Relation of Halogen Position to Physiological Properties in the Mono-, Di-, and Trichlorophenoxyacetic Acids

All the mono-, di-, and trichlorophenoxyacetic acids have been prepared in the highest possible purity, and their melting points have been recorded. Their corresponding amides and anilides have also been made, and their melting points recorded. Four of these acids, ten of the amides, and eleven of the anilides have not previously been reported. 2. All these chlorophenoxyacetic acids, including the four not hitherto tested, have been subjected to selective "hormone" screening tests with tomato plants using the procedure of Zimmerman and Hitchcock (24) at the Boyce Thompson Institute and also to the root-inhibition test of Macht and Livingston (9) using Lupinus albus. 3. The highest physiological activity of chlorophenoxyacetic acids has been shown to be associated with the presence of two unsubstituted positions in the benzene ring para to each other. 4. The possibility of the formation of compounds having quinonoid structure being connected with their maximum herbicidal potency is discussed.