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. A method for preparing a compound, the method comprising the steps of:
activating a silver cathode by anodizing the cathode at a final potential in the range of +1.05 to +1.8 volts;
passing a direct or alternating electric current from an anode to the activated silver cathode through a solution of 3,5-dihalopyridine or 3,5-dihalopicolinic acid of Formula (II)
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 ; and
forming 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 .
2. The method of claim 1 , further including the step of reversing the polarization of the activated cathode.
3. The method of claim 1 in which the 3-halopicolinic acid of Formula I is aminopyralid and the 3,5-dihalopicolinic acid of Formula II is picloram.
4. The method of claim 1 , wherein activating the silver cathode includes activating the silver cathode by anodizing the cathode at a final potential in the range of +1.1 to +1.8 volts.
5. The method of claim 1 , wherein activating the silver cathode includes activating the silver cathode by anodizing the cathode at a final potential in the range of +1.2 to +1.8 volts.
6. The method of claim 1 , wherein activating the silver cathode includes activating the silver cathode by anodizing the cathode at a final potential of +1.8 volts.