CHLORIDAZON

Chloridazon is a selective systemic pyridazinone herbicide historically associated with pre-emergence and early post-emergence weed control in sugar beet and fodder beet.
Chloridazon acts through photosystem-II inhibition and is absorbed principally through the roots of germinating weeds.
Its regulatory importance now extends beyond herbicide formulation to environmental monitoring, groundwater-metabolite analysis and pesticide-fate research.

CHEMICAL IDENTITY AND COMMON NAMES

Chloridazon is the accepted common name for 5-amino-4-chloro-2-phenylpyridazin-3(2H)-one.
The molecule contains a chlorinated pyridazinone ring, an amino substituent and an N-linked phenyl group.
Common names: Chloridazon, Chloridazone, Pyrazon and Pyrazone
Systematic-name variants: 5-Amino-4-chloro-2-phenylpyridazin-3-one, 5-Amino-4-chloro-2-phenylpyridazin-3(2H)-one, 5-Amino-4-chloro-2-phenyl-2H-pyridazin-3-one, 5-Amino-4-chloro-2-phenyl-3(2H)-pyridazinone and 5-Amino-4-chloro-2-phenyl-3(2H)-pyridazone
Alternative systematic names: 5-Amino-4-chloro-2,3-dihydro-3-oxo-2-phenylpyridazine, 4-Amino-5-chloro-1-phenyl-6-pyridazinone, 4-Amino-5-chloro-1-phenyl-6-pyridazone, 1-Phenyl-4-amino-5-chloro-6(1H)-pyridazinone and 1-Phenyl-4-amino-5-chloropyridazin-6-one
Registry-style name: 3(2H)-Pyridazinone, 5-amino-4-chloro-2-phenyl-

Iso-Chloridazon is not another name for active Chloridazon.
Iso-Chloridazon is the biologically inactive positional isomer 4-amino-5-chloro-2-phenylpyridazin-3(2H)-one and is an important technical-material impurity.
The proportion of active Chloridazon relative to iso-Chloridazon is therefore more informative than total pyridazinone content alone.

TECHNICAL IDENTIFICATION

Product name: Chloridazon
CAS number: 1698-60-8
EC number: 216-920-2
Molecular formula: C10H8ClN3O
Molar mass: 221.64 g/mol
Chemical family: Substituted pyridazinone
Functional classification: Selective systemic herbicide
Herbicide group: Photosystem-II inhibitor, Group 5, formerly classified as Group C1
IUPAC name: 5-Amino-4-chloro-2-phenylpyridazin-3(2H)-one
InChIKey: WYKYKTKDBLFHCY-UHFFFAOYSA-N
Canonical SMILES: C1=CC=C(C=C1)N2C(=O)C(=C(C=N2)N)Cl

PHYSICAL AND CHEMICAL PROPERTIES

Appearance of purified material: White to colourless crystalline solid
Appearance of technical material: Pale yellow to brown, nearly odourless powder
Odour: Essentially odourless
Melting behaviour: Approximately 206–210°C with decomposition for purified Chloridazon
Relative density: Approximately 1.54 at 20°C
Water solubility: Approximately 0.34–0.40 g/L at 20°C
Partition coefficient: Log Kow approximately 1.14
Vapour pressure: Approximately 5.4 × 10⁻¹¹ mbar at 20°C
Ultraviolet absorption maximum: Approximately 287 nm in methanol
Volatility: Extremely low under normal storage and application conditions

Chloridazon is more soluble in polar organic solvents such as methanol and acetone than in water.
Its solubility is considerably lower in ethyl acetate, dichloromethane and aromatic hydrocarbons, while solubility in non-polar aliphatic solvents is very low.
The combination of moderate water solubility and negligible vapour pressure favours soil-water transport over volatilisation.

HERBICIDAL MODE OF ACTION

Chloridazon is absorbed mainly through weed roots and is transported upward through the xylem toward emerging shoots and leaves.
Foliar absorption can occur, but root uptake is the principal pathway associated with its characteristic residual soil activity.
Chloridazon binds within the QB region of the D1 protein in photosystem II and interrupts electron transfer during the light-dependent reactions of photosynthesis.
This inhibition suppresses adenosine triphosphate and reducing-power formation while promoting oxidative damage in susceptible plant tissue.
Affected weeds initially exhibit growth arrest and chlorosis, followed by tissue necrosis and seedling death.

Chloridazon belongs to Herbicide Resistance Action Committee Group 5 and the former C1 photosystem-II-inhibitor group.
Repeated dependence on this mode of action can select resistant weed populations.
Authorised programs therefore combine Chloridazon with suitable cultural measures and herbicides having different modes of action.

CROP SELECTIVITY AND RESIDUAL BEHAVIOUR

The historical value of Chloridazon was its selectivity in sugar beet and fodder beet relative to many germinating annual weeds.
Tolerant beet plants metabolise and detoxify Chloridazon more effectively than susceptible weed seedlings.
Crop tolerance nevertheless depends on growth stage, physiological condition, soil characteristics, weather and the composition of the finished formulation.

Chloridazon primarily controls annual broadleaf weeds, including susceptible goosefoot, knotweed and chickweed species, with activity against some young annual grasses.
Its residual performance depends on sufficient soil moisture to move dissolved Chloridazon into the weed-germination zone.
Dry soil can delay activity, while heavy rainfall can increase downward movement and the risk of groundwater contamination.
Organic matter and clay content influence sorption, bioavailability and persistence in treated soil.

PRODUCTION AND TECHNICAL MATERIAL

Industrial Chloridazon production uses controlled construction of the substituted pyridazinone ring followed by selective introduction of the amino group.
A relevant intermediate is 4,5-dichloro-2-phenylpyridazin-3(2H)-one, in which selective replacement of one ring chlorine produces active Chloridazon.
Reaction selectivity is critical because substitution at the alternative position generates inactive iso-Chloridazon.

The isolated product is purified through crystallisation, filtration and washing before controlled drying and milling.
Drying removes process water and residual solvent, while milling establishes the particle-size distribution required for formulation.
Closed handling and effective dust extraction are important during drying, milling, blending and packaging.

Important technical-material constituents include active Chloridazon, iso-Chloridazon, residual dichlorinated intermediate and structurally related pyridazinones.
Residual inorganic salts, water and process solvents can also influence technical quality.
A useful specification therefore controls active assay, iso-isomer content, individual related substances, water, insoluble residue and physical form.

APPLICATIONS AND INDUSTRIES

Sugar-beet weed management

Chloridazon was developed principally for selective control of annual weeds in sugar-beet production.
It was incorporated into pre-emergence and early post-emergence programs where soil residual activity complemented foliar herbicides.
Agricultural use is now limited to jurisdictions in which Chloridazon remains specifically authorised.

Fodder beet and other authorised beet crops

Chloridazon has also been associated with weed management in fodder beet and related authorised beet-crop systems.
Crop suitability cannot be transferred automatically between beet types because registrations, residue limits and crop-safety conditions are jurisdiction-specific.
Only registered formulations and approved label directions establish a lawful agricultural use.

Historical herbicide formulation

Technical Chloridazon has been formulated primarily as suspension concentrates and wettable powders.
Its limited water solubility makes a concentrated true aqueous solution impractical, while its crystalline stability supports finely divided suspension systems.
Technical Chloridazon is a formulation feedstock and is not a ready-to-apply agricultural product.

Environmental and water-analysis laboratories

Chloridazon is analysed in soil, surface water, groundwater, drinking-water sources and agricultural drainage studies.
Laboratories frequently determine both the parent compound and its more mobile desphenyl metabolites.
Liquid chromatography coupled with tandem mass spectrometry provides the selectivity and sensitivity needed for trace-level monitoring.

Herbicide fate and metabolism research

Characterised Chloridazon is used in studies of soil degradation, crop metabolism, leaching and photosystem-II inhibition.
Reference materials for Chloridazon, iso-Chloridazon and the principal groundwater metabolites allow analytical methods to distinguish the active ingredient from transformation products and manufacturing impurities.
These distinctions are essential when reconstructing contamination pathways or evaluating historical pesticide use.

FORMULATION AND PROCESS CONSIDERATIONS

Suspension concentrate formulation requires micronised Chloridazon, effective wetting and dispersing agents, controlled rheology and protection against irreversible sedimentation.
Antifoam agents, preservatives and freeze-protection components may be incorporated when compatible with the active ingredient.
Critical quality attributes include particle-size distribution, suspensibility, viscosity, pourability, wet-sieve residue, sediment volume, redispersibility and resistance to crystal growth.

Wettable powder formulation requires a compatible mineral carrier together with wetting and dispersing components that produce rapid and uniform suspension in dilution water.
Dust generation must be controlled because fine Chloridazon particles can create inhalation exposure and cross-contamination.
Wettability, suspensibility, persistent foam, wet-sieve residue and storage stability are central performance tests.

Formulation-water hardness, electrolyte concentration and pH can alter dispersion behaviour.
Excessive heat, prolonged contact with strongly acidic or alkaline media and incompatible oxidising materials should be avoided.
Pilot-scale aging, accelerated storage, freeze-thaw testing and dilution-water studies establish the physical stability of the complete formulation.

GRADE SELECTION AND PRODUCT SUITABILITY

Technical Chloridazon is intended for authorised pesticide formulation, controlled industrial processing and qualified research programs.
Its specification should define the active-isomer assay separately from iso-Chloridazon and other related pyridazinones.
Particle size and physical form should also correspond to the intended suspension-concentrate or wettable-powder process.

High-purity Chloridazon is suitable for analytical calibration, identity testing, method development, degradation studies and toxicological research.
Characterised iso-Chloridazon is required when laboratories need to quantify the inactive manufacturing isomer independently.
Separate desphenyl-Chloridazon and methyl-desphenyl-Chloridazon reference materials support groundwater and environmental monitoring.

ENVIRONMENTAL FATE AND GROUNDWATER METABOLITES

Chloridazon has moderate water solubility, low hydrophobicity and a representative soil organic-carbon partition coefficient near 120 mL/g.
These properties permit movement through soil water, especially in permeable soils with low organic-carbon content.
Volatilisation is negligible because the vapour pressure of Chloridazon is extremely low.

Degradation rates vary with temperature, soil moisture, microbial activity and soil composition.
Reported soil half-lives range from several weeks to several months under different test and field conditions.
Cool or biologically inactive soil generally slows degradation, while warm and moist soil can accelerate microbial transformation.

A major degradation pathway removes the N-bound phenyl group and produces desphenyl-Chloridazon, also known as 4-amino-5-chloropyridazin-6-one.
Further transformation can produce methyl-desphenyl-Chloridazon, also known as 4-amino-5-chloro-1-methylpyridazin-6-one.
These metabolites are more polar and mobile than parent Chloridazon and can persist in groundwater after the original agricultural treatment has ceased.
They have little or no relevant herbicidal activity but remain important indicators of historical Chloridazon use and subsurface transport.

Chloridazon is very toxic to aquatic organisms and can produce long-lasting environmental effects.
Product, contaminated soil, rinsate and firefighting water must be prevented from entering drains, surface water and groundwater.
Spill response should prioritise dry containment and controlled collection without generating airborne dust.

QUALITY, SPECIFICATIONS AND DOCUMENTATION

Identity testing can combine chromatographic retention, infrared spectroscopy, ultraviolet absorption and mass-spectrometric confirmation.
High-performance liquid chromatography is particularly useful for measuring Chloridazon and resolving the inactive positional isomer.
Detection near the characteristic ultraviolet absorption region around 287 nm can support routine assay and impurity testing.

Technical specifications commonly address Chloridazon assay, iso-Chloridazon, residual dichlorinated intermediate, other related substances, water and insoluble matter.
Formulation-grade evaluation additionally addresses particle size, bulk density, wettability and dispersibility.
Analytical reference materials require identity, purity assignment, homogeneity, stability and traceable documentation.

Procurement documentation can include a certificate of analysis, safety data sheet, technical data sheet, manufacturing-origin information and relevant regulatory statements.
For pesticide-manufacturing programs, technical equivalence and destination-market active-substance requirements must be incorporated into supplier qualification.
Environmental laboratories should specify whether the requirement is for parent Chloridazon, iso-Chloridazon, desphenyl-Chloridazon or methyl-desphenyl-Chloridazon.

SAFETY AND REGULATORY CONSIDERATIONS

Hazard statements commonly associated with Chloridazon include H302, harmful if swallowed, H317, may cause an allergic skin reaction, and H410, very toxic to aquatic life with long-lasting effects.
Dust can irritate the eyes and respiratory tract even where a separate irritation classification is not assigned.
Repeated skin contact should be prevented because Chloridazon can sensitise susceptible individuals.

Suitable controls include enclosed transfer, local exhaust ventilation, chemical-resistant gloves, protective clothing and safety goggles.
A properly selected particulate respirator is required where engineering controls cannot maintain airborne dust at an acceptable level.
Contaminated work clothing should be removed and cleaned before reuse.

Chloridazon is not readily volatile or easily ignited under ordinary storage conditions.
Strong heating and decomposition can release hydrogen chloride, nitrogen oxides, carbon monoxide and carbon dioxide.
Firefighters should use self-contained breathing apparatus and prevent contaminated extinguishing water from reaching the environment.

European Union approval of Chloridazon as a plant-protection active substance expired on 31 December 2018 and was not renewed.
Chloridazon is consequently not approved for plant-protection use in the European Union and is covered by European export-control procedures for banned pesticides.
Agricultural manufacture, sale and use outside the European Union require an active destination-country authorisation, an approved formulation and compliance with applicable residue, import and export controls.

FIRST AID

After inhalation, move the affected person to fresh air and obtain medical attention if coughing, breathing difficulty or other symptoms persist.
After skin contact, remove contaminated clothing and wash the skin thoroughly with soap and water, with medical assessment required if a rash or sensitisation reaction develops.
After eye contact, rinse cautiously with clean water for at least 15 minutes and obtain medical advice if irritation persists.
After ingestion, rinse the mouth, do not induce vomiting and contact a poison centre or physician immediately.
Treatment is symptomatic and supportive because no specific antidote is established for Chloridazon exposure.

HANDLING AND STORAGE

Handle Chloridazon in closed or well-ventilated equipment that limits dust generation.
Avoid breathing dust and prevent contact with skin, eyes and clothing.
Use dedicated or thoroughly cleaned equipment to avoid contamination of other agricultural, food or laboratory materials.

Store Chloridazon in tightly closed, correctly labelled containers in a cool, dry and well-ventilated chemical-storage area.
Protect the material from direct sunlight, excessive heat, moisture, strong oxidising agents and strongly acidic or alkaline substances.
Keep Chloridazon separate from food, animal feed and drinking-water materials.
Use secondary containment where leakage could reach drains or soil.

Collect small spills with a filtered industrial vacuum or by careful dry sweeping that does not disperse dust.
Place recovered material and contaminated absorbents in sealed, labelled waste containers.
Dispose of Chloridazon waste through an authorised hazardous-waste route and never discharge wash water into drains.

PACKAGING, SUPPLY AND PROCUREMENT

Technical Chloridazon can be packed in lined fibre drums or compatible rigid containers that protect the powder from moisture and contamination.
Analytical quantities are packed in tightly sealed laboratory containers selected to preserve identity and purity.
Packaging format should correspond to the grade, quantity, transport classification and intended handling system.

A complete Chloridazon inquiry should state the intended application, required grade, assay, maximum iso-Chloridazon content, particle-size requirement, packaging quantity and destination country.
Requests for environmental analysis should identify the parent compound or exact metabolite required.
Requests connected with pesticide manufacture should also provide the applicable authorisation and technical-equivalence framework.

ATAMAN KIMYA PROCUREMENT AND TECHNICAL SUPPORT

Ataman Kimya supports Chloridazon sourcing for qualified formulation, analytical, environmental and research applications.
Technical coordination can address grade selection, impurity controls, particle-size requirements, packaging and documentation.
Agricultural supply is evaluated within the regulatory status of Chloridazon in the destination market.

Phone: +90 216 577 10 10
Email: info@atamankimya.com