The invention discloses a preparation method of 4-bromo-2, 6-difluorobenzonitrile. In the preparation method,
tetrahydrofuran,
potassium tert butoxide,
petroleum ether, 3, 5-difluorobromobenzene, DMF and n-
butyllithium with the proportion of n-
butyllithium: 3, 5-difluorobromobenzene, which is equal to 1.2:1 and the proportion of DMF: 3, 5-difluorobromobenzene, which is equal to1.6:1 are taken as raw materials to produce 4-bromo-2, 6-difluorobenzaldehyde, and methanoic acid, 4-bromo-2, 6-difluorobenzaldehyde and
hydroxylamine hydrochloride with the weight ratio of the methanoic acid, the 4-bromo-2, 6-difluorobenzaldehyde and the
hydroxylamine hydrochloride equal to 4:1:1.4 are taken as raw materials to prepare the 4-bromo-2, 6-difluorobenzonitrile. The preparation steps of the 4-bromo-2, 6-difluorobenzonitrile are as follows: A: the raw materials are added to a three-necked flask according to the proportion, and are heated and refluxed for 10 hours at normal pressure; B: a
solvent is distilled at normal pressure, then corresponding volume of water is added to the
system to continuously distill, and the 4-bromo-2, 6-difluorobenzonitrile is carried out; and C: the distilled
aqueous solution is naturally cooled to the
room temperature and is carried out suction
filtration; a
filter cake is washed with water to be neutral, and the product is obtained. The method for preparing the 4-bromo-2, 6-difluorobenzonitrile of the invention takes the 3, 5-difluorobromobenzene as a basic
raw material which is cheap, and the whole
process engineering is low in cost, so the 4-bromo-2, 6-difluorobenzonitrile is applicable to
mass production. The preparation method does not adopt the hypertoxic
potassium cyanide and strong corrosive substances such as
sulfuric acid,
bromine, and the like, which are adopted in the existing process, thus reducing the environmental
pollution.