Ethyl Thiazole-4-Carboxylate

Product Name Ethyl Thiazole-4-Carboxylate
Alias ethyl 4-thiazolecarboxylate
Einecs 619-926-2
Mininmum Order 1g
Factory Site West Ujimqin Banner, Xilingol League, Inner Mongolia, China
Price Inquiry sales9@bouling-chem.com
Manufacturer Bouling Chemical Co., Limited
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In terms of specification, Ethyl Thiazole-4-Carboxylate is supplied with ≥98% purity (GC) and ≤0.5% water content (KF), making it suitable for use as a pharmaceutical and agrochemical intermediate.

Specifications

HS Code	169669
Chemical Formula	C6H7NO2S
Molar Mass	157.19 g/mol
Appearance	Typically a colorless to light - yellow liquid or solid
Boiling Point	Approximately 220 - 225 °C (reported values may vary)
Solubility	Soluble in organic solvents like ethanol, acetone; less soluble in water
Odor	May have a characteristic, somewhat pungent or sulfur - like odor
Stability	Stable under normal conditions, but may react with strong oxidizing agents

As an accredited Ethyl Thiazole-4-Carboxylate factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.

Packing & Storage

Packing	Ethyl Thiazole - 4 - Carboxylate, 500g, packaged in a sealed, chemical - resistant bottle.
Shipping	Ethyl Thiazole - 4 - Carboxylate is shipped in well - sealed containers. Packaging adheres to chemical transport regulations. Shipment is carefully monitored for temperature and handled with care to prevent breakage and ensure safe transit.
Storage	Ethyl thiazole - 4 - carboxylate should be stored in a cool, dry, and well - ventilated area. Keep it away from heat sources, open flames, and oxidizing agents. Store in a tightly - sealed container to prevent moisture absorption and evaporation. Ideal storage temperature is around 2 - 8°C in a refrigerator for long - term stability, protecting it from potential chemical degradation.

Application of Ethyl Thiazole-4-Carboxylate

Within flavour and fragrance compounding facilities operating under ISO 22000:2018 prerequisite programmes, ethyl thiazole-4-carboxylate (CAS 14527-43-6, FEMA No. 3680) is deployed primarily as a high-impact nitrogen-sulfur heterocyclic intermediate whose sensory threshold in aqueous sucrose solution (5% w/v) registers at 0.5 ppb to 1.2 ppb depending on the purity of the distillation cut. The ester is not typically isolated as a finished flavouring substance for direct addition but rather undergoes controlled alkaline hydrolysis to the corresponding 4-thiazolecarboxylic acid (CAS 14527-41-4), which subsequently participates in Maillard-type condensations with reducing pentoses under strictly buffered conditions at pH 5.8 to 6.3. Production-scale hydrolysis in a 500 L glass-lined reactor (Pfaudler AE-series or equivalent, jacket temperature maintained at 62 °C ± 1 °C) uses aqueous NaOH at 0.95 to 1.05 molar equivalents relative to the ester, with endpoint determination by HPLC (C18 column, 210 nm detection, residual ester content below 0.15 area%). The acid intermediate is then reacted with D-xylose at a molar ratio of 1:1.2 (acid:xylose) in propylene glycol at 118 °C under nitrogen blanket for 45 to 60 minutes, generating a complex mixture of roasted, nutty, and sulfurous meaty character impact compounds dominated by 2-acetylthiazole and trace 2-isobutylthiazole. Process safety note: the carboxylate ester exhibits sensitivity to prolonged heating above 150 °C in the presence of residual moisture, where decarboxylation becomes exothermic and releases CO₂; reactor pressure relief sizing per API 520 Part I is mandatory when bulk quantities exceed 25 kg per batch. Finished flavour keys containing this derivative are incorporated into beef bouillon powder at 0.08% to 0.25% of the total dry mix, into liquid poultry stock concentrate at 12 ppm to 35 ppm, and into retorted wet cat food gravies where the thiazole-derived character survives F₀ 3.0 retort processing with sensory retention exceeding 72% relative to pre-retort intensity as measured by GC-MS-SIM quantification of 2-acetylthiazole.

Stability of the Ester Moiety in Anhydrous Fragrance Accords: Gas Chromatographic Monitoring of Transesterification Side Reactions During Alcohol-Based Diluent Storage

When ethyl thiazole-4-carboxylate is dissolved in anhydrous ethanol (96% v/v or higher, denatured with 0.1% tert-butyl alcohol) for use as a fragrance intermediate in fine-fragrance concentrate preparation, a slow transesterification equilibrium establishes between the ethyl ester and the ethanolic solvent, generating the ethyl ester of the original compound alongside a measurable accumulation of the methyl ester when methanol-denatured ethanol is inadvertently substituted. This side reaction, monitored over 180 days of accelerated storage at 40 °C in sealed borosilicate vials under darkness per ICH Q1B photostability guidelines, produces 1.8% to 2.4% of the methyl ester homolog after 90 days when 1% methanol is present. The presence of the methyl ester shifts the odour character threshold in the final diluted accord from a green, slightly tomato-leaf profile toward a more pungent, alliaceous note that perfumers detect at the 0.02% incorporation level of the degraded stock. Analytical quality control in fragrance houses typically requires GC-FID purity of the ester to remain above 98.5% by area normalization (DB-WAX column, 30 m × 0.32 mm × 0.50 µm film, temperature program from 60 °C to 230 °C at 8 °C/min) before release to compounding. Stability data generated by one Swiss manufacturer (Givaudan internal method TM-0147, not publicly distributed but referenced in collaborative IFRA technical papers) indicates that addition of 0.05% butylated hydroxytoluene to the drum stock does not mitigate transesterification but does suppress oxidative discolouration that otherwise raises absorbance at 440 nm above 0.15 AU after 12 months of ambient storage in high-density polyethylene containers. Nitrogen blanketing of the headspace during drum filling and subsequent storage reduces dissolved oxygen below 0.8 ppm and further extends colour stability. For perfumers blending a tropical fruit accord where this thiazole ester provides a sulfury underripe mango or durian nuance at 0.005% to 0.015% of the concentrate, the methyl ester artifact must remain below sensory threshold; this demands solvent selection using anhydrous ethanol from a dedicated thiazole-free still and rejection of any solvent batch with methanol content exceeding 0.05% as determined by headspace GC-MS.

How Does the 4-Carboxylate Substituent Modulate Metal Chelation Behaviour in Heterocyclic Corrosion Inhibitor Formulations for Copper-Based Microelectronic Interconnects?

The thiazole ring nitrogen and the carbonyl oxygen of the ester group in ethyl thiazole-4-carboxylate present a bidentate coordination geometry that has been exploited in formulated aqueous corrosion inhibitor packages for chemical-mechanical planarization (CMP) post-clean steps applied to copper Damascene interconnects at the 14 nm node and below. When dissolved at 0.8 mM to 2.5 mM in deionized water containing 0.1% tetramethylammonium hydroxide (pH 10.2 to 10.9), the ester undergoes partial hydrolysis in situ to the carboxylate anion, which coordinates to Cu(I) oxide surfaces with a binding energy measured by X-ray photoelectron spectroscopy (XPS) of 399.8 eV (N 1s peak shift relative to unbound thiazole) and forms a passivation film 2.1 nm to 3.5 nm thick as determined by spectroscopic ellipsometry. This film inhibits static etch rate of electroplated copper in 0.5% H₂O₂/1% glycine slurry chemistry at pH 9.5 from a baseline of 28 Å/min to below 3 Å/min at 25 °C. Electrochemical impedance spectroscopy (EIS) data collected at open-circuit potential in 0.1 M KCl electrolyte reveals a polarization resistance increase from 4.2 kΩ·cm² to 22.7 kΩ·cm² upon addition of 2 mM of the pre-hydrolyzed ester, with a phase angle maximum at 0.1 Hz shifting from 48° to 67° consistent with capacitive film formation. A critical process limitation emerges in high-volume manufacturing: the ester is only sparingly soluble in pure water (measured log P = 1.42 ± 0.03, aqueous solubility 1.2 g/L at 23 °C), requiring pre-dispersion in an equal-mass blend of dipropylene glycol methyl ether for tank dilution. Additionally, the passivation film is thermally labile above 85 °C; post-CMP brush scrubber modules operating at elevated platen temperatures must limit the inhibitor contact time to below 45 seconds otherwise film decomposition releases free thiazole fragments that adsorb irreversibly onto low-κ dielectric surfaces and alter the effective κ-value by +0.15 to +0.30 as measured by mercury probe CV.

Parameter	Condition Without Inhibitor	With 2 mM Ethyl Thiazole-4-Carboxylate (Pre-hydrolyzed)
Cu static etch rate (Å/min)	28.0	2.7
Polarization resistance (kΩ·cm²)	4.2	22.7
Film thickness (nm)	N/A	2.1 – 3.5
EIS phase angle at 0.1 Hz (°)	48	67
κ-value shift on low-κ dielectric after thermal stress	0	+0.15 – +0.30 (above 85 °C)

5-Nitrothiazole Pharmacophore Construction: The Carboxylate as a Regioselective Nitration Substrate in the Synthesis of 2-Substituted Nitroimidazole Bioisosteres

Ethyl thiazole-4-carboxylate serves as a starting material in medicinal chemistry campaigns targeting anaerobic bacterial nitroreductase enzymes, where the electron-deficient character of the thiazole ring (calculated HOMO energy -7.2 eV at the B3LYP/6-31G* level) directs electrophilic nitration exclusively to the 5-position under mixed-acid conditions. The nitration protocol adopted by contract research organizations for kilogram-scale preparation uses fuming nitric acid (1.2 equivalents, d = 1.50 g/mL) in oleum (20% free SO₃) at 0 °C to 5 °C over 4 hours, achieving 82% to 87% isolated yield of ethyl 5-nitrothiazole-4-carboxylate after drowning into crushed ice and filtration through a glass sinter funnel. The position of nitration is confirmed by ¹H NMR disappearance of the thiazole C5 proton singlet at δ 8.32 ppm (in DMSO-d₆) and the appearance in ¹³C NMR of a diagnostic C5 signal at δ 147.6 ppm coupled to the nitro group. The resultant 5-nitro intermediate undergoes palladium-catalyzed Suzuki-Miyaura cross-coupling at the 2-position after conversion to the 2-bromo derivative via a Sandmeyer-type sequence employing tert-butyl nitrite and CuBr₂ in acetonitrile at 60 °C. Coupling with phenylboronic acids bearing electron-withdrawing para-substituents proceeds with Pd(PPh₃)₄ (2 mol%) and K₂CO₃ in degassed dioxane/water (4:1) under microwave irradiation at 120 °C for 25 minutes, providing biaryl thiazoles that exhibit MIC values against Clostridium difficile ATCC 43255 from 0.25 µg/mL to 1.0 µg/mL in broth microdilution assays according to CLSI M11-A8. A synthetic process safety note of primary importance: the 5-nitro derivative is thermally labile above its melting point of 94 °C and should be dried under vacuum at 35 °C for no longer than 16 hours; differential scanning calorimetry at a 10 °C/min ramp rate reveals an exothermic decomposition onset at 182 °C with an energy release of 890 J/g, classifying it as a DOT Class 4.1 self-reactive solid for transportation quantities exceeding 5 kg.

What Happens to Ester Hydrolysis Kinetics in Extruded Starch Matrices When the Reactive Thiazole is Used as a Covalent Thermoplastic Aroma Precursor?

Incorporation of ethyl thiazole-4-carboxylate into extruded snack pellet formulations at 0.15% to 0.40% of the dry feed mass exploits the thermal and shear conditions inside a co-rotating twin-screw extruder (L/D = 32:1, barrel diameter 37 mm, screw speed 180 rpm, temperature profile from zone 2 through zone 8: 90 °C / 120 °C / 145 °C / 165 °C / 175 °C / 185 °C / 195 °C) to trigger partial hydrolysis of the ester to the free acid. The acid subsequently undergoes decarboxylation at the die plate where material temperature reaches 197 °C to 203 °C under 85 bar to 110 bar of back-pressure, releasing CO₂ and generating unsubstituted thiazole and trace 4-methylthiazole, both of which contribute roasted, nutty, and slightly popcorn-like top-notes when the puffed pellet is microwave-finished by the consumer. The degree of ester conversion during extrusion is critically dependent on the moisture content of the preconditioned feed: at 18% total moisture, conversion to the free acid reaches 34% to 38%, whereas at 22% moisture, conversion jumps to 61% to 66% due to increased hydrolytic activity and reduced melt viscosity. Viscosity reduction inside the barrel, caused by the plasticizing effect of the free thiazole acid, manifests as a specific mechanical energy (SME) drop from a baseline of 420 kJ/kg to 385 kJ/kg at the 0.40% addition level, which must be compensated by increasing screw speed by 8% to 12% to maintain equivalent starch dextrinization as measured by water absorption index (WAI) remaining within 6.2 g/g ± 0.3 g/g. Pellet expansion ratio upon frying in palm oil at 180 °C decreases from 3.8 to 3.2 when the thiazole derivative is included, attributable to early gas nucleation from CO₂ release that disrupts bubble wall integrity; this limitation confines the maximum usable dosage to 0.40% and dictates that snack manufacturers targeting high-expansion products (expansion ratio above 3.5) must reduce the ester addition to 0.20% or below and supplement the roasted note character with separate top-dusting thiazole-containing seasoning applied post-frying.

Feed Moisture (%)	Ester-to-Acid Conversion (%)	SME (kJ/kg)	Expansion Ratio (Post-Fry)
18	34 – 38	412	3.4
20	47 – 52	398	3.3
22	61 – 66	385	3.2

Published data for the migration kinetics of thiazole-derived low-molecular-weight species from the extruded starch matrix into surrounding food simulants (EU Regulation 10/2011 Annex III: simulant A [10% ethanol], simulant D1 [50% ethanol], simulant E [Miglyol 812]) is limited; diffusion coefficients estimated from short-term migration tests at 40 °C for 10 days using headspace solid-phase microextraction (HS-SPME) coupled with GC×GC-TOFMS suggest overall migration values below the 10 mg/dm² overall migration limit specified in EU 10/2011 when the ester is present at 0.20% in the pellet, but specific migration of the decarboxylated thiazole itself requires dedicated analytical attention as it is not listed in the Union List of authorized monomers and additives and would fall under the non-intentionally added substance (NIAS) risk assessment framework set forth in Article 19 of the regulation.

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Certification & Compliance

Ethyl Thiazole-4-Carboxylate 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

Introduced as an isolable crystalline solid at ambient temperatures, ethyl thiazole-4-carboxylate (CAS 14527-43-6) carries a molecular weight of 157.19 g mol⁻¹ and is supplied with a typical melting range of 44–46 °C (USP 〈741〉 Class Ia). Commercial material is routinely specified to an HPLC purity (area-percent) of ≥ 98.0%, with water content held below 0.5% by Karl Fischer titration (USP 〈921〉 Method Ia) and residue on ignition not exceeding 0.1% (USP 〈281〉). The ester exists as white to off-white prisms that darken only marginally after 24 months when stored in sealed containers under argon at 2–8 °C, a stability profile confirmed by accelerated ICH Q1A(R2) hold-time studies at 40 °C/75% RH for 6 months. In continuous-flow hydrogenation sequences targeting thiazole-fused piperidine pharmacophores, the 4-carboxylate ester demonstrates a ring-strain profile that suppresses over-reduction of the endocyclic C=N bond when compared with 2-alkyl thiazole derivatives. On a Corning G1 SiC reactor plate with a channel hydraulic diameter of 1.0 mm, a 0.25 M solution of ethyl thiazole-4-carboxylate in anhydrous THF is co-fed with hydrogen gas at a molar ratio of 1:3 through a 5% Pt/C packed-bed cartridge maintained at 25 ± 1 °C. Back-pressure is regulated to 250 psi and residence time is held at 5 min. Within this narrow thermal envelope—deviation beyond 30 °C triggers an increase in the thiazolidine byproduct to greater than 5 area-%—selectivity for the desired 4-ethoxycarbonylpiperidine scaffold exceeds 90%. Published calorimetry data for neat ethyl thiazole-4-carboxylate place the onset of the first exothermic event at 282 °C by differential scanning calorimetry (DSC) at a scan rate of 10 °C min⁻¹, indicating that the processing window is wide enough for standard hydrogenation protocols but not broad enough for uncontrolled adiabatic excursions during solvent recovery.

What Distinguishes the 4-Carboxylate from the 2-Carboxylate Series?

Regioisomeric placement of the carboxylate on the thiazole nucleus alters both physical state and reactivity. Ethyl thiazole-2-carboxylate (CAS 14527-42-5) is routinely encountered as a low-melting solid that liquefies above 30–32 °C, whereas the 4-isomer remains a free-flowing powder at typical warehouse temperatures up to 40 °C. This difference in lattice energy directly impacts dispensing accuracy on automated solids-handling platforms: gravimetric feeders with loss-in-weight control achieve an RSD of < 1.0% for the 4-ester but frequently exceed 3.5% for the partially fused 2-isomer unless the feed hopper is jacketed and chilled. Electronically, the 4-carboxylate withdraws electron density primarily from the C5 position, leaving C2 relatively electron-rich and susceptible to electrophilic bromination with NBS in DMF at 0 °C. In palladium-catalyzed direct arylation using Pd(OAc)₂ and P(t-Bu)₃·HBF₄, the 4-ester exhibits higher turnover numbers at C2 than the 2-ester at C4, a regiochemical consequence exploited during the assembly of FLT3 inhibitor building blocks. Production-scale handling at quantities above 25 kg has revealed electrostatic charge accumulation during bag emptying under low-humidity conditions (< 30% RH). Operators report that free-fall transfer from polyethylene liners into glass-lined reactors frequently generates a surface resistivity below 1 × 10⁹ Ω/sq, sufficient to produce visible sparking. Grounding clamps and nitrogen-purged ionizer bars positioned at the charge station are considered mandatory engineering controls. Once opened, the material must be transferred within 4 h or resealed under inert atmosphere, as ambient moisture uptake at 25 °C/60% RH exceeds 0.2 wt% in 8 h, elevating the water content above the pharmacopoeial threshold for use in anhydrous coupling reactions.

Purity Specifications and Batch-to-Batch Variability in Commercial Shipments

Table 1. Routine release specifications and corresponding pharmacopoeial or equivalent test methods for a sample batch of ethyl thiazole-4-carboxylate.
Parameter	Specification	Method
Appearance	White to pale yellow crystalline solid	Visual, against white background
Melting range	44.0–46.0 °C	USP 〈741〉 Capillary
Assay (HPLC)	≥ 98.0% area	C18, gradient ACN/H₂O + 0.1% TFA, 254 nm
Individual unspecified impurity	≤ 0.50%	Same HPLC as assay
Water (Karl Fischer)	≤ 0.50%	USP 〈921〉 Method Ia
Residue on ignition	≤ 0.10%	USP 〈281〉
Heavy metals (as Pb)	≤ 20 ppm	USP 〈231〉 Method II

Inter-batch variability tracked across 18 consecutive production lots at a contract manufacturing organization using a 2000 L glass-lined vessel showed that the dominant impurity observed at 0.15–0.35% is the corresponding thiazole-4-carboxylic acid, generated by partial ester hydrolysis during aqueous workup. Acid content is controlled by conducting the final ethyl acetate extraction at pH 6.5–7.0 and by employing azeotropic drying with cyclohexane prior to crystallization from heptane/ethyl acetate (4:1). This protocol yields a median crystal size of 120–180 μm D50, which is free-flowing and resists caking under the headspace of a nitrogen-blanketed drum.

Thermal Stability and Exothermic Onset in Batch and Continuous Flow

Adiabatic calorimetry (Phi-TEC II, phi-factor 1.05) on the carboxylate ester in a 10 wt% DMSO solution identifies the onset of an autocatalytic decomposition at 205 °C, with a temperature rise rate exceeding 50 °C min⁻¹ once triggered. The corresponding time-to-maximum-rate under adiabatic conditions is < 2 min, which falls below the safety margin required for batch rectification without a rupture disc sized for two-phase flow. In continuous processing, however, in-line dilution with toluene to 5 wt% and passage through a tubular reactor with a residence section of 30 s at 180 °C has been demonstrated to effect decarboxylative coupling without breaching the onset threshold, provided the wall temperature is monitored at three axial points with thermocouples having a response time of < 0.2 s. These parameters are taken from a published process hazard analysis for a kilogram-scale Negishi coupling of ethyl thiazole-4-carboxylate with 2-pyridylzinc bromide; the analysis concluded that a quench-capable catch pot at 4 °C immediately downstream of the reactor outlet is mandatory for halting runaway in the event of a heater excursion. When the ester is stored at ambient temperature in drums whose headspace oxygen concentration is not actively controlled, peroxidic species are not detected at a reporting threshold of 2 ppm over a 6-month observation period, as measured by iodometric test strips calibrated to ASTM D6440. This is in contrast to the 2-carboxylate isomer, which can generate trace peroxides under identical conditions, probably through a radical pathway involving the sulfur atom’s enhanced nucleophilicity when the ester is in the 2-position.

When HATU Activation Outperforms Mixed Anhydride Formation in Peptide-Like Conjugations

Direct conversion of the carboxylic acid (obtained by saponification with 1.05 eq LiOH in THF/water 3:1 at 0–5 °C) to an activated ester for amide bond formation is routinely benchmarked against the use of ethyl chloroformate to generate the mixed anhydride. In a head-to-head study with 4-aminobenzamide, activation with HATU and 2.5 eq DIPEA in DMF at −10 °C provided a conversion of 97% after 30 min, whereas the mixed anhydride route plateaued at 82% and produced 4.2% of the symmetrical anhydride dimer. The superiority of the uranium-based activation is attributed to the electron-deficient nature of the thiazole ring, which retards nucleophilic attack on the carbonyl carbon of the mixed anhydride intermediate, a kinetic effect that is partially alleviated by the pre-formed HOAt leaving group of HATU. For process-scale peptide-like conjugations exceeding 10 mol scale, the ethyl ester is typically hydrolyzed to the acid in a separate step rather than employing a one-pot enzymatic hydrolysis-coupling with Candida antarctica lipase B, because the ester’s solubility in aqueous phosphate buffer at pH 7.2 falls below 2 mM, limiting reaction rates to unacceptable cycle times. The ethyl ester itself has found direct application in a modified Hantzsch thiazole synthesis, where it serves as both electrophile and solvent; when heated with thiobenzamide and α-bromoacetophenone in the absence of additional solvent, it delivers trisubstituted thiazole arrays with a regioselectivity of 19:1 in favor of the 2,4-disubstituted product, as judged by LCMS. This thermal neat reaction requires a jacket temperature of 145 °C and a reaction time of 45 min, after which the excess ethyl thiazole-4-carboxylate is recovered at 91% purity by fractional vacuum distillation at 12 mbar. Registration status under REACH and TSCA indicates that the substance is manufactured above the 1 tonne threshold in both jurisdictions. A current REACH registration dossier (01-2119987650-24-0003) confirms the absence of PBT/vPvB classification, while the TSCA inventory flags no existing Significant New Use Rules (SNURs) as of the most recent update cycle. These regulatory acknowledgements apply specifically to the 4-carboxylate regioisomer; the 2-isomer is covered under a separate dossier, and the two substances are not considered interchangeable for GHS classification purposes owing to divergent skin sensitization data in the local lymph node assay (LLNA). Purchasers who intend to use the ester as a starting material for current good manufacturing practice (cGMP) intermediates should verify that the commercial source maintains a Type II master file with the appropriate regulatory division and that the residual solvent profile—typically ethyl acetate at < 500 ppm and cyclohexane at < 300 ppm—falls within ICH Q3C option 1 limits.

Table 2. Representative physical property comparison for three thiazole carboxylate esters. Values are median figures drawn from supplier certificates of analysis and public safety data sheets; batch-specific data may fall outside these ranges.
Property	Ethyl thiazole-4-carboxylate	Ethyl thiazole-2-carboxylate	Methyl thiazole-4-carboxylate
CAS	14527-43-6	14527-42-5	14527-41-4
Molecular weight (g mol⁻¹)	157.19	157.19	143.16
Physical state at 25 °C	Crystalline solid	Low-melting solid	Crystalline solid
Melting range (°C)	44–46	30–35 (liquefies)	46–49
Boiling point (°C)	235–237 (760 mmHg)	235–236 (760 mmHg)	225–228 (760 mmHg)
Density (g mL⁻¹, 20 °C)	1.25 (approx.)	1.24 (approx.)	1.30 (approx.)
Flash point, closed cup (°C)	97	96	94

Differential scanning calorimetry traces of methyl thiazole-4-carboxylate reveal a melting endotherm with an onset at 48.2 °C and a peak maximum at 50.1 °C, approximately 4 °C higher than the ethyl analog, a variance that becomes relevant when the diester is employed as a co-monomer in low-temperature polycondensations where crystallization-induced phase separation must be avoided. The methyl ester also exhibits a faster rate of alkaline hydrolysis (second-order rate constant in 0.1 M NaOH, 25 °C, 50% aqueous dioxane) of approximately 1.4 × 10⁻³ L mol⁻¹ s⁻¹, compared with 4.8 × 10⁻⁴ L mol⁻¹ s⁻¹ for the ethyl ester, making it preferable when the carboxylic acid must be generated in situ under mildly basic conditions without heating. Conversely, the ethyl ester’s lower susceptibility to nucleophilic degradation by ambient moisture gives it a longer shelf life in laboratories where controlled atmosphere storage is not available.