Background and overview[1]
Transfluthrin is a pyrethroid insecticide developed and produced by an original German import company in the 1980s. It is mainly used for the prevention and control of sanitary pests and has a rapid impact and killing effect. At present, there are few domestic manufacturers producing pyrethroid pesticides with great market prospects. 2,3,5,6-tetrafluorobenzyl alcohol is an important intermediate in the synthesis of the pyrethroid insecticide perfluthrin.
Preparation[1-2]
Report 1,
Weigh 20.5g pentafluorobenzonitrile, 0.2g 10% Pd/C (produced by Baoji Ruike Pharmaceutical Chemical Co., Ltd.), 70mLTHF, and 9.5g acetic acid into a 250mL autoclave, replace the gas with nitrogen three times, and pass H2 to a pressure of 10 atm, raise the temperature to 55°C, react for 10 hours, take samples for analysis, the raw materials disappear, filter out the insoluble matter, recover the solvent under reduced pressure, and obtain 25.6g of pentafluorobenzylamine acetate, content: 97.9% (HPLC ), yield: 93.8%.
Add 25.6g of pentafluorobenzylamine acetate to 100g of water, slowly add 10.2g of concentrated sulfuric acid, keep the temperature at 55°C, dropwise add 20g of 40% NaNO2 aqueous solution, and use starch-potassium iodide test paper to detect the solution to the test paper Turn into blue, continue stirring for 1 hour and then raise the temperature to 85°C. After hydrolysis for 6 hours, cool to room temperature, separate the organic phase to recover the solvent and dry to obtain 18.1g, which is pentafluorobenzyl alcohol, content: 97.3% (GC), collected Rate: 91.8%.
Add 9.9g of pentafluorobenzyl alcohol into 30mL of methanol, raise the temperature to 50°C, add 5.1g of Zn powder in batches, slowly add 5.5g of concentrated hydrochloric acid dropwise, keep at 50°C for 30 hours, wait until the raw material disappears and filter out by GC Extract the insoluble matter with 2×25mL methylene chloride, combine the organic phases, and dry with anhydrous Na2SO4. Evaporate the organic solvent under normal pressure and then reduce the pressure. Distill, collect fractions at 84-86°C/10.8mmHg, and obtain 8.0g of product, content: 99.0% (GC), yield: 88.8%, mp: 34-36°C.
Report 2,
Add 50 grams of 1,2,4,5-tetrafluorobenzene and 100 grams of anhydrous 2-methyltetrahydrofuran into a 500 ml four-necked flask equipped with mechanical stirring, a thermometer and a constant pressure dropping funnel. Stir and cool to -50°C under protection, dropwise add 220 ml of n-butyllithium n-hexane solution (1.6 mol/L). After the dropwise addition is completed, continue stirring for 0.5 hours, and introduce formaldehyde gas (from more than 20 grams) into the system. Polyformaldehyde is generated after heating and depolymerization, and is slowly brought in by nitrogen flow). After the passage is completed, stirring is continued for 0.5 hours. The reaction system was heated to 5°C, 100 grams of water was added dropwise, filtered, and insoluble matter was removed. The organic phase was separated from the filtrate, and the aqueous phase was extracted twice with 40 grams of 2-methyltetrahydrofuran. The organic phases were combined, dried, desolvated, and distilled. 56.4 grams of 2,3,5,6-tetrafluorobenzyl alcohol was obtained with a purity of 99.3%.
References
[1][Chinese invention] CN200810162344.7 A preparation method of 2,3,5,6-tetrafluorobenzyl alcohol
[2][China invention, China invention authorization] CN201210100387.9 A synthesis method of 2,3,5,6-tetrafluorobenzyl alcohol
