Avermectin

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June 23, 2025, 10:08 AM

Guide

Highlights at a glance

Abamectin is a macrocyclic lactone and glycoside belonging to the avermectin class, primarily composed of ≥80% avermectin B₁a (C₄₈H₇₂O₁₄, MW 873.09 g/mol) and ≤20% B₁b (C₄₇H₇₀O₁₄, MW 859.06 g/mol). It appears as a white to yellowish crystalline powder, is odorless or has a slight odor, and decomposes at 150–155°C without boiling. With extremely low water solubility (7–10 µg/L at 20°C) and high lipophilicity (log K_ow 4.0–4.4), it dissolves well in organic solvents like methanol, acetone, and chloroform. Abamectin is stable under neutral or weakly acidic conditions and normal storage temperatures but degrades in strong alkalis, under heat, and rapidly when exposed to sunlight. Its low vapor pressure and high partition coefficient suggest limited environmental mobility but potential bioaccumulation, though environmental degradation typically reduces persistence. CAS numbers: 71751-41-2 (Abamectin), 65195-55-3 (B₁a), 65195-56-4 (B₁b).

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.