Meta Phenylene Diamine (MPDA) CAS 108-45-2

What is Meta Phenylene Diamine?

Meta Phenylene Diamine is the meta isomer of phenylenediamine — a benzene ring carrying two amino groups at the 1 and 3 positions. It belongs to the aromatic diamine family, and alongside its ortho and para siblings it forms one of the three structural isomers of C₆H₈N₂.

In pure form MPDA is a white to pale-yellow crystalline solid, often supplied as flakes, that darkens toward pink and then red-brown on exposure to air and light. The two free amino groups oxidise readily, and that colour drift is the single most common reason a buyer queries a delivery. In sealed, correctly stored material it is a surface effect rather than a loss of assay, which is why the product is packed under inert gas and kept away from light.

The molecule is weakly basic and freely soluble in water, as well as in ethanol, methanol, acetone and diethyl ether. It forms stable salts with mineral acids, and the hydrochloride and sulphate are frequently the forms actually handled in aqueous dye processes, since the salts resist oxidation better than the free base.

Commercially, MPDA matters because of what those two reactive amine groups allow. They can be diazotised and coupled into azo dyes, condensed with acid chlorides into high-performance polyamides, reacted with epoxide rings to crosslink thermoset resins, or polymerised at a liquid interface to build a separation membrane a fraction of a micron thick. Few intermediates earn their place across so many unrelated industries.

Why the meta isomer specifically

• Chain geometry. The 1,3 substitution forces a kink into any polymer built from it, rather than the straight rod a 1,4 (para) isomer produces. That kink is exactly what gives meta-aramid its flexibility, dyeability and spinnability.
• Moderated reactivity. Both amines remain available for reaction, but the meta arrangement tempers reactivity enough to give workable pot life in epoxy systems, where a para diamine would often be too brisk.
• Coupling versatility. MPDA can act as a diazo component and as a coupling component, which is why it turns up on both sides of so many direct, acid and basic dye routes.
• Water solubility. Free solubility in water makes it practical for aqueous dyeing and for the interfacial polymerisation used in membrane casting, where the amine must sit in the water phase.

How MPDA is Manufactured

The industrial route runs from benzene in three stages. Each one leaves a fingerprint on the finished product, and understanding that helps explain why two suppliers' material can behave differently in the same process.

• Nitration. Benzene is nitrated with mixed acid to nitrobenzene, then nitrated a second time under more forcing conditions to meta-dinitrobenzene. The meta orientation is set here: the first nitro group is a deactivating meta-director, so the second substituent lands predominantly at position 3. Small quantities of the ortho and para dinitro isomers form alongside it, and these are the origin of the isomer impurities seen later.
• Reduction. Both nitro groups are reduced to amines, either by catalytic hydrogenation over a supported metal catalyst or by the older iron–acid (Béchamp) reduction. Catalytic hydrogenation is cleaner and is the dominant modern route; iron reduction tends to leave higher residual metals, which is why the iron figure on a COA is worth reading.
• Purification. The crude diamine is purified by vacuum distillation, by crystallisation, or by both. This is the step that determines final assay and the ortho/para isomer carry-over, and it is where grades genuinely diverge — membrane-grade and fibre-grade material is simply purified harder than standard dye-grade.

Typical Commercial Specification

The figures below are representative of standard commercial-grade MPDA. Tightened specifications for membrane-grade or fibre-grade material are available — send us the spec sheet you work to and we will quote against it.

Physical & Chemical Properties

Reactivity in practice

The chemistry a buyer actually exploits comes down to four reaction types:

• Diazotisation and coupling. Treated with nitrous acid, one or both amines convert to diazonium salts that couple with phenols, naphthols and other activated aromatics to form azo chromophores. This is the foundation of its dye chemistry.
• Acylation and polycondensation. Reaction with acid chlorides gives amides. With isophthaloyl chloride the reaction runs to a high polymer — meta-aramid. With trimesoyl chloride at a water–hexane interface it forms a crosslinked polyamide film microns thin.
• Epoxide ring opening. Each amine hydrogen opens an epoxide ring, so one MPDA molecule can crosslink up to four epoxy groups, producing densely networked thermosets with high heat-distortion temperatures.
• Condensation to heterocycles. With carboxylic acids, aldehydes or carbonyl compounds, MPDA condenses toward benzimidazoles, triazines and related nitrogen heterocycles used in pharma and agro synthesis.

Meta vs Ortho vs Para Phenylenediamine

All three isomers share the formula C₆H₈N₂ and a molecular weight of 108.14, and differ only in where the two amino groups sit on the ring. That single difference changes nearly everything downstream, and the three are not interchangeable in any serious application.

The structural consequence is worth stating plainly: meta gives kinked, flexible polymer chains; para gives rigid, rod-like chains that pack into extremely high-tensile fibre; ortho's adjacent amines close into five-membered rings, which is why it leads to heterocycles rather than polymers. Chelora supplies all three — see Ortho Phenylene Diamine and Para Phenylene Diamine in the product range.

Industries We Supply MPDA To

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

Where MPDA is Used

MPDA is a genuine cross-industry intermediate. These are the end uses our customers buy it for, roughly in order of volume.

In dye manufacture

Diazotised MPDA couples readily with naphthols, phenols and amines to build azo chromophores, and because both amino groups can be diazotised it can anchor disazo structures with two chromophoric arms from a single molecule. Bismarck Brown — among the oldest synthetic dyes still in commercial use — is built this way. In dye work, isomer purity and residual nitro content are the two specification lines that decide whether a shade reproduces batch to batch.

In meta-aramid fibre

Polycondensation of MPDA with isophthaloyl chloride in a polar aprotic solvent yields poly(m-phenylene isophthalamide). Because the meta linkage kinks the chain, the resulting polymer stays soluble enough to spin and flexible enough to weave, while retaining the thermal stability that makes it the standard for firefighter turnout gear, industrial filtration bags and electrical insulation papers. Fibre producers run the tightest specifications in the market, since any monofunctional impurity terminates a growing chain and depresses molecular weight.

In water-treatment membranes

Nearly every thin-film composite reverse-osmosis element in service is built on an interfacial reaction between an aqueous MPDA solution and trimesoyl chloride in a hydrocarbon phase. The polyamide film that forms at that interface is only a few hundred nanometres thick and does the entire salt rejection. At that scale, trace impurities in the amine translate directly into defects in the film, so membrane producers specify the purest grades available.

In epoxy systems

As an aromatic amine hardener, MPDA delivers higher glass-transition temperatures and better solvent and chemical resistance than typical aliphatic amines. The trade-off is a longer, hotter cure and the handling precautions that come with an aromatic amine. It is specified where service temperature matters more than convenience — filament-wound pipe, electrical laminates, chemically resistant linings.

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 isomer profile — gas chromatography, which resolves the meta, ortho and para isomers and quantifies residual aniline.
• Moisture — Karl Fischer titration. Water matters more than it looks: it interferes with acid-chloride polycondensation and with interfacial membrane casting.
• Melting point — a fast, revealing check. A depressed melting range usually means isomer or moisture contamination before any instrument confirms it.
• Residual nitro compounds — HPLC or GC, to confirm the reduction step ran to completion.
• Metals — iron in particular, as a marker of iron-reduction route material and a catalyst for oxidative darkening in storage.
• Appearance and colour — visual against a retained standard, plus solution colour where the end use is shade-sensitive.

Common Process Problems & Likely Causes

When MPDA 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 HDPE-lined fibre drums or multi-wall paper bags with an inner PE liner.
• Bulk packing. 500 kg and 1000 kg jumbo bags on export pallets, for customers running continuous processes.
• Inert blanketing. Packed under nitrogen where the grade and end use call for it, to limit oxidative darkening in storage and transit.
• Storage. Cool, dry, well-ventilated warehouse, out of direct sunlight, away from oxidising agents and acids. Keep containers tightly closed between withdrawals.
• Shelf life. Typically 12 months in unopened original packing under those conditions. Beyond that, re-test rather than assume.
• Transport classification. UN 1673, Phenylenediamines (solid), Class 6.1, Packing Group III — shipped with full dangerous-goods documentation for sea and air freight.
• Container loading. Palletised and shrink-wrapped for FCL; LCL consolidations arranged where volumes do not justify a full container.

Hazards & Safe Handling

MPDA is a toxic substance and 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.

• Exposure control. Handle in a closed system or under local exhaust ventilation. Avoid dust generation when charging; flakes break down to fines with handling.
• PPE. Chemical-resistant gloves, eye protection, coveralls and respiratory protection appropriate to the task.
• Hygiene. No eating, drinking or smoking in the handling area. Wash thoroughly after handling — the substance is readily absorbed through skin, which is the exposure route most often underestimated.
• Incompatibilities. Strong oxidising agents, strong acids, acid chlorides and nitrous acid.
• Spill response. Collect mechanically without generating dust, place in a labelled closed container, and ventilate the area. Do not wash to drain.
• Environment. Do not allow to enter drains, surface water or groundwater. Dispose through a licensed chemical waste contractor.
• Fire. Combustible solid. Decomposition releases nitrogen oxides — use self-contained breathing apparatus.
• First aid. Remove contaminated clothing immediately, wash skin with soap and water, flush eyes for at least 15 minutes, and seek medical attention with the SDS to hand.

Regulatory & Compliance Notes

MPDA is a long-established industrial 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.
• Import registration. Several territories require the importer to hold a registration or notification before a consignment lands. Start that process early — it is the most common cause of delay at destination.
• 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. UN 1673, Class 6.1, Packing Group III. Declarations prepared for IMDG (sea) or IATA (air) as appropriate to the mode.
• Workplace exposure. Occupational exposure limits vary by jurisdiction; set your controls against the limit in force where the material will be handled.
• Waste and effluent. The substance is very toxic to aquatic life. Effluent containing MPDA must be treated or consigned to licensed disposal, never discharged.

We Supply MPDA Worldwide

Chelora Chemicals is a supplier and export partner, not a single-plant trader. We ship Meta Phenylene Diamine from India to customers across Asia, Europe, the Middle East, Africa, and North and South America, handling the export documentation, dangerous-goods 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 dangerous-goods declaration issued as a complete set.
• Flexible volumes. A single 25 kg 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 MPDA from Chelora

We are an independent sourcing and supply partner. For MPDA that means we match the grade to the application rather than selling whatever happens to be in the tank — different material goes to a dye house than to a membrane producer, and pretending otherwise just moves the problem to your QC lab.

• Documentation on every lot. Batch-specific COA, current SDS and TDS issued with the consignment, not weeks afterward.
• 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 and ongoing contract supply.
• Export experience. Dangerous-goods documentation, packing and labelling handled for sea and air freight to any destination.
• Technical support. Direct access to people who know the chemistry, for questions on isomer limits, storage behaviour or substitution.
• Related intermediates. Ortho and Para Phenylene Diamine, toluidines, anisidines, nitroanilines and the wider dye intermediate range from one supplier.

How ordering works

• Send the enquiry. Product, grade or specification, 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 and dangerous-goods document set, and tracked through to arrival.

Related Dye & Amine Intermediates

Buyers of MPDA 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.