2-Amino-1,3-Benzothiazole-6-Carboxylic Acid

Substitution of the benzothiazole nucleus at the 6-position with a carboxylic acid moiety, while retaining the free 2-amino group, generates a heterobifunctional intermediate whose reactivity profile diverges sharply from the isomeric 2-carboxy or 5-carboxy variants. The electron-withdrawing carboxyl group at C-6 deactivates the fused benzene ring toward electrophilic aromatic substitution, directing incoming electrophiles to the C-4 position under controlled nitration or halogenation conditions. Meanwhile, the 2-amino group preserves nucleophilic character at the thiazole carbon, permitting diazotization, acylation, and Schiff base condensation without protection of the distal carboxyl functionality—a synthetic convenience that has led to the molecule's entrenchment in pharmaceutical process chemistry, coordination polymer design, and high-performance pigment manufacture. The acid dissociation constant of the 6-COOH group (pK_a ~3.8-4.2 in aqueous ethanol, determined potentiometrically against Ag/AgCl reference) enables salt formation with pharmaceutical-grade organic bases, improving purification via recrystallization from ethanol-water mixtures at controlled cooling rates of 0.5°C/min to 1.0°C/min. In plant-scale handling, the free acid exhibits a melting point with decomposition above 280°C, necessitating jacketed screw conveyors with nitrogen blanketing for continuous drying post-centrifugation; residual moisture above 0.3 wt% determined by Karl Fischer titration (ASTM E203) has been correlated with caking during intermediate bulk container storage at ambient humidity exceeding 55% RH across three separately monitored production campaigns in multi-purpose GMP suites.

Which Process Parameters Dominate Yield in Anti-Tubercular Diarylquinoline Coupling?

During the convergent assembly of diarylquinoline-class antimycobacterial agents—analogous in architecture to bedaquiline derivatives under investigation by multiple generic API manufacturers—the 6-carboxylic acid group of 2-amino-1,3-benzothiazole serves as the anchor point for amide bond formation with a quinolin-3-yl-ethylamine fragment. The coupling is typically executed via activation with 1.1-1.3 equivalents of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC·HCl) in the presence of 0.1 equivalents of 1-hydroxybenzotriazole (HOBt) hydrate, using anhydrous N,N-dimethylformamide (water content < 100 ppm by Karl Fischer) as solvent. The benzothiazole component is charged at a molar ratio of 1.0:1.05 relative to the amine coupling partner; the slight excess of amine compensates for competing O-acylisourea rearrangement observed when the carboxylic acid is pre-activated for more than 12 minutes at 0-5°C prior to amine addition. Pilot-plant batches exceeding 50 kg input have documented yield erosion from a laboratory-achievable 82-86% to a plant-typical 71-74% when jacket temperature control on the 2000 L glass-lined reactor deviates by more than ±2°C during the 18-hour coupling stage, attributed to accelerated HOBt ester racemization at the benzylic carbon of the quinoline side chain. Compliance pathway: the starting benzothiazole acid must satisfy a purity threshold of ≥99.0% (HPLC, area normalization at 254 nm) with a single unknown impurity ceiling of ≤0.10%, aligning with ICH Q3A guidelines for drug substance intermediates; residual solvents are controlled per USP <467> Method IV, with specific attention to DMF below 880 ppm. The isolated amide intermediate is subsequently telescoped into a demethylation step using 48% aqueous HBr at reflux (118-122°C), yielding the phenolic diarylquinoline that constitutes the penultimate precursor to the hydrochloride salt active pharmaceutical ingredient. Terminal dosage forms include film-coated tablets (hot-melt extrusion with copovidone VA64, barrel temperature profile 130→155→170→165°C across four zones of a Leistritz ZSE 27 MAXX twin-screw extruder, screw speed 200 rpm) and dispersible pediatric tablets meeting WHO Biowaiver criteria for BCS Class II weak bases.

Polybenzothiazole (PBT) and its carboxyl-functionalized copolymers occupy a defined niche in high-temperature proton-exchange membranes and aerospace composite matrices, where the thermal decomposition onset must exceed 450°C under nitrogen (TGA, 10°C/min ramp, ASTM E2550). The 6-carboxylic acid derivative provides a reactive handle for post-polymerization crosslinking or covalent attachment to silane-treated glass fabric without the steric congestion that plagues 2-functionalized monomers. Polycondensation with 3,3′-diaminobenzidine (DAB) in polyphosphoric acid (PPA, 115.3% H₃PO₄ equivalent) at a monomer concentration of 8-12 wt% proceeds through a step-growth mechanism where the 2-amino group participates in thiazole ring formation while the 6-carboxylic acid condenses with the ortho-diamino functionality of DAB to yield a benzimidazole linkage. The polymerization protocol demands a staged temperature ramp: 12 hours at 120°C to effect dehydrochlorination (when the monomer is charged as its hydrochloride salt), followed by 24 hours at 180°C under mechanical stirring in a cylindrical double-helical mixer (torque monitoring used as an indirect measure of intrinsic viscosity buildup). Addition level of the benzothiazole dicarboxylic monomer ranges from 15 mole% to 35 mole% of total diacid, with the balance typically supplied by terephthalic acid; exceeding 40 mole% results in a polymer that is no longer tractable in methanesulfonic acid at 30°C (intrinsic viscosity > 8.0 dL/g), precluding fiber spinning via dry-jet wet spinning. Compliance with aerospace fire-smoke-toxicity mandates requires verification to FAR 25.853(a) Appendix F, Part I vertical burn test (60-second vertical ignition, average char length < 152 mm, afterflame time < 15 seconds) and smoke density measurement per ASTM E662 in flaming mode (D_s at 4.0 minutes < 200). Downstream processes include prepregging of 3K and 12K carbon fiber tows via hot-melt film impregnation (resin content 34±2 wt%, line speed 1.5-3.0 m/min) and autoclave cure under 7 bar external pressure with a final dwell of 2 hours at 370°C. Terminal parts encompass aircraft engine nacelle stiffeners, missile radome structural shells, and compressor blade containment rings qualified to RTCA DO-160G environmental test categories. Published data for specific long-term creep rupture performance above 300°C in oxidative environments is limited; validation programs typically require 10,000-hour coupon testing on a per-part-number basis.

Chelating Architecture and Polarization Resistance in Copper Interconnect Chemical Mechanical Planarization Slurries

In the post-Damascene copper CMP step for nodes at 14 nm half-pitch and below, benzotriazole (BTA) and its 5-carboxy analog (5-CBTA) have long dominated as the passivating corrosion inhibitors on copper lines. Replacement of 5-CBTA with 2-amino-1,3-benzothiazole-6-carboxylic acid in the slurry formulation—typically introduced as the potassium or triethanolammonium salt to ensure solubility above 0.5 wt% at pH 8.5-9.5—shifts the equilibrium film thickness in the recessed dielectric regions while maintaining a sufficiently high static etch rate on the protruded copper features under the downforce of the polishing pad. The molecule adsorbs onto Cu(111) and Cu(100) surface planes through a bidentate configuration involving the endocyclic nitrogen of the thiazole ring and the deprotonated carboxylate oxygen; in-situ spectroscopic ellipsometry measurements (rotating compensator, 70° angle of incidence, spectral range 250-1000 nm) indicate a self-limiting film thickness of 1.8-2.4 nm after 60 seconds of static immersion in a 0.01 wt% solution at pH 9.0—thinner than the 3.0-4.5 nm reported for BTA under identical conditions in published comparative studies using single-crystal copper coupons. Addition level in a typical silica-abrasive slurry (colloidal SiO₂, mean particle size 55 nm, solids loading 5 wt%) ranges from 0.005 wt% to 0.02 wt% of the total formulation; exceeding 0.03 wt% leads to detectably higher post-CMP defect counts attributed to organic residue adsorption resisting the subsequent post-CMP clean step (dilute HF + citric acid, 30 seconds megasonic agitation at 950 kHz). Industrial qualification requires compliance with SEMI C79 (guide for CMP consumables) and measurement of copper removal rate and within-wafer non-uniformity (WIWNU) on 300 mm pattern wafers using a four-point probe (sheet resistance mapping, 49-point polar grid, edge exclusion 3 mm). The polishing is executed on a rotary CMP tool (Ebara FREX or Applied Materials Reflexion LK, platen speed 93 rpm, head speed 87 rpm, downforce 1.5 psi, slurry flow rate 200 mL/min). The end product is a planarized wafer with dishing on 50×50 μm copper pads controlled below 15 nm as measured by atomic force microscopy, proceeding to barrier CMP and subsequent dual-damascene layer stacking.

When the 2-Amino Substituent Competes with Monomer Solubility in Azo Disperse Dye Synthesis for Polyester High-Temperature Exhaustion Dyeing

Millions of kilograms annually of C.I. Disperse Blue and Violet dyes are manufactured using 2-amino-6-substituted benzothiazoles as diazo components, and the 6-carboxylic acid derivative presents a distinctive thermodynamic profile: the carboxyl group confers water solubility under alkaline conditions (as the sodium salt, solubility > 40 g/L at pH 9.5 and 25°C) needed for homogeneous diazotization in aqueous media, yet the free acid form precipitates sharply below pH 4.5, simplifying isolation after coupling. Diazotization is performed by dissolving the sodium salt in water at 0-2°C, adding 1.02 molar equivalents of sodium nitrite, and discharging the mixture into a pre-cooled solution of 2.5 molar equivalents of hydrochloric acid maintained below 5°C in a continuously stirred tank reactor with a jacket outlet temperature of -15°C (brine circulation). The resulting diazonium salt, a pale-yellow suspension, is coupled within 30 minutes to an N,N-dialkylaniline coupling component in acetic acid-sodium acetate buffer at pH 4.0-4.5, yielding a monoazo chromophore with a molar extinction coefficient in the range of 35,000-42,000 L·mol⁻¹·cm⁻¹ in DMF at λ_max. The crude dye is filtered through an agitated Nutsche filter-dryer, washed to conductivity below 200 μS/cm, and dried under vacuum at 80°C to residual moisture ≤0.5%. The industry regulatory framework requires compliance with the ZDHC Manufacturing Restricted Substances List (MRSL) Version 3.1, specifically confirming the absence of restricted arylamines from reductive cleavage (tested per EN 14362-1:2017) and chlorobenzenes below 1.0 mg/kg. The finished disperse dye is standardized to a strength of 200% or 300% (relative to a reference standard) by blending with naphthalene sulfonate-formaldehyde condensate dispersants in a horizontal bead mill (Netzsch LME 4, 0.4-0.6 mm yttria-stabilized zirconia beads, 85% chamber fill, peripheral speed 10-14 m/s), spray-dried to a non-dusting granular powder (bulk density 0.35-0.55 g/cm³), and applied to polyester knitted fabric via high-temperature exhaustion dyeing at 130°C for 45-60 minutes (Mathis Labomat, liquor ratio 1:10) with a color fastness to sublimation rating of 4-5 per ISO 105-P01:1993. The terminal consumer article spans athletic apparel, automotive upholstery, and continuous-filament sewing thread dyed in package form (Obermaier or Galvanin vertical spindle machines, liquor flow reversal every 30 seconds).

In acidic gas reservoirs with coexisting H₂S partial pressures above 0.05 bar and CO₂ partial pressures exceeding 10 bar, the inhibition of localized pitting corrosion on L80-13Cr martensitic stainless steel (UNS S42000, minimum yield strength 552 MPa) demands film-forming organic additives that adsorb competitively with bisulfide and chloride ions at the passive film defect sites. The 2-amino-1,3-benzothiazole-6-carboxylic acid molecule, formulated as a dilute solution in a methanol-water carrier (MeOH:H₂O 70:30 v/v for winterized continuous injection through capillary tubing in subsea umbilical systems), demonstrates a critical micelle concentration (CMC) of approximately 4.2×10⁻⁴ mol/L in synthetic formation brine (total dissolved solids 80,000 mg/L, [Cl⁻] 45,000 mg/L) at 60°C, measured by pendant drop tensiometry (Krüss DSA100, drop volume 8 μL, equilibration time 120 seconds). The inhibitor is injected at a target continuous dosage of 25-50 ppm (v/v) based on total produced water volume, with an initial batch treatment of 500-1000 ppm for 12-24 hours to establish a pre-passivated surface film prior to transitioning to maintenance dosage—a protocol documented in NACE TM0194-2014 (field monitoring of bacterial growth and corrosion inhibitor performance). Electrochemical validation employs linear polarization resistance (LPR) probes with three-electrode configuration (working electrode: L80-13Cr, counter electrode: Hastelloy C-276, reference: Ag/AgCl in saturated KCl, scan rate 0.125 mV/s, range ±15 mV vs. OCP) installed in a side-stream bypass loop at operating pressure, with a target corrosion rate below 0.025 mm/year. Compliance reporting is structured per NACE SP0775-2013 preparation of corrosion management plans, with specific reference to inhibitor availability at the wall calculated from shear stress values from multiphase flow simulations (OLGA or LedaFlow transient models). The inhibited production fluids are routed through three-phase separators (gas-oil-water) where the polar inhibitor partitions predominantly (> 90%) into the aqueous phase, enabling recycling of the inhibitor-laden produced water for reinjection without additional chemical blowdown; oil-phase carryover is quantified by UV-Vis absorbance at the benzothiazole λ_max (295-305 nm) against a matrix-matched calibration curve prepared with the specific crude oil. The final protected asset includes downhole tubing hangers, subsurface safety valves, and the inner wall of flowlines with a design life extension target of 25 years per ISO 21457:2010 materials selection for petroleum and natural gas industries. Published data for inhibitor film persistence under multiphase slug-flow conditions at Froude numbers above 6 remain sparse and constitute an active area for field trial qualification.

Seed treatment formulations targeting Rhizoctonia solani anastomosis group AG-2-2IIIB in sugar beet and Fusarium graminearum in winter wheat increasingly incorporate benzothiazole-6-carboxylic acid esters as systemic acquired resistance (SAR) elicitors, a functional profile that traces back to the structural analogy between 2-aminobenzothiazole derivatives and the endogenous plant signal molecule benzothiadiazole (BTH). The 6-carboxylic acid intermediate is esterified with methanol or ethanol in the presence of thionyl chloride (1.2 equivalents, dropwise addition at -5 to 0°C over 4 hours) to yield the methyl or ethyl ester, which is then formulated into an aqueous suspension concentrate (SC) containing 250 g a.i./L active ingredient, 40 g/L of an alkyl naphthalene sulfonate-formaldehyde condensate dispersant, 5 g/L of a silicone-polyether antifoam emulsion, and xanthan gum thickener to a final viscosity of 300-600 mPa·s at 20 s⁻¹ (Brookfield RVDV-II, spindle #3). Wet milling in a horizontal media mill with 0.2-0.3 mm cerium-stabilized zirconia grinding beads reduces the median particle size to 1.5-2.5 μm (D₅₀, laser diffraction, Malvern Mastersizer 3000 with Hydro MV dispersion unit, obscuration 10-15%), at which point the suspension passes a 75 μm wet sieve retention test per CIPAC MT 185 with retained residue below 0.1%. The formulated product is applied to seed at a rate of 25-50 g a.i. per 100 kg seed in a rotary batch seed treater (Gustafson Accu-Treat or equivalent, atomizer disc speed 10,000 rpm, seed flow rate 500 kg/h), often co-applied with a conventional contact fungicide (fludioxonil at 2.5 g a.i./100 kg seed) and a polymer-based film-coating binder to control dust-off below the Heubach dust-off limit of 0.75 g/100 kg seed as specified in the European Seed Association's ESTA quality assurance protocol. Regulatory compliance intersects with EC Regulation 1107/2009 for plant protection product authorization in the EU, requiring: (a) an acute toxicity assessment yielding an LD₅₀ oral (rat) > 2000 mg/kg; (b) an Ames test (OECD TG 471) with negative mutagenicity across TA98, TA100, TA1535, and TA1537 strains both with and without S9 metabolic activation; and (c) residue decline data from supervised field trials in at least 2 geographically distinct growing seasons establishing a maximum residue limit (MRL) in the harvested commodity per Regulation (EC) No 396/2005. The terminal treated seed—whether pelleted sugar beet seed (pellet weight 25-35 mg per seed, pelleting binder: polyvinyl acetate copolymer) or film-coated wheat caryopses—is packaged in low-dust, low-electrostatic discharge polyethylene bags compatible with pneumatic precision planting equipment operating at ground speeds up to 12 km/h and metering disc vacuum of -35 mbar.

Organometallic Framework Assemblies from the 6-Carboxylate-2-amino Chelate: Topology Control in Cu(II) Paddlewheel SBUs

When reacted with copper(II) nitrate trihydrate in a solvent mixture of N,N-dimethylacetamide (DMAc) and water (3:1 v/v) under solvothermal conditions at 85°C for 48 hours in a Parr acid-digestion vessel with PTFE liner (fill ratio 60%), 2-amino-1,3-benzothiazole-6-carboxylic acid deprotonates in situ to form the μ₂-bridging carboxylate linker that, in combination with the 2-amino group's weak axial coordination to a neighboring Cu(II) center, directs the assembly toward a two-dimensional Kagomé lattice (sql-a topology) rather than the ubiquitous Cu₂(COO)₄ paddlewheel square-grid nets. The chelating mode involves the carboxylate oxygen atoms bridging two Cu(II) centers in a syn-syn geometry (Cu–O bond distances 1.96-2.01 Å from single-crystal XRD refinement at 100 K, Mo Kα radiation, θ range 2.3-28.7°, R₁ < 0.045) while the amino nitrogen provides a weak supplementary bond (Cu–N 2.18-2.24 Å) that is labile under guest exchange. The addition ratio is governed by the stoichiometry of the target network: a 1:1 metal-to-ligand molar ratio yields the two-dimensional layered structure, while an excess of the ligand (1:1.5 M:L) and extended reaction time (72 hours) produce a three-dimensional interpenetrated framework with 42% solvent-accessible void volume (calculated by PLATON SQUEEZE from the refined crystallographic model). For industrial gas separation applications—specifically the kinetic separation of propylene from propane in refinery off-gas streams—the activated MOF powder (degassed at 120°C under dynamic vacuum of 10⁻⁴ mbar for 16 hours) is mixed with a polyetherimide binder (Ultem 1000, 10 wt%) and cast into mixed-matrix membranes on a non-woven polyester support (thickness 200 μm) using a doctor blade with a gap setting of 350 μm, followed by solvent evaporation at 60°C in a nitrogen-purged convection oven. Single-gas permeation measurements at 2 bar feed pressure and 35°C using a constant-volume variable-pressure apparatus (ISO 15105-2:2003 method for determination of gas-transmission rate) yield a C₃H₆/C₃H₈ ideal selectivity of 12-15 with C₃H₆ permeability of 85-110 Barrer. Post-synthesis processing includes a methanol solvent exchange step (repeated three times over 36 hours) prior to the thermal activation to mitigate capillary-force-induced pore collapse, a failure mode documented for isostructural frameworks with aperture diameters below 5 Å. Regulatory treatment is currently governed under the general chemical safety assessment framework of REACH (EC 1907/2006) for substances manufactured or imported at quantities between 1 and 10 tonnes per annum; a Chemical Safety Report is required if the exposure scenario for MOF powder handling identifies a derived no-effect level (DNEL) for inhalation of respirable particulates below 1.0 mg/m³ (8-hour time-weighted average).