US 9,660,311 B2  9  10  wherein R 1  is an aliphatic or aromatic optionally substi› tuted organic radical; and  wherein R 2  is an aliphatic or aromatic optionally substi- tuted organic radical.  In various embodiments the aqueous catholyte of the  instant invention comprises water and, completely or par› tially dissolved therein, an ester of nitric acid that is repre- sented by the general formula:  wherein R is an aliphatic or aromatic optionally substi› tuted organic radical.  In various embodiments the aqueous catholyte of the  instant invention comprises water and, dissolved therein, a  sulfur-containing organic compound such as sulfonic acid or  an amide of sulfonic acid (i.e., a sulfonamide). For instance,  a sulfonic acid represented by the general formula  wherein R represents an organic aliphatic or aromatic group.  Or sulfonamides represented by the general formula  wherein R  1 , R  $^{2}$=an organic aliphatic or aromatic group.  Suitable sulfonic acids include MES (2-(N-Morpholino)  ethanesulfonic acid), MOPS (3-(N-Morpholino)propanesul› fonic acid), BES (N,N-Bis(2-hydroxyethyl)-2-aminoethane- sulfonic acid), TES (2-[ (2-Hydroxy- l, 1-bis(hydroxymethyl)  ethyl)amino ]ethanesulfonic acid), TAPSO (2-Hydroxy-3- [ tris(hydroxymethyl)methylamino ]-1-propanesulfonic  acid), N-[Tris(hydroxymethyl)methyl]-3-amino-2-hydroxy› propanesulfonic acid), HEPPS ( 4-(2-Hydroxyethyl)-1-pip› erazinepropanesulfonic acid), CHES (2-(Cyclohexylamino)  ethanesulfonic acid), 3-Aminobenzenesulfonic acid; for  example MES, MOPS, and HEPPS.  Suitable sulfonamides include o-, m-, p-aminobenzene› sulfonamides, o-, m-, p-methylbenzenesulfonamides, o-, m-,  p-cyanobenzenesulfonamides, 4,4’-diaminobenzenesulpha› nilide.  In various embodiments the aqueous catholyte of the  instant invention comprises water and, dissolved therein, a  phenol. Phenols are organic compounds containing an  hydroxyl group directly attached to an aromatic carbon  atom, and may be represented by the general formula  In yet other alternative embodiments the aminium salt  may be an ammonium salt. For instance, that which is  represented by the general formula (NH$_{4 }$ +)x-,  wherein  x- is  an acid residue.  Alternatively, the aminium salt may be based on a N-het- erocyclic aromatic compound such as imidazole. Particu› larly suitable such salts include imidazolium nitrate, 2-meth› ylimidazolium  nitrate,  4-hydroxymethyl  imidazolium  nitrate, 4-hydroxybenzimidazolium nitrate, 4-methoxyben- zimidazolium  nitrate,  4-(N-methylacetamido)pyridinium  nitrate, o-, m-, p-methylpyridinium nitrate, o-, m-, p-ethyl› pyridinium  nitrate,  2-methoxypyridinium  nitrate,  3-methoxypyridinium nitrate, 3-hydroxypyridinium nitrate,  4-hydroxypyridinium nitrate, 3-fluoropyridinium nitrate,  3-bromopyridinium nitrate, 3-sulfoxypyridinium nitrate,  3-aminopyridazinium nitrate, 3-carboxypyridinium nitrate,  4-methoxypyridazinium nitrate, and 2-amino-4,6-dimethyl  pyrazinium nitrate; for example, imidazolium nitrate.  Particularly suitable such salts include aniline nitrate,  diethylenetriamine nitrate, ethanolamine nitrate, 2-methyl- 1-pyrroline nitrate, methoxyamine nitrate, N-methoxymeth› ylamine nitrate, 1-benzoylpiperazine nitrate, N-methylhy› droxylamine nitrate, 2-aminocyanopropane nitrate, N,N› diethylcyanoacetamide nitrate, dimethylaminoacetonitrile  nitrate, 2,2-diethylaminopropionitrile nitrate, 2-amino-2- cyanoproapne, piperazine dinitrate, N,N-dimethylethylene› diamine dinitrate, N-ethylmorpholine nitrate, and trietha› nolamine nitrate.  In various embodiments the aqueous catholyte of the  instant invention comprises water and, dissolved therein, an  aminium salt formed with inorganic acid. For instance, a salt  represented by the following general formula (HNR $^{1 }$R $^{2}$R 3 t  x-,  wherein  x- represents an inorganic acid residue and R  1 ,  R 2 , R 3  may represent hydrogen atom, and at least one of  them represents an aliphatic or aromatic optionally substi› tuted organic radical. The aminium salt is preferably  selected from chloride, sulfate, perchlorate salts, and even  more preferably is a nitrate.  Particularly suitable phenols include resorcinol, 2-meth- ylresorcinol, gallic acid, 4-nitrocathecol, 4-hydroxybenzoic  acid, 2-nitroresorcinol; for example, a-resorcylic acid, a-re› sorcylonitrile.  Phenol acidity and electrooxidation potential both depend  on its substituents. The oxidation potential of substituted  phenols becomes more positive, and  pKa  values become  more negative with an increase of Hammett’s constant value  of the corresponding substituent. In other words, the direct  electrochemical oxidation of substituted phenol with an  electron-withdrawing group is more difficult, and acidity is  higher than that of substituted phenol with an electron› donating group.  Wherein R 1 , R 2 , R 3 , R 4 , R $^{5}$=H, OH, CH$_{3}$ ,  C$_{2}$H$_{5}$ ,  C$_{3}$H$_{7}$ ,  NH$_{2}$ ,  NO$_{2}$ ,  CN, COOH, SO$_{3}$H, C(R)=O, F, Cl, Br, I, CF$_{3}$ ,  NR$_{3 }$ +,  COOR, CONH$_{2}$ ,  CC1$_{3}$ ,  OR, NR$_{2}$ ;  and R represents H,  or an aliphatic or aromatic organic radical.  ,0  +:/  RO-N  - \ $_{0 }$