Section
| HS Code | 655006 |
| Productname | Solvent Yellow 56 |
| Colorindexnumber | C.I. 11021 |
| Casregistrynumber | 2481-94-9 |
| Ecnumber | 219-616-8 |
| Synonyms | Oil Yellow DE; Sudan Yellow GG; C.I. Solvent Yellow 56; 4-(Phenylazo)-N,N-diethylaniline |
| Chemicalname | 4-(Phenylazo)-N,N-diethylaniline |
| Chemicalclass | Monoazo solvent dye |
| Molecularformula | C16H19N3 |
| Molecularweight | 253.34 g/mol |
| Appearance | Yellow to orange-yellow powder |
| Color | Yellow |
| Physicalstate | Solid |
| Meltingpoint | 94-96 °C |
| Boilingpoint | ~391 °C at 760 mmHg (predicted) |
| Density | ~1.05 g/cm³ (predicted) |
| Flashpoint | ~190 °C (predicted) |
| Solubilityinwater | Insoluble |
| Solubilityinorganicsolvents | Soluble in many organic solvents, oils, waxes, and fuels |
| Primaryuse | Solvent dye for plastics, waxes, oils, fuels, inks, and coatings |
| Typicalpurity | ≥98% (commercial grade) |
| Storageconditions | Store in a cool, dry, well-ventilated area away from light and ignition sources |
As an accredited Solvent Yellow 56 factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Solvent Yellow 56 is packaged in 25 kg net polyethylene-lined fiberboard boxes, securely sealed and clearly labeled for industrial use. |
| Container Loading (20′ FCL) | Solvent Yellow 56 is palletized and securely loaded into a dry 20′ FCL container with moisture protection and even weight distribution. |
| Shipping | Solvent Yellow 56 is typically shipped as a non-regulated solid dye in sealed, properly labeled containers at ambient temperature. Protect from moisture, light, and ignition sources; avoid dust generation. Follow the SDS and applicable local transport regulations; no UN number is assigned unless otherwise specified. |
| Storage | Store Solvent Yellow 56 in a cool, dry, well-ventilated area away from direct sunlight, heat, sparks, and ignition sources. Keep containers tightly closed and protect contents from moisture and dust. Separate from strong oxidizing agents. Use original, clearly labeled containers, avoid dust generation, and wear appropriate personal protective equipment. Follow local chemical storage regulations and emergency procedures. |
| Shelf Life | Typically stable for 2–5 years when stored sealed in a cool, dry, dark place away from moisture and direct sunlight. |
In middle-distillate fuel marking programmes where fiscal differentiation and off-road tax rebate verification require a soluble yellow marker, Solvent Yellow 56 (C.I. 11021, CAS 2481-94-9) is metered as a low-concentration hydrocarbon-soluble marker rather than as a bulk colourant. The dye is a diethylamino-substituted azobenzene derivative with a visible absorption band in the 400–450 nm region, allowing quantification by visible spectrophotometry after extraction from the fuel matrix. Compliance references ASTM D396 for heating oils and ASTM D975 for diesel fuel oils as finished-fuel quality controls, while the addition of a coloured marker is governed by national fiscal or environmental marker schedules and must be confirmed separately for each jurisdiction. The addition ratio in terminal-blended volumes typically falls between 2 mg/kg and 15 mg/kg of finished fuel; below 2 mg/kg, field detection signal-to-noise limits become the controlling parameter, and above 15 mg/kg, tank-wall staining and dye-carrier dilution costs increase without proportional analytical benefit. Production is carried out at loading racks with a positive-displacement dosing skid installed downstream of the custody transfer meter; the neat dye is predissolved in a high-boiling aromatic or naphthenic carrier and injected into the flowing fuel stream, followed by a static mixer with at least 10 elements and batch recirculation for 30–60 min for large tank homogenisation. Finished products include marked off-road diesel, marked heating oil, tax-rebated gas oil, and marine gas oil supplied to fishing and construction fleets. Operational boundary: the dye is not suitable for aviation turbine fuel governed by ASTM D1655, where non-specified additive schedules require formal certification, and it is not intended for use in water-contaminated fuel systems because partitioning into free water can deplete marker concentration in the hydrocarbon phase.
| Application environment | Primary standard/test method | Key control parameter | Typical process range |
|---|---|---|---|
| Middle-distillate fuel marking | ASTM D396, ASTM D975 | Marker concentration | 2–15 mg/kg |
| Dyed industrial lubricants and greases | ASTM D1500, ISO 6743 | Finished fluid colour, lubricant category | 0.005–0.10 wt% |
| Paraffin and microcrystalline wax | ASTM D87, ASTM D721 | Wax melting point, oil content | 50–400 mg/kg |
| Styrenic and acrylic polymer mass coloration | RoHS 2011/65/EU, REACH | Restricted substance compliance | 0.01–0.25 wt% |
| Solvent-borne wood stains and coating toners | ASTM D2244, REACH | Colour difference, chemical registration | 0.1–1.5 wt% |
| Gravure and flexo printing inks | EuPIA exclusion policy, Swiss Ordinance SR 817.023.21 | Migration limits for food packaging | 0.5–3.0 wt% |
Lubricating oil and grease compounding uses Solvent Yellow 56 primarily for batch identification and visual leak detection; the critical thermal boundary is the azo chromophore’s sensitivity to prolonged exposure above approximately 140°C in alkaline thickener systems, where colour fade and oxidative by-products can appear. Addition is therefore made after the saponification and dehydration plateau, during the cooling column or finishing kettle stage below 120°C, and before the final milling pass. Compliance for dyed industrial lubricants references ASTM D1500 for petroleum product colour evaluation and the relevant ISO 6743 categories for hydraulic and gear oil classification; finished greases are checked for worked penetration under ASTM D217. The addition ratio is 0.005–0.03 wt% for liquid lubricants and 0.02–0.10 wt% for lithium complex or calcium greases, with the lower band used when the dye serves only as a tracer and the upper band reserved for deep identification colours. In production, the dye is first dissolved in a naphthenic base oil at 60–80°C using low-shear agitation, then filtered through a 10 µm absolute mesh to prevent insoluble dye specks; for liquid lubricants, this concentrate is metered into the main blending vessel after additive dosing, and for greases it is introduced before a colloid mill or high-pressure homogenizer. Finished products include dyed industrial gear oils in ISO VG 68, 100, and 150, hydraulic fluids, lithium complex greases, and metalworking fluid leak-detection tints. Operational boundary: the product is not recommended for food-grade circulating lubricants unless formal approval under 21 CFR 178.3570 is established, and water-emulsifiable metalworking fluids should be evaluated separately because the dye may partition into the aqueous phase.
When paraffin wax is coloured for candle extrusion or container filling, dry powder addition causes speck formation because Solvent Yellow 56 requires predissolution in a compatible non-polar carrier before it can be distributed in molten wax. Compliance for candle and wax formulations in the EU is governed by REACH registration and the CLP Regulation for classification and labelling; incoming paraffin is controlled by ASTM D87 for melting point and ASTM D721 for oil content where petroleum wax specifications apply. The addition ratio is typically 50–400 mg/kg (0.005–0.04 wt%) of the paraffin mass, with 400 mg/kg limited to deeply shaded decorative articles because migration into adjacent wax layers and packaging films becomes measurable above 0.03 wt%. Production uses a 5–10 wt% stock solution of Solvent Yellow 56 in light mineral oil prepared at 80°C, metered into molten paraffin held at 75–90°C under gentle agitation; high-shear mixing is avoided because air entrainment produces microvoids visible in the finished candle. Finished products include pillar candles, container candles, wax melts, and industrial waxes used in paper coating and protective films. Operational boundary: outdoor exposure should be avoided because lightfastness is insufficient for prolonged UV conditions, and contact with low-density polyethylene packaging can extract the dye if storage exceeds 40°C.
Polymer mass coloration with Solvent Yellow 56 is restricted to indoor or short-exposure styrenic and acrylic applications because the diethylaminoazobenzene chromophore lacks the photostability needed for long-term outdoor UV. Compliance for coloured polymer compounds supplied to the E&E sector references RoHS Directive 2011/65/EU and REACH; for toys, end-use restrictions must be checked against EN 71-3, and for food-contact articles against Regulation (EU) 10/2011, because solvent dyes are not universally listed for these matrices. The addition ratio in translucent styrenic and acrylic compounds ranges from 0.01 wt% to 0.25 wt%; below 0.01 wt%, the yellow tint may not mask raw polymer yellowness differences, and above 0.25 wt%, surface migration becomes measurable under elevated-temperature storage at 60°C. Production generally employs a concentrated masterbatch or a pre-dispersed dye paste rather than direct powder addition; a co-rotating twin-screw extruder with L/D 40:1 and screw speed in the 250–350 min⁻¹ range is operated at a melt temperature between 190°C and 230°C. Pre-drying of polystyrene or PMMA granules at 80°C for 4 h is applied when ambient relative humidity exceeds 60%, reducing moisture-generated splay. Injection moulding settings with clamp force in the 800–1,200 kN range and back pressure of 0.5–1.0 MPa are typical for section thicknesses up to 3 mm. Finished products include indoor polystyrene display profiles, PMMA light diffusers, acrylic cosmetic packaging, and ABS instrument bezels where UV exposure is limited. Operational boundary: not recommended for outdoor glazing or automotive exterior parts because colour shift exceeds perceptual tolerance within 6 months of direct UV exposure; published data for this specific configuration is limited for ASA and polycarbonate blends.
Coatings formulate Solvent Yellow 56 as a transparent yellow dyestuff in low-viscosity solvent-borne wood stains, where pigment-based systems would obscure grain definition. Compliance references ASTM D2244 for colour difference evaluation on coated timber and the relevant REACH registration for the solvent dye as a chemical substance; volatile organic compound content is controlled under the EU Industrial Emissions Directive or national architectural coating rules. Addition ratios in a concentrated wiping stain fall between 0.1 wt% and 1.5 wt% of the liquid formulation, with the lower range producing pale honey tones and the upper range required for deep amber show surfaces. Production uses a pre-dissolution step in a ketone-ester or aromatic solvent blend at 25–40°C, followed by low-speed addition to a nitrocellulose or alkyd binder system; the solution is filtered through a 5–10 µm cartridge before filling to remove undissolved dye particles. Finished products include solvent-borne wiping stains, spray-applied lacquer toners, and industrial wood coatings for interior furniture and joinery. Operational boundary: because the dye is soluble, it can migrate into subsequent clear topcoats if the stain film is not adequately sealed or if strong solventborne topcoats are applied at high wet-film thickness; for exterior wood applications, UV absorbers reduce but do not eliminate fading.
Toluene-based gravure ink formulations for non-food flexible packaging employ Solvent Yellow 56 where high transparency is specified and low-viscosity flow is maintained; the dye does not contribute to ink film opacity or abrasion resistance and is normally combined with a pigment when lightfastness is required. Compliance for printing inks for non-food packaging references the EuPIA exclusion policy for printing inks, REACH, and Swiss Ordinance SR 817.023.21 where migration limits apply to food packaging; for food-contact packaging, the ink supplier must confirm that the final printed article meets overall migration limits under Regulation (EU) 10/2011. The addition ratio typically ranges from 0.5 wt% to 3.0 wt% of the finished liquid ink, depending on print film thickness and required optical density. Downstream production uses a let-down stage: the dye is predissolved in a mixture of toluene and ethyl acetate at 20–30°C, then combined with the binder vehicle and reduced to printing viscosity of 18–25 s on a DIN flow cup 4 mm; the finished ink is filtered through a 10 µm bag filter and adjusted to a colour strength within ±5% of the reference drawdown. Finished products include surface-print gravure inks for metallised film, paper-label flexo inks, and industrial coding inks. Operational boundary: not suitable for retort or microwave packaging where thermal cycling and high migration potential exceed the dye’s performance envelope; published data for this specific configuration is limited for high-barrier laminated structures.
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Solvent Yellow 56 is the Colour Index designation for a non-metallized monoazo dyestuff with CAS Registry Number 2481-94-9, EINECS No. 219-616-4, and C.I. Constitution Number 11021. The active molecule, N,N-diethyl-4-[(E)-phenyldiazenyl]aniline, has the empirical formula C16H19N3 and a relative molecular mass of 253.34 g/mol. It is supplied as a yellow to orange crystalline powder under synonyms that include 4-diethylaminoazobenzene and p-diethylaminoazobenzene. Current supplier-defined product models separate a technical grade for bulk hydrocarbon coloring from a high-purity grade for marker fluids and low-turbidity ink systems; a micronized variant is also available with controlled maximum particle size for dispersion-limited applications. Although no unified ISO or ASTM monograph governs this dye, supplier certificates of analysis commonly list assay at or above 95.0 area% by high-performance liquid chromatography at 420 nm, melting range 42–46 °C by capillary method, loss on drying ≤0.5% at 60 °C, sulfated ash ≤0.1%, and water solubility below 0.1 g/L at 20 °C.
The specification profile of technical-grade Solvent Yellow 56 is supplier-defined. Typical certificates of analysis control dye content by high-performance liquid chromatography at 420 nm, melting range by capillary method at 42–46 °C, loss on drying at 60 °C ≤ 0.5%, sulfated ash ≤ 0.1%, and toluene-insoluble content by membrane filtration. A high-purity marker grade may add maximum moisture specification of 0.3% and a particle-size specification of 100% passing 250 μm; a micronized grade is usually controlled to 95% passing 75 μm. Batch-to-batch shade variation is generally held within ±5% relative to a supplier reference at 420 nm. These values are typical merchant specifications and should be confirmed against the product model used in a specific tolling operation. The dye is soluble at 20–25 °C in toluene, xylene, mineral spirits, and methyl ethyl ketone; solubility in anhydrous ethanol is sufficient for low-viscosity writing inks but lower than in aromatic hydrocarbon carriers.
A production-scale polystyrene masterbatch line using a twin-screw extruder with 40:1 L/D ratio is typically profiled at 160 °C in the feed zone and 210 °C at the die; screw speed is adjusted to keep the melt temperature below 220 °C. Dry dye powder is metered gravimetrically at 0.5–2.0 kg/h into a polymer stream of 5–10 kg/h; liquid dye concentrate is injected through a heated nozzle at 2–5 MPa to avoid upstream temperature spikes. Above 230 °C melt temperature, measurable shade loss and discoloration may occur, so high-shear elements in the screw configuration should be limited in zones where the melt has already reached 210 °C. Published data for this exact extruder configuration is limited, but the temperature limit is consistent with the non-metallized azo structure. The dye is moderately lipophilic. Experimental n-octanol/water partitioning should be determined by OECD Test No. 117 before environmental risk assessment; predicted log P values for this structure exceed 4, but prediction is not a substitute for a measured value in the receiving fuel or solvent. In aqueous waste streams, solubility below 0.1 g/L at 20 °C means that mechanical separation and activated carbon adsorption are more effective than simple dilution.
In hydrocarbon fuel marking, Solvent Yellow 56 is introduced as a dissolved stock solution rather than as dry powder at the injection point. A 1% w/w concentrate in xylene or methyl naphthalene is metered by a positive-displacement pump into the product stream upstream of a static mixer; the target addition rate for visible identification is generally 5–50 mg/kg depending on product path length and end-use specification. Final dose verification is performed by high-performance liquid chromatography with visible detection, but the exact λmax must be determined in the finished fuel matrix because published data for this specific configuration is limited. The dye partitions strongly into the fuel phase under pipeline condensation conditions, which reduces extraction losses into water bottoms. However, Solvent Yellow 56 is not a regulatory fuel marker; in EU fiscal marking applications it must not be used as a substitute for C.I. Solvent Yellow 124 (CAS 34432-92-3) unless national legislation explicitly permits the alternative marker chemistry.
In lubricant and hydraulic fluid dyeing, a 10% w/w mineral-oil stock solution is prepared at 60–80 °C in a jacketed stainless-steel vessel equipped with a low-speed paddle agitator. The product is then delivered at 0.01–0.1% w/w of final fluid to a blending manifold. High-shear dispersion is not required because the dye is in true solution; however, a 40-mesh in-line basket strainer is placed downstream of the metering pump to retain any undissolved coarse material. Production-scale field reports indicate that xylene-based concentrates stored below 0 °C can develop crystalline sediment, so concentrated systems should be maintained at 5–35 °C and recirculated at a velocity above 0.3 m/s if tank dead zones exist. The dye is sensitive to acid-induced protonation at the terminal amine; commercial lubricant packages containing strongly acidic corrosion inhibitors or hydrolysis-prone esters should undergo a 30-day storage stability study at 40 °C before finalization. Shade drift toward orange-red under those conditions indicates acid interaction rather than oxidative fading.
Compared with C.I. Solvent Yellow 33 (47000; CAS 8003-22-3), Solvent Yellow 56 differs in chemical class and thermal ceiling. Solvent Yellow 33 is a quinoline derivative with a greenish yellow shade and is selected for transparent engineering plastics processed above 260 °C; Solvent Yellow 56 is a para-aminoazobenzene with a yellow shade having a red undertone. Its upper processing threshold in general-purpose polystyrene and acrylic is approximately 220 °C. In injection molding trials, holding the melt above 230 °C for 10 minutes can produce a measurable decrease in chroma and an increase in yellow-brown degradation products when measured according to ISO 11664-4; melt residence time should therefore be kept below 90 seconds at full production throughput. Against C.I. Solvent Yellow 14 (12055; CAS 842-07-9), the difference is more shade-related than thermal: Solvent Yellow 14 is a β-naphthol-derived monoazo dye that gives an orange-yellow hue, while Solvent Yellow 56 gives a yellower shade in aliphatic media. Solvent Yellow 56 is also more soluble in mineral spirits at 20–25 °C, reducing the need for preheating in solvent-based ink and wax applications.
| Parameter | Solvent Yellow 56 | Solvent Yellow 33 | Solvent Yellow 14 |
|---|---|---|---|
| C.I. Constitution Number | 11021 | 47000 | 12055 |
| CAS Registry Number | 2481-94-9 | 8003-22-3 | 842-07-9 |
| Chemical class | Non-metallized para-aminoazobenzene | Quinoline derivative | Non-metallized β-naphthol monoazo |
| Solubility in aliphatic hydrocarbons at 20–25 °C | High | Moderate | Moderate to high |
| Shade in aliphatic media | Yellow with red undertone | Greenish yellow | Orange-yellow |
| Upper melt-processing threshold | 220 °C | 260 °C | 200 °C |
| Acid sensitivity | Protonation-induced hue shift | Low | Low |
Lightfastness comparisons should be generated on the final substrate; published supplier data for Solvent Yellow 56 in thin polyethylene terephthalate films is limited. For outdoor signage, accelerated weathering under ISO 105-B02 normally places the product in a moderate to low blue-wool category, and it is therefore not a replacement for pigmented systems. Migration resistance in polyolefins is a known operational boundary. The molecular mass of 253.34 g/mol is not sufficiently high to immobilize the dye in amorphous polyethylene and polypropylene; when such materials are stored at 40 °C, blooming can occur at loadings above 0.05% w/w. Processing plants requiring low migration for toys or food-contact packaging must therefore avoid Solvent Yellow 56 unless a barrier layer or overcoating is proven by extraction testing.
For middle distillate identification, Solvent Yellow 56 can be used for industrial marking of heating oil, certain heavy fuel blends, and selected middle-distillate streams, but only after confirming that the downstream logistics chain does not include aggressive extraction, caustic wash, or oxidative desulfurization. Azo dye fading occurs readily in the presence of strong reducing agents such as sodium hydrosulfite and strong oxidizing agents such as hypochlorite; any carryover of those treatment chemicals into the marked stream will reduce the dye signal. Marking should therefore be positioned after the final product cooler, after coalescer filtration, and before the loading rack, not upstream of hydrotreating or clay filtration. At low dose levels, visible detection is supported by the dye’s broad absorption in the 400–430 nm region; exact absorbance maxima in desulfurized middle distillates may shift because of matrix polarity, and published data for this specific configuration is limited.
In wax and polish production, Solvent Yellow 56 is pre-dispersed at 0.02–0.2% w/w in a molten paraffin pool at 80–120 °C. The molten blend is agitated for 20–30 minutes and screened through a 25 μm bag filter before filling. Acid-catalyzed nitrocellulose lacquers should be tested separately because protonation of the amino group can shift the shade; the critical acidity depends on the binder package. The product should not be used in waterborne systems without a co-solvent because water solubility is below 0.1 g/L at 20 °C.
| Instrument | Required verification for Solvent Yellow 56 |
|---|---|
| REACH Regulation (EC) No 1907/2006, Article 31 | Safety data sheet and registration status must be obtained from the supplying legal entity; substance volume band may affect registration obligations. |
| 21 CFR 178.3297 | Solvent Yellow 56 is not listed as an indirect food-contact colorant for polymers; use in food-contact applications requires explicit clearance. |
| RoHS Directive 2011/65/EU | Applies to finished electrical and electronic equipment; article-level conformity requires testing of lead, cadmium, mercury, hexavalent chromium, PBB, and PBDE. |
| EN 71-3:2019 | Heavy-metal migration must be measured if the dye is used in toy materials; compliance is not implicit for the dyestuff alone. |
In solvent-based flexographic and gravure packaging inks, Solvent Yellow 56 is pre-dissolved in ethyl acetate or methyl ethyl ketone at 20–25 °C and added at the letdown stage. Because the dye is a true solution, color strength is governed by UV-visible transmission rather than pigment particle scattering; in-line spectrophotometric color control will respond to the main absorbance peak, but exact peak position must be characterized on the printed film or pellicle. The product is not a substitute for a high-performance pigment where exterior durability is required; accelerated weathering under ISO 105-B02 typically indicates moderate to low blue-wool performance. For outdoor banners, automotive interior films, or thin-wall packaging stored under high-intensity lighting, Pigment Yellow 138 or Pigment Yellow 74 is technically preferred. The dry powder is a combustible organic dust; powder transfer zones should be assessed by 20-L sphere testing according to ISO/IEC 80079-20-2:2016 before installation of dust explosion protection. Residual dye in mixing tanks is removed with warm toluene or methyl ethyl ketone; waste streams should be collected for incineration or activated carbon adsorption because the dyestuff is poorly water-soluble and can persist in sludges if discharged untreated.
