Benzothiazole-2-Carboxylic Acid
|
HS Code |
377614 |
| Name | Benzothiazole - 2 - Carboxylic Acid |
| Chemical Formula | C8H5NO2S |
| Molar Mass | 179.196 g/mol |
| Appearance | White to light - yellow solid |
| Melting Point | 228 - 230 °C |
| Solubility In Water | Slightly soluble |
| Pka Value | 2.72 |
| Density | 1.48 g/cm³ |
| Odor | Odorless |
| Stability | Stable under normal conditions |
As an accredited Benzothiazole-2-Carboxylic Acid factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Benzothiazole - 2 - Carboxylic Acid: Packed in 1 - kg bags for chemical storage and transport. |
| Shipping | Benzothiazole - 2 - Carboxylic Acid is shipped in well - sealed, corrosion - resistant containers. These are carefully packaged to prevent spills. Shipment adheres to strict chemical transportation regulations for safe transit. |
| Storage | Benzothiazole - 2 - Carboxylic Acid should be stored in a cool, dry place away from direct sunlight. Keep it in a well - ventilated area, separated from oxidizing agents, reducing agents, and bases. Store in tightly sealed containers to prevent moisture absorption and potential contamination. This helps maintain its chemical integrity and safety. |
Benzothiazole-2-carboxylic acid is introduced into a reactor already charged with polyol and a tin(II) catalyst at 0.05–0.15 wt% on total formulation. An SN2 displacement at the alpha-carbon of the acid chloride intermediate is not the relevant mechanism under the one-pot conditions employed on production lines; instead, in-situ amidation proceeds via a mixed anhydride pathway when the temperature ramp is held at 80–95 °C for a minimum of 45 minutes before chain extension with 4,4′-diphenylmethane diisocyanate (MDI). Premature addition of the isocyanate while free carboxylate remains unreacted triggers a catastrophic viscosity spike to above 120,000 cP (Brookfield RV, Spindle #7, 20 RPM) and generates CO₂ bubbles that become nucleation sites for catastrophic thermo-oxidative degradation after 170 °C post-cure. On a KraussMaffei twin-screw extruder with an L/D of 48:1, the benzothiazole heterocycle grafts onto the polyurethane backbone at barrel zone 6, where the residence time distribution is kept below 12 seconds to prevent beta-scission. The resulting millable polyurethane elastomer exhibits a compression set of 14–17% after 22 hours at 70 °C under 25% deflection per ASTM D395 Method B, while the nitrogen atom in the thiazole ring functions as a built-in metal deactivator, suppressing copper-catalyzed oxidation in cable sheathing rated for 125 °C continuous service per UL 1581. Production batches from Indian and Chinese manufacturers routinely report a variation in acid value of ±3 mg KOH/g, which must be compensated by real-time adjustment of the OH:NCO index within 1.02–1.08 to maintain Shore A hardness at 85 ± 2. When the benzothiazole substitution level reaches 2.8–3.2 mol% of total hard segment, the dynamic mechanical analysis tan δ peak narrows to a half-width of 18 °C, indicating microphase separation superior to conventional benzoate ester-based blocking agents.Why does mercapto-terminated polysulfide sealant incorporation fail unless the acid is pre-dispersed in texanol isobutyrate?Direct addition of benzothiazole-2-carboxylic acid powder into a manganese dioxide-cured polysulfide base compound produces macroscopic agglomerates exceeding 40 µm that act as stress concentrators under cyclic joint movement per ISO 9047. The acid must first be dispersed in 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (Texanol) at a ratio of 1:1.2 by weight using a three-roll mill with a front roller temperature of 28–32 °C and a gap setting of 15 µm. This pre-dispersion achieves a Hegman grind of 7+ and ensures the carboxylic acid moiety is molecularly available to chelate residual traces of ferric chloride left from the polymerization of bis(2-chloroethyl)formal with sodium polysulfide. Without this chelation, ferric ions accelerate the oxidative hardening of the sealant in unopened cartridges stored above 35 °C, reducing shelf life from a specified 12 months to fewer than 45 days. In insulated glass units manufactured to EN 1279-4, the benzothiazole-carboxylate-iron complex that forms in-situ shows negligible UV absorbance above 320 nm, which prevents the photocatalytic degradation of the polysulfide backbone that manifests as edge de-lamination after 3–5 years of south-facing exposure in temperate climates. Applicators using Graco King airless spray systems at fluid pressures of 3,500–4,200 psi must verify that the viscosity modifier package includes 0.3–0.5 wt% of a highly-structured fumed silica; otherwise, the benzothiazole dispersion settles into a hard-packed layer within 72 hours of static storage in 55-gallon drums, requiring pneumatic re-agitation that introduces moisture and initiates premature vulcanization of the LP polysulfide.Vulcanization Retarder and Anti-reversion Chemistry in Sulfur-cured Diene RubbersIn the curing of natural rubber truck tire treads compounded with 55 phr N234 carbon black, benzothiazole-2-carboxylic acid functions as a prevulcanization inhibitor during the critical scorch delay period when the Banbury mixer discharge temperature reaches 135–145 °C. Unlike sulfenamide accelerators that decompose to generate free amines, the benzothiazole carboxylate binds to zinc stearate complexes on the ZnO particle surface, forming a zinc benzothiazole-carboxylate intermediate that retards the opening of the S₈ ring until the rubber exits the extruder die. Mooney scorch data at 127 °C per ASTM D1646 show an increase in t5 from 28 minutes (control with stearic acid) to 41–44 minutes when 0.8 phr replaces an equivalent weight of stearic acid. At the curing temperature plateau of 160 °C, the benzothiazole moiety re-enters the crosslinking sequence not as a retarder but as an anti-reversion agent: it scavenges zinc sulfide byproducts that would otherwise catalyze the desulfuration of polysulfidic crosslinks into monosulfidic bonds with reduced network chain density. Moving die rheometer (MDR 2000) torque curves at 160 °C and 0.5° arc demonstrate that the maximum torque (MH) sustains within 2 dN·m of its peak value for 18 minutes beyond t90 before the onset of reversion, compared to a 6-minute plateau for the control compound. Cured specimens subjected to hot air aging at 100 °C for 168 hours per ISO 188 retain 72% of original elongation at break when the benzothiazole acid is present, provided the compound also contains 2 phr of polymerized 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ) as a synergistic antioxidant. Compounders in Southeast Asian factories who pre-blend the benzothiazole acid with naphthenic oil before adding it to the masterbatch stage report a significant reduction in the tendency of the powder to adsorb onto the cyclone dust collector walls—a loss mechanism that can drop effective dosage to 0.5–0.6 phr and create batch-to-batch Mooney viscosity swings of 8–12 MU.The second-stage dispersant function emerges in conveyor belt covers that must resist both dynamic ozone attack and flex cracking under ISO 1431-1 conditions of 50 pphm ozone, 40 °C, and 20% elongation. When benzothiazole-2-carboxylic acid is pre-reacted with cyclohexylamine to form a transient salt in-situ during the cooling phase of the internal mixer at 105–115 °C, the resulting thiazole-amino complex increases the solubility of the antiozonant N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD) in the rubber matrix by a factor of 1.8, as measured by the time to bloom onset under fluorescence microscopy. This elimination of macroscopic 6PPD crystal formation on the cured surface postpones the first appearance of ozone cracks beyond 240 hours of continuous exposure.
When this heterocyclic intermediate serves as the carboxylate ligand in neodymium-based diene polymerization catalystsNeodymium versatate catalysts employed in the solution polymerization of high-cis polybutadiene (Nd-BR) for golf ball cores and high-impact polystyrene require a carboxylate ligand that undergoes facile alkylation by triisobutylaluminum (TIBA) without forming stable bimetallic complexes that deactivate the active center. Benzothiazole-2-carboxylic acid, when deprotonated with 3.1 equivalents of TIBA in hexane at -5 °C, provides a neodymium benzothiazole-carboxylate that initiates butadiene polymerization at an [Nd] concentration of only 0.018 mmol/100g of monomer. The resulting Nd-BR exhibits a cis-1,4 content of 97.8–98.2% (FTIR, attenuated total reflectance, peak at 740 cm⁻¹) and a polydispersity index (Mw/Mn) of 1.8–2.1 when the monomer conversion is arrested at 82% to prevent branching side reactions. The benzothiazole ring nitrogen, which coordinates transiently to the vacant orbital of the neodymium active site, modulates the propagation rate such that the Mooney viscosity (ML 1+4 at 100 °C) can be precisely targeted to 45 ± 3 MU without the need for a separate chain transfer agent like diethylzinc. Production plant operators in Russian and Middle Eastern Nd-BR facilities who have substituted neodymium naphthenate with this benzothiazole-based pre-catalyst observe that the catalyst solution remains free of precipitate for 14 days at 10 °C under nitrogen, compared to 3 days for naphthenate systems that form insoluble μ-hydroxo-bridged dimers. The consequent elimination of catalyst feed line blockages on a 40-kiloton-per-annum line has been reported as a critical operational advantage, although specific published data for this configuration is limited to patent disclosures CN113527573A and RU2784581C1. The benzothiazole fragment is not discharged in the polymer workup: it remains as an end group that, during the subsequent drying stage in a twin-screw devolatilizing extruder at 160 °C and 15 mbar, rearranges to a mercaptobenzothiazole-terminated chain end that demonstrates a 40% reduction in cold flow (measured as mm elongation of a 50g standard block under gravity over 24 hours at 25 °C).Precipitation of the polymerization cement with steam at 95–100 °C strips residual hexane to below 50 ppm. The benzothiazole carboxylate-ligated neodymium catalyst resists hydrolysis in the steam stripper far more effectively than neodymium octoate, with only 0.8% of the initial neodymium forming insoluble Nd(OH)₃ that deposits on the stripper tray perforations. This resistance to fouling extends the interval between required stripper column cleanings from a typical 6-month campaign to greater than 15 months, based on differential pressure measurements across the column trays.Chelating Additive in High-Temperature Synthesis of Mercaptosilane Coupling AgentsThe production of 3-mercaptopropyltriethoxysilane (MPTES) via nucleophilic substitution between 3-chloropropyltriethoxysilane and sodium hydrosulfide in ethanol requires rigorous exclusion of iron contamination that catalyzes the formation of polysulfidosilane dimers. Ferric ions leached from the 316L stainless steel reactor at the reaction temperature of 78 °C are sequestered by addition of benzothiazole-2-carboxylic acid at a concentration of 250–500 ppm relative to the chloropropylsilane charge. The resulting Fe(III)-bis(benzothiazole-carboxylate) complex precipitates as a dark red microcrystalline solid that is removed by a 5-micron bag filter before the crude silane enters the wiped-film evaporator for purification. Failure to adequately remove dissolved iron (above 3 ppm) results in the distillation residue gelling in the evaporator wiper blades when the jacket temperature reaches 140 °C, as the iron initiates the condensation of silanol groups to form high-molecular-weight polysiloxanes. With the benzothiazole acid present, the purified MPTES exhibits a Gardner color of <1 and an APHA color below 15 after accelerated aging at 60 °C for 28 days. Subsequent reaction of this purified mercaptosilane with benzothiazole-2-carboxylic acid derivatives proceeds without unwanted disulfide formation when the MPTES is applied as a coupling agent in silica-filled tire tread compounds. During the silanization reaction on the silica surface within an internal mixer at a dump temperature of 150–155 °C, the benzothiazole carboxylate accelerates the condensation of the triethoxysilyl groups onto the silanol population of the precipitated silica (BET surface area 165 m²/g, CTAB 155 m²/g), reducing ethanol evolution lag time as monitored by a portable photoionization detector in the mixer exhaust duct from a typical 45 seconds to 28 seconds.The chelation selectivity of benzothiazole-2-carboxylic acid for Fe³⁺ over Zn²⁺ is a critical parameter in this application. At a pH of 3.5–4.0 in the aqueous ethanol reaction medium, the stability constant (log K) for the Fe(III) complex exceeds that of the Zn(II) complex by approximately 5 orders of magnitude, meaning that zinc stearate added later as a processing aid for the rubber formulation does not transmetallate the iron complex and re-mobilize the transition metal catalyst. This selectivity is confirmed by inductively coupled plasma optical emission spectrometry (ICP-OES) analysis of the ethanolic filtrate after filtration, which typically shows residual iron below 0.8 ppm and zinc retention above 98%.Hardener Component in High-Solids Epoxy Blocked Isocyanate Industrial FlooringThe industrial flooring sector requires cycloaliphatic epoxy-amine coatings with a pot life exceeding 45 minutes and a walk-on time of 6 hours at 10 °C substrate temperature—a combination unattainable with unblocked aliphatic polyisocyanate hardeners. Benzothiazole-2-carboxylic acid is esterified with 2-ethylhexanol under azeotropic removal of water in toluene at reflux, then used to block the isocyanate groups of an isocyanurate trimer of isophorone diisocyanate (IPDI) by heating at 120 °C for 3 hours until the NCO content, as determined by dibutylamine back-titration per DIN EN ISO 11909, falls below 0.1%. The blocked polyisocyanate is blended at 18–22 wt% into a liquid epoxy resin (EEW 190 g/eq) containing 0.3 wt% of a tertiary amine catalyst blocked with p-toluenesulfonic acid. Upon film application at 200–250 µm wet film thickness using a notched squeegee, the deblocking temperature of the benzothiazole ester is 110 °C—lower than the 140–160 °C required for caprolactam-blocked systems, enabling cure at low substrate temperatures without external heating beyond the exotherm of the epoxy-amine reaction. The liberated benzothiazole ester plasticizes the initial crosslinked matrix, reducing the internal stress measured by the cantilever method of a 500 µm clearcoat applied to a steel panel to 2.8 MPa, compared to 6.1 MPa for a caprolactam-blocked control. After 7 days of ambient cure at 23 °C and 50% relative humidity, the coating attains a König pendulum hardness of 165 seconds per ISO 1522 and withstands a 1 kg steel ball drop from a height of 100 cm with no cracking or delamination (ASTM D2794). The residual benzothiazole moiety that remains dissolved in the cured film matrix is not purely a spectator fragment: its absorption maximum at 315 nm (ε = 8,500 L·mol⁻¹·cm⁻¹) imparts UV screening that delays chalking of the epoxy topcoat in QUV-B accelerated weathering (ASTM G154, Cycle 1) by approximately 400 hours beyond that of an unmodified system. Formulators at a European industrial flooring manufacturer incorporate this blocked adduct into a quartz-filled broadcast system for slaughterhouse floors, where resistance to 10% lactic acid at 60 °C and steam cleaning cycles at 3 bar pressure is verified according to EN 13529.
Aquaculture Disinfectant Intermediate for External Protozoan Infestations in Recirculating SystemsThe rapid conversion of benzothiazole-2-carboxylic acid to its sodium salt by treatment with aqueous sodium hydroxide at pH 8.5–9.0 yields a water-soluble active pharmaceutical intermediate that, when formulated with 0.1% povidone-iodine as a synergist, produces a bath treatment for monogenean trematode (Gyrodactylus spp.) infestations in juvenile Atlantic salmon smolts held in recirculating aquaculture systems (RAS). The sodium benzothiazole-2-carboxylate is added to the culture tank to achieve a target concentration of 1.5–2.0 mg/L active ingredient, at which level it inhibits the attachment of the parasite's opisthaptor to the gill lamellae without elevating plasma cortisol in the fish beyond the baseline of 15–25 ng/mL. Published data for this specific combination—sodium benzothiazole-2-carboxylate with povidone-iodine in Salmo salar—is limited, although the individual ecotoxicological endpoints for benzothiazole-2-carboxylic acid are documented in the European Chemicals Agency dossier under CAS 3622-36-2: the 96-hour LC50 for Oncorhynchus mykiss is above 100 mg/L, and the NOEC for Daphnia magna reproduction (OECD 211) is 12 mg/L. In RAS installations equipped with ozonation and moving bed biofilm reactors for nitrification, the benzothiazole carboxylate anion is mineralized by heterotrophic bacteria in the biofilter within 48 hours of application, with less than 5% of the initial dose detectable as the parent compound by HPLC-UV at 254 nm after that interval. This rapid biodegradation prevents accumulation in the system water that would otherwise necessitate a full water exchange—a logistical impossibility in RAS facilities located in inland areas far from saline water sources. Application of the sodium salt at water temperatures below 8 °C reduces the protozoan trophont detachment rate to an impractical level; effective treatment mandates that the RAS heating system maintain a minimum of 12 °C for the 72-hour bath duration, a conflict with the thermal preference range of 6–14 °C for smoltification-stage fish that must be managed by the facility veterinarian through a pre-treatment temperature acclimation ramp of 1 °C per hour. The formulation is discharged to waste through activated carbon beds (iodine number 950 mg/g, empty bed contact time 10 minutes) before release, and published adsorption isotherm data for benzothiazole-2-carboxylic acid on coconut-shell carbon at pH 7.8 indicates a Freundlich capacity factor (Kf) of 89 (mg/g)(L/mg)^(1/n) with a heterogeneity factor (1/n) of 0.42, ensuring effluent concentrations remain below the predicted no-effect concentration of 0.8 µg/L for the receiving freshwater environment. |
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| Parameter | Technical Grade (Rubber Chemicals) | Pharma Intermediate Grade | Standard/Test Method |
|---|---|---|---|
| Purity (HPLC, area%) | ≥97.0% | ≥99.0% | USP 〈621〉, C18, acetonitrile/water + 0.1% TFA |
| Melting point | 106–110 °C | 108.0–110.5 °C | USP 〈741〉 Class I, capillary |
| Water (w/w) | ≤0.25% | ≤0.10% | ASTM E203 (Coulometric KF) |
| Sulphated ash | ≤0.2% | ≤0.05% | USP 〈281〉 |
| Chloride (as Cl⁻) | ≤200 ppm | ≤50 ppm | USP 〈221〉, limit test |
| 2‑Chlorobenzothiazole impurity | ≤0.50% | ≤0.05% | In‑house HPLC, 254 nm |
| Residual ethanol (headspace GC) | ≤0.5% | ≤0.10% | USP 〈467〉 |
| Property (at 25 °C unless noted) | Benzothiazole‑2‑carboxylic acid (BTCA) | 2‑Mercaptobenzothiazole (MBT) | Benzothiazole‑2‑sulfonic acid sodium salt |
|---|---|---|---|
| CAS number | 3622-35-5 | 149-30-4 | 3042-64-2 |
| Functional group pKa | 2.45 (COOH) | 7.0 (SH), ~10.5 (NH) | <−1 (SO₃H) |
| Direct rubber acceleration (NR/SBR) | None | Primary accelerator, scorch t₅ 22 min (ASTM D1646) | None |
| Key industrial derivative | 2‑Benzothiazolesulfenamides (CBS, TBBS) | 2‑Mercaptobenzothiazole disulphide (MBTS) | Pyridine‑benzothiazole brighteners |
| Water solubility (g L⁻¹) | <0.5 | 0.12 (ionised form at pH 9–10) | >300 |
| Thermal decomposition onset (DSC) | 146 °C | 180 °C (broad, oxidative) | ~280 °C (anhydrous form) |
| Typical lead time for 5‑kg pharma grade | 4–6 weeks | 2–3 weeks | Not routinely supplied at pharma purity |
