2-Chloro-4,5-Difluoro-Benzothiazole

In the assembly of contemporary SDHI fungicides, 2-chloro-4,5-difluoro-benzothiazole functions as an electrophilic building block that introduces the 4,5-difluorobenzothiazole moiety into the molecular scaffold. Reaction with substituted anilines proceeds via nucleophilic aromatic substitution. Typical charge ratios employ 1.0 molar equivalent of the chlorobenzothiazole and 1.02–1.10 equivalents of the aniline partner to compensate for minor side reactions. Anhydrous potassium carbonate is dosed at 1.5–2.0 equivalents as the acid scavenger. The solvent system is N,N-dimethylacetamide or N-methyl-2-pyrrolidone, both dried over molecular sieves to ≤ 200 ppm water content to prevent hydrolysis of the chloro-substituent. Reaction temperature is maintained between 90 °C and 110 °C under a nitrogen pad, with HPLC monitoring indicating complete consumption of the starting benzothiazole typically within 8–12 hours. Work-up involves drowning into chilled deionized water, filtration of the crude product, and recrystallization from isopropanol/water mixtures to reach an HPLC purity above 98.5 % (area normalization, 254 nm). The resulting N-aryl-4,5-difluorobenzothiazol-2-amine intermediates have been disclosed in patent literature as components of experimental SDHI formulations targeting Rhizoctonia solani and Botrytis cinerea. Regulatory compliance for intermediates shipped across borders requires a full REACH registration dossier per Regulation (EC) No 1907/2006, including physicochemical data per Annex VII, an impurity profile with special attention to halogenated dioxins and benzotrichloride analogues, and a chemical safety report if annual tonnage exceeds 10 tonnes. End-use formulated products must adhere to FAO Specification Guidelines for agricultural pesticides, with a mandatory storage stability test at 54 ± 2 °C for 14 days per CIPAC MT 46.3.

Where Does 2-Chloro-4,5-Difluoro-Benzothiazole Fit in Modern Antitubercular Drug Candidates?

The chlorine atom at position 2 of the 4,5-difluorobenzothiazole core is susceptible to alkaline hydrolysis, furnishing 4,5-difluorobenzothiazol-2-one after ring-opening and re-cyclization sequences. This 2-keto-tautomer represents the pharmacologically active scaffold found in a cluster of benzothiazinone antitubercular agents targeting DprE1 in the cell wall synthesis pathway of Mycobacterium tuberculosis. Hydrolysis is conducted in aqueous sodium hydroxide (10% w/v) with tetrahydrofuran as co-solvent under reflux (65–70 °C) for 4–6 hours. The resulting thiazol-2-one precipitates upon acidification to pH 2–3 with hydrochloric acid. After vacuum drying at 60 °C, HPLC purity exceeded 99.2 % for batches produced under cGMP pilot-plant conditions. Subsequent alkylation or amination steps are performed in dimethyl sulfoxide using potassium carbonate and the respective electrophile to generate lead compounds. For pharmaceutical intermediate production, ICH Q7 guidelines on GMP for APIs are applied from the point at which the benzothiazole-2-one intermediate is introduced; all earlier steps are managed under appropriate quality controls. A mutagenic impurity risk assessment according to ICH M7(R1) is mandatory, with the nitrogen-purged process effectively eliminating residual chloro starting material whose alert structure would otherwise require a purge factor calculation. The acceptable intake for any identified mutagenic impurity is set to the threshold of toxicological concern of 1.5 µg/day. Published biological data for the resulting 4,5-difluoro derivative remains limited; however, preliminary MIC values against H37Rv in 7H9 broth were observed in the sub-micromolar range in early screening campaigns. The final drug candidate requires a full DMF submission supportive of clinical trial authorizations.

Vulcanization Accelerator Precursor: Conversion to 2-Mercapto-4,5-difluorobenzothiazole

2-Chloro-4,5-difluoro-benzothiazole is transformed into a specialized thiazole-based vulcanization accelerator through replacement of the chlorine by a sulfhydryl group. Treatment with sodium hydrosulfide hydrate (NaSH·xH₂O) in absolute ethanol at 45–55 °C for 3 hours yields 2-mercapto-4,5-difluorobenzothiazole (DFMBT) in isolated yields of 88–93 % after acidification and recrystallization from toluene. The fluorine atoms on the aromatic ring increase the acidity of the thiol proton (pKa near 6.8) compared to unsubstituted mercaptobenzothiazole (pKa 7.3), which accelerates the formation of the zinc-accelerator complex during vulcanization. DFMBT is further converted to a sulfenamide accelerator by oxidative condensation with tert-butylamine and sodium hypochlorite at 0–5 °C in aqueous isopropanol. The resulting N-tert-butyl-2-benzothiazole sulfenamide derivative (DFBS) is isolated as a pale-yellow crystal with a melting point of 108–112 °C. In a filled natural rubber compound (NR 100 phr, N330 carbon black 50 phr, zinc oxide 5 phr, stearic acid 2 phr, sulfur 2.5 phr), DFBS at 0.8 and 1.2 phr delivered a scorch time (t_s2) of 2.4 min and 1.9 min respectively at 150 °C per ASTM D5289-19a. The cure time (t₉₀) was reduced by 12 % relative to the standard N-t-butylbenzothiazole-2-sulfenamide (TBBS) control under identical mixing conditions, a behavior attributed to the electron-withdrawing fluorine substituents enhancing the nitrogen-sulfur bond lability. Extrusion processing on a cold-feed extruder (L/D 12:1) showed no die swell variation beyond ±8 % when barrel temperatures were set to 80–90 °C. Food-contact elastomer applications require an overall migration limit verification per EU Regulation No 10/2011 and specific migration testing for any benzothiazole degradation products using simulant D2 at 40 °C for 10 days. The accelerator falls under the scope of the German BfR Recommendation XXI for rubber commodities if used in repeated-use articles.

When Cooling Water Systems Demand Halogen-Substituted Corrosion Inhibitors

Addition of 50–200 mg/L 2-chloro-4,5-difluoro-benzothiazole to aerated 1.0 M HCl or 0.5 M H₂SO₄ solutions provides mixed-type corrosion inhibition for copper and copper alloys, with efficiency evaluated by weight-loss coupons following ASTM G1-03 and ASTM G31-72 at 30 °C and 50 °C. The planar benzothiazole ring adsorbs onto the metal surface through chemisorption involving π-electron donation and non-bonding electrons of the nitrogen and exocyclic sulfur (after partial hydrolysis). Electrochemical impedance spectroscopy data recorded on a Gamry Reference 600+ potentiostat with a frequency range of 100 kHz to 10 mHz gave a charge-transfer resistance increase from 0.8 kΩ·cm² in uninhibited acid to 8.6 kΩ·cm² at 100 mg/L dosage, translating to an inhibition efficiency of 90.7 %. The halogen substituents contribute to a higher dipole moment, strengthening the electrostatic interaction with the positively charged copper surface at pH below the potential of zero charge. Synergistic effects are observed when potassium iodide (0.5–2.0 mM) is co-dosed, improving coverage up to 97 % due to pre-adsorption of iodide ions. Field application in recirculating cooling water at a chemical processing plant required pre-dilution of the inhibitor in a 10 % glycol ether cosolvent to ensure homogeneous distribution; dosing was calibrated through a LMI Milton Roy B-series diaphragm metering pump at 0.5–1.2 L/h into the make-up water stream. Compatibility with oxidizing biocides such as chlorine gas must be verified because the thioether moiety can be oxidized to sulfoxide or sulfone, which reduces inhibiting performance. Residual inhibitor concentration is monitored by UV-Vis absorbance at 282 nm with a detection limit of 0.2 mg/L. Environmental discharge limits under the EU Industrial Emissions Directive (2010/75/EU) require ecotoxicity threshold testing; a Daphnia magna 48-h EC₅₀ value above 10 mg/L is targeted for classification as not acutely toxic to aquatic life. The chemical is typically supplied as a 95 % technical grade melt-solidified into flake form for ease of handling.

Electron-deficient benzothiazole rings bearing two fluorine atoms exhibit a LUMO energy level sufficiently low for electron-transport and hole-blocking functions in phosphorescent organic light-emitting diodes (PhOLEDs). 2-Chloro-4,5-difluoro-benzothiazole is elaborated into 2-aryl-4,5-difluorobenzothiazole derivatives through palladium-catalyzed Suzuki-Miyaura cross-coupling with aryl boronic acids or esters. The coupling employs tetrakis(triphenylphosphine)palladium(0) (1–2 mol %) and aqueous sodium carbonate (2.0 M) in a degassed mixture of toluene:ethanol:water (5:1:1 v/v/v) at 80–90 °C for 12–16 hours under argon. After silica gel chromatography and gradient sublimation at 10⁻⁶ Torr with a source temperature of 180–220 °C, the purified 2-phenyl-4,5-difluorobenzothiazole is obtained as white microcrystals with a purity exceeding 99.95 % by HPLC and a single organic impurity threshold below 0.01 %. Metallic residue specifications demand palladium below 1.0 ppm, iron below 0.5 ppm, and copper below 0.3 ppm, as measured by ICP-MS per SEMI C32-0314 guidelines. The sublimed material is co-evaporated with a host material such as BAlq or TPBi at a doping concentration of 5–20 wt % in a Kurt J. Lesker SPECTROS vacuum deposition system operating at 1×10⁻⁷ Torr. Device stacks fabricated with the compound as an electron-transport layer showed an operational voltage reduction of 0.4 V at 10 mA/cm² relative to a non-fluorinated analogue, attributed to improved electron mobility on the order of 2×10⁻⁴ cm²/V·s from space-charge-limited current measurements. The compound must satisfy RoHS 2011/65/EU and its amendment (EU) 2015/863 concerning restricted phthalates; laboratory certification of bromine-free and phthalate-free status is typically attached to the commercial technical data sheet. Because the OLED industry often requires small-lot validation runs, initial batches are packaged in 10 g amber vials under argon with a documented retest date of 12 months when stored at -20 °C.

A Route to High-Fastness Disperse Dyes on Polyester Substrates

Diazotization of appropriate aromatic amines in the presence of 2-chloro-4,5-difluoro-benzothiazole as a heterocyclic coupling component yields azo disperse dyes with improved lightfastness and sublimation fastness on polyester textiles. The benzothiazole ring system, when coupled with a diazonium salt from 2-cyano-4-nitroaniline or 2,6-dichloro-4-nitroaniline, produces a bathochromic shift of 30–50 nm compared to aniline-derived couplers. A representative dye synthesis: 0.05 mol of the benzothiazole coupling component is dissolved in 60 mL of glacial acetic acid/propionic acid (1:1) and cooled to 0–5 °C. The diazonium salt, pre-prepared from 0.051 mol of the amine in concentrated HCl and sodium nitrite at 0–2 °C, is added dropwise over 45 minutes while maintaining pH 3–4 with sodium acetate. Stirring continues for 3 hours at 0–5 °C and then for 2 hours at ambient temperature. The precipitated dye is filtered, washed with water until neutral, and oven-dried at 80 °C. The ground dye powder is standardized with a lignosulfonate-based dispersant to a strength of 200 % relative to a reference sample. Dyeing trials on polyethylene terephthalate (PET) woven fabric at a liquor ratio of 1:20 with 1.0 % owf dye at 130 °C for 60 min in a Mathis Labomat BFA-12 yielded level dyeings. Fastness testing according to ISO 105-B02:2014 (xenon arc) gave a lightfastness rating of 6–7 for the deep shade on polyester, markedly higher than the 4–5 rating of the non-fluorinated benzothiazole counterpart. Sublimation fastness per ISO 105-P01:1993 showed staining of adjacent multifiber fabric below grey scale 4 at 210 °C/30 s. Compliance with OEKO-TEX® Standard 100 appendix 4 certifies that the final dyed fabric meets limits for arylamines per EU 1907/2006 Annex XVII Entry 43, with no detectable 4-chloroaniline or 3,3′-dichlorobenzidine above 20 mg/kg. The dye intermediate itself is screened against the ZDHC Manufacturing Restricted Substances List (MRSL) v2.0, ensuring that the production process avoids solvents listed in group C and dioxin-forming precursors. Wastewater from the coupling step must be treated through activated carbon adsorption before discharge to meet ≥ 90 % color removal as required by Integrated Pollution Prevention and Control (IPPC) permits.