Method for purification of indole derivative trimer, electrode active substance comprising the purified trimer, method for manufacturing the electrode active substance, and electrochemical cell using the same

Abstract

The present invention provides a method for easily removing metal impurities from an indole derivative trimer containing the metal impurities, which method involves mixing the indole derivative trimer containing the metal impurities with an imidazole compound in a solvent comprising water under heating, and filtering and separating the indole derivative trimer, from which the metal impurities have been removed, from the obtained mixture. Further, mixing a protonic acid allows the doping of the indole derivative trimer to be conducted simultaneously with the metal impurity removal, whereby the indole derivative trimer can be used as an electrode active substance of an electrochemical cell.

1 . A method for purification of an indole derivative trimer represented by the following general formula (1):  
     
       
         
         
             
             
         
       
     
     wherein, R each independently represents a hydrogen atom, hydroxy group, carboxyl group, nitro group, vinyl group, halogen atom, acyl group, cyano group, amino group, trifluoromethyl group, sulfonyl group, sulfonic acid group, trifluoromethylthio group, carboxylate ester group, sulfonate ester group, alkoxyl group, alkylthio group, aryloxy group, arylthio group, alkyl group, aryl group or heterocyclic compound residue, by removing a metal impurity contained therein, the method comprises: 
 mixing the indole derivative trimer containing a metal impurity with an imidazole compound to form a complex with the metal impurity in a solvent comprising at least water under heating; and  
 separating the indole derivative trimer, from which the metal impurity has been removed, from the obtained mixture.  
 
   
   
       2 . The method for purification according to  claim 1 , wherein the indole derivative trimer containing a metal impurity has been obtained by chemically polymerizing an indole derivative, represented by the following formula (2):  
     
       
         
         
             
             
         
       
     
     wherein, R each independently denotes the same meaning as R in the general formula (1), by using an oxidizing agent composed of a metal compound.  
   
   
       3 . The method for purification according to  claim 1 , wherein the indole derivative trimer containing a metal impurity is mixed with a protonic acid simultaneously with the imidazole compound or before the imidazole compound is mixed therewith.  
   
   
       4 . The method for purification according to  claim 3 , wherein the protonic acid is mixed as an aqueous solution of not more than 30 weight % in concentration.  
   
   
       5 . The method for purification according to  claim 1 , wherein the metal impurity contains iron as a metal component.  
   
   
       6 . The method for purification according to  claim 1 , wherein the imidazole compound is 1H-imidazole.  
   
   
       7 . The method for purification according to  claim 1 , wherein a mixture of the indole derivative trimer containing a metal impurity, the solvent comprising water and an imidazole compound and/or a protonic acid is subjected to a heat treatment in the temperature range from not less than 80° C. to not more than the reflux temperature of the mixture.  
   
   
       8 . The method for purification according to  claim 1 , wherein after the indole derivative trimer containing a metal impurity is heated in the temperature range from 100 to 300° C., the solvent comprising water and an imidazole compound and/or a protonic acid are mixed therewith.  
   
   
       9 . A method for manufacturing an electrode active substance of an electrochemical cell which comprises an electrolyte comprising a proton source and can operate such that a proton acts as a charge carrier in a redox reaction involved in charge/discharge, the method comprises: 
 mixing an indole derivative trimer represented by the following general formula (1) containing a metal impurity with an aqueous solution of a protonic acid comprising an anion of the same chemical species as an electrolyte used in an electrochemical cell under heating, the formula (1) being:                          wherein, R each independently represents a hydrogen atom, hydroxy group, carboxyl group, nitro group, vinyl group, halogen atom, acyl group, cyano group, amino group, trifluoromethyl group, sulfonyl group, sulfonic acid group, trifluoromethylthio group, carboxylate ester group, sulfonate ester group, alkoxyl group, alkylthio group, aryloxy group, arylthio group, alkyl group, aryl group or heterocyclic compound residue;    sequentially or simultaneously mixing the mixture with an imidazole compound to form a metal complex with the metal impurity; and    separating the indole derivative trimer, from which the metal impurity has been removed and in which the protonic acid anion has been doped, from the obtained mixture.    
   
   
       10 . The method for manufacturing an electrode active substance according to  claim 9 , wherein the indole derivative trimer containing a metal impurity has been obtained by chemically polymerizing an indole derivative, represented by the following formula (2):  
     
       
         
         
             
             
         
       
     
     wherein, R each independently denotes the same meaning as R in the general formula (1), by using an oxidizing agent composed of a metal compound.  
   
   
       11 . The method for manufacturing an electrode active substance according to  claim 9 , wherein the aqueous solution of the protonic acid has a concentration of not more than 30 weight %.  
   
   
       12 . The method for manufacturing an electrode active substance according to  claim 9 , wherein the metal impurity contains iron as a metal component.  
   
   
       13 . The method for manufacturing an electrode active substance according to  claim 9 , wherein the imidazole compound is 1H-imidazole.  
   
   
       14 . The method for manufacturing an electrode active substance according to  claim 9 , wherein the mixture of the indole derivative trimer containing a metal impurity and the aqueous solution of the protonic acid or/and the imidazole compound is subjected to a heat treatment in the temperature range from not less than 80° C. to not more than the reflux temperature of the mixture.  
   
   
       15 . The method for manufacturing an electrode active substance according to  claim 9 , wherein after the indole derivative trimer containing a metal impurity is heated in the temperature range from 100 to 300° C., an aqueous solution of the protonic acid or/and an imidazole compound are mixed therewith.  
   
   
       16 . An electrode active substance comprising an indole derivative trimer obtained by the method for manufacturing according to  claim 9 .  
   
   
       17 . The electrode active substance according to  claim 16 , wherein the indole derivative trimer has a purity of not less than 95%.  
   
   
       18 . An electrochemical cell comprising an electrolyte containing a proton source and capable of operating such that a proton acts as a charge carrier in a redox reaction involved in charge/discharge, wherein the electrochemical cell comprises at least the electrode active substance according to  claim 16 .  
   
   
       19 . An electrochemical cell comprising an electrolyte comprising a proton source and capable of operating such that a proton acts as a charge carrier in a redox reaction involved in charge/discharge, wherein the electrochemical cell comprises at least the electrode active substance according to  claim 17.