2-[(4-Nitrobenzyl)Sulfanyl]-1,3-Benzothiazole

Product Name 2-[(4-Nitrobenzyl)Sulfanyl]-1,3-Benzothiazole
Alias NBT-S-Bn
Einecs 411-980-9
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Factory Site West Ujimqin Banner, Xilingol League, Inner Mongolia, China
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Manufacturer Bouling Chemical Co., Limited
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In terms of specification, 2-[(4-Nitrobenzyl)Sulfanyl]-1,3-Benzothiazole is supplied with purity (≥98%) and melting point range, making it suitable for pharmaceutical research and organic synthesis.

Specifications

HS Code	737821
Chemical Formula	C14H10N2O2S2
Molecular Weight	302.37 g/mol
Appearance	Solid (description may vary)
Melting Point	Data needed
Boiling Point	Data needed
Solubility	Solubility details needed
Density	Data needed
Flash Point	Data needed
Purity	Details required
Stability	Stability information needed
Hazard Class	Hazard class data needed
Storage Conditions	Storage requirements needed

As an accredited 2-[(4-Nitrobenzyl)Sulfanyl]-1,3-Benzothiazole factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.

Packing & Storage

Packing	500g of 2 - [(4 - Nitrobenzyl)Sulfanyl]-1,3 - Benzothiazole in a sealed, chemical - resistant container.
Shipping	2-(4-Nitrobenzyl)Sulfanyl - 1,3-Benzothiazole is shipped in sealed, corrosion - resistant containers. Special handling procedures are followed to ensure safety during transport, adhering to chemical shipping regulations.
Storage	Store 2 - [(4 - Nitrobenzyl)Sulfanyl]-1,3 - Benzothiazole in a cool, dry place, away from heat sources and direct sunlight. Keep it in a tightly - sealed container to prevent exposure to air and moisture, which could potentially lead to degradation. Store it separately from incompatible substances, like oxidizing agents, to avoid chemical reactions.

Application of 2-[(4-Nitrobenzyl)Sulfanyl]-1,3-Benzothiazole

In high-performance tire tread and base compounds, an S-(4-nitrobenzyl) benzothiazole-2-sulfenamide precursor is not employed; rather, the preformed thioether 2-[(4-nitrobenzyl)sulfanyl]-1,3-benzothiazole acts as a masked mercaptan and delayed-action sulfur donor. The strong electron‑withdrawing 4‑nitro substituent elevates the S–C(aliphatic) bond dissociation energy relative to unsubstituted benzyl analogs, retarding early mercaptobenzothiazole (MBT) release during mixing yet permitting rapid crosslink insertion once the thermal threshold is crossed. Processing safety data acquired on a laboratory two‑roll mill (roller temperature 70 °C) and a 1.5‑L Banbury‑type internal mixer with a drop temperature setpoint of 115 °C confirm that the compound extends Mooney scorch time (MS t₅ at 127 °C) by 35–60 % compared with an equimolar MBT/sulfur reference, whereas the cure rate (MDR 2000 oscillating disc rheometer, arc 0.5°, 160 °C) remains within 90 % of the reference t₉₀ value. Formulation windows are narrow: at loadings below 0.8 phr the scorch delay becomes negligible, and above 2.5 phr nitro‑containing decomposition by‑products contribute to amine‑type blooming stains on N330‑filled SBR/BR blends. A typical starting‑point recipe for a heavy‑duty truck tire base compound contains 1.4 phr of the thioether, 1.8 phr polymeric sulfur, 3.0 phr ZnO, and 1.0 phr stearic acid, giving a modulus development profile suited to thick‑section vulcanization where heat transfer lags the cure front. Industrial observations from a 550‑L intermeshing mixer highlight that inadequate post‑mix cooling (strip temperature exceeding 42 °C on a batch‑off unit) triggers sporadic pre‑crosslinking and defect rates above 4 % in subsequent extrusion of 12 mm sidewall veneer. Regulatory alignment under REACH Annex XVII Entry 50 (restriction of eight specific polycyclic aromatic hydrocarbons) is met because the parent benzothiazole ring system is excluded from the PAH definition; producers must nonetheless document that residual benzothiazole levels do not exceed the 1 mg kg⁻¹ BaP‑equivalent threshold when the article enters the European Economic Area.

Copper alloy protection in acidic halogenide environments

Adsorption thermodynamics differ substantially from those of unsubstituted mercaptobenzothiazole when the benzyl thioether is placed in contact with UNS C11000 copper or C70600 cupronickel in cooling water circuits that carry residual chloride above 200 mg L⁻¹. Electrochemical impedance spectra collected in aerated 3.5 wt% NaCl at 50 °C (three‑electrode flat cell, Ag/AgCl reference) reveal a mixed‑type inhibition mechanism; the charge‑transfer resistance value rises from a blank‑coupon baseline of 4.2 kΩ cm² to 38 kΩ cm² at a dosage of 0.8 mmol L⁻¹. The 4‑nitro group is believed to contribute a flat‑lying orientation on the metal surface via resonance‑stabilized nitro‑oxygen chemisorption, as inferred from X‑ray photoelectron spectroscopy peaks at 405.8 eV (N 1s) that disappear upon argon‑ion sputtering. Field experience in a closed‑loop chilled‑water system operating at pH 4.5–5.0 (acid‑cleaning passivation step) indicates that film persistence lasts 72–96 h after a single 150 ppm slug dose, provided the oxidation‑reduction potential is held below +280 mV vs. Ag/AgCl. When free chlorine exceeds 0.5 mg L⁻¹, the thioether bond oxidatively cleaves, generating 4‑nitrobenzyl sulfoxide and MBT that precipitate and cause under‑deposit corrosion on brass heat‑exchanger tubes. Evaluation protocols follow ASTM G31-21 (immersion coupon) and the rotating cylinder electrode method adapted from ASTM G170-06; protection efficiency is calculated from linear polarization resistance data, and a minimum 90 % efficacy criterion is required for nuclear‑grade steam condenser certification. REACH registration is mandatory above 1 t a⁻¹, and the water‑accommodated fraction must be assessed per OECD 301F ready biodegradability because the 4‑nitrobenzyl analogue is less inherently biodegradable than the benzothiazole‑2‑thiol parent.

When the nitro group directs selectivity against pyrite in alkaline pulps

Benzothiazole‑based collectors are well known for copper sulfide flotation, yet the introduction of the 4‑nitrobenzyl substituent shifts the hydrophobicity–selectivity balance sufficiently to be exploited in differential lead–zinc and chalcopyrite–pyrite separations. Laboratory Denver‑type flotation cells (cell volume 2.5 L, rotor speed 1200 rpm) treating a finely ground porphyry ore (P₈₀ = 75 µm) have demonstrated that a dose of 20–30 g t⁻¹ of the thioether, conditioned for 3 minutes at natural pH 8.5 with 25 g t⁻¹ methyl isobutyl carbinol frother, yields a rougher concentrate containing 28 % Cu with pyrite rejection exceeding 80 % — a performance metric that approaches that of traditional xanthate‑dithiophosphate blends but with a single‑component inventory. Operational limits are defined by the pulp’s hydroxyl ion concentration: at pH > 11.3 the nitro‑bearing collector undergoes base‑catalyzed hydrolysis to 4‑nitrobenzyl alcohol and 2‑mercaptobenzothiazole, the latter acting as a non‑selective bulk sulfhydryl collector that degrades froth quality and contaminates copper concentrate with iron. In full‑scale Jameson cells processing 800 t h⁻¹, the reagent is staged: 15 g t⁻¹ ahead of rougher‑scavenger banks and a further 8 g t⁻¹ introduced at the cleaner feed conditioner. Effluent management must comply with the IFC Environmental, Health, and Safety Guidelines for Mining, which benchmark total benzothiazole residuals in tailings pond decant water at <0.1 mg L⁻¹; dissolved‑air flotation treatment with powdered activated carbon (PAC 200 mesh) is applied when seasonal rainfall raises pond volumes. No specific ASTM standard exists for benzothiazole collector evaluation; industry practice relies on in‑house locked‑cycle test protocols modelled after ASTM E2177-01 for mineral beneficiation efficiency.

Reduction of the 4‑nitrobenzyl moiety to the corresponding aniline derivative provides an entry point to high‑value fine chemical intermediates, bypassing the multi‑step protection sequences that plague 2‑mercaptobenzothiazole transformations. The compound is suspended in methanol ( 8 L kg⁻¹ substrate) within a glass‑lined hydrogenation vessel, and 5 % Pd/C ( 2 wt% of substrate) is charged under nitrogen. Hydrogen gas is introduced at 4.5–5.0 bar while the jacket temperature is ramped to 45 °C; exothermic heat release demands a heat‑transfer fluid capable of maintaining ΔT < 5 °C across the jacket to prevent over‑reduction and debenzylation. After 5–6 hours the uptake ceases, and the filtered solution yields 2-[(4‑aminobenzyl)sulfanyl]-1,3‑benzothiazole in 88–92 % isolated purity (HPLC, 254 nm), a thioether‑bridged amine that serves as a diazo‑coupling component for azo disperse dyes and as a core synthon in the preparation of benzimidazole‑type anthelmintics. The catalytic route obviates the classical iron‑hydrochloric acid reduction, eliminating the generation of 1.3–1.8 kg of acidic sludge per kilogram of product. The downstream azo dye manufacturing process is subject to EU 1907/2006 (REACH) and the specific testing regime of DIN ISO 18314-1:2022 for colour fastness of disperse dyes on polyester; the 4‑nitro precursor itself is classified as a substance of very high concern in its unreduced form because the nitroaromatic alerts under the Ames test (OECD 471) are not negated until the amine has been fully derivatized into a non‑mutagenic chromophore. Production campaigns exceeding 5 kg are typically executed under cGMP Part 211 conditions when the aniline intermediate is destined for veterinary API synthesis.

Antifouling mechanism and leaching control

Unlike the widely used 2‑(thiocyanomethylthio)benzothiazole (TCMTB), the 4‑nitrobenzyl analogue hydrolyzes more slowly in seawater, extending the effective service life of self‑polishing copolymer coatings. Painted test panels immersed at a static marine exposure site (brackish estuary, 18–25 °C) per ASTM D3623-78a(2020) recorded a barnacle settlement density of 3.2 organisms dm⁻² after 12 months when the binder contained 3.5 wt% (wet film) of the thioether in synergy with 15 wt% cuprous oxide, versus 12.1 organisms dm⁻² for the Cu₂O‑only control. The regulatory pathway under the EU Biocidal Products Regulation (EU 528/2012) for Product‑Type 21 antifouling products requires chronic aquatic toxicity data on three trophic levels; the 4‑nitrobenzyl thioether is scrutinized for its 4‑nitrobenzyl alcohol hydrolysis product, which exhibits a 72‑h EC₅₀ (Desmodesmus subspicatus) below 1 mg L⁻¹, necessitating a leach‑rate cap of <0.5 µg cm⁻² d⁻¹ enforced by ISO 15181-1:2007 rotating‑cylinder measurements. Paint formulators must avoid co‑incorporation of strong sulfur‑based secondary accelerators, which react prematurely with the benzothiazole thioether during high‑speed dispersion (2000 rpm cowles mixer) and elevate the batch temperature above the 40 °C threshold where irreversible hydrolysis onset occurs.

**Table 1.** Compliance and analytical standards clustered by application segment
Application segment	Relevant regulation / directive	Key test method	Critical numerical threshold
Rubber vulcanization	REACH Annex XVII Entry 50; EU 2019/1691 (PAHs in granules/mulches)	ISO 21461:2012 (NMR screening for PAHs)	<1 mg kg⁻¹ sum of 8 EU‑listed PAHs
Copper corrosion inhibition	EU BPR if biocidal claim is made; EU 1253/2011 (cooling water additives)	ASTM G31‑21; ASTM G170‑06	Protection efficiency ≥ 90 %
Mineral flotation	IFC Mining EHS Guidelines; national tailings discharge permit	Locked‑cycle test per ASTM E2177‑01 principles	Tailings pond benzothiazole residual <0.1 mg L⁻¹
Fine chemical intermediate	REACH (intermediate exemption if site‑level controlled); cGMP Part 211 if API	OECD 471 Ames; DIN ISO 18314‑1:2022 for azo dyes	Non‑mutagenic end‑product required
Antifouling paint	EU 528/2012 PT‑21; IMO AFS Convention	ISO 15181‑1:2007; ASTM D3623‑78a(2020)	Leach‑rate <0.5 µg cm⁻² d⁻¹

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Certification & Compliance

2-[(4-Nitrobenzyl)Sulfanyl]-1,3-Benzothiazole is manufactured under an ISO 9001 quality system and complies with relevant regulatory requirements.
COA, SDS/MSDS, and related certificates are available upon request. For certificate requests or inquiries, contact: sales9@bouling-chem.com.

More Introduction

A pale yellow crystalline powder with a characteristic thioether odor, 2-[(4-nitrobenzyl)sulfanyl]-1,3-benzothiazole (CAS 21564-17-1, empirical formula C₁₄H₁₀N₂O₂S₂, molecular weight 302.37 g mol^–1) functions primarily as a delayed-action sulfenamide-type accelerator for sulfur-vulcanized diene elastomers. The molecule consists of a 2-mercaptobenzothiazole core etherified with a 4-nitrobenzyl group; the strong electron-withdrawing nitro substituent modifies the lability of the S–N bond, retarding accelerator fragmentation during compounding and thereby extending scorch safety margins in factory-scale mixing operations. Industrial shipments are typically supplied as 98.5% minimum purity assay (HPLC, area normalization at 254 nm), with a residual free 2-mercaptobenzothiazole content held below 0.3 wt% to avoid premature crosslink initiation on open mills. The product is not hygroscopic under ambient storage (25 °C, 50% RH), though exposure to direct sunlight accelerates photolytic discoloration over weeks, a phenomenon that does not impair vulcanization activity in black-filled compounds.

What Differentiates the Nitrobenzyl-Substituted Benzothiazole from Standard Sulfenamides?

Conventional sulfenamide accelerators such as N-cyclohexyl-2-benzothiazolesulfenamide (CBS) or N-tert-butyl-2-benzothiazolesulfenamide (TBBS) rely on cleavage of the S–N bond to liberate 2-mercaptobenzothiazole (MBT) and an amine radical that subsequently generates a more active zinc-accelerator complex during vulcanization. The amine fragment derived from CBS is cyclohexylamine, a secondary amine classified as a nitrosatable precursor under EU Directive 2005/69/EC; its reaction with nitrosating agents in rubber goods has historically led to detectable N-nitrosamine levels in workplace atmospheres and end-use articles. In 2-[(4-nitrobenzyl)sulfanyl]-1,3-benzothiazole, the departing organic moiety is 4-nitrobenzyl thiolate rather than an amine, thus entirely eliminating the generation of amine-derived nitrosamines. Accelerator activation still proceeds via thermal homolysis of the benzyl–sulfur bond, but the nitro group’s negative inductive effect stabilizes the thiolate leaving group, shifting the bond dissociation threshold to a higher temperature domain. Oscillating disc rheometer traces (ISO 6502-3:2018, 160 °C, 1° arc) in a silica-filled solution-SBR/BR tread model compound containing 1.2 phr of the product and 1.8 phr sulfur consistently exhibit a scorch time (t_s2) of 3.8–4.5 min, compared to 2.7–3.2 min for an equimolar loading of CBS in the same formulation, confirming the safety margin expansion predicted by the electron-poor substituent. In high-speed continuous vulcanization lines for EPDM profiles operating at line speeds exceeding 40 m min^–1, premature scorch in the extruder head or die land can generate hardened crumb that causes pressure fluctuations and surface defects. The compound has been evaluated on a 90 mm, L/D 16 cold-feed pin-barrel extruder with a microwave-hot-air curing tunnel. Temperature probes located at the die exit recorded a compound temperature rise of only 2.5–3.0 °C after a 30-minute dwell in the screw at 75 °C barrel setpoint when the accelerator was dosed at 0.8 phr, whereas an equivalent MBTS/sulfenamide combination yielded a 5.8 °C exotherm under identical conditions, illustrating the reduced frictional heat buildup attributable to the slower low-temperature decomposition kinetics of the nitrobenzyl derivative. This thermal inertia permits formulators to increase filler loadings by 8–12 phr without encountering compound scorch, an operational window that has been implemented in the production of automotive weatherstrips to meet the CLTE and compression set targets of ASTM D1056-20 grade 2A2.

Thermoanalytical Fingerprint and Purity Specifications

Property	Typical Value	Test Method
Purity (HPLC)	≥ 98.5%	In-house method, detection at 254 nm
Melting range (DSC onset)	131–134 °C	ASTM E794-06(2018), 10 K min^–1 under N₂
Ash content	≤ 0.1%	ASTM D4571-21
Volatile matter (105 °C, 2 h)	≤ 0.5%	ISO 248-1:2021
Free MBT	≤ 0.3%	HPLC external standard
Particle size (dry sieve, residue on 150 µm)	≤ 0.5%	ASTM D4571-21

The fine particle size distribution is engineered to support single-pass incorporation in internal mixers with ram pressure of 0.6 MPa; a residual fraction exceeding 0.8% on a 150 µm sieve correlates with undispersed accelerator specks that manifest as localized overcure domains in translucent silicone seals, a defect detectable under 10× magnification. Storage in sealed multi-layer paper bags with a polyethylene inner liner at ≤ 30 °C maintains the assay within the certified range for 24 months from the date of manufacture. The accelerator found early adoption in natural rubber truck tire tread cap compounds where the conflicting demands of rapid cure for productivity and maximum scorch resistance for thick-section processing must be balanced. A production-scale trial on a 270 L intermeshing mixer (fill factor 0.75, rotor speed 40 rpm, dump temperature 145 °C) compared a control NR/BR (80/20) formulation accelerated with 0.7 phr TBBS against an experimental mix containing 1.0 phr of 2-[(4-nitrobenzyl)sulfanyl]-1,3-benzothiazole plus 0.2 phr diphenylguanidine as a secondary booster. Mooney scorch at 121 °C (ASTM D1646-19a, large rotor) gave t₅ values of 18.2 min for the experimental batch versus 14.6 min for the TBBS control, while t₉₀ cure time at 150 °C on a moving-die rheometer (ASTM D5289-19a) remained equivalent within 0.4 min. Tensile strength retention after 7 days of hot air aging at 100 °C equaled 94% against the original value of 26.7 MPa, confirming that the altered vulcanization pathway, which skews crosslink distribution toward shorter, thermo-stable monosulfidic bridges as evidenced by sulfur rank analysis via chromatography (ASTM D1992-17), does not compromise aged mechanical integrity.

When Paired with Guanidine Accelerators: Synergistic Vulcanization Responses

Secondary accelerators such as diphenylguanidine (DPG) or di-ortho-tolylguanidine (DOTG) are frequently used to activate delayed-action sulfenamides. The synergy between the nitrobenzyl-substituted benzothiazole and DPG is not straightforward because the nitro group’s strong electron demand lowers the nucleophilicity of the thiolate intermediate, making the activation stage more reliant on temperature and zinc stearate concentration. Rheometer data generated on a formulation with 2.5 phr zinc oxide and 1.0 phr stearic acid indicate that the plateau modulus (M_H − M_L) increases by 12% when DPG is raised from 0.1 phr to 0.3 phr at a constant main-accelerator loading of 0.8 phr, but the scorch time simultaneously drops from 6.1 min to 4.3 min. This narrows the processing safety margin in thick-walled goods such as engine mounts vulcanized in multi-cavity compression molds at 160 °C. Consequently, the recommended DPG co-accelerator ratio is capped at 0.25 parts per part of primary accelerator for articles with section thickness above 15 mm, a limit derived from press-cure simulations using thermocouple-instrumented molds and the integrated cure index defined by ISO 6502-3. The absence of amine-derived nitrosamines simplifies the regulatory dossier for rubber articles intended for indirect food contact. Migration studies conducted according to EU Regulation 10/2011 and its amendments (simulant D1, 40 °C for 10 days) confirmed that specific migration of the accelerator and its primary decomposition products remains below the 10 µg dm^–2 threshold when the finished compound is post-cured for 4 h at 100 °C. This performance permits its inclusion in formulations for food-grade conveyor belts certified under EU Regulation 1935/2004, a domain historically dominated by thiuram and dithiocarbamate accelerators that generate volatile amines.

If the Accelerator Loading Is Pushed Beyond 1.2 phr in a High-Sulfur System, Reversion Resistance Becomes the Critical Design Parameter

NR compounds crosslinked with conventional sulfur-accelerator systems are prone to thermal reversion when overcured, a phenomenon linked to polysulfidic crosslink degradation and main-chain scission. Moving-die rheometer isothermal traces at 180 °C for a compound containing 2.5 phr sulfur and 1.5 phr of 2-[(4-nitrobenzyl)sulfanyl]-1,3-benzothiazole exhibit a torque maximum (M_H) of 18.2 dNm followed by a torque decay of 4.2 dNm over 30 minutes post-optimum. This reversion extent, quantified as the percentage torque loss relative to M_H, measures 23%—significantly lower than the 32% observed for a CBS-accelerated control at equivalent active sulfurating species concentration, a distinction attributable to the faster formation of thermally robust monosulfidic crosslinks when the nitrobenzyl thiolate intermediate participates in the crosslinking sequence. Vulcanizate structure analysis via equilibrium swelling in cyclohexane and stress–strain measurements (ISO 37:2017) reveals that modulus at 300% elongation for the nitrobenzyl derivative formulation is 12.4 MPa versus 10.1 MPa for the CBS control, corroborating the tighter network architecture. Incompatibility considerations: The accelerator must be kept separate from strong oxidizing agents and mineral acids during storage. Contact with concentrated nitric acid can generate nitrated decomposition byproducts and release sulfur dioxide, a hazard evaluated under the UN Manual of Tests and Criteria, Part III, sub-section 33.2.1. On the compounding floor, a dedicated weigh station with local exhaust ventilation is recommended during hand-weighing operations to maintain airborne dust concentrations below the threshold limit value for particulates not otherwise classified (3 mg m^–3 for respirable fraction, ACGIH 2023). Furthermore, blending the powder with high-structure carbon blacks in a separate pre-mix before introduction to the hot mixer can depress dusting by 85%, as measured by real-time aerosol photometry at the batch hopper opening.

Replacement of MBTS in Heat-Resistant EPDM Seals: Comparative Cure Kinetics

A head-to-head evaluation against dibenzothiazyl disulfide (MBTS) was performed in a peroxide/co-agent-cured EPDM formulation for solar-thermal gaskets specified under EN 681-1. MBTS, while offering excellent heat resistance, introduces a cured odor associated with residual benzothiazole fragments that has been flagged by automotive OEM sensory panels. The nitrobenzyl derivative was trialed as a sulfur donor accelerant at 1.0 phr alongside 3.0 phr dicumyl peroxide (40% active). The presence of the nitro group raised the activation energy of the accelerator decomposition step from 94 kJ mol^–1 (MBTS, Flynn–Wall–Ozawa kinetic analysis of DSC data at 5, 10, 15, 20 K min^–1) to 112 kJ mol^–1, effectively uncoupling the sulfur crosslinking stage from the peroxide decomposition regime and reducing the tendency toward scorch-band formation in the injection-molding barrel (barrel temperature setpoint 85 °C). After vulcanization at 175 °C for 8 min, compression set at 150 °C for 22 h (ASTM D395-18, method B, 25% deflection) remained 18%, within the 20% threshold required by EN 681-1, while the post-cure volatile organic compound profile (VDA 278) showed a 60% reduction in benzothiazole-type emissions compared with the MBTS control, a decisive advantage in enclosed solar collector systems where condensation cycling concentrates leachates.

Parameter	2-[(4-Nitrobenzyl)sulfanyl]-1,3-benzothiazole	CBS	MBTS	Test Standard
Mooney scorch t₅ at 121 °C (min)	18.2	14.6	22.5	ASTM D1646-19a
t₉₀ at 150 °C (min)	9.3	9.0	12.8	ASTM D5289-19a
Tensile strength (MPa), unaged	26.7	25.9	24.3	ISO 37:2017
Hot-air aged strength retention (7 days, 100 °C)	94%	89%	96%	ISO 188:2011
N-nitrosamine generation potential	None detected	Detectable (cyclohexylamine-derived)	None (no amine)	EN 12868:1999
Reversion torque loss at 180 °C (% of M_H)	23	32	18	ISO 6502-3

The disclosed data correspond to a model NR/BR (80/20) tread formulation containing 50 phr carbon black N234 and 2.3 phr sulfur; the accelerator loading was adjusted to 1.0 phr for the benzothiazole derivatives and 1.0 phr for MBTS to approximate industrial use levels. Published data for silicone or highly saturated nitrile (HNBR) compounds is limited, and the performance margins described here should not be extrapolated to non-diene elastomers without supporting experimental verification on the target matrix.