| abstract |
The invention relates to compounds of formula (I) wherein R<SUP>1</SUP>, R<SUP>2</SUP>, R<SUP>3</SUP> and R<SUP>4</SUP> independently represent OR<SUP>5</SUP> or NR<SUP>6</SUP>R<SUP>7</SUP>; R<SUP>5</SUP>, R<SUP>6</SUP> and R<SUP>7</SUP> independently represent hydrogen, substituted or unsubstituted alkyl, especially C<SUB>1</SUB>-C<SUB>4</SUB> alkyl, or substituted or unsubstituted aryl, especially C<SUB>6</SUB>-C<SUB>10</SUB> aryl; R<SUP>6</SUP>, R<SUP>7</SUP> can also form an aliphatic or aromatic ring, together with the N atom to which they are bonded and optionally other heteroatoms; M represents hydrogen, an equivalent of a monovalent or bivalent metal ion, especially from the group of alkali metals or alkaline earth metals, or of an optionally organically substituted ammonium ion; and B<SUP>1</SUP> represents a bivalent binding link. |