Configurations and Methods of Reduction of Lipoic Acid

Abstract

Lipoic acid is electrochemically reduced to dihydrolipoic acid, preferably in a continuous manner and in a flow-through cell using a cathode that allows a two-electron transfer reaction in highly alkaline medium. In most preferred aspects, the reduced product is continuously removed by a membrane with preferential permeability for dihydrolipoic acid, and the cathode material is carbon felt.

1 . A method of reducing lipoic acid, comprising;
 electrochemically reducing lipoic acid to dihydrolipoic acid in an alkaline electrolyte on a cathode having a composition and configuration effective to allow a two-electron transfer reaction; and   separating the dihydrolipoic acid from the lipoic acid using differential lipophilicity of the dihydrolipoic acid and the lipoic acid.   
   
   
       2 . The method of  claim 1  wherein the alkaline electrolyte has a pH of at 10.0. 
   
   
       3 . The method of  claim 1  wherein the cathode material comprises carbon felt, and optionally wherein the step of electrochemical reducing is performed using an Ir 2 O 3  anode. 
   
   
       4 . The method of  claim 1  wherein the cathode material is configured to allow storage of hydrogen, and optionally wherein the step of electrochemical reducing is performed using an Ir 2 O 3  anode. 
   
   
       5 . The method of  claim 1  wherein the step of separating is performed in a phase separation step in which the dihydrolipoic acid is separated from an aqueous phase in which the lipoic acid is disposed. 
   
   
       6 . The method of  claim 5  wherein the phase separation is performed using a lipophilic solvent or via acidification of the electrolyte. 
   
   
       7 . The method of  claim 1  wherein the step of separating is performed concurrently with the step of electrochemically reducing the lipoic acid. 
   
   
       8 . The method of  claim 1  wherein the step of separating is performed using a membrane that is preferentially permeable to dihydrolipoic acid. 
   
   
       9 . The method of  claim 7  wherein the step of separating is performed using a membrane that is preferentially permeable to dihydrolipoic acid. 
   
   
       10 . The method of  claim 1  wherein the membrane is located in a separation compartment that is fluidly coupled to a cathode compartment in which the lipoic acid is reduced to dihydrolipoic acid, and wherein the separation compartment comprises an outlet for the separated dihydrolipoic acid. 
   
   
       11 . An electrochemical system for reduction of lipoic acid, comprising:
 a flow-through electrolytic cell having an anode compartment with an anode, a cathode compartment with a cathode, and a separator;   wherein the cathode compartment comprises an alkaline electrolyte having a pH of at least 10.0 in which lipoic acid is dissolved, wherein the cathode has a composition and configuration effective to allow a two-electron transfer reaction; and   a power source coupled to the anode and cathode to provide current at a voltage sufficient to reduce lipoic acid to dihydrolipoic acid.   
   
   
       12 . The system of  claim 11  further comprising a separation compartment fluidly coupled to the cathode compartment, wherein the separation compartment comprises a membrane that is preferentially permeable to dihydrolipoic acid, and wherein the membrane is coupled to the separation compartment such that dihydrolipoic acid is preferentially removable from the separation compartment via the membrane. 
   
   
       13 . The system of  claim 12  wherein the membrane comprises a fluorinated polymer. 
   
   
       14 . The system of  claim 12  wherein the separation compartment and the cathode compartment are configured to allow continuous flow of the electrolyte between the separation compartment and the cathode compartment. 
   
   
       15 . The system of  claim 11  wherein the cathode is configured as a flow-through cathode. 
   
   
       16 . The system of  claim 11  wherein the cathode comprises at least one of a carbon felt and a material that allows storage of hydrogen within the cathode, and optionally wherein the anode comprises Ir 2 O 3 . 
   
   
       17 . The system of  claim 11  wherein the separator comprises a cation exchange membrane. 
   
   
       18 . The system of  claim 11  wherein the alkaline electrolyte comprises at least 0.8 M of an alkaline metal hydroxide or alkaline earth metal hydroxide. 
   
   
       19 . The system of  claim 11  wherein the electrolyte, the anode, and the cathode are selected such as to enable reduction of lipoic acid to dihydrolipoic acid at a voltage of about −4.0 V. 
   
   
       20 . The system of  claim 11  wherein the cathode electrolyte comprises at least 50 gram per liter lipoic acid.