Ortho Phenylene Diamine 1,2-Diaminobenzene (OPD) · CAS 95-54-5

What is Ortho Phenylene Diamine?

Ortho Phenylene Diamine, formally 1,2-diaminobenzene, is a benzene ring carrying two amine groups adjacent to one another, formula C₆H₈N₂. At room temperature it is a white to brownish crystalline solid that darkens on exposure to air, melting around 102–104 °C.

Its value as a building block comes from the two adjacent amine groups, which react with carboxylic acids and aldehydes to form benzimidazole rings — a scaffold found throughout pharmaceuticals and agrochemicals — and which also condense with ketones and quinones to build dye and pigment chromophores.

Commercially, it is produced by catalytic hydrogenation of 2-nitroaniline, selectively reducing the nitro group to an amine while leaving the existing amine on the ring intact.

It ships as a toxic solid (Class 6.1) rather than under flammable-liquid classifications — handling follows standard toxic-solid precautions, with particular attention to dust control, skin contact and its classification as a suspected carcinogen and mutagen.

Why Ortho Phenylene Diamine specifically

• The standard route to benzimidazoles. Condensation with carboxylic acids gives 2-substituted benzimidazoles, a core scaffold in pharmaceutical synthesis.
• A key diamine for dye and pigment chemistry. Condensation with diketones and quinones builds chromophores used across the dye and pigment industry.
• An established analytical reagent. OPD is a well-known substrate for horseradish peroxidase (HRP)-mediated ELISA detection, giving 2,3-diaminophenazine on oxidation.
• The specific substitution pattern needed. The ortho (1,2-) pattern is distinct from the meta- and para-phenylenediamine isomers, and routes built around it need this specific isomer.

How Ortho Phenylene Diamine is Manufactured

Ortho Phenylene Diamine is made through a controlled nitration and selective reduction sequence, so supply tracks installed nitroaromatic and hydrogenation capacity rather than a generic aromatics feedstock stream.

• Nitration of aniline (or chlorobenzene route). A nitroaniline precursor, such as 2-nitroaniline, is generated via established nitration chemistry.
• Selective hydrogenation. The nitro group is catalytically reduced to an amine, giving the 1,2-diamine while the existing substituents remain intact.
• Purification. The crude diamine is purified by distillation or crystallisation to the target purity, typically 98% or better.
• Quality release. Melting point, assay and colour are confirmed against specification before the batch is released.
• Finishing and packing. The purified solid, which oxidises and darkens in air, is packed promptly under protective, standard toxic-solid handling conditions.

Typical Commercial Specification

Figures below are representative of commercial-grade ortho phenylene diamine. Tell us your downstream route and the grade you need, and we will advise on the specification to order against.

Physical & Chemical Properties

Behaviour in the process

Ortho Phenylene Diamine's reactivity pattern is what synthesis chemists and analytical labs are buying:

• Benzimidazole condensation. Reaction with carboxylic acids under acid catalysis gives 2-substituted benzimidazoles, a core pharmaceutical scaffold.
• Chromophore condensation. Reaction with diketones and quinones builds dye and pigment chromophores.
• Oxidative colour reaction. HRP-mediated oxidation of OPD gives 2,3-diaminophenazine, the basis of a well-established ELISA detection method.
• Base reactivity. As a weak aromatic amine base, it readily neutralises acids in exothermic reactions to form salts.

Ortho Phenylene Diamine and Related Phenylenediamines

Ortho Phenylene Diamine is one of three phenylenediamine isomers, and the choice between them depends entirely on the substitution pattern the target synthesis needs.

Stated plainly: the choice of phenylenediamine isomer is dictated by the target molecule's exact substitution pattern — a route designed around benzimidazole or chromophore chemistry needs the ortho-isomer, and a different pattern requires a different starting material.

Industries We Supply Ortho Phenylene Diamine To

The same diamine building block feeds a pharmaceutical intermediate plant, a dye and pigment manufacturer, and an analytical/diagnostics reagent producer. What changes is the downstream condensation chemistry and the documentation each requires.

Where Ortho Phenylene Diamine is Used

Ortho Phenylene Diamine is bought for several distinct downstream chemistries. These are the applications our customers use it for.

In pharmaceutical and agrochemical synthesis

OPD is condensed with a carboxylic acid or acid derivative under acid catalysis to form the benzimidazole ring, the core scaffold in a wide range of active pharmaceutical ingredients and benzimidazole-class fungicides. Colour and moisture matter because both can affect condensation yield and product colour.

In analytical and dye applications

In diagnostics, OPD's oxidation to 2,3-diaminophenazine under peroxidase catalysis is the basis of a long-established colorimetric ELISA method. In dye and pigment chemistry, the adjacent diamine condenses with diketones and quinones to build chromophores.

Quality Control & Testing

Every lot is released against a batch-specific Certificate of Analysis, with colour grade and moisture content reported alongside the main assay because both affect downstream reaction and analytical performance.

• 1,2-Diaminobenzene content — by assay, the primary grade measure.
• Melting point — a fast purity and identity check.
• Colour grade — reported because oxidative discolouration is a practical indicator of handling quality since manufacture.
• Moisture content — measured because moisture can affect condensation chemistry yield.

Common Process Problems & Likely Causes

When this diamine causes trouble, it is usually oxidative discolouration or moisture. This table is the shortcut our technical desk works through before anyone opens a complaint file.

Packaging, Storage & Shipping

• Standard packing. Fibre drums or HDPE bags, typically 25 – 200 kg net, with larger bulk formats on contract supply.
• Oxidation protection. Keep sealed and protected from air and light; the diamine darkens progressively on exposure, affecting colour grade.
• Temperature control. Store between 2–30 °C, away from direct sun and heat sources.
• Material compatibility. Avoid contact with strong oxidisers; the material reacts with metals and acids to form salts.
• Shelf life. Best used within a reasonable period of manufacture; colour grade degrades gradually even in sealed storage.
• Transport classification. UN 1673, Phenylenediamines (o-, m-, p-), Class 6.1, Packing Group III. ADR, IMDG, IATA and DOT requirements apply to packing, labelling and routing.

Hazards & Safe Handling

Ortho Phenylene Diamine is toxic if swallowed, causes skin and eye irritation and may cause an allergic skin reaction, and is suspected of causing genetic defects and cancer. It is also very toxic to aquatic life with long-lasting effects, so standard toxic-solid precautions and good laboratory and plant practice apply throughout handling.

• Skin and eye contact. Chemical-resistant gloves and goggles are standard practice; rinse thoroughly with water on contact and seek medical advice for eye exposure.
• Genotoxic and carcinogenic classification. Classified as a suspected mutagen and category 2 carcinogen; minimise exposure and follow your facility's controls for CMR substances.
• Inhalation. Use adequate ventilation and dust control when handling the crystalline solid.
• PPE. Chemical-resistant gloves, safety goggles and, where dust is generated, a suitable respirator.
• Environment. Very toxic to aquatic organisms with long-lasting effects; avoid uncontrolled release to water and follow local effluent rules.

Regulatory & Compliance Notes

Ortho Phenylene Diamine is a registered specialty diamine shipped as a Class 6.1 toxic solid, with CMR (carcinogen/mutagen/reprotoxic) classification in several jurisdictions. Because obligations differ by territory and use, the notes below are orientation rather than legal advice — confirm your own position with your regulatory adviser.

• GHS classification. Classified as toxic, a suspected mutagen and category 2 carcinogen, a skin sensitiser and very toxic to aquatic life; the SDS carries the full hazard statements for your grade.
• REACH and chemical inventories. Registered under EU REACH and listed on major chemical inventories, with CMR-related restrictions applicable in some jurisdictions.
• Dangerous goods transport. UN 1673, Phenylenediamines (o-, m-, p-), Class 6.1, Packing Group III. ADR, IMDG, IATA and DOT requirements apply to packing, labelling and routing.
• HS code. Commonly declared under the phenylenediamine derivatives heading; confirm the exact tariff line with your customs broker for your jurisdiction.
• Quality agreements. Pharma, diagnostics and dye producers commonly expect documented purity, colour grade and change control. Tell us what your agreement requires.

We Supply Ortho Phenylene Diamine Worldwide

Chelora Chemicals is a supplier and export partner, not a single-plant trader. We ship Ortho Phenylene Diamine from India and from partner sources to customers across Asia, Europe, the Middle East, Africa, and North and South America, handling the export documentation 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 ports arranged as routing allows.
• Documentation. Commercial invoice, packing list, certificate of origin, COA and SDS issued as a complete set.
• Flexible volumes. From trial quantities up to repeat bulk shipments 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 Ortho Phenylene Diamine from Chelora

We are an independent sourcing and supply partner. For this product that means settling three things at enquiry: the purity and colour grade your application needs, the packing format, and the quantity you are buying.

• Documentation on every lot. Batch-specific COA with assay, colour grade and moisture, plus the current SDS.
• Analysis before commitment. Representative analysis shared ahead of a commercial order so your lab can qualify the material.
• Quantities. Trial quantities through to larger bulk shipments on contract supply.
• Inspection. Independent third-party inspection available at loading when the contract requires it.
• Related diamines. Meta- and para-phenylenediamine alongside this product from one supplier.

How ordering works

• Send the enquiry. Purity, colour grade, 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 format and a sample COA, normally within one working day.
• Qualify the supply. For first orders or pharma- and diagnostics-grade applications, we share the analysis so your technical team can sign off before you commit.
• Confirm the order. Proforma invoice issued; payment terms agreed against the volume and the relationship.
• Allocation and QC. Material allocated and released against a batch-specific COA, with an independent inspection where the contract calls for it.
• Ship and document. Packed, labelled and loaded with the full export document set, and tracked through to arrival.

Related Diamine & Aromatic Amine Intermediates

Buyers of ortho phenylene diamine often source other diamine and aromatic amine intermediates alongside it. Consolidating them cuts freight cost and gives you a single point of contact for documentation.