2-Metcapto-5-Chloro-Benzothiazole

In the production of polychloroprene extrusion compounds for automotive weatherstrips and hydraulic hoses, premature vulcanization during processing remains the dominant cause of scrap rates exceeding 3.5% of total batch weight. The compound 2-mercapto-5-chlorobenzothiazole is charged at 0.25–0.65 phr into a formulation already containing 5.0 phr zinc oxide, 4.0 phr magnesium oxide, and 40 phr N550 carbon black in a W-type CR matrix. A tangential internal mixer with an intermeshing rotor geometry (NBR-cooled, ram pressure 0.55 MPa) is used to disperse the additive in a single-stage cycle reaching a drop temperature of 108–112 °C. The narrow processing window—the delta between Mooney scorch time t5 at 125 °C and the minimum torque plateau—widens from a baseline of 8.2 min to 14.7 min when 0.4 phr of the mercaptothiazole replaces an equimolar fraction of ethylene thiourea (ETU), while the tΔ30 cure time at 160 °C remains within ±90 s of the ETU reference. On a cold-feed extruder with a 90 mm screw diameter and an L/D ratio of 16:1, head pressure drift across an 8 h production window falls below 1.2 MPa, substantially reducing die-lip build-up and surface roughness (Ra measured at < 1.8 µm per ISO 4287). This scenario directly addresses Regulation (EC) No 1907/2006 (REACH) Annex XVII entry 71, which restricts ETU in articles intended for prolonged skin contact below 0.1%, making the chloro-substituted thiazole a technically compliant alternative without sacrificing vulcanization kinetics. Table 1 summarizes scorch behaviour across three accelerator modifications evaluated on the same base compound.

2-CBST denotes 2-mercapto-5-chlorobenzothiazole. DOTG refers to di-ortho-tolylguanidine. ZDBC is zinc dibutyldithiocarbamate.

What Roles Does 5-Chloro-2-mercaptobenzothiazole Play in NR/BR Tire Tread Formulations Where Secondary Acceleration and Reversion Resistance Are Co-Prioritized?

A passenger car radial tread compound based on 70 phr natural rubber (TSR 20) and 30 phr high-cis butadiene rubber required a Mooney viscosity of 62 ± 3 ML(1+4) at 100 °C to satisfy both silica dispersion targets and tread pattern definition. The sulfenamide primary accelerator TBBS (N-tert-butyl-2-benzothiazolesulfenamide) was dosed at 1.35 phr together with 1.65 phr insoluble sulfur (oil-treated, 80% active). When 0.15 phr of 2-mercapto-5-chlorobenzothiazole was co-fed via a gravimetric downstream weight feeder into a twin-screw shear mixer immediately before an open two-roll mill set at a friction ratio of 1:1.22 and a nip gap of 3.5 mm, the cure curve obtained from an MDR 2000 rheometer (ASTM D5289) at 160 °C indicated a torque increase rate (slope between MH and ML) that was 12% steeper in the initial 2 minutes versus the TBBS-only reference, while the reversion index (MH at 160 °C minus torque after 30 min) narrowed from 0.8 dN·m to 0.3 dN·m. This suggests the chloro-thiol acts as a vulcanization activator, not as a primary accelerator, and partially mitigates the allylic backbone degradation typical of NR during prolonged high-temperature curing cycles. The finished tread cap stock is extruded through a roller-head die at 105 °C and subsequently built into 205/55R16 green tires that are press-cured in a segmented-mold press at 162 °C for 12.5 min. Compliance with EU tire-labelling regulation (EC) 1222/2009 requires rolling resistance measurements per ISO 28580:2018, and the tread abrading surface must additionally conform to ISO 4649 (DIN abrasion) with a loss not exceeding 110 mm³. The presence of a chlorinated benzothiazole accelerator fragment does not contravene the PAH limits set in Commission Regulation (EU) 1272/2013 when the vulcanizate is extracted after 48 h post-cure conditioning.

Corrosion inhibitor packages for industrial circulating cooling water systems frequently rely on azole derivatives to protect copper alloys in heat exchangers and condensers. A blended formulation consisting of 12.0 wt% 2-mercapto-5-chlorobenzothiazole (pre-dissolved in a slightly alkaline, glycol-compatibilized concentrate), 28.0 wt% 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP), 8.5 wt% acrylic acid-2-acrylamido-2-methylpropanesulfonic acid copolymer (AA/AMPS), and deionized water to 100 wt% is metered into the cooling loop via a diaphragm dosing pump at a continuous feed rate to maintain 22–35 mg/L total actives in the circulating water at a pH of 8.0–8.8 and conductivity of 1 800–3 200 µS/cm. Rotating cylinder electrode tests conducted on admiralty brass (Cu-Zn-Sn) and 90/10 copper-nickel alloy coupons per ASTM G185, with linear polarization resistance (LPR) probes installed in the return header of a 5 200 m³/h recirculating system, yield corrosion rates of < 0.003 mm/a for copper alloys at a Langlier saturation index below 2.1. In contrast to benzotriazole (BTA) and tolyltriazole (TTA), the chlorobenzothiazole derivative maintains passivation efficacy when free residual chlorine rises to 0.8 mg/L, a condition commonly encountered during biocide shock dosing in open evaporative cooling towers. The azole consumption rate due to chlorine oxidation, monitored via UV spectrophotometry at 312 nm, approximates 0.17 g/m³·(mg/L·h) of residual oxidant, approximately half the depletion rate observed for TTA under identical alkalinity. The formulated inhibitor product is packaged in 200 L HDPE drums and complies with the corrosion inhibition performance criteria of GB/T 18175-2014, where the mass-loss rate of a rotating A3 carbon steel coupon immersed in standard test water at 50 °C must remain below 0.075 mm/a.

If 2-Mercapto-5-chlorobenzothiazole Is Oxidatively Coupled to Its Disulphide for Broad-Spectrum Biocidal Activity in Leather Finishing

The symmetrical disulphide, bis(5-chloro-2-benzothiazolyl) disulphide, is synthesized by introducing hydrogen peroxide (30% aqueous, 1.05 molar equivalents) into a jacketed 500 L glass-lined reactor charged with 120 kg of the thiol monomer suspended in 240 L of a 0.35 M sodium hydroxide solution containing 0.5 wt% of a non-ionic surfactant (alkylpolyglucoside) at 22–28 °C under mechanical agitation at 180 rpm. The exothermic oxidation must be controlled by a recirculating chiller maintaining a jacket outlet temperature below 30 °C to prevent over-oxidation to the sulfonate derivative, which is inactive against mould. After 2.5 h the pale-yellow precipitate is filtered, washed with deionized water until the filtrate conductivity drops below 50 µS/cm, and dried under vacuum at 60 °C to a moisture content of < 0.3%. The disulphide is then mill-compounded at 3.0 wt% into an aqueous polyurethane top-coat binder (aliphatic polyester-based, solids 28%) that is sprayed onto finished buffalo leather splits intended for automotive seating. Fungal resistance is evaluated per ASTM G21 (7-day incubation) with Aspergillus niger, Penicillium funiculosum, and Trichoderma virens; a rating of 0 (no growth) is maintained when the finished leather contains ≥ 0.2 wt% disulphide on total coating weight. The active ingredient demonstrates a migration half-life of > 60 days in the polyurethane matrix at 60 °C, as determined by accelerated ageing and GC-MS extract quantification. Formulation boundaries are clear: the presence of free ammonia or volatile amine coalescing agents will cleave the disulphide bond prematurely, and storage of the aqueous dispersion must remain within pH 6.5–8.0 and below 35 °C to preserve shelf stability beyond 6 months.

Mineral processing circuits treating porphyry copper ores require selective collectors that reject iron sulfides while maintaining high chalcopyrite and chalcocite recovery at the rougher stage. Laboratory-scale Denver D12 flotation machines operated at 1 200 rpm rotor speed and 4.0 L/min aeration rate were employed to evaluate the response of a Chilean copper ore (Cu head grade 0.62%, pyrite content 3.8% as Fe) when 2-mercapto-5-chlorobenzothiazole was introduced as a co-collector alongside sodium isobutyl xanthate (SIBX). The composite collector was prepared as a 2% stock solution in 0.01 M NaOH and added to the conditioned pulp at a total dosage of 11 g/t of run-of-mine feed, split between 7 g/t SIBX dosed at the conditioning tank and 4 g/t mercaptothiazole staged into the first scavenger bank. Pulp pH was maintained at 9.8 ± 0.2 with lime, and methyl isobutyl carbinol (MIBC) at 18 g/t served as the frother. In a locked-cycle test simulating a rougher-scavenger-cleaner configuration, concentrate Cu grade improved from 24.1% to 27.3% relative to the xanthate-only baseline, while arsenic content (derived from tennantite) dropped below 0.07%, a critical threshold for smelter contracts. The improvement is attributed to the chelating interaction of the nitrogen-sulfur-thiol moiety with Cu(I) surface sites on chalcopyrite, while the chloro substituent reduces precipitation with ferric hydrolysis products, a known artefact of benzotriazole-type collectors. In a 35 000 t/d concentrator implementing this dual-collector scheme, reported recovery gains of 1.1–1.8 percentage points on copper were sustained over a 6-month trial, though published data addressing wear rates on the reagent dosing diaphragm valves due to the alkaline thiolate are sparse. The final copper concentrate is dewatered through a thickener and pressure filter before shipping to a flash smelter.

Disperse Dye Intermediates Derived from 5-Chloro-2-aminobenzothiazole

Azo disperse dyes that exhibit high light fastness on polyester microfiber substrates frequently require a heterocyclic diazo component such as 2-amino-5-chlorobenzothiazole. This amine is not commercially obtained directly but is prepared in the dyestuff synthesis plant by a nucleophilic substitution of 2-mercapto-5-chlorobenzothiazole with anhydrous ammonia under pressure in the presence of a copper(I) catalyst in an autoclave at 12–15 bar and 130 °C for 6 h. The resulting thiol-free amine is isolated by steam distillation and crystallized to a purity exceeding 98.5% (HPLC area). The diazotization procedure requires dissolving 0.2 mol of the amine in 180 mL of 85% phosphoric acid and adding 0.21 mol of sodium nitrite dissolved in 15 mL of concentrated sulfuric acid at –5 to 0 °C to generate the diazonium salt. Coupling is conducted with 0.205 mol of N,N-diethyl-m-toluidine dispersed in ice water containing sulfamic acid at pH 3.5–4.5 and 0–5 °C over 4 h. The precipitated crude dye is isolated by filtration, washed until neutral, and milled with 1.5 times its weight of lignin-based dispersant in a horizontal bead mill charged with 0.4–0.6 mm yttria-stabilized zirconia beads operating at a tip speed of 10 m/s until the average particle size reaches 0.5–1.0 µm (laser diffraction, ISO 13320). The final product, a reddish-blue disperse dye approximating C.I. Disperse Blue 359 in shade, is applied to polyester by high-temperature exhaust dyeing at 130 °C for 45 min, yielding a build-up of 1.0% o.w.f. and wet rub fastness (ISO 105-X12) of 4–5 after reductive clearing. All effluent from the coupling step must be treated by a resin-based phenol adsorber prior to biological treatment to meet GB 4287-2012 discharge limits for absorbed organic halides.

During Manufacture of Rubber-to-Metal Bonding Agents Containing Post-Vulcanization Stabilizers

Engine mounting systems manufactured from natural rubber that are bonded to mild steel inserts via a one-coat adhesive based on chlorinated phenolic resin and hexamethoxymethylmelamine (HMMM) often suffer adhesive coverage loss when the adjacent rubber bulk is compounded with highly active sulfenamide accelerators that generate excessive free sulfur at the metal interface during the post-cure cooling phase, reducing statistically validated bond strength below 4.5 MPa. Incorporation of 0.6–1.2 phr 2-mercapto-5-chlorobenzothiazole into the NR compound (CV-60, 2.2 phr sulfur, 0.9 phr CBS) homogenized in a tangential mixer at 45 °C, followed by sheeting on a two-roll mill at 62 °C, mitigates this interfacial degradation. The reasoning is the thiol’s ability to complex with copper(II) ions that are leached from a brass interlayer electroplated on the steel (Cu 67%, Zn 33%, thickness 12 ± 2 µm), thereby preventing copper-catalyzed oxidative reversion of the rubber network at the bond line. Bonded test buttons cured at 155 °C for 22 min and pulled in tension at 50 mm/min according to ASTM D429 method B exhibit cohesive rubber failure exceeding 95% of the bonded area, compared to 72–80% without the additive. Parts that undergo post-production endurance testing under 50 Hz dynamic shear (vertical preload 300 N, amplitude ±0.5 mm) to 1 × 10⁶ cycles maintain a stiffness decay of < 12%, a requirement specified by vehicle manufacturers. The chloro-substituted thiazole does not migrate appreciably into the adhesive film during curing, thus it does not interfere with HMMM methylol condensation and crosslinking kinetics as confirmed by DSC analysis of the cured film.

Equipment-Side Limitations When Pre-Dispersing Powder Thiazole Accelerators in EPDM Roofing Membrane Compounds

EPDM formulations for single-ply roofing membranes consist of a high-ethylene (72%) terpolymer with 4.5 phr dicumyl peroxide as the primary curing agent. Even minor additions of sulfur-containing secondary accelerators can severely compromise peroxide efficiency unless the curative is delivered in a highly dispersed polymeric carrier. A masterbatch of 35 wt% 2-mercapto-5-chlorobenzothiazole encapsulated in an ethylene-propylene copolymer wax (melting point 78 °C) is prepared on a co-rotating twin-screw extruder with an L/D ratio of 48:1 and a pelleting die face cutter rotating at 2 800 rpm. This masterbatch is let down at 7.0 phr into the final compound on a 150 L intermeshing internal mixer, delivering a net active content of 2.45 phr. The additive acts as a radical trap retarder that moderates the scorch time of the peroxide-induced crosslinking, verified by MDR torque at 175 °C: ts₂ extends from 0.8 min to 1.9 min without reducing the final maximum torque below 22 dN·m. A critical processing constraint emerges during calendering of the formulated compound into 1.5 mm gauge sheets on a three-roll calender (roll temperatures 62, 68, 64 °C, roll speed 18 m/min). If the residual moisture of the masterbatch exceeds 0.15 wt% (Karl Fischer titration, ISO 15512) because of improper dryer dew point control (specification –40 °C), faint surface blistering appears on the cured sheet, rendering it non-compliant with the appearance clause of EN 13956. Therefore, online near-infrared (NIR) moisture monitoring on the feed throat of the calender is mandated for all production runs longer than 4 h.