Electrochemical reductive coupling of phenol derivatives

Abstract

A scalable Ni- or Ni/Pd-catalyzed electrochemical reductive coupling method is disclosed, affording biaryls in good to excellent yield via the electrolysis of lignin-derived aryl sulfonate esters. This method features the enhanced reactivity provided by the combination of transition metal catalysis and electrochemistry and the high selectivity for desired biaryls over other side products. The biaryls find applications in building blocks for high-performance polyesters or PVC plasticizers.

We claim: 
     
         1 . A method of producing one or more desired substituted biaryl products from one or more substituted aryl sulfonate reactants by electrochemical reductive coupling, the method comprising applying an external electromotive force to add electrons to a cathode electrode of an electrosynthetic cell and to simultaneously remove electrons from an anode electrode of the electrosynthetic cell, wherein the cathode electrode is in contact with a liquid phase solution that comprises the one or more substituted aryl sulfonate reactants, whereby the one or more substituted aryl sulfonate reactants are reductively coupled to produce the one or more desired substituted biaryl products. 
     
     
         2 . The method of  claim 1 , wherein the substituted aryl sulfonate reactant is homo-coupled to make the desired substituted biaryl product. 
     
     
         3 . The method of  claim 2 , wherein the liquid phase solution comprises a catalyst that comprises Ni. 
     
     
         4 . The method of  claim 3 , wherein the catalyst is a nickel salt. 
     
     
         5 . The method of  claim 1 , wherein two different substituted aryl sulfonate reactants are cross-coupled to make the desired substituted biaryl product. 
     
     
         6 . The method of  claim 5 , wherein the liquid phase solution comprises a catalyst or a combination of catalysts that together comprise both Ni and Pd. 
     
     
         7 . The method of  claim 6 , wherein the catalyst or the combination of catalysts comprise a nickel salt and/or a palladium salt. 
     
     
         8 . The method of any of  claims 1-7 , wherein the one or more substituted aryl sulfonate reactants are derived from one or more substituted phenols by converting the phenolic-OH to a sulfonate. 
     
     
         9 . The method of  claim 8 , wherein the one or more substituted phenols are derived from lignin. 
     
     
         10 . The method of  claim 9 , wherein the one or more substituted phenols are derived from lignin by depolymerization of the lignin. 
     
     
         11 . The method of  claim 10 , wherein the lignin is depolymerized by structurally modifying the lignin via selective oxidation, followed by base-promoted depolymerization of the structurally modified lignin. 
     
     
         12 . The method of any of  claim 1-4 or 8-11 , wherein the substituted aryl sulfonate reactant has the chemical formula: 
       
         
           
           
               
               
           
         
       
       where Z comprises a sulfonate ester;
 and wherein the desired substituted biaryl product has the chemical formula: 
 
       
         
           
           
               
               
           
         
         wherein R 1 , R 2 , R 3 , R 4  and R 5  are independently selected from the group consisting of hydrogen, an alkoxy, a carboxylic acid, a carboxylate ester, an aldehyde, a ketone, and a dione. 
       
     
     
         13 . The method of  claim 12 , wherein Z comprises a sulfonate having the formula —SO 2 X, where X is OR 11 , and where Ru is a cation, an alkyl, a haloalkyl, an aryl, or a silyl. 
     
     
         14 . The method of  claim 12 , wherein Z is a mesylate, a tosylate, or a triflate. 
     
     
         15 . The method of any of  claims 12-14 , wherein R 2  and R 4  are hydrogen. 
     
     
         16 . The method of any of  claims 12-15 , wherein R 1  and R 5  are each independently an alkoxy or hydrogen. 
     
     
         17 . The method of  claim 16 , wherein the alkoxy is methoxy. 
     
     
         18 . The method of any of  claims 12-17 , wherein R 3  is a carboxylic acid, a carboxylate ester, an aldehyde, a ketone, or a dione. 
     
     
         19 . The method of any of  claim 1 or 5-11 , wherein the substituted aryl sulfonate reactants have the chemical formulas: 
       
         
           
           
               
               
           
         
       
       where Z comprises a sulfonate ester;
 and wherein the desired substituted biaryl product has the chemical formula: 
 
       
         
           
           
               
               
           
         
         wherein R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , R 9 , and R 10  are independently selected from the group consisting of hydrogen, an alkoxy, a carboxylic acid, a carboxylate ester, an aldehyde, a ketone, and a dione. 
       
     
     
         20 . The method of  claim 19 , wherein Z comprises a sulfonate having the formula —SO 2 X, where X is OR 11 , and where Rn is a cation, an alkyl, an aryl, or a silyl. 
     
     
         21 . The method of  claim 19 , wherein Z is a mesylate, a tosylate or a triflate. 
     
     
         22 . The method any of  claims 19-21 , wherein R 2 , R 4 , R 7  and R 9  are hydrogen. 
     
     
         23 . The method of any of  claims 19-22 , wherein R 1 , R 5 , R 6  and R 10  are each independently an alkoxy or hydrogen. 
     
     
         24 . The method of  claim 23 , wherein the alkoxy is methoxy. 
     
     
         25 . The method of any of  claims 19-24 , wherein R 3  and R 5  are each independently a carboxylic acid, a carboxylate ester, an aldehyde, a ketone, or a dione. 
     
     
         26 . The method of any of  claims 1-25 , wherein the method is performed by batch electrolysis. 
     
     
         27 . The method of any of  claims 1-25 , wherein the method is performed by flow electrolysis. 
     
     
         28 . The method of any of  claims 1-27 , wherein the electrosynthetic cell is a divided cell. 
     
     
         29 . The method of any of  claims 1-27 , wherein the electrosynthetic cell is an undivided cell. 
     
     
         30 . The method of any of  claims 1-29 , wherein the liquid phase further comprises one or more organic solvents. 
     
     
         31 . The method of  claim 30 , wherein the one or more organic solvents are selected from the group consisting of acetone, acetonitrile, benzene, 1-butanol, 2-butanol, 2-butanone, t-butyl alcohol, carbon tetrachloride, chlorobenzene, chloroform, cyclohexane, 1,2-dichloroethane, dimethyl carbonate, diethyl carbonate, diethylene glycol, diethyl ether, diglyme (diethylene glycol dimethyl ether), 1,2-dimethoxy-ethane (glyme, DME), 1,3-dimethyl-2-imidazolidinone (DMI), dimethylformamide (DMF), dimethylacetamide (DMA), 1,3-dimethyl-1,3-diazinan-2-one (DMPU), dimethyl sulfoxide (DMSO), 1,4-dioxane, ethanol, ethyl acetate, ethylene glycol, glycerin, heptane, hexamethylphosphoramide (HMPA), methylene chloride, N-methyl-2-pyrrolidinone (NMP), nitromethane, pentane, petroleum ether (ligroine), 1-propanol, 2-propanol, propylene carbonate, pyridine, sulfolane, tetrahydrofuran (THF), 2-methyl tetrahydrofuran toluene, triethyl amine, o-xylene, m-xylene, and p-xylene. 
     
     
         32 . An electrosynthetic cell for use in producing one or more desired substituted biaryl products from one or more substituted aryl sulfonate reactants by electrochemical reductive coupling, the electrosynthetic cell comprising a cathode electrode and an anode electrode, wherein the cathode electrode is in contact with a liquid phase solution that comprises the one or more substituted aryl sulfonate reactants. 
     
     
         33 . The electrosynthetic cell of  claim 32 , further comprising a device configured to externally apply an electromotive force to add electrons to the cathode electrode and to simultaneously remove electrons from the anode electrode, whereby when the electromotive force is applied, the one or more substituted aryl sulfonate reactants are reductively coupled to produce the one or more desired substituted biaryl products. 
     
     
         34 . The electrosynthetic cell of  claim 32 or claim 33 , wherein the cell is configured to homo-couple the substituted aryl sulfonate reactant to make the desired substituted biaryl product. 
     
     
         35 . The electrosynthetic cell of  claim 34 , wherein the liquid phase solution comprises a catalyst that comprises Ni. 
     
     
         36 . The electrosynthetic cell of  claim 35 , wherein the catalyst comprises a nickel salt. 
     
     
         37 . The electrosynthetic cell of  claim 32 or claim 33 , wherein the cell is configured to cross-couple two different substituted aryl sulfonate reactants to make the desired substituted biaryl product. 
     
     
         38 . The electrosynthetic cell of  claim 37 , wherein the liquid phase solution comprises a catalyst or a combination of catalysts that together comprise both Ni and Pd. 
     
     
         39 . The electrosynthetic cell of  claim 38 , wherein the catalyst or the combination of catalysts comprise a nickel salt and/or a palladium salt. 
     
     
         40 . The electrosynthetic cell of any of  claims 32-39 , wherein the one or more substituted aryl sulfonate reactants are derived from one or more substituted phenols by converting the phenolic —OH to a sulfonate. 
     
     
         41 . The electrosynthetic cell of  claim 40 , wherein the one or more substituted phenols are derived from lignin. 
     
     
         42 . The electrosynthetic cell of  claim 41 , wherein the one or more substituted phenols are derived from lignin by depolymerization of the lignin. 
     
     
         43 . The electrosynthetic cell of  claim 42 , wherein the lignin is depolymerized by structurally modifying the lignin via selective oxidation, followed by base-promoted depolymerization of the structurally modified lignin. 
     
     
         44 . The electrosynthetic cell of any of  claim 32-36 or 40-43 , wherein the substituted aryl sulfonate reactant has the chemical formula: 
       
         
           
           
               
               
           
         
       
       where Z comprises a sulfonate ester;
 and wherein the desired substituted biaryl product has the chemical formula: 
 
       
         
           
           
               
               
           
         
         wherein R 1 , R 2 , R 3 , R 4  and R 5  are independently selected from the group consisting of hydrogen, an alkoxy, a carboxylic acid, a carboxylate ester, an aldehyde, a ketone, and a dione. 
       
     
     
         45 . The electrosynthetic cell of  claim 44 , wherein Z comprises a sulfonate having the formula —SO 2 X, where X is OR 11 , and where Ru is a cation, an alkyl, a haloalkyl, an aryl, or a silyl. 
     
     
         46 . The electrosynthetic cell of  claim 44 , wherein Z is a mesylate, a tosylate or a triflate. 
     
     
         47 . The electrosynthetic cell method of any of  claims 44-46 , wherein R 2  and R 4  are hydrogen. 
     
     
         48 . The electrosynthetic cell of any of  claims 44-47 , wherein R 1  and R 5  are each independently an alkoxy or hydrogen. 
     
     
         49 . The electrosynthetic cell method of  claim 48 , wherein the alkoxy is methoxy. 
     
     
         50 . The electrosynthetic cell of any of  claims 44-49 , wherein R 3  is a carboxylic acid, a carboxylate ester, an aldehyde, a ketone, or a dione. 
     
     
         51 . The electrosynthetic cell of any of  claim 32-33 or 37-43 , wherein the substituted aryl sulfonate reactants have the chemical formulas: 
       
         
           
           
               
               
           
         
       
       where Z comprises a sulfonate ester;
 and wherein the desired substituted biaryl product has the chemical formula: 
 
       
         
           
           
               
               
           
         
         wherein R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , R 9 , and R 10  are independently selected from the group consisting of hydrogen, an alkoxy, a carboxylic acid, a carboxylate ester, an aldehyde, a ketone, and a dione. 
       
     
     
         52 . The electrosynthetic cell of  claim 51 , wherein Z comprises a sulfonate having the formula —SO 2 X, where X is OR 11 , and where Rn is a cation, an alkyl, an aryl, or a silyl. 
     
     
         53 . The electrosynthetic cell of  claim 51 , wherein Z is a mesylate, a tosylate or a triflate. 
     
     
         54 . The electrosynthetic cell of any of  claims 51-53 , wherein R 2 , R 4 , R 7  and Ry are hydrogen. 
     
     
         55 . The electrosynthetic cell of any of  claims 51-54 , wherein R 1 , R 5 , R 6  and R 10  are each independently an alkoxy or hydrogen. 
     
     
         56 . The electrosynthetic cell of  claim 55 , wherein the alkoxy is methoxy. 
     
     
         57 . The electrosynthetic cell of any of  claims 51-56 , wherein R 3  and R 5  are each independently a carboxylic acid, a carboxylate ester, an aldehyde, a ketone, or a dione. 
     
     
         58 . The electrosynthetic cell of any of  claims 32-57 , wherein the cell is configured for batch electrolysis. 
     
     
         59 . The electrosynthetic cell of any of  claims 33-57 , wherein the cell is configured for flow electrolysis. 
     
     
         60 . The electrosynthetic cell of any of  claims 32-59 , wherein the cell is a divided cell. 
     
     
         61 . The electrosynthetic cell of any of  claims 32-59 , wherein the cell is an undivided cell. 
     
     
         62 . The electrosynthetic cell of any of  claims 32-61 , wherein the liquid phase further comprises one or more organic solvents. 
     
     
         63 . The electrosynthetic cell of  claim 62 , wherein the one or more organic solvents are selected from the group consisting of acetone, acetonitrile, benzene, 1-butanol, 2-butanol, 2-butanone, t-butyl alcohol, carbon tetrachloride, chlorobenzene, chloroform, cyclohexane, 1,2-dichloroethane, dimethyl carbonate, diethyl carbonate, diethylene glycol, diethyl ether, diglyme (diethylene glycol dimethyl ether), 1,2-dimethoxy-ethane (glyme, DME), 1,3-dimethyl-2-imidazolidinone (DMI), dimethylformamide (DMF), dimethylacetamide (DMA), 1,3-dimethyl-1,3-diazinan-2-one (DMPU), dimethyl sulfoxide (DMSO), 1,4-dioxane, ethanol, ethyl acetate, ethylene glycol, glycerin, heptane, hexamethylphosphoramide (HMPA), methylene chloride, N-methyl-2-pyrrolidinone (NMP), nitromethane, pentane, petroleum ether (ligroine), 1-propanol, 2-propanol, propylene carbonate, pyridine, sulfolane, tetrahydrofuran (THF), 2-methyl tetrahydrofuran toluene, triethyl amine, o-xylene, m-xylene, and p-xylene.