4-Aminophenol Hydrochloride CAS 51-78-5 98% white to beige crystalline powder pharmaceutical intermediate / fur dye and photographic developer

1. Product Overview

4-Aminophenol Hydrochloride, also known as p-Aminophenol hydrochloride or 4-Hydroxyaniline hydrochloride (CAS 51-78-5; molecular formula C₆H₈ClNO; MW 145.59), is the hydrochloric acid salt of 4-aminophenol. It appears as white to off-white or pale beige crystalline powder, readily soluble in water and ethanol, slightly soluble in acetone, and practically insoluble in diethyl ether and nonpolar solvents. The compound darkens on exposure to light and air due to oxidation. Supplied at ≥98% purity (HPLC/Assay), it is widely used as a key pharmaceutical intermediate for synthesizing paracetamol (acetaminophen) and other analgesic/antipyretic drugs, as a fur dye (Fur Brown P, Ursol P) for brown shades in pelts, as a photographic developer (hydroquinone alternative in some B&W formulations), and as a building block in organic synthesis for azo dyes, sulfur dyes, and fine chemicals. For laboratory, industrial intermediate, and authorized research use only; not for direct human/veterinary therapeutic administration.

2. Key Features and Advantages

• High assay ≥98% with low heavy-metal content, suitable for pharma-grade intermediate and API precursor synthesis (paracetamol route via acetylation).

• Readily water-soluble (very sol in water; sol in alcohol), enabling convenient aqueous processing in dye baths, photographic developers, and coupling reactions.

• Stable as dry hydrochloride salt under recommended storage (RT, dry, dark); less prone to oxidation than free base p-aminophenol.

• Dual functionality: aromatic amino (p-NH₂) and phenolic OH (protected/protonated in salt), allowing selective diazotization, electrophilic substitution, and azo-coupling for dye manufacture.

• Consistent crystallinity (white to beige needles/powder), mp ~302 °C (dec.), facilitating melting-point QC and batch release.

• Available in reagent grade (≥98%), AR/BR, and industrial grade (99% tech) for scale-up from lab to bulk API production.

3. Main Applications

• Pharmaceutical intermediate: primary precursor to paracetamol/acetaminophen via acetylation; also used for other p-aminophenol-derived APIs and fine chemical intermediates.

• Fur dyeing: historically known as Fur Brown P, Ursol P, Wool P; used to dye rabbit, mink, and other pelts brown in acidic dye baths (oxidizes to quinone-imine brown pigments).

• Photographic chemistry: employed as a photographic developer (p-aminophenol-based developers are slow but fine-grain; component in some B&W paper/film formulations).

• Dye and pigment synthesis: diazotization followed by azo-coupling to produce azo dyes, sulfur dyes, and hair dye intermediates (p-phenylenediamine adjuncts under regulation).

• Organic synthesis: building block for heterocycles, antioxidants, rubber vulcanization accelerators, and analytical reagents (colorimetric detection of oxidants/nitrites).

• Laboratory reagent: used in educational organic labs for azo dye preparation, oxidation studies, and intermediate-scale API synthesis training.

4. Technical Specifications

5. Storage and Handling

Store as dry powder in a tightly sealed, light-resistant container (amber bottle or foil-wrapped) at 15–25 °C in a cool, dry place; for long-term retention keep at 2–8 °C desiccated. This compound is hygroscopic and highly sensitive to light and air—exposed material darkens (brown to black) due to oxidation to quinone/quinone-imine species; avoid prolonged light exposure and ensure container is closed when not in use. Handle in a well-ventilated area with nitrile gloves, lab coat, and safety goggles; minimize dust generation. Use in fume hood if preparing solutions or heating. Prepare fresh aqueous solutions when possible; discard if solution turns brown/black (indicates oxidation). Do not eat, drink, or smoke in handling areas. Wash hands thoroughly after use. Decontaminate surfaces with water; collect spilled solid and dispose as hazardous organic/ammonium-chloride waste per local regs (WGK Germany 3). Keep away from strong oxidizers, strong bases, and reducing agents.

6. Safety Overview

Classified under GHS as Warning/Danger (GHS07 Xi/Harmful): Hazard statements H302 (Harmful if swallowed), H315 (Causes skin irritation), H319 (Causes serious eye irritation), H335 (May cause respiratory irritation), H341 (Suspected of causing genetic defects—some mutagenicity data), R36/37/38 (Irritating to eyes, respiratory system, skin), R43 (Skin sensitizer—contact may cause sensitization leading to eczema). Precautionary: P261 (Avoid breathing dust), P264 (Wash after handling), P271 (Use outdoors/well-ventilated), P280 (Protective gloves/eyewear), P301+P312 (If swallowed: call poison center), P302+P352 (If on skin: wash with soap), P305+P351+P338 (Eye rinse). Not for human/veterinary therapeutic use; for intermediate, dye, photographic, and research applications only. Skin contact can cause itching/eczema in sensitized individuals; handle as potential irritant and mild mutagen. Transport: not classified as dangerous goods under UN model (NONH in many regions), but some carriers treat as env. hazardous (WGK 3). Consult full SDS before use.