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An improved procedure was proposed for the synthesis of 3 hydroxy 7,8 benzo 1,2,3,4 tetrahydroquinoline, which is used as a reagent for the analytical test reaction for nitrate and nitrite anions based on azo coupling with diazo compounds. 3 Hydroxy 6 (R phenylazo) 7,8 benzo 1,2,3,4 tetrahydroquinolines (R = 2 COOH, 4 COOH, or 4 SO 3 H) were synthesized by azo coupling reactions in 65-70% yields. The structures of these compounds were con firmed by elemental analysis, 1 H NMR and IR spectroscopy, and X ray diffraction. Based on the X ray data, the bathochromic shift in the UV spectrum of the o carboxy isomer compared to the p carboxy isomer (∆λ max = 50 nm) is attributed to a strong intramolecular hydro gen bond.

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