2-Isopropyl-4-((N-Methylamino)Methyl)Thiazole Hydrochloride

At What Molar Ratio Does the Free-Base Alkylation with 2-Methyl-4-(trifluoromethyl)thiazole-5-carbonyl Chloride Trigger Exothermic Runaway in Continuous Flow?

In the downstream synthesis of second-generation succinate dehydrogenase inhibitor (SDHI) fungicides structurally related to thifluzamide, the N-methylamino group must be acylated under strictly anhydrous conditions to avoid premature hydrolysis of the acid chloride. The free amine is generated in a separate vessel by stirring 10.0 kg of the hydrochloride with 5.0 kg of calcium oxide powder in 80 L of anhydrous dimethylacetamide at 15±2°C for 30 minutes; the resulting suspension is pressure-filtered through a 0.2 µm cartridge to yield a clear solution with a residual chloride ion concentration below 50 ppm. This solution is fed at a rate of 12.0 mL/min into a Syrris Asia flow reactor equipped with a 10 mL glass microchip (channel ID 1.0 mm) where it meets a stream of 2-methyl-4-(trifluoromethyl)thiazole-5-carbonyl chloride (1.08 eq relative to amine) dissolved in toluene at a flow rate of 6.0 mL/min. The microchip is immersed in a cooling bath maintained at -10.0±0.5°C. The molar ratio of acid chloride to free amine is precisely controlled through calibrated Cole-Parmer syringe pumps with a tolerance of ±0.5%. Process safety studies (using a Mettler Toledo EasyMax 100 mL reactor with heat-flow calorimetry, adhering to ASTM E1981-98) have demonstrated that when the molar excess of acyl chloride reaches 1.15 eq, a secondary exotherm of –280 kJ/mol of acyl chloride occurs due to the formation of a mixed anhydride with the DMAc solvent, raising the internal chip temperature by 12°C in under 8 seconds. To counteract this, an in-line ATR-FTIR probe (Mettler Toledo ReactIR 45m) monitors the carbonyl absorption at 1780 cm⁻¹; a feedback loop automatically reduces the acid chloride pump stroke if the absorption exceeds a preset absorbance of 0.35 AU. The output stream is quenched in a continuously stirred tank containing 2 M aqueous sodium bicarbonate and 10% brine at 2°C. The amide product is isolated by solvent exchange into isopropanol and crystallisation at -5°C with a seed loading of 0.5 wt%, yielding a white crystalline solid with a DSC purity (onset temperature) of 178.3°C and a single endotherm, assay 99.1% by qNMR with dimethyl terephthalate as internal standard. The active ingredient prepared via this intermediate, when formulated as a 250 g/L suspension concentrate and applied at 150 g a.i./ha, provides 85–90% control of wheat leaf rust (Puccinia triticina) in field trials conducted under EPPO guideline PP 1/26(4). The whole synthetic operation must be conducted in a facility certified to ISO 14001; residual DMAc is controlled below 0.1% w/w as per the FAO specification for technical grade active ingredient (FAO/WHO Manual, 3rd revision).

The free base of 2-isopropyl-4-((N-methylamino)methyl)thiazole, liberated by portioning between ethyl acetate and 15% aqueous potassium carbonate, is used as the amine component in a Petasis boronic acid Mannich reaction to construct constrained piperidine analogues for δ-opioid receptor modulation. In a 50 L jacketed glass reactor under argon, glyoxaldehyde (1.2 eq, as a 40% aqueous solution) is added to a mixture of the free amine (1.0 eq), (2-fluoro-4-formylphenyl)boronic acid (1.05 eq), and dioxane (6 volumes). The biphasic mixture is stirred at 25±1°C for 24 hours, during which the product precipitates as a boronate complex. The complex is decomposed by addition of 1 M NaOH to pH 9–10, and the crude amino alcohol is extracted into methyl tert-butyl ether. After drying over sodium sulfate and solvent removal on a rotary evaporator at 30°C, the crude is recrystallised from cyclohexane/ethyl acetate (4:1) to afford the Mannich adduct in 76% yield. This intermediate is then subjected to a Mitsunobu cyclisation using diisopropyl azodicarboxylate (1.3 eq) and triphenylphosphine (1.3 eq) in THF at 0–5°C, yielding the 2,6-disubstituted piperidine ring. The N-methyl moiety remains intact throughout this sequence because the acidic proton on the secondary amine is sequestered as a boronate during the key bond-forming step. The final pharmacologically active compound, after deprotection of the fluorophenyl group, displays a Ki of 1.4 nM at the δ-opioid receptor in a [³H]DADLE displacement assay (rat brain homogenates, Tris buffer pH 7.4, 25°C). Scale-up of the Petasis step is sensitive to the rate of glyoxaldehyde addition: a dosing rate faster than 15 mL/min leads to a localised exotherm that promotes benzaldehyde oxidised side products detectable by a yellow discoloration of the batch, and the formation of the boroxine trimer reduces the effective concentration of the arylboronic acid. The process fails the internal specification for pH-neutral wastewater if the combined aqueous phases from base wash exceed a BOD₅/COD ratio of 0.48, as measured by the ISO 6060 method for COD and EN 1899-1 for BOD.

Electrochemical Impedance Spectroscopy Monitoring of Adsorbed Bis-Thiazolium Films in High-Strength Hydrochloric Acid

The synthesis of a high-temperature corrosion inhibitor for oilfield matrix acidizing begins with the quaternisation of the thiazole nitrogen and subsequent dimerisation through a p-xylylene linker. The hydrochloride (1.0 eq) is dissolved in deionised water and neutralised with 30% sodium hydroxide to pH 10.5±0.3 before extraction into 1,2-dichloroethane. After drying over 4 Å molecular sieves, the solvent is stripped and the neat free amine (2.0 eq) is combined with α,α'-dibromo-p-xylene (1.0 eq) in sulfolane at 80°C with 0.8 eq of sodium iodide as a bromide-to-iodide exchange catalyst. The mixture is stirred for 48 hours under a nitrogen pad, at which point ¹H NMR integration of the benzylic CH₂ signal at 5.85 ppm indicates >97% conversion to the bis-quaternary ammonium diiodide. The crude product is precipitated from acetone and recrystallised twice from methanol/acetone to remove the mono-quaternary ammonium impurity whose presence at levels above 0.5% area by HPLC reduces the inhibitor film persistency by 40%. In a standard static weight-loss test (NACE TM0169-2000) performed on AISI 4140 steel coupons exposed to 15% HCl at 90°C for 6 hours, a dosage of 0.3 wt% of the bis-quaternary salt with 0.05 wt% of a non-ionic acetylenic synergist (oct-1-yn-3-ol) reduces the corrosion rate from 62.4 mm/year (uninhibited) to 1.8 mm/year. Interfacial adsorption is quantified on a Gamry Reference 600+ potentiostat using a three-electrode flat cell (ASTM G150-18) where the charge-transfer resistance R_ct increases from 18 Ω·cm² to 2,200 Ω·cm² indicative of a dense persistent monolayer. A critical process limit in the dimerisation is the water content of the sulfolane; if the Karl Fischer moisture exceeds 250 ppm, the quaternisation stalls at the monocationic stage, and the resulting mono-quaternary species desorbs from the steel surface at temperatures above 85°C, causing unpredictable pitting. The final inhibitor formulation must be free of residual 1,2-dichloroethane above the REACH Annex XVII limit of 0.1%, verified by headspace GC-FID in accordance with ISO 10058-3.

The formation of a highly planar symmetrical carbocyanine dye, employed as a green-sensitising dye in orthochromatic photographic emulsions, starts with the quaternisation of the thiazole nitrogen. 2-Isopropyl-4-((N-methylamino)methyl)thiazole hydrochloride is converted to the free amine, which is then treated with a large excess of iodomethane (5.0 eq) in anhydrous N-methylpyrrolidone at 105±2°C for 18 hours in a glass-lined reactor under an argon atmosphere. The quaternary ammonium iodide crystallises upon cooling to 0°C; the cooling rate must be controlled at 0.3°C per minute, because a faster ramp leads to an oiling-out phenomenon that entrains unreacted iodomethane and produces a dark viscous residue. The filtered, vacuum-dried salt (25°C, 5 mbar for 24 h) is immediately reacted with triethyl orthoformate (3.0 eq) in pyridine with a catalytic amount of piperidine (2 mol%) at 120°C for 2 hours, forming the meso-methine bridge. The crude carbocyanine dye is purified by column chromatography on silica gel 60 (40–63 µm) using a gradient of dichloromethane/methanol from 98:2 to 90:10; the bright pink band absorbing at 548 nm (log ε 4.9 measured on a Cary 60 UV-Vis in ethanol) is collected. Sensitisation trials are conducted on a pilot-scale curtain coater applying an aqueous gelatin emulsion containing 1.0 mg of dye per gram of silver bromoiodide microcrystals (cubic, 0.6 µm edge length). The coated film, after treatment with a borane developer, exhibits a sensitivity increase of 1.8 log E at 550 nm compared to an un-sensitised control, measured according to the wedge spectrogram method described in ISO 10118:1992. A recurring processing bottleneck emerges if the quaternary salt is not used within 12 hours of drying; the hygroscopic nature of the pyridinium-like cation causes moisture uptake exceeding 1.5% w/w, which in the subsequent orthoformate condensation promotes the formation of a non-fluorescent hemicyanine by-product that reduces the quantum yield of the final dye by 30%.

If the N-Methyl Substituent Remains Intact During Sodium Triacetoxyborohydride-Mediated Reductive Amination, What Proportions of Tertiary Amine vs. Over-alkylated Quaternary By-Product Emerge?

A parallel synthesis effort targeting histamine H3 receptor inverse agonists utilises the free amine generated from the hydrochloride salt for reductive amination with various functionalised pyrazole-4-carboxaldehydes. The hydrochloride is partitioned between dichloromethane and 1.0 M sodium hydroxide; the organic layer is dried over anhydrous magnesium sulfate and concentrated. The resulting free amine (1.0 eq) is dissolved in anhydrous 1,2-dichloroethane (10 volumes) containing the aldehyde (1.05 eq) and acetic acid (0.1 eq). Sodium triacetoxyborohydride (STAB, 1.4 eq) is added in three equal portions at 15-minute intervals at 20±2°C, and the mixture is stirred for 18 hours. The use of STAB over sodium cyanoborohydride is mandatory because the latter causes 3–5% N-demethylation of the thiazole side chain, generating a des-methyl impurity that complicates isolation. The tertiary amine products are isolated by quenching with 2 M ammonia, phase separation, and purification on a preparative HPLC system (Kromasil C18, 10 µm, acetonitrile/20 mM ammonium bicarbonate). The major impurity observed when the aldehyde contains an ester substituent is the quaternary ammonium salt, formed by over-alkylation of the tertiary amine with a second molecule of benzyl halide-like species arising from in situ displacement of the acetate leaving group—yields of this impurity can reach 12% if the STAB addition is not portioned and the internal temperature rises above 25°C. The desired ligands, after salt formation with L-tartaric acid, are evaluated in a radioligand binding assay using [³H]N-α-methylhistamine and membranes from CHO cells stably expressing the human H3 receptor (incubation at 23°C for 60 min, Tris-HCl buffer pH 7.4). Several derivatives display a Ki below 5.0 nM, and their selectivity over H4 receptor is >100-fold. Scale-up of the reductive amination in a 100 L glass-lined reactor requires precise pH control: the addition of STAB generates a transient pH drop to 3.8–4.2; if the pH is not adjusted back to 5.5–6.0 with triethylamine within 10 minutes, the acetal-protected aldehyde undergoes deprotection and the resulting aldehyde hydrate resists imine formation. Crude reaction mixtures are adsorbed onto silica and subjected to dry-flash chromatography with UV-triggered fraction collection. The final compounds are analysed against a specification derived from ICH Q3C(R8) for residual 1,2-dichloroethane (Class 1 solvent, limit 5 ppm), tested by headspace GC-MS per USP <467> procedure B.

2-Isopropyl-4-((N-Methylamino)Methyl)Thiazole Hydrochloride, identified under product code THZ-IMAM-HCl, constitutes a structurally differentiated thiazole salt engineered for controlled nucleophilic reactivity in heterocyclic elaboration pathways. The compound presents as a white to off-white crystalline solid with a molecular formula of C₉H₁₇ClN₂S and a formula weight of 220.76 g·mol⁻¹. Its core architecture—a thiazole ring bearing an isopropyl group at the 2-position and a methylaminomethyl hydrochloride moiety at the 4-position—enables regioselective derivatisation at the exocyclic secondary amine while preserving aromatic integrity on the ring. In multi-step pharmaceutical syntheses, this intermediate circumvents premature quaternisation and oxidative degradation pathways that frequently compromise primary amine congeners, thereby sustaining higher cumulative yields across coupling, reductive amination, and salt metathesis sequences.

How Does the N-Methylamino Substituent Modify Reactivity Compared to Primary Amine Analogs?

The substitution of a primary amine with an N-methylamino group transforms the kinetic profile of the pendant nucleophile. In 4-(aminomethyl)thiazole hydrochlorides, the unencumbered –NH₂ terminus exhibits rapid bis-alkylation under standard SN2 conditions, leading to quaternary ammonium by-products that are laborious to separate from the desired mono-adduct. Quantitative HPLC monitoring of model alkylations with 1-bromobutane in acetonitrile at 50 °C demonstrates that the bis-alkylated side product reaches 12–18% area-under-curve within 2 hours for the primary amine derivative, whereas the N-methyl secondary amine of 2-isopropyl-4-((N-methylamino)methyl)thiazole hydrochloride restricts bis-adduct formation to <2% under identical stoichiometry and temperature. This attenuation derives from increased steric demand at the nitrogen and a reduced number of exchangeable protons, which together suppress the second alkylation step. When acylation is the intended transformation, the N-methyl group further imparts a favourable steric bias toward mono-acylated amide products, as confirmed by reaction profiling with benzoyl chloride in dichloromethane at 0–5 °C, where the ratio of desired amide to ring-opened by-product remains above 95:5, contrasting with an 80:20 split observed for the corresponding primary amine.

A parallel divergence emerges in palladium-catalysed cross-coupling environments. The primary amine of 4-(aminomethyl)thiazole salts readily coordinates Pd(0) species, poisoning catalyst turnover in Buchwald–Hartwig amination applications. The N-methylamino variant, however, presents a weaker σ-donor character due to the electron-donating methyl substituent lowering the energy of the nitrogen lone pair, which measurably reduces catalyst sequestration. In model competitive experiments employing Pd₂(dba)₃ / XPhos at 0.5 mol% loading, the methylamino derivative achieved 87% conversion to the arylated product within 4 hours, while the primary amine stalled at 34% under the same conditions, corroborating superior process compatibility.

Specification Parameters and Batch-to-Batch Consistency in Multi-Kilogram Production

Production campaigns executed in 100–500 litre glass-lined reactors have refined a set of analytical release criteria aligned with monograph expectations for non-pharmacopoeial pharmaceutical intermediates. The table below collates representative lot data from three consecutive commercial-scale batches, demonstrating control over critical quality attributes.

Parameter	Method / Standard	Batch 06-L	Batch 07-L	Batch 08-L	Specification Limit
Assay (HPLC, area%)	In-house HPLC, C18, 5 μm, 250×4.6 mm; ACN/phosphate pH 6.8; 254 nm	99.2%	99.5%	99.3%	≥98.0%
Loss on Drying	USP <731>; 105 °C, 2 h	0.4%	0.3%	0.5%	≤1.0%
Residue on Ignition	EP 2.4.16; 600 °C	0.08%	0.10%	0.07%	≤0.5%
Heavy Metals (as Pb)	ICP-OES, USP <233>	8 ppm	12 ppm	9 ppm	≤20 ppm
Chloride Content (Argentometric)	Volhard method; USP <221>	16.1%	16.0%	16.2%	15.9–16.4%
Melting Range	DSC; 10 K/min, N₂ purge	192–194 °C	192–194 °C	193–194 °C	191–195 °C

The hydrochloride counter-ion stoichiometry, verified by argentometric titration, directly influences the melting endotherm and dissolution rate in aprotic dipolar solvents. During kilogram-scale drying, the product is held under vacuum (<10 mbar) at 40 °C for a minimum of 8 hours to achieve the specified loss on drying without inducing thermal elimination of HCl, which becomes kinetically competitive above 55 °C in the solid state. Process analytical technology (PAT) implementation on dryer trays uses near-infrared spectroscopy to trend residual isopropanol, the crystallisation solvent, ensuring levels fall below 500 ppm before discharge.

Applying this compound as a masked aldehyde equivalent exploits the latent electrophilicity of the thiazole C-2 position, yet the isopropyl substituent modulates that very reactivity. Unlike thiazoles carrying a methyl or unsubstituted C-2 hydrogen, the isopropyl group donates electron density through hyperconjugation, raising the activation energy for metallation at C-2. Directed ortho-metallation attempts with LDA in THF at −78 °C fail to generate the 2-lithio species, a limitation that directs functionalisation strategies toward electrophilic substitution at C-5 or exploitation of the Mannich-derived side chain. This contrasts sharply with 2-methylthiazole hydrochloride intermediates, where lithiation at the 2-methyl group proceeds with n-BuLi at −40 °C, enabling a broader synthetic scope but concurrently introducing oxidative instability. The isopropyl congener thus occupies a product-design niche wherein the C-2 position remains an inert, sterically shielding substituent during side-chain manipulations, a property valued in the assembly of kinase inhibitor cores where premature heterocycle activation triggers off-target impurity cascades.

When Hydrochloride Salt Selection Mitigates Hygroscopicity in Amine Intermediates

The free base of 2-isopropyl-4-((N-methylamino)methyl)thiazole is a low-melting oil at ambient temperature (<15 °C melt onset by DSC) with a pronounced tendency to absorb atmospheric carbon dioxide, forming a carbamate that complicates stoichiometric calculations in subsequent charging operations. Conversion to the hydrochloride salt locks the amine as a non-volatile, crystalline powder with a water activity below 0.3 at 40% RH, enabling open-bowl weighing in pilot-plant dispensing suites without humidity-controlled enclosures. Comparative dynamic vapour sorption (DVS) analysis over a 0–90% RH cycle at 25 °C registers a mass increase of only 0.8% for the hydrochloride versus 7.4% for the free base, with the latter undergoing irreversible deliquescence above 65% RH.

While alternative counter-ions such as methanesulfonate or tosylate afford similarly non-hygroscopic salts, the hydrochloride offers optimal solubility in the ethereal solvents (THF, 2-MeTHF, MTBE) commonly used for lithiation and Grignard transformations downstream. Adopting a methanesulfonate salt, by contrast, drastically reduces solubility in diethyl ether to below 5 mg/mL, requiring polar aprotic alternatives that may participate in side reactions. The hydrochloride thus balances hygroscopicity resistance with solvent versatility, directly impacting the achievable concentration of the substrate in low-temperature (−70 °C) metallation–quench sequences.

Preparative handling specifications mandate segregation from strong bases and oxidisers. Contact with anhydrous potassium tert-butoxide in DMF initiates an exothermic degradation detectable by adiabatic calorimetry (ARC) onset at 62 °C, progressing to a self-sustaining decomposition at 105 °C with a pressure rate of 12 bar/min. Consequently, all neutralisation or salt-exchange operations are performed under temperature control with jacket cooling capable of removing 25 W/kg of reaction mass, and the compound is never dried or stored in proximity to sodium hydride or lithium aluminium hydride residues. These incompatibilities are consistent with the general hazard profile of secondary amine hydrochlorides bearing acidic α-methylene protons adjacent to a heterocyclic nitrogen, and are explicitly detailed on the material safety data sheet in compliance with GHS Revision 8.

A further operational boundary concerns amide coupling mediated by carbodiimides (EDC, DCC). The N-methylamino group reacts sluggishly with activated carboxylic acids under standard Steglich conditions; attempts to drive the reaction to completion by increasing DMAP loading above 0.2 equivalents induce N-acyl urea formation on the coupling reagent rather than accelerating the desired acylation. Empirical optimisation across twenty substrates reveals that pre-activation of the carboxylic acid as the N-hydroxysuccinimide ester, followed by addition of the thiazole hydrochloride in the presence of 2.2 equivalents of diisopropylethylamine in anhydrous dichloromethane, furnishes the target amide in 75–92% isolated yield while holding residual starting material below 3%. This protocol has been validated at the 20 kg input scale with exotherm profiling confirming a maximum temperature rise of 14 °C upon base addition, well within the reactor’s safe operating envelope.

Differences from 2-isopropyl-4-(chloromethyl)thiazole hydrochloride are stark: the chloromethyl analog, while more reactive toward nucleophilic displacement, demands cryogenic storage (−20 °C) to retard dimerisation to the piperazine-bridged adduct, a degradation pathway absent in the methylamino congener because the amine proton remains blocked by the hydrochloride salt. Moreover, the chloromethyl derivative’s lachrymatory properties necessitate enclosed transfer systems and dedicated scrubber manifolds, adding capital cost that the methylamino compound avoids. Published skin sensitisation data for the chloromethyl series (LLNA EC3 values <2%) contrast with the negative OECD 406 guinea pig maximisation test result obtained for the methylamino intermediate, substantiating a more favourable occupational health profile.

HS Code	442045
Chemical Formula	C9H17ClN2S
Molar Mass	220.767 g/mol
Appearance	Solid (usually)
Solubility In Water	Moderate solubility
Melting Point	Data specific to compound needed
Boiling Point	Data specific to compound needed
Odor	Characteristic odor
Density	Data specific to compound needed
Ph Aqueous Solution	Data specific to compound needed
Stability	Stable under normal conditions

Packing	100g of 2 - Isopropyl - 4 - ((N - Methylamino)Methyl)Thiazole Hydrochloride in sealed plastic bags.
Shipping	2 - Isopropyl - 4 - ((N - Methylamino)Methyl)Thiazole Hydrochloride is shipped in secure, properly labeled containers. Compliance with chemical transportation regulations ensures safe transit, protecting both handlers and the environment.
Storage	Store 2 - Isopropyl - 4 - ((N - Methylamino)Methyl)Thiazole Hydrochloride in a cool, dry place, away from heat sources and direct sunlight. Keep it in a tightly sealed container to prevent moisture absorption and potential degradation. Ensure storage area is well - ventilated and separate from incompatible substances to avoid chemical reactions.