Improved preparation method of 3,6-dichloro salicylic acid

Abstract

The invention discloses an improved preparation method of 3,6-dichloro salicylic acid. The improved preparation method of 3,6-dichloro salicylic acid comprises the following steps: carrying out reaction on 2,5-dichlorophenol and an alkali liquor, then adding an organic solvent, and carrying out reduced pressure dehydration; adding potassium carbonate, a dehydrating agent and a stabilizer after dehydration is finished, and carrying out reaction at the temperature of 130-140 DEG C for 30-60 minutes; adding materials into a high pressure autoclave, heating to 130-140 DEG C, then introducing CO2, and carrying out high pressure carboxylation reaction; carrying out aftertreatment after the reaction is finished, so that 3,6-dichloro salicylic acid is obtained. The improved preparation method of 3,6-dichloro salicylic acid has the advantages that oxygen is isolated before dehydration and carboxylation, so that oxidation of oxygen to a product is avoided; the dehydrating agent and the stabilizer are added before carboxylation, so that water in a system and positive hydrogen ions generated during carboxylation are further removed, stability of the system is maintained, yield is guaranteed and appearance of the product is greatly improved, usage amount of potassium carbonate is reduced, and an aftertreatment process is simplified; besides, modification on equipment is less, the current production enterprises can implement improvement conveniently, and quick benefit can be obtained.

Description

technical field

[0001] The invention relates to a preparation method of 3,6-dichlorosalicylic acid, in particular to an improved preparation method of 3,6-dichlorosalicylic acid based on the prior art. Background technique

[0002] Industrial grade 3,6-dichlorosalicylic acid is an off-white solid with a melting point of 181-183°C. It is the main raw material for the manufacture of 3,6-dichloro-2-methoxybenzoic acid (dicamba), and it is also an important chemical intermediate. Dicamba is a high-efficiency, low-toxicity, broad-spectrum herbicide, which is widely used at home and abroad, especially the recent promotion of dicamba-resistant transgenic crops has greatly increased the market demand. Therefore, how to efficiently and simply synthesize the key intermediate 3,6-dichlorosalicylic acid is worth studying.

[0003] At present, the synthesis method of 3,6-dichlorosalicylic acid mainly uses 2.5-dichlorophenol as the starting material, reacts with alkaline substances in a...