Green and Metal-free Catalytic Oxidation of Urazoles into Triazolinediones by Guanidinium Nitrate and Catalytic Amounts of Silica Sulfuric Acid

Aromatization of 1,3,5-Trisubstituted of 4,5-Dihydro-1H-Pyrazoles by In-Situ Generation of I+from Hydrogen Peroxide/Acids/Iodide Potassium or Sodium Systems

“…[45][46][47][48][49][50][51][52][53][54][55] The salient catalytic activities attributed to silica sulfuric acid have encouraged us, in the second part of the present paper, to use various solvents like CH 3 CN, MeOH, H 2 O, EtOH, EtOAc, CH 2 Cl 2 and CCl 4 used for aromatization of 1,3,5-triphenyl-2-pyrazolines (1a) as model reaction, EtOH:H 2 O (10:1, v/v) was the solvent of choice as best results in terms of the yield was obtained using SSA (0.02 g), H 2 O 2 (1 mL) and KI (0.016 g) for 1 mmol of 1,3,5-triphenyl-2-pyrazolines when the reaction was run at 80 o C for 15 min in 90% yield (Table 3). Similarly, to illustrate the scope and usefulness of this methodology, a number of reactions were conducted (Scheme Literature data.…”

Triazolinediones as Highly Enabling Synthetic Tools

“…156 However, when a catalytic amount of silica-bound sulfuric acid was used in combination with ammonium nitrate, a variety of urazoles were converted with near quantitative yields while reaction times were only slightly prolonged. 157 Similar results were obtained when aluminum nitrate, 158 urea nitrate, 163 and guanidinium nitrate 159 were examined as alternative nitrate source. When oxidation reactions were carried out in the absence of silica-bound sulfuric acid, no conversion of 4-phenylurazole was detected after several hours.…”