Preparation of 4,6-Dinitrobenzofuroxan Salts

The first salts of 4,6-dinitrobenzofuroxan (potassium, sodium, ammonium, and silver) were prepared by Drost in 1899. The product of precipitation of 4,6-DNBF by potassium bicarbonate was however misidentified as the potassium salt of m-dinitro-o-dinitrosobenzene. The other salts were also thought to be salts of the 

KDNBF is produced by neutralization of an aqueous solution of 4,6-dinitrobenzofuroxan or its sodium salt with a soluble potassium salt (bicarbonate, carbonate, nitrate, chloride) [14, 15, 17, 18, 34]. Various crystal modifiers may be used such as Tween 80 (polyoxyethylenesorbitan monooleate), PVA, dextrin, etc., for preparation of spherical KDNBF [22, 33, 35]. Temperature, stirring speed, dripping speed of reactants, and cooling time all have significant influence on crystal shape and size [22]. The product prepared at our department is shown in Fig. 7.2. It is further possible to prepare KDNBF from an acetone/water environment yielding golden platelets melting at 209 °C with explosion [36]. It is recommended to prepare KDNBF by precipitation from its aqueous solution [17, 37]. 

When methanol is used instead of an aqueous environment, potassium salts of methoxy derivates of dinitrobenzofuroxan or dinitrobenzofurazan (depending on reaction conditions) form instead of KDNBF [7]. 

The sodium salt of 4,6-DNBF may be prepared in the same way as described above when a sodium salt (bicarbonate) is used for the reaction. Other salts of 4,6-DNBF may be prepared by precipitation of aqueous solutions of the sodium salt of 4,6-DNBF by relevant soluble metallic inorganic salts (e.g., nitrate, chloride) 

One of the problems related to the preparation of 4,6-DNBF by nitration of benzofuroxan is its variable yield and the amount of side products. It was found by HPLC that up to 10 % of the isolated product may be 5,6-DNBF. This negatively influences the color and the shape of the resulting potassium salt [38], Spear et al. however disagree with this and report that the presence of the 5,6-DNBF isomer in the nitrated product is below 1 % [31], 

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