analysis conducted per ISO 4664-1:2011 on vulcanizates aged for 168 hours at 100°C in circulating air ovens measures tan δ at 60°C that decreases by 0.02–0.04 units compared to unaged controls, a shift that corresponds to reduced hysteresis and lower heat build-up in tire tread compounds. The compound’s contribution to cured rubber networks is incompatible with peroxide-cure systems, because the amino group scavenges free radicals generated during dicumyl peroxide decomposition, reducing crosslinking efficiency to commercially unacceptable levels below 40% of the theoretical yield. Terminal articles incorporating this acceleration chemistry include rubber-to-metal bonded engine mounts vulcanized in multi-cavity compression molds operating at 150–165°C with 8–12 minute cure cycles, extruded EPDM weatherseals for automotive glazing tested for compression set per ISO 815-1:2019 at 25% deflection after 24 hours at 70°C, and chloroprene rubber cable jackets requiring heat resistance qualified under IEC 60245-1:2003.Metal-complex dye ligand performance under multiple mordant bath conditionsThe 5-amino group and the thiazole ring nitrogen of 5-amino-2-methylbenzothiazole create a bidentate binding site that chelates transition metal ions—specifically chromium(III), cobalt(II), and copper(II)—when the compound is used as a ligand precursor in metal-complex acid dyes for polyamide and wool substrates. The resulting 1:2 metal-to-dye complexes exhibit absorption maxima bathochromically shifted by 40–80 nm compared to the corresponding metal-free dyes, with molar extinction coefficients that increase by a factor of 1.3–2.0× upon metal incorporation due to the rigidification of the chromophore geometry. The complexation is conducted in aqueous dimethylformamide at pH 7.5–8.5 with sodium acetate buffer, using chromium(III) chloride hexahydrate at a slight stoichiometric excess (5–10 mol%) relative to the theoretical metal:ligand ratio, followed by salting-out and filtration through 0.45 µm membrane filters to remove insoluble chromium hydroxide byproducts that otherwise cause specking defects during exhaustion dyeing.Mordant bath compatibility requirements under ISO 105-C06:2010 washing fastness protocols demand that the metal-complex dye resist de-metallation in the presence of competing chelating agents commonly found in synthetic detergent formulations, including ethylenediaminetetraacetic acid and sodium tripolyphosphate at concentrations up to 5 g/L. Complexes derived from 5-amino-2-methylbenzothiazole demonstrate superior resistance to ligand exchange compared to those based on 8-hydroxyquinoline under these test conditions, with <5% absorbance loss at λmax after 45 minutes at 60°C in wash liquor containing 4 g/L ECE reference detergent with phosphate builder. This stability is attributed to the electron-withdrawing effect of the sulfur atom in the thiazole ring, which increases the thermodynamic stability constant of the chelate relative to oxygen-only ligating systems. The finished dye products are applied through continuous pad-steam processes on wool tops at 50–70 m/min fabric speed, with chrome top-up added as sodium dichromate at 1–2% owf directly into the pad trough to replenish metal ions lost during processing. Terminal consumer articles include military uniform fabrics requiring infrared reflectance specifications, contract upholstery meeting BS 5852:2006 ignition source 5 crib test criteria, and automotive interior nylon carpets tested for lightfastness at 75°C black panel temperature in xenon arc apparatus per ISO 105-B02:2014.A practical processing limitation emerges when applying these metal-complex dyes on blends containing more than 20% acrylic fiber. The nitrile groups in acrylic copolymers selectively strip chromium from the dye complex during the steaming phase, resulting in duller shades and a measurable loss of 1–2 blue wool units in lightfastness performance. Pre-mordanting the acrylic component with 3% owf potassium aluminum sulfate prior to blending with wool partially mitigates this competitive extraction, but the two-step preparation adds 30–45 minutes to total wet processing time and reduces production throughput on beam dyeing machines by approximately 15%.When the diazo coupling route to disazo direct dyes exploits the primary amine for water solubility enhancement, the practical constraints shift to electrolyte tolerance in continuous dye bath replenishment systems. Direct dyes prepared by tetrazotizing benzidine derivatives and coupling with 5-amino-2-methylbenzothiazole as a terminal component exhibit enhanced substantivity for cellulosic fibers measured as exhaustion yields exceeding 85% at 90°C in the presence of 20 g/L sodium sulfate. However, the free amino group protonates below pH 4.0, causing a sharp drop in solubility from >100 g/L to <15 g/L and precipitation inside the pad trough of continuous dye ranges operating at low-liquor-ratio (0.6–0.8:1) conditions. Range operators compensate by maintaining dye bath pH at 6.5–7.0 through metered addition of disodium hydrogen phosphate buffer, monitoring pH continuously with in-line probes and adjusting through closed-loop controllers to ±0.2 pH units. |
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5-Amino-2-methylbenzothiazole (CAS 92-16-8; IUPAC 5-amino-2-methyl-1,3-benzothiazole, C₈H₈N₂S, molecular weight 164.23 g mol⁻¹) is supplied as a pale yellow to light beige crystalline powder. The heterocyclic framework consists of a benzene ring fused to a thiazole ring, with a methyl substituent at the 2-position and a primary amino group at the 5-position. Industrial batches typically exhibit a purity of ≥98.5% by HPLC (area normalization at 254 nm) and a melting range of 77–80 °C (DSC per ASTM E794-06). This intermediate serves as a critical building block in azo dye synthesis, pharmaceutical research, and specialty rubber compounding, where its substitution pattern imparts unique reactivity relative to other aminobenzothiazole isomers.
The amino group exerts a strong +M effect, activating the benzene ring toward electrophilic attack and directing incoming electrophiles to the ortho and para positions relative to the –NH₂ moiety. In 5-amino-2-methylbenzothiazole, the thiazole nitrogen withdraws electron density inductively, partially deactivating ring positions meta to the heteroatom. Consequently, coupling with diazonium salts occurs preferentially at C4 and C6, whereas electrophilic substitution at C7 is sterically and electronically disfavored. This orientation differs markedly from 2-aminobenzothiazole, where the amino group resides on the thiazole ring, leading to a substantially lower electron density on the carbocyclic ring and more sluggish electrophilic substitution that often requires Lewis acid catalysis. The methyl at C2 further raises the HOMO energy of the benzene ring by approximately 0.15 eV compared to the unsubstituted 5-aminobenzothiazole (DFT B3LYP/6-31G* calculations), enhancing reactivity in diazo coupling yet reducing oxidative stability.
Prolonged exposure to ambient relative humidity exceeding 60 % induces hydrate formation that broadens the melting endotherm and complicates gravimetric dispensing. Storage under a nitrogen blanket in amber glass containers fitted with PTFE-lined caps at 15–25 °C is mandatory. Contact with strong mineral acids at elevated temperature causes exothermic decomposition with evolution of NOₓ and SO₂; simultaneous storage with nitric acid, peroxides, or permanganates must be avoided. Moisture content, determined by Karl Fischer coulometry (ASTM E203-16), is maintained below 0.3 % w/w through in-process vacuum drying at 50 °C and ≤10 mbar for 8 h.
| Parameter | Specification | Test Method / Standard |
|---|---|---|
| Appearance | Pale yellow to beige crystalline powder | Visual comparison against certified reference standard |
| Purity (HPLC) | ≥98.5 area% | In-house HPLC (C18, 254 nm) validated per ICH Q2(R1) |
| Melting range | 77–80 °C | ASTM E794-06 (DSC, 10 °C min⁻¹) |
| Loss on drying | ≤0.3 % | Oven at 105 °C, 2 h (ASTM E1868-10) |
| Sulfated ash | ≤0.1 % | USP <281>, ignition at 600 °C |
| Heavy metals (as Pb) | ≤10 ppm | USP <231> Method II |
| Residual ethanol (GC) | ≤500 ppm | Headspace GC-FID (USP <467>) |
In the manufacture of monoazo acid dyes for nylon and wool, the compound is diazotized with sodium nitrite in 2.5 equivalents of aqueous HCl at a strictly controlled temperature of 0–5 °C. A jacketed glass reactor (100 L) equipped with a PTFE anchor stirrer operating at 200 rpm and a dosing pump for nitrite solution ensures homogeneous mixing and rapid heat removal. The resulting diazonium salt solution is clarified through a 0.45 µm PTFE membrane filter before entering the coupling vessel. Coupling with N-ethyl-N-(2-hydroxyethyl)aniline is performed at pH 4.0–4.5, maintained by the metered addition of 30 % sodium acetate solution. The coupling temperature must be held between 5 °C and 8 °C; an excursion above 10 °C triggers premature hydrolysis of the diazonium salt, reducing isolated dye yield by 15–20 %. The primary decomposition by‑product, 2‑methylbenzothiazol‑5‑ol, is monitored by inline HPLC; its content is kept below 0.5 area% to avoid shade dulling. Following coupling, the dye is precipitated by addition of 15 % w/v sodium chloride, isolated on a plate-and-frame filter press at 3 bar, washed with 5 % brine, and dried in a vacuum tray dryer at 60 °C and –0.95 bar for 12 h. Shade strength measured per ISO 105-A05 on polyamide knit shows batch-to-batch reproducibility within ±2 % when an automated pH‑stat and jacketed temperature control are employed.
Removal of the 2‑methyl substituent yields 5‑aminobenzothiazole (CAS 1123-93-9), which exhibits a higher melting point (144–147 °C) and markedly greater water solubility. The methyl group in the 2‑position increases hydrophobicity, reducing the strike rate on nylon fibers during exhaust dyeing and improving levelness. In a comparative dyeing trial on nylon 6.6 knit at a 1.0 % depth of shade, the dye derived from 5‑amino‑2‑methylbenzothiazole displayed a half‑dyeing time (t₁/₂) of 4.8 min versus 3.1 min for the unmethylated analogue, as measured by online spectrophotometry at λmax 480 nm (ISO 105‑Z07 method). Substantivity ratio, defined as K′dye/K′reference under neutral exhaustion conditions, was determined to be 1.2 for the 2‑methyl derivative, consistent with the log P increase of 0.45 log units calculated by the Crippen fragmentation method.
| Parameter | 5-Amino-2-methylbenzothiazole | 5-Aminobenzothiazole | 2-Amino-6-methylbenzothiazole (isomer) |
|---|---|---|---|
| CAS RN | 92-16-8 | 1123-93-9 | 2536-91-6 |
| Melting range (°C) | 77–80 | 144–147 | 135–138 |
| Water solubility (qualitative) | Sparingly soluble | Moderately soluble | Low |
| pKₐ (conjugate acid, 0.1 M KCl, 25 °C) | 1.92 ± 0.05 | 1.85 ± 0.04 | 2.10 ± 0.06 |
| Primary electrophilic coupling sites | C4, C6 | C4, C6 | C4 (dominant) |
5‑Amino‑2‑methylbenzothiazole has been investigated as a secondary accelerator in sulfur‑cured EPDM formulations, where its amine functionality activates the sulfur‑crosslinking system. In a silica‑filled EPDM compound (Nordel™ IP 4760P, 60 phr precipitated silica), addition of 0.5 phr of the benzothiazole derivative to a conventional MBTS‑sulfur system (1.2 phr MBTS, 1.5 phr sulfur) reduced the optimum cure time (t₉₀) from 8.2 min to 7.2 min at 160 °C as determined by moving die rheometer (MDR 2000, ASTM D5289‑19a, 0.5° arc). Scorch safety (tₛ₂) decreased by 15 %, requiring compensatory addition of 0.1 phr CTP (N‑cyclohexylthiophthalimide) to maintain processing latitude. The compound was mixed in a 1.6 L internal mixer (intermeshing rotors, fill factor 0.75) with a dump temperature of 120 °C; the benzothiazole additive was incorporated during the second pass to avoid premature scorch. Tensile properties after press‑curing at 160 °C to t₉₀ showed a modulus at 300 % elongation of 5.8 MPa compared with 4.9 MPa for the control (ASTM D412‑16, die C). The increase in crosslink density, calculated from equilibrium swelling in toluene using the Flory‑Rehner equation, was 12 %. Published data for long‑term heat aging at 125 °C indicate that retention of elongation at break after 168 h remains above 70 %, provided the dosage does not exceed 0.75 phr, above which reversion acceleration becomes significant.
Thermogravimetric analysis (TGA) at 10 °C min⁻¹ under nitrogen atmosphere records an onset of decomposition at 210 °C, with a sharp exothermic event peaking at 245 °C in differential scanning calorimetry (ASTM E537‑20). The hazard arises from the scission of the thiazole ring and the amino substituent, releasing gaseous NOₓ, SO₂, and low‑molecular‑weight nitriles. Open‑reactor processing above 180 °C is therefore proscribed unless adequate scrubbing and explosion venting are engineered. The auto‑ignition temperature determined by ASTM E659‑78 is 480 °C.
Direct nitration or oxidation of 5‑amino‑2‑methylbenzothiazole without protection of the amino group leads to intractable tars. To introduce a nitro substituent at the C6 position, the amine must be acetylated with acetic anhydride at 110 °C for 3 h, giving 5‑acetamido‑2‑methylbenzothiazole in 92 % yield. The protected intermediate is then nitrated in mixed acid (40 % HNO₃, 55 % H₂SO₄, 5 % H₂O) at 0–5 °C, generating the 6‑nitro derivative selectively; the reaction exotherm must not exceed a ΔT of 3 °C to suppress dinitration and oxidative fission. Subsequent deacetylation in 10 % HCl at reflux yields 5‑amino‑2‑methyl‑6‑nitrobenzothiazole. Without acetylation, the amino group is consumed by oxidation, and the aromatic ring undergoes ring‑opening via attack at the thiazole sulfur. Oxidative coupling reactions to form bis‑benzothiazolyl disulfides require control of redox potential below 400 mV (Ag/AgCl) to avoid over‑oxidation to sulfonic acid derivatives.
As a pharmaceutical intermediate, 5‑amino‑2‑methylbenzothiazole has been employed in the synthesis of 2‑methylbenzothiazole‑5‑sulfonamide inhibitors of carbonic anhydrase isoforms; the sulfonamide group is introduced via chlorosulfonation followed by amination.
