CHLOROTHALONIL

Chlorothalonil is a broad-spectrum, non-systemic chloronitrile fungicide and antimicrobial active ingredient with preventive activity against numerous fungal diseases.
The molecule remains on treated surfaces, where its multisite reactivity interferes with fungal thiols, glutathione and several thiol-dependent enzymes before infection becomes established.
Chlorothalonil is commercially important in authorised crop-protection, turf, ornamental and material-preservation applications, while its regulatory status differs substantially between jurisdictions.

CHEMICAL IDENTITY AND COMMON NAMES

Chlorothalonil is the common name for a tetrachlorinated aromatic dinitrile whose two nitrile groups occupy the 1 and 3 positions of the benzene ring.
The preferred systematic name is 2,4,5,6-tetrachlorobenzene-1,3-dicarbonitrile, while tetrachloroisophthalonitrile remains the best-established technical alternative.
The abbreviations TPN and m-TCPN refer to the same active ingredient and should not be confused with Chlorothalonil metabolites or related chlorinated benzonitriles.

Synonyms and Common Names: Chlorothalonil (ISO), Chlorthalonil, Clorotalonil, Tetrachloroisophthalonitrile, 2,4,5,6-Tetrachloroisophthalonitrile, Perchloroisophthalonitrile, Tetrachlorobenzene-1,3-dicarbonitrile, 2,4,5,6-Tetrachlorobenzene-1,3-dicarbonitrile, 2,4,5,6-Tetrachloro-1,3-benzenedicarbonitrile, 1,3-Benzenedicarbonitrile, 2,4,5,6-tetrachloro-, Isophthalonitrile, tetrachloro-, 1,3-Dicyanotetrachlorobenzene, 1,3-Dicyano-2,4,5,6-tetrachlorobenzene, 2,4,5,6-Tetrachloro-1,3-dicyanobenzene, 2,4,5,6-Tetrachloro-3-cyanobenzonitrile, 2,4,5,6-Tetrachloro-m-benzenedinitrile, Tetrachloro-m-phthalodinitrile, Tetrachloro-meta-phthalo-dinitrile, m-Tetrachlorophthalonitrile, meta-Tetrachlorophthalonitrile, meta-Tetrachlorophthalodinitrile, 2,4,5,6-Tetrachloroisophthalodinitrile, m-TCPN, meta-TCPN, TPN

TECHNICAL IDENTIFICATION

CAS Number: 1897-45-6
EC / EINECS Number: 217-588-1
CIPAC Number: 288
CLP Index Number: 608-014-00-4
Molecular Formula: C8Cl4N2
Molar Mass: 265.91 g/mol
Preferred IUPAC Name: 2,4,5,6-Tetrachlorobenzene-1,3-dicarbonitrile
Chemical Class: Chloronitrile fungicide and halogenated aromatic dinitrile
Fungicide Resistance Group: Multisite Group M05
InChIKey: CRQQGFGUEAVUIL-UHFFFAOYSA-N
Canonical SMILES: ClC1=C(Cl)C(C#N)=C(Cl)C(C#N)=C1Cl

PHYSICAL AND CHEMICAL PROPERTIES

Physical State: Crystalline solid
Appearance of Pure Chlorothalonil: Colourless to white crystals
Appearance of Technical Chlorothalonil: Off-white to light-grey powder or granules
Odour: Odourless when pure, with a slightly pungent odour possible in technical material
Melting Point: 250–251 °C
Reported Boiling Point: Approximately 350 °C at 101.3 kPa
Relative Density: Approximately 1.8 at 25 °C
Vapour Pressure: Approximately 7.6 × 10⁻⁵ Pa at 25 °C
Water Solubility: Approximately 0.6–1.2 mg/L at 25 °C
Solubility in Xylene: Approximately 80 g/L
Solubility in Dimethylformamide: Approximately 30 g/L
Solubility in Acetone: Approximately 20 g/L
Solubility in Dimethyl Sulfoxide: Approximately 20 g/L
Partition Coefficient: Log Kow approximately 2.94 at 25 °C
Flammability: Non-flammable under standard test conditions
Explosive Properties: Non-explosive
Volatility: Very low under normal handling and application conditions
Hydrolytic Stability: Stable in acidic and neutral water, with progressively faster degradation under alkaline conditions

The very low water solubility of Chlorothalonil makes concentrated true aqueous solutions impractical and favours finely divided suspension formulations.
The low vapour pressure limits evaporative loss, while strong affinity for organic matter promotes retention on foliage, soil particles, suspended solids and dry coating films.
Prolonged alkaline exposure accelerates hydrolysis, making formulation pH and compatibility with high-pH mineral systems important technical considerations.

FUNCTIONAL CHARACTERISTICS

Chlorothalonil functions as a contact protectant and does not provide meaningful systemic movement through plant tissues.
Uniform preventive coverage is therefore central to performance because untreated growth and tissue formed after application are not protected by redistribution from older surfaces.
The active deposit inhibits spore germination, zoospore movement and early infection processes rather than curing established internal infections.

The electron-deficient chlorinated aromatic ring reacts with nucleophilic sulfhydryl groups in fungal glutathione, amino acids, peptides and proteins.
Glutathione depletion is followed by inhibition of thiol-dependent glycolytic and respiratory enzymes, disrupting several essential metabolic sites simultaneously.
This multisite mechanism places Chlorothalonil in Group M05 and gives the active ingredient a low inherent risk of selecting resistance compared with single-site fungicides.

Rainfastness, adhesion and redistribution are determined largely by the finished formulation rather than by systemic uptake.
Chlorothalonil is consequently used preventively and can complement authorised single-site fungicides in resistance-management programs.
The combination of surface persistence and multisite activity is particularly useful where repeated infection cycles create sustained disease pressure.

PRODUCTION AND TECHNICAL MATERIAL

The principal industrial route to Chlorothalonil is catalytic chlorination of isophthalonitrile, also known as 1,3-dicyanobenzene.
Vaporised isophthalonitrile is contacted with chlorine at elevated temperature in a controlled catalytic reactor, replacing the four aromatic hydrogen atoms with chlorine and generating hydrogen chloride as a reaction by-product.
Reaction temperature, chlorine distribution, residence time and catalyst condition are managed to maximise tetrachlorination without excessive formation of overchlorinated by-products.

The reactor stream is cooled to recover crude Chlorothalonil, followed by purification, drying and particle-size adjustment.
Purification may employ controlled condensation, thermal separation or recrystallisation to reduce incompletely chlorinated nitriles, pentachlorobenzonitrile, residual isophthalonitrile and other process-related impurities.
The purified solid is milled or wet-milled to meet the particle-size requirements of the intended formulation.

Hexachlorobenzene and decachlorobiphenyl are critical relevant impurities in technical Chlorothalonil.
An established technical reference specification uses a minimum Chlorothalonil purity of 985 g/kg, a maximum hexachlorobenzene content of 0.04 g/kg and a maximum decachlorobiphenyl content of 0.03 g/kg.
Control of these trace chlorinated impurities is a central element of technical-equivalence assessment, supplier qualification and environmental compliance.

APPLICATIONS AND INDUSTRIES

Preventive crop-protection programs

Chlorothalonil is employed as a preventive foliar fungicide on authorised food and non-food crops exposed to leaf spots, blights, rusts, anthracnose, downy mildew and other susceptible fungal diseases.
The protective deposit limits germination and penetration at the crop surface, making coverage before infection more important than curative timing.
Registered labels determine the authorised crop, disease, application interval, maximum seasonal amount, buffer distance and preharvest interval.

Potatoes, peanuts and field crops

Chlorothalonil has established uses in potato programs directed at early and late blight and in peanut programs directed at leaf-spot diseases.
Authorised cereal and field-crop uses employ the same multisite protectant action against susceptible foliar pathogens.
The active ingredient is particularly useful as a resistance-management partner because several fungal metabolic targets are affected at the same time.

Vegetable, fruit and tree crops

Chlorothalonil has been used on authorised tomatoes, onions, cucurbits, herbs, berries, fruit trees and nut trees to protect exposed tissue against susceptible blights, mildews, rots and leaf spots.
The lack of systemic redistribution requires complete spray coverage of infection-prone surfaces and renewed protection of developing growth.
Crop-specific residue limits and harvest restrictions are integral to the selection of a lawful finished product.

Turf, ornamentals and managed landscapes

Chlorothalonil supports preventive management of susceptible leaf spots, anthracnose, blights and other fungal diseases on authorised non-residential turf, sod, golf-course surfaces, ornamental plants, shrubs and nursery stock.
Formulations intended for these sites prioritise uniform spray deposition, suspension stability and resistance to wash-off.
Use on residential turf or other public-access sites is governed by the exact local registration and label restrictions.

Coatings and construction materials

Chlorothalonil functions as an antimicrobial dry-film preservative in authorised paints, coatings, plasters, sealants, caulks, adhesives and selected concrete or masonry products.
Low water solubility helps retain the active ingredient within the cured film, where Chlorothalonil suppresses fungal defacement and mildew growth on exposed surfaces.
Particle dispersion, colour contribution, alkaline stability and leaching behaviour are important when Chlorothalonil is incorporated into mineral or polymeric matrices.

Wood, lumber and industrial material preservation

Chlorothalonil is incorporated into authorised wood and lumber treatments to inhibit surface fungi and protect stored or installed materials from fungal staining and deterioration.
Industrial preservative systems require uniform distribution through the coating or treatment layer without excessive dust generation during manufacture.
Authorised antimicrobial programs may also include selected metals, building components and dry-end papermaking applications.

Analytical and environmental laboratories

High-purity Chlorothalonil is used for chromatographic calibration, residue-method development, environmental-fate studies, toxicological research and formulation analysis.
Separate reference materials for 4-hydroxychlorothalonil and other transformation products support soil, surface-water, groundwater and food-residue monitoring.
Isotopically labelled material can serve as an internal standard in trace-level mass-spectrometric methods.

GRADE SELECTION AND PRODUCT SUITABILITY

Technical Chlorothalonil is selected for authorised pesticide or antimicrobial formulation, with active assay and relevant-impurity control forming the primary chemical criteria.
Hexachlorobenzene and decachlorobiphenyl limits deserve explicit attention because total assay alone does not demonstrate an acceptable impurity profile.
Manufacturing-process consistency, colour, water content, insoluble residue and residual isophthalonitrile also contribute to technical-material evaluation.

Formulation-grade Chlorothalonil requires a physical form matched to suspension concentrate, water-dispersible granule or wettable-powder production.
Particle-size distribution affects milling energy, suspensibility, wet-sieve residue, sedimentation, nozzle passage, surface coverage and biological performance.
A narrow, controlled distribution reduces coarse residue while avoiding unnecessary ultrafine dust.

Analytical-grade Chlorothalonil is selected for identity testing, purity assignment, method validation and instrument calibration.
Certified solutions provide convenient calibration for routine residue analysis, while neat reference material is suitable for preparation of independent stock solutions.
Metabolite-specific standards are required because parent Chlorothalonil does not represent the chromatographic or toxicological behaviour of its transformation products.

FORMULATION AND PROCESS CONSIDERATIONS

Suspension concentrates, water-dispersible granules and wettable powders are the principal agricultural formulation types for Chlorothalonil.
The low aqueous solubility means that performance depends on maintaining finely divided solid particles rather than dissolving the active ingredient in the spray water.
Wetting agents and dispersants must rapidly deagglomerate the particles and maintain a uniform suspension across different water hardness and dilution conditions.

Suspension concentrates require controlled wet milling, rheology modification, antifoam management, microbial preservation of the water phase and protection against sediment compaction.
Important tests include particle-size distribution, viscosity, pourability, spontaneity of dispersion, suspensibility, wet-sieve residue, redispersibility, freeze-thaw stability and accelerated storage stability.
Crystal growth and irreversible settling can reduce dose uniformity and obstruct filters or spray nozzles.

Water-dispersible granules reduce airborne powder during handling and must disintegrate rapidly without producing persistent coarse fragments.
Granule strength must balance resistance to shipping abrasion with fast dispersion in the spray tank.
Wettable powders require effective wetting, low persistent foam, controlled dustiness and dependable suspensibility after dilution.

Registered combination formulations may pair Chlorothalonil with systemic or locally systemic fungicides to combine preventive multisite protection with complementary internal activity.
Chemical compatibility, formulation pH, particle interactions and storage behaviour must be established for the complete composition.
Strongly alkaline media are avoided because alkaline hydrolysis can reduce active content during storage.

Dry-film preservative concentrates require uniform incorporation into the coating, adhesive or sealant matrix.
Premixing or dispersion concentrates can improve distribution and limit direct handling of dry technical powder.
High-pH plasters and cementitious systems require particular attention to active stability, while exterior products require leaching controls that protect aquatic environments.

ENVIRONMENTAL FATE AND TRANSFORMATION PRODUCTS

Parent Chlorothalonil has low water solubility and strong soil adsorption, with reported soil organic-carbon partition coefficients spanning approximately 900–14,000 mL/g.
The parent compound therefore has low mobility in many soils but can reach surface water through spray drift, erosion and runoff of particle-bound residues.
Once in water, Chlorothalonil associates strongly with suspended solids and sediment and can degrade through photolytic, hydrolytic and microbial pathways.

Aerobic soil degradation commonly occurs over days to several weeks, with reported half-lives frequently within approximately 10–40 days.
Persistence increases where low temperature, limited microbial activity or other site conditions slow transformation.
Hydrolysis is slow in acidic and neutral water and becomes faster as pH rises into the alkaline range.

A major transformation product is 4-hydroxychlorothalonil, also identified as SDS-3701 or R182281.
This metabolite is more mobile and persistent in soil than parent Chlorothalonil and can contribute to groundwater exposure.
Additional groundwater metabolites include R417888, R419492, R471811, R611968, SYN507900, SYN548008 and SYN548580.
Environmental monitoring programs therefore require analytical coverage beyond the parent active ingredient.

Chlorothalonil is very toxic to aquatic organisms and can produce long-lasting effects.
Spray drift, runoff, process wastewater, contaminated rinsate and firefighting water must be prevented from reaching surface water, groundwater and drainage systems.
Containment is especially important during technical-material formulation, coating manufacture, equipment cleaning and spill response.

QUALITY, SPECIFICATIONS AND DOCUMENTATION

Chromatographic assay establishes Chlorothalonil content and separates manufacturing-related nitriles from the principal component.
Trace-level gas chromatographic methods are used for hexachlorobenzene, decachlorobiphenyl and other volatile or semi-volatile chlorinated impurities.
Identity can be supported by infrared spectroscopy, mass spectrometry and comparison of chromatographic retention behaviour.

Technical-material review should include Chlorothalonil assay, hexachlorobenzene, decachlorobiphenyl, other related substances, water, insoluble matter, appearance and particle size.
Formulation evaluation additionally covers active-content tolerance, pH, density, wetting, dispersibility, suspensibility, wet-sieve residue, persistent foam and storage stability.
Dry-film preservative grades benefit from colour, dispersion and matrix-compatibility data relevant to the intended coating or construction material.

A Certificate of Analysis records the batch-specific assay and controlled impurities.
A Safety Data Sheet communicates classification, exposure controls, transport information and emergency measures, while a Technical Data Sheet describes the commercial form and relevant performance parameters.
Pesticide and antimicrobial procurement also requires manufacturing-origin information, technical-equivalence documentation and destination-market regulatory records.

SAFETY AND REGULATORY CONSIDERATIONS

The harmonised hazard profile of Chlorothalonil includes H330, fatal if inhaled, H335, may cause respiratory irritation, H318, causes serious eye damage, H317, may cause an allergic skin reaction, H351, suspected of causing cancer, and H410, very toxic to aquatic life with long-lasting effects.
The inhalation classification makes dust prevention and closed transfer particularly important for technical powder and wettable-powder operations.
Repeated or sensitising skin exposure and direct eye contact must also be prevented.

Suitable controls include enclosed charging, local exhaust ventilation, high-efficiency dust collection, chemical-resistant gloves, protective clothing and sealed eye or face protection.
Respiratory protection appropriate for highly toxic particulate exposure is required when containment and ventilation do not fully prevent inhalation.
Eating, drinking and smoking are excluded from Chlorothalonil handling areas.

The approval of Chlorothalonil as a plant-protection active substance was not renewed in the European Union in 2019.
Member States were required to withdraw plant-protection authorisations by 20 November 2019, and the final grace periods expired by 20 May 2020.
The decision reflected unresolved concerns involving groundwater metabolites, aquatic organisms, possible genotoxicity and the assessment of residues in drinking-water sources.

Chlorothalonil remains registered for specified conventional and antimicrobial uses in the United States under an interim registration decision issued in January 2025.
The associated measures include reduced maximum annual amounts, aquatic and conservation-area buffers, restrictions for saturated soils, controls for groundwater-vulnerable areas and additional occupational respiratory protection for certain antimicrobial uses.
Other countries apply their own active-substance approvals, crop registrations, residue limits, antimicrobial-use conditions and import or export controls.

FIRST AID

Inhalation: Move the exposed person immediately to fresh air, keep the person at rest and obtain emergency medical attention because inhaled Chlorothalonil can cause severe respiratory effects.
Skin Contact: Remove contaminated clothing and wash the affected skin thoroughly with soap and water, then obtain medical attention if irritation or an allergic reaction develops.
Eye Contact: Rinse cautiously with clean water for at least 15 minutes, remove contact lenses when easy to do and obtain urgent medical assessment because serious eye damage can occur.
Ingestion: Rinse the mouth, do not induce vomiting and obtain immediate medical or poison-centre assistance.
Note to Physicians: No specific antidote is established, so treatment is supportive with particular attention to respiratory function, eye injury and signs of sensitisation.

HANDLING AND STORAGE

Handle Chlorothalonil in closed systems or under effective local exhaust ventilation and avoid every operation that disperses dry powder into the workplace.
Use dedicated transfer equipment or validated cleaning procedures to prevent cross-contamination of other agricultural, industrial or laboratory materials.
Wash exposed skin thoroughly after handling and remove contaminated protective clothing before leaving the controlled area.

Store Chlorothalonil in tightly closed, correctly labelled containers in a cool, dry, locked and well-ventilated chemical-storage area.
Protect Chlorothalonil from moisture, excessive heat and prolonged contact with strongly alkaline materials, strong oxidising agents and reactive nucleophiles.
Keep Chlorothalonil separate from food, beverages, animal feed, medicines and drinking-water materials.

Isolate spills, stop dust movement and prevent entry into soil, drains or water.
Collect dry material with a filtered industrial vacuum or carefully dampened collection method rather than uncontrolled dry sweeping.
Place recovered material, contaminated absorbents and cleaning residues in sealed, labelled containers for authorised hazardous-waste management.

PACKAGING AND PROCUREMENT CONSIDERATIONS

Technical Chlorothalonil is packed in tightly sealed, moisture-resistant lined drums or rigid containers designed to control dust and protect the active ingredient during transport and storage.
Formulation-grade packaging should support closed or low-dust charging into the production process.
Analytical material and certified solutions are packed in chemically compatible laboratory containers that preserve concentration and purity.

A precise procurement request identifies the intended agricultural, antimicrobial, formulation or analytical application and the destination country.
The request should state the required assay, maximum hexachlorobenzene and decachlorobiphenyl contents, particle-size profile, physical form, quantity, packaging and documentation package.
Formulators should also identify the intended formulation type, target active concentration and relevant dispersion or wetting requirements.

Ataman Kimya supports professional Chlorothalonil procurement with attention to grade selection, relevant-impurity controls, particle size, formulation requirements, regulatory documentation, packaging and destination-market supply conditions.
For Chlorothalonil specifications, documentation, packaging options and supply inquiries, contact Ataman Kimya at +90 216 577 10 10 or info@atamankimya.com.