Avermectin

1.Chemical and Physical Properties

1.1 Chemical Identity

• Common Name: Abamectin; Avermectins
• Chemical Name (IUPAC for Abamectin B₁a component): (10E,14E,16E,22Z)-(1R,4S,5'S,6S,6'R,8R,12S,13S,20R,21R,24S)-6'-[(S)-sec-butyl]-21,24-dihydroxy-5',11,13,22-tetramethyl-2-oxo-(3,7,19-trioxatetracyclo[15.6.1.1⁴˒⁸.0²⁰˒²⁴]pentacosa-10,14,16,22-tetraene)-6-spiro-2'-(tetrahydropyran)-12-yl 2,6-dideoxy-4-O-(2,6-dideoxy-3-O-methyl-α-L-arabino-hexopyranosyl)-3-O-methyl-α-L-arabino-hexopyranoside
  • Abamectin is a mixture containing ≥80% avermectin B₁a and ≤20% avermectin B₁b (differs by a methylene group on the sec-butyl side chain).
• CAS Registry Number: 71751-41-2 (for Abamectin); 65195-55-3 (for avermectin B₁a); 65195-56-4 (for avermectin B₁b)
• Chemical Class: Macrocyclic lactone; Avermectin; Glycoside
• Molecular Formula:
  • Avermectin B₁a: C₄₈H₇₂O₁₄
  • Avermectin B₁b: C₄₇H₇₀O₁₄
• Molecular Weight:
  • Avermectin B₁a: 873.09 g/mol
  • Avermectin B₁b: 859.06 g/mol

1.2 Key Physical Properties

• Appearance: White to off-white or yellowish crystalline powder.
• Odour: Odourless or very slight odour.
• Melting Point: Approximately 150-155°C (decomposes). Technical products may have a wider range.
• Boiling Point: Decomposes before boiling.
• Vapour Pressure: Extremely low (e.g.,
• Density: Approximately 1.16 g/cm³ at 20°C.
• Solubility:
  • Water: Very low; approximately 7-10 µg/L (ppb) at 20°C.
  • Organic Solvents: Soluble in many organic solvents like acetone, methanol, ethanol, toluene, chloroform, ethyl acetate; sparingly soluble in hexane.
• Log K_ow (Octanol-Water Partition Coefficient): Typically around 4.0-4.4, indicating high lipophilicity and potential for bioaccumulation in fatty tissues if exposure is continuous, though rapid degradation often limits this.

1.3 Key Chemical Properties

• Stability:
  • Relatively stable in neutral and weakly acidic solutions.
  • Hydrolyzes in strong alkaline solutions.
  • Susceptible to photodegradation (degrades rapidly in sunlight on surfaces).
  • Stable to heat under normal storage conditions but decomposes at high temperatures.