2-Amino-4-Methylbenzothiazole
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HS Code |
353293 |
| Chemical Formula | C8H8N2S |
| Molecular Weight | 164.23 g/mol |
| Appearance | Solid (usually white to off - white powder) |
| Melting Point | 127 - 131 °C |
| Solubility In Water | Insoluble |
| Solubility In Organic Solvents | Soluble in common organic solvents like ethanol, acetone |
| Odor | Odorless or very faint odor |
| Stability | Stable under normal conditions, but may react with strong oxidizing agents |
As an accredited 2-Amino-4-Methylbenzothiazole factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 250g of 2 - Amino - 4 - Methylbenzothiazole packaged in a sealed plastic bottle. |
| Shipping | 2 - Amino - 4 - Methylbenzothiazole is shipped in well - sealed, corrosion - resistant containers. Shipment follows strict chemical transport regulations, ensuring proper handling to prevent spills and maintain product integrity during transit. |
| Storage | 2 - Amino - 4 - methylbenzothiazole should be stored in a cool, dry, and well - ventilated area. Keep it away from sources of heat, ignition, and incompatible substances such as strong oxidizing agents. Store in tightly sealed containers to prevent moisture absorption and potential degradation. Avoid prolonged exposure to light as it may affect its stability. |
What Limits Diazo Coupling Yield at Commercial Tonnage for Acrylic Dyeing?2-Amino-4-methylbenzothiazole undergoes diazotization in aqueous hydrochloric acid with sodium nitrite below 5 °C. The resulting diazonium salt exhibits high electrophilicity and couples with tertiary aromatic amines to form 2-arylazo-4-methylbenzothiazole cationic dyes. Plant-scale production in glass-lined batch reactors, with typical heat transfer areas of 3.5 m² per 1000 L, demands strict temperature control. Deviation to 8 °C increases diazonium decomposition rate by a factor of 3.2, generating nitrophenol tar by-products that necessitate post-reaction filtration through a sparkler filter pre-coated with diatomaceous earth. The stoichiometric ratio of NaNO₂ to amine is maintained at 1.02:1.00; excess nitrous acid is destroyed by sulphamic acid addition prior to the coupling stage. Coupling with N,N-dimethylaniline at pH 4.0–4.5, adjusted by a sodium acetate buffer, yields a brilliant greenish-yellow chromophore. Dyebath exhaustion on polyacrylonitrile reaches 92% at 105 °C under weakly acidic conditions. After coupling, the dye is precipitated by salting out with 15% w/v NaCl, isolated via a membrane filter press with chamber thickness of 40 mm, and dried in a fluid bed dryer to a residual moisture of ≤0.5%. Commercial standardisation with dextrin brings the product to 200% strength relative to standard. OEKO-TEX Standard 100 Annex 4 compliance requires verified absence of free amine residues at ≤150 mg/kg using LC‑MS/MS validated per DIN EN ISO 17234-1. Light fastness on acrylic, tested to ISO 105‑B02, rates 4–5.
Disperse dye manufacture utilises 2-amino-4-methylbenzothiazole as the heterocyclic diazo component in combination with aniline-based or pyridone couplers to produce rubine to blue disperse dyestuffs for polyester. In a typical production campaign, the wet presscake of the coupled product, with moisture content near 40%, is transferred to a horizontal bead mill fitted with 1 mm yttria-stabilised zirconia beads. The dispersing agent condensation product of naphthalenesulphonic acid with formaldehyde (dispersant NNO) is dosed at a weight ratio to dry dye of 1.2:1.0. Milling continues until the 95th percentile particle size passes 1.0 µm, verified by laser diffraction on a Malvern Mastersizer. The resultant aqueous dispersion is spray‑dried to granular form, achieving a bulk density of 0.45 g/cm³. High-temperature exhaust dyeing of polyester fabric at 130 °C for 60 min under 2 bar pressure yields build‑up to 2.0% owf standard depth. Sublimation fastness per ISO 105‑P01 is rated 3–4 at 180 °C, restricting use in automotive textiles unless post‑treated with a fixation agent. ZDHC MRSL Version 3.1 conformance demands that the concentrated disperse formulation contain no alkylphenol ethoxylates, verified via ISO 18254‑1. Sulfenamide Accelerator Synthesis: Amine‑to‑Mercapto Conversion and Scorch PerformanceConversion of 2‑amino‑4‑methylbenzothiazole to 2‑mercapto‑4‑methylbenzothiazole (4‑methyl‑MBT) proceeds via a high‑pressure ammonium polysulphide reaction at 160 °C and 8 bar in a Hastelloy C‑22 autoclave. Subsequent oxidation with hydrogen peroxide (35%) in sulphuric acid media yields the corresponding benzothiazole disulphide (4‑methyl‑MBTS). Alternatively, the mercaptan is treated with cyclohexylamine and sodium hypochlorite at pH 9.0–9.5 to produce N‑cyclohexyl‑2‑benzothiazole sulphenamide (4‑methyl‑CBS). The methyl substitution at position 4 raises the scorch delay by 12% relative to unsubstituted CBS at 135 °C, determined by a moving‑die rheometer (MDR) per ISO 6502. In a silica‑filled natural rubber tread compound — NR SIR20 100 phr, silica 70 phr, zinc oxide 3 phr, stearic acid 2 phr, sulphur 1.8 phr, accelerator 1.5 phr — 4‑methyl‑CBS delivers a minimum torque ML of 1.2 dNm and a torque increase ΔS of 12.8 dNm. The processing safety window T5 extends to 8.2 min at 140 °C, sufficient for triple‑extrusion operations. Caution: The intermediate 4‑methyl‑MBT is a skin sensitiser and must be handled in closed systems, with dermal exposure maintained below 0.1 mg/m³ (8‑h TWA). REACH Annex XVII entry 72 restricts residual free amine in the finished sulphenamide to ≤0.5%. 2‑Amino‑4‑methylbenzothiazole serves as a starting material for the synthesis of 2‑amido‑4‑methylbenzothiazole derivatives screened against voltage‑gated sodium channels. Synthesis in a Good Manufacturing Practice (GMP) kilo‑lab requires re‑crystallisation from toluene/hexane (1:3 v/v) to reach purity ≥99.5% by HPLC area normalisation at 254 nm; individual unspecified impurity limits are set at <0.10% in accordance with ICH Q3A. Residual solvents are removed in a vacuum tray dryer (60 °C, 5 mbar) until toluene content is <890 ppm per USP 〈467〉 Class 2. The compound is then activated with carbonyl diimidazole in tetrahydrofuran to afford a reactive amide intermediate, which is quenched with substituted anilines at 0–20 °C. Bioburden in the isolated intermediate must be <50 CFU/g and endotoxins <0.5 EU/mg for injectable‑grade API camphorsulphonate salt formulations. Stability under long‑term storage (25 °C/60% RH) over 12 months shows <0.2% degradation to 2‑amino‑4‑methylbenzothiazole 5‑oxide when packaged in double LDPE bags inside a fibre drum. When Mild Steel Pickling Baths Operate Above 60°C, Inhibition Efficiency Declines Irreversibly2‑Amino‑4‑methylbenzothiazole acts as a mixed‑type corrosion inhibitor for mild steel in 1 M HCl at 25–60 °C. Weight‑loss trials conducted per ASTM G31‑72 with AISI 1018 coupons over a 24 h exposure demonstrate inhibition efficiency η = 97.1% at an inhibitor concentration of 0.5 g/L. At 60 °C efficiency declines to 89%, attributable to partial desorption; above 65 °C the Langmuir adsorption isotherm fails and pitting initiates at MnS inclusions. Synergism with 0.1 g/L potassium iodide enhances efficiency to 99.2% through co‑adsorption. Electrochemical impedance spectroscopy (EIS) in a flat cell (Ag/AgCl reference, platinum counter, scan ±10 mV vs. OCP) yields a charge transfer resistance Rct rising from 120 Ω·cm² (blank) to 4,950 Ω·cm² with inhibitor. The compound is incompatible with nitric acid due to oxidation of the thiazole ring. For industrial pickling baths, the inhibitor is added as a 10% active ethoxylated alcohol solution; bath life typically extends to 48 operating hours before top‑up is required. The formulation exhibits a BOD/COD ratio of 0.08, indicating poor inherent biodegradability — discharge consents under EU Directive 2010/75/EU require pre‑treatment via wet air oxidation. Residue Limits and Aerobic Half‑Life in Benzothiazole Carbamate InsecticidesConversion to N‑(4‑methylbenzothiazol‑2‑yl)methyl carbamate involves reaction with methyl isocyanate in toluene under catalytic triethylamine at 40 °C. This carbamate serves as a precursor to benzothiazole‑type insecticides exhibiting contact and stomach action on Lepidoptera. Technical‑grade intermediate must conform to FAO specifications for relevant plant protection products: purity ≥97%, water content <0.3%, and acetone insolubles <0.05%. During scale‑up in a 2000 L glass‑lined reactor, the exotherm must be controlled below 45 °C to avoid polymerisation of methyl isocyanate; a 30% molar excess of the isocyanate is used with a residence time of 3 h. Residue analysis in target crops, such as brassica, follows the QuEChERS method (EN 15662) with LC‑MS/MS quantification, achieving a limit of determination of 0.01 mg/kg. The 4‑methyl homologue exhibits a shorter environmental half‑life — aerobic soil DT50 = 7.2 d — than the unsubstituted variant, facilitating residue compliance under EU MRL Regulation (EC) No 396/2005.
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2-Amino-4-methylbenzothiazole (CAS 1477-42-5; IUPAC designation 4-methyl-1,3-benzothiazol-2-amine) is a heterocyclic primary amine that functions as a strategic intermediate in several industrial synthesis chains: sulfenamide accelerator production for sulfur-vulcanized rubber, heterocyclic disperse dye manufacture, and acid-pickling corrosion inhibitor formulations. The compound possesses a molecular mass of 164.23 g·mol⁻¹ and crystallizes as an off-white to pale yellow powder with a melting range of 128–132 °C when assayed at or above 98.0 % by area-normalised HPLC. Its dual donor structure — the endocyclic thiazole nitrogen and the exocyclic –NH₂ group — enables bidentate chelation with transition metal ions (Cu⁺, Fe²⁺, Zn²⁺), a ligand behaviour that directly separates its corrosion inhibition profile from that of mercaptobenzothiazole analogues and that simultaneously imposes strict limits on its direct use in copper-contaminated rubber masterbatches to prevent premature crosslinking.
Two primary commercial grades circulate in the merchant market: a technical-grade material with ≥98.0 % assay (HPLC, 254 nm) and a purified grade delivering ≥99.0 % assay with residual aniline-type impurities capped below 0.3 %. The technical grade is adequate for sulfenamide accelerator sequences — where the amine is oxidized with sodium hypochlorite in the presence of cyclohexylamine to form N-cyclohexyl-2-benzothiazolesulfenamide (CBS) — because the co-produced disulfide and slightly colored by-products are purged during the subsequent methanol wash step. In disperse dye synthesis, conversely, the purified grade is mandated: coupling with diazotised 4-nitroaniline yields an azo chromophore whose shade can deviate by ΔE > 1.5 (CIELAB, D65/10° observer as per ISO 105-A05:1996) when the amine input carries more than 0.2 % of the oxidative dimer, 2,2′-diamino-4,4′-dimethyl-azobenzothiazole. Iron content exerts an outsize influence on the melting behaviour; a rise in residual Fe above 15 mg·kg⁻¹ depresses the onset of melt by 2–3 K and broadens the melting interval, a phenomenon traceable to eutectic formation with iron-amine complexes visible on differential scanning calorimetry traces.
| Parameter | Typical Value | Test Basis |
|---|---|---|
| Assay (HPLC, area%) | 99.2–99.5 % | In-house method; C18 column, MeCN/H₂O 65:35, 254 nm |
| Melting point | 130.0–131.5 °C | USP ⟨741⟩ Class I capillary |
| Loss on drying (60 °C, vacuum) | ≤0.5 % | Ph. Eur. 2.2.32 |
| Sulphated ash | ≤0.1 % | Ph. Eur. 2.4.14 |
| Heavy metals (as Pb) | ≤10 mg·kg⁻¹ | USP ⟨231⟩ Method II |
| Residual 4-methylaniline | ≤0.15 % | GC-FID, DB-5 column |
Material stored in ambient warehouses with relative humidity persistently above 60 % will adsorb moisture to levels exceeding 1.0 % within 72 h, leading to soft cake formation that resists free flow through rotary valve feeders. Pre-drying in a vacuum tray dryer at 55 °C and 10 mbar for 4 h is standard practice before dispensing into reactor drop-charges to guarantee consistent stoichiometry in sulfenamide oxidation runs.
Laboratory evaluations employing ASTM G31-72 gravimetric immersion and ASTM G59-97 potentiodynamic polarization protocols place the 4-methyl derivative among the high-efficiency benzothiazolic inhibitors for mild steel in 1 M HCl. At a dosage of 200 mg·L⁻¹, weight loss recorded on SAE 1010 coupons after 6 h at 303 K corresponds to an inhibition efficiency of 93–95 %; unsubstituted 2-aminobenzothiazole yields 88–91 % under identical conditions. Electrochemical impedance spectra fitted to a simple Randles circuit reveal a charge-transfer resistance jump from 28 Ω·cm² (blank) to 540 Ω·cm² for the methylated candidate, versus 410 Ω·cm² for the parent amine, confirming that the +I effect of the 4-methyl group raises the HOMO energy and strengthens chemisorption onto the partially vacant d-orbitals of iron. A Langmuir adsorption isotherm calculated from surface coverage data produces an adsorption equilibrium constant Kads of 1.7 × 10⁴ L·mol⁻¹ and a standard free energy ΔG°ads of −34.8 kJ·mol⁻¹, straddling the physisorption–chemisorption boundary. The practical ceiling appears at 65 °C; above this temperature the protective film desorbs progressively, driving efficiency below 70 % regardless of concentration. A critical operational boundary arises when pickling brasses or bronzes: the amine’s affinity for Cu⁺ ions strips copper from the alloy surface into solution, locally raising Cu²⁺ concentration and triggering galvanic microcells that can pit the steel substrate faster than an uninhibited acid. This stands in direct contrast to 2-mercaptobenzothiazole (MBT), which passivates copper via an insoluble mercaptide layer but risks forming sludge that clogs spray nozzles in continuous strip-pickling lines.
| Inhibitor (200 mg·L⁻¹) | Weight loss (mg·cm⁻²) | Inhibition efficiency (%) | Corrosion rate (mm·y⁻¹) |
|---|---|---|---|
| Blank (uninhibited) | 7.85 | — | 17.9 |
| 2-Aminobenzothiazole | 0.92 | 88.3 | 2.10 |
| 2-Amino-4-methylbenzothiazole | 0.41 | 94.8 | 0.94 |
| 2-Mercaptobenzothiazole | 0.68 | 91.3 | 1.55 |
The data should be treated as indicative because the 4-methyl isomer’s solubility limit in 1 M HCl at 303 K is approximately 340 mg·L⁻¹; beyond this concentration, microcrystalline precipitates reduce the effective surface coverage. Field trials in hot-rolled coil pickling at a throughput of 180 tonnes·h⁻¹ demonstrated that blending the amino compound with a non-ionic ethoxylated dispersant at a mass ratio of 4:1 postponed the onset of inhibitor dropout until bath temperatures reached 78 °C, extending the allowable production window.
Although 2-amino-4-methylbenzothiazole itself exhibits negligible accelerator activity in sulfur vulcanization of natural rubber (scorch time ts2 at 160 °C on an MDR 2000 rheometer remains above 12 min even at 5 phr), it functions as the primary amine building block for delayed-action sulfenamide accelerators. Industrial synthesis of N-cyclohexyl-2-benzothiazolesulfenamide proceeds by oxidising the amine with sodium hypochlorite (active chlorine 13–15 %) in the presence of cyclohexylamine at pH 9.5–10.2 and 15–20 °C, maintaining a molar stoichiometry of amine:cyclohexylamine:NaOCl of approximately 1.0:1.05:1.03. The exothermic oxidative coupling generates −178 kJ·mol⁻¹ of heat; failure to maintain jacket brine circulation at −10 °C on a 5 m³ glass-lined reactor with anchor agitation at 60 rpm results in a temperature excursion that accelerates hypochlorite decomposition and raises the level of the undesired disulfide by-product to above 8 % w/w in the crude cake. The 4-methyl substitution sterically shields the exocyclic nitrogen, slowing the rate of electrophilic attack by chlorine species compared to the unsubstituted 2-aminobenzothiazole; this translates to a 15–20 % longer reaction time to reach 98 % conversion under the same conditions — an effect that demands careful adjustment of residence time in continuous flow tubular reactors operating at Reynolds numbers between 2,500 and 4,000 to avoid unreacted amine carryover that poisons the downstream vulcanization process by scavenging zinc oxide.
When the resulting sulfenamide is evaluated in a carbon black-filled natural rubber compound (formulation: NR SMR 20 100, N330 50, ZnO 5, stearic acid 2, sulphur 2.5, CBS 0.6 phr) according to ISO 3417:2023 (rotorless curemeter, 160 °C, 0.5° arc), the material produced from the 4-methyl-bearing amine delivers a scorch time ts2 of 4.2 min and a cure time t90 of 8.8 min, versus 3.9 min and 8.2 min for an accelerator derived from unsubstituted 2-aminobenzothiazole. The increment in scorch delay is directly attributable to the slightly higher steric bulk impeding the initial amine exchange with cyclohexylamine on the zinc-accelerator complex, a fine difference that becomes operationally critical on large truck tyre curing presses where a 30-second scorch safety margin differentiates a fully filled mould from a partially scorched charge.
The 4-methyl isomer must be distinguished from 2-amino-6-methylbenzothiazole (CAS 2536-91-6), which bears the methyl group on the position para to the endocyclic nitrogen. In electrophilic substitution reactions such as nitration in mixed acid, the 4-isomer directs incoming NO₂⁺ predominantly to the 6-position (ortho/para to the methyl group), giving a 70:30 ratio of 6-nitro to 5-nitro product, while the 6-methyl isomer yields almost exclusively the 4-nitro derivative. This regioisomeric preference is exploited in the manufacture of bis-azo disulfo dyes where a specific substitution pattern on the benzothiazole nucleus dictates the bathochromic shift. Against 2-hydrazino-4-methylbenzothiazole, the amino compound exhibits far lower acute aquatic toxicity (96-h LC₅₀ on Danio rerio > 100 mg·L⁻¹ according to OECD Test Guideline 203) because the hydrazine moiety of the latter confers a strong genotoxic alert under ICH M7 classification. Compared with 2-mercapto-4-methylbenzothiazole, the amino form eliminates the thiol odour and the tendency to generate insoluble copper(I) salts that harden process water circuits, yet it also lacks the ability to form stable zinc dialkyldithiocarbamate-type complexes that accelerate thiuram-cured systems. As a result, the amino compound positions itself as a specialty intermediate rather than a direct performance chemical, its value residing in the downstream molecular structures it enables rather than in any single neat-property advantage.
A further operational boundary manifests during storage and formulation with amine-reactive resins. Contact with epoxy systems based on bisphenol A diglycidyl ether (EEW 180–190 g·eq⁻¹) at elevated processing temperatures (> 60 °C) initiates an exothermic addition of the aromatic amine onto the oxirane ring, consuming the inhibitor and generating a crosslinked adduct that precipitates as a gritty solid in the coating premix. This limits the use of 2-amino-4-methylbenzothiazole as a direct corrosion-inhibitive pigment to thermoplastic lattices and solvent-borne alkyd primers devoid of epoxy functional groups. In polyamide-cured epoxy maintenance coatings, the compound can be microencapsulated in a urea-formaldehyde shell (particle size D₅₀ 18–22 µm) to delay interaction until film micro-cracking exposes the capsule contents to the steel substrate, a technique documented in patent literature but still limited to high-value offshore splash-zone applications where cost per litre tolerates a 15–20 € premium over conventional zinc phosphate pigmentation.
Residual solvent from synthetic work-up — typically n-heptane or cyclohexane used as a displacement washing medium — must be driven below 200 mg·kg⁻¹ before the amine enters a vulcanization accelerator reactor train, because residual hydrocarbon fragments alkylate the benzothiazole ring under oxidative conditions, forming persistent impurities that co-crystallise with the sulfenamide product and cause filter-clogging fines during product isolation on a horizontal vacuum belt filter equipped with a 15-µm monofilament polypropylene cloth. This purification step, routinely monitored by headspace GC-FID calibrated against EPA Method 5021A, adds 6–8 % to the processing cost but reduces reject batches by at least 80 % in continuous campaigns exceeding 120 hours.
