Properties and preparation of fenitrothion_Industrial additives

Background and overview^[1]

Fenitrothion (fenitrothion) is an organophosphorus pesticide. It has medium toxicity and low toxicity to humans and animals. The acute oral LD₅₀ in rats is ~800 mg/kg, and the acute dermal LD₅₀ in rats is 1200 mg/kg. Fenitrothion has contact and gastric poisoning effects, no systemic or fumigation effect, medium residual effect period, broad insecticidal spectrum, special effect on Lepidoptera larvae, and can also control Hemiptera, Coleoptera and other pests. This agent is stable to light and is easily decomposed and invalidated when exposed to high temperatures. It is hydrolyzed in alkaline media. Iron, tin, aluminum, copper, etc. will cause the agent to decompose. It can be stored in a glass bottle for a long time. The current preparation method is to prepare the fenitrothide. The phosphorus content is low, there are many by-products, and the pollution is serious.

Physical and chemical properties^[2]

The appearance is white or light yellow crystalline powder with no visible foreign impurities. The specific gravity is 1.219g/m³ at 25℃; the melting point is 78-81℃; the vapor pressure (20℃) is 2.3×(minus 7 of 10) Pa; the solubility in water is extremely low at room temperature and can be dissolved in Ketones, alcohols and aromatic hydrocarbon solvents. The density is 1.3227. When hydrolyzed by alkali, the half-life in 30℃ and 0.01mol sodium hydroxide is 272min. Distillation will cause the pp adhesion promoter to isomerize. Melting point 0.3℃, boiling point 140~145℃/13.3Pa, insoluble in water (14mg/L), but soluble in most organic solvents, low solubility in aliphatic hydrocarbons. Vapor pressure 0.80mPa (20℃).

Features^[2]

Trans-cypermethrin is a third-generation pyrethroid insecticide. It is mainly used for the prevention and control of agricultural and forestry pests such as field crops, cash crops, vegetables, and fruit trees, as well as household hygiene pests such as vegetables, mosquitoes, and bedbugs. It has It has the characteristics of high antitoxicity, broad spectrum, low toxicity to humans and animals, rapid action, and long-lasting effect. It has contact and stomach poisoning, egg killing, and antifeedant activity against pests, but it has no systemic effect. It is resistant to rain erosion and is particularly effective against pests that have become resistant to organophosphorus pesticides. Due to years of continuous use and cross-resistance issues with organophosphorus and carbamates, pests have generally developed strong resistance to these pesticides, and their control effects are no longer as good as before.

Preparation^[1]

A preparation process for fenitrothion, the steps are as follows:

(1) Preparation of m-cresol and sodium nitrite mixture: First, pump the sodium nitrite solution from the sodium nitrite storage tank into the sodium nitrite metering tank using a submersible pump, and add 850Kg of 32% nitrite to the sodium nitrite metering tank. The sodium solution is added to the mixing kettle, and then a submersible pump is used to drive the m-cresol in the m-cresol storage tank into the m-cresol metering tank. 421kg of m-cresol is also added to the mixing kettle, and the mixing kettle is started for stirring. Mix the two materials evenly and keep the mixture at room temperature for later use;

(2) Nitrosification reaction: After checking that the equipment is normal, first pump the dilute nitric acid prepared in the dilute acid storage tank into the dilute acid metering tank using a submersible pump, and then put 5950Kg of 18-20% dilute nitric acid into the dilute acid metering tank. In the nitrification kettle, start the nitrification kettle for stirring, and at the same time open the cooling brine in the nitrification kettle jacket and the cooling pipe, cool the material to below -8°C, and then add m-cresol and sodium nitrite to the nitrification kettle. The mixed liquid, sodium nitrite and m-cresol is added into the nitrification kettle from the bottom valve of the kettle through the flow meter under full stirring; the initial feeding flow is controlled at about kg/h, so that the incoming sodium nitrite generates a certain concentration of nitrous acid. , after ten minutes, speed up the feeding speed and control the flow rate to 600kg/h to keep the reaction temperature between -9°C; after the feeding is completed, keep it warm for 0.5h; during the insulation, turn off the frozen brine to allow the material temperature to rise naturally; after the insulation is completed , the reaction is completed, open the bottom valve of the kettle, and put the slurry material into the oxidation kettle to be oxidized;

(3) Oxidation reaction: After the nitrosation reaction materials are put into the oxidation kettle, start stirring, turn on the hot water pump, and use hot water in the hot water tank to heat it up. When it reaches 12°C, stop heating and let it rise slowly. to 24°C, keep warm for 1.5h, the keeping temperature should not exceed 28°C, then raise the temperature to 40°C, stop heating, let it slowly rise to 44°C, start the timer to keep warm for 0.5h, the keeping temperature should not exceed 48°C, and oxidize after the heat preservation is completed The reaction ends;

(4) Crude nitrate filtration: Cool the material in the oxidation kettle to below 27°C, stop stirring, and let it stand for 45 minutes. First, put down the supernatant liquid for about 8 minutes, and then put the upper slurry in batches. into a centrifuge for filtration to obtain crude nitrate;

(5) Condensation reaction: On the basis of checking that the equipment and instruments are normal, heat the water in the water metering tank to 85°C, accurately add 1800kg to the condensation beating kettle, start stirring, add 240Kg of soda ash, and stir for 10 minutes to dissolve; Put 480Kg of crude nitrate into the condensation beating kettle, control the temperature at 63°C, and stir for 30 minutes. After it is fully dissolved into sodium phenol salt, press it into the condensation kettle; add 90kg of liquid caustic soda dropwise, and measure the pH value. The pH value is required to be between 8 and 9. , after adjusting, stir for 10 minutes; cool to 52°C, add 30kg of sodium dithionite, and keep warm for 1 hour at a temperature of 50-55°C; open the frozen brine and cool to 25°C, add 10kg of cuprous chloride, and stir for 10 minutes; 560kg (content: 90%) methyl monochloride is dropped into the condensation kettle, the dropping time is 1 hour, the temperature is 25-30°C; after the dripping is completed, the temperature is maintained at 25-30°C for 1 hour, and then the temperature is slowly raised to 60°C , heating time 1h, sampling and analysis to ensure complete reaction of methyl monochloride; add 2000kg toluene, stir for 0.5h, control the temperature at about 60℃; add 40Kg 703 activated carbon, then raise the temperature to 60℃, keep it warm for 30 minutes, press filter , start the cycle first when filtering, wait until the filtrate is transparent, start filtering, finish filtering, add��700kg toluene, rinse the filter cake;

(6) Alkali washing and water washing: Pump the materials in the benzene oil intermediate storage tank into the water washing kettle, let it stand for 20 minutes, and separate the lower layer; turn on the stirring, pour in the measured 1800kg60℃ alkali solution, and stir After 30 minutes, stop stirring, let it stand for 20 minutes, and separate the lower layer; when washing, add 2000Kg of 50°C hot water to the washing kettle each time, and the operation method is the same as alkali washing. Wash with water twice in total. After washing, put the material into the benzene oil storage tank;

(7) Desolvation: one-stage flat plate distillation. After checking that the equipment, instruments and valves are normal, use a pump to pump the materials in the benzene oil storage tank into the flat plate metering tank, turn on the flat plate vacuum and wait until the vacuum degree is ≥ 0.085MPa. , open the chilled brine valve of the condenser, slowly open the steam valve and benzene oil inlet valve. After the distillate temperature reaches 75°C, adjust the benzene oil feed valve, control the benzene oil feed amount at about 650Kg/h, and adjust the steam valve. The steam pressure is controlled below 0.3MPa; after the flat plate distillation is completed, close the steam inlet valve and open the circulating water inlet valve to cool down; after the temperature in the flat plate evaporator drops to normal temperature, stop the flat plate vacuum and close the circulating water. For two-stage falling film distillation, after checking that the equipment, instruments, and valves are normal, use a pump to pump the material that has been distilled on the first-stage flat plate into the high-level falling film tank. Turn on the first-stage vacuum pump. After the vacuum degree is ≥0.09MPa, open the frozen brine valve. , steam inlet valve, slowly open the feed valve, until the falling film temperature reaches above 95°C, adjust the feed valve to control the feed amount at about 2000Kg/h, adjust the steam valve, and control the steam pressure below 0.3MPa; after completion, proceed For secondary falling film distillation, turn on the secondary vacuum pump. When the vacuum degree is ≥ 0.098MPa, open the steam inlet valve and slowly open the feed valve. After the falling film temperature reaches 124°C, adjust the feed valve to control the feed amount at 750Kg/h. Left and right, adjust the steam valve, the steam pressure is controlled below 0.3MPa, and the falling film temperature is controlled at 126~128°C; after the end, close the steam inlet valve, drain the steam, close the secondary vacuum pump, open the circulating water to cool down, and wait for the film to fall After the temperature in the evaporator drops to normal temperature, the first level of vacuum is stopped, the circulating water is closed, and the finished product fenitrothion is obtained.