The preparation method is that ammonium salt and methyl chloroacetate undergo a liquid-liquid heterogeneous reaction to obtain oxysulfur phosphate. The reaction equation is shown in the figure:
1150kg ammonium salt, 1300kg methyl chloroacetate and a certain amount of phase transfer catalyst were added in a 1000L reactor, reacted at 58~64 ℃ for 80min, and then stratified. The lower crude ester is distilled in a 1500L refining kettle, and methyl chloroacetate is distilled to recover and apply. The vacuum at the end point of distillation is controlled to be ≤ 93kPa and the temperature is ≤ 120 ℃ to obtain refined oxysulfur phosphate. The reaction has a small heat release and a mild reaction. In the production process, methyl chloroacetate is used in excess, which can not only increase the conversion rate of ammonium salt, but also protect the generated oxysulfur phosphate.