2,6-diaminopyridine (20 g, 0.18 mol) and DL-malic acid (27 g, 0.2 mol) were used as raw materials in a 500 mL three-necked round-bottomed flask equipped with a dosing funnel, thermometer and mechanical stirrer. The mixture was cooled in an ice-water bath, and concentrated sulfuric acid (100 mL) was added slowly dropwise, with the rate of dropwise acceleration controlled to keep the reaction temperature from exceeding 45 °C. Subsequently, the addition funnel was replaced with a reflux condenser and the reaction mixture was heated to 110°C and maintained for 3 hours. Upon completion of the reaction, the solution was transferred to a 1 L beaker, cooled to 0 °C via an ice-water bath, and adjusted to pH=8 by slowly adding aqueous NH4OH (300 mL).The crude product was collected by vacuum filtration and the filter cake was washed with 2 L of water. The solid product was ground with a 1:9 (v:v) water:methanol mixture and collected again by vacuum filtration to afford 7-amino-2-hydroxy-1,8-diazanaphthalene as a tan powder in 25 g (86% yield). The product was structurally confirmed by 1H NMR (500 MHz, DMSO-d6) and 13C NMR (126 MHz, DMSO-d6) as well as mass spectrometry (ESI, CH3OH).
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