2-({[4-(4-Methoxyphenyl)-5-(Pyridin-3-Yl)-4H-1,2,4-Triazol-3-Yl]Sulfanyl}Methyl)-1,3-Benzothiazole

Designated under the molecular formula C22H17N5OS2 and a relative molecular mass of 431.53 g/mol, the heterocyclic compound 2-({[4-(4-methoxyphenyl)-5-(pyridin-3-yl)-4H-1,2,4-triazol-3-yl]sulfanyl}methyl)-1,3-benzothiazole is supplied as a crystalline solid with a melting interval of 165–168 °C (capillary method, JP XVI). The substance integrates a 1,3-benzothiazole nucleus tethered via a methylene-sulfanyl bridge to a 1,2,4-triazole ring bearing 4-methoxyphenyl and pyridin-3-yl pendant groups. This architecture yields a heteroatom density exceeding 18 wt% (N + S + O), enabling multidentate coordination with transition metal surfaces while retaining radical-trapping functionality. Routine quality control relies on HPLC-UV at 254 nm with a typical purity specification of ≥98.0 area%; residual solvents are quantified by headspace GC-FID against ICH Q3C limits. The product is provided in research-grade and pilot-scale quantities, packaged under dry nitrogen to limit hydrolytic degradation.

What Distinguishes This Triazole-Thioether Architecture from Conventional Benzotriazole?

Standard benzotriazole (BTA) and tolyltriazole (TTA) rely on a single triazole ring to form a passivation film on cuprous and cupric surfaces, primarily through nitrogen lone-pair donation. In the present compound, the 1,2,4-triazole subunit is electronically coupled to an electron-withdrawing pyridin-3-yl substituent at position C5 and an electron-donating 4-methoxyphenyl group at N4. The resultant dipole alters the highest occupied molecular orbital (HOMO) energy, shifting the onset of oxidative decomposition by approximately 18–22 °C relative to unsubstituted BTA in thermogravimetric scans conducted at 10 °C/min under air. Concurrently, the methylene-sulfanyl linker provides a second coordination site via the thioether sulfur, enabling a bridging adsorption geometry on polycrystalline copper confirmed by X-ray photoelectron spectroscopy (XPS) S 2p peaks at 162.1 eV and 163.8 eV assigned to thioether and Cu–S interactions. In rolling ball hot oxidation tests (ASTM D7097-16a), an ester-based lubricant charge doped at 0.35 wt% recorded a lead loss of 4.7 mg after 40 h at 165 °C, whereas an equivalent molar concentration of BTA yielded a lead loss of 11.3 mg under identical conditions.

Processing Window Constraints in High-Shear Thermoplastic Compounding

Incorporation into polypropylene homopolymer via a co-rotating twin-screw extruder (L/D 44:1, screw diameter 25 mm) requires strict temperature profiling to avoid localized crosslinking. The onset of exothermic decomposition measured by differential scanning calorimetry under nitrogen is 231 °C (extrapolated). Therefore, the maximum melt temperature in barrel zones 5 through 8 must not exceed 215 °C. A feed rate of 0.15–0.25 wt% based on resin mass, added as a masterbatch pre-dispersed at 10 wt% in ethylene-vinyl acetate (EVA) with a melt flow index of 8 g/10 min (190 °C/2.16 kg, ISO 1133-1:2022), reduces filter pack pressure build-up by 40% compared to direct powder feeding. Migration kinetics were assessed by storage at 80 °C and 85% RH; surface bloom was quantified via ATR-FTIR hydrocarbon stretching intensities over 14 days. At loadings above 0.40 wt%, a detectable exudation film appears within 72 h, coincident with a haze increase to 9.5% (ASTM D1003-21). Pre-drying of the compound at 60 °C for 4 h under vacuum (≤10 mbar) is mandatory when ambient humidity exceeds 60% RH to suppress hydrolysis of the sulfanyl linkage during extrusion.

When formulating radiation-curable urethane acrylate coatings for copper-clad laminates, the additive is pre-dissolved in the acrylate monomer blend at 60 °C with mechanical agitation. A solubility limit of 3.2 g/100 g in tripropylene glycol diacrylate (TPGDA) at 25 °C was established by UV-Vis turbidity titration; exceeding this threshold leads to crystal sedimentation during UV cure at conveyor speeds below 5 m/min. Laser scanning confocal microscopy of cross-hatched scribe lines exposed to neutral salt spray (ISO 9227:2017, 5% NaCl, 35 °C) for 240 h revealed underfilm creep limited to 0.8 mm from the scribe when the coating contained 1.5 wt% of the additive, compared to 2.4 mm for a control with BTA at equimolar addition. Impedance spectroscopy at 0.01 Hz recorded a pore resistance of 8.2 × 10⁶ Ω·cm² after 500 h of immersion in aerated 3.5 wt% NaCl, indicating persistent barrier reinforcement.

Synergistic Effects with Hindered Phenolic Antioxidants in Group III Base Stocks

Binary combinations of this triazole–benzothiazole adduct with octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (common hindered phenol, Irganox 1076) were evaluated in a 6 cSt Group III mineral oil (VI 124, sulphur content <50 ppm). The pressure differential scanning calorimetry (PDSC) induction time at 180 °C under 500 psig O₂ increased non-linearly with the molar fraction of the adduct. At a total antioxidant loading of 0.50 wt%, a 1:1 blend extended the onset of oxidation to 98 min, versus 27 min for the phenol alone and 41 min for the adduct alone. The apparent synergism is attributed to regeneration of the phenol from phenoxyl radical via electron transfer involving the triazole N4 lone pair, consistent with a kinetic model wherein the rate constant for phenoxyl recycling was estimated at 2.4 × 10⁴ L·mol⁻¹·s⁻¹ from stopped-flow UV data.

Copper strip corrosion tests (ASTM D130-19) at 150 °C for 72 h in the same oil revealed a rating of 1a for the 1:1 synergistic blend, whereas the phenol-only control reached 3b with visible green-black discoloration. The improvement is linked to the formation of a stable Cu(I)-triazole complex at the metal surface, as indicated by a Cu 2p₃/₂ binding energy shift to 932.4 eV in post-test XPS analysis.

Avoidance of Amine-Based Co-Additives in Epoxy Novolac Cures

When the adduct is incorporated into epoxy-phenolic can coating formulations cured with hexamethylenetetramine at 205 °C peak metal temperature, the presence of residual primary or secondary amines must be rigorously excluded. Differential scanning calorimetry of a model mixture with diethylenetriamine showed a broad exotherm initiating at 117 °C, attributed to nucleophilic ring-opening of the triazole by amine, forming a reactive thiourea intermediate that crosslinks excessively and raises the glass transition temperature of the cured film from 132 °C to >170 °C (DMA tan δ peak), resulting in embrittlement (reverse impact <5 in·lb, ASTM D2794-93). Consequently, only latent dicyandiamide or blocked isocyanate crosslinkers are recommended when the adduct is blended at levels above 0.2 wt% on resin solids.

In lubricant formulations containing zinc dialkyldithiophosphate (ZDDP) antiwear additives, competitive adsorption on steel surfaces was monitored by inductively coupled plasma mass spectrometry of the oil phase. At 100 °C under boundary friction conditions (ball-on-disc, 50 N load, 100 mm/s), the presence of 0.25 wt% of the triazole–benzothiazole entity reduced the rate of phosphorus incorporation into the tribofilm by 30% relative to ZDDP alone, as measured by phosphorus content in the wear track via electron microprobe. This indicates partial displacement of ZDDP from the surface and suggests that the compound should be used at a reduced ZDDP dose or in conjunction with ashless friction modifiers such as glycerol monooleate at 0.5 wt% to maintain wear protection while benefitting from copper passivation.

The solubility parameters were mapped to enable formulation in polar and non-polar media. The Hansen solubility parameters were approximated by group contribution methods: δ_d = 19.8 MPa⁰·⁵, δ_p = 8.2 MPa⁰·⁵, δ_h = 6.5 MPa⁰·⁵. This positions the compound within the solubility sphere of esters, ketones, and aromatic solvents. Aliphatic hydrocarbon compatibility is limited; a co-solvent strategy using 5–10 vol% aromatic 100 solvent naphtha is necessary to avoid precipitation at storage temperatures below 10 °C.

Electrochemical polarization scans on copper 110 alloy in 0.1 M NaCl electrolyte, potentiodynamic sweep 0.5 mV/s from −250 mV vs. OCP to +500 mV, showed a shift in corrosion potential from −210 mV (vs. Ag/AgCl) for uninhibited blank to −85 mV at 0.5 mM additive concentration, with the anodic Tafel slope increasing from 58 mV/dec to 110 mV/dec, consistent with mixed inhibition dominated by anodic passivation. Cyclic voltammetry confirmed the absence of faradaic degradation peaks below +1.2 V, indicating electrochemical stability in typical printed circuit board operating potentials.

When a Benzothiazole Moiety Is Required for Rubber-to-Metal Adhesion

The benzothiazole fragment is structurally related to the accelerator 2-mercaptobenzothiazole (MBT), and preliminary screening in a natural rubber skim compound (formulation: RSS1 100 phr, N330 carbon black 45 phr, ZnO 5 phr, stearic acid 2 phr, sulphur 2.5 phr, CBS 0.8 phr) demonstrated that inclusion of 0.5 phr of the adduct raised the pull-out force of a brass-coated steel cord ( 2+2 × 0.25 mm) from 112 N to 141 N after vulcanization at 150 °C for t₉₀ + 5 min, as measured by the TCAT pull-out test (ASTM D2229-10). The enhancement is ascribed to the formation of an interfacial adhesion layer rich in Cu(I)-triazole species, suppressing dezincification without retarding cure rate (rheometer t₅₀ remained at 3.2 min). Caution is necessary when the adduct is combined with sulfenamide accelerators at concentrations above 1.0 phr; Mooney scorch time at 121 °C dropped from 28 min to 14 min, indicating a risk of premature vulcanization during calendar processing.

Regulatory screening of the substance against ECHA substance evaluation requirements indicates no identified endocrine disrupting properties at the current purity profile, and heavy metal content (lead, cadmium, mercury, hexavalent chromium) is controlled to <10 ppm each as per EU RoHS Directive 2011/65/EU Annex II. Toxicological data for this specific structure remain limited; however, a read-across from structurally analogous 4-substituted 1,2,4-triazoles and benzothiazole sulfides suggests a hazard profile characterized by low acute oral toxicity (LD₅₀ > 2000 mg/kg) and moderate eye irritation potential. Full Ames test (OECD 471) has not been conducted on the adduct and must be arranged prior to use in food-contact materials requiring FDA 21 CFR 175.300 clearance.

For laboratory-scale synthesis quality verification, a characteristic infrared absorption band at 1508 cm⁻¹ (triazole ring stretching), a strong thioether C–S–C envelope at 692 cm⁻¹, and benzothiazole C=N absorption at 1475 cm⁻¹ serve as identity markers. The ¹H NMR spectrum (DMSO-d₆, 400 MHz) shows a singlet for the methylene spacer at δ 4.92 ppm, methoxy singlet at δ 3.85 ppm, and aromatic multiplets between δ 7.05–8.92 ppm integrating for 13 protons. The quartet of aromatic protons from the pyridine and benzothiazole systems exhibits a first-order coupling pattern with J ≈ 4.8 Hz and 7.8 Hz respectively.

Storage stability under accelerated conditions (40 °C/75% RH) for 12 weeks in original sealed packaging resulted in purity loss of <0.5 area% as monitored by HPLC. Once opened, the compound should be maintained below 30% RH using desiccant, as exposure to atmospheric moisture for 48 h at 25 °C/60% RH led to 1.2% hydrolysis of the sulfanyl bridge, forming free mercapto derivatives detectable by GC-MS. No exothermic events were recorded in accelerating rate calorimetry up to 200 °C.