Section
| HS Code | 652697 |
| Product Name | Acid Orange II |
| Synonyms | Orange II; Acid Orange 7; C.I. Acid Orange 7 |
| Ci Number | 15510 |
| Cas Number | 633-96-5 |
| Einecs Number | 211-199-0 |
| Molecular Formula | C16H11N2NaO4S |
| Chemical Class | Monoazo acid dye |
| Appearance | Orange to red-orange powder |
| Color Shade | Orange |
| Solubility | Soluble in water and ethanol |
| Application | Dyeing wool, silk, nylon, leather, paper, and ink |
| Storage Conditions | Store in a cool, dry, well-ventilated area away from light |
As an accredited Acid Orange II factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Acid Orange II, 100 g, packaged in an amber glass bottle with screw cap and hazard label. |
| Container Loading (20′ FCL) | Acid Orange II in 25 kg bags on pallets, loaded into a clean, dry 20′ FCL, away from moisture and incompatible materials. |
| Shipping | Acid Orange II (C.I. 15510; CAS 633-96-5) is generally not regulated as dangerous goods for transport. Ship in closed, labeled containers protected from moisture, heat, and dust. Use appropriate PPE and follow local/national transport regulations. |
| Storage | Store Acid Orange II in a cool, dry, well-ventilated area away from direct sunlight, heat, moisture, and ignition sources. Keep containers tightly closed and labeled; avoid dust generation and inhalation. Segregate from strong oxidizers, acids, bases, food, and feed. Use secondary containment where appropriate and follow local regulations for hazardous chemical storage and waste. |
| Shelf Life | Stable for several years when kept dry, tightly sealed, and protected from light and heat; follow supplier expiry. |
Acid Orange II in protein fibre exhaustion dyeing is circulated in soft water at a 1:10–1:20 liquor ratio in winch or overflow machines for wool slubbing, wool tops and ammonia-premordiated silk. A starting formulation of 1.0–4.0% o.w.f. dye is first dissolved at 60°C; 10–20% o.w.f. anhydrous sodium sulphate is then added to suppress fibre surface charge. The bath is acidified with 1.0–2.0% o.w.f. formic acid 85% to pH 3.0–3.8; sulfuric acid can replace formic acid for shade correction, but the faster strike above 90°C increases uneven uptake on damaged fibre ends. The bath is raised from 40°C to 98°C at 1.0–1.5°C/min and held for 45–60 min. Because the monosulfonated molecule reaches exhaustion through high-temperature equilibrium, early fast heating produces migration differences between wool tip and root. After the hold, the bath is cooled to 70°C before overflow rinsing, and a synthetic tanning agent afterfix may be applied at 2–4% o.w.f. at pH 4.0–4.5 to improve wet fastness. Water hardness above 100 mg/L CaCO₃ is corrected with 0.5–1.0 g/L tetrasodium EDTA or a polyphosphate sequestrant to prevent metal-dye complex dulling. End products include woven outerwear, narrow woven labels, wool felt and embroidery yarn where exterior lightfastness is not specified. Wet fastness on unmodified wool is the principal boundary: BS EN ISO 105-C06 A2S washing typically yields lower ratings than milling dyes on the same substrate, and lightfastness under BS EN ISO 105-B02 is limited, so outdoor wool end uses require plant-specific fastness verification before release.
On polyamide warp-knit and tufted carpet substrates, Acid Orange II is applied in beam, package or overflow jet machines at pH 4.5–5.5 controlled by ammonium sulphate 2.0–4.0 g/L and acetic acid 0.3–0.8 mL/L. A medium-depth shade requires 1.0–2.5% o.w.f. dye; pale shades use 0.1–0.5% o.w.f. with a fatty amine ethoxylate levelling auxiliary at 0.5–1.5 g/L. The exhaustion difference between nylon 6 and nylon 66 is operationally significant. Nylon 6 approaches equilibrium at 95–100°C, while nylon 66 requires 105–115°C in fully flooded jet machines to improve migration into tight filament bundles. Acid Orange II has good migration on nylon 6 and can mask light barrel from denier variation; on higher-crystallinity nylon 66 the migration window is shorter and barre coverage is less reliable. The bath is started at 40°C, held for 10 min, raised at 1.0°C/min to target, and held for 30–45 min. After shower washing, an anionic fixative may be applied at 1–3% o.w.f. to raise perspiration and water fastness. End products include dyed nylon tricot, lingerie components, sock linings and indoor carpet with low ultraviolet exposure. Automotive nylon carpet or exterior webbing is outside the robust range of this dye: BS EN ISO 105-B02 at 1/1 standard depth on nylon is generally below that required for SAE J1885 interior automotive weathering, so product-specific fade testing is mandatory before release.
Acid Orange II is introduced into the retanning-dyeing-fatliquoring sequence of chrome-tanned crust in stainless steel or wooden drums at 150–400% float, 55–60°C and 1.0–3.0% dye on shaved weight. The bath is preadditized with 0.5–1.5% sodium formate and 0.2–0.5% sodium bicarbonate to hold pH 4.2–4.8 during penetration; Acid Orange II strikes quickly on chrome-tanned cationic sites, so drum speed is held at 6–10 rpm and the dye is predissolved at 70°C before addition. Penetration continues for 20–30 min, followed by 0.3–0.8% formic acid 85% diluted 1:10 and fed over 15–20 min to pH 3.8–4.0 for fixation. Fatliquoring follows at 55°C with 4–8% sulfated natural or synthetic oil to restore leather softness. The finished leather is sammed, set out, vacuum dried and conditioned for 24 h. End uses comprise bookbinding leather, desk accessories, inner lining leather and low-light garment leather. Azo-colorant compliance is controlled at the leather stage by EN ISO 17234-1; processors must verify that batch impurities do not release listed amines because Acid Orange II is a monoazo dye and reductive cleavage products must be controlled by supplier disclosure. The small molecular volume also gives moderate perspiration migration under ISO 11641, so leather for light-coloured garment linings should be fixated and tested before cutting.
On sulfuric acid anodized aluminium coatings of 12–20 µm thickness, Acid Orange II is adsorbed from an aqueous dye bath containing 1.0–5.0 g/L dye solids adjusted to pH 5.0–5.5 with sodium acetate/acetic acid buffer. The bath is held at 55–65°C in a stainless steel or polypropylene tank with low-level air agitation; immersion time ranges from 5 min for pale shades to 20 min for full shades. The anodizing electrolyte is typically 150–200 g/L sulfuric acid at 18–22°C and 1.3–1.5 A/dm², but dye uptake is governed more by pore diameter and coating thickness than by rack voltage alone. After dyeing, a two-step rinse at pH 5.0–6.0 prevents acid drag-in from shifting the sealing bath. Sealing is conducted in 4–6 g/L nickel acetate at 96–100°C for 2.0–2.5 min/µm of coating, or in hydrothermal water at 98–100°C for the same cycle time. End uses are restricted to indoor architectural trim, signage, appliance fascia and decorative aluminium articles; exterior exposure is not recommended because the chromophore has limited lightfastness under ISO 2135 and will fade before anodized inorganic pigments. Processors should reference ISO 2135 accelerated lightfastness and pilot rack validation before quoting multi-year exterior guarantees.
In paper and paperboard manufacture, Acid Orange II can be applied either as a beater dye or at the size press, but its sulfonated anionic character gives low substantivity to cellulosic fibres without cationic mordants. In beater dyeing, 0.1–0.5% dye on bone-dry fibre is added to the pulper 10–15 min before alum; 1.0–2.0% aluminium sulphate solution is then added to adjust the stock to pH 4.5–5.2, and a cationic retention aid at 0.02–0.05% is metered before the headbox. The short contact time in high-speed paper machines creates shade variation if broke recycling changes conductivity; white-water conductivity above 2000 µS/cm can lower dye retention and must be monitored at the tray. At the size press, a 0.05–0.20% dye solution is prepared at 50–60°C with oxidized starch or carboxymethylcellulose as carrier; pickup of 6–10 g/m² per side is typical for coloured interleaving and cover papers. End products include folder stock, decorative wrapping, tissue and index cards where water bleed is acceptable indoors. Direct food-contact proposals require migration testing under EN 645 and EN 646 or equivalent buyer protocols; this dye is not a listed food colourant and must not be used in uncoated food-contact papers without regulatory clearance from the target market.
| Substrate/process | pH window | Temperature range | Primary auxiliaries | Key boundary/standard |
|---|---|---|---|---|
| Wool winch exhaust | 3.0–3.8 | 96–98°C | Sodium sulphate 10–20% o.w.f.; formic acid 1–2% o.w.f. | BS EN ISO 105-C06 A2S wet fastness below milling-dye baseline |
| Nylon 6 overflow jet | 4.5–5.5 | 95–100°C | Ammonium sulphate 2–4 g/L; acetic acid 0.3–0.8 mL/L | BS EN ISO 105-B02 below SAE J1885 automotive interior target |
| Nylon 66 beam | 4.5–5.5 | 105–115°C | Ammonium sulphate 2–4 g/L; levelling auxiliary 0.5–1.5 g/L | Barre coverage less reliable than nylon 6 |
| Chrome-tanned leather drum | 4.2–4.8 penetration; 3.8–4.0 fixation | 55–60°C | Sodium formate 0.5–1.5%; formic acid 0.3–0.8% | EN ISO 17234-1; ISO 11641 perspiration migration |
| Sulphuric anodized aluminium | 5.0–5.5 | 55–65°C | Sodium acetate/acetic acid buffer | ISO 2135 limited exterior lightfastness |
| Paper size press | 4.5–5.2 wet end | 50–60°C | Aluminium sulphate 1–2%; cationic retention aid 0.02–0.05% | EN 645/EN 646 for food-contact clearance |
Water-based fountain pen, rollerball and stamp-pad ink formulations use Acid Orange II as an anionic colorant at 2.0–5.0 wt% dye content. The dye is dissolved in deionized water at 50–60°C before adding 5–10 wt% glycerol or propylene glycol as humectant and 0.2–0.5 wt% preservative; the finished ink is adjusted to pH 6.5–7.5 with triethanolamine or sodium hydroxide. Filtration through 0.45–0.80 µm polypropylene or glass-fibre cartridges removes undissolved aggregates; if the dye has been stored at relative humidity above 60%, it should be predried at 40°C for 4–6 h to avoid agglomeration. The monoazo structure has limited lightfastness in dilute ink film, so end products are confined to writing, stamping and office stationery where archival permanence is not required. Long-term stability is sensitive to multivalent metal ions from tap water; deionized water or condensate with conductivity below 20 µS/cm is specified to prevent precipitation with calcium and magnesium. Batch-to-batch shade deviation in ink concentrates is controlled by spectrophotometric strength comparison at λmax 483 nm in a 1 cm cell against a working standard.
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Acid Orange II, indexed under C.I. 15510 and CAS 633-96-5, is the sodium salt of 4-[(2-hydroxy-1-naphthyl)azo]benzenesulfonic acid and carries the molecular formula C16H11N2NaO4S with a formula weight of 350.32 g/mol. The product is a monoazo acid dye; its aqueous absorption maximum is between 483 nm and 486 nm under neutral to weakly acidic conditions. Commercial dry forms are typically dark orange to red-brown powders or granular crystals, while analytical grades are supplied for use as anionic dye probes in adsorption and photodegradation research. The molecule contains a single sulfonate group; this is the primary structural distinction from disulfonated orange acid dyes such as C.I. Acid Orange 10, and it lowers aqueous solubility while increasing substantivity toward hydrophobic substrates. Acid Orange II is not a reactive dye and does not form covalent bonds with cellulose; it binds to wool, silk, nylon and leather through ionic attraction to protonated amino groups plus van der Waals and hydrophobic interactions. In markets where food or pharmaceutical colorant positive lists do not include C.I. 15510, the material is restricted to industrial dyeing, printing and laboratory applications. EINECS number 211-199-0 identifies the substance in European chemical inventories.
Acid Orange II exhausts onto wool only when the fiber carries a net positive charge on amino groups; therefore bath pH controls the rate and extent of dye uptake. At pH values above 5.5, exhaustion is incomplete because the carboxylate and sulfonate groups in the fiber reverse the surface charge. At pH values below 3.0, the number of protonated sites is high and strike rate becomes rapid, but this creates two production risks: skittery, uneven dyeing on compact yarn packages, and hydrolytic damage to the wool cuticle. Mill recipes for medium-depth shades typically set the bath at 35–40 °C with 1–3% owf Acid Orange II, 5–10% anhydrous sodium sulfate, and sufficient acetic acid or acetic acid/sodium acetate buffer to hold pH at 3.5–4.5. The dyeing machine is then ramped to 96–98 °C over 30–45 min and held for 45–60 min. In overflow jet dyeing of piece goods at a liquor ratio of 1:8–1:12, effective circulation and fabric speed are critical because the dye has a short levelling phase after the bath reaches 80 °C. Level dyeing agents are typically required for pale shades at 0.5% owf or below. After dyeing, residual dyebath should not be discharged without chelation or precipitation because Acid Orange II is a poorly biodegradable azo dye under conventional aerobic wastewater treatment.
Wet fastness and lightfastness are lower than milling acid dyes of similar hue. Published ISO 105-B02 values for unmodified acid orange dyeings on wool commonly appear near 3–4 at 1/1 standard depth; ISO 105-C10 wash tests often show visible staining of adjacent wool and nylon. Cationic synthetic tanning agents improve wet fastness but may decrease lightfastness by 0.5–1.0 point and cause a slight reddening of the final shade. The processing window for the final pH adjustment is therefore narrow: a drop below pH 3.0 in the last 10 min of the dyeing cycle increases the risk of surface bronzing on fabric contact areas, while a final pH above 4.5 can leave unconverted dyebath color that shifts shade during rinsing.
Release specifications for industrial and analytical Acid Orange II are not defined by a single global standard, but the following acceptance ranges appear in publicly available certificates of analysis for commercial lots. The analytical grade is typically standardized by visible spectrophotometry against a reference lot and may be packaged with a certificate showing loss on drying and residual solvent results. Industrial grades are adjusted with diluents such as sodium sulfate or dextrin; this affects apparent dye content and should be considered when scaling a laboratory formulation to production.
| Parameter | Industrial grade | Analytical grade |
|---|---|---|
| Appearance | Dark orange to red-brown powder | Dark orange crystalline powder |
| Dye content by visible spectrophotometry | ≥85.0% | ≥95.0% |
| Water-insoluble matter | ≤0.5% | ≤0.1% |
| Loss on drying at 105 °C | ≤5.0% | ≤3.0% |
| pH of 1% aqueous solution | 7.0–9.0 | 6.5–7.5 |
| λmax in water | 483–486 nm | 483–486 nm |
Acid Orange II is chemically stable under normal acid dyeing temperatures, but prolonged exposure above 105 °C during drum drying or thermofixation can reduce brightness, particularly if residual acid is present. The azo bond is stable under acidic conditions but is susceptible to reductive cleavage; therefore, the dye should not be combined with strong reducing agents such as sodium hydrosulfite in the dyebath or in formulated inks without controlled redox conditions. In stainless steel equipment, the acidic bath at pH 3.5–4.5 does not require special alloy selection beyond standard 316L dyeing vessels; however, carbon steel transfer lines should be avoided because low pH and dissolved oxygen can release iron ions that form dull complexes with the ortho-hydroxy azo ligand. The dry powder is hygroscopic and should be stored below 60% relative humidity; opened containers should be closed immediately after weighing. Pre-dissolution of Acid Orange II is recommended at 70–80 °C with moderate stirring; boiling the stock solution for more than 20 min can cause local evaporation and aggregation at the liquid surface.
In leather drum dyeing, substitution of Acid Orange II for a disulfonated orange dye changes exhaustion rate and penetration. Acid Orange II carries one sulfonate group and is therefore less hydrophilic than C.I. Acid Orange 10; it strikes the wet-blue surface more quickly, especially in the acidic conditions used after chromium tanning. A production drum recipe for milled or corrected grain side leather can use 60–100% water at 35–45 °C, 1.0–2.5% Acid Orange II based on wet-blue weight, and 1–2% diluted formic acid added in two separated feeds. The drum runs for 40–60 min; penetration can be improved by adding 0.5–1.0% of a low-charge amphoteric or weakly anionic levelling agent before the dye. If Acid Orange 10 is replaced weight-for-weight, the Acid Orange II bath often shows higher initial surface dye uptake, and the addition of anionic retanning agents during the same wet cycle can strip the unfixed dye more readily. Comparative trials in drum dyeing show that final bath exhaustion is typically 5–15% lower for Acid Orange II when anionic acrylic syntans are added at 2–4% after dye fixation; the weaker electrostatic binding associated with a single sulfonate group permits greater displacement from leather protein carboxylate sites. To avoid bronzing, the dye should be pre-dissolved at 1:10 hot water and not added directly to the drum as dry powder.
| Property | Acid Orange II | Acid Orange 10 |
|---|---|---|
| Colour Index | C.I. 15510 | C.I. 16230 |
| Molecular weight | 350.32 g/mol | 452.37 g/mol |
| Sulfonate groups per molecule | 1 | 2 |
| Visible absorption maximum in water | 483–486 nm | 475–478 nm |
| Solubility behavior | Moderate; higher hydrophobic binding | Higher; greater levelling tendency |
| Preferred substrates | Wool, nylon, leather, paper wet-end | Leather, paper, biological staining |
In paper wet-end coloring, the addition point relative to alum and cationic retention aid determines retention and two-sidedness. Acid Orange II has low direct substantivity to bleached kraft pulp, so it is usually added at 0.05–1.0% on oven-dry fiber after refining but before the headbox, followed by 0.5–1.5% poly-DADMAC or 0.5–1.0% alum at pH 4.8–5.3. If alum is added before the dye, cationic aluminum species may form a lake with the anionic dye too early, producing mottled formation and reduced brightness. Because the dye is not chemically bonded, recirculated whitewater can carry residual color from the wire section back to the thick stock loop. Published retention data for Acid Orange II in specific paper grades is limited; however, anionic dyes of this class generally require cationic retention aids to exceed 60% retention, and values above 90% require active wet-end charge control. Foaming can occur in high-speed gap formers when residual dispersants from dye standardization interact with anionic trash; antifoam addition should be evaluated only after a dye-compatibility jar test. Acid Orange II is not a suitable replacement for a cationic dye in colored tissue or packaging grades because its anionic charge requires a retention aid, and it bleeds in water-fastness tests compared with direct dyes of similar hue.
Photocatalytic and Fenton-based degradation studies frequently select Acid Orange II as a model anionic monoazo pollutant because its single sulfonate group gives moderate water solubility and the naphthol chromophore permits real-time monitoring by UV-visible spectrophotometry. A typical bench-scale slurry reactor uses a 50–200 mL volume with an initial dye concentration of 10–50 mg/L, a catalyst loading of 0.5–1.5 g/L TiO2 P25, and UV-A irradiance in the range 3–8 mW/cm2 at the reactor window. Removal is reported as the decrease in absorbance at 484 nm, but this measurement alone can overestimate mineralization because the azo chromophore is cleaved before the resulting aromatic intermediates are completely oxidized. Reaction endpoints should therefore include dissolved organic carbon or chemical oxygen demand data. Acid Orange II is advantageous for batch studies because it does not require surfactant to dissolve at these concentrations; however, the initial solution pH must be controlled to 5.5–7.0 to avoid pH-dependent shifts in the absorption maximum. In comparative photocatalysis, direct kinetic comparisons across dye structures are valid only when lamp irradiance, catalyst surface area and dissolved oxygen are held constant.
