Benzothiazole, 2-Methyl-
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HS Code |
643114 |
| Chemical Formula | C8H7NS |
| Molecular Weight | 149.213 g/mol |
| Appearance | Yellow - brown solid |
| Odor | Faintly aromatic |
| Melting Point | 13 - 14 °C |
| Boiling Point | 231 - 232 °C |
| Density | 1.16 g/cm³ |
| Solubility In Water | Insoluble |
| Solubility In Organic Solvents | Soluble in ethanol, ether, chloroform |
| Flash Point | 104 °C |
| Stability | Stable under normal conditions |
As an accredited Benzothiazole, 2-Methyl- factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 2 - Methyl - benzothiazole: Packed in 1 - kg bottles for chemical storage and transport. |
| Shipping | 2 - Methyl - benzothiazole is shipped in tightly sealed, corrosion - resistant containers. They are carefully packed to prevent leakage. Shipment follows strict regulations for hazardous chemicals, ensuring safe transportation. |
| Storage | 2 - Methyl - benzothiazole should be stored in a cool, dry, well - ventilated area, away from heat sources and ignition points. Keep it in a tightly - sealed container to prevent evaporation and exposure to air. Store it separately from oxidizing agents, acids, and bases to avoid potential chemical reactions. This helps maintain its stability and ensures safe storage. |
Discoloration in the finished diene rubber article often traces back to residual amine stabilizers migrating to the surface under dynamic load and UV exposure. Replacing a conventional staining antioxidant with a thiazole-tethered phenolic derivative synthesized from 2-methylbenzothiazole circumvents this chromophore drift. The precursor 2-methylbenzothiazole is first alkylated at the methyl group via a Grignard intermediate prepared from methylmagnesium chloride in tetrahydrofuran at −5 °C to 0 °C, then quenched with 3,5-di-tert-butyl-4-hydroxybenzyl bromide. The resulting compound—2-(3,5-di-tert-butyl-4-hydroxybenzyl)benzothiazole—exhibits a molecular weight of 367.5 g/mol and a melting point of 118–120 °C, allowing metered feeding into a co-rotating twin-screw extruder with barrel temperatures zoned from 130 °C to 165 °C. Compound loading in EPDM roof membrane formulations ranges from 0.8 phr to 2.5 phr, with the upper boundary dictated by a sharp viscosity inflection measured on a Mooney viscometer (ML 1+4 at 125 °C) that exceeds 85 MU beyond 2.8 phr. Long-term oven aging per ISO 11346:2023 demonstrates that the retained elongation at break after 1,008 h at 130 °C falls from 62% to 48% when filler surface pH exceeds 9.2, because alkaline silica accelerates thiazole ring hydrolysis. A separate processing hazard appears when the masterbatch is stored under ambient humidity above 70% RH for more than 48 h: moisture uptake promotes β-scission in the polymer backbone during extrusion, lowering the average chain length and reducing the final compound’s tear strength (ASTM D624 die C) below 28 kN/m. On a calender line producing 1.2 mm thick single-ply membranes, edge trims containing the thiazole-grafted antioxidant can be reground and reintroduced at up to 15% reclaim ratio without detectable loss in seam peel adhesion, as confirmed by ASTM D413 hot-air welded specimens.When 2-Methylbenzothiazole Serves as the Core Building Block for Thiazole-Accelerated VulcanizationThe most rigorously mapped industrial consumption of 2-methylbenzothiazole enters the organic accelerator supply chain, where it is oxidized to 2,2’-dithiobis(benzothiazole) (MBTS) or transformed into the zinc mercaptobenzothiazole salt (ZMBT). In the MBTS route, 2-methylbenzothiazole is first demethylated through a patented vapor-phase oxidative ammonolysis at 390–420 °C over a vanadium-phosphorus oxide catalyst bed with a contact time of 0.3–0.7 s, yielding benzothiazole. The benzothiazole is then converted to 2-mercaptobenzothiazole (MBT) via a sodium hydrosulfide melt at 220 °C, and the subsequent oxidative coupling with hydrogen peroxide at pH 4.5–5.0 precipitates MBTS having a free MBT content below 0.5 wt%. Production-scale reactors equipped with Hastelloy C-276 agitators must maintain a peroxide dosing rate not exceeding 0.12 mol/h per mol MBT to avoid the irreversible sulfonate overoxidation byproduct. In a typical truck tire tread compound based on a natural rubber/butadiene rubber (70/30) blend, MBTS combined with a sulfenamide co-accelerator at a total accelerator loading of 1.8 phr shifts the scorch time (ts2, MDR at 160 °C, ISO 6502) from 2.4 min to 4.1 min compared to the MBT-only system, yet delivers a state-of-cure t90 within 8.2 min and a tensile strength exceeding 22 MPa after optimum cure (ASTM D412, die C). Mold fouling observed in multi-cavity injection presses after 3,000 cycles correlates with residual methyl-group-containing impurities that survive the demethylation step; a threshold of 0.08% 2-methylbenzothiazole in the feed benzothiazole is set as the release criterion before MBT synthesis.Why Do Cooling Water Formulators Select 2-Methylbenzothiazole Over Tolyltriazole?Tolyltriazole dominates yellow metal protection, but 2-methylbenzothiazole offers a distinct advantage in closed-loop cooling circuits operating above 55 °C where elevated chloride concentrations (300–600 mg/L) promote crevice corrosion on admiralty brass heat exchanger tubes. The thiazole ring coordinates with Cu(I) through the nitrogen and exocyclic sulfur atoms, forming a 0.8–1.5 nm thick monolayer that exhibits a charge-transfer resistance measured by electrochemical impedance spectroscopy exceeding 120 kΩ·cm² after 72 h immersion in ASTM D1384 corrosive water. A commercial formulation concentrates 2-methylbenzothiazole to 15–25% active in a solvent blend of diethylene glycol monobutyl ether and water, with the pH buffered to 9.0 ± 0.3 using 2-amino-2-methyl-1-propanol to prevent ring protonation that would otherwise reduce adsorption density. Field data from a 2,400 MW combined-cycle power plant documented a uniform corrosion rate on 90/10 Cu-Ni of less than 0.025 mm/year over an 18-month cycle when the residual inhibitor was maintained at 8–12 mg/L, as measured by UV absorbance at 315 nm. However, a known incompatibility arises with oxidizing biocides: chlorine or bromine dosed above 0.5 mg/L free residual cleaves the thiazole ring, generating sulfonate byproducts that not only lose inhibition but also reduce the system pH, accelerating galvanic attack at tube-to-tubesheet joints. Dosing must be sequenced with a 60-minute delay after biocide shock, and a supplementary filming amine is recommended when free chlorine demand cannot be reliably dechlorinated.Direct amination of the 2-methyl group yields 2-(aminomethyl)benzothiazole, a pharmacophore embedded in muscle relaxant candidates targeting the glycine receptor. The synthesis proceeds through a Ritter reaction with sodium cyanide and sulfuric acid at 5–10 °C to produce the intermediate nitrile, followed by catalytic hydrogenation over Raney nickel at 4.0 MPa and 80 °C. During the hydrogenation step, the formation of the secondary amine dimer must be kept below 1.5 area% (HPLC, C18 column, UV 254 nm), which necessitates a precise hydrogen uptake cutoff at 2.05 eq and rapid cooling of the autoclave to below 30 °C within 15 min. The free base is isolated by distillation at 110–112 °C at 1.3 kPa and immediately converted to the hydrochloride salt for stability. In an in vitro assay measuring glycine-induced chloride current via patch clamp on spinal dorsal horn neurons, the hydrochloride salt potentiates the current amplitude by 170% at a concentration of 2.5 µM, with an EC50 of 0.8 µM. The key impurity 2-methylbenzothiazole itself acts as a weak competitive antagonist with an IC50 of 18 µM; thus, the residual starting material limit in the active pharmaceutical ingredient is capped at 0.10% (ICH Q3A Table 2). Tablets compressed with a direct blend of the hydrochloride and lactose monohydrate must achieve a content uniformity (Ph. Eur. 2.9.40) with an acceptance value below 5.0, a parameter that degrades when the particle size D90 of the milled drug substance exceeds 45 µm, leading to segregation during hopper discharge on a rotary tablet press running at 80,000 tablets/h.
Directing Cyanine Dye Spectral Sensitivity: Substituent Effects at the 2-PositionPhotographic emulsion sensitization capitalizes on the electron-rich benzothiazole heterocycle to shift the absorption maximum of carbocyanine dyes into the red and near-infrared region. Condensation of 2-methylbenzothiazole with triethyl orthoformate in refluxing acetic anhydride containing 4 mol% zinc chloride generates the vinylogous amidinium intermediate, which upon subsequent coupling with a quaternized indolenine salt yields an unsymmetrical dicarbocyanine dye absorbing at 680–720 nm. The exact λmax is tunable by the counterion: iodide shifts the solution peak to 712 nm in methanol, whereas perchlorate moves it to 698 nm, as measured by a diode-array spectrophotometer with 1 nm resolution. Modern organic light-emitting diode (OLED) display patterning uses these benzothiazole-derived dyes as near-infrared absorbers in photoresist compositions for photolithographic edge definition at 365 nm (i-line). The dye loading in the propylene glycol monomethyl ether acetate (PGMEA) based resist is limited to 1.8 wt% solids because above this threshold the optical density at 700 nm exceeds 2.2 per micron, causing undercutting during the development step with 2.38% tetramethylammonium hydroxide developer. A single batch of 2-methylbenzothiazole destined for dye synthesis requires a purity higher than 99.5% with less than 0.1% of any isomeric methylbenzothiazole, because the 4-methyl isomer yields a dye bathochromically shifted by an additional 28 nm, disrupting the multi-layer registration tolerance in a three-chip DLP projector color wheel.Fungicidal Safener Synthesis Requires Strict Anhydrous Conditions and Boron Trifluoride CatalysisIn the agrochemical sector, 2-methylbenzothiazole acts as the scaffold for dichloroacetamide safeners that protect cereal crops from chloroacetanilide herbicide injury. The thiazole nitrogen is chloracetylated with chloroacetyl chloride in toluene at 0 °C, consuming 1.02 eq of triethylamine as an acid scavenger. The crude 2-chloroacetyl-2-methylbenzothiazole is then condensed with the ethyl ester of proline in acetonitrile under reflux, using 0.15 eq of boron trifluoride diethyl etherate to drive the acyliminium cyclization to a fused imidazo[1,2-b]benzothiazole derivative. The cyclization step is sensitive to protic impurities: water content in the acetonitrile must not exceed 150 ppm (Karl Fischer) to avoid premature hydrolysis of the electrophilic chloroacetyl intermediate, which forms a benzothiazole amide hydrolysis side product that reduces the overall yield below 55%. In field trials across 12 sites on maize (Zea mays L.) treated with S-metolachlor at 1.6 kg/ha, the addition of 0.3 kg/ha of the safener elevated the crop injury index from 18% to below 4% when measured at the V3 growth stage, while maintaining a weed control efficacy above 92% on Setaria species.
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Benzothiazole, 2-methyl- (CAS 120-75-2), a heterocyclic scaffold comprising a benzene ring fused to a thiazole bearing a methyl substituent at the 2-position, is supplied as a pale-yellow to amber liquid with a characteristic roasted, sulfurous odor profile. Commercial specifications typically start at ≥98.0% purity for general industrial synthesis and reach ≥99.5% for pharmaceutical intermediate and flavor use, with residual moisture controlled below 0.1 wt% via Karl Fischer titration per ASTM E203. Its functionality spans nucleophilic building block in polymethine cyanine dye synthesis, copper corrosion inhibitor in aqueous metalworking fluids, and FEMA GRAS flavoring substance (FEMA No. 3253), where it imparts coffee-like notes at part-per-billion dosage. Compared to unsubstituted benzothiazole, the electron-donating methyl group raises the boiling point by approximately 7–9 °C and moderates electrophilicity at the C-2 position, altering kinetic profiles in quaternization reactions with alkyl halides. Relative to 2-mercaptobenzothiazole, the 2-methyl- analog lacks the thiol moiety, eliminating disulfide crosslinking pathways and rendering it suitable for non-sulfur-curing polymer applications.
In aluminum rolling coolant formulations, 2-methylbenzothiazole is blended at 0.5–1.5 wt% as a copper passivator to mitigate galvanic corrosion in bimetallic circuits containing yellow brass components. Field data from a recirculating coolant loop operating at 45–50 °C and pH 8.5–9.0 indicate that copper dissolution rates measured via ICP-OES remain below 0.1 mg/L over 3,000 hours when the benzothiazole concentration is maintained above the critical micelle dilution threshold of 0.3 wt%. Performance is evaluated using copper strip corrosion testing per ASTM D130 (at 100 °C for 3 h), achieving a classification of 1a to 1b. At addition levels exceeding 2.0 wt%, viscosity excursions of 15–20% have been recorded in semi-synthetic emulsions, requiring rebalancing of the emulsifier package and pre-dilution of the inhibitor in a co-solvent such as diethylene glycol monobutyl ether to maintain dispersion in high-hardness water (above 400 ppm CaCO₃).
The quaternization of 2-methylbenzothiazole with short-chain alkyl iodides to form 2,3-dimethylbenzothiazolium salts is a foundational step in preparing indocarbocyanine and thiacarbocyanine sensitizers for photographic emulsions. The reaction proceeds via an SN2 mechanism at the endocyclic nitrogen, where the electron-releasing methyl group reduces the partial positive charge on the thiazole ring. Comparative nucleophilicity parameters (N, s) derived from Mayr-type reference electrophile scales position 2-methylbenzothiazole 0.3–0.5 units lower than benzothiazole, corresponding to a 2- to 3-fold decrease in reactivity toward diarylcarbenium ions. When the reaction is performed in acetonitrile at 60 °C with a 1.5-fold excess of methyl iodide, the observed pseudo-first-order rate constant for benzothiazole quaternization is approximately 2.8 × 10⁻³ s⁻¹; the 2-methyl analog reaches comparable conversion with a rate constant of 1.2 × 10⁻³ s⁻¹ under identical conditions, as reported in peer-reviewed J. Heterocyclic Chem. kinetic studies.
On a production scale, the exotherm generated during quaternization in a 2,000-L glass-lined reactor necessitates controlled alkyl halide dosing over 6–8 h to maintain an internal temperature below 40 °C. A failure to control the addition rate leads to localized overheating, promoting the formation of over-quaternized 2,3,3-trimethylbenzothiazolium by-products and dark-colored degradation species that can reduce the optical density of the final dye. Post-reaction workup requires aqueous sodium carbonate washing to neutralize the hydriodic acid generated, with a target residual halide content below 100 ppm to avoid catalyst poisoning in subsequent cross-coupling steps.
The compound exhibits a normal boiling point of 238–240 °C at atmospheric pressure, with a flash point of 102 °C (closed cup, ASTM D93). To obtain pharmaceutical-intermediate grade material, vacuum fractional distillation is performed at 5–10 mmHg, yielding a heart cut boiling at 118–122 °C. Distillation behavior is characterized according to ASTM D1160, with a refractive index of 1.6130–1.6160 at 20 °C (ASTM D1218) serving as an in-process quality indicator. Prolonged heating above 150 °C under air triggers autoxidation, generating 2-methylbenzothiazole N-oxide and ring-opened sulfinic acid derivatives. After 24 h at 160 °C, the peroxide value rises to 10–15 meq/kg (ASTM E298), accompanied by a color shift toward a dark brown hue exceeding 200 APHA. Therefore, storage under a nitrogen headspace and processing temperatures capped at 140 °C are prescribed for any operation longer than 4 h.
The odor threshold of 2-methylbenzothiazole in water is 0.02 µg/L, roughly 25-fold lower than benzothiazole’s threshold of 0.5 µg/L, enabling a more potent delivery of coffee, cocoa, and roasted meat notes at trace dosages. The methyl substitution also suppresses the quinoline-like off-note that benzothiazole-containing blends can develop after UV exposure, a degradation pathway that generates 2-hydroxybenzothiazole and related photoproducts. Flavor-grade material must comply with the FCC monograph, requiring GC assay of ≥99% purity with FID detection and a benzothiazole impurity level not exceeding 0.1%. The sensory impact is further modulated by the enantiomeric purity of the flavor matrix; published data for this specific configuration in chiral terpene carriers is limited, but formulation trials consistently show that a concentration above 50 ppb in low-fat media introduces astringent, burnt-sulfur notes, defining a narrow working window.
| Parameter | Industrial Grade | Flavor Grade (FEMA) | Pharmaceutical Intermediate | Test Method |
|---|---|---|---|---|
| Assay (GC area-%) | ≥98.0 | ≥99.0 | ≥99.5 | ASTM D4058 / In-house GC-FID |
| Moisture (KF, wt%) | ≤0.1 | ≤0.05 | ≤0.03 | ASTM E203 |
| APHA Color | ≤100 | ≤50 | ≤30 | ASTM D1209 |
| Freezing Point (°C) | 13–15 | 14–15 | 14–15 | ASTM D1015 |
| Heavy Metals (as Pb, ppm) | ≤10 | ≤5 | ≤2 | USP <231> |
| Residual Solvent (ethyl acetate, ppm) | ≤500 | ≤200 | ≤50 | USP <467> |
| Chloride Content (ppm) | ≤200 | ≤50 | ≤10 | Ion chromatography (USP <221>) |
Residual chloride in 2-methylbenzothiazole presents a critical risk in downstream cross-coupling reactions that employ palladium catalysts, where inorganic halide levels above 50 ppm have been shown to poison catalytic sites and reduce turnover numbers by 30–40% in Buchwald-Hartwig aminations. For active pharmaceutical ingredient (API) starting material, a chloride specification of ≤10 ppm is enforced, measured by suppressed conductivity ion chromatography against a 5-point calibration curve. Additionally, iron contamination must remain below 10 ppm (determined by ICP-MS following microwave-assisted acid digestion), as iron catalyzes chromogenic oxidation that can discolor the final drug substance. When processing batches intended for GMP intermediates, the product is filtered through a 0.2 µm membrane and packaged in amber glass with a nitrogen overlay, then stored at 2–8 °C to suppress radical-mediated photodegradation that otherwise generates trace benzothiazole and 2-methylmercaptobenzothiazole in as little as 72 h under ambient fluorescent light. For manufacturers operating in stainless steel 316L equipment, the process stream must be kept above 16 °C to avoid solidification in transfer lines, yet any continuous exposure to temperatures exceeding 120 °C in the presence of chloride exceeds the material’s intergranular corrosion threshold and mandates a post-campaign eddy current inspection of weld seams.
Combining 2-methylbenzothiazole with strong oxidizing agents—particularly nitric acid at concentrations above 30%—leads to rapid exothermic decomposition with an onset temperature near 80 °C as determined by differential scanning calorimetry (ASTM E537). The reaction generates sulfur dioxide, oxides of nitrogen, and char, requiring process safety interlocks such as redundant temperature probes and pressure-relief systems sized for a 200 L/s vent rate in a 500-L reactor. Mixtures with alkali metals or alkali amides also present a deflagration hazard and are to be avoided.
| Compound | CAS | MW (g/mol) | Boiling Point (°C) | Melting Point (°C) | Key Functional Group | Representative Application |
|---|---|---|---|---|---|---|
| Benzothiazole | 95-16-9 | 135.19 | 230–232 | 2 | Unsubstituted thiazole | Flavor, photographic intermediate |
| 2-Methylbenzothiazole | 120-75-2 | 149.21 | 238–240 | 14–15 | 2-methyl group | Cyanine dye precursor, corrosion inhibitor |
| 2-Mercaptobenzothiazole (MBT) | 149-30-4 | 167.25 | 305–310 (decomp.) | 177–179 | Thiol (–SH) | Rubber vulcanization accelerator |
| 2-Aminobenzothiazole | 136-95-8 | 150.20 | 310–312 | 128–130 | Primary amine (–NH₂) | Pharmaceutical intermediate |
The absence of a thiol group in 2-methylbenzothiazole precludes its participation in sulfur-vulcanization crosslinking, a mechanistic distinction that allows it to function in non-curing polymer systems and halogen-free flame retardant formulations where thiol-induced degradation must be avoided. In contrast to the highly polar 2-aminobenzothiazole, the methyl derivative offers superior compatibility with low-polarity hydrocarbon solvents, expanding its utility in oil-soluble corrosion inhibitor packages.
