5-Chloro-2-Mercaptobenzothiazole

Does Chlorinated Mercaptobenzothiazole Shift the Torque Equilibrium in Peroxide-Cured HNBR Compounds?

In hydrogenated acrylonitrile-butadiene rubber (HNBR, 34–44 % ACN content) compounds designed for sour gas wellhead seals and subsurface safety valve elements, the cure system often relies on 1,3- and 1,4-bis(tert-butylperoxyisopropyl)benzene at 4.5–6.8 phr activity on silica support. When 5‑Chloro‑2‑mercaptobenzothiazole is co‑incorporated at 0.35–0.65 phr as a cure rate modifier, the oscillating‑disc rheometer trace (ASTM D2084‑19a, 0.5° arc, 177 °C) reveals a distinct plateau‑broadening effect: the torque rise after t₉₀ is suppressed to less than 0.09 dN·m per minute over a 12‑minute holding interval, attributed to thiol radical trapping of non‑productive alkoxy fragments. The addition protocol demands strict temperature control—the chlorinated accelerator is mill‑incorporated on a water‑cooled two‑roll mill (friction ratio 1.15:1, nip gap 0.38–0.55 mm) at stock temperatures not exceeding 62 °C, because premature homolysis of the peroxide at hot Banbury drop temperatures above 118 °C leads to irreversible scorch nodules. Downstream processing involves transfer‑molding into multi‑cavity compression molds (clamping force 220 metric tons) with the first‑stage preform held at 88 °C for 110 seconds under vacuum. Terminal articles are NORSOK M‑710-qualified annular blowout preventer packers and ISO 23936‑2:2011‑compliant elastomeric seals for rapid gas decompression service, where the chlorothiazole‑modified vulcanizate maintains a compression set below 17 % after 72 h at 150 °C per ISO 815‑1:2019 method B, compared to 24–27 % for a control using 2‑mercaptobenzothiazole at equal sulfur‑adjusted stoichiometry. REACH Annex XVII entry 50 regarding PAH restrictions does not apply to this high‑purity chlorinated thiazole, and the compound neither generates free amines that could combine with nitrosating agents under EU Directive 93/11/EEC nor exceeds the extractable N‑nitrosamine detection limit of 0.01 mg/m² as measured by chemiluminescence detection per EN 12868:2017.

The integration of precipitated silica (BET surface area 165–185 m²/g) into passenger car radial tread cap compounds typically introduces a competitive adsorption equilibrium between the poly‑sulfidic silane coupling agent and the zinc‑accelerator complexes formed during sulfur crosslinking. In such highly filled systems, 5‑Chloro‑2‑mercaptobenzothiazole operates as a non‑nitrosatable auxiliary accelerator that retards the initial vulcanization onset by selectively sequestering Zn²⁺ ions liberated during thiuram or sulfenamide decomposition, thereby extending the flow‑relevant scorch window without diluting the final crosslink density. A representative dosage of 1.25–1.65 phr is introduced together with a primary sulfenamide (CBS or TBBS at 1.4–1.8 phr) during the final mixing stage of a tandem‑mix procedure: a 320‑litre intermeshing rotor internal mixer (tangential rotor design, L/D equivalent 1.65) is employed with a fill factor held between 0.68–0.72; the second‑pass dump temperature is restricted to 103–108 °C, after which the compound is sheeted on a single‑pass twin‑screw roller die and fed into a continuous salt‑bath vulcanization line (LCM‑type) operating at 215±3 °C with residence time maintained at 4.8–5.2 minutes. Post‑cure dynamic mechanical analysis (ISO 4664‑1:2022, tensile mode, 10 Hz, temperature sweep −40 to +80 °C) reveals a tan δ at 60 °C lowered by 0.011–0.018 units relative to an equivalent mercaptobenzothiazole control, which maps to a predictive fuel‑efficiency improvement of approximately 0.8–1.2 % under the UN ECE R117.02 coast‑down classification. Migration kinetics of the chlorinated accelerator into the adjacent skim compound were evaluated by liquid chromatography‑tandem mass spectrometry (LC‑MS/MS) on a 0.5 mm cryo‑microtomed interlayer; at a total accelerator loading of 2.9 phr, the equilibrium concentration of the chlorinated thiol in the skim reached 0.12 mg/dm³ after 7 days at 70 °C, well below the critical blooming threshold of 0.35 mg/dm³ established for this polymer pair. The finished tread cap compound is certified to comply with EU 1907/2006 (REACH) Annex XVII entry 50, with the sum of eight regulated PAHs below the 0.5 mg/kg detection limit by GC‑MS following AfPS GS 2019:01 PAK extraction procedure.

When Benzotriazole-Tolerated Make-Up Water Chemistry Fails to Inhibit Copper Cracking in Multi-Metal Cooling Loops

Closed‑loop chilled‑water and tempered‑water circuits that mix yellow brass (UNS C26800) valve bodies with 90/10 cupro‑nickel heat exchanger plates frequently encounter a shift from uniform passivation to under‑deposit pitting when makeup water alkalinity drops below 40 mg/L as CaCO₃ and chloride ions exceed 55 mg/L. Under such regime, 5‑Chloro‑2‑mercaptobenzothiazole is dosed as an anodic chemisorption inhibitor at a continuous residual of 6–14 mg/L actives, maintained through a closed‑feedback controller linked to a total organic carbon analyzer with a mercaptan‑specific electro‑oxidation signal channel. The inhibitor stock solution is prepared as a 15 % w/w active dispersion in a non‑ionic surfactant‑stabilized aqueous carrier and injected via a magnetically coupled diaphragm metering pump (stroke frequency 110 spm) into the return header at a point where turbulence intensity ensures an average velocity of 1.2 m/s on the 316L stainless steel injection quill, eliminating local overshoot beyond 28 mg/L that could plasticize acrylic inspection window seals. The adsorbed film coverage on a 70‑30 brass coupon was evaluated by electrochemical impedance spectroscopy (ASTM G106‑20) at 0.01 Hz after 168 h immersion in the treated loop water at 35 °C; the charge transfer resistance increased by a factor of 4.8 relative to the uninhibited baseline, and the derived corrosion rate fell to 0.018 mm/year as corroborated by linear polarization resistance measurements (ASTM G59‑20). The inhibition mechanism is sensitive to free chlorine, and the operating procedure mandates that the hypochlorite biocide injection point be located at least 15 pipe diameters upstream of the chlorothiazole feed to prevent oxidation to inactive disulfide dimers. The treated water must satisfy the copper release limit of ≤ 0.2 mg/L under ISO 3613:2010 and the corrosivity classification Class 1a per ASTM D1384‑18 when tested on CDA 110 copper coupons. This corrosion inhibition approach extends the service interval of gasketed plate‑and‑frame heat exchangers in semiconductor fab utility water from a baseline of 14 months to over 45 months before plate re‑torquing is required, as determined by ultrasonic wall‑thickness mapping at the 0.6 mm resolution level.

5‑Chloro‑2‑mercaptobenzothiazole serves as a thiol‑terminated intermediate for constructing asymmetric disulfide‑based post‑cure activators and metal‑deactivator complexes used in ethylene‑vinyl acetate (EVA) encapsulant films. The synthetic route involves controlled condensation with a chlorinated alkyl tertiary amine under mildly alkaline conditions (pH 8.2–8.7) at a temperature ramp of 55–65 °C inside a borosilicate glass‑lined reactor (DIN 28136‑1 rated) fitted with an anchor‑paddle agitator operated at a tip velocity not exceeding 3.1 m/s to minimize vortex entrainment of atmospheric oxygen that would oxidize the thiol to the homodisulfide. The reaction mass passes through a continuous flow falling‑film crystallizer with a jacket set to −8 °C and a scraper surface speed of 0.12 m/s, yielding a 98.7–99.2 % pure intermediate by normalised HPLC‑UV area at 254 nm. This intermediate is downstream functionalized to 2‑benzothiazolyl polysulfides that function as regenerative chain‑transfer agents in Vamac®‑type ethylene‑acrylic elastomer curing, where they react with residual peroxide fragments to restore active crosslinking sites. The entire synthetic chain and the derived biocidal formulations placed on the EU market fall within the scope of EU Biocidal Products Regulation 528/2012 and require an Article 95 listing for the active substance supplier. An industrial‑scale batch record documented 1,250 kg of the chlorinated thiol processed with a consistency in melting point (85.5–86.8 °C) that varied by less than 1.2 °C across 11 consecutive batches, demonstrating well‑characterised synthetic robustness suitable for ISO 9001:2015 process capability reporting.

Exudate Layer Thickness Mapping by Confocal Raman Microscopy on Polymer-Coated Nitrile Glove Surfaces

In the production of accelerator‑cured nitrile butadiene rubber (NBR) examination gloves via a continuous ceramic‑former coagulant dipping line, the surface bloom of sulfur‑containing accelerators critically governs both the particle‑cleanliness rating under ISO 14644‑1 Class 100 conditions and the extractable protein surrogate response in the modified Lowry assay of ASTM D5712‑15. When 5‑Chloro‑2‑mercaptobenzothiazole is incorporated as a secondary accelerator at 0.6–1.0 phr alongside zinc dibutyldithiocarbamate (ZDBC, 0.8 phr) and colloidal sulfur (1.2 phr) into a pre‑vulcanized NBR latex compound of 42 % total solids content, the resulting dipped film exhibits a surface exudate layer that can be mapped by confocal Raman microspectroscopy (532 nm excitation, 100× / 0.9 NA objective). Spectral integration of the C–Cl stretching band at 730–740 cm⁻¹ integrated across a 50 × 50 µm raster field revealed that at addition levels above 0.85 phr, the chlorinated thiol segregates into discrete crystallite domains of 1.8–3.5 µm Feret diameter as measured by scanning electron microscopy at 5 kV on gold‑sputtered cryofractured cross‑sections. This bloom is accompanied by an increase in the powder‑free surface’s dynamic coefficient of friction from 0.33 to 0.52 against a cotton substrate per ASTM D1894‑14, triggering rejection under the donning smoothness criteria of EN 455‑2:2015. To maintain a residual surface concentration below the 0.45 µg/cm² threshold detectable by solvent‑swab HPLC‑UV, the dipping compound is processed through a 3‑stage post‑leach cascade: a first station with deionized water at 72 °C for 38 seconds, a second with a 0.5 % w/w sodium lauryl sulfate surfactant bath at 55 °C, and a final polymer‑coating tank that deposits a 0.05‑µm hydrophobic polyurethane lining. The finished glove is rated for medical use under FDA 21 CFR 177.2600 as a repeat‑use article, with overall migration into 3 % w/v acetic acid simulant not exceeding 3.6 mg/dm² at 40 °C for 10 days per EN 1186‑1:2002. Production‑scale dipping lines using ceramic formers (surface porosity 0.8 µm) and a 12‑meter sintering oven passing through four zones (125 °C, 138 °C, 148 °C, 142 °C) recorded a lot‑to‑lot pin‑hole defect rate (AQL 1.5, 1000 mL water leak test) of less than 0.08 % when the chlorinated thiol content was kept within the 0.6–0.8 phr window, confirming that migration‑related film defects are well‑controlled within the published formulation design limits.