Background and overview[1]
The chemical stability and physiological activity of organofluorine compounds are significantly higher than other compounds, and they have strong fat solubility and hydrophobicity. Verification shows that fluorine-containing medicines and pesticides are less toxic and less toxic than other products in terms of performance. It has higher efficacy and stronger metabolism, so it is widely used in the fields of medicine and pesticide manufacturing. In addition, market prospects can also be seen in some other fields, such as the development and application of synthetic fluorine-containing dyes, fluorine-containing surfactants, fabric finishing agents, coatings, etc. 3,5-Difluorophenol is a gray-white crystal with a melting point of 51 to 55°C. It is mostly used in the synthesis of liquid crystal materials, antifungal agents, etc. It is also used in the synthesis of dyes, plastics and rubber additives. It is an important intermediate for medicines, pesticides, and liquid crystal materials. , there is demand in the market, but there are no synthetic reports in China.
Preparation[1]
A method for preparing 3,5-difluorophenol, including the following specific steps:
(a) Raw material preparation: 99% mass fraction of 3,4,5-trifluoroaniline, 98% mass fraction of concentrated sulfuric acid, 50% aqueous solution of hypophosphorous acid, all industrial supplies, sodium nitrite and Dichloromethane, chemically pure; sodium nitrite and dichloromethane as catalysts.
(b) Preparation of diazonium salt: Add 3,4,5-trifluoroaniline dropwise into reaction bottle A containing an appropriate amount of 50% sulfuric acid solution, stir while adding, and control the reaction. The temperature is lower than 30°C. When more than half of the 3,4,5-trifluoroaniline is added dropwise, the water bath temperature rises to 55°C to speed up the dropping speed; reaction bottle A is made of polyethylene.
(c) Reaction: After the dropwise addition is completed, cool to below 20°C, then add 30% sodium nitrite solution with a mass fraction of 30% to reaction bottle A, control the dropwise speed, maintain the reaction temperature, and determine with starch potassium iodide test paper At the end of the reaction, the dripping was stopped to obtain a diazonium salt solution; the reaction temperature was kept below 20°C.
(d) Hydrolysis of diazonium salt: Stir the diazonium salt solution for 2 hours at 45-50°C, filter after cooling to obtain an orange-yellow transparent solution, add an appropriate amount of hypophosphorous acid solution with a mass fraction of 50% Pour into reaction bottle B, then add an appropriate amount of catalyst, stir and heat to 50°C, drop the diazonium salt solution, control the dropping speed and ensure the reaction temperature is 50~55°C, cool to room temperature after the dropwise addition is completed, and continue stirring for 0.5h. A mixed liquid was obtained; reaction bottle B was made of polyethylene.
(e) Separation and purification: Extract the mixed solution three times with an appropriate amount of methylene chloride, combine the extracts, evaporate the methylene chloride under normal pressure, and then perform distillation under reduced pressure to obtain 3,5-difluorophenol solid. The purity of the obtained 3,5-difluorophenol solid can reach more than 98%, and the yield is more than 68%.
Main reference materials
[1] CN201610772273.7 Preparation method of 3,5-difluorophenol
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