Ortho Nitro Chloro Benzene (ONCB) 1-Chloro-2-nitrobenzene · CAS 88-73-3

What is Ortho Nitro Chloro Benzene (ONCB)?

Ortho Nitro Chloro Benzene, universally shortened to ONCB, is the ortho isomer of chloronitrobenzene, formula C₆H₄ClNO₂. It has a low melting point, around 31–33 °C, so it is handled and shipped as either a pale yellow liquid or a low-melting solid depending on ambient temperature, with a distinct aromatic odour.

Like its para isomer, ONCB carries two reactive handles on the same ring: the nitro group can be reduced to an amine, and the chlorine is activated for nucleophilic substitution. Because the two substituents sit ortho to each other, reduction and substitution chemistry on ONCB builds 1,2-disubstituted aromatics — most importantly o-phenylenediamine, the precursor to benzimidazole-ring fungicides and a range of other heterocyclic chemistry.

Commercially, ONCB is co-produced with PNCB in the same nitration of chlorobenzene and separated from it by fractional crystallisation and distillation, since PNCB's higher melting point makes the two isomers separable at scale.

ONCB is a regulated toxic chemical, handled with the same general precautions as other chloronitrobenzenes: skin absorption, irritancy and toxic-goods transport classification govern its storage and shipping.

Why ONCB specifically

• The specific route to o-phenylenediamine. Amination of the chlorine followed by reduction of the nitro group gives o-phenylenediamine, the building block for benzimidazole fungicides and many heterocyclic pharma intermediates.
• A route to o-anisidine and o-chloroaniline. Substitution or direct reduction gives these further intermediates used across the dye and agrochemical industries.
• A carbofuran intermediate. ONCB is a documented chemical intermediate in the synthesis of the carbamate insecticide carbofuran.
• Co-produced with PNCB. Because both isomers come from the same nitration step, ONCB supply and pricing track PNCB demand as much as ONCB demand itself.

How ONCB is Manufactured

ONCB is made by nitrating chlorobenzene, and the isomer split with PNCB is what drives the separation train that follows.

• Nitration of chlorobenzene. Chlorobenzene is nitrated with a mixed acid (nitric acid and sulfuric acid) under controlled temperature, giving a mixture of ortho-nitrochlorobenzene (ONCB) and para-nitrochlorobenzene (PNCB), with a small amount of the meta isomer.
• Quenching and separation. The reaction mass is quenched, the spent acid is separated for recovery or disposal, and the crude nitrochlorobenzene oil is washed.
• Isomer separation. ONCB and PNCB are separated by fractional crystallisation (PNCB has the higher melting point) and/or distillation, since both isomers have real commercial value.
• Purification. The separated ONCB is further purified by distillation or recrystallisation to the target purity, typically 99% or better.
• Finishing. The purified material is packed as a liquid, or allowed to solidify in low-melting-solid packaging depending on the customer's handling preference.

Typical Commercial Specification

Figures below are representative of commercial-grade ONCB. 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

ONCB's reactivity pattern is what downstream chemists are buying:

• Activated nucleophilic substitution. The ortho-nitro group activates the chlorine for substitution by ammonia, amines and alkoxides, enabling routes to o-phenylenediamine, o-anisidine and related 1,2-disubstituted aromatics.
• Clean nitro reduction. Catalytic or chemical reduction converts the nitro group to an amine without disturbing the chlorine, a route to o-chloroaniline.
• Isomer sensitivity. Downstream selectivity and impurity profiles depend on how much para- and meta-isomer is carried into the reaction, which is why isomer purity is specified tightly.
• Combustible, low-melting solid. ONCB is combustible and, because it melts close to ambient temperature, can shift between solid and liquid states in storage, which handling procedures should account for.

ONCB, Its Isomers and Related Intermediates

ONCB is one of three nitrochlorobenzene isomers produced from the same nitration step, and buyers often need to distinguish between them and nearby intermediates.

Stated plainly: the choice between ONCB and PNCB is not a substitution decision but a structural one — each isomer leads to a different family of downstream products, and a process built around one cannot simply switch to the other.

Industries We Supply ONCB To

The same low-melting intermediate feeds an agrochemical plant, a dye-intermediate works and a rubber-chemical producer. What changes is the downstream chemistry and the documentation each requires.

Where ONCB is Used

ONCB is bought almost entirely as a chemical intermediate rather than a standalone product. These are the downstream chains our customers build from it.

In agrochemical and benzimidazole chemistry

ONCB is converted to o-phenylenediamine by amination and reduction, and the diamine is then cyclised to build the benzimidazole ring that underpins fungicides such as carbendazim-type actives and a range of benzimidazole-based pharmaceuticals. Isomer purity matters here because para- and meta-isomer carry-over generates off-target by-products that complicate purification of the final active ingredient.

In dye and rubber-chemical manufacture

Nucleophilic substitution of the chlorine with an alkoxide, followed by reduction of the nitro group, builds o-anisidine — a dye and pigment intermediate — while direct reduction gives o-chloroaniline for further dye and rubber-chemical synthesis.

Quality Control & Testing

Every lot is released against a batch-specific Certificate of Analysis, with isomer content reported alongside purity because it governs downstream selectivity.

• ONCB content — by gas chromatography, the primary grade measure.
• Isomer ratio (para, meta) — reported because carry-over changes downstream impurity profiles.
• Melting point — a fast indicator of purity and isomer content.
• Residual chlorobenzene — reported as an unreacted-feedstock impurity.
• Moisture — measured to limits relevant to handling and downstream reaction stoichiometry.
• Colour (molten) — an indicator of thermal history and trace contamination.

Common Process Problems & Likely Causes

When ONCB causes trouble, it is usually isomer carry-over, moisture or physical-state handling issues. This table is the shortcut our technical desk works through before anyone opens a complaint file.

Packaging, Storage & Shipping

• Standard packing. Drums or ISO tank containers for liquid; HDPE-lined bags for solid, depending on ambient temperature and your preference.
• Temperature awareness. Because ONCB melts close to ambient temperature (31–33 °C), expect it to shift between solid and liquid states in transit and storage; this is normal and does not indicate degradation.
• Material compatibility. Avoid contact with strong oxidisers and strong reducing agents.
• Segregation. Keep apart from food, feed and incompatible chemicals in storage and transport, per its toxic classification.
• Shelf life. Stable in sealed, dry packaging; moisture ingress is the main degradation route.
• Transport classification. UN 1578, chloronitrobenzenes, Class 6.1 (toxic), packed per ADR, IMDG, IATA and DOT rules.

Hazards & Safe Handling

ONCB is a toxic chemical that is absorbed through skin as well as by inhalation, and is an irritant to skin and eyes, which makes closed handling and good PPE central to safe use.

• Toxicity. Exposure must be kept as low as technically possible, with closed handling and local exhaust ventilation.
• Skin absorption. Like other chloronitrobenzenes, ONCB is absorbed through intact skin. Impermeable gloves and clothing are required.
• Irritancy. Causes skin and eye irritation on direct contact; rinse thoroughly with water and seek medical advice if symptoms persist.
• Dust and combustibility. Avoid generating dust when handling the solid form; the material is combustible and can release toxic fumes if it burns.
• PPE. Chemical-resistant gloves, goggles or a face shield, and respiratory protection appropriate to the dust or vapour exposure.
• Environment. Avoid release to waterways and follow local effluent and waste-disposal rules.

Regulatory & Compliance Notes

ONCB is a regulated toxic chemical with specific occupational and transport rules. 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. Typically classified as acutely toxic with skin and eye irritation; the SDS carries the full hazard statements for your grade.
• Occupational exposure regulation. Many jurisdictions apply skin-notated exposure limits for chloronitrobenzenes and require good industrial hygiene practice.
• REACH and chemical inventories. Registered under EU REACH and listed on major chemical inventories.
• Dangerous goods transport. UN 1578, chloronitrobenzenes, Class 6.1 (toxic). ADR, IMDG, IATA and DOT requirements apply to packing, labelling and routing.
• HS code. Commonly declared under the nitrated-and-halogenated hydrocarbon heading; confirm the exact tariff line with your customs broker for your jurisdiction.
• Quality agreements. Agrochemical and pharma producers commonly expect documented isomer, moisture and colour limits and change control. Tell us what your agreement requires.

We Supply ONCB Worldwide

Chelora Chemicals is a supplier and export partner, not a single-plant trader. We ship ONCB from India and from partner sources to customers across Asia, Europe, the Middle East, Africa, and North and South America, handling the export documentation, toxic-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 ports arranged where toxic-goods rules and routing allow.
• Documentation. Commercial invoice, packing list, certificate of origin, COA, SDS and the Class 6.1 transport declaration issued as a complete set.
• Flexible volumes. From drum and bag 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 ONCB from Chelora

We are an independent sourcing and supply partner. For ONCB that means settling three things at enquiry: the isomer purity your process tolerates, whether you need it as a liquid or solid, and the toxic-goods documentation that moves it legally across your shipping lane.

• Documentation on every lot. Batch-specific COA with ONCB content, isomer ratio, melting point and moisture, plus SDS and Class 6.1 transport paperwork.
• Analysis before commitment. Representative analysis shared ahead of a commercial order so your lab can qualify the material.
• Physical form. Liquid or low-melting solid packing, matched to your handling setup.
• Quantities. Drum and bag trial quantities through to full bulk shipments on contract supply.
• Inspection. Independent third-party inspection available at loading when the contract requires it.
• Related intermediates. PNCB, o-nitroaniline and o-chloroaniline alongside ONCB from one supplier.

How ordering works

• Send the enquiry. Isomer purity, 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, physical form and a sample COA, normally within one working day.
• Qualify the supply. For first orders or pharma-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 and Class 6.1 transport document set, and tracked through to arrival.

Related Nitroaromatics & Aniline Intermediates

Buyers of ONCB often source the para isomer or downstream aniline intermediates alongside it — agrochemical and dye producers typically buy several of these in the same programme. Consolidating them cuts freight cost and gives you a single point of contact for documentation.