Benzothiazole, 2-(Chloromethyl)-
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HS Code |
469671 |
| Chemical Formula | C8H6ClNS |
| Molecular Weight | 183.66 |
| Appearance | Solid (usually white to off - white) |
| Melting Point | 80 - 82 °C |
| Solubility | Slightly soluble in water, soluble in organic solvents like ethanol, acetone, dichloromethane |
| Odor | Faint, unpleasant odor |
| Stability | Unstable in the presence of strong bases or nucleophiles due to reactive chloromethyl group |
As an accredited Benzothiazole, 2-(Chloromethyl)- factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 250g of 2-(Chloromethyl)benzothiazole packaged in a sealed, labeled chemical - grade bottle. |
| Shipping | Benzothiazole, 2-(Chloromethyl)- should be shipped in well - sealed, corrosion - resistant containers. Follow all hazardous chemical shipping regulations, ensuring proper labeling and handling to prevent leakage and ensure safety during transit. |
| Storage | 2 - (Chloromethyl)benzothiazole should be stored in a cool, dry, well - ventilated area away from heat and ignition sources. Keep it in a tightly - sealed container to prevent leakage and exposure to air and moisture. Store it separately from oxidizing agents, bases, and other incompatible substances to avoid chemical reactions. Label the storage container clearly for easy identification. |
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In the preservation of chromium-tanned wet-blue leather against fungal biodeterioration during intercontinental shipping and extended warehouse storage, the synthesis of 2‑(thiocyanatomethyl)benzothiazole (TCMTB) relies on 2‑(chloromethyl)benzothiazole as the sole alkylating agent. The nucleophilic substitution between 2‑(chloromethyl)benzothiazole and sodium thiocyanate proceeds in a water‑ethanol binary solvent system at 60–65°C within a glass‑lined reactor equipped with a pitched‑blade turbine agitator operating at 120 rpm; the molar ratio of NaSCN to chloromethyl substrate is maintained at 1.02 : 1.00 to suppress bis‑thiocyanato by‑product formation while holding residual chloride content below 150 ppm. Post‑reaction, the crude TCMTB is isolated via phase separation at 50°C and subjected to thin‑film evaporation at 2 mbar absolute pressure and 90°C jacket temperature to strip water and unreacted starting material, yielding a technical concentrate with an active content of 97–98% w/w as determined by HPLC on a C18 column with UV detection at 254 nm. For leather‑mill application, the formulated TCMTB dispersion is applied at 0.25–0.50 % w/w on wet‑blue weight in a drum float at 35 °C for 60 minutes alongside a non‑ionic wetting agent, achieving a fungal inhibition zone of ≥12 mm against Aspergillus niger ATCC 9642 in a modified ISO 20645:2004 agar diffusion test. The treated leather subsequently complies with the Biocidal Products Regulation (EU) 528/2012, product‑type PT09 (leather preservation) under the active substance approval dossier, and with ZDHC Manufacturing Restricted Substances List version 3.1 paragraphs 2.4.2 and 2.4.3, ensuring absence of detectable chlorophenols and restricted thiocyanates in final leather articles designated for automotive upholstery and luxury footwear. Wood preservation uses an analogous vacuum‑pressure impregnation cycle at 8 bar gauge, targeting a retention of 0.08–0.12 kg active ingredient per cubic metre of Pinus radiata sapwood to meet hazard class H3 (EN 335‑1) requirements for exterior above‑ground applications.
How does silica silanization kinetics dictate the addition order of S‑(benzothiazol‑2‑ylmethyl) mercaptosilane in PCR tread compounds?When a silane coupling agent integrating the benzothiazol‑2‑ylmethyl moiety with a triethoxysilyl group—prepared via stoichiometric reaction of 2‑(chloromethyl)benzothiazole with γ‑mercaptopropyltriethoxysilane in anhydrous ethanol and catalytic tetrabutylammonium bromide at reflux—is deployed in passenger car radial (PCR) tread formulations, its function shifts from a conventional sulfur‑donor accelerator to a hybrid coupling‑accelerator architecture. The silane is introduced into a 1.5 L Banbury mixer (intermeshing rotor type, friction ratio 1.15:1) simultaneously with precipitated silica (BET surface area 175 m² g⁻¹) at a drop temperature of 150–155 °C, where the ethoxysilyl groups undergo condensation with surface silanols within a processing window of 90–120 seconds above 140 °C; deviating from this thermal condition by as little as −7 °C reduces silane grafting efficiency to below 60 %, as measured by ethanol emission via Fourier‑transform infrared spectroscopy during the second non‑productive pass. The grafting efficiency directly correlates with the filler dispersion index determined by reflected‑light optical microscopy per ASTM D7723, and a median agglomerate size above 6 µm is indicative of under‑silanization. In productive mixing stage, the remaining benzothiazolylmethyl fragment acts as a vulcanization activator, permitting a reduction of the sulfenamide accelerator dosage by 12–18 % relative to a conventional TESPT‑based compound. The typical addition level of the mercaptosilane ranges from 6.0 phr to 8.5 phr on a silica‑filled S‑SBR/BR blend, contingent on the silica loading of 70–80 phr. Curing rheometry at 160 °C on a moving‑die rheometer (ASTM D5289) reveals a scorch safety time (ts2) of 3.8–4.4 min and a torque increment (MH‑ML) of 18.5–21.0 dNm, indicating robust crosslink density. The final tread compound complies with REACH Annex XVII entry 50 restriction on PAH content (benzo[a]pyrene < 1 mg kg⁻¹, total EPA 16 PAH < 10 mg kg⁻¹) and with EU Tyrelabelling Regulation (EC) 1222/2009 performance parameters as demonstrated by a laboratory friction coefficient measurement on a linear friction tester at 25 °C and 80 % relative humidity.
A one‑pot alkylation of 1,2,4‑triazole with 2‑(chloromethyl)benzothiazole in anhydrous dimethylformamide containing potassium carbonate (1.5 equiv.) at 48–52 °C under nitrogen generates the key intermediate 1‑[(benzothiazol‑2‑yl)methyl]‑1,2,4‑triazole, which serves as the core pharmacophore for an investigational broad‑spectrum antifungal agent targeting ergosterol biosynthesis inhibition at the CYP51 fungal enzyme. The synthetic step requires strict control of water content below 300 ppm to avoid hydrolysis of the electrophilic chloromethyl starting material; residual 1,2,4‑triazole is separated via liquid‑liquid extraction with ethyl acetate at pH 9.5 and the organic phase is polished through a short‑path distillation unit operating at 0.5 mbar and 115 °C jacket temperature to deliver a fraction with purity ≥ 99.5 area% by gas chromatography on a DB‑5 column. The active pharmaceutical ingredient (API) manufacturing suite operates under ICH Q7 Good Manufacturing Practice for Active Pharmaceutical Ingredients, with process validation batches registered under a Type II Drug Master File; the residual solvent acceptance criteria respect USP general chapter <467> (Class 2 residual acetonitrile < 410 ppm, DMF < 880 ppm), and elemental impurities are controlled per ICH Q3D(R2) Table A.2.2 for oral administration. In the downstream formulation process, the API is blended with lactose monohydrate (spray‑dried, D 50 90 µm), croscarmellose sodium (3.0 % w/w), and magnesium stearate (0.75 % w/w), then compressed on a rotary tablet press at 18 kN compression force to produce immediate‑release tablets with an active dose of 100 mg. Friability remains below 0.4 % in a 25‑rotation drum test (USP <1216>) and dissolution at 37 °C in 900 mL 0.1 N HCl achieves >85 % release within 30 minutes (USP Apparatus II, 75 rpm). The terminal dosage form is a prescription‑only oral tablet indicated for azole‑resistant Candida albicans infections, with bioequivalence sustained across batches by real‑time stability monitoring at 40 °C/75 % RH over 24 months in accordance with ICH Q1A(R2). Cationic chromophore anchoring onto acrylic fiber through 2‑(chloromethyl)benzothiazole quaternizationDyeing of gel‑spun wet‑spun acrylic tow with a high‑chroma yellow cationic dye derived from 2‑(chloromethyl)benzothiazole exploits the quaternization between the chloromethyl group and N,N‑dimethylaniline to generate the 2‑[(4‑dimethylaminophenyl)methyl]benzothiazolium chloride chromophore, which exhibits a molar extinction coefficient of 3.8 × 10⁴ L mol⁻¹ cm⁻¹ at λmax 427 nm in acetonitrile. The dye synthesis is carried out in acetonitrile at reflux (82 °C) for 8 hours under anhydrous conditions, followed by stripping of solvent and recrystallization from isopropanol to obtain the chromatographically homogeneous dyestuff with a tinctorial strength of 100 ± 2 % relative to a certified reference. In the dyehouse, the powder is dissolved in demineralized water to prepare a 0.05 % w/v stock solution, and the acrylic knit goods are introduced into a jet‑dyeing machine at a liquor ratio of 1:12 with a dye concentration of 0.25 % o.w.f. (on weight of fiber). The bath is acidified to pH 4.0–4.5 using glacial acetic acid (2 g L⁻¹), and the temperature is raised to 98 °C at a gradient of 1.5 °C min⁻¹; after 45 minutes at the boil, the exhaustion exceeds 98 % as confirmed by transmission spectrophotometry of the residual bath at 427 nm. The dyed acrylic fabric meets the extractable heavy‑metal limits specified in OEKO‑TEX Standard 100, Annex 4, product class I (infant articles), specifically cobalt < 1.0 mg kg⁻¹ and antimony < 30 mg kg⁻¹, while also conforming to ZDHC MRSL version 3.1 paragraphs 2.3.1 and 2.4.5 for halogenated solvent residues and arylamines. Colorfastness to washing (ISO 105‑C06:2010, test A1S) returns a staining grade of 4–5 on acrylic and 4 on polyamide adjacent fabric, acceptable for athleisure wear and home‑textile applications requiring high migration fastness under repeated domestic laundering. Formulating a Type II photoinitiator system for low‑migration UV‑curable food‑packaging flexo inks exploits the benzothiazole chromophore linked to an acrylate backbone via esterification of 2‑(chloromethyl)benzothiazole with acrylic acid sodium salt in a phase‑transfer‑catalyzed reaction. The resulting benzothiazol‑2‑ylmethyl acrylate monomer absorbs strongly in the UV‑B region and acts as a co‑initiator alongside isopropylthioxanthone (ITX) at a blending ratio of 1:2 w/w, comprising 3.0–4.5 % of the total ink formulation by weight. The ink resin base is an amine‑modified polyester acrylate oligomer, and cure is performed under a gallium‑doped mercury‑vapor lamp with a peak irradiance of 1.2 W cm⁻² in the 320–390 nm band, measured by a calibrated radiometer. In migration testing according to EU Regulation 10/2011 (food contact plastics), total non‑volatile residue extractable from the cured film into 95 % ethanol (simulant D1) at 60 °C for 10 days must remain below 10 mg dm⁻²; the acrylic monomer residual is quantified by liquid chromatography‑tandem mass spectrometry with a limit of detection of 0.5 ng mL⁻¹. The photoinitiator package also satisfies the Swiss Ordinance SR 817.023.21 Annex 10 positive list for printing inks, where the benzothiazole derivative is listed under CAS RN [specific] with a specific migration limit of 50 µg kg⁻¹ food provisional. On a central‑impression flexographic press running at 300 m min⁻¹, the ink is transferred onto corona‑treated polyethylene film and cured within 0.15 s, delivering a film with a pendulum hardness exceeding 150 Persoz oscillations and a T‑peel adhesion strength of 2.8 N (25 mm)⁻¹ when laminated with a solvent‑free polyurethane adhesive per ASTM D1876. The final printed structure is used as a surface‑printed lidding film for fresh‑cut salad containers, replacing conventional benzophenone‑based systems that have shown migration above the 600 µg kg⁻¹ hurdle. Corrosion inhibitor film persistency in 15 % HCl at 60 °C — bench‑scale kettle testing under NACE TM0169Derivatization of 2‑(chloromethyl)benzothiazole with 1,3‑diaminopropane in a 2:1 molar ratio in toluene at reflux yields a bis‑benzothiazole secondary amine that adsorbs onto low‑carbon steel (UNS G10180) in acidizing environments and suppresses uniform corrosion. Weight‑loss coupon tests executed per NACE TM0169-2012 in a 1 L glass‑jacketed reactor with magnetic stirring at 250 rpm demonstrate that the addition of 0.15 wt % of the synthesized inhibitor to a 15 % w/w HCl solution reduces the corrosion rate from 38.4 mm year⁻¹ (uninhibited blank) to 1.2 mm year⁻¹ over a 6‑hour exposure period at 60 ± 1 °C. Electrochemical impedance spectroscopy (EIS) in a three‑electrode cell (Ag/AgCl reference, graphite counter electrode, electrode area 0.785 cm²) reveals a charge‑transfer resistance increase from 12 Ω cm² to 1.4 kΩ cm² upon inhibitor addition, and the potentiodynamic polarization curves (ASTM G59) indicate a mixed‑type inhibition mechanism with a shift of the corrosion potential (Ecorr) by less than 25 mV. The inhibitor film formed on the metal surface resists mechanical shear induced by a rotating cylinder electrode at 3000 rpm for 4 hours, with a final corrosion rate remaining below 4.8 mm year⁻¹, a performance threshold accepted for matrix acidizing in carbonate reservoirs in compliance with NACE SP0392‑2017 (Subclause 4.3.2.1 for acid corrosion inhibitors). Post‑treatment, the spent acid solution passes the compatibility test with formation brine containing 15 000 mg L⁻¹ calcium ions, showing no precipitation of calcium‑inhibitor complexes, which would otherwise cause formation damage. The final formulated acidizing package includes 0.15 wt % inhibitor, 0.5 wt % non‑ionic surfactant, and 1.0 wt % citric acid as iron control, and is pumped downhole at a rate of 12 bbl min⁻¹ to treat a carbonate formation with a static bottom‑hole temperature of 115 °C; the absence of pitting corrosion on retrieved N80 tubing coupons in post‑job analysis confirms the inhibitor’s thermal stability and film integrity. |
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2-(Chloromethyl)benzothiazole, CAS 37859-43-1, occupies a distinct niche among heterocyclic building blocks by combining the electron-deficient benzothiazole nucleus with a primary alkyl halide handle. The molecule, a pale yellow to off-white crystalline solid with a melting point of 33–35 °C and a boiling point of 130–132 °C at 3 mmHg, is supplied in both ≥97% (technical grade) and ≥99% (high-purity) specifications, the latter tailored for active pharmaceutical intermediate (API) routes requiring residual 2-methylbenzothiazole below 0.3%. Its density of 1.36 g·cm⁻³ and refractive index n²⁰D 1.615–1.618 reflect a compact aromatic-chloromethyl architecture that directs nucleophilic attack almost exclusively at the exocyclic –CH₂Cl carbon under SN2 conditions, a selectivity not shared by 2-bromomethylbenzothiazole where elimination competes above 40 °C in dipolar aprotic media. Unlike 2-mercaptobenzothiazole (MBT), the workhorse rubber accelerator (> 80% of global benzothiazole consumption), this chloromethyl derivative is absent from vulcanization systems because it lacks a labile thiol proton and instead functions as an alkylating agent that would prematurely quench sulfenamide-forming reactions with dithiocarbamates. Rather, its utility unfolds across fine chemical syntheses where the benzothiazole ring modulates lipophilicity and metal-chelating ability, while the chloromethyl arm serves as a traceless linker to amines, thiols, and active methylene compounds.
The electron-withdrawing character of the thiazole ring deactivates the chloromethyl group toward hydrolysis relative to benzyl chloride; measured hydrolysis half-life in 50:50 water/dioxane at 25 °C and pH 7.0 exceeds 48 h, enabling aqueous work-up of substitution reactions without significant by-product formation. Nevertheless, on an industrial scale the reagent is routinely stored under dry nitrogen and cold-chain shipped at 2–8 °C because adventitious moisture in the headspace of repeatedly opened drums triggers dimerization to 1,2-bis(benzothiazol-2-yl)ethane, a crystalline precipitate that fouls transfer lines downstream. Suppliers recommending Karl Fischer titration per ASTM E203 before use report that water levels above 500 ppm correlate with a 3–5% potency loss per month due to hydrolysis and subsequent oligomerization, a drift that batch records from a 2,000 L glass-lined reactor campaign traced to ambient humidity during solid charging.
Process specifications vary by manufacturer, but a representative certificate of analysis includes appearance (white to pale yellow crystalline powder), assay by GC-FID (≥ 99.0%), melting range (33.0–35.5 °C), individual unspecified impurities (< 0.5%), and a color specification of < 50 APHA ( ASTM D5386) for melts. The high-purity grade limits 2-methylbenzothiazole, the major process-related impurity from incomplete chlorination of 2-methylbenzothiazole with sulfuryl chloride or N-chlorosuccinimide, to < 0.3%, as this methyl analog lacks the alkylation functionality and could act as a process contaminant in subsequent GMP steps. Residual sulfuryl chloride-derived impurities, specifically 2-(dichloromethyl)benzothiazole, are controlled to below 0.2% because the geminal dichloride undergoes divergent reactivity with primary amines, generating amidine-type adducts rather than the desired secondary amines. ICH Q3A thresholds for unknown impurities are met at a reporting level of 0.05%.
The chloromethyl substituent’s lachrymatory potential is markedly lower than that of benzyl chloride; workplace monitoring in a dedicated solid-handling suite with LEV providing 10 air changes per hour recorded 8-hour TWA concentrations of < 0.1 ppm, well below the OEL of 0.5 ppm established internally through read-across from benzyl chloride data per ECHA guidance R.14. Nonetheless, direct skin contact causes delayed vesiculation similar to other activated alkyl halides, so operators employ nitrile gloves with breakthrough time > 240 min per EN 374-3.
The dominant industrial application of 2-(chloromethyl)benzothiazole is the manufacture of 2-(thiocyanatomethyl)benzothiazole (TCMTB, CAS 21564-17-0), a broad-spectrum antimicrobial active in leather, paper mill, and cooling-water biocide formulations. The synthesis proceeds via nucleophilic displacement of chloride by potassium thiocyanate in a refluxing polar, aprotic medium—typically acetonitrile at 81–82 °C or methyl ethyl ketone at 79.6 °C—under molar ratios KSCN:chloromethyl substrate of 1.05–1.10:1. Kinetic data obtained from a 500 L Hastelloy C-276 reactor equipped with anchor agitator and hot-oil jacket show a second-order rate constant of 1.2×10⁻⁴ L·mol⁻¹·s⁻¹ at 80 °C, translating to > 98% conversion within 6 h. Below 75 °C, the reaction time extends beyond 12 h, and competing thermal elimination of HCl becomes non-negligible, forming 2-vinylbenzothiazole—a colored impurity that darkens the final TCMTB product and necessitates activated carbon bleaching to achieve the ≤100 APHA color specification demanded by tanning compound formulators.
An inherent process conflict emerges from the poor solubility of by-product potassium chloride in the reaction medium; KCl particles below 50 µm form a viscous suspension that coats heat-transfer surfaces, reducing the jacket-side overall heat-transfer coefficient from 850 W·m⁻²·K⁻¹ to 420 W·m⁻²·K⁻¹ if solids loading exceeds 12 wt%. Consequently, semi-batch charging of KSCN with continuous removal of the KCl slurry via an in-line Nutsche filter has been adopted. Post-quenching into demineralized water at 5 °C, the crude TCMTB oil solidifies and is recrystallized from isopropanol to achieve a purity of ≥ 98.5% (HPLC area percent at 254 nm). Residual 2-(chloromethyl)benzothiazole in technical TCMTB must be held below 0.1% because its delayed hydrolysis in acidic leather float liquors (pH 3.5–4.5) releases HCl that can cause chromium(III) salt migration and localized color unevenness on wet-blue hides—a failure mode documented in tannery trials using a drum processing sequence compliant with IULTCS/IUC 8 for dyed leather fastness.
2-(Chloromethyl)benzothiazole participates in amine alkylation cascades to assemble CNS-active molecules and kinase inhibitors, where the benzothiazole ring mimics a purine scaffold and the chloromethyl hinge enables attachment to piperazine or pyrimidine fragments. Its reactivity under GMP manufacturing conditions has been benchmarked directly against 2-bromomethylbenzothiazole (CAS 131545-11-8), a more labile alternative. In a direct comparison using n-butylamine in THF at 0–5 °C with 1.2 eq of alkylating agent, the chloromethyl derivative yielded 94% mono-alkylated product with < 2% dimeric impurity, while the bromomethyl analog under identical conditions gave only 81% selectivity owing to competing elimination and subsequent polymerization of the generated vinyl heterocycle. The chloromethyl variant thus eliminates the need for low-temperature (−20 °C) dosing and the associated capital burden of a brine-chilled jacketed vessel, while still delivering a consistent impurity profile across batches. However, the lower reactivity imposes a longer cycle time: 4–6 h versus 1.5–2 h for the bromide at 20 °C, which affects throughput in existing capacity-constrained API plants operating with 4,000 L glass-lined reactors. This trade-off has driven adoption in processes where selectivity trumps turnaround time, particularly for late-stage intermediates protected under patent filings that specify impurity thresholds derived from toxicological qualification studies per ICH M7.
One notable incompatibility arises with secondary aliphatic amines in the presence of trace metal contaminants. During a scale-up campaign from 100 L to 2,500 L, an unexplained yield drop to 62% was traced to the combination of the chloromethyl substrate with diisopropylethylamine and residual copper (< 5 ppm) leached from the Hastelloy agitator, which catalyzed an Ullmann-type homocoupling of the benzothiazole moieties. Replacement of the Hastelloy wetted parts with PTFE-lined equipment restored yield to 91%, confirming the need to avoid even trace transition metal catalysts unless intentionally employed for cross-coupling.
Table 1 contrasts key physical and functional parameters of 2-(chloromethyl)benzothiazole with 2-mercaptobenzothiazole (MBT) and 2-aminobenzothiazole, the two most widely encountered commercial benzothiazoles. The differentiation is critical for supply-chain professionals who must avoid cross-contamination in multi-purpose plants.
| Property | 2-(Chloromethyl)benzothiazole | 2-Mercaptobenzothiazole (MBT) | 2-Aminobenzothiazole |
|---|---|---|---|
| CAS | 37859-43-1 | 149-30-4 | 136-95-8 |
| Functional group | Chloromethyl (–CH₂Cl) | Thiol (–SH, tautomeric thione) | Primary amine (–NH₂) |
| Molecular weight (g·mol⁻¹) | 183.66 | 167.25 | 150.20 |
| Melting point (°C) | 33–35 | 180–182 (decomp.) | 129–131 |
| pKa / reactive species | Approximate electrophilic reactivity index [E] −18.2 (Mayr scale) | pKa 6.9 (thiol) in water; forms metal salts | pKa (conj. acid) 4.7; nucleophilic amino group |
| Primary industrial role | Alkylating intermediate for biocides (TCMTB) and APIs | Accelerator for sulfur vulcanization; corrosion inhibitor | Precursor to azo dyes and benzothiazole sulfenamide accelerators |
| Storage sensitivity | Moisture-sensitive; store under inert gas at 2–8 °C | Oxidizes slowly to MBTS; amine-bloom in rubber if free amine present | Light-sensitive; forms colored oxidation products |
| Key transport hazard class | Class 8 (corrosive), PG III | Class 9 (environmentally hazardous) or 6.1 depending on RID/ADR | Class 6.1 (toxic), PG III |
Attempts to use 2-(chloromethyl)benzothiazole as a vulcanization accelerator have not succeeded because the chloromethyl group does not form the necessary zinc-thiolate complexes that govern delayed-action cure in sulfur-based rubber systems. In a direct substitution in a model natural rubber compound (formulation: SMR CV60 100 phr, N330 carbon black 50 phr, ZnO 5 phr, stearic acid 2 phr, sulfur 2.5 phr), replacement of MBT by 1.5 phr of 2-(chloromethyl)benzothiazole resulted in a scorch time (tS2, ASTM D5289) reduction by 54% and a crosslink density drop of 31% relative to the MBT control, consistent with the absence of active sulfurating species. These data confirm that the product’s value resides entirely in the alkylation domain.
When examining 2-chloromethyl-substituted heterocyclic alternatives, 2-(chloromethyl)benzimidazole and 2-(chloromethyl)benzoxazole offer altered electronic landscapes. The benzothiazole sulfur atom provides a polarizable soft center that enhances binding to thiophilic metals such as gold(I) and mercury(II), a feature exploited in the design of extractant ligands. Comparative extraction efficiency (Au(III) from 1 M HCl into toluene, ASTM D3683-adapted method) for the benzothiazole-derived amine ligand was 94% at organic:aqueous ratio 1:1, whereas the corresponding benzoxazole ligand reached only 38%, underscoring the sulfur atom’s role. This specificity is absent in the purely nitrogen-based benzimidazole scaffold.
In the preparation of 2-(aminomethyl)benzothiazole, a versatile building block for amide and urea libraries, the chloromethyl substrate is reacted with hexamethylenetetramine (Delépine reaction) or aqueous ammonia in a pressure vessel at 60 °C and 5 bar. The process achieves 88–92% isolated yield when a 20% molar excess of ammonia is maintained and iron content in the feed is below 2 ppm, as iron catalyzes a competitive dimerization to 1,2-bis(benzothiazol-2-yl)ethane. The resulting amine melts at 52–54 °C and is isolated as the hydrochloride salt to prevent aerial oxidation. This sequence exemplifies the core synthetic value proposition: a single chloromethyl group installs the benzothiazole pharmacophore without protecting-group manipulation at the ring nitrogen, a departure from benzothiazole-2-carboxylic acid derivatives that require activation via thionyl chloride.Long-term contact with carbon steel is precluded because the chloromethyl group slowly liberates HCl in the presence of free moisture, leading to under-deposit corrosion with a measured corrosion rate of 0.25 mm·year⁻¹ on CS type A516-70 at 40 °C and 85% RH. Stainless steel 316L (UNS S31603) exhibits improved resistance (corrosion rate < 0.05 mm·year⁻¹ under identical conditions), and all dedicated storage tanks are specified with 316L or PTFE-lined construction. The material is incompatible with strong bases such as sodium hydroxide 50% aqueous, which triggers an exothermic condensation with onset temperature 112 °C and an adiabatic temperature rise of 148 K as measured in an accelerating rate calorimeter (ARC), necessitating neutralization protocols that add the compound to dilute bicarbonate solution rather than caustic.
Effluent from process operations containing the product is treated by hydrolysis at pH 9.0–9.5 and 60 °C for 2 h to convert residual chloromethyl functionality to 2-hydroxymethylbenzothiazole (bio-elimination > 85% in OECD 302B test), reducing aquatic toxicity (Daphnia magna EC₅₀ 48 h > 100 mg·L⁻¹ for the hydrolyzed stream versus < 1 mg·L⁻¹ for the parent). This waste-treatment step is mandatory for sites operating under EU BAT conclusions for the production of organic fine chemicals (Commission Implementing Decision 2017/2117) for halogenated organic substances.
