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

What is Meta Phenylene Diamine (MPDA)?

Meta Phenylene Diamine is benzene carrying two amine groups in the 1,3-positions, and that geometry is the reason it exists as a separate commercial product rather than as a by-product of its isomers. The meta arrangement means the two nitrogens are not electronically conjugated with each other through the ring the way they are in the para isomer. In practical terms it gives a diamine that is reactive but not indiscriminately so, that forms polymers with a kinked rather than rod-like backbone, and that resists oxidation noticeably better than para-phenylenediamine does.

The largest single outlet is meta-aramid fibre. Polycondensed with isophthaloyl chloride, MPDA gives poly(m-phenylene isophthalamide) — the polymer behind flame-resistant protective clothing, high-temperature filtration media, electrical insulation paper and honeycomb core. The meta linkage is what makes this fibre what it is: the kinked chain cannot pack into the extended, highly crystalline structure that para-aramid forms, so the result is a fibre with modest tensile strength but outstanding thermal stability, inherent flame resistance and textile processability. Where para-aramid is chosen for strength, meta-aramid is chosen for heat, and the isomer of the diamine is the whole difference.

Dyestuff chemistry is the other historic pillar. Both amine groups diazotise and couple readily, and the meta relationship makes MPDA an effective bifunctional coupling component, so it appears throughout direct, acid and disperse dye ranges and in several pigment classes. It is also a long-standing building block for Bismarck Brown and related colourants, and for a range of fluorescent and functional dyes. Separately, MPDA is used as an epoxy curing agent where high glass-transition temperature and chemical resistance matter more than colour stability, as a urethane elastomer chain extender, and as an intermediate for polyimides, ion-exchange resins, rubber chemicals, corrosion inhibitors and petroleum additives.

The practical handling issue with MPDA is colour. Like most aromatic diamines it oxidises on air exposure, developing yellow then brown colour that is not reversible, and it does so faster when warm. For fibre and dye applications where colour is part of the specification, that means nitrogen-blanketed storage, short residence times in a melt tank and a disciplined approach to part-used packaging. Chelora reports colour on the melt on every batch precisely because it is the figure that tells you the thermal and oxidative history of the material you have received.

What fibre, dye and resin producers specify

• Isomer purity ortho- and para-phenylenediamine controlled to low levels, because both behave differently in polycondensation and in coupling.
• High assay for polymer use Aramid polycondensation is a stoichiometric reaction that builds molecular weight — any monofunctional impurity caps a chain and costs degree of polymerisation.
• Low colour Reported on the melt. Aromatic diamines darken irreversibly on air exposure, and in fibre and dye work colour carries straight through to the product.
• Low moisture Water consumes acid chloride in aramid synthesis and interferes with anhydrous epoxy and isocyanate chemistry.
• Low iron and ash Trace metals catalyse darkening and can affect dye shade and polymer colour.
• Form that suits the process Flake, prill or molten bulk. Dust handling and melt management trade off against each other and the right answer depends on your plant.

How MPDA is Manufactured

MPDA is made by reducing m-dinitrobenzene. The meta substitution pattern is established in the nitration step upstream, where the first nitro group directs the second to the meta position, so the isomer distribution is inherited rather than separated out later.

• Dinitration of benzene Benzene is nitrated to nitrobenzene and then further nitrated. The nitro group is meta-directing, so the second substitution gives predominantly m-dinitrobenzene with small amounts of the ortho and para isomers.
• Isomer purification The crude dinitrobenzene is purified by crystallisation or distillation. This is the step that sets the final isomer specification, since the isomers are not separated after reduction.
• Catalytic hydrogenation Both nitro groups are hydrogenated to primary amines over a supported metal catalyst. The reaction is strongly exothermic and heat removal governs the plant design.
• Catalyst recovery and dehydration Catalyst is separated and recovered, and the water of reaction removed. Residual water matters directly to downstream aramid and epoxy users.
• Distillation and forming The diamine is distilled under vacuum to remove light and heavy fractions and to control colour, then filled molten, or flaked or prilled and bagged.

Typical Commercial Specification

Typical fibre-grade specification. Verify against your own current COA before publishing these figures or writing them into a purchase specification.

Physical & Chemical Properties

Reactivity in practice

MPDA is a difunctional primary aromatic amine, and its two industrial pillars — polycondensation and diazo coupling — both follow directly from that. The meta geometry governs how the resulting chains and chromophores are shaped.

• Polycondenses with acid chlorides and dianhydrides With isophthaloyl chloride it gives meta-aramid; with dianhydrides, polyamic acids and polyimides. The kinked backbone is a direct consequence of the 1,3-substitution.
• Cures epoxy resins Reacts with epoxide groups to give a highly crosslinked network with high glass-transition temperature and good chemical resistance. Aromatic cure, so colour stability is limited.
• Diazotises and couples Both amine groups undergo diazotisation and azo coupling, which is the basis of its long use as a bifunctional dye and pigment intermediate.
• Reacts with isocyanates Chain extender and curative chemistry in urethane elastomers, giving urea hard segments.
• Oxidises on air exposure Develops yellow then brown colour irreversibly, faster when warm. The reason nitrogen blanketing is standard rather than optional.
• Attacks copper, brass and aluminium Use stainless steel or suitably lined equipment throughout, including valves and instrument tails. Trace copper also accelerates darkening.

MPDA Compared With The Other Phenylenediamine Isomers

The three phenylenediamine isomers share a formula and almost nothing else. Where the two amine groups sit on the ring decides whether they are electronically coupled to each other, how readily the molecule oxidises, what shape a polymer built from it takes, and — as it turns out — how each one is regulated. Buying the wrong isomer is not a grade error; it is a different product.

Put plainly: ortho gives you heterocycles, para gives you strength and redox chemistry, and meta gives you heat resistance and colour. The aramid case is the clearest illustration — the same polycondensation chemistry with the para isomer produces a high-strength structural fibre, and with the meta isomer produces a flame-resistant textile fibre. Nothing about the processing changes; only the position of one amine group.

Industries We Supply MPDA To

MPDA reaches the market almost entirely through downstream products — fibres, dyes, resins — so the industries below are the ones that consume what is made from it.

Where MPDA is Used

Three applications account for most consumption, and the technical detail that matters sits inside them rather than across a long list.

Meta-aramid polycondensation and why purity is non-negotiable

Aramid synthesis is a step-growth polycondensation, which means molecular weight is built from near-perfect stoichiometry between a diamine and a diacid chloride. Any monofunctional impurity terminates a growing chain, and in step-growth polymerisation a small amount of chain terminator costs a disproportionate amount of degree of polymerisation — and therefore of fibre strength. Water is worse than an impurity, because it hydrolyses the acid chloride and destroys the stoichiometry outright. This is why fibre-grade MPDA is specified at 99.5% minimum with moisture at 0.2% maximum and isomers individually controlled, and why fibre producers care about the certificate rather than the nominal grade. The para isomer is a particular concern here: it is difunctional, so it polymerises happily, but it builds a rod-like segment into a polymer whose entire design depends on being kinked.

Epoxy cures: what you gain and what you give up

MPDA-cured epoxies reach high glass-transition temperatures with excellent chemical and solvent resistance, which is why the combination persists in tooling resins, filament-wound pressure vessels and chemical-resistant linings. The trade-offs are real and worth stating. The diamine is a solid, so it must be melted or dissolved and the mix handled warm; pot life at cure temperature is short; and because the cure is aromatic, the finished part absorbs UV and yellows over time. If colour stability matters more than peak heat resistance, a cycloaliphatic hardener such as IPDA is the better answer and the trade is a lower glass-transition temperature. You cannot have maximum heat resistance and water-white colour stability from the same amine class.

Managing colour: the one handling issue that matters

MPDA oxidises in air to yellow and then brown, and the change does not reverse. Warmth accelerates it sharply, so a melt tank held hot in air will cost colour by the hour. The controls are not complicated but they do need to be deliberate: blanket melt tanks and part-used packaging with nitrogen, hold at the lowest workable temperature with the shortest practical residence, keep material out of direct light, eliminate copper from the system since it catalyses the oxidation, and buy in pack sizes you will actually consume. For dye and fibre work a darkened batch may be unusable even though its assay is still perfectly in specification, which is exactly why we report colour on the melt rather than treating it as cosmetic.

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 by GC Confirms purity against the fibre-grade specification, where chain-terminating impurities cost molecular weight directly.
• Isomer distribution by GC ortho and para quantified individually, because they behave differently in polycondensation and coupling.
• Moisture by Karl Fischer Controlled at fill and protected in transit. Water hydrolyses acid chloride and wrecks aramid stoichiometry.
• Colour on the melt (APHA) Reports the oxidative and thermal history of the batch, which matters as much as assay in dye and fibre work.
• Iron and trace metals Held low, since they catalyse darkening and can shift dye shade.
• Melting point Confirms identity and the absence of significant isomer or oligomer drift.
• Ash and insolubles Guards against particulates that show as defects in spun fibre and cast film.
• Retained samples under nitrogen Held against every batch so a fibre, dye or cure problem can be traced to the material or ruled out.

Common Process Problems & Likely Causes

Problems traced back to MPDA are nearly always colour, moisture or isomer content rather than the amine chemistry itself. The sequence below is how we work through them with customers.

Packaging, Storage & Shipping

• 25 kg lined bags Flake or prill in moisture-barrier liners. Prill dusts noticeably less than flake where handling is manual.
• 200 kg drums For users melting a full drum into a holding tank, nitrogen-blanketed on request.
• Heated isotanks Molten bulk with closed transfer for continuous fibre and dye producers.
• Storage Cool, dry, dark, tightly closed and nitrogen-blanketed where colour is part of the specification. Away from oxidisers and acids.
• Materials of construction Stainless steel or suitably lined vessels and lines. No copper, brass, bronze or aluminium anywhere in the system, valves and instrument tails included.
• Shelf life Typically 12 months in unopened, blanketed original packing. Beyond that, re-test colour and assay rather than assume.

Hazards & Safe Handling

MPDA is acutely toxic by several routes, is a skin sensitiser and is very toxic to aquatic life. It is also handled hot in most applications. The controls below reflect normal industrial practice; always work from the current Safety Data Sheet and your own site risk assessment and occupational health requirements.

• Acute toxicity by several routes. MPDA is classified as acutely toxic orally, dermally and by inhalation. Exposure control has to address all three — skin contact is not a secondary concern here, and gloves are as important as respiratory protection.
• Skin sensitisation. MPDA is a recognised skin sensitiser. Once a worker is sensitised the response can be triggered by exposures far below those that caused it, so the objective is to prevent first contact rather than to manage repeated low-level exposure.
• Closed handling and local extraction. Design open handling out where you can: pre-weighed charges, closed transfer from melt tank, local exhaust at bag slitting, charging and sampling points. General ventilation alone is not adequate at open transfer.
• Dust control. Flake and prill generate fine dust that is both an inhalation and a skin-contact route. Use extraction at handling points, never dry-sweep spilled solid, and prefer prill over flake where handling is manual.
• Hot material. Molten MPDA is handled well above ambient. Insulate lines and valves, use a face shield at sampling points, and never open a sight glass or sample valve on a hot line without full PPE.
• PPE. Impervious gloves with a documented breakthrough time for aromatic amines, chemical goggles or face shield, and coveralls giving full skin coverage. Change contaminated gloves rather than washing them.
• Aquatic toxicity and spill response. Very toxic to aquatic organisms with long-lasting effects. Bund storage, contain spills, collect solid material for licensed disposal and keep everything out of drains and surface water. Do not flush away.
• First aid. Remove contaminated clothing immediately and wash skin thoroughly with soap and water. Flush eyes with running water for at least fifteen minutes. Seek medical attention after any significant skin, eye or inhalation exposure, and for molten contact cool with water without attempting to remove adhered material.

Regulatory & Compliance Notes

MPDA is not subject to the authorisation regimes that govern some aromatic amines, but it does carry specific consumer-product prohibitions alongside its occupational classification. The notes below are orientation, not a compliance opinion.

• Occupational classification. Acute toxicity and skin sensitisation classifications drive exposure control, health surveillance where national law requires it, and the training and PPE programme at the user's site. Confirm what applies in your jurisdiction before material arrives.
• Prohibited in cosmetics. m-Phenylenediamine and its salts are prohibited in cosmetic products in the EU and on equivalent lists in several other markets. Despite its historical association with hair-dye chemistry, it has no permitted cosmetic use in those jurisdictions — note that the para isomer is treated differently and is restricted rather than prohibited.
• Azo colourant restrictions. Textile and leather articles are subject to restrictions on colourants that can release certain aromatic amines, with specified test methods and detection limits. Which amines are listed varies by regime, so confirm the position for your product and market with your own adviser rather than assuming.
• Inventory status. Listed on the principal chemical inventories in the major importing regions. Ask us for the inventory confirmation relevant to your destination country.
• Transport classification. UN 1673, Phenylenediamines, Class 6.1, Packing Group III. Molten shipments fall additionally under elevated-temperature provisions. Confirm the current entry on the SDS before each shipment.
• Import registration and end use. Several territories require the importer to hold a registration or notification before a consignment lands, and for some destinations we will ask for a short statement of intended use before shipping. Starting that early is the single best way to avoid delay at destination.

We Supply MPDA Worldwide

Chelora Chemicals is a supplier and export partner, not a single-plant trader. We ship Meta Phenylene Diamine (MPDA) 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 drum for laboratory qualification, through LCL consolidations, up to repeat full 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

MPDA is bought for quite different reasons by fibre producers, dye houses and resin formulators, and the right grade and format depend on which you are.

• Tell us the application Aramid polycondensation, dye coupling and epoxy cure put the emphasis on different parts of the specification. Knowing which lets us match grade rather than quote a generic one.
• Specify the isomers individually If your chemistry is sensitive to the para or ortho isomer, write individual limits into the specification rather than relying on a total-impurity figure.
• Decide flake, prill or molten Dust exposure and thermal colour management trade off against each other. We will recommend based on how you charge rather than defaulting to bags.
• Ask for nitrogen-blanketed packing For colour-sensitive work this does more for usable shelf life than anything else, and it is available on drums and bulk.
• Batch documentation COA with assay, individual isomer figures, moisture, colour and iron, plus the current SDS and TDS with every consignment.
• Supply continuity Scheduled call-offs against a contract with inventory cover, so a fibre line or a dye campaign is not exposed to spot availability.

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 Amines & Intermediates

Related aromatic amines and the aliphatic and cycloaliphatic amines we supply alongside them for polymer, dye and resin chemistry.