2-(Methylsulfanyl)-1,3-Thiazole

What Causes Phase Separation in High‑Sugar Beverages Containing 2‑(Methylsulfanyl)‑1,3‑Thiazole?

When the thioether is injected into a sucrose‑sweetened (65 °Brix) carbonated drink concentrate at ambient temperature, the solubility limit — measured spectrophotometrically at λ = 258 nm — is approximately 12 mg·L⁻¹ in the aqueous phase; exceeding that threshold without a co‑solvent leads to surface oiling and off‑ratio dosing throughout the production run. A pre‑blend of 1 part 2‑(methylsulfanyl)‑1,3‑thiazole with 9 parts anhydrous ethyl alcohol (≥ 99.8 % GC purity, denatonium‑free) or propylene glycol (USP grade) is filtered through a 0.45 µm PTFE membrane before dosing into the syrup stream at a volumetric rate calibrated to deliver 5–50 ppb in the ready‑to‑drink beverage. Standardised turbulence mixing (Reynolds number > 4000 maintained for at least 45 seconds in an in‑line static mixer with 12 helical elements) ensures homogeneous distribution. Long‑term stability testing under ICH Q1A conditions (40 °C/75 % RH) in PET bottles reveals 15–20 % potency loss over 12 weeks when pH is 3.0–3.5, attributed to acid‑catalysed cleavage of the methylsulfanyl group generating trace methanethiol; the shift is minimised by buffering with sodium citrate to pH 4.8–5.2, keeping potency decline below 5 % in the same interval. The final beverage specification requires a combined headspace integrity check (HS‑GC‑MS, Tenax TA trap, desorption at 280 °C) to confirm absence of methyl sulfide artefacts above 1 ppb odour threshold.

Encapsulation‑Extended Release in Powder Detergent Perfumery

A laundry powder base containing sodium carbonate, sodium percarbonate, and TAED (tetraacetylethylenediamine) creates an oxidising alkaline environment (wash liquor pH 10.2–10.8) that degrades unsheltered 2‑(methylsulfanyl)‑1,3‑thiazole within the first 5 minutes of the main wash cycle. Deposition onto cotton fabrics becomes negligible, and the characteristic roasted‑nut note is not perceived post‑drying. A fluid‑bed Wurster coating (GPCG‑1, Glatt, inlet air temperature 50 °C, product temperature 35–38 °C, spray rate 8 g·min⁻¹) applies a hydrogel shell — cross‑linked sodium alginate (2 % aqueous solution, cross‑linked with 0.5 M CaCl₂ bath, wash‑dried) — onto a core of porous silica (Syloid® 244 FP) pre‑loaded with 12 wt% neat fragrance. The encapsulated particle exhibits a burst release below 10 % after 20 minutes in a Tergotometer wash test (AATCC TM 212‑2018) and reaches 85 % total release only after 45 minutes, ensuring aroma survives the wash and deposits on the fabric. A detergent formulation containing 0.3 wt% of these capsules was evaluated in a front‑loading machine (Miele W1, cotton cycle 40 °C, water hardness 250 ppm CaCO₃); panelists (n = 30, ISO 8589:2007 sensory booth) detected the target note on dry textiles at a significance of p < 0.05 vs. unperfumed control. No staining was observed according to ISO 105‑C10:2006 (colour fastness to washing with soap).

In commercial-scale compounding lines (L/D 40:1 co‑rotating twin‑screw, Coperion ZSK‑26 MC18, screw speed 300 rpm), the neat thioether is handled under nitrogen blanket (O₂ < 0.5 vol%) owing to its autoxidation tendency at temperatures above 60 °C. Catalytic amounts of 0.02–0.05 wt% dl‑α‑tocopherol are incorporated into the perfume pre‑mix to suppress sulfoxide formation during storage in HDPE drums at 25–30 °C for up to 6 months; without antioxidant, peroxide values rise to 8 meq/kg within 8 weeks and induce off‑notes described as “sulphury‑onion” in consumer home‑use tests (IHUT, n = 120). The IFRA Standard 49th Amendment does not assign a restriction for this substance; however, the supplier’s certificate of analysis must report residual solvents (GC‑FID headspace, USP <467> method IV) below 50 ppm cumulatively, with benzene < 0.1 ppm.

When Chlorination Exotherms Exceed 85 °C During SOCl₂‑Assisted Conversion

Conversion of 2‑(methylsulfanyl)‑1,3‑thiazole to 2‑chlorothiazole and its 5‑(chloromethyl) analogue serves as a gateway to the neonicotinoid insecticides thiamethoxam, clothianidin, and thiacloprid. In a 500‑L glass‑lined reactor (Pfaudler AE type, half‑pipe jacket, turbine agitator, tip speed 3.2 m·s⁻¹), thionyl chloride (2.8 molar equivalents) is added dropwise to a chlorobenzene solution of the substrate at 50 °C over 6–8 hours under atmospheric pressure while scrubbing evolved HCl and CH₃SCl through a 20 % NaOH packed column. The reaction exotherm must be strictly maintained below 85 °C; excursions beyond this threshold initiate runaway polysulfide gelation, reducing the distillable yield of 2‑chlorothiazole to 55–60 % compared with the typical 78–84 % (vacuum fractionation, 40 mmHg, overhead 88–92 °C, purity > 99 % via GC‑FID on DB‑5 column). A safety integrity level (SIL‑2) interlock couples the jacket cooling supply with the SOCl₂ dosing pump; multiple plant‑scale campaigns have demonstrated that a controlled isothermal profile (80 ± 2 °C) avoids exotherm‑related contamination. The chlorobenzene mother liquor is quenched into ice‑water (2 °C), and the organic phase is neutralised with 5 % sodium bicarbonate to pH 6.5–7.0 before drying over anhydrous Na₂SO₄. Regulatory compliance for export to the EU requires a REACH registration for the intermediate delivered at this stage or a strict non‑isolated intermediate justification under Article 2(8). Analytical monitoring of residual thionyl chloride and methyl sulfenyl chloride adducts is performed by ion chromatography (IC, Metrosep A Supp 5 column, 1.0 mmol/L NaHCO₃/Na₂CO₃ eluent) with a quantitation limit of 5 ppm.

Achieving ≤50 ppm Residual Solvent in 2‑Aminothiazole Production — High‑Pressure Aminolysis Considerations

When the methylsulfanyl leaving group is displaced by ammonia in an ethanolic medium, 2‑aminothiazole is obtained as a white crystalline solid that enters multiple small‑molecule active pharmaceutical ingredient (API) trees, notably for non‑steroidal anti‑inflammatory thiazolecarboxamides and heterocyclic kinase inhibitors. The batch protocol loads 1.0 kmol substrate and 4.0 kmol anhydrous ammonia (in 14 % w/w ethanolic solution, HPLC‑grade ethanol, water < 0.1 %) into a Hastelloy C‑276 high‑pressure autoclave (rated 100 bar, 200 °C). After nitrogen purge cycles (3 × 5 bar), the vessel is heated to 145 °C with stirring at 500 rpm, generating an autogenous pressure of 18–22 bar held for 10 hours. End‑of‑reaction IPC by TLC (silica gel 60 F₂₅₄, ethyl acetate/hexane 1:1 v/v) or online Raman spectroscopy (peak disappearance at 1348 cm⁻¹, C‑S‑CH₃ stretch) confirms > 98 % conversion. The crude slurry is cooled to 5 °C, and the filter cake is washed with cold ethanol (−10 °C) to remove dissolved mercaptan by‑products; reslurrying in n‑heptane at 60 °C reduces methyl mercaptan odour below sensory threshold. Drying under vacuum (10 mbar, 50 °C, 24 h) delivers 2‑aminothiazole with a purity of ≥ 99.5 % (HPLC, 210 nm, C18 column, acetonitrile/water 30:70). Residual solvent analysis according to Ph.Eur. 2.4.24 (headspace GC‑FID) must show ethanol ≤ 500 ppm, n‑heptane ≤ 50 ppm, and ammonia pass by ion‑selective electrode. The material is manufactured under ICH Q7 cGMP for starting materials used in APIs destined for US DMF or CEP filing, with specifications cross‑referencing EMA/CHMP/ICH/454044/2015 for mutagenic impurity risk assessment — a sulfonate ester purge factor calculation is mandatory if the downstream sulfonic acid coupling step is employed.

In inert‑atmosphere glovebox chemistry (MBraun, < 0.1 ppm O₂, < 0.1 ppm H₂O), 2‑(methylsulfanyl)‑1,3‑thiazole functions as a neutral N,S‑bidentate ligand that chelates palladium(II) and copper(I) centres for cross‑coupling catalysis. When equimolar [Pd(CH₃CN)₂Cl₂] is stirred with the ligand in anhydrous dichloromethane (dried over CaH₂, distilled) at 25 °C for 3 h, the resultant complex precipitates as an air‑sensitive yellow solid — single‑crystal X‑ray diffraction confirms a square‑planar geometry with Pd–N(thiazole) bond length of 2.028 Å and Pd–S(thioether) distance of 2.281 Å. The pre‑catalyst shows turnover frequencies of 8900 h⁻¹ (Suzuki–Miyaura, 4‑bromotoluene + phenylboronic acid, K₂CO₃, THF/water, 60 °C, GC yield basis) and maintains activity over 5 consecutive recycles when immobilised on mesoporous silica (MCM‑41, pore diameter 2.8 nm) at a loading of 0.15 mmol·g⁻¹. Catalyst screening is conducted on a Chemspeed SWING platform with 24‑parallel reactors to map substrate scope against 20 aryl bromides; the decision threshold for further scale‑up is set at an isolated yield > 85 % and residual Pd ≤ 10 ppm (ICP‑MS, Agilent 7800). All manipulations of the free ligand and its metal complexes follow strict oxygen exclusion because the thioether moiety oxidises to sulfoxide within 2 h upon exposure to ambient air, verified by FT‑IR monitoring (S=O stretch appearance at 1040 cm⁻¹). The ligand supply for kilo‑lab runs is typically double‑recrystallised from n‑hexane/ethyl acetate 4:1 under argon and sealed into PTFE‑lined aluminium pouches with a desiccant sachet.

In the landscape of heterocyclic odorants, 2-(Methylsulfanyl)-1,3-thiazole (CAS 5053-24-7) occupies a narrow but commercially significant band between pyrazine-derived roasted notes and thiazole-based green-sulfury profiles. The molecule is a substituted 1,3-thiazole bearing a thiomethyl group at the 2-position, with empirical formula C₄H₅NS₂ and a molecular weight of 131.22 g·mol⁻¹. Technical-grade material is typically supplied as a pale yellow to amber liquid with a boiling range of 195–198 °C at atmospheric pressure and a density of 1.24–1.27 g·cm⁻³ at 20 °C. The flash point, measured by Pensky-Martens closed cup (ASTM D93-20), rests near 78 °C, placing it in a combustible liquid classification under GHS. Gas chromatographic purity, determined according to ASTM D7515-19 with FID on a polar capillary column, routinely exceeds 98.0% area for standard commercial lots, with the primary impurity being the unsubstituted 1,3-thiazole or traces of 2-mercaptothiazole retained from the synthetic route.

Because the thiomethyl substituent lowers the partial vapour pressure relative to simple alkyl thiazoles, the compound exhibits a delayed, sustained release profile in dry food matrices—a property exploited in retorted soups and long-boil bouillons where peak loss of top notes during thermal processing would otherwise compromise sensory fidelity. Published equilibrium headspace concentrations over a 0.5% w/w aqueous sucrose solution (pH 5.0, 80 °C) derived from SPME‑GC/MS measurements indicate an air/water partition coefficient roughly 2.3× lower than that of 2-isobutylthiazole under identical conditions. Consequently, formulation adjustments as small as 0.1 ppm can shift the perceivable odour intensity from “background sulfury reinforcement” to “meaty-dominant character” in finished broths, a sensitivity not observed with the more volatile alkyl congeners.

Synthetic Route-Dependent Impurity Signatures

Two primary manufacturing pathways dominate production-scale batches: condensation of methyl thiocyanate with 2-mercaptoethylamine hydrochloride under alkaline conditions, and the direct S-methylation of 2-mercaptothiazole with dimethyl sulphate in a biphasic water‑toluene system. The methylation route, when catalysed by tetra‑n-butylammonium bromide at 5 mol% loading and maintained at 45 ± 2 °C for a residence time of 6 h, yields a crude product containing 1.8–2.4% residual 2-mercaptothiazole unless a post-reaction oxidative scavenging step with dilute hydrogen peroxide (0.5% aq.) is introduced. This residual thiol, if not controlled below 0.15%, acts as a latency catalyst in ester-based flavour solvent systems, accelerating the hydrolysis of triacetin at elevated storage temperatures and causing an olfactory drift toward acetic acidity after 6–8 weeks at 40 °C. Condensation-based routes avoid this thiol carryover but instead generate trace 2-(methylsulfinyl)-1,3-thiazole (0.3–0.7%) if air sparging is insufficient during workup, introducing an oxidized note detectable by a trained sensory panel at concentrations above 0.05 ppb in air.

Specification sheets for high‑resolution flavour compounding therefore include a sulphoxide limit by HPLC‑UV at 254 nm (column: C18, 5 µm, mobile phase acetonitrile/water 60:40, isocratic), with a reporting threshold of 0.05% area. The same method resolves the 4-methyl positional isomer, which co-elutes with the desired 2-substituted product under standard non-polar GC conditions but possesses a distinct, lingering musty note that diminishes flavour freshness in tomato‑based savoury formulations.

Representative analytical panel for a lot conforming to EC Regulation 1334/2008 flavour substance criteria
Parameter	Method	Specification	Typical Result
Assay (2-(methylsulfanyl)-1,3-thiazole)	GC‑FID (ASTM D7515-19)	≥ 98.0%	98.7%
Refractive index (n_D²⁰)	ISO 280:1998	1.5940–1.5980	1.5962
Residual 2‑mercaptothiazole	HPLC‑UV (in‑house)	≤ 0.15%	0.09%
Sulphoxide (2-(methylsulfinyl)-1,3-thiazole)	HPLC‑UV (in‑house)	≤ 0.10%	0.03%
Water content	Karl Fischer (ISO 760:1978)	≤ 0.1%	0.05%

What Distinguishes This Thiomethyl Congener from 2-Acetylthiazole in Thermally Processed Matrices?

The question arises routinely in process flavour development when manufacturers consider substituting 2‑acetylthiazole (CAS 24295-03-2) with the thiomethyl derivative to achieve a more rounded, meaty aroma. While both compounds share the thiazole ring, their performance under retort conditions diverges sharply. 2‑Acetylthiazole, with a carbonyl function, participates in Maillard‑type secondary reactions with residual amino acids in meat slurries, gradually converting to 2‑(1‑hydroxyethyl)thiazole and further dehydration products that diminish the desired popcorn‑ nutty character. The thiomethyl group lacks this carbonyl reactivity, so the compound remains substantially intact during thermal processing at 121 °C for 60 min, as evidenced by recovery rates exceeding 94% from a model beef broth matrix versus 72–78% for 2‑acetylthiazole under the same autoclave profile (data from a C‑100 Tag sealed‑vial simulation, internal study). The trade-off is a higher odour detection threshold: orthonasal threshold in water falls near 0.8–1.2 ppb compared to 0.1 ppb for 2‑acetylthiazole, meaning that dose levels must be approximately 5‑ to 8‑fold higher to achieve equivalent suprathreshold intensity in a neutral carrier.

Below the temperature where hydrolytic ring‑opening of the thiazole nucleus becomes kinetically competitive, another differentiation emerges in solubility‑limited dosing. The aqueous solubility of 2‑(methylsulfanyl)‑1,3‑thiazole at 20 °C is limited to roughly 800–1000 mg·L⁻¹, whereas 2‑acetylthiazole exceeds 4000 mg·L⁻¹. In oil‑in‑water emulsions stabilized with gum arabic, this lower aqueous affinity pushes the thiomethyl compound more rapidly into the lipid phase, shifting the air/lipid/water partition equilibrium and intensifying aroma release during consumption of high‑fat liquid products such as UHT‑processed cream soups. Formulators exploit this behaviour by reducing the absolute addition by 12–15% relative to an equivalent 2‑acetylthiazole‑flavoured control, mitigating cost while maintaining retronasal impact as measured by time‑intensity sensory panels.

When Purity Alone Fails: The Role of Trace Metal Chelation in Oxidative Stability

Compliance with a 98.0%+ GC assay is necessary but insufficient to guarantee shelf‑life stability in clear, non‑nitrogen‑flushed packaging. The thiomethyl ether linkage is susceptible to autoxidation at the sulfur atom when dissolved in limonene‑ or ethanol‑based carriers exposed to ambient oxygen and UV light. Bulk samples containing dissolved iron above 0.5 ppm, as measured by ICP‑OES after microwave digestion, exhibit a sulphoxide growth rate of 0.04–0.06% per day under accelerated storage at 45 °C in sealed quartz‑window cells, whereas iron‑scavenged material (< 0.1 ppm Fe) held under identical conditions shows no detectable increase over 30 days. This sensitivity mandates the addition of 5–10 ppm of a food‑grade metal chelator such as citric acid monohydrate or disodium EDTA when formulating with the neat compound in oxygen‑permeable HDPE containers. ISO 15302:2007 for the determination of benzo[a]pyrene and other polycyclic aromatic hydrocarbons is not directly applicable, but the same oxidative vulnerability necessitates storage under dry nitrogen blanket (oxygen headspace < 0.5% v/v) for bulk quantities exceeding 25 kg.

Automated compounding lines handling the product at ambient temperature on a rotary filling machine (e.g., a Krones Modufill with volumetric pistons) must incorporate a closed-loop nitrogen purge on the dosing hopper after each 200‑L drum changeover. Failure to maintain positive nitrogen pressure during extended idle periods—such as weekend shutdowns—has been documented to generate a visible yellowing of the liquid within 48 h, correlating with a sulphoxide level spike to 0.8% and the appearance of a faint machine‑oil off‑note detectable in a triangle test (α=0.05, n=30 panelists).

Differences in Polymer Matrix Partitioning Compared to Alkyl‑Thiazoles

A less obvious differentiator relevant to encapsulated flavour delivery is the migration rate of 2‑(methylsulfanyl)‑1,3‑thiazole through low‑density polyethylene (LDPE) films. In a migration cell conforming to EN 1186‑1:2002 at 40 °C for 10 days, the permeation coefficient through a 50 µm LDPE film is 3.8×10⁻¹¹ m²·s⁻¹, roughly 60% of the value measured for 2‑isobutylthiazole. The reduced mobility is attributed to the larger cross‑sectional diameter of the thiomethyl substituent and a marginally higher interaction energy with the amorphous phase of the polyethylene matrix. This has practical consequences for dry soup mixes packaged in LDPE‑lined cartons: flavour fade due to scalping occurs at a rate of 0.12% loss per day at 23 °C for the thiomethyl compound, compared to 0.21% per day for 2‑isobutylthiazole. Processors who previously over‑dosed the alkyl congener by 20% to compensate for scalping losses can, after reformulation, reduce the addition rate while staying within the same regulatory maximum use level defined in Annex I of EC 1334/2008 (category 12.5: soups and broths, at an individual concentration not exceeding 2 mg·kg⁻¹).

Published data for this specific configuration is limited regarding long‑term interactions with cyclic olefin copolymer (COC) barrier layers, but preliminary shelf‑life assessments on a COC‑coextruded PP pouch indicate no detectable loss of the thiazole after 12 months at 25 °C and 60% RH, suggesting that adoption of COC liners can effectively eliminate the need for over‑dosage entirely. This contrasts with 2‑acetylthiazole, which demonstrates a measurable uptake in COC (partition coefficient K_COC/air ≈ 120 at 25 °C) due to polar interactions between the carbonyl group and the polymer’s norbornene‑derived moieties.

No manufacturing transfer from a homogenized liquid pre‑mix to a spray‑dried carrier in a co‑current Buchi B‑290 aspirating at 90% vacuum achieves a retention efficiency of 88–92% for the thiomethyl thiazole when using a wall‑material ratio of gum arabic to maltodextrin DE‑12 at 30:70 w/w and inlet/outlet temperatures of 180/85 °C. The same process for 2‑methylthiazole yields retention of only 65–72% due to the latter’s higher vapour pressure at the dryer exit temperature. This retention gap directly influences the shelf‑life of the encapsulated powder; a 6‑month stability trial at 35 °C in aluminium‑foil‑sealed glass jars recorded a headspace thiomethyl thiazole concentration decline of less than 4% from the initial value, whereas 2‑methylthiazole‑containing powders lost 18% under identical conditions.

Comparative retention and stability of three thiazole flavourants in spray‑dried maltodextrin matrices (B‑290, inlet **180 °C**, outlet **85 °C**)
Compound	Retention after drying (%)	Headspace loss after 6 months at 35 °C (%)	GC‑MS recovery from matrix (%)
2‑(Methylsulfanyl)‑1,3‑thiazole	90 (SD 3.1)	3.8 (SD 1.2)	96.2 (SD 2.7)
2‑Acetylthiazole	78 (SD 4.0)	12.4 (SD 2.9)	87.6 (SD 3.4)
2‑Methylthiazole	68 (SD 5.3)	18.1 (SD 4.5)	79.0 (SD 5.0)

When handling the neat liquid, compatibility with common dispensing pump materials must be verified. EPDM and silicone seals swell by 12–15% in volume after 72 h of continuous exposure at 25 °C, leading to premature seal failure on diaphragm metering pumps. PTFE or EPDM with PTFE encapsulation eliminates this swell. Operators on semi‑automated batching stations using volumetric piston fillers calibrated for flavour chemicals with lower surface tension (e.g., ethyl butyrate) note a systematic underfeed of 2–3% due to the higher kinematic viscosity of 2‑(methylsulfanyl)‑1,3‑thiazole (2.4 cSt at 40 °C) compared to the calibration fluid, a discrepancy corrected by gravimetric verification every 500 cycles per ISO 8655‑6:2022 recommendations.

HS Code	711856
Chemical Formula	C4H5NS2
Molar Mass	131.22 g/mol
Appearance	Colorless to pale yellow liquid
Odor	Characteristic sulfurous odor
Density	1.28 g/cm³ (approximate)
Boiling Point	194 - 196 °C
Solubility In Water	Insoluble
Solubility In Organic Solvents	Soluble in many organic solvents like ethanol, ether
Flash Point	Approx. 79 °C

Packing	100 - gram bottles for 2-(Methylsulfanyl)-1,3-Thiazole with tight - sealed packaging.
Shipping	2-(Methylsulfanyl)-1,3 -Thiazole, a chemical, should be shipped in containers suitable for hazardous substances. Ensure proper labeling, compliance with safety regulations, and secure packaging to prevent leakage during transit.
Storage	2-(Methylsulfanyl)-1,3 -Thiazole should be stored in a cool, dry, well - ventilated area, away from heat sources and open flames. Keep it in a tightly sealed container to prevent evaporation and exposure to air and moisture, which could potentially cause decomposition or reaction. Store separately from oxidizing agents and incompatible substances.