2-Mercapro Thiazole

Crosslink density and mechanical property gradient: 2-Mercapto Thiazole in SBR 1502 / NR (70/30) blend cured at 160 °C to t90 per ISO 6502-2:2018

2-MT Loading (phr)

ts2 (min)

t90 (min)

MH − ML (dN·m)

Tensile Strength (MPa) ISO 37

Elongation at Break (%)

Hardness (Shore A) ISO 48-4

0.3

5.1

12.4

8.7

18.3

560

0.7

3.8

9.2

10.4

21.6

490

1.2

2.5

7.1

12.1

23.1

420

2.0

1.6

5.3

14.8

22.4

340

What Limits Substitutional Alloy Corrosion Inhibition on Copper Substrates in Acidified Chloride Media?

Adsorption of 2-Mercapto Thiazole onto copper and its alloys—C11000 electrolytic tough pitch copper, C26000 cartridge brass (70% Cu, 30% Zn), and C70600 copper-nickel (90/10)—proceeds via thione-thiol tautomerism wherein the deprotonated thiolate form coordinates through the exocyclic sulfur atom to the metal surface, with the endocyclic nitrogen and ring sulfur acting as secondary donor sites. Electrochemical evaluation conducted in 3.5 wt% NaCl adjusted to pH 4.0 with acetic acid follows ASTM G59-23 for potentiodynamic polarization: a three-electrode flat cell with a saturated calomel reference electrode (SCE), platinum counter electrode, and working electrode polished to 1200-grit SiC finish immersed for 1 h at open-circuit potential (OCP) prior to scanning at 0.1667 mV/s from −250 mV to +250 mV versus OCP. At a 2-MT concentration of 150 mg/L, the corrosion current density (i_corr) on C11000 decreases from 8.2 μA/cm² (uninhibited) to 0.34 μA/cm², corresponding to an inhibition efficiency of 95.9% calculated via the Tafel extrapolation method. Impedance spectra acquired at OCP over 100 kHz to 10 mHz with 10 mV RMS perturbation and fitted to a Randles equivalent circuit modified with a constant-phase element (CPE) indicate that charge-transfer resistance (R_ct) rises from 2.1 kΩ·cm² to 48.7 kΩ·cm² upon inhibitor addition, while the CPE exponent (n) narrows from 0.82 to 0.91, reflecting reduced surface heterogeneity as the adsorbed film homogenizes. A breakdown potential shift of +180 mV versus SCE is recorded, elevating the pitting resistance of the inhibited surface above the practical threshold for seawater-cooled heat exchanger service. Prolonged immersion testing per ASTM G31-21 in stagnant 3.5 wt% NaCl at 25 ± 1 °C for 720 h yields a mass loss of 0.12 mg/cm² for inhibited C70600 versus 4.8 mg/cm² for the uninhibited control; scanning electron microscopy (SEM) of the exposed surfaces confirms that localized dealloying—preferential zinc dissolution in brass—is suppressed by approximately 87% based on energy-dispersive X-ray spectroscopy (EDS) spot analyses taken at 20 random surface coordinates. The inhibitor film is self-limiting and does not require pre-passivation, but film integrity degrades irreversibly at operating temperatures exceeding 65 °C, where thermogravimetric desorption data indicate a 50% mass loss from the chemisorbed layer within 2 h. In closed-loop cooling systems treated with 2-MT at 75–200 mg/L, compatibility with triazole-based inhibitors such as benzotriazole (BTA) must be verified via sequential dosing trials, as competitive adsorption can reduce the coverage density of either species when co-dosed at equimolar ratios.

Formulating 2-Mercapto Thiazole into recirculating evaporative cooling water at 15–50 mg/L active concentration suppresses planktonic bacterial populations by 3–4 log10 reductions within 6 h of initial dosing, evaluated via heterotrophic plate count (HPC) on R2A agar incubated at 28 °C for 7 days per ISO 6222:1999. The biocidal mechanism is attributed to thiol-mediated disruption of the cytoplasmic membrane proton gradient in Gram-negative organisms including Pseudomonas aeruginosa and Klebsiella pneumoniae, with minimum inhibitory concentration (MIC) values of 8 μg/mL and 16 μg/mL respectively determined by broth microdilution in Mueller-Hinton medium per CLSI M07-A10 methodology. At use concentrations, 2-MT hydrolyzes slowly at alkaline pH typical of cooling tower sump water (pH 8.5–9.2), losing approximately 25% of its active biocidal titer over a 72 h half-life interval; this necessitates a slug-dosing regimen of 30–50 mg/L administered every 48–72 h rather than continuous low-level feed. Compatibility with phosphonate scale inhibitors (1-hydroxyethylidene-1,1-diphosphonic acid, HEDP at 10–15 mg/L) and acrylate copolymer dispersants is confirmed through static beaker tests at 40 °C showing no precipitation or loss of turbidity over 96 h, though oxidation with residual free chlorine above 0.5 mg/L accelerates thiol-to-disulfide conversion and deactivates the molecule within 15 min. A halogen-free biocide program using 2-MT in combination with isothiazolinone (methylchloroisothiazolinone/methylisothiazolinone at 1.5 mg/L) yields synergistic biofilm removal in pilot-scale cooling rigs with carbon steel heat exchanger tubes instrumented with electrochemical biofilm monitoring probes (ASTM E2647-13), where the time to detect exponential biofilm growth extends from 7 days (untreated) to 31 days. Discharge of blowdown water containing residual 2-MT must be evaluated against local effluent toxicity thresholds; published data for this specific compound's aquatic toxicity profile (Daphnia magna 48 h EC50) remains limited, and end-users are advised to request supplier-supplied biodegradation screening per OECD 301F before discharge authorization.

When Collector Adsorption Kinetics Govern Sulfide Mineral Recovery in Froth Flotation Circuits

Dosing 2-Mercapto Thiazole as a secondary or auxiliary collector in the rougher bank of a copper sulfide concentrator processing chalcopyrite-dominant ore at a grind size of P80 = 75 μm enhances copper recovery by 2–4 percentage points when added at 5–20 g/t ore following primary xanthate conditioning (sodium isobutyl xanthate, SIBX at 15–25 g/t). Adsorption is measured via ultraviolet-visible depletion assays on filtered tailings liquor at the characteristic absorbance band of λ_max = 278 nm; residual collector concentration in the aqueous phase drops below 1 mg/L within 3 min of addition to a 30 wt% solids slurry at pH 10.5 (adjusted with lime), indicating near-complete uptake onto chalcopyrite and pyrite surfaces. Micro-flotation tests on pure chalcopyrite (−106 + 75 μm fraction) in a modified Hallimond tube with nitrogen gas at 20 mL/min and 2 min flotation time produce a maximum recovery of 93% at 1 × 10⁻⁴ M 2-MT concentration and pH 10.0, exceeding the 85% recovery obtained with SIBX alone at identical molar dosage. The thiol functionality chemisorbs preferentially onto copper sites exposed along the (112) cleavage plane of chalcopyrite, as verified by X-ray photoelectron spectroscopy (XPS) showing a S 2p binding energy shift from 162.1 eV (free 2-MT) to 163.8 eV (surface-bound thiolate), while iron sites on pyrite gangue exhibit weaker physisorption. On production-scale mechanical flotation cells (forced-air, 50 m³ tank volume, rotor speed 7.5 m/s tip velocity), 2-MT is introduced via a dedicated reagent distribution ring at the cell feed box to minimize pre-oxidation in the conditioning tank. Froth stability is moderated; excessive 2-MT dosages above 30 g/t produce overly persistent froths with entrainment of fine (−10 μm) gangue silicates, elevating the final concentrate silica content to 8–12% SiO₂—a penalty that triggers smelter deductions. A mixed collector system incorporating 2-MT at 8 g/t with sodium dithiophosphate at 12 g/t optimizes the grade-recovery curve, yielding a rougher concentrate assaying 18–22% Cu at 88–91% recovery in plant trials operated at 25–35% solids by weight in the pulp phase. The reagent is prepared as a 1–2 wt% alkaline stock solution in 0.05 M NaOH and must be consumed within 8 h of make-up to avoid oxidative dimerization to the corresponding disulfide, detected as a turbidity increase and a secondary absorbance peak at 310 nm.

Electroless and Electrolytic Plating Bath Stabilization Through Heterocyclic Thiol Addition

Incorporation of 2-Mercapto Thiazole at 0.5–5 mg/L into acid copper sulfate electroplating baths (200 g/L CuSO₄·5H₂O, 50 g/L H₂SO₄, operated at 3–5 A/dm² cathode current density, 20–25 °C) serves a dual function as a grain refiner and a leveling auxiliary that shifts the cathodic overpotential by 30–50 mV at constant current density, as measured against a copper reference electrode in a Hull cell (267 mL, 2 A, 5 min panel plating). Scanning electron micrographs of deposits plated from baths containing 2 mg/L 2-MT reveal a reduction in average crystallite size from 0.8 μm to 0.25 μm, with corresponding specular reflectance at 60° incidence (ISO 2813:2014) improving from 420 gloss units to 680 gloss units on bright acid copper deposits of 25 μm thickness. The compound co-adsorbs with chloride ions (50–80 mg/L Cl⁻) and polyethylene glycol (PEG, 200–400 mg/L, molecular weight 4000–8000) at the cathode diffusion layer, suppressing dendritic growth in high-aspect-ratio through-holes of printed circuit boards where the throwing power—quantified by the ratio of deposit thickness at the hole center to that at the board surface per IPC-6012D Class 3 requirements—increases from 0.65 to 0.82. Continuous bath maintenance requires dosing 2-MT via a make-up solution delivered through a metering pump synchronized to ampere-hour consumption at a rate of 0.04–0.08 g per 1000 Ah. Bath decomposition products accumulate as oxidized disulfide species that are not electroactive at the cathode; these are periodically removed by activated carbon treatment at 2 g/L carbon with 4 h contact time in a batch purification loop, restoring the original bright plating range of 1–8 A/dm². Excessive 2-MT concentrations above 10 mg/L cause cathode passivation and a sharp drop in current efficiency from 98% to 72%, manifested as a dark brown, powdery deposit at current densities below 1 A/dm².

Synthetic Intermediate Routes to 2-Aminothiazole Pharmacophores and Agrochemical Actives

2-Mercapto Thiazole serves as a thiol nucleophile in the construction of C–S bonds within heterocyclic scaffolds destined for pharmaceutical and crop protection screening libraries. Alkylation at the exocyclic sulfur with substituted benzyl chlorides, phenacyl bromides, or 2-chloroacetamide derivatives in refluxing acetonitrile or dimethylformamide (DMF) at 70–85 °C for 4–8 h in the presence of anhydrous potassium carbonate (1.5–2.0 molar equivalents) yields 2-(substituted thio)thiazoles in 72–91% isolated yields after silica gel column chromatography (230–400 mesh, ethyl acetate/hexane gradient). The transformation proceeds cleanly under these conditions, with the mercapto group exhibiting a pKa of approximately 7.2—sufficiently acidic for deprotonation by mild carbonate bases without generating the ring-opening byproducts observed with stronger alkoxide nucleophiles. A parallel synthetic entry involves oxidative dimerization to 2,2′-dithiobis(thiazole) using iodine in ethanolic sodium hydroxide (0.1 M I₂, 0.2 M NaOH, 30 min at 25 °C) to form a disulfide bridge that can subsequently be cleaved in situ with triphenylphosphine in wet tetrahydrofuran (THF) for thiol exchange reactions with cysteine residues in peptide conjugation studies. When 2-MT is employed as a building block for agrochemical actives—specifically acaricidal and nematicidal lead structures—the thiazole ring is elaborated via diazotization and Sandmeyer-type displacement at the 5-position or through electrophilic bromination using N-bromosuccinimide (NBS, 1.05 eq) in chloroform at 0–5 °C to yield 5-bromo-2-mercapto thiazole, a key intermediate with documented activity against Tetranychus urticae at foliar application rates of 50–100 g/ha in greenhouse efficacy screens. The mercapto group must be protected as the corresponding tert-butyl thioether via treatment with tert-butyl chloride and triethylamine in dichloromethane prior to further transformations requiring strongly basic or nucleophilic conditions that would otherwise consume the free thiol, a workflow consistent with Good Laboratory Practice (OECD GLP Principles) documentation required for registration data submission.

As the primary heterocyclic thiazole accelerator in industrial rubber compounding, 2-mercaptobenzothiazole (MBT, CAS 149-30-4) functions via a zinc-mediated mechanism to activate elemental sulfur for crosslinking. On a Werner & Pfleiderer GK 45 E intermeshing internal mixer with a chamber volume of 45 L, batch temperature excursions above 110°C during ram-down incorporation of MBT powder have repeatedly caused premature scorch in carbon-black-filled natural rubber stocks—a failure mode traced to the accelerator’s low decomposition threshold and high reactivity with sulfur donors at elevated shear temperatures. The typical activation energy for MBT-accelerated vulcanization, derived from Arrhenius plots of oscillating disc rheometer data per ASTM D2084, lies in the range 85–95 kJ/mol, indicating sensitivity to thermal history that demands strict control of dump temperatures below 120°C. MBT is supplied as a pale-yellow to tan powder with a characteristic amine-like odor, and its performance as a general-purpose fast primary accelerator is intimately tied to the co-presence of zinc oxide and stearic acid; without these activators, the cure rate collapses and the crosslink density, measured as the torque increment (M_H − M_L) from ASTM D5289, drops by 40–60% in unfilled NR formulations.

Analytical Specifications and the Minimum Purity Barrier for Compound Consistency

Processors reliant on statistical process control of vulcanizate properties demand stringent lot-to-lot uniformity. A typical commercial specification for rubber-grade MBT is summarized in the following table; deviations beyond the stated limits have been correlated with oscillating cure times in continuous vulcanization tunnels processing EPDM automotive seals.

Parameter	Method Reference	Typical Specification
Assay (as MBT)	ISO 6685:2014 (potentiometric titration)	95.0% minimum
Melting point (capillary)	DIN 53736	178–182°C
Loss on drying (70°C, vacuum)	ISO 787-2	0.5% maximum
Ash content (550°C)	ISO 247-1	0.5% maximum
Residue on 150 µm sieve	ISO 2591-1	0.1% maximum
Free 2-aminothiophenol	Internal (HPLC, UV 254 nm)	0.3% maximum

Free amine content above 0.3% introduces an undesirable plasticizing effect that reduces Mooney viscosity of the green compound and can shift the scorch time (ts₂ at 121°C) by up to 15%, as observed in factory trials with SBR/BR tread compounds. Material retained on a 150 µm screen—typically agglomerates formed during storage at relative humidity above 60%—acts as a dispersion defect nucleus, leading to localized overcure domains visible in microtome sections of the cured article under dark-field microscopy.

What Kinetic Parameters Define the Processing Safety Window of MBT Versus MBTS in NBR?

In nitrile rubber compounds formulated with 1.2 phr sulfur and 5 phr ZnO, a moving-die rheometer comparison at 150°C (ASTM D5289, arc 0.5°) reveals the fundamental kinetic trade-off: MBT provides rapid onset of cure but sacrifices scorch safety, while its oxidized disulfide derivative, 2,2′-dithiobis(benzothiazole) (MBTS), delays crosslinking onset by a factor of 2–3×. The table below records representative rheometric data from a controlled laboratory mixing study using a 1.6 L Banbury-type tangential internal mixer with a fill factor of 0.75.

Property	MBT (1.5 phr)	MBTS (1.5 phr)	Comment
M_L (dNm)	2.1	2.0	Similar plasticizing effect
M_H (dNm) − M_L	12.4	11.8	Crosslink density comparable
ts₂ (min)	2.7	7.3	Scorch margin critical for injection molding
t₉₀ (min)	6.8	13.5	Productivity loss on long cure lines
Cure Rate Index	15.2 min⁻¹	6.8 min⁻¹	Defined as 100/(t₉₀−ts₂)

The narrow scorch delay of MBT—ts₂ below 3 minutes—is borderline for large injection-molded parts requiring long cavity fill times; processors compensate by reducing barrel temperature setpoints to 80–85°C and employing modified MBT formulations with retarders such as phthalic anhydride. By contrast, the MBTS-induced induction period accommodates the thermal history of a 12- to 15-second injection stroke at 95°C without scorch, but the substantially longer t₉₀ reduces throughput on press-cure lines. In continuous hot-air curing of profiles, the difference in cure rate translates directly to line speed limitations: MBT-based compounds can be processed at 18–22 m/min, whereas MBTS limits the line to 10–13 m/min for an equivalent state of cure, as measured on the extrudate by solvent swell ratio per ISO 1817.

When the Zinc Oxide Activator Concentration Falls Below 3 phr in MBT-Accelerated Systems

MBT’s vulcanization mechanism proceeds through the formation of zinc mercaptide complexes that require a stoichiometric excess of ZnO relative to the accelerator. When ZnO loading drops below 3 phr in a natural rubber formulation containing 0.8 phr MBT, the cure efficiency becomes non-linear: the crosslink density ratio (M_H − M_L) reduces by only 12% at 2.5 phr ZnO but collapses by 35% at 1.5 phr ZnO, accompanied by a rise in the free sulfur extractable content from 0.15% to 0.9% (measured by HPLC after ASTM D297 extraction). This threshold behavior has been documented on production-grade two-roll mills where ZnO dispersion quality, assessed by an optical dispersion rating below 3 per ISO 11345, interacts with MBT activation. In zinc-deficient compounds, the resulting vulcanizate exhibits a permanent set under constant deflection (ASTM D395, Method B, 70°C) that deteriorates from 8% to 22%, a mode of failure observed in static seals after 1000 hours of aging.

Pre-Dispersed MBT Masterbatch Processing and Blooming Mitigation in Extruded Profiles

Direct addition of MBT powder at loadings above 1.8 phr into low-polarity polymers such as EPDM or IIR frequently results in surface bloom—a visible crystalline film consisting of recrystallized accelerator that can impair adhesion during post-vulcanization bonding. The phenomenon is governed by the solubility limit of MBT in the rubber matrix, which is approximately 1.2% w/w at 23°C in EPDM with 55% ethylene content. Switching to a predispersed masterbatch (MBT adsorbed on a silica/process oil carrier at 70% active content) reduces local supersaturation during mixing because the release profile is diffusion-controlled. In an industrial twin-screw extruder (Leistritz ZSE 40 MAXX, L/D 44) used for continuous profile curing, the masterbatch form enabled a 2.2 phr active MBT loading without bloom over a 6-month warehouse storage period at 40°C, whereas the neat powder at the same active level produced bloom within 72 hours. The dispersion grade improved from 4.2 (powder) to 6.8 (masterbatch) on the ISO 11345 scale of 1–10, correlating with a 20% reduction in fatigue crack growth rate in DeMattia flex testing (ASTM D813, 5 mm stroke).

Compliance with food-contact regulations must be verified for each application. Under FDA 21 CFR 177.2600, MBT is permitted in rubber articles intended for repeated contact with dry food, subject to a total accelerator migration limit not exceeding 15 ppm in food-simulating solvents. The specific migration limit under Commission Regulation (EU) No 10/2011, as amended, for 2-mercaptobenzothiazole (FCM substance No. 476) is 0.1 mg/kg. Extraction testing according to EN 1186 series on a peroxide/MBT co-cured EPDM compound showed that MBT migration is strongly pH-dependent, with a 3-fold increase when the simulant pH shifts from 4.0 to 7.0, a factor to incorporate into compliance assessments for acidic vs. neutral food types.

In contrast to sulfenamide accelerators such as N-cyclohexyl-2-benzothiazolesulfenamide (CBS), MBT does not undergo a thermal decomposition step to release the active thiazole moiety; its activity is immediate upon zinc complex formation. This kinetic difference makes MBT unsuitable as a sole accelerator in high-speed steel cord skim compounds where delayed action is mandatory to permit flow of the rubber into cord interstices before crosslinking freezes the structure. In such applications, a typical accelerator system displaces MBT with CBS at 0.6–1.0 phr and retains MBT only as a secondary booster at 0.1–0.2 phr to fine-tune the modulus at full cure. The substitution increases the processing safety index (ts₂/t₉₀) from 0.40 to 0.62, a shift that has been validated on a Berstorff ZE 130 single-screw extruder feeding a multi-daylight press.

Storage instability under humid conditions is a recognized limitation. MBT exhibits hygroscopicity above 60% relative humidity at 25°C, absorbing up to 1.2% moisture within 24 hours, which triggers hydrolysis to 2-aminothiophenol and carbon disulfide in alkaline environments. Warehouses storing MBT in tropical climates must maintain a dew point below 5°C in sealed containers with desiccant breathers; failure to do so results in a drop in assay to 92–93% and a corresponding increase in scorch tendency that has caused full-batch rejections in truck tire tread production lines. The compatibility window with amine-based antioxidants should be assessed case-by-case: direct blends of MBT with diphenylamine derivatives stored above 40°C have shown exothermic reactions at the particle interfaces, visible as discolored agglomerates after 4 weeks of storage.

HS Code	854613
Name	2-Mercapto Thiazole
Chemical Formula	C3H3NS2
Molar Mass	115.19 g/mol
Appearance	White to light yellow crystalline powder
Odor	Characteristic sulfurous odor
Solubility In Water	Slightly soluble
Melting Point	127 - 131 °C
Boiling Point	285 - 287 °C
Flash Point	126 °C
Pka Value	3.43
Density	1.42 g/cm³

Packing	2 - Mercapto Thiazole packaged in 1 - kg bags for easy handling.
Shipping	2 - Mercapto Thiazole is shipped in well - sealed, corrosion - resistant containers. Packaging adheres to strict chemical transportation regulations. Shipment is carefully monitored to maintain safety during transit.
Storage	2 - Mercapto Thiazole should be stored in a cool, dry, well - ventilated area. Keep it away from heat sources, open flames, and oxidizing agents. Store in tightly - sealed containers to prevent moisture absorption and exposure to air, which could potentially lead to degradation. Avoid storing near incompatible substances to ensure safety and maintain its chemical integrity.