This type of compound is a special intermediate for the synthesis of phosphorothioate pesticides, with the following structural general formula:
Among them, the most representative are methyl chloride and ethyl chloride, which can be used to synthesize many kinds of phosphorothioate pesticides; in addition, it can also be hydrolyzed by chloride to obtain another type of intermediate sulfur (alcohol) instead of phosphate, and then synthesize sulfur (alcohol) instead of phosphate pesticides.
There are two main methods for synthesizing chloride: phosphorus pentasulfide method and phosphorus trichloride method.
(1) phosphorus pentasulfide method
That is, P2S5 is used as the starting material to obtain sulfide first, and then chlorination to obtain the corresponding chloride.
The equipment used in this method is relatively simple, the quality and yield of chloride are ideal, and it is suitable for large-scale industrial production. However, the main problem of this method is that the post-treatment is relatively complicated, the by-product inorganic chloride S2Cl2 is difficult to remove, and it will directly affect the quality of chloride and final product. A lot of work has been done in this area at home and abroad to find a variety of methods to remove S2Cl2 from crude chloride. The sodium sulfite method and the alkali sulfide treatment method are mainly used in China. Among them, the alkali sulfide treatment method is more advanced, that is, the reaction liquid and the alkali sulfide (sodium, potassium, ammonium salt) aqueous solution are mixed according to specific conditions to dissolve the original S2Cl2 in the reaction liquid is decomposed. For example, control the pH of chlorinated liquid alkali treatment = 6~9, preferably in the range of 7~8, the sulfide concentration is not less than 0.8~1mol/L, and the crystalline sulfur precipitate can be filtered out. S2Cl2 NaS[pH=6~9]→2NaCl 3S↓
In addition, PCl3 can also be used for treatment to convert part of S2Cl2 into PSCl3. After distilled to remove PSCl3, the purity of chloride can reach 98%. There are many post-treatment methods for chloride, such as secondary chloride method, distillation method with additives, heat treatment method, distillation residue set usage, etc.
(2) phosphorus trichloride method
Using phosphorus chloride as the starting material, it reacts with the corresponding alcohol under the catalysis of organic base or inorganic base.
This method is relatively simple to operate and is adopted by most factories in China. Its main problem is that the three chlorine atoms of thion trichloride can be replaced by alkoxy groups one by one to form dichloride, chloride and trialkyl phosphorothioate respectively. In order to improve the yield of chloride, the reaction is generally carried out in two steps. The first step is to obtain dichloride. This step is faster and easy to proceed. Then alkaline substances (such as NaOH alcohol solution, solid alkali, etc.) are used as binding Acid agent, the second chlorine atom is replaced to obtain chloride.