Process for preparing solid (chlorine methylene) dimethyl ammonium chloride

A method for preparing solid (chlorine methylene) dimethyl ammonium chloride. The method comprises: carrying out acylating chlorination reaction on raw materials of phthalic anhydride and thionyl chloride to obtain o-phthaloyl chloride; o-phthaloyl chloride reacting with N,N-dimethylformamide to obtain (chlorine methylene) dimethyl ammonium chloride and phthalic anhydride; dissolving the generated phthalic anhydride in excessive N,N-dimethylformamide; and obtaining solid (chlorine methylene) dimethyl ammonium chloride through solid-liquid separation. The method discharges sulfur dioxide through the first step of reaction, so that sulfur dioxide does not need to be forcedly removed in a high vacuum condition, thereby making the reaction condition mild and the implementation easy.