Background and overview[1]
Currently, the internationally adopted method is to neutralize the guanidine carbonate aqueous solution with a phosphoric acid aqueous solution, and then proceed to evaporate, concentrate and crystallize it. This method not only uses expensive raw material guanidine carbonate, but also makes it difficult for the product to crystallize in water. According to literature reports, Japan’s annual output in 1978 was 120 tons of monoguanidine dihydrogen phosphate and biguanide hydrogen phosphate. In addition, there are also production reports in the Federal Republic of Germany, Australia, and India. In the early 1990s, my country’s Zhejiang Juzhou Chemical Factory reported that it had tried production using this method. However, due to poor crystallization, the product was in the form of a paste and has been discontinued.
Preparation[1]
A new synthesis method that uses very common starting materials and adopts a new synthesis process to prepare monoguanidine dihydrogen phosphate and biguanide hydrogen phosphate: In a 1000 ml glass three-necked bottle, add 1 mol of industrial grade Mix dicyandiamide and 2.1 moles of ammonium chloride for a melting reaction, raise the temperature to 170-230°C, react for 2-3 hours, cool and then add 500 ml of methanol as the solvent American DuPont, stir and dissolve, then add flake solid hydrogen 2.1 moles of sodium oxide, the amount of solvent is 4 times the volume of the molten flake solid sodium hydroxide. After 2 hours of reflux reaction, the free guanidine mixture is obtained, the polyurethane raw material is cooled, and filtered. The filtered residue can be recycled into melamine and chlorine. Sodium chloride, the filtered filtrate is neutralized with 85% industrial phosphoric acid to a pH value of 8 to obtain a white precipitate of diguanidine hydrogen phosphate or neutralized to a pH value of 4 to obtain a white precipitate of monoguanidine dihydrogen phosphate. After aging, suction filtration and drying, the white powdery diguanidine phosphate or dihydrogen monoguanidine phosphate is obtained. The output rate is as high as about 80%. The filtrate after filtration can recover about 60% of methanol through distillation, and the residual liquid remains in the reaction kettle. After evaporation, concentration and crystallization, dihydrogen phosphate or monoguanidine dihydrogen phosphate can be obtained.
Main reference materials
[1] CN97105223.9 Synthesis method of monoguanidine dihydrogen phosphate and biguanide hydrogen phosphate
