Abstract: Monosubstituted oxalic acid derivatives of the general formula (I) [A]+[O—C(O)—C(O)—O—X???(I) Wherein the meaning is for [A]+ a cation made from an organic moiety A having a formally positively charged heteroatom selected from the group consisting of nitrogen, phosphorus and sulfur X is a C1 to C30 organic residue and wherein the following compounds (I) are disclaimed: Tetramethylammonium monomethyloxalate Methyltri(alkyl)ammonium monomethyloxalate Trimethyl(1-hydroxyethyl)ammonium monomethyloxalate Methyltriethylammonium monomethyloxalate Tetraethylammonium monomethyloxalate n-Propyltriethylammonium mono-n-propyloxalate n-Butyltriethylammonium mono-n-butyloxalate Benzyltriethylammonium monobenzyloxalate cyclohexyldimethylammonium monomethyloxalate Dimethyl-phenylammonium monomethyloxalate.