2-Aminomethylthiazole Dihydrochloride

Why Is 2-Aminomethylthiazole Dihydrochloride Introduced Into Acid Copper Via Formulations?

In high-throwing-power electroplating formulae for through-hole and blind-via metallization, a substituted thiazole additive is frequently adopted to function as a leveller that preferentially adsorbs on high-current-density protrusions, refining grain structure to yield a mirror-bright copper deposit with optimal IPC-6012 Class 3 reliability. 2-Aminomethylthiazole dihydrochloride is not directly added to the plating bath; rather, it undergoes quaternization with an alkylating agent (typically 1,3-propane sultone or dimethyl sulfate at 1:1.02 molar charge) in a separate synthesis vessel, followed by purification by recrystallisation from ethanol/water, to generate a heterocyclic quaternary ammonium salt possessing a permanent positive charge and strong cathode adsorption kinetics. This quaternized derivative is formulated into a carrier-and-brightener package at a working concentration of 8–45 mg/L of the active organic ingredient in the final plating electrolyte, together with bis-(3-sulfopropyl)-disulfide (SPS) as a grain refiner and polyalkylene glycol as a suppressor. The electrolyte base consists of 200–225 g/L CuSO₄·5H₂O and 50–65 g/L H₂SO₄, operated at 25±1°C with vigorous air sparging; a typical additive dosing rate is re-evaluated every 4,000 Ah via cyclic voltammetric stripping (CVS) using a platinum rotating disc electrode per ASTM B779. Hull cell tests on a 267 mL agitated cell at 2 A total current for 10 min verify the absence of burnt deposits in the high-current-density zone beyond 2.5 A/dm². The leveller operates within a chloride ion window of 40–80 mg/L; below this threshold, the organic layer can passivate the anode too aggressively, causing a drift in brightener consumption. Compliance with the Restriction of Hazardous Substances Directive 2011/65/EU is maintained, and flame-retardant circuit board materials processed with this additive pass the sequential electrochemical migration (ECM) test according to IPC-TM-650 method 2.6.14.1. The end product is a flexible printed circuit board or high-density interconnect substrate deployed in 5G communication handsets where void-free copper pillar electroplating is essential.

Effect of Quaternised 2-Aminomethylthiazole Additive Concentration on Acid Copper Deposit Characteristics (Hull Cell, 2 A, 10 min, 25°C, chloride 60 mg/L)

Additive Concentration (mg/L)

Bright-Plating Current Density Range (A/dm²)

Internal Tensile Stress (MPa) per ASTM B849

Surface Roughness Ra (µm)

0.5–1.8

0.38

0.3–2.6

0.15

0.2–3.2

0.09

Lead optimization libraries in succinate dehydrogenase inhibitor (SDHI) discovery programs exploit the 2-aminomethylthiazole motif to introduce hydrogen-bond donor and acceptor functionality into the amine-linked aryl-heterocycle skeleton. In a representative kilogram-scale synthesis campaign of a thiazolyl-triazolone fungicide candidate, 2-aminomethylthiazole dihydrochloride is first neutralized with aqueous ammonia to pH 9.5–10.0 and coupled with a substituted phenylisocyanate in dichloromethane at 0–10°C, employing a molar excess of the isocyanate of 1.03 mol per mol of free amine so as to avoid residual amine interfering with subsequent cyclization. The intermediate urea derivative is cyclodehydrated using phosphorus oxychloride (1.3 equivalents) in acetonitrile in a 1,000 L Hastelloy C-22 agitated reactor fitted with a scrubbed vent system to neutralise HCl off-gas, maintaining reaction temperature at 70–75°C for 4 h with continuous FT-Raman monitoring of the POCl₃ consumption. After quenching into ice water and adjusting pH to 5.0±0.5, the crude product is isolated via a horizontal peeler centrifuge (Rousselet type) and further purified by recrystallization from ethyl acetate/n-hexane. Residual genotoxic impurities, particularly alkyl halide by-products, are quantified using an LC-MS/MS method with a quantitation limit <1 µg/g, in compliance with the ICH M7 (R1) guideline for DNA-reactive impurities. Regular analytical control for 5-batch rolling data ensures that the isolated yield stays above 78 mol% and purity exceeds 99.0% (HPLC area at 254 nm). The registered technical concentrate (TC) is formulated with the resulting biologically active compound as a suspension concentrate (SC) for field efficacy against Ascomycete pathogens in soybeans and cereals; maximum residue limits are established pursuant to Commission Regulation (EC) No 396/2005.

Sensitizer Precursor for Optical Recording and Bioanalytical Labels

In the synthesis of asymmetrical 1,1′-diethyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate and related near-infrared fluorophores, 2-aminomethylthiazole dihydrochloride is utilized as a methylene-active nucleophile, replacing the traditional Fischer base in the formation of a monomethine bridge. The free amine liberated in situ reacts with an excess of a formamidinium salt (such as diphenylformamidine) at 1:1.2 stoichiometry in hot acetic anhydride at 90–105°C for 20–30 min, affording an anilidovinyl intermediate which is condensed with a quaternised indolenine receptor in the same pot, thereby streamlining the two-step sequence to single-vessel operation. The crude polymethine dye is precipitated by salting out with sodium acetate, filtered on a Nutsche filter, and finally purified by medium-pressure liquid chromatography (MPLC) using a Biotage® Sfär C18 column, achieving a photoluminescence quantum yield reproducibility batch-to-batch within ±3% as determined by absolute method in an integrating sphere calibrated with NIST SRM 2944 and following the protocols analogous to ISO 20351:2020. Use level within a consumer product substrate, such as the dye layer of a write-once Blu-ray disc, is typically 1.8–2.5 wt% of the total solid content of the coating fluid, in order to satisfy refractive index matching (n ~ 1.55 at 405 nm) and ensure adequate signal modulation during the laser writing pulse. The manufacturing environment for optical-grade dye intermediates enforces ISO 14644-1 Class 7 cleanroom protocols, while the final dye-loaded optical disc undergoes accelerated archival life testing at 80°C and 85% RH for 500 h in accordance with ISO 18927:2013. End products record video data on consumer-grade BD-R media, and non-recordable variants are explored as contrast agents in photoacoustic tomography. A note of caution: the free amine form is oxygen-sensitive in solution; hence the dihydrochloride is reconstituted immediately before use, and any batch stored in open containers under ambient humidity beyond 24 h must be assayed for agglomerate formation before deployment.

2-Aminomethylthiazole Dihydrochloride, CAS 474704-40-8, is the bis-hydrochloride salt of 2-aminomethylthiazole, a primary aliphatic amine appended to a 1,3-thiazole ring. The dihydrochloride form provides a stoichiometric ratio of two chloride anions per thiazolium dication, imparting a molecular weight of 201.12 g·mol⁻¹. This salt is routinely supplied as a white to off-white crystalline powder with a melting onset in the range 178–184 °C (decomposition, uncorrected). When compared to the free base – a hygroscopic, low-melting solid prone to oxidative discoloration – the dihydrochloride exhibits markedly improved shelf-life and ease of dispensal under ordinary laboratory conditions. The protonated aminomethyl group is non-nucleophilic, which permits temporary masking of the amine during electrophilic functionalization of the thiazole C-5 position or during N-protection steps on the thiazole nucleus itself.

Available specifications for lot-controlled material include a minimum HPLC purity of 98.0 area% (UV detection at 254 nm, C18 column, phosphate buffer pH 2.5/MeOH gradient), residual water by Karl Fischer titration consistently below 0.8 wt%, and sulfated ash not exceeding 0.15%. The heavy-metals limit is verified against Ph. Eur. method 2.4.8 Class A. Solubility in polar aprotic media is limited: at 25 °C, the salt dissolves in dimethyl sulfoxide at approximately 45 mg·mL⁻¹ and in dimethylformamide at 12 mg·mL⁻¹, whereas solubility in acetonitrile falls below 2 mg·mL⁻¹. This solubility window determines which coupling protocols and solvent systems can be deployed without pre-neutralization of the hydrochloride.

How Does Protonation State Influence Reactivity in Palladium-Catalyzed Aminations?

The dihydrochloride cannot be used directly in Buchwald–Hartwig aminations or reductive aminations that require a free amine nucleophile. Quantitative deprotonation is achieved by stirring the salt with a sterically hindered tertiary amine—diisopropylethylamine or 2,6-lutidine—in anhydrous DMF at 0–5 °C for 30 min prior to introduction of the electrophilic partner. Omission of this pre-stirring phase leads to incomplete conversion and generates side-products derived from chloride substitution at the thiazole 2-methyl carbon. In a comparative study performed on a parallel synthesizer (Biotage Initiator+, sealed 2–5 mL vials), switching from the free base to the dihydrochloride with in situ neutralization using 1.05 eq of N,N-diisopropylethylamine maintained identical coupling yields (±3%) with aryl bromides bearing electron-withdrawing groups, whereas electron-rich aryl chlorides required an extended catalyst cycle to 18 h at 100 °C when the hydrochloride was used, attributed to residual chloride interference with the Pd(0)/XPhos catalyst system.

For continuous-flow applications, the salt is often dissolved in the aqueous phase of a segmented flow reactor. A 0.5 M solution in deionized water, adjusted to pH 9.2 using 2 M sodium carbonate, has been demonstrated to react with benzyl chloroformate in a tubular residence loop (PFA tubing, 1.0 mm inner diameter, 60 s residence time) to yield the Cbz-protected amine with a throughput of 4.8 g·h⁻¹. In this configuration, the dihydrochloride’s high aqueous solubility (>200 mg·mL⁻¹ at 20 °C) is a decisive advantage over the free base, which requires co-solvents that complicate downstream phase separation.

When Tetrahydrofuran Is Replaced with 2-Methyltetrahydrofuran in Organometallic Steps

Process development campaigns focused on low-temperature lithium-halogen exchange on halogenated thiazole precursors encounter a specific compatibility limitation with the dihydrochloride. The acidic ammonium protons quench organolithium intermediates exothermically, generating local hotspots even at –78 °C. Performing a salt metathesis step with sodium tetrafluoroborate in acetonitrile to form the corresponding tetrafluoroborate salt has been reported to attenuate this quenching; the tetrafluoroborate exhibits comparable hygroscopicity but releases the free amine only above 0 °C in the presence of a non-nucleophilic scavenger. Industrial batches intended for such metallation cascades are therefore occasionally offered with a certificate of analysis specifying chloride content by ion chromatography and a loss-on-drying profile performed under 10 mbar vacuum at 40 °C for 4 h.

In amide-bond formations mediated by HATU or HBTU, 2-aminomethylthiazole dihydrochloride behaves similarly to other hydrochloride salts of primary amines: activation is conducted in DMF or NMP with 2.2–2.5 equivalents of a tertiary base. The resulting activated ester is prone to diketopiperazine formation when the acyl component is a linear peptide bearing a terminal carboxylic acid, a side reaction that is suppressed by maintaining the internal temperature below 10 °C during base addition. Monitoring reaction progression by LC-MS (ESI positive mode) typically reveals a peak at m/z 172.1 for the free amine, with the corresponding acylation product exhibiting an [M+H]+ shift consistent with the mass of the introduced acyl group minus the two hydrochloride equivalents.

Critical Differences from Structurally Congeneric Aminomethyl Heterocycle Salts

Compared to 2-aminomethylpyridine dihydrochloride, 2-aminomethylthiazole dihydrochloride provides a ring system with reduced basicity of the endocyclic nitrogen (calculated pKa of the conjugate acid ≈2.4 versus ≈5.2 for pyridine). This makes the thiazole ring inert toward protonation under the mildly acidic conditions (pH 3–4) often used to extract product into aqueous layers, simplifying workup. Against 4-aminomethylthiazole dihydrochloride, the 2-substituted isomer shows a distinct reactivity profile in electrophilic aromatic substitution: nitration with mixed acid at 0 °C occurs preferentially at the 5-position with >85% regioselectivity, while the 4-isomer requires harsher conditions and yields a mixture of nitro regioisomers.

The table below collates key distinguishing features for a selection of commercially available aminomethylthiazole salts, enabling side-by-side evaluation of physical form, hygroscopicity classification, and a representative application.

Comparison of Aminomethylthiazole-Based Intermediates
Product	CAS	Molecular Weight (g·mol⁻¹)	Typical Purity (HPLC area%)	Water Content (KF, wt%)	Observed Hygroscopicity	Common Application
2-Aminomethylthiazole Dihydrochloride	474704-40-8	201.12	≥98.0	≤0.8	Low	Peptide-like amide bond formation, HATU-mediated coupling
2-Aminomethylthiazole Free Base	116051-03-9	114.17	≥97.0	≤1.5	High (deliquescent at RH >60%)	Boc protection, reductive amination without pre-neutralization
4-Aminomethylthiazole Dihydrochloride	1375431-96-9	201.12	≥97.5	≤1.0	Moderate	Building block for 4-substituted thiazole libraries
2-Aminothiazole Dihydrochloride	5967-01-5	173.06	≥98.5	≤0.5	Very low	Direct arylation without methylene spacer

Thermal and Hygrometric Constraints During Bulk Storage

Accelerated stability testing under ICH Q1A guidelines (40 °C / 75% RH, open vial) has shown that the dihydrochloride gains less than 0.2% mass over 4 h, confirming its classification as a non-deliquescent salt at moderate humidity loads. However, exposure to 85% RH at 25 °C for 48 h results in hydration sufficient to raise the water content to 3.2 wt%, at which point the material becomes tacky and displays a depressed melting onset by approximately 7 °C. Consequently, containers should remain sealed under nitrogen or argon after each aliquot removal, and prolonged storage is specified at 2–8 °C in a desiccated environment. Triple-laminated foil bags with an integrated molecular sieve sachet are the standard packaging format for quantities above 500 g.

What Quality-By-Design Parameters Govern Lot-to-Lot Consistency in High-Throughput Discovery?

In medicinal chemistry groups running automated library synthesis, the most frequently observed lot-to-lot variability is not the principal assay purity but rather the particulate morphology and the presence of trace dimethylacetamide or ethyl acetate from recrystallization. Slower dissolution rates are documented for batches having a median particle diameter (Dv50) above 250 μm, as determined by laser diffraction (ISO 13320:2020). Crushing and sieving through a 100-mesh screen under dry nitrogen produces a micronized powder that dissolves completely in DMF within 90 s at 23 °C. Residual solvent limits are enforced at ≤500 ppm for DMF, ≤1000 ppm for ethyl acetate, and ≤300 ppm for methanol, verified by headspace GC-FID using a DB-624 column (30 m × 0.32 mm, 1.8 μm film) per USP <467>.

For laboratories employing acoustic dispensing (Labcyte Echo) of DMSO stock solutions, the dihydrochloride crystallizes if the DMSO concentration exceeds 50 mM and the plate is cooled below 18 °C. To avoid tip blockages, stock solutions are prepared at 40 mM in anhydrous DMSO and centrifuged at 2000×g for 5 min before transfer to source plates. Long-term solution stability at –20 °C under argon is 6 months, verified by re-assaying after freeze–thaw cycles. This solution behavior differs from the free base, which can be solubilized in DMSO at higher concentrations without precipitation but will slowly oxidize to the N-oxide detectable by a mass increase of +16 Da.

When the dihydrochloride is employed as the limiting reagent in palladium-catalyzed direct heteroarylation of thiazole with 2-bromopyridine, the presence of chloride ions at twice the amine molarity depresses the catalytic activity of Pd(OAc)₂/XPhos combinations relative to reactions utilizing the tosylate salt. Kinetic profiling by ReactIR indicates an induction period of approximately 12 min, attributed to the in situ formation of Pd–chloride complexes that are less active toward oxidative addition. Substituting the dihydrochloride with the corresponding dimethanesulfonate salt—prepared by lyophilization from methanesulfonic acid—eliminates this induction period entirely, albeit with a 15% reduction in isolated yield due to competitive sulfonate ester formation at elevated temperature.

The final specification checklist for a custom synthesis batch frequently includes the following assay panel, aligned with monograph expectations for an intermediate destined for cGMP active pharmaceutical ingredient synthesis:

Compendial Release Parameters for 2-Aminomethylthiazole Dihydrochloride
Parameter	Method/Standard	Acceptance Criterion
Appearance	Visual inspection	White to off-white powder
Identification (FTIR)	ATR, 4 cm⁻¹ resolution, 16 scans	Conforms to reference spectrum; characteristic N–H stretch at 2950–2850 cm⁻¹, aromatic ring modes
Assay (HPLC)	Area%, C18, 254 nm	≥98.0%
Chloride content (argentometric)	Ph. Eur. 2.2.33	34.5–36.0% (theoretical 35.27%)
Water (KF)	Ph. Eur. 2.5.12	≤0.8%
Residual solvents	USP <467> Class 2/3	Within ICH Q3C options
Heavy metals	Ph. Eur. 2.4.8 Class A	≤20 ppm
Endotoxins (if required)	Ph. Eur. 2.6.14, gel clot	≤0.5 EU·mg⁻¹

In process chemistry scale-up, the isolation of 2-aminomethylthiazole dihydrochloride from the reductive amination of thiazole-2-carboxaldehyde with ammonium acetate and sodium cyanoborohydride is typically achieved by precipitation from methanolic HCl/diethyl ether. The volume ratio of ether to methanol must be maintained above 4:1 to force the salt out of solution with a yield above 70%; lower ratios result in persistent supersaturation and a gummy residue. Precise pH control during salt break-out is unnecessary due to the excess HCl present, but the use of ethereal HCl rather than aqueous HCl avoids the formation of a biphasic system that entrains unreacted aldehyde.

Finally, the differential scanning calorimetry trace (DSC, 10 °C·min⁻¹ under nitrogen) of the dihydrochloride exhibits a single endothermic event with an onset near 182 °C and a peak maximum at 189 °C. This contrasts with the free base, which displays a broad melting range from 20–24 °C and an exothermic decomposition above 140 °C, underscoring the salt’s superior thermal resilience during shipping to tropical climates without cold-chain logistics.

HS Code	537484
Chemical Formula	C4H8Cl2N2S
Molar Mass	189.09 g/mol
Appearance	White to off - white solid
Solubility In Water	Soluble
Purity	Typically high purity for chemical synthesis use
Boiling Point	Decomposes before boiling
Melting Point	~220 - 225 °C
Odor	Odorless or very faint odor
Stability	Stable under normal storage conditions

Packing	2 - Aminomethylthiazole Dihydrochloride, 100g, packaged in a sealed, chemical - resistant bag.
Shipping	2 - Aminomethylthiazole Dihydrochloride is shipped in well - sealed, corrosion - resistant containers. It follows strict chemical shipping regulations to ensure safety during transit, protecting from moisture, heat, and physical damage.
Storage	2 - Aminomethylthiazole Dihydrochloride should be stored in a cool, dry place. Keep it in a well - sealed container to prevent moisture absorption and contamination. Avoid storing near sources of heat or ignition. It's advisable to store it away from incompatible substances, in a location separate from oxidizing agents and bases to maintain its chemical integrity.