Method for preparing 2-(4-methoxy phenoxy) propionic acids

Abstract

The invention relates to a method for preparing 2-(4-methoxy phenoxy) propionic acids. The method includes adding, by weight, 183 parts of hydroquinone and 202.5 parts of S-methyl 2-chloropropionate into a reaction kettle, adding, by weight, 100 parts of sodium hydroxide for a first batch, raising the temperature of the reaction kettle to 70 DEG C to 80 DEG C, reserving the temperature for 8 hours, and reducing the temperature of the reaction kettle to the room temperature after reaction; adding, by weight 128 parts of hydrochloric acid into the reaction kettle, keeping the pH to be about 5 to 6, and reacting the hydroquinone with the hydrochloric acid in a weak acidic environment to produce hydroquinone; adding an extracting agent 4-methyl-2-pentanone into the reaction kettle, layering the solution, wherein an organic layer is the hydroquinone and the extracting agent, and a water layer is an intermediate A/B, methanol and a salt solution; separating an organic phase mixture, reducing the pressure to distill the 4-methyl-2-pentanone, and subjecting hydroquinone crystals to centrifugal separation; and adding, by weight, 128 parts of hydrochloric acids into a dealcoholized aqueous phase, regulating the pH to be 1 to 2, reacting the intermediate under an acid precipitation condition, and precipitating the 2-(4-methoxy phenoxy) propionic acids after adding acids. The method for preparing 2-(4-methoxy phenoxy) propionic acids has the advantages of being simple to operate, low in cost, small in pollution, and suitable for industrial large scale application.

Description

[0001] technical field [0002] The invention relates to a preparation method of a herbicide intermediate, in particular to a preparation method of 2-(4-oxyphenoxy)propionic acid. Background technique [0003] 2-(4-Oxyphenoxy)propanoic acid with the formula HOC 6 h 4 OCH (CH 3 )COOH is light brown oily liquid, odorless and tasteless. It is the key intermediary of phenoxypropionic acid herbicides such as diclofenac, diclofop, etc. This kind of high-efficiency herbicide can selectively control annual or perennial grass weeds, and the dosage is small, and it is harmless to humans and animals. Therefore, it is widely used in various countries. [0004] The difficulty in the synthesis of this intermediate compound is: one, hydroquinone is easily oxidized by air in alkaline solution; two, two phenolic hydroxyl groups of hydroquinone can undergo nucleophilic substitution simultaneously; Acid in alkaline solution α-chlorine is easily OH - replace. At present, in the existing ...

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Problems solved by technology

[0005] The disadvantage of method (1) is that expensive dimethyl sulfoxide and α-bromopropionic acid are used. Although α-bromo is prone to nucleophilic substitution, it also increases the tendency of hydroquinone double substitution. Substitution requires an excessive amount of hydroquinone. For example, the molar ratio of hydroquinone to α-chloropropionic acid is 2.5:1, which causes a lot of waste of hydroquinone. The entire reaction time is about 40 hours , so this method is costly and time-consuming

[0006] Method (2) needs to be protected with nitrogen, and the intermediate treatment is troublesome, and the highly toxic and explosive diazomethane is used. Therefore, the large-scale use of this method is also limited

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