2-Amino-4,6-Difluorobenzothiazole

During process development of a third-generation EGFR tyrosine kinase inhibitor targeting exon 20 insertion mutations, the 2-amino-4,6-difluorobenzothiazole motif is introduced as a key hinge-binding scaffold via a palladium-catalysed Buchwald–Hartwig amination. The reaction is conducted in a 500 L glass-lined reactor equipped with a retreat-curve impeller and a nitrogen blanketing system; the coupling partner is a fully characterised chloropyrimidine intermediate with a water content below 0.05 % (KF). The critical starting material is charged at a molar ratio of 1.00–1.05 eq relative to the limiting aryl halide to suppress the formation of a des-fluoro dimer impurity that becomes detectable above 1.08 eq. Catalyst loading—Pd₂(dba)₃ at 1 mol% and Xantphos at 2 mol%—is optimised to balance turnover frequency against residual palladium carry-over. Post-reaction work-up incorporates a treatment with trimercaptotriazine-functionalised silica (Palladium scavenger) at 50–55 °C for 4 h, followed by filtration through a 0.45 µm PTFE cartridge and a two-stage vacuum distillation to swap the solvent into pharmaceutical-grade ethyl acetate. The crude product is crystallised from ethyl acetate/n-heptane (1:3 v/v) with a cooling ramp of 0.2 °C/min between 45 °C and –5 °C, yielding a polymorph that matches the reference pattern by XRPD. The isolated intermediate consistently meets a purity specification of ≥99.5 area% (HPLC, 210 nm) with a single unknown impurity ceiling of ≤0.10 %. Compliance is maintained against ICH Q7 (Sections 12.1 and 14.3) for GMP manufacture of APIs, ICH Q3D elemental impurity control (Pd PDE 100 µg/day; target <10 ppm in the isolated intermediate under a 10 g daily dose assumption), and ICH Q3C residual solvents, with ethyl acetate and n-heptane restricted to Class 3 limits. The final drug substance—a benzothiazole-pyrimidine inhibitor with a molecular weight near 580 Da—is processed into 25 mg and 50 mg film-coated tablets and is indicated for patients progressing on first-line osimertinib therapy.

Introducing the 2-amino-4,6-difluorobenzothiazole scaffold into the acid moiety of a pyrazole-4-carboxamide SDHI fungicide shifts the log P into a window that balances foliar uptake and phloem mobility. The amidation is executed in a 1,000 L Hastelloy C-22 reactor with jacket temperature control capable of maintaining the reaction mass at –5 to 0 °C during the addition of 2-chloronicotinoyl chloride. A molar ratio of benzothiazole amine to acyl chloride of 1:1.02 is employed; the slight excess of acyl chloride is quenched after completion by controlled addition to a chilled aqueous bicarbonate solution, minimising hydrolysis to the corresponding acid that could otherwise partition into the product phase. Triethylamine (1.05 eq) is used as a hydrochloride scavenger, and the reaction solvent is anhydrous tetrahydrofuran with a water content verified by Karl Fischer titration below 0.03 %. On a single manufacturing campaign, reactor fouling with a brown gummy reside was traced to localised overheating when the jacket setpoint was inadvertently raised above 2 °C before the end of addition, necessitating a controlled addition time of not less than 90 minutes. The isolated product is crystallised from methanol/water (70:30 v/v), dried in a double-cone vacuum dryer at 45 °C (50 mbar), and milled to a volume-median particle size (D_v50) of 8–15 µm. Regulatory alignment is achieved through compliance with FAO Specification 503/TC (active ingredient purity ≥98 %), CIPAC Handbook M methods for physicochemical characterisation, and monitoring of ICH Q3C-listed solvents, with methanol kept below 3,000 ppm. The 2-amino-4,6-difluorobenzothiazole content in the finished technical concentrate formulation is 950 g/kg (minimum), and the product is registered for the control of Zymoseptoria tritici in winter wheat at an application rate of 125 g ai/ha.

High-contrast vertical alignment (VA) liquid crystal mixtures demand dielectric anisotropy values exceeding 8.5, a target frequently addressed by terminal 4,6-difluorobenzothiazole moieties because the fluorine substitution pattern depresses the dipole component perpendicular to the molecular long axis while boosting the parallel component. The precursor monomer is constructed via a Suzuki–Miyaura cross-coupling between a 2-amino-4,6-difluorobenzothiazole-derived boronic ester and a laterally substituted bromo-biphenyl core. Following optimisation of the palladium catalyst cycle—using Pd(OAc)₂ with SPhos at 0.5 mol% under reflux in a toluene/ethanol/water ternary system—the crude monomer is purified by flash chromatography over silica gel (elution with 98:2 petroleum ether/ethyl acetate) and recrystallised twice from absolute ethanol to achieve an individual impurity ceiling of ≤0.05 % by GC. The purified monomer is then blended into a multi-component liquid crystal host at a concentration of 12–25 wt%, depending on the required birefringence (Δn target 0.102–0.115) and clearing point (T_NI > 75 °C). Formulation is carried out in an ISO 14644-1 Class 5 cleanroom; the mixture is homogenised under a dry nitrogen blanket at 80 °C for 3 h, passed through an alumina column to strip residual chloride and sodium ions, and filtered through a 0.2 µm PTFE membrane. The filled test cell must deliver a voltage holding ratio (VHR) of ≥99.5 % at 60 °C and 1 V, measured in accordance with IEC 61747-2-2; any batch failing to meet this threshold is reworked through a secondary ion-exchange adsorbent treatment. Individual metal ion concentrations—Na, K, Ca, Mg—are monitored by ICP-MS and held below 1 ppm for each species, while total chloride is below 1 ppm. The final negative-type mixed liquid crystal is encapsulated in fused-silica cells with a cell gap of 3.2 µm and deployed in 55-inch and 65-inch ultra-high-definition television panels utilising an IPS-Pro architecture.

Navigating Halogen Content Pass/Fail in Dichroic Dye Intermediates for Automotive Displays

Meeting stringent automotive OEM requirements begins with the selection of a halogen-controlled intermediate, because even trace levels of extractable organohalogens can elevate the volatile organic compound (VOC) profile above the thresholds defined in VDA 278. 2-Amino-4,6-difluorobenzothiazole is diazotised in a stirred tank with jacket control at 0–5 °C using sodium nitrite (1.02 eq) in 30 % aqueous hydrochloric acid, and the resulting diazonium salt is coupled with N,N-diethylaniline at a molar ratio of 1:1.05 in a pH 4.0–4.5 acetate-buffered medium. The low pH window is critical; excursions above 4.8 promote the formation of a triazene by-product that co-crystallises with the target azo dye and shifts the hue angle by 3–5°. The presscake is washed with demineralised water at 60 °C until the filtrate conductivity falls below 50 µS/cm, vacuum-dried at 70 °C, and micronised to a D₉₀ below 5 µm. The final dispersed dye formulation contains 40 wt% of the pure dye, with the benzothiazole-based chromophore imparting a bluish-red shade on polyester. Compliance with OEKO-TEX Standard 100 (Annex 4, limit 20 mg/kg per prohibited aromatic amine) and REACH Annex XVII Entry 43 (azo dye cleavage limit 30 mg/kg) is verified by EN 14362-1:2017 extraction, while total halogen content analysed by combustion ion chromatography is maintained below 150 ppm for chlorine and 50 ppm for bromine, as required by a major European vehicle manufacturer’s material specification. The exhaust dyeing process for polyester seat fabric is conducted in a high-temperature jet-dyeing machine at 130 °C for 45 minutes, achieving a build-up of 1.2 % owf to meet the desired deep shade for a luxury SUV interior.

A narrow-bandgap non-fullerene acceptor (NFA) with an A-DAD-A architecture requires terminal electron-withdrawing groups that combine deep lowest unoccupied molecular orbital (LUMO) levels with adequate solubility in non-halogenated processing solvents. The fluorinated benzothiazole-2-amine serves as a precursor to an end-cap unit after conversion to a 2-(2-oxoindolin-3-ylidene)benzothiazole moiety through a Knoevenagel condensation pathway. In the synthesis of a Y-series analogue, the benzothiazole-derivative end-cap is condensed with a 2,5-diformyl-thienothiophene-based central core in a chloroform/pyridine mixture under reflux for 12 h; the stoichiometric ratio of end-cap to dialdehyde core is held at 2.2:1 to drive full conversion and avoid mono-adduct impurities that act as charge-trapping sites. The crude product is precipitated from methanol, collected by centrifugation, and purified by gradient silica-gel chromatography (chloroform followed by 95:5 chloroform/ethyl acetate). After vacuum drying at 60 °C for 24 h, the acceptor material exhibits a decomposition temperature (T_d, 5 % weight loss) above 320 °C by TGA. Device fabrication in an inverted architecture (ITO/ZnO/PM6:acceptor/MoO₃/Ag) yields a power conversion efficiency of 16.2 % with a certified value referenced to an NREL-calibrated silicon photodiode; storage stability under ISOS-L-1 (shelf life in dark, ambient atmosphere) shows less than 5 % degradation after 1,000 h. To meet electronic-grade requirements, the material is subjected to an additional Soxhlet extraction with methanol and acetone, reducing palladium content to <5 ppm (ICP-MS) and total halides below 50 ppm. The product is shipped in amber glass vials sealed under argon and is intended for the fabrication of solution-processed bulk-heterojunction solar modules.

If Sublimation Purity Falls Below 99.995%: Impact on Electron Mobility in Phosphorescent OLEDs

Charge transport layers in phosphorescent organic light-emitting diodes suffer an exponential drop in electron mobility when deep traps originating from alkali metal impurities (Na, K) exceed a concentration of approximately 1 ppb, a failure mode rarely flagged by routine HPLC analysis that may report only 99.5 % purity while masking nanogram-level ionic contaminants. The synthesis of a benzothiazole-based electron-transport material (ETM) begins with a Suzuki coupling between a 2-amino-4,6-difluorobenzothiazole-derived pinacol boronate and a brominated terphenyl core at a molar ratio of 1:2.2, catalysed by Pd(PPh₃)₄ (0.8 mol%) in refluxing toluene/aqueous K₂CO₃ under strictly oxygen-free conditions. The organic phase is washed with 0.05 M EDTA disodium salt solution (three cycles at 60 °C) to sequester ionic palladium residues, followed by activated carbon treatment and passage through a silica plug. Crucial to achieving semiconductor-grade purity is a two-cycle gradient sublimation in a horizontal quartz tube furnace: the first pass at 250–260 °C under a vacuum of 1×10⁻⁶ Torr removes volatile precursors, and the second pass at 280 °C with a temperature gradient of 2 °C/min across a 15 cm hot zone isolates the purest fraction. At the midpoint of the second sublimation, the collected material exhibits a HPLC purity exceeding 99.99 % (evaporative light scattering detection) and a sodium content of 0.3 ppb by high-resolution ICP-MS, which correlates with an electron mobility of 3.2×10⁻⁴ cm²/V·s at an electric field of 6×10⁵ V/cm measured by the time-of-flight method. The refined ETM is co-evaporated with a host and an emitter under a chamber base pressure of 5×10⁻⁷ Torr to construct a red-emitting phosphorescent device; any deviation of the sublimation cut that introduces material with 0.25 ppb sodium rapidly degrades the external quantum efficiency (EQE) by more than 15 % relative to the pristine batch. The facility maintains a quality management system aligned with SEMI C43 guidelines for electronic chemicals, and each lot is supplied with a certificate of analysis quantifying 17 elemental impurities by ICP-MS, residual palladium (<0.5 ppm), and HPLC purity at two wavelengths (254 nm and 350 nm).

Published data for the dielectric permittivity gradient as a function of benzothiazole monomer weight fraction in a specific 15-component VA mixture is limited; however, internal development runs on a 55-inch pilot line indicate that increasing the content of the fluorinated monomer from 12 wt% to 25 wt% extends the driving voltage margin by 0.4 V at –20 °C while raising rotational viscosity (γ₁) by approximately 18 %, requiring compensation in the column spacer design to maintain a fall time below 8 ms.