Process for preparing 2-alkyne 1-acetals

Abstract

Process for preparing 2-alkyne 1-acetals of the general formula I, where the radicals have the following meanings: R 1 is hydrogen, C 1 -C 20 -alkyl, C 2 -C 20 -alkenyl, C 2 -C 20 -alkynyl, C 3 -C 12 -cycloalkyl, C 4 -C 20 -cycloalkylalkyl, C 4 -C 10 -aryl, with these radicals optionally being able to be substituted by hydroxy, halogen, C 1 -C 6 -alkoxy, (C 1 -C 6 -alkoxy)carbonyl, carboxyl or nitrile groups, R 2 is C 1 -C 6 -alkyl or a radical of the general formula II where R 1 is as defined above, R 3 has the same meaning as the radical R 2 , by electrochemically oxidizing a compound of the general formula III where the radical R 1 has the same meaning as in the general formula I, in the presence of C 1 -C 6 -alkyl alcohols (alcohol A) or as such.

1 . A process for preparing 2-alkyne 1-acetals of the general formula I,  
     
       
         
         
             
             
         
       
     
     where the radicals have the following meanings: 
 R 1  is hydrogen, C 1 -C 20 -alkyl, C 2 -C 20 -alkenyl, C 2 -C 20 -alkynyl, C 3 -C 12 -cycloalkyl, C 4 -C 20 -cycloalkylalkyl, C 4 -C 10 -aryl, with these radicals optionally being able to be substituted by hydroxy, halogen, C 1 -C 6 -alkoxy, (C 1 -C 6 -alkoxy)carbonyl, carboxyl or nitrile groups,  
 R 2  is C 1 -C 6 -alkyl or a radical of the general formula II  
                     
 where R 1  is as defined above,  
 R 3  has the same meaning as the radical R,  
 by electrochemically oxidizing a compound of the general formula III  
                     
 where the radical R 1  has the same meaning as in the general formula I,  
 in the presence of C 1 -C 6 -alkyl alcohols (alcohol A) or as such.  
 
   
   
       2 . The process according to  claim 1 , wherein 2-propyn-1-ol or 2-butyne-1,4-diol is used as compound of the general formula III and methanol is used as alcohol A.  
   
   
       3 . The process according to  claim 1 , wherein the process is carried out in an electrolyte comprising sulfuric acid, sulfonic acids or carboxylic acids.  
   
   
       4 . The process according to  claim 1 , wherein the process is carried out in an electrolyte comprising less than 20% by weight of water.  
   
   
       5 . The process according to  claim 1 , wherein the process is carried out in an electrolyte comprising one or more compounds selected from the group consisting of sodium, potassium, lithium, iron, tetra(C 1 -C 6 -alkyl)ammonium salts with sulfate, hydrogensulfate, alkylsulfates, arylsulfates, halides, phosphates, carbonates, alkylphosphates, alkylcarbonates, nitrate, alkoxides, tetrafluoroborate or perchlorate as counterion or ionic liquids as electrolyte salt.  
   
   
       6 . The process according to  claim 1 , wherein the process is carried out in a bipolar capillary gap cell or plate stack cell or in a divided electrolysis cell.  
   
   
       7 . The process according to  claim 1 , wherein at least 2 mol of the alcohol A are used per mole of hydroxyl groups borne by the compound of the general formula III when using a compound of the general formula III bearing 2 or more alcoholic hydroxyl groups.  
   
   
       8 . The process according to  claim 1 , wherein from 5 to 20 mol of the alcohol A are used per mole of hydroxyl groups borne by the compound of the general formula III when using a compound of the general formula III bearing 2 or more alcoholic hydroxyl groups.  
   
   
       9 . The process as claimed in  claim 1 , wherein the process is carried out with current densities in the range from 1 to 1000 mA/cm 2 .  
   
   
       10 . The process as claimed in  claim 1 , wherein the process is carried out with current densities in the range from 10 to 100 mA/cm 2 .