An electrochemical method for preparing vanillin or its derivatives

Abstract

The present invention relates to an electrochemical method for preparing vanillin or its derivatives in the presence of a mediator. The mediator can be recycled and reused and therefore no salt is formed by the end of the reaction, which makes the method more environmental-friendly. Furthermore, lower potentials are needed when the mediator is used by comparing to prior arts.

1 . An electrochemical method for converting a compound of formula (I) to a compound of formula (II) in the presence of a solvent and a compound generating a mediator in reduced form in the solvent, 
       
         
           
           
               
               
           
         
         wherein:
 M P+  is a cation selected from group consisting of H + , NH 4   +  and metal cation; 
 p is the valence of M; 
 R 1 , R 2 , R 3  and R 4 , independently from each other, are selected from the group consisting of: a hydrogen atom, an alkyl group, an alkoxy group, a hydroxyl group, a halogen atom, a haloalkyl group and a perhaloalkyl group; 
 R 5  represents a hydrogen atom, an alkyl group, a cycloalkyl group, an aryl group or an aralkyl group. 
 
       
     
     
         2 . The method according to  claim 1 , wherein R 1  or R 3  is an alkoxy group. 
     
     
         3 . The method according to  claim 2 , wherein R 1  or R 3  is selected from the group consisting of methoxy, ethoxy, propoxy and butoxy and R 2  or R 4  is a hydrogen atom. 
     
     
         4 . The method according to  claim 1 , wherein R 5  is a hydrogen atom or an alkyl group. 
     
     
         5 . The method according to  claim 1 , wherein the compound of formula (I) is 4-hydroxy-3-methoxy mandelic acid or 4-hydroxy-3-ethoxy mandelic acid. 
     
     
         6 . The method according to  claim 1 , wherein the compound generating a mediator in reduced form in the solvent is selected from the group consisting of alkali metal bromides, alkali metal chlorides, alkali metal iodides, ammonium bromide, iron salts, cerium salts, manganese salts, copper salts, cobalt salts and chromium salts. 
     
     
         7 . An electrochemical method for converting a compound of formula (I) as defined in  claim 1  to a compound of formula (II) as defined in  claim 1  comprising following steps:
 (i) dissolving a compound generating a mediator in reduced form in a solvent to obtain a solution; 
 (ii) adding the solution obtained at step(i) to an electrochemical reactor; 
 (iii) passing current to the electrochemical reactor to oxidize the mediator in reduced form to a mediator in oxidized form; 
 (iv) contacting the compound of formula (I) with the mediator in oxidized form obtained at step (iii) to produce the compound of formula (II). 
 
     
     
         8 . The method according to  claim 7 , wherein in step(i), the concentration of the compound generating a mediator in reduced form in the solution is in the range of 0.05 M to 2 M. 
     
     
         9 . The method according to  claim 7 , wherein in step(iii) and (iv), the reaction temperature is from 0° C. to 100° C.. 
     
     
         10 . The method according to  claim 7 , wherein the molar ratio of the compound of formula (I) in step(iv) to the compound generating a mediator in reduced form in step(i) is equal to or higher than 1. 
     
     
         11 . An electrochemical method for converting a compound of formula (I) as defined in  claim 1  to a compound of formula (II) as defined in  claim 1  in an electrochemical reactor comprising both an anode and a cathode, this method comprising the following steps:
 a) dissolving the compound of formula (I) and a compound generating a mediator in reduced form in a solvent to obtain Solution A; 
 b) dissolving a compound generating a mediator in reduced form in a solvent to obtain Solution B; 
 c) adding Solution A to the compartment having the anode and Solution B to the compartment having the cathode; 
 d) passing current to the reactor to produce the compound of formula (II). 
 
     
     
         12 . The method according to  claim 11 , wherein in step a), the molar ratio of the compound of formula (I) to the compound generating a mediator in reduced form is equal to or higher than 1. 
     
     
         13 . The method according to  claim 11 , wherein the concentration of the compound generating a mediator in reduced form in Solution A of step a) or in Solution B of step b) is in the range of 0.01 M to 1 M. 
     
     
         14 . The method according to  claim 11 , wherein in step a), the concentration of the compound of formula (I) in Solution A is in the range of 0.1 M to 1 M. 
     
     
         15 . The method according to  claim 11 , wherein in step d), the reaction temperature is from 0° C. to 100° C.. 
     
     
         16 . The method according to  claim 8 , wherein in step(i), the concentration of the compound generating a mediator in reduced form in the solution is in the range of 0.1 M to 0.5 M. 
     
     
         17 . The method according to  claim 9 , wherein in step(iii) and (iv), the reaction temperature is from 10° C. to 30° C. 
     
     
         18 . The method according to  claim 10 , wherein the molar ratio of the compound of formula (I) in step(iv) to the compound generating a mediator in reduced form in step(i) is from 1.5 to 5.0.