Organic Solid Acid/NaNO₂: An Efficient System for the Oxidation of Urazoles and Bis-Urazoles under Mild and Heterogeneous Conditions

Abstract

Various organic solid acids/NaNO 2 were used as effective oxidizing agents for the oxidation of urazoles and bis-urazoles to their corresponding triazolinediones under mild and heterogeneous conditions at room temperature with good-to-excellent yields.

Triazolinediones as Highly Enabling Synthetic Tools

“…Several (in)­organic salts and/or acids can be used to generate nitrogen­(IV) oxides . As is well-known, sodium nitrite (NaNO 2 ) will generate nitrosonium ions, via protonation and dehydration, in the presence of strong organic and inorganic acids , such as oxalic acid, NaHSO 4 , , Mg­(HSO 4 ) 2 , KHSO 5 (oxone), H 5 IO 6 or HIO 3 , 1,3,5-triazine-2,4,6-triyltrisulfamic acid (TTSA), sulfamic or isocyanuric acid, H 3 [P­(Mo 3 O 10 ) 4 ], and acetic acid . Shorter reaction times have been obtained when wet silica is added to the reaction mixture.…”

“…Shorter reaction times have been obtained when wet silica is added to the reaction mixture. More heterogeneous reaction conditions, and easier workups, have been achieved by using solid-supported acids, such as sulfuric, nitric and phosphoric acid adsorbed on silica, ,, silica chloride in combination with wet silica (liberating HCl), , and sulfonated polystyrenes and nitric acid on poly­(4-vinylpyridinium) and poly­(vinylpyrrolidone) (PVP–HNO 3 ) . The PVP-supported nitric acid and the silica-supported analogue (SiO 2 –HNO 3 ) also generate triazolinediones from urazoles in the absence of sodium nitrite because of the nitric acid autoionization process.…”