Preparation method of 3-fluoro-4-cyanophenol

[0024] A preparation method of 3-fluoro-4-cyanophenol, which adopts 2,4-difluorobenzonitrile to obtain 2-fluoro-4-alkoxybenzonitrile through substitution reaction, and then obtains 3-fluorobenzonitrile through hydrolysis reaction -4-cyanophenol, its synthetic route is as follows:

[0025]

[0026] (I) Substitution reaction

[0027] Add 2,4-difluorobenzonitrile, catalyst and solvent into the reaction vessel and stir. The solvent is any one of tetrahydrofuran, dioxane, dimethyl sulfoxide or methyl tetrahydrofuran. The amount of solvent added 2 to 4 times the mass of the reactant; the catalyst is β-cyclodextrin or a mixture of β-cyclodextrin and starch with a mass ratio of 1 to 5:1, and the amount of catalyst added is 1 to 3% of the mass of the reactant, and then Add sodium alkylate in 2 to 4 times, the sodium alkylate is any one of sodium tert-butoxide, sodium isopropoxide, sodium tert-amyloxide or sodium n-butyloxide, 2,4-difluorobenzene The molar ratio of forminonitrile and

[0031] (I) Substitution reaction: Add the reactant 2,4-difluorobenzonitrile, catalyst and tetrahydrofuran into the reaction vessel, the amount of tetrahydrofuran added is twice the mass of the reactant, and the catalyst is β-cyclodextrin and starch according to the mass ratio 3:1 mixture, the amount of catalyst added is 2% of the mass of reactant, heat preservation at 10°C, add sodium tert-butoxide in 2 times, the total amount of sodium tert-butoxide added is the molar weight of 2,4-difluorobenzonitrile 1.1 times of 2-fluoro-4-alkoxybenzonitrile was obtained after 3 hours of reaction. The yield of this step is 95%, and the product purity is 85%.

[0032] (II) Hydrolysis reaction: Add 35% hydrochloric acid to the reaction solution containing 2-fluoro-4-alkoxybenzonitrile, the molar ratio of hydrochloric acid to 2-fluoro-4-alkoxybenzonitrile is 1 :8, slowly drop the toluene solution of 2-fluoro-4-alkoxybenzonitrile at 30°C, the molar ratio of 2-fluoro-4-alkylbenzonitrile to toluen

[0034] Embodiments 2-5 adopt the same method steps as the above-mentioned embodiment 1, and the different process parameters are shown in Table 1. The implication represented by the abbreviations that appear in the table is: "catalyst (m%)" represents the mass fraction that catalyst accounts for reactant in step (I), and " reactant: sodium alkyl alkoxide (mol) " refers to 2,4-di The mol ratio of fluorobenzonitrile and sodium alkyl alkoxide; "Raw material: inorganic acid (mol)" in the step (II) refers to the mol ratio of 2-fluoro-4-alkoxybenzonitrile and inorganic acid. "Insulation time" refers to the incubation reaction time after adding raw materials.

[0035] Table 1

[0036]

[0037]