Preparation method of 3,4-dicyanofuroxan

The invention discloses a preparation method of 3,4-dicyanofuroxan (DCFO). The preparation method comprises the following specific steps: adding nitric-sulfuric acid into a dichloromethane dispersion liquid of cyanoacetic acid, and continuously stirring the mixture to finish reaction; then cooling the mixture; continuously adding cold water into a reaction system; then separating a solvent phase and a water phase from an extraction liquid; washing the solvent phase with saturated table salt water to neutral; performing drying, filtration and solvent recovery on the solvent phase to separate a 3,4-dicyanofuroxan solid product. By replacing a trifluoroacetic acid reaction medium by dichloromethane, the yield of a target product is remarkably increased, the method is simple and feasible to operate, and the raw materials are easily available and are relatively low in cost. By dropwise adding a mixed acid nitrifying agent into a non-reactive medium, influence of water in the raw material on reaction can be removed