Background and overview【1】
Methidathion is a dithiophosphate insecticide and a broad-spectrum organophosphorus insecticide. Methidathion has contact and stomach poisoning effects on pests and mites. It has special effects on controlling scales and can also control a variety of cotton pests. Mode of action: Cephalosporin has stomach poisoning and contact killing effects. It can penetrate into plant tissues and is not afraid of wind and rain. It can kill pests in leaves or peels, as well as pests on the back of leaves that have not been exposed to pesticides. Residual period of effectiveness and damage: Apply the pesticide on apples and dilute it 1000 times. After 20 days, the control effect against codling moth larvae is still 95%. For citrus brown orchards, apply the pesticide diluted 1000 times and the residual effect will be more than 30 days. Tetraphos is safe for crops. Spray the young leaves of apple trees with 40-ring EC diluted times, and observe for 10 days that there is no phytotoxicity.
Methophos is applied before fruit trees bloom and is effective on overwintering larvae and eggs about to hatch. Most of the formulations of zaphosphos are emulsifiable concentrates, which are highly toxic and smelly. They use a large amount of organic solvents, causing great pollution to the environment and endangering human health. In view of the excellent control effect of fenfos on scale insects, if the use of organic solvents can be reduced through the improvement of dosage forms, and its toxicity can be reduced, it will have a significant effect on adjusting the upgrading of my country’s preparation product structure and promoting the improvement of social and ecological benefits. .
In response to this situation, the United Nations Nantong Pesticide Formulation Development Center developed 350g/L saprofen microencapsulated suspension. Microcapsule suspension uses polymer materials as the capsule wall or membrane, and uses chemical or physical chemical methods to wrap the pesticide active substance as the capsule core to form a microcapsule with a semi-permeable membrane, and They are stably dispersed and floated in water as a continuous phase at a certain concentration. The capsule diameter of microcapsule suspension is generally 1 to 20 nm compared to PVC stabilizer. The active substances in the capsule core are slowly released under controlled conditions to meet appropriate control efficacy requirements. Compared with conventional pesticide dosage forms, microcapsule suspensions have the advantages of extending drug efficacy, reducing dosage, reducing the toxicity of highly toxic pesticides, preventing decomposition and volatilization of active ingredients, improving drug stability, reducing environmental pollution, reducing fish poisoning, and encapsulating odors, etc. .
Application and research effects【1】
1. Toxicology test results show that 350g/L saprofos microcapsule suspension is a moderately toxic pesticide, while conventional formulations of emulsifiable concentrate are mostly highly toxic pesticides. Compared with it, the toxicity is significantly reduced.
2. The results of the field efficacy test show that 350g/L fenfos microencapsulated suspension has good control effect on citrus tree scale insects, has good quick-acting properties and significant long-lasting effects. Under the test dosage, as the dosage increases, the control effect improves.
3. The same dosage of methaphin microencapsulated suspension and methionfos emulsifiable concentrate have equivalent quick-acting control effects on citrus tree scale insects, and the long-lasting insecticidal effect is better than that of citrus emulsifiable concentrate. It can be seen that after being made into a microencapsulated suspension, fenfos can prolong the efficacy and improve the effect of pesticide application.
4. 350g/L fenfos microencapsulated suspension is suitable for application to the young nymph stage of citrus tree scale insects. The dosage is 350-437.5 mg/kg, and the spray is evenly applied to 1350kg of water per hectare. There is no harm to citrus trees at the test dose and no adverse effects on the natural enemies of major pests.
5. As people’s awareness of safety, environment, ecology and sustainable development continues to increase, the international development of pesticide formulations is currently moving towards safe, green and low-priced water-based formulations and dust-free formulations. Development direction of solid granular preparations. As one of the most technologically advanced new pesticide formulations, microencapsulated suspensions occupy a very small share of the pesticide formulation market due to its difficult process and technology and long development time, and are far from being ranked among the main pesticide formulations. status, but in view of its many attractive advantages and functions, it has increasingly attracted widespread attention from multinational agrochemical companies and scientific research institutions. It is believed that microencapsulated suspensions will become an important development direction of pesticide preparations.
Application【1】
Methophos has contact killing, stomach poisoning and penetrating effects. It can penetrate into plant tissues and is effective against photoinitiator chewing and sucking mouthpart pests. It is also effective against scale insects (including shield worms and soft worms). , cotton aphid, powdery mildew) has excellent control effect. It is very effective against borer pests, burrowing pests and leaf cluster pests, and is effective in preventing organophosphorus-resistant pests.
Suitable for preventing and controlling various pests on fruit trees, cotton, tea trees, vegetables and other crops. Tetraphos is mainly used to control scale insects on citrus and other fruit trees. It can also control other pests, such as lepidoptera, aphids, weevils, fruit flies, etc. in beet, cotton, grape, pear, rape, sunflower, potato and other crops. . It is currently an effective agent for preventing and controlling scale insects.
Preparation【2】【3】
Synthetic route one:
1. Preparation of sodium methylxanthate
In a 250m1 reaction bottle, add 40g sodium hydroxide (l mol), 76g carbon disulfide C1moU, 35g methanol (1.1mol), and 5OmI water, heat to reflux and stir for about 0.5h, cool to ((0-5)℃, Filtration under reduced pressure, vacuum drying, and 115 g of white and slightly green crystalline solid were obtained, with a yield of 88%.
2. Preparation of methylthioacetate
In the 5OOmI reaction bottle, add 169g of crude sodium methylxanthate (1.3mo1) and 200m1 of water, and add 80g of hydrated sodium (80%, about 1.3mo1) dropwise at (25-30)°C with stirring. After the dropwise addition is completed, react at 40°C for about 4 hours, then cool to ((0-5)°C, there isA large amount of solid precipitated, and the filtered solid was vacuum-dried to obtain 105 g of crude methylthioretin as gray fine crystals with a yield of 76%. The measured melting point was (70-73) ℃, and the literature report is ( 74-75)℃.
Preparation of 3. 2-methoxy-1, 3, 4-thiadiazol-5(4H)one
Desolubilize 106g (1mol) methylthioregroup in 200m1 water, place it in a 500ml reaction bottle, then add 50ml concentrated hydrochloric acid, stir and cool to ((0-5)°C, bubble in phosgene for about 99g (1 mol), the reaction was completed for 1 hour, and then the unreacted phosgene was removed by air bubbling. Filter out the precipitated solid, wash it twice with 100 ml ice water, dry it under vacuum, dissolve the product in ethyl acetate, and filter Remove the insoluble matter, recover the solvent under reduced pressure, and recrystallize the residue with a 1:1 mixture of methanol and water to obtain 67.4g of white crystalline powder, with a yield of 51% and a melting point of (112-113)°C. Literature The value is (113-114)℃.
4. Synthesis of fenfosate
Add 29.3g of the pre-prepared 70% concentrated sulfuric acid into a 150ml Erlenmeyer flask, add 18g of O,O-dimethylphosphorodithioate (95%, 0.108mol) and 2-methoxy under magnetic stirring. 14g (0.105mol) of base-1,3,4-thiadiazole-5(4H)one, add 3.2g of paraformaldehyde (95%, 0.1mol) in batches at (20～25)℃, and control the reaction temperature to (20～25)℃, the feeding time is about 0.5h, then raise the temperature to 30℃, keep stirring for 1.5h, after the reaction is completed, extract twice with 100mol dichloroethane, then wash with 50ml of water, and finally use dilute alkali Liquid to adjust the organic layer to neutral, wash it again with water, separate the layers, dry the organic layer with anhydrous magnesium sulfate, evaporate the solvent under reduced pressure, and obtain 25g of waxy substance, the content of which is 93.1% after chromatographic analysis, and the yield is 73.2%.
Synthetic route two:
This route is divided into four steps. The total yield based on CS2 is about 44%, and the product purity reaches 95%. The reaction conditions are mild, no special equipment is required, and the intermediates in each step do not need to be purified. The next reaction can be carried out continuously, and the route is easy to realize industrialization.
1. Synthesis of sodium methoxydithiocarbamate. Add 8g (95%, 0.1mol) NaOH and 40 mL anhydrous methanol to a 100mL four-neck flask, stir to dissolve, add 14.6g (0.192 mol) CS2 at low temperature, maintain this temperature for a while, then rise to room temperature for reaction. After desolvation, yellow sodium salt is obtained.
2. Synthesis of methyl hydrazinothiocarbamate.
Add the sodium salt obtained in the previous step to 15 mL of water, dissolve it and transfer it to a 10 mL four-neck bottle. Add 11.75g (85%, 0.2 mol) NH2NH2·H2O dropwise at low temperature. After the drops are completed, the temperature is raised to room temperature for 2 h. Filter to get the product.
3. Synthesis of 5-methoxy-1,3,4-thiadiazole-2(3H)-one
Add 15 mL HCl and 45 mL water to the product in the previous step to make a hydrochloride aqueous solution. Add phosgene at 0°C. After the reaction is completed, filter and wash with water to obtain 14 g of white product, with a yield of 56%, m. p112～114℃.
4. Synthesis of fenfosate
In a 100 mL four-neck bottle, add 5.8g concentrated sulfuric acid, 2.6g (95%, 0.019mol) 5-methoxy-1,3,4-thiadiazole-2(3H)-one and 3.44 g (90%, 0.0196 mol) dimethyl phosphorodithioate, add 0.59 g (0.0196 mol) formaldehyde in batches with stirring, complete the addition, react at room temperature for 1 hour, add 30 mL dichloroethane to extract, dichloroethane The alkane layer was washed with water, dried and concentrated to obtain 4.5 g of product, yield 80%, content 95%, m.p. 39°C.
Main references
[1]Zhang Dongsheng, Zhong Sulin, Cao Xiongfei, Cao Xinmei, Li Xiaodong. Research on the toxicity and application of zaprofen microencapsulated suspension [J]. Modern Pesticides, 2009, 8(03): 25-27.
[2]Xue Mei, Liu Yuxiu, Cao Ruzhen. Synthesis of methotrexate [J]. Journal of Shihezi University (Natural Science Edition), 2000(04):302-337.
[3]Huang Zhendong, Chen Daomao, Chen Weimin. Synthesis of methalphos [J]. Pesticides, 1999(03):13.
