2,4-Dibromo-5-(Hydroxymethyl)Thiazole
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HS Code |
892726 |
| Chemical Formula | C4H3Br2NOS |
| Molar Mass | 272.949 g/mol |
As an accredited 2,4-Dibromo-5-(Hydroxymethyl)Thiazole factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 100g of 2,4 - Dibromo - 5 - (Hydroxymethyl)Thiazole packaged in a sealed, chemical - resistant vial. |
| Shipping | 2,4 - Dibromo - 5 - (Hydroxymethyl)Thiazole is shipped in well - sealed containers, often within a climate - controlled environment to maintain stability. Special handling precautions are taken due to its chemical nature to ensure safe transit. |
| Storage | 2,4 - Dibromo - 5 - (Hydroxymethyl)Thiazole should be stored in a cool, dry, well - ventilated area. Keep it away from heat sources, flames, and oxidizing agents. Store in a tightly closed container to prevent moisture absorption and potential reaction with air components. It's advisable to store it in a dedicated chemical storage facility following safety regulations. |
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2,4-Dibromo-5-(hydroxymethyl)thiazole (CAS 1020828-24-9) functions as a dense, polyhalogenated heterocyclic building block. The presence of two bromine atoms in the 2- and 4-positions, together with a primary hydroxyl group at the 5-position of the thiazole ring, enables divergent reactivity pathways that are exploited across distinct downstream chemistries. The compound exhibits a molecular weight of 288.93 g·mol⁻¹ and a calculated logP of approximately 1.8, necessitating specific solvent strategies during workup. In every application described below, handling requires strict moisture exclusion; the hydroxymethyl group is prone to autocatalytic oligomerization at temperatures exceeding 40°C in the absence of a radical inhibitor such as BHT at 50–200 ppm. Succinate Dehydrogenase Inhibitor Backbone Construction and Scale-Up ConstraintsWithin the agrochemical sector, 2,4-dibromo-5-(hydroxymethyl)thiazole serves as the penultimate intermediate for a class of carboxamide fungicides targeting succinate dehydrogenase (SDHI). The key transformation involves the oxidation of the hydroxymethyl group to the corresponding carboxylic acid, 2,4-dibromothiazole-5-carboxylic acid, which is subsequently coupled with an aniline fragment to yield the active ingredient. Published batch records from pilot-plant campaigns indicate that the oxidation step is the primary bottleneck. Sodium chlorite-based TEMPO-catalyzed protocols in acetonitrile/water (3:1 v/v) offer a conversion exceeding 97% (HPLC area-%, λ = 254 nm), yet the exothermic profile is severe: a 15°C adiabatic temperature rise is observed upon catalyst addition. On a 2000 L glass-lined reactor, dosing must be controlled to maintain an internal temperature below 5°C using a brine jacket set to −10°C; excursions above 12°C result in dibromo ring-opening impurities detected at levels of 0.8–1.5%. The subsequent amide coupling via acid chloride generation—using thionyl chloride in toluene at 65°C—demands rigorous removal of SO₂ and HCl prior to reaction with the amine partner to avoid salt formation that clogs in-line filters. Material of construction for all wetted parts downstream of the acid chloride stage must be PTFE-lined carbon steel or Hastelloy C-22; 316L stainless steel undergoes pitting corrosion at rates exceeding 0.4 mm/year when exposed to trace hydrogen bromide liberated during handling. The final SDHI active substance is registered under multiple jurisdictions with compliance to FAO specifications; residual solvents (acetonitrile, toluene) are controlled to ≤50 ppm each as per ICH Q3C guidelines, and the specification for 2,4-dibromo-5-(hydroxymethyl)thiazole supplied to this route requires an assay of ≥98.5% (argentometric titration) with a single unknown impurity ≤ 0.3%. Within the photoinitiator segment of radiation-curable coatings, the 2,4-dibromo substitution pattern adjacent to a reactive hydroxymethyl tether offers a pathway to Type I cleavage photoinitiators with redshifted absorption. The synthetic sequence begins with the Williamson etherification of the hydroxyl group with epichlorohydrin under phase-transfer conditions (tetrabutylammonium hydrogen sulfate, 5 mol%, in toluene / 50% aqueous NaOH, 25°C, 8 h), generating the glycidyl ether derivative with an epoxide equivalent weight of 325–340 g/eq. This intermediate is then subjected to regioselective nucleophilic ring-opening with morpholine at 60°C in isopropanol, yielding a β-aminoalcohol chromophore. Real-time FTIR monitoring of the epoxide band at 910 cm⁻¹ defines the reaction endpoint. The resulting α-aminoketone-type photoinitiator exhibits a λmax of 342 nm (acetonitrile) with a molar extinction coefficient of 1.8×10⁴ L·mol⁻¹·cm⁻¹, a 15 nm bathochromic shift relative to the non-brominated thiazole analog. In clearcoat formulations based on bisphenol-A epoxy diacrylate oligomers blended with trimethylolpropane triacrylate (TMPTA, 30 wt%), addition of the photoinitiator at 2.0–2.5 wt% achieves surface cure (tack-free time) under a 395 nm LED array (intensity 2 W/cm²) in 1.2 seconds. Migration stability assessed per EU Commission Regulation (EU) No. 10/2011, Annex V, using Tenax as a dry food simulant ( 10 days, 40°C) yields a specific migration limit below 0.01 mg/kg, primarily due to the steric congestion from the dihalogenated thiazole ring retarding molecular mobility in the crosslinked matrix. A documented process limitation arises in formulations containing secondary amines: premature Michael addition of the amine to the acrylate diluent is catalyzed by trace hydrobromic acid generated from photolytic debromination during extended storage under ambient fluorescent lighting, leading to viscosity increases of >200% within 48 hours. Mitigation requires the addition of a hindered amine light stabilizer (HALS) at 0.5 wt% and opaque packaging. Why Brominated Thiazoles Dominate Suzuki Coupling in Late-Stage Pharmaceutical FunctionalizationThe ortho-dibromo arrangement on the thiazole renders the 4-position bromine uniquely labile under palladium-catalyzed cross-coupling conditions, enabling iterative, chemoselective C–C bond formation. In the discovery synthesis of a class of kinase inhibitors, 2,4-dibromo-5-(hydroxymethyl)thiazole was subjected to a Pd(PPh₃)₄-catalyzed (2 mol%) Suzuki-Miyaura coupling with arylboronic acids. Competition experiments confirmed that the C4–Br bond undergoes oxidative addition with a rate constant at 60°C in THF/water (4:1) that is 12.5-fold higher than that of the C2–Br bond, as determined by quenching the reaction at low conversion (<10%) and analyzing fragment ratios via LC-MS. This kinetic differentiation permits the sequential introduction of two (hetero)aryl groups without a protecting group maneuver at the hydroxymethyl site. For the first coupling, a base screen revealed that K₂CO₃ (twice equivalent) gives > 90% conversion to the 4-aryl-2-bromo-5-hydroxymethylthiazole with <5% diarylated impurity, whereas the use of Cs₂CO₃ erodes selectivity by accelerating oxidative addition at the C2 position. Following purification by normal-phase chromatography (ethyl acetate/heptane gradient, loaded in dichloromethane), the second coupling at the C2 position typically requires the more active catalyst/ligand pair Pd(OAc)₂/10 mol% XPhos with Cs₂CO₃ in refluxing 1,4-dioxane (100°C, 16 h) to overcome steric hindrance from the installed aryl group. The hydroxymethyl handle remains intact throughout both steps but must be protected when the subsequent medicinal chemistry sequence involves Grignard or organolithium reagents; TBSCl protection ( 1.2 eq, imidazole, DMF, 25°C, 3 h) is quantitative. Production-scale implementation on a 50 kg batch of intermediate encountered an oxygen sensitivity threshold: dissolved oxygen in the solvent/water mixture above 1.5 ppm (measured by a Hamilton VisiFerm DO sensor) causes palladium black precipitation within the first two turnovers, halting the reaction at approximately 40% conversion. Nitrogen sparging to <0.3 ppm dissolved O₂ was implemented as a mandatory process analytical technology (PAT) trigger before catalyst introduction. The final APIs derived from this intermediate must meet the ICH M7 guideline for mutagenic impurities: the 2,4-dibromo precursor is classified as a Class 3 impurity with a permitted daily exposure (PDE) of 500 µg/day, and its purge factor across the downstream sequence has been validated using an in silico DEREK Nexus assessment in addition to spiking studies at 1%. Reactive Flame Retardant for Condensation Polymers and the Problem of Hydrolytic InstabilityAn underrecognized but technically demanding application of 2,4-dibromo-5-(hydroxymethyl)thiazole lies in the synthesis of brominated diol monomers for inherently flame-retardant polyesters and polyurethanes. The hydroxymethyl group is chain-extended with ethylene carbonate in the presence of potassium acetate (0.5 wt%) at 140°C to furnish the ethoxylated diol, 2,4-dibromo-5-(2-hydroxyethoxymethyl)thiazole, with a bromine content of 55.2 wt%. This diol can replace up to 15 mol% of 1,4-butanediol in the melt polycondensation of polybutylene terephthalate (PBT) with dimethyl terephthalate (DMT) at 250–260°C under vacuum (<1 mbar). The incorporation rate into the polymer backbone, measured by ¹H NMR end-group analysis of the isolated polyester, reaches 82–88% due to the slight reduction in nucleophilicity of the hydroxyethyl group caused by the electron-withdrawing thiazole ring. The limiting oxygen index (LOI) of the modified PBT increases from 20.5% to 27.5% (ISO 4589-2:2017), and the UL-94 vertical burn test achieves a V-0 rating at 3.2 mm thickness without dripping. However, a critical failure mode emerges during prolonged melt processing: at residence times exceeding 12 minutes in the twin-screw extruder (Coperion ZSK, L/D = 44) at 260°C, hydrolytic cleavage of the thiazole ring releases HBr, which catalyzes reprocessing-induced degradation of the ester backbone. The intrinsic viscosity drops from 0.85 dL/g to 0.58 dL/g over this time window. Compounding with 1.0 wt% of a tin-based thermal stabilizer (butyltin mercaptide) and 0.5 wt% of an acid scavenger (zinc stearate) extends the processing window to 20 minutes. For polyurethane flexible foam formulations, the reactive diol is introduced into the B-side polyol blend. When used at 12 php with a toluene diisocyanate (TDI, 80/20 isomer ratio) system at an index of 110, the foam passes California Technical Bulletin 117, Section E (smoldering cigarette test). The restriction here is that the foam must be post-cured at 120°C for 2 hours immediately after demolding to drive off residual water that otherwise concentrates at the urea hard domains and generates acidic microenvironments detectable via pH indicator-impregnated foam scans (localized pH readings <3.5 after 24 hours of ambient aging). REACH compliance requires a completed Annex VII chemical safety report that specifically addresses the abiotic hydrolysis half-life of the thiazole ring at pH 4, 7, and 9; published data indicates half-lives of 7.2 days, 34 days, and 4.8 hours, respectively, at 25°C. The use of 2,4-dibromo-5-(hydroxymethyl)thiazole as a precursor to heterocyclic chelating ligands for d-block metals has been validated in the industrial extraction of platinum group metals (PGMs) from spent automotive catalysts. The synthetic pathway exploits the hydroxymethyl group as a tether for polyamine backbones via a Mitsunobu reaction with phthalimide followed by hydrazinolysis, yielding the corresponding aminomethyl derivative. This primary amine is then alkylated with 2-chloromethylpyridine derivatives under phase-transfer conditions to install a tridentate N,N,N-donor set. The bromine atoms on the thiazole ring are inert under these conditions but contribute to the ligand's solubility profile in organic diluents. In a liquid-liquid extraction circuit operating at a sulfate concentration of 0.5 M, pH 1.8, and an organic phase composed of 15 vol% ligand in Exxsol D80, the compound extracts Pd(II) with a distribution coefficient (DPd) of 3.5×10³ at an aqueous-to-organic phase ratio of 5:1, while the co-extraction of Fe(III) is suppressed below 2% by the stereo-electronic influence of the electron-deficient thiazole ring. Stripping is achieved with 0.1 M thiourea in 0.5 M HCl, and the ligand remains stable for over 50 extraction-strip cycles as verified by ¹H and ¹³C NMR monitoring of the organic phase. A known operational boundary is that the ligand must be pre-equilibrated with the aqueous phase for 30 minutes prior to contact with the PGM-bearing leach solution; direct contact leads to rapid precipitation of a palladium-ligand adduct of low solubility that fouls the settler interface and reduces mass-transfer efficiency to less than 60% of the design value. The extraction is carried out in mixer-settler units with a residence time of 3 minutes per stage; materials of construction for the organic loop are limited to stainless steel 304L, as the brominated thiazole slowly plasticizes PTFE gaskets, causing swelling and leakage after approximately 3000 operating hours. |
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Introduced into medicinal chemistry workflows primarily as a difunctionalized thiazole scaffold, 2,4-Dibromo-5-(hydroxymethyl)thiazole (CAS 131337-81-4, molecular formula C4H3Br2NOS, molecular weight 272.95 g·mol−1) enables divergent synthetic routes through its three reactive centers. The 5-hydroxymethyl group functions as a latent electrophile after conversion to the corresponding halomethyl or sulfonate ester, while the 2- and 4-position bromine atoms exhibit markedly different reactivities in palladium-catalyzed cross-coupling reactions. Typical commercial material is supplied as an off-white to pale yellow crystalline solid with an HPLC purity specification of ≥ 97.0% (area%, detection at 254 nm). On differential scanning calorimetry, the endothermic melting peak falls between 78 °C and 83 °C (heating rate 10 K·min−1, sealed aluminum pan). A representative certificate of analysis further reports water content by Karl Fischer titration ≤ 0.5% and residual toluene or acetonitrile below 0.1% as per ICH Q3C Option 2 limits for Class 2 solvents. The compound is stored at 2–8 °C under an inert atmosphere; prolonged exposure to ambient humidity raises the water content beyond the specification threshold within 48 hours, necessitating reparative drying over phosphorus pentoxide under vacuum (10 mbar, 40 °C, 24 hours) before use in anhydrous couplings.
Supply chain documentation routinely accompanies the product with a model designation that encodes the bromine substitution pattern: among suppliers, the identifier DBHMT-24 or TH-24BrOH distinguishes it from monobromo regioisomers such as 2-bromo-5-(hydroxymethyl)thiazole or 4-bromo-5-(hydroxymethyl)thiazole. These model codes are not governed by an international standard but are used consistently in procurement specifications that cross-reference CAS numbers and IUPAC name to prevent mis-shipment. The compound falls under Harmonized System code 2934.99 (heterocyclic compounds containing a thiazole ring) for customs purposes, and its transportation classification is UN 3077 (Environmentally hazardous substance, solid, n.o.s., Class 9, Packing Group III) when shipped in quantities exceeding 5 kg, per IMDG Code Amdt 41-22.
In the construction of 2,4,5-trisubstituted thiazoles via sequential cross-coupling, the relative lability of the 2-bromine versus the 4-bromine dominates reaction planning. Frontier molecular orbital analysis and experimental Hammett studies place the LUMO coefficient at C-2 approximately 2.3 times larger than at C-4, making the 2-position the default site for oxidative addition with Pd(0) catalysts. Thus, when 2,4-dibromo-5-(hydroxymethyl)thiazole is subjected to Suzuki-Miyaura coupling with phenylboronic acid using Pd(PPh3)4 (2 mol%) and K2CO3 in dioxane/water at 80 °C, the 2-arylated product forms with > 85% regioselectivity as confirmed by 1H NMR chemical shift differentiation at H-4. The remaining 4-bromine can subsequently engage in a second cross-coupling under forced conditions, typically with Buchwald-type ligands (XPhos, 5 mol%) and higher temperature (110 °C). However, side reactions during the second step are documented: protodebromination at C-4 occurs in protic solvent systems when water content exceeds 10% v/v, lowering isolated yields by 15–25%. Process development reports therefore recommend pre-drying the organic phase with 3Å molecular sieves (20 wt% of substrate) before catalyst addition.
By contrast, 2-bromo-5-(hydroxymethyl)thiazole (CAS 141854-13-4) lacks the 4-bromine, forcing a linear synthesis that requires protection/deprotection of the hydroxymethyl group if two different aryl groups are intended. The dibromo analog thus condenses a three-step sequence into two, reducing the cumulative consumption of protecting groups (typical TBDMS-Cl usage drops from 1.5 equiv to 0.8 equiv per mole of product) and shortening the synthetic route by approximately 12–18 hours of reactor time when scaled to 100 mmol. This operational advantage has been cited in process chemistry manuscripts evaluating cost contributions of the thiazole building block, where the price premium of the dibromo compound is partially offset by solvent and labor savings if the sequence exceeds 50 g scale. Nonetheless, published data for the direct head-to-head economic comparison under cGMP batch records is limited, and actual cost parity depends on the recovery efficiency of palladium from the dual coupling.
Accelerated stability studies (40 °C/75% RH, open dish) indicate that 2,4-dibromo-5-(hydroxymethyl)thiazole degrades via two parallel pathways: hydration of the thiazole ring at the 2-position and oxidative dimerization of the alcohol moiety. After 30 days under these conditions, HPLC purity falls from 97.5% to 89.2%, with the dimer (di-thiazolyl ether) accounting for 6.8% of total area and the ring-opened thioamide species constituting 1.3%. Kinetic fitting to the Arrhenius equation, using data points at 25 °C, 40 °C, and 60 °C, yields an activation energy (Ea) of 58.3 kJ·mol−1 for the dimerization pathway, suggesting that cold-chain storage (2–8 °C) extends shelf life to > 24 months when sealed under nitrogen. Containers furnished with a desiccant canister (silica gel, 10 g per 100 g product) maintain headspace relative humidity below 15% over a 12-month period in refrigeration, as validated by a probe measurement campaign using Rotronic HC2A-S sensors.
Incompatibility arises with amine bases stronger than pKa (conjugate acid) 8.5. Triethylamine, often present in Sonogashira coupling cocktails, induces 4-bromine displacement to form the 4-(diethylamino)thiazole derivative at rates exceeding 0.5%·h−1 at 60 °C. Consequently, protocol adaptations substitute hindered amine bases such as 2,6-lutidine (pKa 6.7) when 4-selective coupling is required. This constraint differs markedly from monobromo thiazoles, where amine-induced displacement is not a competitive process due to the absence of the activating electron-withdrawing effect of the second bromine. The difference in pKa threshold defines an operational boundary that process chemists must respect when designing telescoped sequences that avoid intermediate isolation.
Activation of the hydroxymethyl group to 2,4-dibromo-5-(chloromethyl)thiazole (CAS 853805-16-4) is performed with thionyl chloride in dichloromethane at 0–5 °C. Under these conditions, 99% conversion is achieved within 2 hours, liberating SO2 and HCl. However, gas evolution creates a processing bottleneck in glass-lined reactors at > 20 L scale, where the off-gas scrubber must be sized for a peak flow rate of 0.8 L·min−1 per mole of substrate, based on calorimetric data from a Mettler Toledo RC1e instrument. The resulting chloromethyl compound alkylates phenols and heterocyclic amines with almost quantitative yields at 25–40 °C in acetone using K2CO3 (2 equiv). A direct comparison with 5-(chloromethyl)thiazole (lacking bromines) reveals that the dibromo backbone increases the electrophilicity of the chloromethyl carbon, reducing the required alkylation temperature by 15–20 °C for identical substrates and halving reaction times. This is attributed to the −I effect of the two bromine atoms, which lowers the LUMO energy of the thiazole ring and delocalizes negative charge in the transition state. The difference is quantifiable via Hammett substituent constants: σm for bromine is 0.39, compared to σm = 0.0 for hydrogen, giving a cumulative Δσ of 0.78 for the 2,4-disubstituted system.
Non-dibromo analogs such as 2-bromo-4-methyl-5-(hydroxymethyl)thiazole incorporate an electron-donating methyl group, which offsets the activation and necessitates elevated temperatures (60–70 °C) for the same alkylation step. The dibromo compound therefore provides a wider thermal processing window for installations where temperature-sensitive functional groups are present elsewhere in the substrate, a factor that has been exploited in the synthesis of quinolone antibiotic precursors, as retrieval from the patent literature indicates.
| Building Block | Temperature (°C) | Time to >95% Conversion (h) | Isolated Yield (%) |
|---|---|---|---|
| 2,4-Dibromo-5-(hydroxymethyl)thiazole (via chloromethyl) | 25 | 4.0 | 92 |
| 2-Bromo-5-(hydroxymethyl)thiazole (via chloromethyl) | 40 | 8.5 | 87 |
| 5-(Hydroxymethyl)thiazole (via chloromethyl) | 55 | 12.0 | 81 |
| 4-Bromo-2-methyl-5-(hydroxymethyl)thiazole (via chloromethyl) | 50 | 10.0 | 83 |
Superficially, mixing and milling of the solid compound before formulation into stock solutions is straightforward; a single sentence suffices: the powder can be homogenized with a mortar and pestle and dissolved in anhydrous THF to prepare 0.2 M stocks for automated liquid handlers.
When 2,4-dibromo-5-(hydroxymethyl)thiazole is precipitated rapidly from ethyl acetate/heptane mixtures, a partially amorphous phase is isolated that exhibits a glass transition at −12 °C and a cold crystallization exotherm at 52 °C (DSC, 10 K·min−1). This amorphous content, confirmed by modulated DSC to be as high as 18% w/w in fast-cooled batches, significantly alters bulk powder flow properties. Using a Freeman Technology FT4 powder rheometer, the specific energy (SE) of the fully crystalline lot (99% crystallinity by XRPD) was measured at 4.2 mJ·g−1, while the lot with 18% amorphous fraction registered 7.8 mJ·g−1. The elevated specific energy translates into inconsistent dispensing from drum containers fitted with butterfly valves: gravimetric delivery accuracy for a 50 g target mass varied by ± 3.2 g (n=30) for the amorphous-containing batch versus ± 0.9 g for the crystalline reference. Users weighing out sub-gram quantities for microscale parallel synthesis therefore require heat-annealed material: heating the powder to 65 °C for 2 hours under nitrogen reduces amorphous content below 2% and brings the SE back to 4.3 mJ·g−1, effectively eliminating the dosing bias. This step is not indicated for monobromo analogs, which typically crystallize rapidly without significant amorphous trapping owing to their lower molecular complexity, and thus do not generate the same dispensing irregularity.
Batch-release chromatograms (C18 column, 150 × 4.6 mm, 5 μm particle size, gradient from 20% to 90% acetonitrile in 0.1% formic acid over 25 min) consistently detect two characteristic process impurities at relative retention times (RRT) 0.72 and 1.28. The impurity at RRT 0.72 corresponds to 2,4-dibromo-5-formylthiazole, an over-oxidation product from the hydroxymethylation step, with a typical abundance of 0.3–0.8%. When this impurity exceeds 1.2%, downstream Suzuki coupling with electron-rich boronic acids suffers from catalyst poisoning, presumably through aldehyde coordination to palladium. Several contract manufacturing organizations have tightened in-house limits to NMT 0.5% for the formyl analog, invoking USP General Chapter <621> as a chromatographic framework, even though no official monograph exists for this compound. The impurity at RRT 1.28 is the debrominated dimer resulting from Ullmann-type homocoupling, which accumulates during storage if headspace oxygen is not controlled. Its level is kept below 0.2% at the time of packaging, and a re-test date of 12 months from manufacture is assigned after a seal-integrity test per ASTM F2338-09 on the primary container closure.
| Parameter | Method | Specification | Result (Batch ZC2407-102) |
|---|---|---|---|
| Appearance | Visual inspection (Ph. Eur. 2.2.1) | Off-white to pale yellow crystalline powder | Off-white crystalline powder |
| Assay (HPLC) | RP-HPLC-UV at 254 nm | ≥97.0% area | 98.3% |
| Melting point | DSC (ASTM E793-06) | 78–83 °C | 80.4 °C |
| Water (KF) | Coulometric KF (ISO 760-1978) | ≤0.5% | 0.22% |
| Residual solvents | GC-HS (Ph. Eur. 2.4.24) | Toluene ≤0.1%, MeCN ≤0.1% | Toluene 0.04%, MeCN not detected |
| Impurity (RRT 0.72) | HPLC as above | ≤0.5% | 0.32% |
| Impurity (RRT 1.28) | HPLC as above | ≤0.2% | 0.08% |
Regulatory alignment for non-GMP material often follows REACH registration requirements for intermediates under Article 2(9) of the REACH Regulation (EC) No 1907/2006, exempting it from full substance evaluation when used strictly as a site-limited intermediate. However, if the substance is placed on the European market for R&D purposes alone, a dossier covering tonnage band 1–10 tonnes/year typically suffices, accompanied by IUCLID section 5 toxicological data relying on read-across from structurally related bromothiazoles. The dibromo compound demonstrates lower acute aquatic toxicity than expected from log P estimations: a Daphnia magna acute immobilization test (EC50) performed under OECD Test Guideline 202 returned a value of 12.8 mg·L−1, placing it outside the most severe acute category.
Regarding downstream metal-catalyzed transformations, the quality of the palladium scavenger step influences ultimate product purity when the compound is used as a late-stage intermediate. Post-coupling treatment with a thiol-functionalized silica gel (Si-Thiol, 1.5 mmol·g−1 loading) reduces residual Pd from 320 ppm to 4 ppm after a 30-minute batch slurry at 50 °C, meeting the ICH Q3D concentration limit for oral drug products (Pd: ≤10 μg/day for a 10 g/day dose). This step is unreported on monobromo thiazoles because they rarely require a second high-loading palladium cycle, where metal carryover becomes acute. The ability to implement an efficient scavenging protocol without crystallizing the thiazole intermediate is thus a specific process feature arising from the dibromo substitution pattern.
Compatibility with large-scale continuous flow setups has been assessed on a Vapourtec R-Series system equipped with a 10 mL tubular reactor coil. A homogeneous solution of 2,4-dibromo-5-(hydroxymethyl)thiazole (0.5 M in DMF) mixed with a pre-formed catalyst solution of Pd(dppf)Cl2 and a boronate ester at 120 °C with a residence time of 20 minutes achieved 94% conversion with a steady-state back-pressure of 4 bar, suggesting no fouling from bromide salt precipitation. This contrasts with observations on 4-bromo-5-(hydroxymethyl)thiazole, where salt deposition required periodic back-flushing every 6 hours. The presence of the 2-bromine in the dibromo compound alters the solubility of the generated alkaline bromide byproduct, maintaining a clear reactor stream under otherwise identical conditions.
