5-(Trifluoromethyl)-1,3-Thiazole-4-Carboxylic Acid

When DAR-Controlled Conjugates Demand a Stability-Enhancing Thiazole Spacer

Antibody-drug conjugate (ADC) platforms with a drug-to-antibody ratio (DAR) targeted at 7.8 ± 0.4 exploit the acid as a bifunctional linker element. The terminal carboxylate is activated via in situ conversion to the acyl fluoride using 1.05 molar equivalents of cyanuric fluoride and 1.20 molar equivalents of pyridine in dichloromethane at 0 °C to 5 °C, generating a species reactive enough to acylate the sterically hindered 4-aminobenzyl alcohol motif of the cathepsin B-cleavable Val-Cit-PAB linker without observable racemization (< 0.3% D-enantiomer by chiral HPLC with a Chiralpak IA-3 column, eluting with n-hexane/ethanol/diethylamine 80:20:0.1 v/v/v). The entire process sequence, from acidic chloride transfer through hollow-fiber nanofiltration (molecular weight cut-off 200 Da polyamide membrane, 3 bar transmembrane pressure) to high-vacuum drying at 40 °C/1 mbar for 18 hours, is executed in a containment isolator achieving an occupational exposure band of 3 (10–100 ng/m³ 8-hour TWA per ASTM E2610-18) when handling the final conjugated intermediate prior to bioconjugation to a humanized IgG1κ monoclonal antibody via thiol-maleimide chemistry on interchain cysteines reduced with TCEP at 2.75 molar equivalents per antibody. The finished conjugate, a lyophilized powder for concentrate for solution for infusion, complies with the aseptic processing requirements of 21 CFR 211.113(b) and the bacterial endotoxin threshold of < 0.25 EU/mg per USP <85>.

What Limits Oxidative Dimerization During SDHI Fungicide Scaffold Assembly?

Processing to a succinate dehydrogenase inhibitor (SDHI) fungicide active ingredient, specifically a 2-(difluoromethyl)-5-(trifluoromethyl)-1,3-thiazole-4-carboxanilide derivative, begins with the formation of the acid chloride using thionyl chloride (1.35 molar equivalents) and a catalytic quantity of dimethylformamide (0.05 molar equivalents) in toluene at reflux (110 °C jacket temperature). An exotherm to 124 °C is recorded when the batch size exceeds 800 L glass-lined reactor volume unless a controlled dosing ramp of 2.5 L/hour is applied. The resultant acid chloride solution is filtered through a 0.2 µm polypropylene depth filter to remove insoluble thiazole dimer formed via a competing single-electron-transfer pathway (< 0.7% w/w of the acid mass). Immediate coupling with 1.00 molar equivalent of 2-(3,5-dimethylphenoxy)aniline in the presence of 1.10 molar equivalents of powdered potassium carbonate (325 mesh, reactive grade) in methyl ethyl ketone yields the free base pesticide with an isolated purity of 99.1% after a single recrystallization from 2-propanol/water (70:30 v/v, cooling gradient 0.5 °C/min to 10 °C). The formulated end product, a 500 g/L suspension concentrate, is manufactured through horizontal bead milling (zirconia beads, 0.6–0.8 mm diameter, 85% chamber fill) to achieve a particle size of D₅₀ < 2.5 µm ( ISO 13320 ), and its 2-year shelf-life stability at 25 °C/60% RH is confirmed according to CIPAC MT 46.3, with compliance to FAO Specification 202/S/TC(2023) and EPA 40 CFR Part 180 sub-part C tolerances for cereal grains.

High-Temperature Anhydride Cyclization for JAK-1 Selective Inflammatory Pathway Blockers

The bridging of two equivalents of the thiazole carboxylic acid via a triphosgene-mediated cyclodehydration (using 0.35 molar equivalents of bis(trichloromethyl)carbonate in refluxing 1,2-dichloroethane) generates a symmetrical anhydride that serves as the electrophilic warhead during the synthesis of Janus kinase 1 (JAK-1) selective inhibitors for rheumatoid arthritis. The addition of the powdered anhydride in four equal portions at 15-minute intervals to a slurry of 4-(4-methylpiperazin-1-yl)aniline hydrochloride (2.05 molar equivalents) and triethylamine (4.20 molar equivalents) in acetonitrile at 22–28 °C yields the target bis-amide, which crystallizes directly from the reaction medium with an X-ray powder diffraction pattern (Cu Kα radiation, 2θ 8.7°, 14.2°, 21.9°) matching that of the monohydrate Form A registered in the Common Technical Document (CTD) Module 3.2.S.2. The residual isobutyl alcohol arising from the upstream hydrolysis of the isobutyl ester is controlled to < 5000 ppm per ICH Q3C Class 3 limits, monitored online via a headspace gas chromatography system (FID, column HP-5ms 30 m × 0.25 mm × 0.25 µm). The final pharmaceutical presentation, a tablet core containing 15 mg or 30 mg of the free base embedded in a hypromellose-based controlled-release hydrophilic matrix, achieves a t_90% dissolution index of 8 hours in USP Apparatus II at 50 rpm in phosphate buffer pH 6.8.

5-(Trifluoromethyl)-1,3-thiazole-4-carboxylic acid can be reacted with 3.20 molar equivalents of (3-aminopropyl)trimethoxysilane in dry toluene (50 mg/mL acid concentration) under reflux with azeotropic removal of water for 6 hours to produce a silanizing ligand. This ligand is chemically bonded to 5 µm spherical silica gel (pore diameter 120 Å, specific surface area 300 m²/g) at a surface coverage density of 3.8 µmol/m², determined by the depletion method and elemental analysis for sulfur. The resulting reversed-phase/ion-exchange mixed-mode chromatographic stationary phase exhibits a carbon load of 13.2% and a ligand density of 340 µmol/g, designed for the baseline separation of structurally homologous perfluorinated sulfonamide pollutants under isocratic conditions (acetonitrile/20 mM ammonium acetate buffer pH 4.0 , 45:55 v/v ). Column validation follows the extended van Deemter protocol of USP <621>, requiring a reduced plate height of h = 2.1 for the naphthalene peak at an optimized linear velocity of 1.8 mm/s, with a tailing factor of 1.02 at 5% peak height. The end product, a 250 mm × 4.6 mm i.d. stainless-steel HPLC column packed at 350 bar using a high-pressure slurry technique in acetone, is qualified under a quality management system aligned with ISO 9001:2015 and audited against ASTM E2857-22 for general-purpose liquid chromatography columns.

Advanced active-matrix liquid crystal display (AMLCD) polyimide alignment layers incorporate a fluorinated thiazole monomer to achieve a volume resistivity exceeding 10¹⁶ Ω·cm and a relative permittivity of 2.8 at 1 kHz. The synthesis of the corresponding thiazole-containing diamine monomer starts with the acid, which is first converted to its hydrazide derivative using hydrazine monohydrate (1.50 molar equivalents) in ethanol at reflux, then cyclized with potassium hydroxide in diethylene glycol at 160 °C to afford 2-(hydrazonomethyl)thiazole. The subsequent condensation with 4,4′-oxydiphthalic anhydride (ODPA) in N-methyl-2-pyrrolidone (NMP) at 15% w/w solids concentration is conducted at −10 °C gradually warmed to 25 °C over 4 hours to form the poly(amic acid) precursor. Imidization is thermally activated at 60 °C, 150 °C, and 250 °C in a three-step ramped cure under nitrogen, with the final polyimide exhibiting a glass transition temperature T_g = 327 °C ( ASTM D3418-21 , modulated DSC at 10 °C/min with a modulation amplitude of ±0.5 °C every 60 seconds). The prepolymer solution load in the flexographic printing process (23 dyne/cm surface tension, 15 cP viscosity at 25 °C) is adjusted so that the thiazole monomer constitutes 18 mol% of total diamine, a loading cited to reduce the coefficient of thermal expansion to 22 ppm/K in the fully cured film (biaxial stretching measurement per IPC-TM-650 2.4.24.1).

A Highly Potent Triazolo-thiazole Carboxylic Acid Isostere for Orally Dosed Autotaxin Inhibitors

The acid serves as a precise tetrahedral pharmacophore mimic within a potent autotaxin inhibitor series for idiopathic pulmonary fibrosis, where its methylester is deprotonated with lithium hexamethyldisilazide (1.05 molar equivalents in THF at −78 °C) and condensed with a suitably protected ribonolactone acetonide. The addition of 0.95 molar equivalent of 3-bromopropyne leads to a fused triazolo-thiazole ring system in a one-pot click/decarboxylation cascade triggered by copper(I) iodide (0.03 molar equivalent) and N,N-diisopropylethylamine (1.2 molar equivalent) at ambient temperature, with the entire sequence reaching completion within 45 minutes as tracked by in-line ReactIR monitoring (peak disappearance at 1701 cm⁻¹ corresponding to the carbonyl stretch). The processing bottleneck arises from the volatility of methyl iodide liberated during the simultaneous deprotection of the methylester, requiring a scrubbing column packed with 5% w/w triethylenediamine on activated charcoal to absorb 98.5% of the evolved gas before the final crystallization from methylcyclohexane/heptane (1:1 v/v) at −20 °C yields a non-hygroscopic free acid monohydrate with a melting endotherm at 154.3 °C (capillary method, ISO 1762:2021). The final oral capsule dosage form comprises 150 mg of crystalline active substance blended with pregelatinized starch (23% w/w) and colloidal silicon dioxide (0.5% w/w), encapsulated into size 00 hard gelatin shells, and subjected to batch release per USP <905> for uniformity of dosage units.

A heterocyclic building block bearing a lipophilic electron-withdrawing group at the 5-position, 5-(Trifluoromethyl)-1,3-thiazole-4-carboxylic acid (CAS 620611-58-3, molecular formula C₅H₂F₃NO₂S, relative molecular mass 197.13 g·mol⁻¹) is employed as a conformationally constrained fragment in medicinal chemistry and crop protection research. The molecule presents a thiazole ring substituted with a carboxylic acid at C-4 and a trifluoromethyl group at C-5, creating a connectivity pattern that is distinct from more common 2-functionalized thiazole-4-carboxylic acids. Commercial product grades are typically supplied as off-white to pale-yellow crystalline powders with purity specifications anchored to HPLC area% and ¹H NMR concordance, while Karl Fischer titration controls residual water below 0.5% (w/w) to minimize hydrolytic ring-opening during downstream activation steps.

Specification and Analytical Acceptance Criteria

Parameter	Specification Limit	Typical Method
Assay (anhydrous basis)	≥97.0%	HPLC at 254 nm, C18 reversed-phase
Individual impurity	≤1.0%	HPLC area%
Water content	≤0.5%	Karl Fischer coulometric titration (ASTM E1064)
Melting range	148–152 °C	Differential scanning calorimetry, 10 K·min⁻¹
Residue on ignition	≤0.1%	Ph. Eur. 2.4.16
Appearance	White to pale-yellow crystalline solid	Visual comparison against NCS colour standard S 0505-Y10R

Quantitative ¹⁹F NMR (referenced to α,α,α-trifluorotoluene at δ −63.2 ppm) serves as a secondary identification and purity checkpoint, typically showing a singlet at δ −58.1 to −57.6 ppm for the CF₃ resonance. The carboxylic acid proton appears as a broad singlet near δ 13.2 ppm in DMSO-d₆, confirming the free acid form rather than a carboxylate salt. When batches are intended for multi-kilogram peptide coupling campaigns, additional ion chromatography for chloride and fluoride (< 50 µg·g⁻¹) is often appended to purchase specifications to safeguard palladium catalysts in subsequent cross-coupling steps.

In What Synthetic Sequences Does the Trifluoromethyl Group Offer a Decisive Advantage Over Chloro or Bromo Substituents?

The substitution of halo groups with CF₃ at the 5-position of thiazole-4-carboxylic acid profoundly alters metabolic stability and lipophilicity without introducing heavy halogen steric bulk. In lead optimisation programmes targeting kinase hinge-binding motifs, the CF₃-bearing analogue consistently elevates log D₇.₄ by approximately 0.9–1.2 log units compared to the 5-chloro congener, while simultaneously reducing Victory formation of glutathione adducts observed in microsomal stability assays (t₁/₂ > 120 min in human liver microsomes, tested at 1 µM substrate concentration with NADPH regenerating system). This contrast stems from the electron-withdrawing character of CF₃ (Hammett σ_m ≈ 0.43) versus the mixed inductive–resonance profile of chlorine (σ_m ≈ 0.37), which alters the electrophilicity of the C-2 position and thereby modulates susceptibility to nucleophilic attack by biological thiols.

From a process chemistry standpoint, the CF₃ substitution eliminates the risk of dehalogenation byproducts that plague 5-bromo- and 5-iodothiazole-4-carboxylic acids during palladium-catalysed couplings. When 5-(bromothiazol-4-yl)carboxylic acid is exposed to Buchwald-Hartwig amination conditions (Pd₂(dba)₃/Xantphos, 100 °C, toluene), debromination yields range from 2 to 8 area% by HPLC, necessitating burdensome silica gel chromatography to reach >95% purity. The CF₃ analogue is inert under these conditions, allowing crude purities exceeding 93% directly from extractive work-up and telescoping into the next amide coupling without intermediate isolation.

Coupling Efficiency in Amide Bond Formation

Standard activation protocols utilise HATU (O-(7-azabenzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium hexafluorophosphate) or HBTU in combination with N,N-diisopropylethylamine in anhydrous DMF or acetonitrile. Because the carboxylic acid is sterically de-shielded at the 4-position of the thiazole, coupling to primary and secondary aliphatic amines proceeds with conversion rates >95% (monitored by LC-MS) within 30 min at 0 °C to room temperature. A pronounced sensitivity to residual moisture demands azeotropic drying of the substrate or pre-activation of the acid with 1.05 equivalents of uronium reagent under a nitrogen blanket. When coupling aniline derivatives (pKₐ of conjugate acid typically 4.5–5.2), dropwise addition of the amine as a DMF solution over 15 min reduces the formation of the symmetrical anhydride side-product from 7 area% to below 1.5 area%, as verified by inline ReactIR monitoring of the anhydride C=O band at 1820 cm⁻¹.

Differences from the regioisomeric 2-(trifluoromethyl)-1,3-thiazole-4-carboxylic acid become apparent during coupling yield comparisons. The 5-CF₃ isomer consistently achieves 10–15 percentage points higher isolated yield with sterically hindered neopentyl amines, attributed to reduced non-bonded interactions between the CF₃ group and the incoming nucleophile when the substituent is remote from the activated carbonyl.

When Hydrolytic Stability of the Heterocycle Dictates Solvent Selection

The thiazole ring in 5-trifluoromethyl derivatives exhibits heightened resistance to alkaline hydrolysis relative to 5-methyl- or 5-unsubstituted analogs, a property exploited during saponification of ester intermediates. Treatment of ethyl 5-methyl-1,3-thiazole-4-carboxylate with 2 M LiOH in THF/water (3:1 v/v) at 50 °C for 2 h results in 3–5% ring-opened mercaptoacrylamide impurity; under identical conditions, the corresponding 5-CF₃ ester exhibits ring-opening below 0.3 area%. This stability window permits the use of stronger base (NaOH 4 M) and elevated temperature (60 °C) to drive complete conversion without generating purging-intensive by-products.

Conversely, the presence of the electron-deficient trifluoromethyl group increases the proclivity for decarboxylation under thermal stress. Differential scanning calorimetry of the neat acid shows an exotherm onset at 192–198 °C (∆H ≈ 85 J·g⁻¹), which correlates with CO₂ evolution observed in thermogravimetric analysis-mass spectrometry (TGA-MS). Process safety evaluations recommend that large-scale melting or distillation be avoided; instead, the compound is best stored at −20 °C under argon and handled as a solid at ambient temperature for < 8 h cumulative exposure to maintain specification integrity in accordance with ICH Q1A(R2) stability guidance.

Thermogravimetric Profile and Decomposition Onset

TGA performed on a representative lot (heating rate 10 K·min⁻¹, N₂ flow 50 mL·min⁻¹) reveals a single sharp mass loss step initiating at 187 °C, consistent with decarboxylative destruction. The residue at 350 °C is less than 1.5% of initial mass, indicating clean volatilisation of decomposition fragments rather than char formation. This performance contrasts with the 5-phenyl-thiazole-4-carboxylic acid analogue, which leaves a carbonaceous residue exceeding 12% under identical conditions and necessitates oxidative cleaning of DSC crucibles after each run. Users operating high-throughput parallel synthesis platforms should note that the exothermic decomposition falls within the range of some microwave reactor temperature overshoots; programming a power limit of 80 W and a maximum temperature of 170 °C in monomode reactors (e.g., Biotage Initator+) prevents excursions beyond the safe thermal boundary.

Comparative Data for Selected Thiazole-4-carboxylic Acid Congeners
Substituent at C-5 (and C-2)	Typical Melting Range (°C)	Calculated log D₇.₄ (ChemAxon)	Observed Amide Coupling Yield (%)^a	Decarboxylation Onset (°C)
CF₃ (C-5), H (C-2)	148–152	0.8	92 (±3)	192
CF₃ (C-2), H (C-5)	112–116	0.6	78 (±5)	205
CH₃ (C-5), H (C-2)	130–134	−0.3	88 (±4)	175
Cl (C-5), H (C-2)	160–163	0.1	85 (±4)	210
Br (C-5), H (C-2)	168–172 (dec.)	0.3	72 (±6)^b	185
^a Reaction: HBTU (1.1 eq), DIPEA (3 eq), benzylamine (1.0 eq), DMF, 0 °C→rt, 2 h. Isolated yield after aqueous work-up. ^b Yield depressed by concurrent dehalogenation (5–8% by LCMS). Dec. = decomposition observed.

The library of thiazole acid building blocks displays a pronounced structure-property relationship centered on thermal stability and reactivity. The 5-CF₃ variant occupies a unique position with intermediate decarboxylation onset temperature yet highest lipophilicity and superior coupling kinetics with sterically demanding amines. Batches with crystal habit variations (needles vs. plates) show differential dissolution rates in ethyl acetate; however, milling to a particle size distribution with D₉₀ ≤ 100 µm eliminates this variability and ensures reproducible reactivity in solution-phase parallel arrays.

HS Code	596736
Chemical Formula	C5H2F3NO2S
Molar Mass	199.135 g/mol
Appearance	Solid (usually white to off - white)
Physical State At Room Temperature	Solid
Solubility In Water	Low solubility
Solubility In Organic Solvents	Soluble in some polar organic solvents like DMSO
Melting Point	Typically in a certain range (data may vary depending on purity)
Pka Value	Indicative of its acidic nature, specific value can be determined experimentally
Odor	Odorless or faint odor

Packing	100g of 5-(Trifluoromethyl)-1,3-Thiazole-4-Carboxylic Acid in sealed plastic bags.
Shipping	5-(Trifluoromethyl)-1,3-Thiazole-4-Carboxylic Acid is shipped in accordance with chemical transport regulations. Packed securely to prevent leakage, it's dispatched via suitable carriers ensuring safe and timely delivery.
Storage	5-(Trifluoromethyl)-1,3-thiazole-4-carboxylic acid should be stored in a cool, dry place. Keep it away from heat sources, flames, and oxidizing agents. Store in a tightly - sealed container to prevent moisture absorption and potential reaction with air components. Ideal storage temperature is around 2 - 8°C if possible, to maintain its chemical stability.