5-Chloro-1,3-Benzothiazole-2-Thiol

Sulfur-vulcanized diene rubber compounds: scorch delay and modulus development

In the mixing of a 100 phr NR/BR truck tread masterbatch loaded with 55 phr N234 carbon black, the replacement of conventional 2-mercaptobenzothiazole (MBT) with 5-chloro-1,3-benzothiazole-2-thiol on an equimolar basis shifts the processing safety envelope. The electron-withdrawing 5-chloro substituent depresses thiol acidity relative to MBT, retarding the formation of the zinc-complex accelerator species required for rapid sulfur crosslinking. On a 75 L intermeshing Banbury line (Pomini F-270) with dump temperatures kept below 125 °C, the compound exhibits a Mooney scorch delay (MS-t5 at 120 °C, ASTM D1646-19) that is routinely 35–50 % longer than the MBT control, allowing safer multi-pass silica coupling silanisation steps without incipient scorch. Cure rheometry taken on an MDR 2000E at 155 °C (ASTM D5289-17) reveals a distinct thermal lag: t_s2 typically moves to 4.3–5.0 min, and t₉₀ stretches to 11–14 min, compared with 2.1–2.8 min and 6.5–8.0 min for MBT in the identical accelerate-to-cure formulation. The delta torque (M_H–M_L) decreases by 8–12 %, yielding a softer vulcanizate that benefits tear propagation resistance along belt edges. Factory-scale extrusion of sidewall profiles through a 200 mm pin-barrel cold-feed extruder (Troester GS 200) requires compensatory screw-speed reduction of 5-7 rpm to avoid porosity because the delayed crosslinking onset shifts the blow point deeper into the curing press.

Blending 5-chloro-1,3-benzothiazole-2-thiol with sulfenamide accelerators such as N-cyclohexyl-2-benzothiazole sulfenamide (CBS) at a mass ratio of 1:3 recovers much of the crosslinking deficiency while preserving the scorch margin. In an EPDM radiator hose cover compound (ENB content 4.5 wt%, ethylene 57 %) based on a sulfur donor system (2.0 phr DTDM, 0.5 phr TBzTD), the chloro-thiol operates as a cure modifier. The improved solubility parameter mismatch in the hydrocarbon matrix reduces accelerator blooming on the green stock surface during 24 h conditioning at 23 °C and 60 % RH. Compliance with FDA 21 CFR 177.2600 for dry-food-contact gaskets is technically attainable with appropriate post-cure washing, provided that residual free 5-chloro species — detectable via headspace GC-MS — fall below the 0.5 µg/cm² migration limit per EN 1186-1:2002 simulant testing. Operational constraints must be observed: when batch temperatures exceed 135 °C in the presence of zinc oxide and adsorbed moisture, hydrolytic dechlorination can generate trace HCl, accelerating silica flocculation and degrading the coupling agent. Formulators therefore impose a moisture specification of <0.15 wt% Karl Fischer on the thiol raw material and mandate swept-volume venting on open mills processing silica-filled stocks.

Data acquired on NR RSS1 based compound per ASTM D3182-21; rheometer ASTM D5289-17.

When 5-chloro substitution directs regioselective heterocycle elaboration

In the GMP synthesis of a bicyclic triazolo-benzothiazole pharmacophore targeting a CNS receptor, 5-chloro-1,3-benzothiazole-2-thiol serves as the nucleophilic anchor for a chemoselective S-alkylation step. Under an argon blanket in a 500 L glass-lined reactor (Pfaudler), the thiol is dissolved in anhydrous N,N-dimethylformamide (8 vol relative to thiol weight) together with milled potassium carbonate (1.3 equiv). The mixture is cooled to 0–5 °C before a controlled addition of 1.05 equiv of 2-bromo-4′-fluoroacetophenone dissolved in 2 vol DMF over 90 min. Careful temperature control is mandatory: the reaction exotherm can spike to 18 °C in under 15 s if the dosing line loses prime, leading to a critical rise in the dimeric disulfide impurity (CAS-identical side product) beyond the allowable 0.10 % area threshold by HPLC. After 14 h at 20–25 °C, the slurry is drowned into 10 vol of purified water, and the crude ketone intermediate is isolated on a centrifuge, washed to conductivity <50 µS/cm, and recrystallized from isopropanol/n-heptane (4:1 v/v). The dried intermediate undergoes ring closure with hydrazine hydrate in ethanol at reflux to yield a tricyclic scaffold used in the manufacture of a GABA_A receptor modulator. Batch record analysis over 12 commercial lots confirms that the 5-chloro substituent suppresses the formation of the regioisomeric [1,2,4]triazolo[4,5-b] isomer (typically <1.5 %) compared with the unsubstituted benzothiazole analog where isomer ratios of 8–12 % are observed, a difference attributed to the electronic deactivation of the benzene ring toward electrophilic attack during the cyclocondensation step. The final active pharmaceutical ingredient specification mandates residual thiol levels below 25 ppm by LC-MS/MS, requiring a dedicated charcoal decolorization step and a final recrystallization that drives the recovery cost but is essential for ICH Q3A(R2) compliance. Pre-drying of the DMF solvent over 4Å molecular sieves to <100 ppm water is enforced, because water ingress promotes hydrolysis of the α-bromoketone, lowering yield below the economical 82 % threshold.

Herbicidal sulfonylurea intermediates derived from benzothiazole thiol

Acetolactate synthase (ALS) inhibitors with a benzothiazolyl-sulfonylurea backbone demand a high-purity mercapto building block capable of coupling with a sulfamoyl chloride under strictly anhydrous, low-temperature conditions. In a typical campaign, 5-chloro-1,3-benzothiazole-2-thiol is converted to the corresponding sulfenyl chloride in situ by treatment with sulfuryl chloride (1.02 equiv) in dichloromethane at -10 °C to -5 °C in a jacketed Hastelloy reactor. After 45 min, the resultant sulfenyl chloride solution is slowly transferred into a chilled solution of methyl 2-aminosulfonylbenzoate (0.98 equiv) and triethylamine (1.2 equiv) in dichloromethane/acetonitrile (4:1 v/v). The condensation mixture is agi-tated for 16 h with a stepwise warming to 20 °C, then quenched with 5 % w/w aqueous sodium bicarbonate. The organic layer containing the sulfenamide ester intermediate is concentrated below 35 °C under vacuum to prevent thermal rearrangement. The isolated product, a pale-yellow solid with a melting point of 149–152 °C, serves as the penultimate precursor to a post-emergent sulfonylurea herbicide formulated as a 50 % WG (water-dispersible granule). FAO specification FAO/WHO 2017 drives purity requirements: the metsulfuron-methyl analog derived from this route must contain less than 0.5 % w/w of the des-chloro impurity, as field-bioassay data indicate a 20–30 % loss in broadleaf control when the impurity exceeds 1.2 %. Pilot-plant records show that cross-contamination with even 50 ppm of the non-chlorinated benzothiazole-2-thiol during precursor solid handling leads to an out-of-specification impurity profile, necessitating dedicated stainless-steel IBCs and a validated cleaning protocol with 0.1 N NaOH. The process mass intensity (PMI) for this intermediate is typically 18–22 kg waste per kg of product, primarily driven by the aqueous work-up and recrystallization from methylcyclohexane, and is managed under REACH Article 37(4) substance reporting for tonnage bands above 10 t/year.

What role does a halogenated mercaptobenzothiazole play in silver halide microcrystal growth?

During the double-jet precipitation of a silver iodobromide (AgBrI, 4.5 mol% I⁻) octahedral emulsion at 70 °C and pAg 7.8, the addition of 5-chloro-1,3-benzothiazole-2-thiol as a gelatin-stabilized aqueous dispersion (0.5 g/L) modifies the growth habit and monodispersity. The thiol adsorbs preferentially on the {111} octahedral faces, reducing the edge-growth velocity relative to the corner growth, thus increasing the form factor (cubicity) and narrowing the size distribution from a coefficient of variation of 22 % to 12 % at an addition rate of 1.2 mmol per mole of precipitated silver. Photographic activity tests in a standard color paper coating (cyan layer, coupler C-16) reveal that the adsorbed thiol functions as a latent-image stabilizer, raising the speed-grain ratio by 0.08 log E units. Its sensitivity to oxidation dictates that the emulsion must be handled under amber safelight in a nitrogen-purged vessel; dissolved oxygen levels exceeding 2 mg/L promote disulfide formation, which acts as a desensitizer and produces a visible grey background fog with an increase in D_min of 0.12–0.18 at a disulfide level of 100 ppm based on silver. The intact thiol is removed during the noodle washing step using ion-exchange water at 8 °C and does not appear in the final dry film at a detection limit of 0.01 µg/m². However, photographic-grade raw material must satisfy a strict specification of <0.3 wt% ash and <25 ppm iron, as metal contaminants catalyze fog center formation during shelf storage at 40 °C / 70 % RH over 6 months.

Acid copper plating brightener carrier: adsorption-desorption hysteresis on cathodic surface

In high-acid, low-copper via-filling electrolytes for HDI printed circuit boards operating at a Cu²⁺ concentration of 40 g/L, sulfuric acid 180 g/L, and chloride ion 50–70 ppm, 5-chloro-1,3-benzothiazole-2-thiol functions as a carrier molecule whose fractional surface coverage governs the rate of copper electrodeposition in the mass-transport-limited region. Cyclic voltammetry on a platinum rotating disk electrode (RDE) at 1000 rpm and a scan rate of 50 mV/s (ASTM B832-93 modified) distinguishes the thiol from standard commercial carriers (e.g., safranine-based dye carriers): the cathodic adsorption peak shifts negatively by 120–150 mV relative to typical dye systems, and more critically, the desorption hysteresis is 2.3 times larger, meaning the carrier remains anchored on the cathode surface into the initial Tafel region of copper deposition. At a plating bath concentration of 12–18 mg/L, in conjunction with bis(3-sulfopropyl)disulfide (SPS) at 1.2–1.8 mg/L and polyethylene glycol (4000 Da) at 200 mg/L, the formulation produces a superfilling capability with a throwing power (Harring-Blum cell) of 82–88 % for through-holes with an aspect ratio of 12:1. Hull cell panels (267 mL, 2 A, 5 min) reveal a reduction in the low-current-density hazy band between 0.5–2.0 ASD, attributed to the suppression of preferential {111} texture growth. The carrier is consumed through electrochemical oxidation at the counter electrode and by drag-out, requiring a replenishment rate of 8–12 g per 1000 Ah of plating charge, verified by HPLC quantitation with UV detection at 274 nm. An operational restriction applies when chloride ion drops below 35 ppm: the carrier’s inhibiting layer becomes non-uniform, causing a phenomenon of step-plating (tornado-like mounds) that increases surface roughness (Ra) from <0.15 µm to >0.55 µm as measured by laser confocal microscopy. Replenishment of the carrier must be conducted via a pre-diluted 1 % v/v methanolic solution injected directly into the eductor loop to avoid localized clouding in the bulk electrolyte.