4-Aminophenol CAS 123-30-8

What is 4-Aminophenol?

4-Aminophenol is the para isomer of aminophenol — a benzene ring carrying a hydroxyl group and an amino group directly opposite each other, C₆H₇NO. That arrangement is what makes it the workhorse feedstock for paracetamol: acetylate the amine and you have the finished drug substance in one step.

It is a white to pale cream crystalline powder melting at about 186–190 °C with decomposition. It is only sparingly soluble in cold water, freely soluble in alcohol and in dilute acid, and it darkens on exposure to air and light as the aminophenol oxidises toward quinoneimine species. Colour stability, not assay, is usually the first thing a buyer asks about.

Chemically it is both a phenol and a primary aromatic amine, which gives it two reactive handles. The amine acetylates, alkylates, diazotises and condenses; the phenol ethers, esterifies and couples. That dual functionality is why it reaches so far beyond pharmaceuticals into dyes, photographic developers and fuel additives.

Commercially, 4-aminophenol is a high-volume pharmaceutical intermediate rather than a specialty. Its demand is anchored almost entirely to paracetamol production, with secondary markets in oxidative hair colourants, black-and-white photographic developers, rubber antioxidants and lubricant additives.

Why 4-aminophenol specifically

• One step from paracetamol. Acetylation with acetic anhydride converts it directly to acetaminophen — no protecting groups, no rearrangement, which is why no alternative feedstock has displaced it.
• Para substitution matters. The 2- and 3-isomers exist and are useful, but only the para arrangement gives the geometry paracetamol needs. Isomer content is a specification item, not a detail.
• Two independent reactive sites. A primary aromatic amine and a phenolic hydroxyl on the same ring, each addressable on its own, which is what makes it so productive in dye and developer chemistry.
• Readily reduced and oxidised. Its redox behaviour is the basis of its use as a photographic developer and as an antioxidant intermediate — and also the reason it needs protecting from air.

How 4-Aminophenol is Manufactured

4-Aminophenol is made either by reducing a nitro compound or by the acid-catalysed rearrangement of phenylhydroxylamine. The nitrobenzene route dominates on cost.

• Catalytic hydrogenation of nitrobenzene (Bamberger route). Nitrobenzene is hydrogenated over a platinum catalyst in dilute sulphuric acid. The intermediate phenylhydroxylamine rearranges in the acid medium directly to 4-aminophenol. This is the principal commercial route because it starts from a cheap bulk feedstock.
• Reduction of 4-nitrophenol. 4-Nitrophenol is reduced catalytically or with iron and acid. The route is cleaner and gives a lower-colour product, which is why fine chemical and low-colour grades often come from it, but the feedstock costs more.
• Neutralisation and isolation. The product is liberated from its sulphate or hydrochloride salt, crystallised, washed and dried. Isolation conditions set the crystal habit, the bulk density and much of the colour.
• Colour protection. Because the material oxidises in air, finishing and packing are done with reduced air contact and sometimes under nitrogen. Low-colour grades are stabilised and packed tighter than technical grades.

Typical Commercial Specification

Figures below are representative of standard pharmaceutical-grade material. Low-colour and tightened-impurity grades are available — send us the specification you work to and we will quote against it.

Physical & Chemical Properties

Reactivity in practice

An aromatic amine and a phenol on the same ring, para to each other. The chemistry follows from that:

• Acetylation to paracetamol. Acetic anhydride acetylates the amine selectively under aqueous conditions, giving acetaminophen in a single high-yielding step.
• Oxidative coupling. In the presence of an oxidant it couples with dye intermediates, which is the basis of its use in permanent hair colourants and photographic development.
• Diazotisation and azo coupling. The primary aromatic amine diazotises normally, opening the azo dye and pigment chemistry.
• Air oxidation. The same ease of oxidation that makes it useful as a developer makes it darken in storage — a handling constraint rather than a defect.

4-Aminophenol vs the Other Aminophenols and Nitro Precursors

Aminophenols are chosen by where the two groups sit on the ring. The substitution pattern decides the geometry of everything built from it, and substituting across isomers is never a like-for-like swap.

Stated plainly: the para arrangement is what paracetamol needs, and nothing else substitutes for it. The ortho isomer closes into five-membered benzoxazole rings that the para isomer cannot form at all, and the meta isomer serves a different dye market entirely. Where the isomers do meet is in your specification — ortho content in para-grade material is an impurity to be limited, not a bonus.

Industries We Supply 4-Aminophenol To

The same white powder leaves our warehouse for very different factories. What changes between them is not the CAS number but the grade, the colour limit and the documentation each sector expects.

Where 4-Aminophenol is Used

4-Aminophenol is overwhelmingly a paracetamol feedstock, but a meaningful second market sits behind it. These are the end uses our customers buy it for.

In paracetamol manufacture

The route is short and well understood: 4-aminophenol is slurried in water and acetylated with acetic anhydride, and the paracetamol crystallises on cooling. Because the step is so direct, almost nothing in the feedstock is removed by the chemistry — colour bodies, the ortho isomer and residual 4-nitrophenol all carry through to the crude product and have to be purified out downstream. That is why paracetamol makers specify the impurity profile rather than just the assay, and why they care how the drums were stored.

In hair colourants

In oxidative hair colour, 4-aminophenol works as a precursor that is oxidised in situ and couples with a second component to build the chromophore inside the hair shaft. Cosmetic users typically have tighter heavy metal and trace amine limits than pharmaceutical users, and a different colour specification, so a grade that satisfies an API plant is not automatically a cosmetic grade.

In photographic chemistry

As a developing agent it reduces exposed silver halide to metallic silver, and the fact that it oxidises easily is precisely the point. This market is small now but persistent, and its users tend to buy modest quantities to a tight colour and purity specification.

As a dye and additive intermediate

Diazotisation and coupling give azo colourants; condensation routes feed rubber antioxidants and fuel additive chemistry. These buyers are usually more tolerant on colour and more sensitive on price than pharmaceutical buyers, which is why technical grade exists as a separate commercial product.

Quality Control & Testing

Every lot is released against a batch-specific Certificate of Analysis. The methods behind the numbers are standard across the industry, and we are happy to share them or to work to your own in-house test protocol.

• Assay and related substances — HPLC, quantifying 4-nitrophenol, the ortho isomer and aniline alongside the main component.
• Melting range — a fast, revealing check. A depressed or broad range usually means moisture or impurity carry-over before anything else shows up.
• Colour of solution — the figure that predicts how the material will behave in a paracetamol batch, and the one most affected by storage.
• Loss on drying and sulphated ash — moisture and inorganic residue, both of which affect downstream yield calculations.
• Heavy metals and iron — relevant for pharmaceutical and cosmetic service, and a common cause of colour drift.
• Residual solvents — where the grade and the customer's regulatory position call for it.

Common Process Problems & Likely Causes

When 4-aminophenol misbehaves in a plant, the cause is usually one of a short list of things. This table is the shortcut our technical desk works through before anyone opens a complaint file.

Packaging, Storage & Shipping

• Standard packing. 25 kg net in fibre drums with polyethylene liners, or in HDPE laminated bags, palletised and shrink-wrapped.
• Air and light exclusion. The material oxidises and darkens in air. Keep liners tied and drums closed, and avoid leaving part-used containers open on the shop floor.
• Inert blanketing. Low-colour grades are packed with reduced air contact and can be nitrogen-flushed where the application justifies it.
• Storage. Cool, dry, well-ventilated and dark, away from oxidising agents, acids and sources of ignition.
• Materials of construction. Lined or stainless steel, or suitable plastics. Avoid prolonged contact with unlined mild steel, which both contaminates the product and drives colour.
• Shelf life. Typically 24 months in unopened original packing under those conditions. Beyond that, re-test rather than assume — colour and assay are the figures to repeat.
• Transport classification. Generally shipped as a non-dangerous good for most modes; where a destination or carrier requires a classification it is handled as a toxic solid, n.o.s., Class 6.1, Packing Group III. Confirm against the current SDS and the shipper's declaration for your destination and mode.

Hazards & Safe Handling

4-Aminophenol is harmful if swallowed, a skin sensitiser and an eye irritant. It must be handled by trained personnel under a proper risk assessment. The classifications below are indicative — the current SDS supplied with your consignment is the governing document.

• Sensitisation. Aminophenols are recognised skin sensitisers, and the hair colourant literature on them is extensive. Once a worker is sensitised, exposures previously tolerated can provoke a reaction, so preventing first contact matters far more than managing repeat contact.
• Dust control. The main occupational exposure is airborne dust during charging and transfer. Handle in a closed system, under local exhaust ventilation, or with a dust-controlled charging arrangement.
• PPE. Chemical-resistant gloves, dust goggles, and a suitable respirator where dust is generated. Overalls that do not carry dust home.
• Health effects. Harmful if swallowed, with the aromatic amine family's associated concerns about blood effects on significant exposure. Several jurisdictions apply a suspected-mutagenicity classification — check your own regulatory position.
• Incompatibilities. Strong oxidising agents, acid chlorides, nitrous acid and alkali metals. Oxidiser contact is both a safety and a quality issue.
• Spill response. Avoid raising dust. Sweep or vacuum carefully into a labelled closed container, ventilate, and wash the area down afterwards.
• Environment. Harmful to aquatic life. Do not allow to enter drains, surface water or groundwater. Dispose through a licensed chemical waste contractor.
• First aid. Remove contaminated clothing, wash skin with plenty of water and soap, flush eyes for at least 15 minutes, and seek medical attention with the SDS to hand. Report any skin reaction, which may indicate developing sensitisation.

Regulatory & Compliance Notes

4-Aminophenol is an established industrial and pharmaceutical chemical and is listed on the major national chemical inventories. Because obligations differ by territory, volume and use, the notes below are orientation rather than legal advice — confirm your own position with your regulatory adviser before importing.

• Inventory status. Listed on the principal chemical inventories in the major importing regions. Ask us for the inventory confirmation relevant to your destination country.
• Pharmacopoeial position. Supplied to agreed technical or pharmaceutical specifications. Where your filing references a monograph or a specific impurity limit, send it with the enquiry so the grade is quoted correctly.
• Cosmetic use. Use in oxidative hair colourants is regulated by concentration in several territories, including under the EU Cosmetics Regulation annexes. Confirm the permitted level for your market and formulation.
• Impurity limits in API supply chains. Where the material feeds a regulated drug substance, the nitrophenol and isomer limits may be part of your marketing authorisation rather than merely a purchase specification. Agree them in writing.
• Hazard communication. Supplied with an SDS compliant with the format applicable to your region, and labelled in line with the GHS classification for the product.
• Dangerous goods. Generally not restricted for transport; where a classification applies it is a Class 6.1 toxic solid, Packing Group III. Confirm against the current SDS; declarations prepared for IMDG (sea) or IATA (air) as appropriate.

We Supply 4-Aminophenol Worldwide

Chelora Chemicals is a supplier and export partner, not a single-plant trader. We ship 4-Aminophenol from India to customers across Asia, Europe, the Middle East, Africa, and North and South America, handling the export documentation, customs paperwork and freight so the material arrives ready to use.

• Incoterms. EXW, FOB, CIF, CFR and DAP quoted to suit your purchasing terms and freight arrangements.
• Ports. Regular shipments through Nhava Sheva (JNPT) and Mundra, with other Indian ports arranged where it suits the routing.
• Documentation. Commercial invoice, packing list, certificate of origin, COA, SDS and any required end-use or pharmacopoeial declarations issued as a complete set.
• Flexible volumes. A single drum for laboratory qualification, through LCL consolidations, up to repeat full container loads on a supply contract.
• Supply continuity. Because we are independent of any one producer, a plant turnaround or a shipping disruption at one source does not have to become your stock-out.

Buying 4-Aminophenol from Chelora

We are an independent sourcing and supply partner. For 4-aminophenol that means confirming two things at enquiry: the colour and impurity limits your process actually needs, and whether the material is going into a regulated drug substance, a cosmetic or a technical application — because the right grade differs between them.

• Documentation on every lot. Batch-specific COA including related substances and colour, current SDS and TDS.
• Samples before commitment. Trial quantities for process qualification ahead of a commercial order.
• Quantities. From a single 25 kg drum through to full container loads on contract supply.
• Export experience. Packing, labelling and export documentation handled for sea and air freight.
• Technical support. Direct access to people who know the chemistry, for questions on isomer content, colour stability or acetylation behaviour.
• Related intermediates. Salicylic acid, guaiacol and the wider pharmaceutical intermediate range from one supplier.

How ordering works

• Send the enquiry. Product, grade or pharmacopoeia standard, quantity, destination port and the Incoterm you buy on. If you have a spec sheet, attach it — it saves a round trip.
• We quote. Price, lead time, packing and a sample COA, normally within one working day.
• Sample and qualify. For first orders or critical applications, we send a trial quantity so your lab can sign off before you commit.
• Confirm the order. Proforma invoice issued; payment terms agreed against the volume and the relationship.
• Production and QC. Material allocated and released against a batch-specific COA, with a pre-shipment sample where the application calls for it.
• Ship and document. Packed, labelled and loaded with the full export document set, and tracked through to arrival.

Related Pharmaceutical Intermediates & Excipients

Buyers of 4-aminophenol usually source several of these alongside it. Consolidating them on one order cuts freight cost and gives you a single point of contact for documentation.