Chlorpyrifos

1.Chemical and Physical Properties

1.1 Chemical Identity

• Common Name: Chlorpyrifos
• Chemical Name (IUPAC): O,O-diethyl O-(3,5,6-trichloro-2-pyridinyl) phosphorothioate
• CAS Registry Number: 2921-88-2
• Chemical Class: Organophosphate insecticide/acaricide
• Molecular Formula: C₉H₁₁Cl₃NO₃PS
• Molecular Weight: 350.59 g/mol

1.2 Key Physical Properties

• Appearance: Pure chlorpyrifos is a white or colorless crystalline solid. Technical grade material is often a yellowish to brownish granular solid or liquid.
• Odour: Mild mercaptan or garlic-like odour.
• Melting Point: 42-43.5°C.
• Boiling Point: Decomposes at temperatures above ~160°C before boiling at atmospheric pressure.
• Vapour Pressure: 2.5 mPa (1.87 x 10⁻⁵ mmHg) at 25°C. It is considered semi-volatile, meaning it can volatilize from treated surfaces and contribute to atmospheric transport.
• Density: 1.398 g/cm³ at 43.5°C.
• Solubility:
  • Water: Very low; approximately 1.4 mg/L (ppm) at 25°C.
  • Organic Solvents: Soluble in most organic solvents, including acetone, xylene, methanol, and dichloromethane.
• Log K_ow (Octanol-Water Partition Coefficient): ~4.7 - 5.3, indicating it is highly lipophilic and has a high potential to bioaccumulate in the fatty tissues of organisms.

1.3 Key Chemical Properties

• Stability:
  • Relatively stable in neutral and acidic conditions.
  • Hydrolyzes rapidly under alkaline (high pH) conditions.
  • Subject to photodegradation in sunlight.

2.Production Technologies

2.1 Synthesis Overview

1. Synthesis of the intermediate 3,5,6-trichloro-2-pyridinol (TCP): This is the key precursor. It is generally manufactured from pyridine or 2-picoline through a multi-step chlorination and hydrolysis process.
2. Condensation Reaction: TCP is reacted with O,O-diethyl phosphorochloridothioate (DECTP) in the presence of a solvent and a base (like potassium carbonate or an amine) to neutralize the hydrochloric acid byproduct. The resulting crude chlorpyrifos is then purified.

2.2 Key Raw Materials

• Pyridine or 2-Picoline
• Chlorine gas
• Thiophosphoryl chloride (PSCl₃) or Phosphorus oxychloride (POCl₃)
• Ethanol
• Bases (e.g., sodium hydroxide, potassium carbonate)
• Solvents

2.3 Formulation

• Emulsifiable Concentrates (EC): A very common liquid formulation.
• Granules (GR): For soil application.
• Wettable Powders (WP)
• Suspension Concentrates (SC)
• Microencapsulated Suspensions (CS): Designed for slower release and reduced applicator exposure.
• Baits, Dusts, and Seed Treatments

3.Applications

3.1 Mode of Action

• Chlorpyrifos is a non-systemic, broad-spectrum insecticide with contact, stomach, and fumigant action. Its ability to act as a fumigant makes it particularly effective against soil-dwelling pests.
• It is an acetylcholinesterase (AChE) inhibitor. It irreversibly binds to the AChE enzyme in the nervous system, preventing the breakdown of the neurotransmitter acetylcholine. This leads to an accumulation of acetylcholine at the nerve synapse, causing continuous nerve firing, convulsions, paralysis, and ultimately death of the insect.
• It is classified in Group 1B by the Insecticide Resistance Action Committee (IRAC).

3.2 Crops and Uses

• Agricultural Uses (Historical): Corn, soybeans, cotton, wheat, rice, citrus, apples, nuts, various fruits and vegetables.
• Non-Agricultural Uses: Turf on golf courses, termite control in buildings, mosquito control (larvicide), and indoor pest control (e.g., cockroaches, ants). Note: All residential indoor and outdoor uses were banned in the US in 2000.

3.3 Pests Controlled

• Soil Pests: Corn rootworms, wireworms, grubs, cutworms.
• Chewing Insects: Caterpillars (e.g., armyworms, bollworms), beetles (e.g., weevils).
• Sucking Insects: Aphids, leafhoppers, scale insects, whiteflies.
• Other Pests: Termites, flies, mosquitoes, mites.

3.4 Applications Methods

• Foliar spray
• Soil broadcast or in-furrow application
• Seed treatment
• Termiticide barrier drench for building foundations

4.Market Analysis

4.1 Global Market Overview

• For decades, chlorpyrifos was one of the world's top-selling insecticides due to its efficacy and low price.
• The market has dramatically collapsed in North America and Europe following regulatory bans.
• It is still produced and used in some countries in Asia, South America, and Africa, but its global market share is in steep decline as more countries move to restrict or ban it.

4.2 Key Market Dynamics

• Drivers (Historical): Broad-spectrum control, low cost, effectiveness against key pests (especially in soil and for termites).
• Restraints/Challenges (Current and Overwhelming):
  • Documented neurodevelopmental toxicity in children.
  • Widespread regulatory bans and phase-outs.
  • Extreme toxicity to aquatic life, birds, and bees.
  • Development of resistance in some pest populations.
  • Strong public opposition and litigation.

5.Upstream and Downstream Linkages

5.1 Upstream Linkages(inputs for production)

• Basic Chemicals: Pyridine, chlorine, phosphorus-based compounds.
• Chemical Intermediates: 3,5,6-trichloro-2-pyridinol (TCP), O,O-diethyl phosphorochloridothioate (DECTP).
• Suppliers of these materials are in the global bulk and specialty chemical industries.

5.2 Downstream Linkages(outputs and consumers)

• Agrochemical Formulators: Purchase technical grade chlorpyrifos to produce end-use products (in countries where it is still allowed).
• Distributors and Retailers: Supply formulated products to end-users.
• End-Users:
  • Farmers (in regions where it is still permitted).
  • Pest Control Operators (PCOs) for termite control and other non-food uses.
  • Golf course superintendents.