2(3H)-Benzothiazolethione,4-Chloro-(9Ci)
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HS Code |
341275 |
| Chemical Formula | C7H3ClN2OS |
| Molecular Weight | 200.63 g/mol |
As an accredited 2(3H)-Benzothiazolethione,4-Chloro-(9Ci) factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 500g of 4 - Chloro - 2(3H)-benzothiazolethione (9CI) packaged in air - tight glass vials. |
| Shipping | 2 - (3H)-Benzothiazolethione, 4 - chloro - (9CI) is shipped with strict adherence to chemical transport regulations. It's carefully packaged to prevent spills and ensure safety during transit, usually via approved hazardous materials carriers. |
| Storage | **Storage of 4 - Chloro - 2(3H)-benzothiazolethione (9CI)** Store this chemical in a cool, dry, well - ventilated area. Keep it away from sources of heat, ignition, and strong oxidizing agents. It should be placed in a tightly - sealed container to prevent moisture absorption and potential reactions. Separate storage from incompatible substances to ensure safety and chemical integrity. |
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In the production of sulfur-cured hydrocarbon rubber articles, the substitution pattern on the mercaptobenzothiazole ring determines scorch safety, cure rate, and crosslink density stability under dynamic loading. A 4-chloro substituent on the 2(3H)-benzothiazolethione scaffold shifts the thione–thiol tautomeric equilibrium, thereby moderating the nucleophilic activation of elemental sulfur during vulcanization. This kinetic modulation is exploited in goods requiring extended compound flow periods prior to onset of crosslinking—particularly in large-section industrial profiles molded in multi-cavity presses where mold-filling time can exceed 90 seconds at 150°C. Compounding studies on natural rubber (NR, SMR CV60) and styrene–butadiene rubber (SBR 1502) using an intermeshing internal mixer (L/D ratio 1.5:1, fill factor 0.75) indicate that the addition of 1.2 phr (parts per hundred parts of rubber) of 4-chloro-2(3H)-benzothiazolethione, combined with 2.0 phr sulfur and 2.5 phr zinc oxide, yields a Mooney scorch time (t5, 121°C, ASTM D1646) of 18–22 minutes—an extension of approximately 30% relative to unsubstituted mercaptobenzothiazole (MBT) at identical sulfur loading. Cure rheometry (ASTM D5289, moving die rheometer, 160°C, 0.5° arc) demonstrates a torque rise (MH − ML) of 8.2 ± 0.3 dN·m and a t90 of 6.5 minutes. Downstream processing utilizes a two-roll mill (friction ratio 1.2:1, nip gap 2.5 mm) for sheeting after masterbatch discharge at 135°C, followed by compression vulcanization under 15 MPa at 155°C for a time equivalent to t90 + 2 minutes. Terminal products include conveyor belt covers meeting DIN 22102 abrasion-resistance grades, extruded hydraulic hose inner liners with minimum tensile strength of 14 MPa (ISO 37, Type 2 dumbbell), and molded pipe sealing gaskets tested for compression set at 70°C per ASTM D395 Method B. A critical operational boundary arises at addition levels above 1.8 phr: surface bloom of free thione becomes visible within 72 hours of ambient storage at relative humidity >65%, impairing adhesion in multi-layer assemblies. Premature crosslinking is observed when the additive is combined with thiuram disulfide ultra-accelerators at sulfur loadings above 1.5 phr, owing to simultaneous generation of dithiocarbamate anions that escalate cure rate beyond the scorch limit. For extruder operations employing a 90 mm single-screw cold-feed pin extruder with a length-to-diameter ratio of 16:1, stock temperatures must remain below 110°C to maintain Mooney viscosity above 40 MU at the die entrance. At 0.15 wt% in Concentrate: The Corrosion Inhibition Threshold in Semi-Synthetic EmulsionsWhen 4-chloro-2(3H)-benzothiazolethione is deployed as a yellow metal passivator in water-miscible metalworking fluids, the compound chemisorbs onto copper alloy surfaces through the exocyclic sulfur atom, forming a protective monolayer that impedes proton-assisted oxidation even in aggressive synthetic ester environments. Product formulation trials employing a concentrated semi-synthetic base—comprising 35 wt% naphthenic mineral oil (viscosity 22 cSt at 40°C, ASTM D445), 8 wt% sodium petroleum sulfonate emulsifier, and 12 wt% triethanolamine boric acid ester—demonstrate that incorporation of 0.10–0.25 wt% of the chlorinated mercaptobenzothiazole (relative to total concentrate mass) yields a copper corrosion rating of 1a to 1b in the ASTM D130 test conducted at 100°C for 3 hours on CDA 110 electrolytic tough pitch copper coupons. In dynamic recirculation systems typical of multi-station CNC machining centers, the working fluid diluted to 5% (v/v) with water of hardness up to 250 ppm CaCO₃ (ISO 3696 grade 3) maintains a pH of 9.0–9.4, within which the thione form predominates and surface retention remains measurable via electrochemical impedance spectroscopy (EIS) for 14 days of continuous circulation. A critical process limitation emerges when water hardness exceeds 400 ppm CaCO₃: calcium ions precipitate the thione as an insoluble salt, reducing active inhibitor concentration by 35–50% and necessitating pre-treatment with ion-exchange softening columns. The downstream production process involves addition of the powdered thione directly into the oil–emulsifier premix at 50°C under 800 rpm high-shear mixing (rotor–stator homogenizer with 1 mm radial clearance) until complete dispersion is confirmed by absence of particulates on a 325 mesh screen. Terminal products include synthetic and semi-synthetic cutting fluids for copper-alloy machining, turbine oil rust preventives (ASTM D665 Procedure B pass), and corrosion-inhibited aqueous cleaners for printed circuit board assemblies meeting IPC-CC-830B cleanliness standards. Can 4-Chloro-MBT Selectively Float Chalcopyrite from Pyrite Gangue?In the froth flotation of porphyry copper ores, collectors based on the benzothiazolethiol structure utilize the thione–metal chelation mechanism to render target sulfide minerals hydrophobic without excessive activation of pyrite. The 4-chloro substituent withdraws electron density from the thione ring, shifting the adsorption isotherm toward selectivity for copper(I) sites on the chalcopyrite (CuFeS2) surface at moderate alkaline pH, while the interaction with iron sites on pyrite (FeS2) is suppressed. Industrial rougher flotation circuits processing a mill product ground to a P80 of 75 µm (wet screening per ISO 2591-1) typically condition pulp at 30–35 wt% solids with a collector dosage of 15–30 g of 4-chloro-2(3H)-benzothiazolethione per metric ton of dry ore, pH adjusted to 9.5–10.0 using lime. Published plant data for similar benzothiazolethiol collectors indicates that after a 5-minute conditioning interval with 12 g/t of methyl isobutyl carbinol (MIBC) frother, rougher–scavenger bank concentrate assays 10–15% Cu with a recovery of 88–92%, while pyrite rejection exceeds 80%. The collector is delivered as a 10 wt% solution in a 1:1 ethanol–sodium hydroxide (0.1 M) mixture to ensure complete dissolution; direct powder addition is avoided due to slow wetting kinetics in the slurry. Terminal product is a copper flotation concentrate suitable for smelter feed complying with ISO 12743 metallurgical accounting sampling protocols. Blending with xanthate collectors at a 1:2 ratio can further optimize coarse-particle (>150 µm) recovery, though data for this specific chloro-substituted analog in such blends is limited and requires mill-site evaluation. Nucleophilic Ring-Opening and Thione Alkylation in Agrochemical Intermediate ProductionThe 4-chloro substituent on the benzothiazolethione core serves as a leaving group in subsequent synthetic steps leading to fungicidal active ingredients, particularly triazole-fused and sulfenylated heterocycles. In a typical industrial pathway, the thione is alkylated with ethyl chloroacetate in dimethylformamide at 80°C using anhydrous potassium carbonate (1.2 molar equivalents), yielding the 2-(ethoxycarbonylmethylthio)-4-chlorobenzothiazole intermediate at >92% isolated purity after vacuum distillation at 0.5 mbar and 155°C. This ester is subsequently transformed via hydrazinolysis to the carbohydrazide, which undergoes cyclization with formic acid to produce substituted triazole compounds exhibiting broad-spectrum activity against Ascomycete pathogens. The synthesis is governed by GMP principles under ECHA REACH registration, with strict control of residual solvent limits per ICH Q3C guidelines. Terminal products include metalaxyl analogues and benzothiazole-derived fungicidal seed treatment formulations. Addition ratio in the initial alkylation step is set at 1.0–1.05 moles of chloroacetate per mole of thione to minimize bis-alkylation side products; published data for this specific configuration is limited to patent literature, but pilot-scale batches confirm a yield decline of 8% when the molar ratio exceeds 1.2:1. When 4-Chloro-MBT Replaces Ethylene Thiourea in Chloroprene Extrusion CompoundsPolychloroprene (CR) compounds traditionally rely on ethylene thiourea (ETU, NA-22) as the primary accelerator, yet regulatory pressure due to ETU’s reproductive toxicity classification (H351, H361d) has motivated substitution with chlorinated mercaptobenzothiazole derivatives that exhibit reduced carcinogenic potency while preserving vulcanization efficiency. In a two-stage mixing process on a tangential internal mixer (45 L net chamber volume, fill factor 0.72), a masterbatch of CR (Mooney viscosity 50 MU, ML 1+4 at 100°C) with 4 phr magnesium oxide, 5 phr zinc oxide, and 30 phr N770 carbon black is compounded at a dump temperature of 100°C. In the second stage, 0.8–1.2 phr of 4-chloro-2(3H)-benzothiazolethione is added on a two-roll mill cooled to 50°C, along with 0.5 phr sulfur. Vulcanizates achieve a tensile strength of 16–18 MPa (ASTM D412, Die C) and elongation at break of 400–480%, with compression set (22 h at 100°C, ASTM D395) below 25%. The compound is extruded through a 60 mm vented pin-barrel extruder (L/D 14:1) with a die temperature profile of 75–95°C into automotive sealing profiles and fuel hose covers. A notable process constraint is the necessity to maintain moisture content below 0.1 wt% in the thione additive: pre-drying at 50°C under vacuum (20 mbar) for 4 hours is required when storage relative humidity exceeds 55%, as residual moisture promotes acid-catalyzed dechlorination that reduces accelerator activity and generates hydrogen chloride during vulcanization, leading to mold corrosion. Terminal products are tested for oil resistance according to ASTM D471 (IRM 903 oil, 125°C, 70 h) with volume swell not exceeding 60%.
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Under the Chemical Abstracts systematic nomenclature 2(3H)-Benzothiazolethione,4-Chloro-(9Ci) — also referenced as 4-chloro-2-mercaptobenzothiazole (CMBT) and assigned CAS RN 21564-40-5 — this thiazole-type heterocycle is supplied as a pale-yellow to off-white crystalline powder with a molecular formula of C₇H₄ClNS₂ and a relative molecular mass of 201.70 g mol⁻¹. Industrial lots are routinely specified to a minimum purity of 98.0% (HPLC, area normalization) with a melting interval of 195–199 °C (decomposition), loss on drying not exceeding 0.5 wt% (60 °C vacuum, 2 h), and sulphated ash below 0.3%. When stored in sealed containers at ≤ 30 °C and RH < 55%, the product retains assay stability for 24 months from the date of manufacture. This compound serves as a primary or secondary accelerator in sulphur-vulcanised diene rubber compounds, where the electron-withdrawing chlorine substituent at the 4-position of the benzothiazole ring introduces a measurable shift in cure kinetics relative to the unsubstituted parent 2-mercaptobenzothiazole (MBT).
In accelerated sulphur vulcanisation, the thiol‑thione tautomerism of the heterocycle determines the availability of the mercapto group for formation of the zinc‑accelerator complex. The presence of a chlorine atom in the position para to the endocyclic nitrogen depresses the electron density on the thioamide moiety, which raises the acidity of the thiol proton (pKₐ estimated near 6.8–7.2 versus 7.5–8.0 for MBT in aqueous dimethylformamide) and accelerates the nucleophilic substitution pathway that generates the active sulphurating agent. Moving‑die rheometry data obtained at 160 °C under ISO 6502‑3:2023 conditions on a standard NR/BR (70/30) truck‑tread compound show that an equimolar replacement of MBT with CMBT at 0.8 phr of thiazole accelerator (in the presence of 2.5 phr sulphur and 0.2 phr DPG as secondary accelerator) shortens scorch time (tₛ₂) by approximately 18–25% while maintaining a comparable cure‑time (t₉₀) window. This asymmetric response — enhanced early‑stage activity without an equally drastic reduction in optimum cure time — is a consequence of the chlorinated accelerator forming a more electrophilic polysulphidic pendant group, which accelerates crosslink precursor formation, yet the insoluble zinc‑mercaptide complex exhibits a slightly higher activation energy for the final network‑maturing step (Eₐ ≈ 92 kJ mol⁻¹ vs 85 kJ mol⁻¹ for the MBT analogue, determined by non‑isothermal DSC via the Kissinger method, ASTM E2890‑21).
Where the processing operation imposes a narrow scorch safety margin — for example, in hot‑feed extruders with screw L/D ratios above 20:1 running at head temperatures exceeding 120 °C — partial replacement of a delayed‑action sulphenamide (CBS or TBBS) with CMBT at 5–15% of the total accelerator loading allows fine‑tuning of the scorch delay without resorting to secondary retarders such as PVI. Factory‑floor audits on a 90 mm pin‑barrel cold‑feed extruder processing a 60 Shore A EPDM profile compound recorded that substituting 0.15 phr of CBS with 0.12 phr of CMBT reduced Mooney scorch (MS‑t₅ at 125 °C, ISO 289‑1:2023) from 14.2 min to 11.6 min without inducing porosity in the vulcanizate after continuous‑salt‑bath curing at 220 °C. This ability to trim the induction period by a predictable interval is a distinctive operational differentiator that MBT, MBTS, or the sulphenamides alone cannot deliver with the same stoichiometric precision.
| Accelerator (1.0 phr) | ML (dN·m) | MH (dN·m) | ts2 (min) | t90 (min) | Cure rate index (min⁻¹) |
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| MBT | 1.04 | 7.24 | 4.6 | 11.8 | 13.9 |
| CMBT | 1.09 | 7.58 | 3.5 | 10.9 | 13.5 |
| MBTS | 0.98 | 7.03 | 5.8 | 14.3 | 11.8 |
Crosslink speciation analysis via equilibrium swelling and thiol‑amine chemical probe decomposition (ASTM D6814‑02, reapproved 2023) reveals that CMBT‑accelerated networks in natural rubber yield a polysulphidic crosslink fraction (Sₓ, x ≥ 3) that is 6–9% lower than that obtained with MBT at identical accelerator/sulphur ratios, with a corresponding increase in the disulphidic and monosulphidic fractions. The skewed distribution lowers the average sulphur rank from approximately 2.8 to 2.4 after a standard cure to t₉₀, which manifests in compression set measurements (method B, 70 h/100 °C, ISO 815‑1:2019) that are improved by 3–5% absolute. This behaviour is exploited in heat‑resistant sealing compounds where the process specification forbids the use of fully EV (efficient vulcanisation) cure packages because of tear‑strength penalties; replacing 25–35% of the thiazole component with CMBT provides a semi‑EV character that meets tear resistance minima under ASTM D624‑20 (die C) while achieving compression set values below 28%.
Published data for CMBT in hydrogenated nitrile (HNBR) compounds remains sparse; however, statistically designed experiments on 2‑L laboratory internal mixers (fill factor 0.72, rotor speed 40 min⁻¹) indicate that the chlorine atom does not retard the peroxide‑coagent cure mechanism. The accelerator is therefore compatible with dual‑cure (peroxide/sulphur) systems, where it functions solely in the sulphur‑mediated phase without scavenging oxy radicals at typical FEF carbon‑black loadings of 40–55 phr.
In the absence of basic fillers, the slightly acidic character of the thiol group (pKₐ approximately two‑tenths lower than MBT) can depress the ZnO activation equilibrium if the stearic acid level drops below 0.5 phr; this manifests as a plateau in torque rise at around 60% of full cure. The mitigation is straightforward — maintain a stearic acid:ZnO molar ratio of at least 0.25 — but underscores a process boundary that is not encountered with the more weakly acidic MBTS or the neutral sulphenamides.
Surface bloom of unreacted accelerator and its zinc complexes is a persistent cosmetic defect in white and translucent NR/SBR mouldings. Thermogravimetric analysis (TGA, 10 K min⁻¹ under nitrogen) places the sublimation‑onset temperature of CMBT at 205 ± 3 °C, roughly 12–15 °C above that of MBT, which correlates with a lower vapour pressure at vulcanisation temperature and a reduced propensity for surface migration during post‑cure cooling. Accelerated blooming tests (72 h at 40 °C/95% RH) on a TPE‑S shoe‑sole compound pigmented with 2.5 phr TiO₂ showed no visible efflorescence for CMBT‑containing samples versus a faint but measurable haze (L* Δ > 1.2 units) for the MBT control. This property, while not unique to the chloro‑substituted analogue — CMMBT (4‑methyl‑2‑mercaptobenzothiazole) gives comparable results — is delivered without the odour issues associated with some alkyl‑substituted thiazoles, because the chlorine substituent is not released as a volatile thiol under service temperatures below 100 °C.
| Property | CMBT | MBT | MBTS | CBS |
|---|---|---|---|---|
| CAS RN | 21564-40-5 | 149-30-4 | 120-78-5 | 95-33-0 |
| Melting point (°C, decomp.) | 195–199 | 178–182 | 167–170 | 96–101 |
| Assay (min. %) | 98.0 | 97.0 | 97.0 | 97.5 |
| Free chlorine (water extract) | < 0.05% | N/A | N/A | N/A |
| Solubility in acetone (25 °C, g/100 mL) | ~12 | ~8 | <1 | >30 |
| Regulatory status (EU, indicative) | REACH registered, not CLP-classified |
Skin sens. 1A | Skin sens. 1 | Skin sens. 1 |
Regulatory awareness is necessary when selecting 2(3H)-Benzothiazolethione,4-Chloro-(9Ci) for articles destined for indirect food contact or potable water applications. Unlike MBT, which is classified as Skin Sens. 1A under CLP Regulation (EC) No 1272/2008 and appears on several restricted-substances lists for food-contact elastomers, the halogenated congener, as of the date of this document, is not harmonised for the same hazard endpoints. Nevertheless, migration testing to EN 1186 or FDA 21 CFR 177.2600 is case‑specific and must be performed on the finished article; the absence of an active harmonised classification does not constitute a positive clearance for use in potable‑water seals (EN 681‑1) or baby‑article teats (EN 1400). Users should request the full toxicological summary and verify local regulatory alignments before incorporating the accelerator in articles covered by food‑contact legislation.
Particle‑size distribution of standard commercial CMBT is controlled to D₉₀ ≤ 45 µm (laser diffraction, ISO 13320:2020), which is comparable to typical MBT and MBTS powders. However, the marginally higher acetone solubility of CMBT means that dispersion in the rubber matrix benefits from a partial solubilisation mechanism during the early mixing stages if the batch temperature reaches 70–80 °C before the oil injection point. In upside‑down mix sequences on a 1.6 L tangential internal mixer (rotor speed 55 min⁻¹), addition of the accelerator together with carbon black and zinc oxide at time zero, followed by oil addition at 35 s, yielded dispersion ratings of A2–A3 on the ISO 11345:2022 visual scale — a half‑point improvement over MBT processed under identical energy input. This advantage erodes if batch temperature at the start of the second pass exceeds 110 °C, because premature reaction with sulphur donors can generate bound accelerator species that are no longer available for network formation; the safe maximum dump temperature for single‑pass mixing with CMBT, when sulphur is present from the outset, is 105 °C.
With pre‑dispersed masterbatches (70% active on EPDM/EVA binder), the 4‑chloro derivative can be let down at 1.2–1.5 mm chip thickness without causing undispersed “accelerator speck” defects in thin‑gauge calendered sheeting 0.4 mm thick, as verified by transmitted‑light microscopy under 200× magnification. Such masterbatch forms are preferred when gravimetric feeding into a continuous mixer faces a feed‑rate tolerance tighter than ±0.5%, because the diluted form reduces feeder sensitivity at low per‑cent‑recipe levels (≤ 0.3 phr of pure accelerator).
The 4‑chloro substituent also raises the accelerator’s density (crystal density calculated from single‑crystal XRD: 1.62 g cm⁻³ compared to 1.42 g cm⁻³ for MBT). While this is a minor formulation adjustment for volume‑based gravimetric blenders, it alters the volume fraction of accelerator in the compound by approximately 5% rel. when weight‑for‑weight substitution is made; where compound specific gravity is tightly specified (e.g., ±0.02 on a 1.18 g cm⁻³ foam EVA midsole), the recipe must be corrected by converting all parts per hundred rubber to volume fractions instead of mass fractions.
