Lubricant Additives - Amine Antioxidants Series: Alkylated Diphenylamine (CAS 68411-46-1) opens the Amine Antioxidants subcategory - the second class of primary antioxidants in the Sinolook additive range, complementing the Phenolic AO series (BHT · DTBP · High-MW Phenolic Esters). Aromatic amine antioxidants differ from phenolics in two critical respects: (1) high-temperature superiority - amine AOs retain radical-scavenging efficacy above 150°C where phenolics are thermally consumed faster; (2) partial catalytic regeneration - the diarylamine nitrogen radical (Ar₂N•) intermediate can re-react with hydroperoxides to regenerate active antioxidant species, giving higher effective molar consumption efficiency per molecule vs phenolic AOs. This is why industrial long-drain and aviation lubricant formulations combine both types: phenolic ester (covers 60–150°C) + amine AO (covers 120–200°C+) for complete oxidation temperature coverage. SAPS-free (C/H/N - zero ash, S, P, metals). Sinolook Amine AO series: Alkylated Diphenylamine CAS 68411-46-1 (this) · other amine AO grades.
✅ SAPS-Free (Ash 0%, Zero S/P) · Amine AO · High-Temp Primary AO (120–200°C+) · Catalytic Radical Scavenging · Diarylamine · Amber Liquid · Purity ≥95% · FP ≥200°C · Engine Oil · Turbine · PAO/Ester · Aviation
Alkylated Diphenylamine
ADPA / Alkyl Diphenylamine / Aromatic Amine Antioxidant / Alkyl diphenylamine / CAS 68411-46-1 / Liquid / Purity ≥95% / Amine AO
| CAS Number | 68411-46-1 |
| Chemical Type | Aromatic amine antioxidant - dialkyl diphenylamine (diarylamine class); secondary amine (N–H); N is the sole heteroatom (no S, P, metals) |
| Structure | Two phenyl rings bridged by –NH– (diphenylamine core); one or both rings carry alkyl substituents (C4–C12 alkyl groups) at para/ortho positions - as shown by R–Ph–NH–Ph in the skeletal formula. The alkyl groups increase MW, reduce volatility, and improve oil solubility vs unsubstituted diphenylamine (DPA, CAS 122-39-4). CAS 68411-46-1 is a commercial mixture of mono- and dialkylated diphenylamine homologues with various alkyl chain lengths. |
| Synonyms | ADPA · Alkyl DPA · Alkylated DPA · Dialkyl diphenylamine antioxidant · Alkyl diphenylamine · Aromatic amine antioxidant · Stabilizer DPA |
| ★ SAPS Status | ✅ Zero ash / sulphur / phosphorus / metals
ADPA contains only C, H, N - nitrogen is NOT a SAPS element (SAPS = Sulphated Ash, Phosphorus, Sulphur). Zero contribution to all three SAPS parameters. Fully compatible with ACEA C1–C5, API SP, CK-4/FA-4 SAPS limits at any treat rate. The N content does not register in ASTM D482 (ash), D4951 (P), or D1552/D4294 (S) measurements. |
| Appearance | Amber to light brown liquid Deep amber colour is characteristic - darker than phenolic AOs; colour does not indicate impurity or degradation at delivery; the amine chromophore (extended conjugation across Ph–N–Ph) inherently absorbs visible light in the blue region, producing the amber appearance. Colour darkens further in service as amine is consumed - used oil colourimetry can be a rough qualitative AO depletion indicator. |
| Purity / Grade | Standard ≥95.0% (GC) ≥95% total active amine content (GC area); minor components are other alkylated DPA homologues, all antioxidant-active; custom purity tiers on request. |
Alkylated Diphenylamine - High-Temperature Mechanism & Why Amine AOs Outperform Phenolics Above 150°C
Alkylated Diphenylamine (CAS 68411-46-1) belongs to the diarylamine (secondary aromatic amine) class of antioxidants - the highest-performance primary antioxidants for lubricant applications involving continuous operation above 150°C. The molecule consists of two phenyl rings connected through a secondary amine nitrogen (–NH–), with alkyl substituents on one or both rings. The alkyl groups serve two purposes: they prevent the parent diphenylamine from crystallising (DPA, CAS 122-39-4 is a solid melting at 53°C), and they increase the electron density of the aromatic rings - enhancing the N–H bond's hydrogen-donating reactivity, making the alkylated product a more effective antioxidant than unsubstituted DPA. CAS 68411-46-1 encompasses a commercial mixture of mono- and dialkylated diphenylamine homologues with C4–C12 alkyl chain lengths, producing a liquid product at ambient temperature.
The antioxidant mechanism of alkylated DPA is more complex and more efficient than simple phenolic H-atom donation. It operates as a partially regenerating radical scavenger - through a multi-step nitrogen-centred intermediate pathway that effectively consumes more than one radical per molecule before the antioxidant is irreversibly spent. This "catalytic" character is the primary reason why amine AOs are preferred over phenolic AOs in the most demanding long-drain and high-temperature lubricant applications.
Ar₂N–H + ROO• → Ar₂N• + ROOH
The N–H hydrogen is donated to a peroxyl radical (ROO•), forming a diarylaminyl radical (Ar₂N•) and hydroperoxide (ROOH). The diarylaminyl radical is exceptionally stable - the unpaired electron is delocalised across both phenyl rings (cross-conjugation through N), making it effectively a "persistent radical" that does not rapidly initiate new chains. At this stage, one ROO• has been consumed - same as phenolic AO Step 1.
Ar₂N• + ROO• → Ar₂N–OOR (aminyl-peroxyl adduct)
The diarylaminyl radical reacts with a second ROO• to form a nitroxide-type intermediate (Ar₂N–OOR). This step removes a second peroxyl radical - effectively doubling the radical-scavenging yield vs. phenolic AOs (which consume only 1 ROO• per molecule at this stage). The nitroxide intermediate is still reactive and continues consuming radicals.
Ar₂N–OOR + ROOH → Ar₂N–OH + products
The nitroxide intermediate can react with hydroperoxides (ROOH - the same species that ZDDP decomposes) to regenerate a hydroxylamine (Ar₂N–OH). The hydroxylamine Ar₂N–OH can in turn donate its O–H hydrogen to ROO• (Ar₂N–OH + ROO• → Ar₂N–O• + ROOH), further extending the radical-scavenging cycle. This partial regeneration is why amine AOs appear to deplete more slowly in service than phenolic AOs at equal initial treat rates.
Eventual end products: quinone-imine / diphenylamine-derived chromophores
After multiple radical-scavenging cycles, the amine is irreversibly converted to stable quinone-imine products (highly conjugated, deep amber/red-brown coloured). These products are the source of the characteristic colour darkening of used lubricant oil that has consumed its amine AO reserve - monitoring used oil colour by UV-Vis spectrophotometry or RULER voltammetry can track ADPA depletion in service. Final products are non-corrosive, non-sludge-forming stable chromophores.
Optimal range: ~60–150°C
O–H BDE ~78 kcal/mol; fast H-donation to ROO•; excellent coverage at moderate temperatures. Above ~150°C, phenoxy radical increasingly undergoes β-scission (C–C bond breaking) → AO consumed without radical termination; depletion rate accelerates sharply above 160°C.
★ Optimal range: ~120–200°C+
N–H BDE ~73 kcal/mol (lower than O–H of phenols → even more reactive toward ROO•); aminyl radical (Ar₂N•) is more stable at high temperatures - delocalisation across two aromatic rings prevents β-scission; partially regenerating mechanism extends effective operating life. Remains active at temperatures where phenolics fail.
Full coverage: 60–200°C+
The optimal long-drain lubricant AO strategy: Phenolic ester (L01/L57) 0.3–0.5 wt% + ADPA 0.2–0.4 wt% + ZDDP 0.7–1.2 wt%. Phenolic covers moderate-temp; ADPA covers high-temp; ZDDP destroys hydroperoxides at all temperatures. Together they provide complete AO protection across the full lubricant service temperature range with maximum drain interval.
| Appearance | Amber to light brown liquid |
| Purity (GC) | ≥95.0% |
| ★ Flash Point | ≥200°C (ASTM D93) |
| Ash Content ✅ | 0% - truly ashless |
| KV @40°C | High viscosity (grade dependent; ~500–3000 cSt typical) |
| Pour Point | <–10°C (liquid at ambient) |
| Shelf life | 24 months (sealed, cool/dry storage) |
| Compatibility | All base oils (Group I–V); compatible with phenolic AO, ZDDP, dispersants, detergents |
Technical Specification
Total active diarylamine content; mixture of mono-/dialkyl DPA homologues all AO-active; custom ≥98% on request for premium formulations
High flash point - non-flammable classification; no ADR Class 3 transport restrictions; safe storage in standard heated warehouses; significantly safer than 2,6-DTBP (FP ~114°C)
✅ Truly ashless - C/H/N formula; zero metals, S, P; N is NOT a SAPS element; complete SAPS freedom at any treat rate
Amine value (mgKOH/g equivalent N) is the key AO capacity indicator for amine antioxidants - higher amine value = more active N–H groups per gram = higher AO reserve. COA reports amine value per lot; custom grades available with target amine value ranges.
| Parameter | Specification | Test Method | Technical Note |
|---|---|---|---|
| Appearance | Amber to light brown liquid | Visual | Deep amber colour is inherent to the diarylamine chromophore (Ph–N–Ph π-conjugation absorbs 400–450 nm blue light → amber appearance); darker colour vs phenolics is normal and expected; very dark brown/black may indicate over-oxidation in storage - verify with amine value test |
| Purity (GC) ★ | ≥ 95.0% | GC area % | Total active diarylamine content; CAS 68411-46-1 is commercially a mixture - minor components are other chain-length alkyl DPA homologues, all antioxidant-active; ≥98% custom grade available on request for premium applications |
| ★ Amine Value | Grade dependent - reported per lot | ASTM D2896 or D974 | Key performance parameter for amine AOs - directly measures active N–H concentration (mgKOH/g equivalent). Higher amine value = more AO capacity per gram. Target amine value ranges available on request; specify application and drain interval for grade recommendation |
| Ash Content ✅ | 0% (ashless) | ASTM D482 | ✅ Truly ashless. C/H/N only - nitrogen burns cleanly to N₂ + NO_x in combustion (no metallic residue). SAPS-free. ACEA C1–C5 compliant at any treat rate. |
| ★ Flash Point | ≥ 200°C | ASTM D93 (PM) | ★ High FP advantage: no ADR Class 3 flammable liquid classification; safe standard warehouse storage; clearly superior to 2,6-DTBP Mixture (FP ~114°C) and meaningfully better than BHT (FP 127°C) |
| KV @40°C (cSt) | ~500–3000 (high viscosity liquid) | ASTM D445 | High viscosity liquid - pumps and transfer lines should be sized for high-viscosity liquid at operating temperature; warmth to 40–50°C significantly reduces viscosity for easier transfer; IBC heating jackets recommended for bulk handling |
| Water Content (KFT) | ≤0.10% | Karl Fischer | Amine AOs can absorb atmospheric moisture - seal containers after use; moisture promotes oxidative degradation of the amine in storage; N₂ blanket for open IBCs recommended |
| Packaging | 25 kg pail · 200 kg steel drum · 1000 L IBC · Flexitank bulk | - | Shelf life 24 months sealed; store cool (15–30°C), dry, away from light; avoid contact with strong oxidising agents (nitric acid, peroxides) or strong acids/bases in storage vicinity |
Applications & Dosage Guidance
1. Long-Drain Engine Oils - AO Stack Primary Component
ADPA is a standard component of the three-component AO stack (ADPA + phenolic ester L01/L57 + ZDDP) used in API SP, ILSAC GF-6, ACEA C3, and OEM-spec long-drain engine oils (15,000–30,000 km drain intervals). ADPA at 0.2–0.4 wt% covers the high-temperature oxidation window (150–200°C sump peak temperatures in modern turbocharged engines - particularly LSPI-prevention oil grades), while L01/L57 at 0.3–0.5 wt% covers moderate temperatures. Together they provide continuous AO protection from cold-start to operating temperature across the full drain interval. RULER voltammetry studies confirm that ADPA-containing AO stacks retain significantly higher AO reserve at 15,000 km vs phenolic-only stacks - directly supporting extended drain approval by OEMs.
2. Turbine & Compressor Oils - Long-Life Industrial Service
For gas turbine oils (IEC 60296, GEK-32568, Pratt & Whitney PWA 521/522, Rolls-Royce OMAT series), steam turbine oils (ASTM D4293, R&O turbine oil), and industrial compressor oils (ISO VG 32–100, DIN 51506), ADPA at 0.1–0.3 wt% either alone or combined with BHT 0.2 wt% + L01 0.2 wt% provides the highest achievable ASTM D2272 RPVOT oxidation induction times (>3000 minutes for premium PAO turbine oil blends with optimised AO stack). The high flash point (≥200°C) and low volatility of ADPA ensures it remains in the oil phase throughout the turbine operating cycle with minimal evaporative loss, unlike lower-FP phenolics. For aviation turbine lubricants (MIL-PRF-23699, Type II and IIIA), amine AOs are the primary approved antioxidant class at the high operating temperatures involved (175–250°C peak).
3. Synthetic PAO / Ester / PAG Lubricants
Synthetic base stocks - particularly PAO (Group IV), polyol ester (POE, used in aviation MIL-PRF-23699 and industrial applications), PAG (water-glycol hydraulic fluids, refrigeration compressors), and diester (ester turbine oil) - require antioxidants with excellent synthetic base stock compatibility. ADPA's alkylated aromatic structure gives it excellent solubility and compatibility with all Group I–V base oils, including PAO (non-polar) and ester (polar) chemistries. In POE-based lubricants (aviation, refrigeration), ADPA at 0.3–0.6 wt% is particularly effective at protecting the ester C=O groups from oxidative hydrolysis - a failure mode specific to ester base stocks. For PAG compressor lubricants, ADPA at 0.2–0.4 wt% maintains oxidation stability across the wide PAG operating temperature range (–40°C to +150°C).
4. Greases - High-Temperature Service
In high-temperature greases (lithium complex, calcium sulfonate complex, polyurea - all with operating temperatures up to 180–220°C in bearing applications), ADPA is the preferred amine antioxidant due to its high-temperature efficacy and low volatility. At elevated grease operating temperatures, phenolic AOs (BHT, L01) are rapidly consumed; ADPA's aminyl radical persistence and partial regeneration mechanism maintain effective AO protection for significantly longer intervals before regreasing is required. The liquid form of ADPA (vs solid phenolic AO powders) also simplifies incorporation into grease manufacturing - it can be added directly to the base oil/soap blend during the saponification or hot-fill stage. Typical treat: 0.1–0.3 wt% on finished grease weight, typically combined with L01 0.1–0.2 wt% for dual AO coverage.
| Application | ADPA Treat Rate | Recommended Co-AO | Key Standard |
|---|---|---|---|
| Long-drain PCMO engine oil (15,000+ km) | 0.2–0.4 wt% | L01 0.3–0.5 wt% + ZDDP 0.7–1.2 wt% | Seq. IIIGH, API SP, ACEA C3, RULER depletion |
| Turbine oil (gas/steam, ISO VG 32–100) | 0.1–0.3 wt% | L01 0.1–0.2 wt% (+ BHT 0.1–0.2 wt% optional) | ASTM D2272 (>3000 min target), IEC 60296, GEK-32568 |
| Aviation turbine lubricant | 0.5–1.0 wt% | L57-type (POE compatible) 0.3–0.5 wt% | MIL-PRF-23699, MIL-PRF-7808, DEF STAN 91-101 |
| Hydraulic oil (ISO VG 32–68) | 0.1–0.3 wt% | HP-136-type 0.1–0.2 wt% | Denison HF-0/2, Vickers M-2950-S, DIN 51524 |
| PAO/POE/PAG synthetic lubricant | 0.2–0.8 wt% | L57-type 0.3–0.5 wt% + ZDDP (if P budget allows) | ASTM D6186 PDSC, D2272 RPVOT, D943 TOST |
| Grease (Li-complex, polyurea, CaSO₃) | 0.1–0.5 wt% | L01-type 0.1–0.2 wt% | ASTM D3527 (bearing life), D942 (oxidation stability) |
Frequently Asked Questions
Q: Is Alkylated Diphenylamine truly SAPS-free? The molecule contains nitrogen.
Yes - nitrogen (N) is NOT a SAPS element. The SAPS acronym stands for Sulphated Ash (measured by ASTM D482), Phosphorus (ASTM D4951/ICP), and Sulphur (ASTM D1552/D4294/ICP). These three parameters were selected in ACEA/ILSAC specifications because: (1) metallic ash physically blocks DPF and GPF particulate filters; (2) phosphorus permanently deactivates TWC catalyst washcoat (Al₂O₃/CeO₂/ZrO₂) by forming a phosphate glass layer; (3) sulphur deactivates the precious metal catalytic sites (Pt, Pd, Rh) by sulphate formation. Nitrogen from amine antioxidants does none of these things - it burns to N₂ and NO_x in combustion (which, while contributing to NO_x emissions, is a separate regulatory concern not captured in the SAPS framework). ADPA at any treat rate contributes zero to ASTM D482 ash, zero P, and zero S - it is fully SAPS-compliant for all ACEA and API specifications with SAPS limits.
Q: Why does used oil containing ADPA appear dark/discoloured? Is this a problem?
The darkening of used oil containing amine antioxidants is normal, expected, and not a quality problem. As ADPA is consumed through the radical-scavenging cycle, it is converted to stable quinone-imine products - these are highly conjugated aromatic compounds (the characteristic dark chromophores also seen in aged diphenylamine-containing products like rubber accelerators and hair dyes). The quinone-imine products are chemically inert, non-corrosive, non-sludge-forming, and do not affect lubricant performance. The colour development is actually a useful indicator of ADPA depletion - as ADPA is consumed, the oil darkens progressively. The correlation is not perfectly linear, but a significant colour change from amber to dark brown/black in used oil is qualitatively consistent with approaching AO exhaustion. Quantitative ADPA depletion measurement requires RULER voltammetry (ASTM D6971) or UV-Vis spectrophotometry at the ADPA absorption wavelength (~280 nm).
Q: Can ADPA be used as the sole antioxidant, or does it always need to be combined with phenolic AOs?
ADPA can be used as a sole primary antioxidant in some applications - particularly in aviation turbine oils (MIL-PRF-23699 and similar high-temperature specifications where amine AOs are preferred by specification) and in industrial turbine/compressor oils where the continuous operating temperature exceeds 160°C (making phenolic AOs less effective). However, for most automotive and industrial lubricant formulations, the industry consensus is that combining ADPA with a high-MW phenolic ester (L01/L57) provides better oxidation protection than either alone at the same total AO treat rate. The reason is complementary temperature windows: at moderate temperatures (60–150°C), phenolic AOs are more reactive toward ROO• and provide faster chain termination; ADPA is less reactive in this range. At high temperatures (150–200°C+), the situation reverses. A 50:50 molar combination of phenolic ester + ADPA delivers broad-spectrum AO coverage at temperatures from cold-start to maximum operating temperature - consistently outperforming single-AO approaches in ASTM D2272 RPVOT, D943 TOST, and Sequence IIIGH engine tests. ZDDP (secondary AO) is then added as the third component to destroy hydroperoxides generated by both AO mechanisms.
Technical & Regulatory References
GC (purity ≥95%) · ASTM D2896 / D974 (amine value - primary AO capacity measure) · ASTM D482 (ash = 0%) · ASTM D93 (flash point ≥200°C) · ASTM D445 (KV @40°C) · KFT (water ≤0.10%) · ASTM D2272 RPVOT (oxidation induction - primary performance test) · ASTM D943 TOST (long-duration oxidation, 1000–10,000+ hours) · ASTM D6186 PDSC (OIT screening) · ASTM D6971 RULER voltammetry (AO depletion monitoring in used oil) · Sequence IIIGH (engine oil oxidation)
Engine oils: API SP/SN+/SN · ILSAC GF-6A/B · ACEA C1–C5 (SAPS-free ✅ - N ≠ SAPS) · ACEA E6/E9 · CK-4/FA-4 · VW 508.00/509.00 · BMW LL-04 · MB 229.5/229.71 · Turbine: IEC 60296 · GEK-32568 · Pratt & Whitney PWA 521/522 · Rolls-Royce OMAT · DIN 51515 · Aviation: MIL-PRF-23699 (Type II/IIIA) · MIL-PRF-7808 · DEF STAN 91-101 · Compressor: DIN 51506 · ISO VG 32–150 R&O and AW · Hydraulic: Denison HF-0/2 · DIN 51524-2/3 · ISO 4406 · Greases: NLGI 1–3 · ASTM D3527 · ASTM D942
CAS 68411-46-1 · EINECS registered (mixture) · REACH compliant · TSCA listed · ✅ SAPS-free (ash 0%, S 0%, P 0% - N is NOT a SAPS element) · Flash point ≥200°C: non-flammable (no ADR Class 3 restrictions) · GHS SDS available (GHS07 - harmful if swallowed; skin/eye irritant; typical for amine compounds at industrial handling exposure levels; PPE: gloves, goggles, ventilation) · RoHS compliant · Not food-grade (aromatic amine - not approved for food-contact applications) · Shelf life 24 months sealed
Phenolic AO Series ✅: BHT (CAS 128-37-0) · 2,6-DTBP Mixture (CAS 14972-27-9) · High MW Phenolic Ester Series (L01/L57/HP-136) → Amine AO Series: Alkylated Diphenylamine CAS 68411-46-1 ✅ (this) · other amine AO grades → ZDDP Anti-Wear/AO Series ✅ (full range)
ADPA · CAS 68411-46-1 · Alkylated Diphenylamine · Purity ≥95% · Ash 0% · FP ≥200°C · SAPS-Free · Amber Liquid · 25 kg / 200 kg / 1000 L IBC · COA/TDS/SDS · 24-Month Shelf Life
Request Pricing, TDS & Technical Support
Specify application (engine oil / turbine / aviation / compressor / grease), base oil type, drain interval, and temperature profile. We recommend the optimal treat rate and co-AO combination (ADPA + phenolic ester + ZDDP stack). Amine value target specification available for OEM DI package development. Samples (50–500 mL) available for formulation trials. IBC and flexitank supply for bulk industrial use.
Amine Antioxidants Series:
Alkylated Diphenylamine CAS 68411-46-1 ✅ (this) · other amine AO grades → Phenolic AO Series ✅ (BHT · DTBP · High-MW Phenolic Ester) · ZDDP Series ✅
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