Electrochemical reduction of halogenated 4-aminopicolinic acids

1. An improved process for the preparation of a 4-amino-3-halopicolinic acid of Formula I

wherein

X represents Cl or Br,

Y represents H, F, Cl, Br or C 1 -C 4 alkyl, with the proviso that when X is Cl, Y is not Br, and

R independently represents H or C 1 -C 4 alkyl,

in which a direct or alternating electric current is passed from an anode to a silver cathode through a solution of a 4-amino-3,5-dihalopicolinic acid of Formula II

wherein

X, Y and R are as previously defined, and

wherein

both of X are either Cl or Br,

at a cathode potential of about −0.4 to about −1.7 volts relative to an Ag/AgCl (3.0 M Cl − ) reference electrode, the improvement characterized by activating the cathode in the presence of the 4-amino-3,5-dihalopicolinic acid of Formula II, about 1 to about 4 wt % excess of alkali metal hydroxide and about 0.5 to about 4 weight percent of an alkali metal chloride, bromide or sulfate.

2. The process of claim 1 in which the silver cathode is activated by anodization in the presence of from about 0.5 to about 4 wt % NaCl, about 1 to about 4 wt % excess NaOH and about 1 to about 20 wt % 4-amino-3,5-dihalopicolinic acid of Formula II at a potential of at least 0.3 to about 0.7 volts followed by reverse polarization.

3. The process of claim 1 in which the 4-amino-3-halopicolinic acid of Formula I is aminopyralid and the 4-amino-3,5-dihalopicolinic acid of Formula II is picloram.