Preparation
(1) Add guanidine hydrochloride (1 kg) and water (4 kg) to the reactor and stir until the guanidine hydrochloride is completely dissolved. Then add toluene (1.6 kg, with a mass ratio of 1:0.4 to water), and then slowly add hydrazine hydrate (1.05 kg, with a molar ratio of 1:2.0 to guanidine hydrochloride) at a dropping rate of 2.25 kg/h. After the addition is complete, react at 60°C for 10 h. Adjust the pH to 2.5 with hydrochloric acid, let stand, and separate the layers. Take the aqueous layer and distill to concentrate it until a trace amount of precipitate appears in the aqueous layer, obtaining a concentrated solution of about 2.5 kg. During the reaction, the tail gas is passed into a tail gas absorption device. The byproduct ammonia gas generated during the reaction is absorbed by a three-stage acid solution to obtain an ammonium salt solution. The acid solutions are, in order: 85% phosphoric acid aqueous solution, 50% phosphoric acid aqueous solution, and 30% phosphoric acid aqueous solution; (2) The concentrated solution was added to the high-level tank of the reactor. Anhydrous ethanol (10 kg) was added to the reactor, and the concentrated solution was added dropwise at a rate of 3 kg/h while stirring. Crystals precipitated, and after standing for 30 min, they were filtered. The crystals were washed three times with 5.0 kg of cold water and dried to obtain 1.288 kg of white target product. The total yield was 98.0%, and the purity was 99.5% as determined by HPLC.
