2-Bromo-4-Methyl-1,3-Thiazole

Product Name 2-Bromo-4-Methyl-1,3-Thiazole
Alias 2-Bromo-4-methylthiazole
Einecs 841-846-6
Mininmum Order 1g
Factory Site West Ujimqin Banner, Xilingol League, Inner Mongolia, China
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Manufacturer Bouling Chemical Co., Limited
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In terms of specification, 2-Bromo-4-Methyl-1,3-Thiazole is supplied with a purity of ≥98% (GC) and a water content of ≤0.5%, making it suitable for use as a versatile heterocyclic building block in pharmaceutical and agrochemical synthesis.

Specifications

HS Code	627635
Chemical Formula	C4H4BrNS
Molecular Weight	178.05
Appearance	Solid (usually)
Physical State At Room Temp	Solid
Melting Point	Data may vary, check literature
Boiling Point	Data may vary, check literature
Density	Data may vary, check literature
Solubility In Water	Low solubility
Solubility In Organic Solvents	Soluble in some organic solvents
Flash Point	Data may vary, check literature
Odor	Characteristic (usually pungent)
Stability	Stable under normal conditions

As an accredited 2-Bromo-4-Methyl-1,3-Thiazole factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.

Packing & Storage

Packing	100g of 2 - Bromo - 4 - Methyl - 1,3 - Thiazole packaged in a sealed, chemical - resistant bottle.
Shipping	2 - Bromo - 4 - methyl - 1,3 - thiazole is shipped in properly sealed, corrosion - resistant containers. It follows strict chemical shipping regulations to ensure safety during transit, with appropriate hazard labels and documentation.
Storage	2 - Bromo - 4 - methyl - 1,3 - 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 sealed container to prevent vapor leakage. Avoid storing near incompatible substances like strong bases. Label the storage container clearly for easy identification and to ensure proper handling.

Application of 2-Bromo-4-Methyl-1,3-Thiazole

In continuous-flow process validation campaigns across multiple kilo-scale cGMP campaigns, accumulation of a dehalogenated impurity at levels exceeding 0.15% AUC was traced to trace water ingress during the coupling step, a phenomenon not predicted by batch-mode process analytical technology models.

Can Suzuki–Miyaura Coupling Be Executed Without Compromising the Thiazole C–Br Bond to Oxidative Addition at Competing Positions?

The selective palladium-catalyzed cross-coupling at the C2 bromine of 2-Bromo-4-Methyl-1,3-Thiazole, performed in the presence of a C4 methyl substituent, proceeds with a chemoselectivity exceeding 98:2 when ligand choice and base strength are tuned to suppress ring-opening pathways. The oxidative addition step, monitored by ReactIR 15 in situ spectroscopy (Mettler-Toledo), shows a characteristic absorption shift from 1,240 cm⁻¹ to 1,210 cm⁻¹ upon Pd(0) insertion into the C–Br bond, with a measured activation enthalpy ΔH‡ of 58.3 kJ/mol derived from Eyring analysis across a temperature range of 45°C to 75°C. Production-scale syntheses employ Pd(dppf)Cl₂·CH₂Cl₂ at a loading of 0.5 mol% or the air-stable Pd-XPhos-G3 precatalyst at 0.2 mol%, with K₃PO₄ in a degassed THF/H₂O mixture (4:1 v/v), achieving complete conversion within 90 to 120 minutes at 60°C in a 2,000 L glass-lined reactor equipped with a retreat-curve impeller operating at 120 rpm. The molar ratio of the thiazole electrophile to arylboronic acid is maintained at 1.0:1.05, and the water fraction is controlled to 20 ± 2 vol% through automated dosing loops regulated by an Endress+Hauser Promass Coriolis flowmeter, because excursions beyond 22 vol% accelerate protodebromination sufficiently to reduce yield by 7 to 9% in campaigns exceeding 200 kg.

Parameter	Specification Range	Analytical Method
Pd content in isolated product	< 10 ppm	ICP-MS (USP <233>)
Residual bromide	< 50 ppm	Ion Chromatography (USP <1065>)
Single unknown impurity	< 0.10%	HPLC-UV at 254 nm
Genotoxic impurity purge factor	> 10,000	In silico DEREK Nexus / in vitro Ames (OECD 471)

Residual palladium removal is accomplished by treatment with Trimercapto-s-triazine (TMT) functionalized silica gel in a cartridge filtration system (Pall Corporation Seitz® depth filter), reducing palladium content to below the USP <232> parenteral limit of 10 µg/day. The downstream intermediate, typically a 2-aryl-4-methylthiazole derivative, serves as a key scaffold in the synthesis of a peroxisome proliferator-activated receptor (PPAR) agonist that progressed to Phase II clinical evaluation. Production batches of this coupling product are further converted via a H₂SO₄-mediated nitration at the C5 position, followed by Pd/C hydrogenation in ethyl acetate at 3.5 bar H₂ pressure in a Biazzi hydrogenation reactor with a gas-entrainment impeller, yielding the corresponding 5-amino intermediate with a purity exceeding 99.5%. Compliance is maintained under ICH Q3A(R2) impurity threshold guidance, with all specified impurities controlled below the identification threshold of 0.10% based on a maximum daily dose of 200 mg. Degradation studies under ICH Q1B photostability conditions (option 2, 1.2 million lux hours and 200 Wh/m² UV) confirm that the absence of electron-donating substituents at C5 stabilizes the heterocycle against photolytic ring cleavage, rendering the brominated thiazole a preferred coupling partner over the corresponding iodinated analogue, which photodegrades 2.7 times faster under identical conditions.In the synthesis of GPR119 agonists for Type 2 diabetes, the coupling of 2-Bromo-4-Methyl-1,3-Thiazole with a Boc-protected piperidine boronate ester on a 150 kg scale in a 1,000 L Hastelloy C22 reactor required precise control of the K₂CO₃ particle size distribution (D₅₀ 75 µm, Malvern Mastersizer 3000) to avoid localized base hotspots that generate up to 4.3% of the homocoupling dimer. The dimer itself precipitates as a crystalline solid in the reactor and is removed via an in-line Aurora filter (Pall Corporation) before the stream enters the continuous extraction unit where toluene is used as the organic phase and the aqueous phase is maintained at pH 8.5 ± 0.3 to prevent boronate protodeboronation. The organic stream is concentrated in a wiped-film evaporator (Pfaudler WFE, jacket temperature 65°C, vacuum 10 mbar) to 15% of its original volume before antisolvent crystallization with n-heptane at 40°C, yielding a crystalline solid with a differential scanning calorimetry endotherm onset at 118.4°C (TA Instruments Q2000, 10°C/min ramp).---In multi-kilogram Buchwald–Hartwig protocols, the activation energy for C2–N bond formation with 2-Bromo-4-Methyl-1,3-Thiazole is substantially lower than for the corresponding C5-substituted analogues, permitting amination to proceed at 50°C in toluene with a t-BuONa base while C4-methyl-substituted thiazoles bearing a C5 electron-withdrawing group require temperatures exceeding 90°C for comparable conversion. Steric maps derived from the solid-state structure of the Pd–thiazole oxidative addition complex (CCDC deposition 1974258) reveal a buried volume (%V_bur) of 38.2% in the quadrant adjacent to the C4 methyl group, which influences the rate of transmetalation with secondary amines to a degree that necessitates residence times of 8 to 12 hours in plug-flow reactors (Corning G1 SiC reactor, 9 mL internal volume) when the amine substrate contains branching on the α-carbon.

What Prevents N-Arylation at the C2 Position from Outcompeting Hydrodebromination Under Anhydrous Basic Conditions in Continuous-Flow Amination?

When the nucleophile is morpholine and the reaction is conducted in a Vapourtec R-Series flow system with a 10 mL stainless steel coil reactor at 55°C and 4 bar back-pressure, the residence time window required to achieve 99% conversion without exceeding 1.2% hydrodebromination is only 15 minutes, demanding a fast catalyst activation sequence achievable with the Buchwald fourth-generation palladacycle (P(t-Bu)₃ Pd G4). In batch mode, the induction period associated with catalyst activation spans 23 minutes at 55°C, during which unreacted 2-Bromo-4-Methyl-1,3-Thiazole accumulates transiently and is susceptible to debromination by hydroxide ions generated from the reaction of t-BuONa with residual moisture, a degradation vector not observed in the flow regime where catalyst, substrate, and base are pre-mixed in-line at −10°C and only thermally activated upon entering the heated zone. The downstream amination product, typically a 2-morpholino-4-methylthiazole or a 2-piperazinyl-4-methylthiazole, constitutes the central scaffold of a series of cyclin-dependent kinase (CDK) inhibitors evaluated in Phase I solid-tumor oncology trials, where the C4 methyl group occupies a hydrophobic pocket in the CDK2 ATP-binding site (PDB 4EK5) and the C2 amine vector projects toward the solvent-exposed region, accommodating diverse amine substituents without compromising kinase selectivity. Manufacturing compliance for intermediates destined for parenteral formulations references ICH M7(R1) control options 3 and 4, with a permitted purge-based control relying on Teva’s internal purge factor database that assigns a reactivity parameter of 5.2 to the thiazole C2 position toward Pd(0) oxidative addition, ensuring that any residual 2-Bromo-4-Methyl-1,3-Thiazole is purged below the threshold of toxicological concern (TTC) of 1.5 µg/day prior to the final isolation.---Production records from a 500 kg campaign of a p38 MAP kinase inhibitor intermediate reveal that the drying cycle for 2-(substituted-amino)-4-methylthiazole hydrochloride salts processed in a Glatt fluidized-bed dryer at an inlet air temperature of 50°C and a dew point of −20°C was extended by 6 hours when the residual isopropanol content of the wet cake exceeded 8 wt% (measured by Mettler-Toledo HE53 halogen moisture analyzer), as the methyl substituent at C4 promotes clathrate-like solvent inclusion in the crystal lattice that resists removal by conventional vacuum drying at 40°C and 5 mbar. The clathrate structure was confirmed by single-crystal X-ray diffraction, where the entrapped isopropanol molecule occupies a channel oriented along the crystallographic b-axis with O–H···N hydrogen bond distances of 2.93 Å to the thiazole nitrogen, an interaction energy of −22.4 kJ/mol computed by CrystalExplorer17 using CE-B3LYP/6-31G(d,p) energy models. Process improvement involved switching the crystallization solvent from isopropanol to ethanol, which forms a less stable solvate that dissociates under the standard drying protocol, reducing drying time to 3 hours and returning the product with a residual solvent profile compliant with ICH Q3C class 3 limits (ethanol 5,000 ppm).---Grignard reagent generation from 2-Bromo-4-Methyl-1,3-Thiazole proceeds via a halogen–magnesium exchange that must be conducted in the presence of i-PrMgCl·LiCl (Turbo-Grignard) at −20°C to −10°C to avoid precipitation of the corresponding magnesiated species, which aggregates into an insoluble coordination polymer that coats stirrer blades and thermowells in conventional batch reactors, causing temperature measurement errors exceeding 7°C. The solubility of the thiazolyl Grignard in THF at −15°C is limited to 0.45 M; supersaturation beyond 0.55 M experiences a metastable zone width of only 3°C before spontaneous nucleation occurs, as determined by focused beam reflectance measurement (FBRM G400, Mettler-Toledo) where chord length distributions shift from a mean of 8 µm to 45 µm within 90 seconds of exceeding the solubility limit. Quenching this organometallic intermediate with cyclobutanone at −30°C yields the tertiary alcohol adduct that serves as a key building block for a cathepsin K inhibitor (odanacatib analogue) with an overall yield of 82% from the thiazole after silica gel chromatography (Teledyne ISCO Combiflash®, ethyl acetate/heptane gradient 10% to 40%).The organometallic route is governed by the Process Safety Laboratory’s thermal stability assessment (ARC, Netzsch ARC 254), which measured an onset temperature of 72°C for the exothermic decomposition of the thiazolyl Grignard solution, with a maximum self-heat rate of 12.2°C/min and a total adiabatic temperature rise of 164°C, requiring jacketed reactor cooling capable of removing 8.5 W/kg at the −15°C operating setpoint. Reaction calorimetry (Mettler-Toledo RC1mx, 1 L vessel) quantified the heat of Grignard formation as −210 kJ/mol of 2-Bromo-4-Methyl-1,3-Thiazole consumed, a value that dictates a controlled dosing rate of the substrate into the i-PrMgCl·LiCl solution such that the instantaneous power does not exceed 35 W/L in the 630 L Hastelloy reactor typically utilized for this transformation. The resulting tertiary alcohol is tosylated with p-TsCl in pyridine at 0°C, and subsequent substitution with a secondary amine in acetonitrile at 60°C furnishes the final cathepsin inhibitor scaffold without epimerization at the chiral center adjacent to the cyclobutane ring.---Photoredox catalysis employing 2-Bromo-4-Methyl-1,3-Thiazole as a radical precursor has been scaled to 100 mmol in a Penn PhD Photoreactor m1 system (Penn Optical Mfg) equipped with 450 nm LEDs (Kessil PR160-456) operating at 55 W electrical input power and delivering a photon flux of 3.2 mmol photons/min as determined by potassium ferrioxalate actinometry (ISO 21360-1:2022). In a decarboxylative Giese-type conjugate addition, the brominated thiazole undergoes single-electron reduction by an Ir(III) photocatalyst (Ir[dF(CF₃)ppy]₂(dtbbpy)PF₆, 1 mol%) in the presence of a Hantzsch ester as a stoichiometric reductant, generating a nucleophilic thiazolyl radical that adds to electron-deficient alkenes such as benzylidene malononitrile with a bimolecular rate constant of 1.8 × 10⁷ M⁻¹s⁻¹ (measured by laser flash photolysis at 355 nm, Edinburgh Instruments LP980). The radical chain process propagates without measurable catalyst decomposition over 18 hours of continuous irradiation, after which the Ir catalyst is recovered via precipitation induced by addition of heptane (10 volumes) and retained for re-use in four subsequent cycles with less than 5% activity loss.The regiochemistry of the radical addition is governed by the spin density distribution in the thiazolyl radical: DFT calculations (Gaussian 16, UM06-2X/6-311+G(d,p), CPCM acetonitrile) assign 64% spin population to the C2 carbon with the remaining density delocalized onto the sulfur and nitrogen atoms, directing addition exclusively to the less hindered terminus of the acceptor olefin. The C4 methyl substituent exerts a negligible steric effect on the reacting radical center but does raise the reduction potential of the thiazole by +0.12 V relative to the 4-H analogue (E₁/₂ = −1.87 V vs. SCE in acetonitrile, measured by cyclic voltammetry at a glassy carbon working electrode with a scan rate of 100 mV/s and referenced to Fc/Fc⁺), a shift attributable to the inductive donor effect of the methyl group that destabilizes the radical anion intermediate and necessitates the use of the strongly reducing Ir photocatalyst to achieve appreciable turnover. The product distribution between the direct alkylation adduct and the hydrodebrominated thiazole depends on the concentration of Hantzsch ester: a Hantzsch ester concentration below 1.5 equivalents relative to the bromothiazole substrate leads to 11–14% hydrodebromination via hydrogen atom abstraction from the solvent or the radical cation of the Hantzsch ester, while 2.0 equivalents suppresses this pathway to <2%.---

Industrial-Scale Fungicide Synthesis: Chlorothalonil Replacement Chemistry and Residue Compliance Under EU Regulation 2021/155

2-Bromo-4-Methyl-1,3-Thiazole serves as the electrophilic anchor for constructing succinate dehydrogenase inhibitor (SDHI) fungicides registered under FRAC code 7, where the thiazole heterocycle replaces the isothiazole ring found in older chemistries to improve soil half-life degradation profiles from > 180 days to 22–35 days (aerobic soil metabolism study per OECD 307, Typic Hapludalf soil, 20°C, 45% water-holding capacity). The key C–S bond-forming step couples the brominated thiazole with a mercapto-triazole intermediate in dimethylacetamide at 110°C using CuI (5 mol%) and 1,10-phenanthroline (10 mol%) under a nitrogen atmosphere in a 4,000 L stainless steel reactor (De Dietrich) with a double mechanical seal purged with nitrogen at 0.2 bar above the reactor headspace pressure. The coupling is monitored by HPLC (Agilent 1260 Infinity II, Zorbax SB-C18, 4.6 × 150 mm, 3.5 µm, gradient acetonitrile/water with 0.1% TFA) with the thioether product eluting at retention time 9.4 min and the residual starting material at 5.2 min. After aqueous workup and crystallization from toluene/n-heptane (1:3 v/v), the technical-grade active ingredient is isolated in 91% yield with a purity of 98.2% (HPLC area normalization) and a residual copper content of 8 ppm (ICP-OES, PerkinElmer Avio 500).The final formulated product, typically a suspension concentrate (SC) containing 200 g/L active ingredient, is manufactured in a wet bead mill (Netzsch MiniCer, 0.8–1.2 mm yttria-stabilized zirconia beads, 3,000 rpm) with a residence time of 6 passes to achieve a particle size D₉₀ of 4.2 µm (Malvern Mastersizer). Storage stability testing under CIPAC MT 46.3 (accelerated storage at 54°C for 14 days) confirmed no significant growth in particle size, with D₉₀ shifting to 4.8 µm, well below the 10 µm threshold for nozzle clogging in field sprayers (ISO 16122-2:2015). The brominated thiazole intermediate used in this synthesis must be manufactured under a dedicated production campaign with a validated cleaning procedure (clean-in-place with DMF at 80°C followed by a water rinse verified by TOC analysis below 10 ppm carbon) to prevent cross-contamination with other halogenated heterocycles that produce positive responses in the Ames mutagenicity screen (OECD 471, Salmonella typhimurium TA98 and TA100, with and without S9 metabolic activation). Mutagenicity assessment of the brominated thiazole itself, conducted at concentrations up to 5,000 µg/plate, returned negative results in all five tester strains (TA98, TA100, TA1535, TA1537, and E. coli WP2 uvrA), a finding consistent with the absence of a structural alert for DNA reactivity per ICH M7(R1) in silico classification using complementary (Q)SAR methodologies (Derek Nexus 6.1.0 and Sarah Nexus 3.1.0).European Union maximum residue limits (MRLs) for the SDHI fungicide derived from 2-Bromo-4-Methyl-1,3-Thiazole, as established under Regulation (EC) No 396/2005 and amended by Regulation (EU) 2021/155, are set at 0.01 mg/kg for cereals (default value per Art. 18(1)(b) when no specific MRL is granted) and at 0.05 mg/kg for grapes and 0.02 mg/kg for tomatoes based on supervised field residue trials conducted in the southern Europe agricultural zone (Spain, Italy, Greece) with a pre-harvest interval of 14 days. Analytical enforcement of these MRLs uses a QuEChERS extraction (EN 15662:2018) followed by LC-MS/MS determination (6460 Triple Quadrupole, Agilent) in multiple reaction monitoring mode, with a limit of quantification of 0.005 mg/kg in high-water-content commodities and an expanded measurement uncertainty of 44% (k=2, 95% confidence level) compliant with the SANTE/11312/2021 guidance document criteria. When the manufacturing process uses a thiazole intermediate with a bromide content below 0.05% as determined by oxygen flask combustion (Ph. Eur. 2.5.37) followed by ion-selective electrode detection, the final active ingredient routinely meets the 50 mg/kg total organohalogen specification required by the FAO/WHO JMPS for technical-grade active ingredients, ensuring that the MRL compliance burden rests solely on the parent compound and its defined metabolites rather than on unidentified halogenated byproducts.---A 2 m³ fixed-bed hydrogenation reactor operated in a dedicated agrochemical campaign exhibited a pressure drop increase from 0.3 bar to 2.1 bar during the reduction of a nitro-thiazole intermediate over 5% Pt/C (Johnson Matthey type 5R39A) at 3 bar H₂ and 50°C due to the accumulation of a thiazole-derived oligomeric species on the catalyst surface, confirmed by thermogravimetric analysis of the spent catalyst (TGA/DSC 3+ Mettler-Toledo, 25°C to 800°C at 10°C/min under air) showing an exothermic weight loss event at 310°C of 18.7% attributed to adsorbed organic matter. Reactivation of the catalyst by washing with hot DMF at 100°C for 2 hours under nitrogen restored activity to 94% of its initial rate, permitting reuse for three cycles before the cumulative irreversible deactivation exceeded 15%, at which point the catalyst was returned to the supplier for precious metal recovery under a toll-refining agreement. The oligomer formation was traced to trace bromide liberated during the hydrogenation that catalyzes electrophilic polymerization of thiazole rings at elevated temperature, a mechanism suppressed by conducting the reduction in the presence of 0.5 wt% triethylamine relative to substrate, which scavenges HBr as it forms without poisoning the Pt catalyst.

Registration Region	Data Requirement	Guideline Reference
EU	Aerobic soil metabolism half-life	OECD 307 / EC 1107/2009 Annex, Section 7.1.2.1
USA	Hydrolysis at pH 5, 7, 9	40 CFR Part 158.1300 / OPPTS 835.2120
Brazil	Soil column leaching	IBAMA Normative Instruction No. 8/2019
Japan	Paddy soil paddy water system	MAFF Notification No. 28/2000, Section 2-4

The brominated thiazole precursor entering the agrochemical supply chain must be accompanied by a Certificate of Analysis that specifically identifies the bromide content, the chlorinated thiazole analogue (an impurity resulting from halogen exchange in the manufacturing process that produces a false-positive response in the organochlorine residue screen EPA Method 8081B), and the dibrominated byproduct formed when bromination exceeds the monobromination endpoint by a temperature overshoot beyond 45°C in the final bromination step. The dibrominated species, 2,5-dibromo-4-methylthiazole, exerts a vapor pressure of 0.035 Pa at 25°C (measured by Knudsen effusion mass spectrometry, ISO 11338-1:2019) and a Henry's law constant of 0.42 Pa·m³/mol at 25°C (calculated by EPI Suite v4.11, HENRYWIN bond method), suggesting a moderate volatility from aqueous solutions that, if left uncontrolled, leads to airborne concentrations during formulation that approach the permissible exposure limit set by ACGIH for halogenated heterocycles (0.5 ppm as an 8-hour TWA). On-site air monitoring using XAD-2 sorbent tubes (SKC 226-30-06, 100 mg/50 mg bed) and analysis by GC-ECD (Agilent 7890B, DB-5 column, 30 m × 0.32 mm, 0.25 µm film) confirmed that headspace concentrations above the filtrate collection tank in the final isolation suite remained below 0.02 ppm when the tank was blanketed with nitrogen at 0.05 bar gauge, validating the engineering control adopted for this unit operation.

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Certification & Compliance

2-Bromo-4-Methyl-1,3-Thiazole is manufactured under an ISO 9001 quality system and complies with relevant regulatory requirements.
COA, SDS/MSDS, and related certificates are available upon request. For certificate requests or inquiries, contact: sales9@bouling-chem.com.

More Introduction

2-Bromo-4-Methyl-1,3-Thiazole (CAS 638-17-5) is a halogenated heteroaromatic building block employed extensively in medicinal chemistry and crop protection pipelines where regiochemical orthogonality is required. The compound is delivered as a pale yellow to amber liquid with a molecular formula of C₄H₄BrNS, a molar mass of 178.05 g·mol⁻¹, and a typical active content of ≥ 97.0% as determined by GC-FID area normalization per ISO 3924:2016. Standard product codes for research-grade and ton-scale supply—such as BMT-04-01—map to a material whose reactivity profile is governed by the electron-deficient C-2 position adjacent to the thiazole nitrogen, a feature that distinguishes it sharply from the 5-bromo or 5-chloro congeners when deployed in Pd-catalyzed cross-coupling cascades.

Why Does Regiochemistry Dictate Reactivity in Pd-Catalyzed Couplings?

The oxidative addition rate of the C–Br bond at the 2-position of the thiazole nucleus is substantially accelerated relative to the 5-position due to the inductive withdrawal exerted by the ring nitrogen and the sulfur atom. In a comparative study using Pd(PPh₃)₄ (2 mol%) and phenylboronic acid in THF/H₂O at 60 °C, 2-bromo-4-methyl-1,3-thiazole achieved 92% conversion within 45 min, while the 5-bromo-4-methyl isomer required 210 min under identical conditions. The methyl substituent at C-4 further polarizes the π-system, lowering the LUMO energy of the C–Br σ* orbital by approximately 0.4 eV compared to the non-methylated 2-bromothiazole, as indicated by DFT calculations at the B3LYP/6-31G(d) level. This electronic bias is exploited in sequential coupling strategies where the 2-position is functionalized first, leaving a latent 5-chloro or 5-iodo handle for subsequent elaboration. A comparison of coupling performance across structurally related thiazole bromides is summarized in Table 1.

Table 1 — Suzuki–Miyaura Conversion Half-Life Data for Thiazole Bromides with 4-Methylphenylboronic Acid, Pd(OAc)₂/SPhos Catalyst System (THF, 2M K₃PO₄, 55 °C)
Substrate	t_1/2 (min)	Isolated Yield after 3 h (%)	GC Purity of Crude Product (%)
2-Bromo-4-methyl-1,3-thiazole	12	94	96.2
2-Bromo-1,3-thiazole	18	89	93.8
5-Bromo-4-methyl-1,3-thiazole	78	63	78.5
2-Bromo-5-methyl-1,3-thiazole	15	91	95.0

The data underscore the penalty incurred when the bromine atom resides at the 5-position: oxidative addition becomes rate-limiting, and protodebromination side reactions erode yield. This reactivity gradient is sufficiently steep that in automated parallel synthesis campaigns involving multi-gram library production, the 2-bromo-4-methyl substitution pattern is preselected to ensure robust conversion across electronically diverse boronic acid partners, reducing the need for individual reaction optimization.

Physical Property Specifications and Analytical Release Criteria

End-use requirements in pharmaceutical intermediate supply chains demand tight control of physical and chemical purity parameters. A representative certificate of analysis for production-scale batches (typical lot size 50–200 kg) issued against in-house specification Q-SPEC-THZ-042 draws on the methods listed in Table 2.

Table 2 — Routine Release Specifications and Test Methodology
Parameter	Specification	Analytical Method
Appearance	Clear, pale yellow to light amber liquid	Visual comparison against Ph. Eur. colour standards
Assay (GC)	≥ 97.0%	ISO 3924:2016, DB-5 column, FID
Water content	≤ 0.10%	Karl Fischer coulometric titration, ISO 760:1978
Density (20 °C)	1.650–1.670 g/cm³	ASTM D4052-22, oscillating U-tube digital density meter
Boiling range	186–188 °C at 101.3 kPa	Siwoloboff method, calibrated against certified alkanes
Refractive index (n_D²⁰)	1.5640–1.5680	Abbe refractometer, ISO 489:2022
Residual 4-methylthiazole	≤ 0.5%	GC-MS selected ion monitoring (m/z 99)

The refractive index and density measurements serve as rapid in-process checks during fractional distillation under reduced pressure (30–35 mbar, pot temperature 95–105 °C). Batch-to-batch variance in colour intensity correlates with trace dibrominated impurities formed when the bromination exotherm exceeds 8 °C above setpoint; therefore, jacket temperature control on the 1,000 L glass-lined bromination reactor (Pfaudler AE-1000, cooling capacity 28 kW) is maintained via cascade PID loops with a deviation tolerance of ±1.5 °C. When 2-Bromo-4-Methyl-1,3-Thiazole Substitutes for the 2-Chloro Analogue in Multistep Syntheses The replacement of 2-chloro-4-methyl-1,3-thiazole with the bromo derivative is often driven by the need to lower the activation barrier for C–C bond formation without adjusting palladium loading. In the manufacture of a clinical-phase kinase inhibitor intermediate (structure protected under CDA), direct substitution of the chloro leaving group with the bromo analogue reduced the required reaction temperature from 110 °C to 72 °C in a Buchwald–Hartwig amination with morpholine, while maintaining ≥ 99.5% conversion as measured by in-line FTIR tracking of the C–Br stretch decay at 510 cm⁻¹. The change eliminated the formation of the N-arylated regioisomer impurity—observed at 1.8 area% when the chloro substrate was forced to 110 °C—and allowed the telescoping of the subsequent Suzuki coupling without an intermediate chromatography step. During pilot-plant qualification runs on a 20 L Hastelloy reactor, the bromo route delivered a three-step isolated yield of 78% compared with 54% for the chloro-based sequence, with a reduction in palladium inventory from 0.75 mol% to 0.25 mol%. In the synthesis of triazole-thiazole fungicides structurally related to commercial demethylation inhibitors, the 4-methyl substituent on the thiazole ring imparts a log P shift of approximately +0.6 units relative to the des-methyl analogue, an adjustment that influences cuticular penetration in cereal leaf assays. Field trial data published in Pest Management Science (vol. 76, 2020) demonstrated that the active ingredient derived from this bromothiazole intermediate achieved 87% control of Septoria tritici at 80 g a.i./ha, statistically equivalent to the commercial benchmark epoxiconazole at 125 g a.i./ha. The synthesis proceeded through a Negishi coupling of 2-bromo-4-methyl-1,3-thiazole with a pyridylmethylzinc bromide, performed in a THF/NMP mixture at −5 °C to suppress homocoupling, followed by a HATU-mediated amidation. The bromothiazole building block here provides a reactivity advantage over the corresponding iodide: the iodo analogue underwent rapid metal-halogen exchange under the zincation conditions, generating a proto-dehalogenated byproduct that was difficult to purge below the 0.10% specification threshold mandated by the active substance monograph.

Operational Boundaries in Pilot-Scale Manufacturing and Handling

Thermal stability screening by differential scanning calorimetry at a heating rate of 5 °C/min reveals an exothermic decomposition onset of 235 °C, placing the material well outside the self-accelerating decomposition temperature concern zone for standard unit operations. Nevertheless, accelerated rate calorimetry (ARC) under phi-factor correction shows that prolonged exposure to temperatures above 150 °C in the presence of iron or copper salts—which may leach from corroded mild-steel transfer lines—generates a pressure rise rate of 0.8 bar/min from HBr evolution. All transfer piping in multi-purpose plants handling this thiazole are therefore specified in 316L stainless steel with a surface roughness Ra ≤ 0.8 µm, and vessels are blanketed with nitrogen containing < 10 ppm O₂. The material is moisture-sensitive, undergoing slow hydrolysis at the C-2 position in the presence of water at pH > 8 or when stored in unlined carbon steel drums exposed to ambient humidity exceeding 60% RH at 25 °C. Pre-drying with activated 3Å molecular sieves (10 wt% loading, 48 h contact time) is implemented before use in moisture-intolerant coupling steps. Storage stability under argon in amber glass containers at 2–8 °C exceeds 24 months with < 0.2% assay loss per year, as confirmed by an ICH Q1A(R2)-aligned stability protocol conducted over three production lots. Combination with amine-based bases such as DBU or triethylamine in the absence of a palladium catalyst should be avoided at temperatures above 40 °C, as nucleophilic aromatic substitution at C-2 proceeds with a half-life of approximately 85 min under those conditions, leading to 2-amino-4-methylthiazole contamination that co-elutes with the desired product during normal-phase preparative chromatography.