2-Thienyl-4-Thiazole Ethyl Methanoate

What Are the Organoleptic Drivers of This Ester in Processed Meat Flavours?

Formulators at a European flavour house established that addition rates in thermally processed meat analogues fall between 0.05 and 2.0 ppm (weight/weight in the finished food), a narrow window where the ester imparts roasted, lightly sulfidic brown notes reminiscent of thiamin degradation products. Evaluation in a model ground chicken system (fat content 12 %, sodium chloride 1.5 %) via gas chromatography–olfactometry coupled with aroma extract dilution analysis (GC–O/AEDA) according to ISO 13301:2018 gave a flavour dilution (FD) factor of 128 at a linear retention index of 1845 on a DB-WAX column; the compound was sensorily perceived as savoury, crust-like and faintly oniony at the sniffing port. The critical processing difficulty is the compound’s vulnerability to acid-catalysed ester hydrolysis when dispersed in aqueous flavour bases at pH below 4.5; pre-emulsification in a high-oleic sunflower oil carrier stabilised with 0.1 % rosemary extract (antioxidant) is therefore mandated before blending in a ribbon mixer running at 45 rpm for 12 min. On a 2000 L jacketed stainless steel vessel commissioned for a stock bouillon premix, residual moisture in the triacetin diluent had to be held below 0.05 % Karl Fischer, because drift above this limit generated 2-(thiophen-2-yl)thiazole-4-carboxylic acid detectable by HPLC at 254 nm (method based on USP general chapter <621>), shifting the sensory profile toward an undesirable sour off-note. Regulatory status in the United States requires careful documentation as the substance is not currently listed in 21 CFR §172.515; structurally related thiazole esters are recognised as flavour constituents in a number of FEMA GRAS compounds, and a full safety evaluation under JECFA specifications for flavouring agents is typically requested for new substance dossiers. In the European Union, registration under Regulation (EC) No 1334/2008 on food flavourings demands a five-batch certificate of analysis, validated sensory profiling according to EN ISO 8587:2007, and migration data when the flavour is incorporated into a multilayer laminate. The finished flavour formulation is dosed into instant noodle seasoning powder, retorted soups or plant-based burger patties, where interaction with cysteine and reducing sugars in the Maillard cascade can amplify the meaty character or, under excessive thermal load (>121 °C for 30 min), degrade the thienyl ring and liberate hydrogen sulfide above the sulfurous defect threshold.

Generating Orthogonal Reactivity for Heterocyclic Drug Scaffolds Via the 4-Carboethoxy Group

A key strategic advantage of ethyl 2-(thiophen-2-yl)thiazole-4-carboxylate in medicinal chemistry is that the ester handle can be manipulated orthogonally in the presence of the electrophile-sensitive thiophene ring without protection at the 2-position. Saponification with lithium hydroxide monohydrate (1.2 eq.) in a 3:1:1 mixture of tetrahydrofuran, methanol and water at 0 °C for 45 min yields the corresponding carboxylic acid in excess of 95 % conversion with no detectable thienyl ring-opening by ¹H NMR. This acid is then activated with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDCI) and 1-hydroxybenzotriazole (HOBt) in anhydrous dimethylformamide to couple with a range of primary and secondary amines, a transformation that has been exploited to generate focused libraries targeting dipeptidyl peptidase-4 (DPP-4) and phosphoinositide 3-kinase (PI3K) isoforms. On a pilot scale (5 kg batch) the coupling was run in a 50 L glass-lined reactor equipped with a retreat-curve impeller at 150 rpm; the exotherm upon EDCI addition required jacket cooling to hold internal temperature strictly below +5 °C, because higher temperatures promote racemisation of any chiral amine component and accelerate N-acylurea side-product formation. Purification of the resulting amide normally employs normal-phase flash chromatography on silica gel (230–400 mesh) with a 20–50 % ethyl acetate in heptane gradient, though for GMP intermediate production under ICH Q7 guidelines, a switch to preparative HPLC with a C18 stationary phase and acetonitrile/water (0.1 % trifluoroacetic acid) mobile phase was implemented to ensure residual palladium, originating from an earlier Suzuki–Miyaura coupling on the thienyl ring, remained below 10 µg/g as measured by inductively coupled plasma mass spectrometry per USP <233>. Residual tetrahydrofuran and dimethylformamide are quantified by headspace gas chromatography with flame ionisation detection in accordance with USP <467>, applying acceptance criteria of 720 ppm for THF and 880 ppm for DMF. The terminal drug substances containing this building block have been described as selective kinase inhibitors; in one published series the thienyl-thiazole scaffold occupied the hinge-binding region and the ethyl ester was hydrolysed in the final step to a carboxylate that engaged a lysine salt bridge, a design confirmed by X-ray co-crystallography at 1.9 Å resolution.

The convergent strategy for synthesising broad-spectrum carboxamide fungicides relies on the generation of an acyl chloride intermediate from 2-(thiophen-2-yl)thiazole-4-carboxylic acid, which is rapidly consumed because the free acid exhibits poor solubility in non-polar media. A standard activation protocol adds oxalyl chloride (1.5 eq.) and a catalytic quantity of anhydrous dimethylformamide (0.05 eq.) to a suspension of the acid in dichloromethane at 0 °C under a nitrogen sweep; vigorous gas evolution (CO, CO₂) is observed, and the mixture is allowed to warm to 20 °C over 2 h. Stripping of excess oxalyl chloride under reduced pressure with a rotary evaporator operated at 35 °C bath temperature and 20 mbar leaves the crude acyl chloride as a yellow oil, which is immediately dissolved in anhydrous acetonitrile and added dropwise to a chilled (5 °C) solution of a substituted aniline and triethylamine (2.2 eq.) as an acid scavenger. In field trials the resulting carboxamide demonstrated activity against Botrytis cinerea and Rhizoctonia solani at application rates of 100–250 g a.i./ha, though the methyl ester analogue often exhibited superior phloem mobility in systemic assessments conducted under OECD Guideline 506. Process robustness on a 2000 L Hastelloy C-22 reactor at a contract manufacturing site encountered a significant exotherm during the acid chloride coupling when the amine feed was accelerated; a safety limit of adiabatic ΔT below 50 °C was established using reaction calorimetry (Mettler Toledo RC1e) with a heat transfer coefficient of 250 W·m⁻²·K⁻¹, and the jacket was programmed to switch to brine circulation when the temperature reached 12 °C. The technical material was isolated by solvent swap into toluene and crystallisation by slow cooling to -5 °C, giving a polymorphically stable Form A with a melting point of 168–170 °C and a purity of 98.5 % by ASTM D3465 GC. For formulation as a suspension concentrate, the active ingredient was milled in a wet bead mill with 0.4–0.6 mm yttrium-stabilised zirconia beads until the particle size distribution reached a Dv90 below 5 µm confirmed by laser diffraction using ISO 13320:2020. Regulatory submission to the European Commission under Regulation (EC) No 1107/2009 requires a five-batch analysis and validated methods for relevant impurities such as the hydrolysed acid (≤0.15 %) and the dimeric thienyl disulfide (≤0.10 %). The formulated product is packaged in fluorinated high-density polyethylene containers and stored at ambient conditions with a shelf-life of 24 months verified by accelerated stability testing at 54 °C per FAO/WHO pesticide formulation guidelines.

When Ethyl 2-(Thiophen-2-yl)thiazole-4-carboxylate Serves as a Comonomer in Low-Bandgap Polymers

When this ester monomer is copolymerised with an electron-rich 2,5-bis(trimethylstannyl)thiophene via palladium-catalysed Stille cross-coupling, the resulting alternating donor–acceptor architecture exhibits an optical bandgap as low as 1.8 eV in thin films, positioning the material as a potential absorber in bulk-heterojunction organic photovoltaic cells. The polymerisation is executed in a glovebox under dry argon (H₂O < 0.1 ppm, O₂ < 0.1 ppm) using tris(dibenzylideneacetone)dipalladium(0) (2.5 mol%) and tri(o-tolyl)phosphine (10 mol%) in anhydrous chlorobenzene at 110 °C for 48 h; precise control of the stoichiometric ratio (1.000:1.005 monomer:stannyl comonomer) is necessary to achieve a weight-average molecular weight (Mw) above 30 kDa for film-forming properties. After quenching with 2-tributylstannylthiophene and subsequent iodine-catalysed chain-end capping, the crude polymer is purified by sequential Soxhlet extraction with methanol, acetone and hexane, followed by recovery of the polymer fraction from the chlorobenzene extract and precipitation into methanol. The dried solid is characterised by gel permeation chromatography in tetrahydrofuran at 35 °C with refractive index detection and polystyrene calibration according to ASTM D5296-19; a 50:50 copolymer typically yields an Mw of 38 kDa and a polydispersity index of 2.1. Cyclic voltammetry on drop-cast films immersed in acetonitrile with 0.1 M tetrabutylammonium hexafluorophosphate, referenced versus ferrocene/ferrocenium, gives an oxidation onset at approximately +1.05 V vs. Ag/AgCl, corresponding to a HOMO energy level of roughly –5.4 eV when calibrated against a vacuum level of –4.8 eV for ferrocene; published data for this exact ester copolymer are scarce, so the figures should be interpreted as indicative of the thienyl-thiazole donor capacity. Thin-film processing by blade-coating on polyethylene terephthalate substrates requires adjusting the solution viscosity to 25–35 cP at a solid content of 15 mg/mL in o-dichlorobenzene, with a doctor blade gap of 200 µm and a coating speed of 5 cm/min on a substrate heated to 70 °C, yielding 100 nm films with a root-mean-square roughness below 0.5 nm by atomic force microscopy. In device integration, the electron acceptor commonly selected is [6,6]-phenyl-C₆₁-butyric acid methyl ester in a 1:1.2 weight ratio, and the inverted architecture (ITO/ZnO/active layer/MoO₃/Ag) is tested under simulated AM 1.5G illumination at 100 mW/cm² following ASTM E1021-15 spectral responsivity guidelines; preliminary power conversion efficiencies of 3.2–4.0 % have been noted in patent literature for structurally analogous thiazole-containing copolymers. Key failure mechanisms include photo-oxidation of the thienyl ring at the methylene position of the ester group, generating a carbonyl defect that traps charge carriers and increases series resistance; accelerated ageing tests under continuous illumination in air at 65 °C demonstrate a half-life of 120 h, necessitating encapsulation with commercial getter-loaded barrier films having a water vapour transmission rate below 5×10⁻⁴ g·m⁻²·day⁻¹.

The ethyl methanoate moiety serves as a temporary protecting group for the carboxylic acid during thienyl ring halogenation, a transformation notoriously difficult with the free acid because of decarboxylation under electrophilic conditions. Bromination with 1.0 eq. of N-bromosuccinimide in a mixture of acetic acid and chloroform at 25 °C selectively installs a bromine atom at the 5-position of the thiophene in 85 % yield while the ester remains intact; subsequent Sonogashira coupling with trimethylsilylacetylene under standard conditions (Pd(PPh₃)₂Cl₂, CuI, Et₃N, THF, 60 °C, 8 h) extends the π-system, and the silyl group is removed with tetrabutylammonium fluoride. The ester is frequently used as a precursor to aldehydes through a two-step sequence: reduction with diisobutylaluminium hydride (DIBAL-H) in dichloromethane at –78 °C affords the corresponding primary alcohol, which is then oxidised with Dess-Martin periodinane to the aldehyde in a combined yield of 78 % over both steps. This aldehyde participates in Knoevenagel condensations with malononitrile in ethanol catalysed by piperidine, generating dicyanovinyl derivatives that exhibit strong solvatochromism. When introduction of a trifluoromethyl group is required, the carboxylic acid obtained from ester hydrolysis is converted to the corresponding acid fluoride using cyanuric fluoride and pyridine, then treated with sulfur tetrafluoride in a Hastelloy-lined pressure vessel at 85 °C for 16 h, circumventing heavy-metal-based trifluoromethylation. The commercial supply chain for this building block relies on a release specification that guarantees consistent performance across the above transformations; Table 2 lists the typical certificate-of-analysis parameters accepted by major pharmaceutical discovery groups, employing methodologies codified by international pharmacopoeial and ASTM standards. A recurring quality issue involves the presence of 2-cyanothiophene as a contaminant arising from thermal degradation of the thiazole ring during distillation; short-path vacuum distillation at a pressure below 0.5 mbar with an oil bath temperature not exceeding 140 °C is therefore recommended, with the receiving flask cooled to –20 °C by a recirculating chiller. Purified material is packaged in amber borosilicate glass ampoules under argon and stored at 2–8 °C; under these conditions no significant increase in hydrolysis product is detected by GC per ASTM D3465 over a 36-month period.

Cyclometalated Iridium(III) Complexes Bearing the Thienyl-Thiazole Ligand

Cyclometalation with iridium trichloride hydrate (IrCl₃·3H₂O) in a 3:1 mixture of 2-ethoxyethanol and water forms a chloro-bridged dimer in which the deprotonated 2-(thiophen-2-yl)thiazole acts as a C^N chelating ligand via the thienyl carbon and the thiazole nitrogen; the reaction is maintained at 120 °C under nitrogen for 24 h, after which the dimer is cleaved with a bidentate ancillary ligand such as acetylacetonate (acac) or picolinate in the presence of sodium carbonate. Although a systematic photophysical dataset for the ethyl ester derivative remains unpublished, a closely analogous complex incorporating a methyl ester substituent at the 4-position exhibited a photoluminescence quantum yield (PLQY) of 0.52 measured in deoxygenated toluene by an absolute integrating sphere method based on ISO 23603:2005 principles, and this value serves as a reference point for performance assessment. Purification of the heteroleptic iridium complex requires gradient column chromatography on silica gel deactivated with triethylamine, followed by recrystallisation from dichloromethane/hexane to give an orange-red solid. Device fabrication in a vacuum thermal evaporator (base pressure 2×10⁻⁷ mbar) dopes the emitter at 6 wt% into a 4,4′-bis(N-carbazolyl)-1,1′-biphenyl host matrix to construct phosphorescent organic light-emitting diodes (PhOLEDs) with the architecture ITO/MoO₃/TAPC/host:emitter/TmPyPB/LiF/Al. Electroluminescent characterisation of the analogue yields a current efficiency of 38 cd/A and an external quantum efficiency of 12.5 % at a luminance of 1000 cd/m², with a device lifetime T50 exceeding 800 h at an initial luminance of 5000 cd/m² when encapsulated under nitrogen. For high-purity sublimation-grade material required in OLED pilot lines, the complex is subjected to three-zone gradient sublimation with temperature zones set to 260 °C, 200 °C and 25 °C under a vacuum of 5×10⁻⁶ mbar; the recovered sublimate achieves an assay of 99.95 % by HPLC with detection at 370 nm, and trace metal contamination is verified to be below 1 ppm for each of Na, K and Fe via ICP-OES according to EN 71-3:2019 migration modelling, satisfying the purity requirements of evaporated OLED manufacturing. The ligand itself, prior to metalation, must be free from coordinating sulfur-containing impurities; a pre-treatment with a copper(I) iodide scrubber column removes residual thiol traces that would otherwise create non-emissive dark sites in the phosphorescent film. During prolonged storage of the iridium complex in solid form, exposure to ambient humidity above 40 % RH causes slow hydrolysis of the ethyl ester pendent group with a half-life of approximately 150 days at 25 °C, necessitating vacuum-sealed packaging with molecular sieve desiccant for shelf-stability.