Physical/Chemical Properties

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Chemical Name
O,O-diethyl O-(3,5,6-trichloro-2-pyridyl)phosphorothioate

Common Name
Chlorpyrifos (BSI, E-ISO, ANSI, ESA, BAN)

Molecular Weight
350.6

Empirical and Structural Formula
C9H11Cl3NO3PS

CAS Registry Number
2921-88-2

State
Crystalline solid

Color
White to tan

Odor
Mild mercaptan

Melting Point
41.5 – 42.5° C

Boiling Point
> 300° C

Vapor Pressure
3.35 mPa at 25° C

Density
1.51 g/ml at 21° C

Solubility, Mean

Acetone	>400 g/L at 20o C
Dichloromethane	>400 g/L at 20o C
Ethyl Acetate	>400 g/L at 20o C
Methanol	250 g/100mL at 20o C
Toluene	>400 g/L at 20o C
n-Hexane	>400 g/L at 20o C
Water	1.05 ppm (w/v at 25o C)

Partition Coefficient (n-octanol and water)
Kow = 50,000

Stability
a) in sterile buffered water
pH 4.7 at 25o C: half-life of 63 days
pH 6.9 at 25o C: half-life of 35 days
pH 8.1 at 25o C: half-life of 23 days

b) in organic solvents

There have been no signs of degradation in xylene-range aromatic solvents used in formulations of chlorpyrifos.