Silver cathode activation
View Patent ↗The selective electrochemical reduction of halogenated 4-aminopicolinic acids is improved by activating the cathode at a final potential from about +1.0 to about +1.8 volts.
1. An improved process for the preparation of a 3-halopyridine or 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;
R 1 represents Cl or CO 2 H; and
R 2 represents H or NH 2
in which a direct or alternating electric current is passed from an anode to a silver cathode through a solution of a 3,5-dihalopyridine or 3,5-dihalopicolinic acid of Formula II
wherein
X, Y, R 1 and R 2 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 by anodizing the cathode at a final potential of +1.2 volts followed by reverse polarization.
2. The process of claim 1 in which the 3 halopicolinic acid of Formula I is aminopyralid and the 3,5-dihalopicolincic acid of Formula II is picloram.