Preparation method of dicamba

The invention relates to a preparation method of dicamba and belongs to the technical field of preparation of herbicide dicamba. The preparation method of dicamba comprises the following technical steps of: performing directional chlorination, catalysis and melt crystallization on benzene used as a raw material so as to generate 1,2,4-trichlorobenzene; then hydrolyzing by use of 1,2,4-trichlorobenzene so as to generate a 2,5-dichlorophenol and 2,4-dichlorophenol mixture; then separating and purifying so as to obtain 2,5-dichlorophenol; preparing 3,6-dichlorosalicylic acid by use of 2,5-dichlorophenol; and performing methylation, saponification and acidification reaction on 3,6-dichlorosalicylic acid so as to obtain dicamba. By virtue of optimization of technical steps and parameters, the whole preparation process is simple, the cost is low, the yield is high, the selectivity is high, the wastewater quantity is obviously reduced, and the equipment utilization ratio is improved.