1,4-Dihydroxyquinoxaline-2,3(1H,4H)-dione

The asymmetric unit of the title compound, C8H6N2O4, contains one half-molecule; a twofold rotation axis bisects the molecule. The quinoxaline ring is planar, which can be attributed to electron delocalization. In the crystal structure, intermolecular O—H⋯O hydrogen bonds link the molecules into R 2 2(10) motifs, leading to layers, which interact via phenyl–phenyl interactions (C⋯C distances in the range 3.238–3.521 Å).

The asymmetric unit of the title compound, C 8 H 6 N 2 O 4 , contains one half-molecule; a twofold rotation axis bisects the molecule. The quinoxaline ring is planar, which can be attributed to electron delocalization. In the crystal structure, intermolecular O-HÁ Á ÁO hydrogen bonds link the molecules into R 2 2 (10) motifs, leading to layers, which interact via phenylphenyl interactions (CÁ Á ÁC distances in the range 3.238-3.521 Å ).

Comment
Quinoxalines are of interest owing to their biological activities. They seem to have very interesting anticancer activity (Zarranz et al., 2004). For example, 3-aminoquinoxaline-2-carbonitrile 1,4-dioxide have been studied extensively as bioreductive cytotoxic agent. It was found to be an efficient agent and causes redox-activated DNA damage (Chowdhury et al., 2004), even more active than the first drug clinically used as bioreductive cytotoxic agent (Monge et al., 1995;Fuchs et al., 2001). A nonconvenient synthesis of the title compound, (I), was reported previously (Elina & Tsyruľ nikova, 1963), via the hydrolysis of 2-amino-3-hydroxyquinoxaline 1,4-dioxide, which results as a side product (4%) from oxidation of 2-acetamidoquinoxaline with acetic peroxide acid using boiling HCl solution. We report herein a novel simple synthetic method for (I), along with its crystal structure.
The new synthetic strategy for (I), (Fig. 1), is based on the reaction of (1) with NaOH solution, yielding (2) in an S N Ar reaction, which upon hydrolysis with boiling HCl solution, via protonation of amine followed by the attack of water molecule, yielded (I) in a good amount (90%).
The asymmetric unit of the title compound, (I), (Fig. 2) contains one half-molecule. The quinoxaline ring is planar, which can be attributed to a wide range of electron delocalization. Bond lengths and angles are in accordance with the corresponding reported values in 1,4-dihydroquinoxaline −2,3-dione core (Oxtoby et al., 2005) and other similar N-alkyl quinoxalines (Akkurt et al., 2004;Mustaphi et al., 2001). The existence of (I) in the dione form is evident from C1-O2 In the crystal structure, intermolecular O-H···O hydrogen bonds (Table 1) link the molecules into R 2 2 (10) motifs ( Fig.   3) (Bernstein et al., 1995) leading to layers running along the c axis (Fig. 4). Molecules within layers are further interacting via phenyl···phenyl interactions (Dance, 1996), where the layers parallel to a axis interact in an offset stacking motif (C···C distances in the range of 3.238-3.521 Å).

Experimental
For the preparation of (I), to a suspension solution of (1) (2.02 g, 10 mmol) (Ley & Seng, 1975) in ethanol (20 ml), NaOH (20 ml, 10%) was added to give a deep blue solution. After refluxing for 5 h, the brown solution was allowed to cool to room temperature. The resulting mixture was then treated with HCl (30 ml, 10%), refluxed for another 5 h and then supplementary materials sup-2 allowed to stand undisturbed. The resulting residual brown solid was filtered off, washed with cold water (5 ml) and then by cold ethanol (5 ml Fig. 1. Schematic representation for the steps through which reaction proceeds.