3,5-dinitro-4-methoxyaminobenzoic acid and its derivatives

The synthesis of the 3,5-dinitro-4-methoxyaminobenzoic acid (1) and its der ivatives (2-6, 7c and 8c) was studied. The two pK(a) values of the acid 1 ( 4.50 and 9.75) have been determined; both the mono- and the di-potassium sa lts (2 and 3, respectively) were prepared. The methyl ester 4 can be synthe sised from the dipotassium salt 3 and methyl iodide in stoichiometric amoun ts, while with an excess of methyl iodide, methylation occurs both at the a mino and the carboxy groups (trimethyl derivative 6). The ester 4 has one p K(a) 8.60; its potassium salt 5 gives with crown ether 18-C-6 a blue comple x. The ester 4 reacts with an excess of DPPH (free radical) affording the b lue betainic compound (1-picryl-2-[4-(4-carbomethoxy-2,6-dinitrophenylamino )phenyl]-diazenium betaine) 7c; the betaine 7c is reduced with ascorbic aci d affording the yellow-orange compound (1-picryl-2-phenyl-2-[4-(4-carbometh oxy-2,6-dinitrophenyl-amino)phenyl]-hydrazine) 8c. Electronic, H-1-NMR and (1)3C-NMR spectra are reported.