Ioxynil [3,5-Diiodo-4-hydroxybenzonitrile ] 
Bromoxynil [3,5-Dibromo-—4-hydroxybenzonitrile ] 
Photolysis of 3,5-diiodo-4-hydroxybenzonitrile (ioxynil) was a factor 
in its herbicidal action. The herbicidal and molluscicidal actions of 
ioxynil and bromoxynil, the bromine analog, are more toxic in light than 
in dark. When irradiated with ultraviolet light for 20 hours, in benzene, 
ioxynil was converted into 3,5~diphenyl-4-hydroxy-benzonitrile. The 
corresponding monoiodo derivative gave 3-phenyl-5-hydroxybenzonitrile. 
Within tissues of plants, ioxynil probably liberates free radicals which 
interfere with plant functions (1440). 
After ioxynil was fed to a cow, a compound was isolated from the urine 
that appeared to be a conjugate of 3-iodo-4-hydroxybenzonitrile (459). 
In acid soils, ioxynil was precipitated. 3,5-diiodo-4-hydroxybenzamide, 
the benzoic acid analog and traces of iodide were found. In sterile soils 
this does not occur (1535). 
Bromoxynil, fed to Holstein cows, was excreted intact and as an un- 
identified conjugate in urine (1258). 
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