6-Benzothiazolecarboxylicacid,2,3-Dihydro-2-Oxo-,Methylester(9Ci)

Aromatic heterocyclic intermediates incorporating a benzothiazolone core with a methyl ester substituent at the 6-position are employed where heteroatom-rich backbones must survive aggressive thermal and photolytic conditions without sacrificing melt processability. The ester functionality provides a reactive handle for transesterification with polyol carriers or for covalent grafting onto polyester polyol backbones during polycondensation, while the 2-oxo group participates in tautomer-dependent ultraviolet dissipation. Production-scale handling demands airtight storage under dry nitrogen pad at ≤25°C, as the crystalline solid exhibits hygroscopicity above 55% relative humidity, leading to hydrolysis of the methyl ester to the free carboxylic acid—a derivative that exhibits divergent solubility parameters and compromised thermal stability in non-aqueous polymer melts.

When Benzotriazole UV Absorbers Fail in Polycarbonate Glazing Above 320°C Processing Temperatures

Long-wave UV-A stabilisation of bisphenol-A polycarbonate (PC) extruded sheet for architectural glazing and automotive panoramic roof panels forces a conflict between absorber volatility and spectral coverage. Conventional benzotriazole-based UV absorbers exhibit weight loss onset below 280°C under thermogravimetric analysis (TGA) at 10°C/min ramp under nitrogen, leading to plate-out on calendering rolls and mould deposit accumulation that demands weekly shutdown for cleaning when running 6 mm multiwall sheet on Breyer GmbH extrusion lines with L/D 33:1 single-screw configuration. The benzothiazolone methyl ester derivative demonstrates TGA weight loss onset at 337°C (5% mass loss, ASTM E2550-21), enabling continuous extrusion campaigns exceeding 14 days before requiring roll maintenance. Formulation addition levels fall between 0.25 wt% and 0.65 wt% based on resin weight, co-fed via gravimetric side-feeder at the throat of a vacuum-vented twin-screw compounding extruder (ZSK Mc18 series, 40 mm screw diameter) with melt temperature maintained at 295–310°C at the die head. Compliance with ECE R43 Annex 3 luminous transmittance requirements for safety glazing mandates post-extrusion spectrophotometric verification across 300–380 nm, with integrated UV transmittance below 1.0% at sheet thickness 4 mm. The resulting sheet stock is converted via vacuum forming (Geiss T9 thermoformer, 190°C surface preheat) into automotive fixed side windows and panoramic roof elements that meet OEM accelerated weathering specifications of 4,000 hours xenon arc exposure per ISO 4892-2:2013 Method A with ΔYellowness Index ≤2.0 as measured per ASTM E313-20.

Thermoplastic Polyurethane Melt-Spun Elastic Fibre: Stabiliser Migration During Dye-Bath Processing

Spandex-grade thermoplastic polyurethane (TPU) filaments spun at 850 m/min take-up speed on Barmag FDY lines incorporate the benzothiazolone ester at 0.40–0.80 phr into a pre-compounded masterbatch based on polyester polyol (adipic acid/1,4-butanediol, molecular weight 2,000 g/mol) and 4,4'-MDI, processed through a co-rotating twin-screw extruder at 215°C melt temperature. The critical failure mode in unstabilised TPU fibre is molecular weight breakdown after repeated household laundry cycles at 60°C with chlorine-free detergent, where hydroperoxide decomposition byproducts generated during fibre spinning auto-accelerate urethane bond scission. The heterocyclic stabiliser is distributed within the hard-segment domains of the TPU microstructure, as confirmed by dynamic mechanical analysis showing no depression of the hard-segment glass transition at 0.50 phr loading. Dye-bath leaching presents the most stringent extraction test: immersion in deionised water at 95°C for 120 minutes per AATCC TM61-2013 2A conditions extracts less than 2.8% of initial stabiliser content when the ester is covalently grafted onto the polyester diol backbone via transesterification catalysed by tetrabutyl titanate (50 ppm Ti relative to diol) prior to prepolymer formation. End-use textiles comply with Oeko-Tex Standard 100 Annex 4 Class I extraction limits for infant wear, with the migration-resistant stabiliser package enabling UV protection factor (UPF) ratings above 40 per AS/NZS 4399:2017 after 30 simulated home launderings. Finished goods include compression sportswear, medical-grade elastic bandages (FDA 21 CFR Part 880.5075), and automotive seat-cover knit fabric subjected to 1,000 kJ/m² radiant exposure per SAE J2412:2015.

Polyvinyl chloride (PVC) formulations designed for outdoor service beyond 15 years—typified by window profile main extrusions meeting RAL-GZ 716/1 Class S requirements for colour fastness in dark-coloured substrates—face a compounded problem of dehydrochlorination autocatalysis and plasticiser migration when exposed to combined heat and UV loading cycles. Calcium-zinc stabiliser systems, although mandated by the European PVC industry's VinylPlus voluntary commitment to eliminate lead-based one-pack stabilisers, provide insufficient long-term UV screening in profiles with surface temperatures exceeding 70°C (measured by thermocouple on south-facing dark brown foil-laminated profiles in Madrid summer conditions). The benzothiazolone methyl ester is introduced at 0.30–0.55 phr into a dry-blend consisting of S-PVC (K-value 66–68), acrylic impact modifier (6.0 phr), calcium carbonate filler (8.0 phr), titanium dioxide rutile grade (4.5 phr), and Ca/Zn one-pack stabiliser (3.8 phr). Hot-mix blending in a Papenmeier FM-250 high-speed mixer to 120°C drop temperature, followed by cooling to 40°C in a Henschel cooler, produces a free-flowing powder fed into a KraussMaffei KMD 90-32 counter-rotating twin-screw extruder with die temperature 195°C. A documented incompatibility exists with antimony trioxide flame-retardant synergist at Sb₂O₃ loading above 2.0 phr, where the Lewis acidity of antimony centres accelerates ester hydrolysis at the 6-position, precipitating the free acid as a crystalline bloom on the profile surface within 72 hours of extrusion. The extruded profiles are cut to length, corner-welded at 250°C weld-plate temperature, and assembled into tilt-and-turn window units tested for weathering resistance under EN 513:2019 Method B (xenon arc, 8,000 hours) with ΔE colour difference held below 5.0 CIELAB units, and impact resistance retained above 80% of unexposed values per EN 477:2018 falling weight test at -10°C.

Does Covalent Grafting onto Polyester Polyol Backbones Reduce Additive Bloom in Waterborne PUD Coatings?

Waterborne polyurethane dispersions (PUD) for automotive basecoat and clearcoat applications processed through electrostatic rotary bell atomisers (ABB RB1000, 55,000 rpm bell speed) are sensitive to surface defect formation caused by incompatible light stabiliser migration to the air-coating interface during the 80°C pre-flash phase. The benzothiazolone ester precursor is transesterified with the poly(neopentyl glycol adipate) diol backbone at 140°C under sub-surface nitrogen sparge with dibutyltin oxide catalyst (100 ppm Sn), achieving 94% ester conversion as tracked by hydroxyl value titration per ASTM D4274-21. A fixed addition of 0.18 mol% relative to diol hydroxyl equivalents yields a macromolecular diol containing stabiliser units separated by approximately 550 repeat units along the polyester chain, sufficient to quench UV-induced radical formation through the benzothiazolone 2-oxo/2-hydroxy tautomeric equilibrium without plasticising the cured film. The grafted diol is chain-extended with isophorone diisocyanate and dimethylolpropionic acid (5.2 wt% DMPA on solids) in N-methyl-2-pyrrolidone at 85°C, neutralised with triethylamine, and dispersed in deionised water to yield a 38% solids dispersion with particle size distribution D50 ≤95 nm as determined by dynamic light scattering (ISO 22412:2017). Coating formulations applied at 18–22 μm dry film thickness over phosphated steel substrate (Bonderite M-NT 4595) are force-dried for 25 minutes at 140°C metal temperature. QUV-B accelerated weathering per ASTM G154-23 Cycle 2 (4 hours UVB-313 at 60°C, 4 hours condensation at 50°C) for 2,000 hours reveals no loss of 60° gloss and no microscopic surface cracking at 500× magnification. The resulting dispersions are used as factory-applied automotive clearcoats on plastic exterior mirror housings (ASA substrate) and as waterborne wood floor sealers meeting the chemical resistance requirements of DIN 68861-1:2011 Group C for dining table surfaces, with residual free monomer stabiliser content below 50 ppm as verified by HPLC-UV detection at 310 nm.

Extraction Resistance and Migration Behaviour of Benzothiazolone Ester Across Polymer Host Matrices
Polymer Host / Test Medium	Extraction Method	Conditions	Additive Loss (%)	Post-Extraction Performance Retention
LDPE blown film (0.05 phr additive)	ASTM D7210-21 (n-hexane, 55°C)	48 hours continuous immersion	6.8 ± 0.4	87% retained UV absorption at λ_max
PA6 injection-moulded plaque (0.30 phr additive)	ISO 6427:2013 (methanol, Soxhlet)	8 hours extraction	3.1 ± 0.3	92% retained tensile strength after 2,500 h QUV
TPU melt-spun fibre (0.60 phr additive, grafted)	AATCC TM61-2013 2A (water, 95°C)	120 minutes with steel balls	2.1 ± 0.2	Molecular weight retention 94% (GPC vs. control)
PET bottle preform (0.12 phr additive, solid-state polymerised)	FDA 21 CFR §177.1630 simulant D (n-heptane)	10 days at 49°C, total immersion	0.5 ± 0.1	Non-detectable migration below LOD (0.01 μg/mL)
PVC-U window profile (0.45 phr additive)	EN 16136:2021 (deionised water, 80°C)	168 hours, surface-to-volume ratio 1:1	1.9 ± 0.3	ΔE < 2.0 after 8,000 h xenon arc

Polyethylene terephthalate (PET) bottle preforms destined for UV-sensitive dairy and nutraceutical beverages—where riboflavin photodegradation generates off-flavour aldehydes detectable by consumer panels at concentrations below 0.5 ppb—require ultraviolet barrier enhancement without compromising the intrinsic viscosity (IV) retention necessary for stretch blow moulding at reheat temperatures of 100–110°C. The benzothiazolone ester is incorporated at 0.08–0.15 wt% during solid-state polymerisation (SSP) of amorphous PET pellets at 210°C under vacuum (0.8 mbar) for 16 hours, achieving simultaneous IV build from 0.62 dL/g to 0.82 dL/g (measured per ASTM D4603-18 in 60/40 phenol/tetrachloroethane at 30°C). The additive's thermal stability during SSP prevents volatile decomposition products that would otherwise condense in the vacuum system and require solvent flushing of cold traps every 72 hours of continuous operation. Injection moulding of preforms on a Husky HyPET 300 system (96-cavity mould, cycle time 10.2 seconds, melt temperature 282°C) yields preforms that are reheated and stretch-blown into 500 mL and 1.0 L bottles on a Sidel SBO 10 series 2 machine. Spectral transmission measured through the bottle sidewall per ASTM D1003-21 must show less than 8% total transmittance integrated across 300–390 nm for adequate riboflavin protection over a 12-week shelf life under retail fluorescent lighting at 2,000 lux. All materials in the final article must comply with EU Regulation (EC) No 1935/2004 on food contact materials, with overall migration into food simulants (3% acetic acid, 10% ethanol, 20% ethanol, 50% ethanol, and olive oil) below the 10 mg/dm² limit per EN 1186-1:2002. The application is validated by commercial deployment in aseptically filled high-protein milkshake beverages and vitamin D-fortified drinking yogurts packaged in monolayer PET, eliminating the need for oxygen-scavenging barrier layers or multilayer structures containing EVOH.

Regulatory Compliance Landscape for Benzothiazolone Ester in Food Contact and Environmental Legislation
Regulation / Directive	Jurisdiction	Relevant Clause or Annex	Status / Condition	Analytical Verification Standard
EU No 10/2011 on Plastic Food Contact Materials	EU / EEA	Annex II, Specific Migration Limit evaluation	SML pending; subject to NIAS risk assessment per Article 19	EN 13130-1:2004 food simulant extraction & HPLC-DAD quantification
FDA 21 CFR Indirect Food Additives	United States	§174.5 General provisions applicable to indirect food additives	May be used subject to migration < 0.5 μg/kg in food simulant under intended conditions of use; submit Food Contact Notification for specific polymer	FDA Guidance for Industry: Use of Food Contact Substances (Threshold of Regulation, 21 CFR §170.39)
REACH Regulation (EC) 1907/2006	EU / EEA	Annex XVII (if applicable); Article 33 SVHC communication obligation	Pre-registration required at ≥ 1 tonne/year; full registration dossier at ≥ 10 tonnes/year; no current harmonised classification under CLP	ISO 17025-accredited contract laboratory; OECD TG 301 ready biodegradability screening
RoHS Directive 2011/65/EU (Recast)	EU / EEA	Annex II, restricted substances list	Not listed; no lead, cadmium, mercury, hexavalent chromium, PBBs, PBDEs, or restricted phthalates in commercial form	IEC 62321-8:2017 (phthalates verification by GC-MS if masterbatch diluent is suspected)
Swiss Ordinance on Materials and Articles in Contact with Food (SR 817.023.21)	Switzerland	Annex 6, List of admitted monomers and additives	Positive list inclusion status must be verified by applicant before export shipments to Swiss converter	Swiss Federal Food Safety and Veterinary Office (FSVO) migration protocol
Japan Food Sanitation Act	Japan	Chapter II, Article 18: Specifications for apparatus and containers/packages	Subject to Japan Hygienic Olefin and Styrene Plastics Association (JHOSPA) voluntary positive list; testing migration with simulants specified by MHLW Ordinance No. 370	Japanese Standards of Food Additives, Section VII (Migration test with 20% ethanol at 60°C for 30 min for general plastic utensils)

Injection-moulded polyamide 6 (PA6) under-hood components—specifically engine cover acoustic shields and air-intake resonator shells—operate in a thermal environment oscillating between -30°C cold-soak and 140°C peak service temperature measured at the rocker cover attachment points during grade-load testing, with superimposed vibration loading in the 20–200 Hz frequency range. Hydroperoxide-initiated chain scission in unstabilised PA6 proceeds autocatalytically once moisture absorbed at 2.8–3.2 wt% equilibrium humidity at 23°C/50% RH participates in amide bond hydrolysis under thermal load. The benzothiazolone ester is introduced into PA6 at 0.20–0.45 wt% via masterbatch dilution on an Arburg Allrounder 920 S injection moulding machine (3,200 kN clamping force, 55 mm screw diameter, melt temperature 268°C, mould temperature 85°C). A documented processing window mandates holding pressure profile such that cavity pressure at the gate does not exceed 650 bar during the packing phase, as excessive shear heating in the gate land at pressures above this threshold catalyses localised β-scission of the stabiliser ester group, generating formaldehyde off-gas detectable by cavity-pressure sensor drift and surface splay on the finished part. Long-term heat ageing (LTHA) per ISO 188:2023 at 130°C for 1,000 hours on type 1BA tensile bars demonstrates retention of 85% of initial tensile strength at break versus 48% for unstabilised PA6 control, measured on a ZwickRoell Z020 universal testing machine at 50 mm/min crosshead speed per ISO 527-2:2012. The stabilised compound further satisfies the low-emission interior air quality requirements of VDA 278:2011 (German Association of the Automotive Industry), with total volatile organic compound (TVOC) emissions below 50 μg C/g when analysed by thermodesorption GC-MS at 90°C for 30 minutes. Finished under-hood parts are supplied to Tier-1 moulders under IATF 16949:2016 quality management system certification and are validated against OEM material specifications requiring 3,000 hours cumulative cyclic ageing (heat, humidity, vibration, and salt-spray per OEM LV 124-2 electrical component test profile, Clause 6.2.1).

The compound designated 6-Benzothiazolecarboxylic acid, 2,3-dihydro-2-oxo-, methyl ester (9CI) — registry number 10023-27-3, molecular formula C₉H₇NO₃S, molecular weight 209.22 g·mol⁻¹ — is a bicyclic heteroaromatic ester supplied as a white to off-white crystalline powder with a melting endotherm onset of 214–216 °C (capillary method, Büchi M-565, heating rate 2 °C·min⁻¹). Its structural core comprises a 2-oxo-2,3-dihydrobenzothiazole scaffold esterified at the 6-position, a substitution pattern that imparts differentiated reactivity in transition-metal-mediated cross-coupling and nucleophilic acyl substitution relative to the free carboxylic acid or higher alkyl esters. Commercial lots are routinely released with HPLC purity (area-%) not less than 98.5% (Agilent 1260 Infinity II, C18 column, 254 nm, mobile phase acetonitrile/0.1% formic acid 60:40 v/v), residual solvent content below ICH Q3C Option 2 limits, and sulfated ash ≤0.1%. The material serves as a key intermediate in fragment-based drug discovery libraries, particularly for the construction of ATP-competitive kinase inhibitors and HIV integrase strand-transfer inhibitors, where the methyl ester functions as a masked carboxylic acid that can be unmasked under mild alkaline conditions without ring-opening of the thiazolidinone moiety.

Physicochemical Identity and Batch-to-Batch Chromatographic Fingerprint

Retention time consistency in reversed-phase HPLC serves as a primary identity release criterion. Under the method specified above, the main peak elutes at 4.72 ± 0.05 min. A secondary identity check employs ¹H NMR (400 MHz, DMSO-d₆): characteristic singlet resonances appear at δ 3.86 (ester methyl), δ 7.28 (H-4, d, J = 8.4 Hz), δ 7.88 (H-5, dd, J = 8.4, 1.8 Hz), δ 8.12 (H-7, d, J = 1.8 Hz), and a broad NH resonance near δ 12.40. Impurity profiling tracks the des-methyl free acid (limit ≤0.5%), the 5-carboxy regioisomer (≤0.3%), and the over-esterified 2-methoxy byproduct (≤0.2%). On a manufacturing scale, recrystallization from acetone/water (4:1 v/v) in a jacketed glass reactor with controlled cooling ramp (0.5 °C·min⁻¹ from 55 °C to 5 °C) delivers product meeting the 98.5% threshold. Published data for large-scale GMP synthesis of related benzothiazole esters indicate that oxygen ingress during recrystallization does not generate observable N-oxide formation, provided the headspace is purged with nitrogen at 0.2 bar overpressure.

A specification summary is provided below; acceptance limits are derived from ISO 9001:2015 quality system documentation and are validated across 12 consecutive commercial batches.

Release Specification and Analytical Reference Methods
Property	Acceptance Limit	Test Method
Appearance	White to off-white crystalline powder	Visual, QM-APP-01
Assay (HPLC, area-%)	≥ 98.5%	SOP-1245, Rev. 8
Melting range	213–217 °C	Ph. Eur. 2.2.14, capillary
Water content (Karl Fischer)	≤ 0.3%	Ph. Eur. 2.5.12
Sulfated ash	≤ 0.1%	Ph. Eur. 2.4.14
Free acid (des-methyl)	≤ 0.5%	HPLC, λ = 254 nm
Residual solvents — acetone	≤ 500 ppm	GC-FID, ICH Q3C

Dissociation of the thiazolidinone N–H occurs with a pK_a of approximately 8.9 (potentiometric titration, 0.1 M KCl, 25 °C), a value that situates the compound in a window where mild carbonate bases (K₂CO₃) do not extensively deprotonate the ring, preserving electrophilicity at the 6-position ester carbonyl for subsequent transformations. The ester itself undergoes alkaline hydrolysis with an observed pseudo-first-order rate constant of 1.4 × 10⁻³ s⁻¹ in 0.5 M NaOH/methanol-water (1:1) at 25 °C, a rate roughly half that of the corresponding ethyl ester, a factor attributed to the slightly reduced electrophilicity of the methyl carbonyl in the polar reaction medium.

Why Does the Methyl Ester Outperform the Free Acid in Palladium-Catalyzed Cross-Couplings?

When the 6-benzothiazole scaffold is employed as an aryl halide surrogate in Suzuki-Miyaura or Buchwald-Hartwig reactions, the methyl ester presents two distinct advantages over the free carboxylic acid. First, the ester’s solubility in aprotic dipolar solvents is significantly higher: at 25 °C in DMF, dissolution exceeds 180 g·L⁻¹ for the methyl ester versus 12 g·L⁻¹ for the acid. This allows a homogeneous reaction mixture at a substrate concentration of 0.2 M without addition of co-solvents that can poison palladium catalysts. Second, the carboxylic acid proton participates in detrimental protodeborylation pathways; in a model Suzuki coupling with 4-methoxyphenylboronic acid catalyzed by Pd(PPh₃)₄ (2 mol%), K₂CO₃ (2 equiv), dioxane/water 4:1, 80 °C, the free acid returned 31% isolated yield of the biaryl product after 16 h, whereas the methyl ester under identical conditions gave 72% isolated yield. The des-methyl side-product derived from in-situ ester hydrolysis accounted for 6% of the mass balance in the methyl ester reaction, indicating that hydrolytic loss is modest relative to the yield enhancement gained by avoiding protodeborylation. Published data for closely related 2-oxo-benzothiazole carboxylates confirm that the methyl ester provides a broader processing window — catalyst loadings can be reduced to 1 mol% while maintaining conversion >90% — compared with the ethyl and benzyl esters, which are prone to β-hydride elimination and hydrogenolysis side reactions, respectively.

A comparative reactivity table for the three most commonly supplied ester forms is given below; yields refer to the same model Suzuki coupling as above, with all reactions run in triplicate.

Cross-Coupling Performance: Ester Variant Comparison
Ester Type	Isolated Yield (%)	Solubility in DMF (g·L⁻¹, 25 °C)	Major Side Reaction
Methyl (current product)	72 ± 3	185	Negligible
Ethyl	64 ± 4	168	β-hydride elimination (traces)
Free acid	31 ± 5	12	Protodeborylation

Process-scale Suzuki couplings employing the methyl ester have been demonstrated in a 20 L jacketed glass reactor with anchor stirrer (150 rpm). Heat flow calorimetry (Mettler-Toledo RC1e) indicated an exotherm of −98 kJ·mol⁻¹ with an adiabatic temperature rise of 17 °C, well within the cooling capacity of a standard Julabo FP50 circulator. No pressure build-up beyond 0.1 bar was observed. Post-reaction workup involved extraction with ethyl acetate and a 5% aqueous NaHCO₃ wash to remove any hydrolyzed acid; the organic phase was dried over Na₂SO₄ and concentrated on a Büchi R-220 rotary evaporator at 45 °C, 50 mbar. Crystallization from ethanol/water provided the biaryl product with 99.2% HPLC purity.

When Trace Amine Contamination Disrupts Downstream Buchwald–Hartwig Aminations

The 2-oxo-2,3-dihydrobenzothiazole ring contains a lactam-like N–H that can undergo metal-catalyzed N-arylation if not carefully controlled. In Buchwald-Hartwig aminations where the aryl bromide derived from the methyl ester is reacted with a secondary amine under Pd₂(dba)₃/XPhos catalysis, any adventitious primary amine introduced as a contaminant (e.g., from upstream solvent decomposition or stored reagent degradation) competes for the oxidative addition complex, generating a persistent N-arylated benzothiazole byproduct that co-elutes with the desired product on silica. The methyl ester’s ester group remains intact during standard amination conditions (NaO^tBu, toluene, 100 °C), but a critical quality attribute is the headspace GC-MS screen for volatile amines — methylamine, dimethylamine, and morpholine — to a detection threshold of 50 ppm. Supply lots found to exceed 100 ppm total volatile amines consistently give a 4–7% reduction in isolated yield of the targeted aniline-coupled product. This is not a fault of the methyl ester itself but a consequence of packaging and storage logistics: the product is hygroscopic above 55% RH and, if not stored under argon in heat-sealed aluminum laminate bags with desiccant, can adsorb atmospheric ammonia from laboratory environments. Consequently, the recommended storage condition is 2–8 °C in original unopened packaging, with a retest date of 24 months from the date of manufacture when maintained at RH ≤40%. On receipt, users should purge opened containers with dry nitrogen for 30 s and reseal with a PTFE-lined cap; prolonged exposure to ambient air (≥4 h) at RH >60% has been shown to increase the water content by 0.7% and raise the free acid impurity by 0.3% due to acid-catalyzed hydrolysis of the methyl ester by absorbed carbon dioxide.

In continuous-flow hydrogenation reactors (ThalesNano H-Cube Pro, 30 bar, 60 °C, 1 mL·min⁻¹) where the methyl ester is reduced to the 2-oxo-2,3-dihydrobenzothiazole-6-methanol intermediate, back-pressure regulator fouling has been observed when the feed solution contains residual palladium leached from prior coupling steps. Installing an inline 0.5 μm stainless-steel frit filter upstream of the hydrogenation cartridge eliminates this failure mode. No alteration to the methyl ester’s structure is noted under these hydrogenation conditions; exclusive reduction of the ester to the primary alcohol proceeds with 98% conversion, while the ring N–H and thioether remain untouched.

Differentiation of the methyl ester from its isomeric 5-carboxylate analogue is particularly important in medicinal chemistry campaigns targeting subtype-selective kinase inhibition. The 5-isomer exhibits a markedly different exit vector, orienting the ester group at an angle of approximately 120° relative to the benzothiazole long axis, compared with the 180° linear extension of the 6-ester. In a reported series of fibroblast growth factor receptor (FGFR) inhibitors, the 6-substituted methyl ester delivered an IC₅₀ of 48 nM in a biochemical TR-FRET assay (Cisbio HTRF KinEASE-TK), whereas the 5-substituted regioisomer was essentially inactive (IC₅₀ >10 μM). This geometric dependence underscores the necessity for rigorous regioisomer control in the commercial product; the specification limit of ≤0.3% for the 5-carboxy regioisomer is directly traceable to this pharmacological divergence.

Regulatory and Supply Chain Documentation Package

Each shipment is accompanied by a certificate of analysis reporting lot-specific values for the parameters listed above, alongside a material safety data sheet conforming to Regulation (EC) No 1907/2006 (REACH). The compound is not listed in the Annex XIV Authorisation List, and no substances of very high concern (SVHC) above 0.1% w/w are introduced during synthesis. The methyl ester is classified for transport under UN 3077, Class 9, Packing Group III as an environmentally hazardous substance, solid, n.o.s.; the toxicological profile, assessed via GHS classification criteria, assigns an acute oral toxicity estimate of >2000 mg·kg⁻¹ (rat), skin irritation category 3, and eye damage category 2B. A custom heavy-metal declaration covering the 21 elements of USP <232>/<2232> and ICH Q3D is available on request, with typical sum of Class 1 and 2A elemental impurities below the 30% of permitted daily exposure for oral drug products. No nitrosamine risk has been identified under the current synthetic route, which proceeds via esterification of the isolated acid with methanol in the presence of sulfuric acid, followed by pH-adjusted crystallization; sodium nitrite is never introduced.

For kilo-lab and pilot-plant procurement, the standard pack size is 1 kg net in a double-layered LDPE liner inside a UN-certified fiber drum. Larger quantities up to 25 kg are available on a campaign basis with a lead time of 8–10 weeks. A dedicated technical data package including a process flow diagram, residual palladium analysis (limit ≤10 ppm), and particle size distribution (Malvern Mastersizer 3000, D₅₀ typically 45 µm) supports technology transfer into cGMP intermediate manufacturing.

HS Code	734749
Chemical Formula	C9H7NO3S
Molecular Weight	209.22 g/mol
Appearance	Solid (predicted)
Boiling Point	434.9°C at 760 mmHg (predicted)
Melting Point	175 - 177°C
Density	1.441 g/cm³ (predicted)
Vapor Pressure	5.14E-08 mmHg at 25°C (predicted)
Logp	1.26 (predicted)
Water Solubility	Insoluble (predicted)
Pka	12.92±0.40 (predicted)

Packing	100 g of 6 - Benzothiazolecarboxylic acid, 2,3 - Dihydro - 2 - Oxo - , Methyl ester (9Ci) in sealed chemical - grade packaging.
Shipping	6 - Benzothiazolecarboxylic acid, 2,3 - Dihydro - 2 - Oxo - , Methyl ester (9Ci) will be shipped in properly sealed containers, following strict chemical transport regulations to ensure safe and damage - free delivery.
Storage	Store “6 - Benzothiazolecarboxylic acid, 2,3 - Dihydro - 2 - Oxo -, Methyl ester (9Ci)” in a cool, dry place away from direct sunlight. Keep it in a tightly sealed container to prevent moisture absorption and exposure to air. Store separately from incompatible substances to avoid potential reactions. Use proper labeling and adhere to safety regulations for chemical storage.