Synthesis of 4-azido-3-diazo-3H-pyrazolo[3,4-b]quinoline

A solution of NaNO₂ (0.19 g, 2.8 mmol) in water (1.0 mL) was added dropwise to a solution of 3-amino-4-hydrazino-1H-pyrazolo[3,4-b]quinoline (0.20 g, 0.9 mmol) in H₂SO₄ (5 mL, 70%) cooled in ice–salt to -10 °C, while the temperature of the reaction mixture was maintained at -10 to -5 °C. The reaction mixture was kept at -5 °C for 1 h and then poured into ice–water (50 mL). The resulting precipitate was collected by filtration, washed with water (100 mL), dried and recrystallized from toluene to give the brownish needles of the diazo compound (0.14 g, 60%), mp 138–140 °C (explosive decomp.). Differential scanning calorimetric data: 132.7 °C (onset), 139.1 °C (reaction peak), ΔH = –348 mcal mg^-1 (reaction enthalpy); no mp (Found C, 51.15; H, 1.86; N, 47.05. C₁₀H₄N₈ requires C, 50.85; H, 1.71; N, 47.44%); νmax/cm^-1 2123 s (N₃, N₂), 2089 sh, 1598 s (C=C); δ 7.75 (t, J 7, 1 H, ArH), 7.94 (t, J 7, 1 H, ArH), 8.18 (d, J 7, 1 H, ArH), 8.31 (dd, J 1.5 and 7, 1 H, ArH).

Stadlbauer, W.; Hojas, G. J. Chem. Soc. Perkin. Trans 1 2000, 3085-3087.

L-prolylglycine (H₂progly) (0.376 g, 2.18 mmol) and [Cr(ClO₄)₃] • 6H₂O (1.0 g, 2.18 mmol) were dissolved in methanol (16 cm³). Diethylenediamine (0.225 g, 2.18 mmol) was added to the solution. The reaction mixture was heated with continuous stirring for 1.5 hr at 65 °C. And then KOH (0.245 g, 4.36 mmol) dissolved in methanol (4 cm³) was added. After additional heating for 23 hr, the solution was cooled and KClO₄ that had settled out was removed by filtration. The solution was then evaporated to dryness. The residue was dissolved again in a minimum amount of water and passed through a Sephadex G-10 column. It eluted as two bands. The first violet band eluted was identified as [Cr(L-progly) ₂]⁺ by comparing electronic spectral data. The second brownish red band was collected and concentrated. After standing for several days, water-soluble brownish red precipitate was collected by filtration, washed with ethanol, and air-dried.
Caution! Although we have experienced no difficulty with the present perchlorate salt, this should be regarded as a potentially explosive compound and treat with care.
Anal. Found: C, 30.09; H, 6.01; N, 16.21. Calcd. for Cr(C₁₁H₂₃N₅O₃)ClO₄ • H₂O: C, 29.84; H, 5.68; N, 15.82. Analysis for C, H, and N was performed by a carlo Erba 11080 Elemental Vario EL analyzer at Taegu division of KBSI. The mid-infrared spectrum was obtained with a Mattson Infinities series FT-IR spectrometer using a KBr pellet. The room-temperature visible absorption spectrum was recorded by using a Cary 5e spectrometer. The emission and excitation spectra at 77 K were measured on a Spex Fluorolog-2 spectrofluorometer as described previously.

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