Benzothiazole-2-Thiol
|
HS Code |
137451 |
| Chemical Formula | C7H5NS2 |
| Molar Mass | 167.25 g/mol |
| Appearance | Yellowish - white to light - tan solid |
| Odor | Characteristic sulfur - like odor |
| Melting Point | 180 - 182 °C |
| Solubility In Water | Insoluble |
| Solubility In Organic Solvents | Soluble in many organic solvents like ethanol, acetone |
| Pka | about 3.59 |
| Density | 1.42 g/cm³ |
| Stability | Stable under normal conditions, but may react with strong oxidizing agents |
As an accredited Benzothiazole-2-Thiol factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Benzothiazole - 2 - Thiol packaged in 1 - kg bags for convenient handling. |
| Shipping | Benzothiazole - 2 - Thiol is shipped in tightly sealed, corrosion - resistant containers. Transport follows strict hazardous chemical regulations, ensuring proper handling to prevent leakage and environmental or safety risks during transit. |
| Storage | Benzothiazole - 2 - Thiol 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 moisture and air exposure, which could lead to degradation. Store separately from oxidizing agents and incompatible substances. Follow local safety regulations for chemical storage. |
In the compounding of natural rubber (NR) truck tire tread formulations, 2-mercaptobenzothiazole (MBT) is metered at 0.8–1.2 parts per hundred rubber (phr) into a tangential Banbury mixer (Farrel type, 270 L net chamber volume) alongside 2.5 phr sulfur, 50 phr N330 carbon black, and 0.3 phr diphenylguanidine (DPG) as a secondary activator. The batch is dropped at a stock temperature not exceeding 115°C to prevent premature crosslinking catalyzed by the acidic thiol group of MBT in the presence of basic amine species; failure to observe this thermal ceiling routinely manifests as a sharp reduction in Mooney scorch (MS-t5) from a target of 28–32 min at 121°C down to 12–15 min, rendering the stock unprocessable on two-roll mills during subsequent sheeting. Vulcanization kinetics, monitored using a moving-die rheometer per ASTM D5289, show a characteristic inversion of the cure curve where the torque increment (MH−ML) peaks at 1.0 phr MBT and then declines beyond 1.5 phr due to excessive network chain scission, a phenomenon confirmed by equilibrium swelling experiments (toluene) yielding crosslink densities of 16.2×10⁻⁵ mol/cm³ at 1.0 phr versus 13.8×10⁻⁵ mol/cm³ at 2.0 phr. The finished compounds are calendered into breaker plies for all-steel radial truck tires (315/80R22.5) and fire-resistant conveyor belts tested per ISO 340:2022; compliance with EU 1907/2006 (REACH) Annex XVII restriction on polycyclic aromatic hydrocarbons is maintained because MBT itself does not introduce benzo[a]pyrene contamination channels. A critical processing limitation emerges when MBT is co-formulated with thiuram disulfides: the combination accelerates vulcanization to such an extent that the scorch safety margin collapses below 3 min at 135°C, forcing compounders to replace MBT with its delayed-action sulfenamide derivatives in high-speed extrusion lines. Equipment-specific experience from a twin-screw roller-head extruder (L/D 16:1, pin-barrel design) confirms that compound viscosity at the die must be maintained above 18 ML(1+4)100°C to avoid porosity in the extrudate; MBT-laden batches exhibit narrower processing windows because the thiol moiety interacts with zinc oxide (5 phr) to form zinc mercaptide complexes that increase melt elasticity, requiring barrel zone temperatures to be lowered by 4–7°C compared with CBS-based compounds.What factors govern the oxidative condensation pathway when synthesizing N-cyclohexylbenzothiazole-2-sulfenamide from MBT?The manufacturing of the delayed-action accelerator CBS proceeds via oxidative coupling of MBT with cyclohexylamine in an aqueous alkaline medium, typically in a 5,000 L glass-lined agitated reactor equipped with a jacket cooling system capable of maintaining 0–5°C. The stoichiometric recipe charges MBT (1.0 molar equivalent) dissolved in 15 wt% sodium hydroxide solution, cyclohexylamine (1.05 equivalents), and a sodium hypochlorite oxidizer (1.10 equivalents) dosed through a dip pipe at a controlled rate of 12–15 L/min to keep the exotherm below 8°C; excursions above 10°C promote over-oxidation to the inactive benzothiazyl disulfide (MBTS), reducing the CBS yield below the economic threshold of 92%. Post-reaction, the slurry is neutralized with 30% sulfuric acid to pH 7.5–8.0, filtered on a rotary vacuum drum filter, washed with deionized water to a conductivity of <200 μS/cm, and dried in a fluidized-bed drier at inlet air temperature 65°C until the moisture content drops below 0.3 wt%. Product shipped under CAS 95-33-0 must comply with TSCA (40 CFR Part 710) inventory requirements and K-REACH registration; the residual free amine level is capped at 0.5% to meet the purity specification of ≥99.0% by HPLC (ASTM D4937 analogous elution). The fine granular CBS is packed in 25 kg EVA-lined woven bags and integrated into downstream rubber mixing operations where its delayed action permits processing temperatures up to 130°C before the onset of cure.Corrosion film formation on yellow metal surfaces in inhibited turbine oil circuitsIndustrial turbine oils blended to ISO VG 46 viscosity grade use MBT at concentrations of 0.15–0.50 wt% as a copper-passivating agent, frequently co-formulated with tolyltriazole (TTAA) at half the MBT loading to achieve synergistic coverage on bronze thrust bearing pads and brass oil cooler tubing. The addition sequence in the blending kettle (jacketed, impeller tip speed 3.5 m/s) demands that MBT be predissolved in a polar cosolvent—typically diethylene glycol monobutyl ether at 10 wt%—before injection into the base oil at 60–65°C; direct powder addition results in undispersed agglomerates that settle in storage tanks and fail the ASTM D130 copper strip test, yielding a 3a tarnish rating instead of the required 1b after 3 h at 100°C. The formulated oil must also pass the ASTM D665 rust test (Procedure B, synthetic seawater) with no visible corrosion on steel coupons, a condition that can be compromised if the MBT content drifts below 0.10 wt% because the inhibitor's chemisorption onto cuprous oxide (Cu₂O) becomes thermodynamically disfavored at operating temperatures exceeding 90°C. Field monitoring from a 150 MW steam turbine lubrication circuit revealed that MBT depletion occurred at a rate of 12–18% per 8,000 operating hours, necessitating a make-up dose via the kidney-loop polishing filter to maintain the rotating bomb oxidation test (RBOT, ASTM D2272) value above 800 min. An operational incompatibility surfaces with zinc dialkyldithiophosphate (ZDDP) antiwear additives: competitive adsorption displaces MBT from the metal surface, and the resulting film contains localized zinc mercaptide deposits that promote galvanic corrosion if chloride contamination exceeds 50 ppm.In the selective flotation of lead from a finely disseminated galena-sphalerite-pyrite orebody, MBT is conditioned as a primary collector into the ball mill discharge slurry at a dosage regime of 40–80 g/t dry ore—the exact rate calibrated by an in-stream X-ray fluorescence (XRF) analyzer measuring head-grade fluctuations between 3.2% and 6.8% Pb. Pulp chemistry is buffered to pH 9.5–10.0 with hydrated lime to ensure that the thiol functional group (pKa ≈ 6.8) remains predominantly in the deprotonated, surface-active form capable of coordinating with Pb sites on the galena {100} cleavage plane; this pH window also depresses pyrite response by passivating Fe species without the need for additional cyanide. The rougher circuit employs a bank of 14 Denver DR-500 mechanically agitated flotation cells (tank volume 2.8 m³ each) operating at an impeller speed of 1,200 rpm and a froth depth of 15 cm, producing a rougher concentrate grading 28–35% Pb that advances to a regrind mill (P80 =38 μm) ahead of three cleaning stages. While no dedicated ISO standard governs collector formulation, the concentrator operation aligns with ISO 14001:2015 environmental management for tailings discharge and monitors residual MBT in process water via UV absorbance at 320 nm to stay below the 0.05 mg/L ecotoxicity threshold for freshwater daphnia. A documented operational failure mode occurs when the conditioning pH drops below 9.0: MBT protonates and precipitates as an insoluble crystalline solid, stripping the collector inventory from the circuit within 90 min and collapsing the cumulative Pb recovery from 89% to below 55%.When MBT is integrated into a methylhexahydrophthalic anhydride/epoxy network for cast-resin dry-type transformersMBT functions as a latent accelerator in bisphenol A diglycidyl ether (DGEBA)—methylhexahydrophthalic anhydride (MHHPA) systems at addition levels of 0.5–2.0 phr, where it reduces the onset temperature of the ring-opening polymerization from 152°C to 137°C as measured by differential scanning calorimetry (DSC, ASTM E1356) at a 10°C/min ramp. The formulation is processed in a vacuum planetary mixer (vacuum level 5 mbar) at 70°C to degas the resin before being gravity-poured into a mold shell containing a dry-type transformer winding (34.5 kV class) preheated to 100°C. The cure profile follows a stepped protocol: 2 h at 120°C for gelation, ramp to 150°C over 1 h, and post-cure at 150°C for 4 h. Glass transition temperature (Tg) determined by dynamic mechanical analysis (ASTM D7028) reaches 141–146°C at 1.0 phr MBT, but the value falls to 132°C at 2.0 phr because the benzothiazole moiety acts as a chain-transfer agent that reduces the crosslink density of the epoxy network, a trade-off acceptable only in applications where the electrical insulation system is rated for Class F (155°C) rather than Class H. The cured resin must comply with the dielectric dissipation factor requirement of tan δ ≤ 0.015 at 100°C and 50 Hz per IEC 60455-2:2022; moisture ingress from inadequate pre-drying of MHHPA (water content >0.1%) causes MBT to hydrolyze into mercaptobenzothiazole crystals that nucleate voids, leading to partial discharge inception voltages (PDIV) below the 1.5 U₀ acceptance threshold.
Values represent the mean of five laboratory batches mixed on a laboratory two-roll mill (200×400 mm, friction ratio 1:1.2); cure time fixed at T90. Control of Aspergillus niger proliferation on chrome-tanned bovine leather stored in wet-blue stateIn leather manufacturing, a 0.12–0.30 wt% addition of MBT (based on shaved wet-blue weight) is dispersed into the fatliquoring emulsion—a blend of sulfonated fish oil and synthetic ester at 8% offering—and applied in a stainless-steel tanning drum (diameter 3.2 m, rotating at 12 rpm) during the post-tanning step at 45°C for 40 min. The benzothiazole-2-thiol forms a hydrophobic barrier on collagen fibers that inhibits spore germination of Aspergillus niger and Penicillium chrysogenum during the prolonged transportation of wet-blue hides from tanneries in subtropical zones (humidity routinely >85% RH) to manufacturing sites in temperate regions; without such treatment, visible fungal spotting appears within 72–96 h at 28°C. The active substance must be pre-emulsified with a nonionic surfactant (HLB 13–15) at a surfactant-to-MBT ratio of 1:4 to ensure stable suspension in the float; direct powder addition results in an uneven distribution that leaves untreated patches where the color fastness to rubbing (assessed per ISO 11640:2018) is reduced by half a grey scale point. Regulatory compliance requires that the commercial biocide product holding MBT be registered under the Biocidal Products Regulation (EU) 528/2012 for product-type 9 (fiber, leather, rubber, and polymerized materials preservatives), and the percentage of free thiol in the leather article must not exceed 50 mg/kg to align with emerging constraints from the ZDHC Manufacturing Restricted Substances List (MRSL) 2025. Process data indicate that the fungistatic efficacy collapses when the chrome content of the wet-blue falls below 4.0% Cr₂O₃ because the surface protonation of collagen carboxyl groups at a lower chrome fixing shifts the hide surface toward an acidic micro-environment where MBT is protonated and desorbs from the substrate.
Base oil: Group II, sulfur <50 ppm; all blends contain a phenolic antioxidant (0.25%) and aminic antioxidant (0.10%). Tarnishing 1a indicates negligible discoloration. |
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Benzothiazole-2-thiol (CAS 149-30-4), known industrially as 2-mercaptobenzothiazole or MBT, constitutes a primary thiazole-based accelerator for sulfur vulcanization of diene elastomers, along with utility as a corrosion inhibitor in metalworking fluids and a flotation collector for oxidized sulfide ores. Commercial grades are typically supplied as a pale-yellow powder or pastille with a melting range of 177–181 °C (technical grade), a purity of ≥96.0% by HPLC, ash content ≤0.5%, and free acidity (as H₂SO₄) ≤0.05%. The compound functions by forming a zinc–thiolate complex in situ when combined with zinc oxide and stearic acid, thereby activating elemental sulfur and directing crosslink formation toward predominantly mono- and disulfidic bridges at typical cure temperatures of 140–160 °C. Unlike sulfenamide accelerators such as N-cyclohexyl-2-benzothiazole sulfenamide (CBS) or N-tert-butyl-2-benzothiazole sulfenamide (TBBS), MBT exhibits minimal delayed-action character, which constrains processing safety in thick-section articles cured above 150 °C. Its molecular weight of 167.25 g/mol and limited solubility in aliphatic hydrocarbons (<0.1 g/100 mL in n-heptane at 25 °C) govern migration kinetics in multi-layer co-vulcanized assemblies.
The scorch behavior of benzothiazole-2-thiol is inherently tied to the critical time required for the Zn–MBT complex to react with sulfur and form the active sulfurating agent. In carbon black-filled natural rubber (NR) compounds processed on a 1.5 L internal mixer with intermeshing rotors (fill factor 0.75) and a dump temperature of 130 °C, the Mooney scorch time (MS t₅ at 121 °C, ASTM D1646) is typically 16–22 min when MBT is dosed at 1.0 phr in combination with 2.5 phr sulfur and 5.0 phr ZnO. This compares poorly to the 28–35 min achieved with MBTS (dibenzothiazyl disulfide) at equimolar thiazole content, because the disulfide must first undergo reductive cleavage to regenerate the active thiolate, providing an inherent induction period. The narrow processing window becomes acute on continuous vulcanization lines (e.g., liquid salt bath curing at 220 °C for thin-walled EPDM profiles), where the total heat history at the die exit must remain below the scorch onset temperature of 109 °C measured by differential scanning calorimetry (DSC) under nitrogen at 10 K/min. Plant-scale troubleshooting records indicate that hot summer ambient conditions (mill room > 35 °C) can reduce MBT compound shelf life to less than 4 hours when zinc oxide particle size falls below 0.3 µm, accelerating premature complex precipitation on the elastomer surface (blooming). As a countermeasure, pre-dispersed MBT masterbatches (75% active on EPDM/EVA binder) are recommended when two-roll mill processing temperatures exceed 60 °C and relative humidity remains above 65%.
Without a dedicated <h2> demarcation, the following text addresses the role of benzothiazole-2-thiol in oxidative coupling reactions during latex dipping. In prevulcanized natural rubber latex compounds for medical glove production (total solids content 62%, KOH number 0.55), MBT is frequently paired with a dithiocarbamate ultra-accelerator at a ratio of 1:1.5 to balance film modulus and extractable protein levels. The thiol group participates directly in the reductive cleavage of sulfur–nitrogen bonds on the dithiocarbamate-complexed rubber chain, generating mixed disulfide crosslink precursors that mature during post-leaching vulcanization at 100 °C for 30 min. A documented failure mode occurs when MBT is overdosed beyond 1.8 phr total solids in low-zinc (0.25 phr ZnO) formulations: the excess thiol scavenges zinc ions, deactivating the dithiocarbamate system and causing a catastrophic drop in tensile strength (measured per ASTM D412 Die C) from 28 MPa to below 18 MPa with only a 0.3 phr increment. This non-linear dose–response plateau illustrates the stoichiometric sensitivity of MBT relative to the more forgiving dosage curves of sulfenamide accelerators.
Benzothiazole-2-thiol particle size distribution is a primary driver of micro-dispersion quality in high-hardness tread compounds. Industrial MBT synthesized via the aniline–carbon disulfide–sulfur route under high-pressure conditions (2.5 MPa, 250 °C) yields a median particle diameter (D50) of 22–28 µm after standardized air-jet milling; however, agglomerate formation during bulk bag storage can shift D50 above 45 µm within 90 days if warehouse temperature cycles exceed 10 °C diurnal variation. In a 270 L tangential internal mixer processing a 70/30 NR/BR blend with 50 phr N330 carbon black, the incorporation of coarser MBT particles manifests as surface crater defects counted under 10× magnification (> 15 defects/dm²), traced to local over-cure zones where accelerator-rich domains reach crosslink densities 1.8–2.2 × 10⁻⁴ mol/cm³, measured by equilibrium swelling in toluene using the Flory–Rehner equation. Dispersion optimization demands that the MBT be added at the masterbatch stage alongside carbon black at a ram pressure of 0.6 MPa rather than at the final curative addition step, a procedure that increases the incorporation time by 30–45 seconds but lowers the Payne effect ΔG’ (at 0.5% strain, ISO 13145) from 480 kPa to 310 kPa. This sequence differs markedly from that employed for MBTS, whose lower melting point (120–126 °C) allows downstream compounding on an open mill without generating insoluble crystalline agglomerates.
| Accelerator | Dosage (phr) | MS t₅ (121 °C, min) | t₉₀ cure time (160 °C, min) | Tensile strength (MPa) | 300% modulus (MPa) |
|---|---|---|---|---|---|
| MBT (Benzothiazole-2-thiol) | 1.2 | 18.4 | 6.2 | 26.5 | 12.3 |
| MBTS (Dibenzothiazyl disulfide) | 1.5 | 29.7 | 6.8 | 27.1 | 12.8 |
| CBS (N-cyclohexyl-2-benzothiazole sulfenamide) | 1.0 | 34.2 | 5.5 | 28.0 | 13.5 |
a Formulation: SMR CV60 100 phr, N330 50 phr, ZnO 5 phr, stearic acid 2 phr, sulfur 2.25 phr. Mooney scorch per ASTM D1646; curemeter per ISO 3417 at 1.67 Hz, 0.5° arc. Tensile per ASTM D412 Die C.
The vulcanization efficiency of benzothiazole-2-thiol collapses when the ZnO concentration drops beneath the stoichiometric threshold required to sustain the chelated zinc–accelerator–sulfur intermediate. In a silica-filled SBR tread compound (silica 80 phr, silane TESPT 6.4 phr), reducing ZnO from 3.0 phr to 1.5 phr while keeping MBT at 0.8 phr shifts the crosslink type distribution, determined by thiol–amine chemical probe analysis, from 65% polysulfidic to 42% polysulfidic, with a corresponding increase in unreacted accelerator residues detected by HPLC extraction. The processing consequence on a pin-barrel cold-feed extruder (L/D 14:1, die swell ratio target 1.25) is a fluctuation in die swell of ±0.08 units correlating with ZnO lot-to-lot surface area variability (4–9 m²/g BET). At the lower boundary, inadequate zinc ion availability retards complex formation to such an extent that the modulus development stagnates; MDR rheometer traces show an isothermal torque increase (S’ max – S’ min) of only 8.4 dN·m at ZnO 1.5 phr versus 14.2 dN·m at 5 phr. This behavior is in contrast to dithiophosphate accelerators, which maintain effective vulcanization at ZnO levels as low as 1.0 phr due to a different ligand-exchange mechanism, and it underscores why MBT-based compounds are seldom used in zinc-free or “zinc-reduced” rubber goods unless supplemented with a strong zinc-complexing co-agent.
Chloroprene rubber (CR) compounding with benzothiazole-2-thiol presents an entirely different activation pathway because CR cures via metal oxide crosslinking rather than sulfur vulcanization. Here MBT serves as a scorch inhibitor by buffering the released hydrogen chloride and moderating the polymerization of 2-chloro-1,3-butadiene oligomers at the zinc oxide surface. Typical dosage in a mercaptan-modified CR (Mooney ML 1+4, 100 °C, 48 MU) is 0.35–0.5 phr, added simultaneously with MgO (4 phr) on a cooled two-roll mill at 50–55 °C. Overdosing to 1.0 phr extends the Mooney scorch time beyond 30 min at 121 °C but generates an undesirable binodal cure curve on the MDR—an early torque plateau at 3.0 dN·m after 4 min and a delayed second rise beginning 12 min into the test—producing heterogeneous crosslink structures that fail dynamic fatigue testing (De Mattia, ASTM D813) at 45% fewer cycles than the 0.5 phr reference. Publication of precise Arrhenius kinetic parameters for this inhibition is limited, but empirical molding shop data on 500-ton compression presses indicate that MBT-containing CR compounds must be cured at press temperatures of 160 ± 2 °C to avoid the onset of reversion, a tighter tolerance than the ±5 °C permissible for ethylene thiourea (ETU)-cured alternatives.
Benzothiazole-2-thiol functions as a selective collector for tarnished galena and activated sphalerite in circuits requiring separation from pyrite at alkaline pH. Electrochemical impedance spectroscopy on a polished pyrite electrode in borate buffer (pH 9.2) shows that MBT chemisorbs via the exocyclic sulfur atom, forming a ferric–thiolate surface complex with a charge transfer resistance of 4.7 kΩ·cm² at 1 × 10⁻⁴ M collector concentration, compared to 12.3 kΩ·cm² on galena, confirming the differential hydrophobicity exploited in plant practice. In a porphyry copper operation processing 85,000 t/d, reagent protocols add MBT at 8–12 g/t of ore ahead of the first rougher bank at pH 10.5 (lime-regulated), generating a copper concentrate grade of 28% Cu with a pyrite rejection exceeding 75%. The major operational limitation is the rapid oxidation of the thiol group to the corresponding disulfide in aerated pulps: dissolved oxygen levels above 6 ppm reduce the effective MBT half-life to less than 7 minutes in the conditioning tank, requiring staged addition across multiple flotation cells. This behavior contrasts with xanthate collectors, which form more stable dixanthogen species under identical oxidation potentials, and dictates that pulpers and transfer launders be designed with minimized free-fall to limit air entrainment.
| Property | Test Method | Powder Grade | Pastille Grade |
|---|---|---|---|
| Assay (MBT) | HPLC (UV 280 nm) | ≥96.0% | ≥96.5% |
| Melting point | Capillary, USP | 177–181 °C | 177–181 °C |
| Ash content | ISO 247 | ≤0.5% | ≤0.3% |
| Residue on 63 µm sieve | ISO 2591-1 | ≤0.2% | ≤0.1% |
| Bulk density | ISO 60 | 0.55–0.65 g/cm³ | 0.70–0.80 g/cm³ |
b Data representative of product supplied in 25 kg multi-wall paper bags with PE liner; pastilles also available in 500 kg flexible intermediate bulk containers.
The waterborne corrosion inhibition mechanisms of benzothiazole-2-thiol exploit its capacity to form a polymeric [Cu(I)MBT] film on copper and brass surfaces. In a synthetic cooling water matrix ( 200 ppm CaCO₃ hardness, 50 ppm chloride, pH 8.0 ), potentiodynamic polarization scans at 0.5 mV/s demonstrate a shift in the copper corrosion potential from −10 mV (SCE) for uninhibited water to +92 mV (SCE) with 10 ppm MBT, accompanied by a decrease in the anodic current density at +100 mV overpotential from 18 µA/cm² to 1.2 µA/cm². Compatibility restrictions arise in formulations containing oxidizing biocides: chlorine residuals exceeding 0.5 ppm free Cl₂ degrade the thiol moiety to the inactive benzothiazole sulfonate, as confirmed by LC–MS monitoring of the m/z 214 decay product. Field experience on a 5,000-ton chiller loop indicated that a switch from MBT to tolyltriazole (TTA) required a complete system flush to prevent the formation of a mixed-ligand film with compromised barrier properties, underscoring the lack of interchangeability within the azole inhibitor class.
