6-Amino-7-Bromobenzothiazole

In the multi-step synthesis of orally administered kinase inhibitors featuring a 2-arylbenzothiazole backbone, the purification and handling of 6-Amino-7-bromobenzothiazole must conform to ICH Q7 Good Manufacturing Practice for Active Pharmaceutical Ingredients and the requirements of 21 CFR 210/211. The compound is received as an off-white crystalline powder with a purity specification of ≥99.0% determined by HPLC (area%, detection at 254 nm) and a bromide content of 26.0–27.5% by potentiometric titration. For the pivotal Suzuki-Miyaura fragment coupling, the amine group is first protected. In a typical 500 L glass-lined reactor under nitrogen, the 6-Amino-7-bromobenzothiazole is dissolved in anhydrous THF (5–8 volumes) and treated with di-tert-butyl dicarbonate (1.08 eq) in the presence of 0.05 eq DMAP at 20–25°C for 6–8 hours to install a Boc protecting group. After aqueous work-up and crystallization from n-heptane/EtOAc, the Boc-protected intermediate is subjected to Pd-catalyzed coupling with an arylboronic acid pinacol ester using tetrakis(triphenylphosphine)palladium(0) at 0.8 mol% loading in a toluene/water biphasic system containing 2.0 eq K₂CO₃ at 80±2°C. The coupling proceeds with strict exclusion of oxygen to prevent catalyst deactivation; dissolved oxygen levels are maintained below 0.5 ppm by argon sparging. Following acid-mediated Boc deprotection (HCl in dioxane, 4.0 M, 3.0 eq) and neutralization, the crude API intermediate is crystallized from EtOH/water (70:30 v/v) to yield a polymorphically consistent material. The hydrochloride salt is then formulated into the final dosage form — typically an immediate-release tablet containing 50–200 mg of the benzothiazole-based active, embedded in a matrix of microcrystalline cellulose, croscarmellose sodium, and magnesium stearate. Compliance with ICH Q3D for elemental impurities is verified by ICP-MS per USP <232>/<233>, and residual palladium is controlled to <10 ppm. The final drug product is a potent ATP-competitive inhibitor targeting solid-tumor kinase mutations, for which the upstream intermediate’s batch-to-batch consistency and controlled regioisomeric purity (>99.5%) are critical to meeting specifications for dissolution (Q=80% in 30 min, USP Apparatus II, 50 rpm, pH 6.8 buffer).

Why is the 7-Bromo Substituent Critical for Wash Fastness in Polyester Dyeing?

The electron-withdrawing bromine atom at the 7-position of the benzothiazole ring significantly deepens the hue and enhances the dipole moment of the derived azo disperse dye, shifting the absorption maximum into the 570–610 nm region and boosting the dye’s substantivity for polyethylene terephthalate (PET) fibres during high-temperature exhaust dyeing. In the standardised synthesis pathway, 6-Amino-7-bromobenzothiazole is diazotised in 30% sulfuric acid using a 1.02 molar equivalent of sodium nitrite at 0–5°C, with the reaction endpoint monitored by starch-iodide paper and maintained for 2 hours to ensure complete conversion while avoiding nitrous acid decomposition. The resulting diazonium salt solution is clarified by filtration over a diatomaceous earth pad and then coupled with an N,N-dialkylaniline coupler (e.g., N,N-diethyl-m-toluidine) at a strict 1:1.00 molar ratio in an ice-water bath at 8–12°C, maintaining pH 4.8–5.2 through controlled addition of sodium acetate buffer. After coupling, the crude presscake is subjected to high-shear dispersion in a bead mill (Netzsch LMZ, 0.3 mm yttria-stabilised zirconia beads, 2000 rpm, residence time 45 min) in the presence of lignosulfonate dispersants (30–40 wt% on dry dye) until the particle size distribution reaches D₅₀ <0.8 µm and D₉₀ <1.5 µm as verified by laser diffraction. The milled dispersion is then spray-dried to produce a non-dusting granulate. For the dyer, the recommended application rate in exhaust dyeing of woven polyester is 1.0–3.0% o.w.f. at a liquor ratio of 1:10, holding at 130°C for 45–60 min in a high-temperature beam dyeing machine. The dyed fabric is subjected to reduction clearing with sodium dithionite (2 g/L) and NaOH at 70°C for 20 min to remove surface-deposited dye. The dye complies with the ZDHC Manufacturing Restricted Substances List V3.1, OEKO-TEX Standard 100 (Annex 4 limits for arylamines), and REACH Annex XVII (entries 43 and 72). The terminal product is a standardized blue disperse dye, typically supplied as a 200% or 300% strength powder, evaluated for key fastness using the test methods shown in the attribute matrix.

Incorporation of 6-Amino-7-bromobenzothiazole as an asymmetric, halogenated diamine monomer into aromatic polyimides yields films with a refractive index (n_TE) exceeding 1.72 at 633 nm and a birefringence below 0.008, making the polymer suitable as a planarisation layer in flexible organic light-emitting diode (OLED) stacks. The polymerization procedure demands absolute stoichiometric control: the diamine and a selected dianhydride (typically 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) or pyromellitic dianhydride (PMDA)) are dissolved in anhydrous N-methyl-2-pyrrolidone (NMP) at 15–20 wt% total solids, with the diamine:dianhydride molar ratio held at 1.000:0.995–1.000 to achieve a target inherent viscosity of 0.8–1.2 dL/g (0.5 g/dL in NMP, 30°C). The exothermic polyaddition is carried out in a jacketed reactor with thorough mechanical stirring, maintaining the internal temperature at 10–15°C for 6–8 hours under a dry nitrogen purge to prevent acylation side reactions. The resulting polyamic acid (PAA) solution is degassed under vacuum and cast onto a glass carrier plate using a slot-die coater with a lip gap of 350–400 µm; the wet film is sequentially heated to 80°C (30 min), 150°C (30 min), 250°C (60 min), and finally 300°C (30 min) under flowing nitrogen to complete thermal imidisation. The free-standing film exhibits a glass transition temperature (T_g) in the range 285–320°C as measured by DMA (ASTM D7028). The product is employed as a transparent flexible substrate or as a planarisation and passivation layer in roll-to-roll fabrication of active-matrix OLED displays. Regulatory compliance is demonstrated via RoHS 2011/65/EU verification on homogeneous materials, adherence to IPC 4203A for flexible base dielectrics, and UL 94 V-0 flame classification for the completed circuit substrate. Finished articles include foldable smartphone display films and high-temperature dielectric interlayers.

Safener-Precursor Engineering and Acetolactate Synthase Inhibition Pathways

Within the crop protection sector, the benzothiazole ring acts as a bioisostere for the widely exploited pyrimidine and triazine scaffolds in ALS-inhibiting herbicides, and the 6-amino-7-bromo substitution pattern allows for regio-selective functionalisation at the C2-position to tailor phytotoxicity. The starting material is reacted with methyl chloroformate (1.05 eq) in a biphasic mixture of dichloromethane and saturated aqueous NaHCO₃ at 0–10°C to form the corresponding methyl carbamate, which is isolated as a solid of >98.5% purity by GLC. This carbamate is subsequently treated with a substituted aniline in refluxing toluene in the presence of 0.1 eq 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as a catalyst to generate the target sulfonylurea herbicide precursor. The reaction mass is vacuum-stripped of solvent, and the product is triturated with isopropanol to remove unreacted aniline; the process delivers a typical yield of 82–88% over two steps. The technical-grade active ingredient is then formulated into a water-dispersible granule (WG) by blending with a wetting agent (alkylnaphthalene sulfonate, 3–5 wt%), a disintegrant (sodium bicarbonate), and a carrier (kaolin) before extrusion and spheronisation at 60°C inlet air temperature. The final product is a selective post-emergence herbicide for broadleaf weed control in cereal crops, applied at 15–45 g a.i./ha. Every shipment of the 6-Amino-7-bromobenzothiazole intermediate destined for an agrochemical use pattern must be accompanied by certification of compliance with the FAO specification for relevant impurities (water content <0.5%, sulphated ash <0.1%), US EPA 40 CFR Part 158 data requirements for product chemistry, and the European Regulation (EC) No 1107/2009 Annex II data points for the five-batch analysis. Analytical reference standards are cross-checked against CIPAC methods MT 18.1 and MT 46.3. During the development of the manufacturing process, particular attention is given to the containment of brominated dust and the monitoring of airborne concentrations to below the OEL of 0.1 mg/m³ (as total dust) per the supplier’s safety data sheet, in accordance with local occupational health provisions.

If the Diffusion Length Must Be Sub-45 nm, Bromobenzothiazole-Derived PAGs Offer a Pathway

For 193 nm immersion lithography at half-pitch nodes below 45 nm, the photoacid generator (PAG) must exhibit an exceptionally low diffusion coefficient inside the deprotected resist matrix to preserve acid latent image contrast. A novel class of non-ionic PAGs synthesised from 6-Amino-7-bromobenzothiazole takes advantage of the compound’s aromatic bromide for subsequent generation of a 7-sulfonate photoacid precursor through Ullmann-type coupling or aromatic nucleophilic substitution. In a typical PAG synthesis, the primary aromatic amine is diazotised with nitrous acid at -5 to 0°C and then treated with a perfluoroalkyl sulfonamide to yield a thermally stable diazosulfone. The isolated PAG is blended into a positive-tone 193 nm resist formulation at a solid weight loading of 5.0–12.0 wt% relative to the total polymer solids. The resist mixture consists of a methacrylate co-polymer bearing acid-labile adamantyl ester groups, the benzothiazole PAG, a secondary amine quencher (0.5–2.0 wt%), and propylene glycol methyl ether acetate (PGMEA) as the spin-casting solvent. The formulation is filtered through a 0.02 µm UPE membrane and applied on a 300 mm silicon wafer using a TEL CLEAN TRACK ACT 12 coater/developer system, with dynamic dispense at 1500 rpm to achieve a film thickness of 110±5 nm. Soft bake is carried out at 110°C for 90 seconds on a proximity hot plate, followed by exposure through an attenuated phase-shift mask on an ASML TWINSCAN NXT:1950i scanner at 193 nm, a numerical aperture of 1.35, and an exposure dose ranging 18–35 mJ/cm². After a post-exposure bake at 120°C for 60 seconds, the wafer is developed in 0.26 N tetramethylammonium hydroxide for 30 seconds and rinsed. The resulting resist patterns demonstrate a critical dimension of 38 nm dense lines with line-width roughness (LWR) below 3.5 nm (3σ). The composition adheres to SEMI C63 guidelines for resist quality, and halogen content is verified via combustion ion chromatography (IEC 62321) in support of the manufacturer’s REACH compliance obligations. The final product is a custom-developed 193 nm photoresist supplied in 1 L NOWPak canisters, validated for use in advanced logic foundry processes.

Modification at the 7-Position of the Benzothiazole Fluorophore Enables Ratiometric Hg²⁺ Detection

The inherent fluorescence of the benzothiazole chromophore is strongly modulated by the nature of the substituent at the 7-position, and 6-Amino-7-bromobenzothiazole serves as the key building block for constructing ratiometric Hg²⁺-selective probes through post-functionalisation with a xanthene-dye fragment. In the synthetic protocol, a DMF solution of the benzothiazole amine is treated with rhodamine B isothiocyanate or an activated rhodamine B carboxylic acid derivative at a molar ratio of 1:1.2 with 1.1 equivalents of HBTU as the coupling activator and 2.5 equivalents of N,N-diisopropylethylamine at ambient temperature for 12 hours. The crude conjugate is purified by silica gel flash chromatography (eluent CH₂Cl₂/MeOH 95:5), yielding a pale pink solid. A stock solution of the probe is prepared at 1.0 mM in DMSO, and working dilutions of 10 µM in HEPES-buffered aqueous acetonitrile (pH 7.2) are employed for spectroscopic titration. Upon incremental addition of Hg²⁺ (added as perchlorate salt, 0–1.5 equivalents), the emission maximum shifts from 480 nm to 585 nm due to Hg²⁺-promoted spirolactam ring-opening of the rhodamine moiety, enabling ratiometric quantification with a detection limit of 12 nM. The manufacturing process for the intermediate is conducted under the quality management system of ISO 9001:2015; final probe kits sold for environmental analysis must comply with the performance requirements of ISO 17378-2 for mercury determination in water and analogous US EPA method 245.1. Downstream processable formats include the impregnation of the probe into sol-gel derived ormosil thin films on glass slides, which are sealed into thermoplastic cartridges for use with a portable fluorescence photometer. The commercial product is a disposable mercury-sensing card containing four indicator spots, each coated with 5 µL of a 0.5 wt% PVC-membrane cocktail incorporating the benzothiazole-rhodamine conjugate and a plasticiser.