CS216466B1 - Process for refining crude 2-methylphenoxyacetic acid - Google Patents

Abstract

The invention relates to a method for refining crude 2-methylphenoxyacetic acid contained in the form of its sodium salt in an alkaline aqueous solution and contaminated by the presence of sodium 2-methylphenolate, in which the pH of the solution is adjusted by adding hydrochloric acid to a value of 6.3 to 6.7 and the released 2-methylphenol is extracted continuously countercurrently with toluene using vibrational movement at a temperature of 50 to 90 ° C, with the volumetric flow ratio of the aqueous and organic phases being 1.5: 1 to 3: 1. The acid is an intermediate for the production of the herbicide 2-methylchlorophenoxyacetic acid.

Description

The present invention provides a process for refining crude 2-methylphenoxyacetic acid. This acid is an intermediate for the production of 2-methylchlorophenoxyacetic acid herbicide (11CPA) widely used in agriculture.

In the preparation of 2-methylphenoxyacetic acid by reaction of the sodium salt of 2-methylphenol (o-react) and sodium monochloroacetate in an alkaline medium, ee gives a reaction mixture representing an aqueous solution of sodium 2-methylphenoxyacetate and an unreacted excess of sodium 2-methylphenol (o-creeolate). The presence of this starting material is undesirable since it would cause unacceptable contamination of the product and losses if it were not separated and recovered from the reaction mixture before further processing. The prior art refining process consists in distilling unreacted 2-methylphenol from the reaction medium with steam. However, steam distillation does not allow the separation of 2-methylphenol in the reaction medium, which then accumulates in the finished product and impairs this impermissibly.

Surprisingly, the above-mentioned drawbacks of the present process have been eliminated by the present invention, which is based on a process for refining 2-methylphenoxyacetic acid contained in the reaction mixture resulting from its preparation in the form of its sodium salt and contaminated mainly by unreacted sodium 2-methylphenol (o-cresol). The pH of the solution is adjusted to 6.3-6.7 by the addition of hydrochloric acid so that the mixture contains, in addition to the sodium salt of 2-methyphenoxyacetic acid, undissociated 2-methylphenol, which is continuously extracted countercurrently by vibration. The extraction is carried out at a temperature of 50 to 90 ° C and the ratio of the flow rates of the aqueous and organic phases ee is between 1.5: 1 and 3: 1. The aqueous raffinate is freed from the entrained and dissolved toluene and 2-methylphenol residues by aseotropic distillation, the toluene obtained by distillation ee being combined with a toluene extract. The refined aqueous solution of 2-methylphenoxyacetic acid sodium salt is further processed. The toluene extract is then freed from 2-methylphenol by re-extraction with aqueous sodium hydroxide solution, and the toluene is separated from the aqueous phase by simultaneous purification by azeotropic distillation. The obtained aqueous solution of sodium 2-methylphenoleate is reacted.

This way has several advantages. Firstly, it allows to obtain a high purity of the 2-methylphenoxyacetic acid output acid. At the same time, losses of 2-methylphenol can be minimized. Efficient vibration extraction also allows to reduce the consumption of toluene and thus the energy consumption for its distillation. The described continuous refinement is also a basic prerequisite for the continualization of the whole production and thus reducing its labor intensity.

The continuous refining process of 2-methylphenoxyacetic acid is carried out by adjusting the reaction mixture to a value of 6.3-6.7 by adding hydrochloric acid. The treated aqueous reaction mixture was countercurrently extracted with toluene at a temperature of 50-90 ° C and at a water / organic phase volume ratio of 1.5: 1 to 3: 1. Upon extraction, unreacted 2-methylphenol is transferred to toluene. The aqueous phases were freed of the toluene residue by azeotropic distillation and this stream was further processed to 2-methylchlorophenoxyacetic acid. The toluene extract ee is combined by the extract of the first azeotropic distillation a

216 466 extracts 2-methylphenol with an aqueous sodium hydroxide solution. After the second extraction, the stream (both aqueous and toluene phases) is subjected to a second azeotropic distillation. The residue is returned to the reaction, and the distillate is reused for the first extraction.

Exemplary embodiment

Extraction of the reaction mixture containing 30.5 wt. % sodium 2-methylphenoxyacetic acid, 5.3 wt. % Of 2-methylphenol, 9.9 wt. % sodium chloride, 3.3 wt. sodium glycollate and the remainder of the water and having a pB value of 6.5 with toluene in a vibratory tray extractor at 80 ° C. The extractor had an internal diameter of 15 cm and an effective length of 4 m, accommodating 39 trays with teflon perforated plates, which were given a vibration movement in the vertical direction with an amplitude of 0.2 cm and a frequency of 3.4 Hz. The volume flow rate of the aqueous phase was 180 L / h, toluene 90 L / h. The aqueous phase was scattered. The final concentration of 2-methylphenol in the aqueous phase was 30 ppm.

Claims (1)

OBJECT OF THE INVENTION A process for the refining of crude 2-methylphenoxyacetic acid contained as its aqueous salt in an alkaline aqueous solution and contaminated by the presence of sodium 2-methylphenoleate, characterized in that the pH of the solution is adjusted to 6.3-6.7 and the liberated 2- The methylphenol is extracted continuously in countercurrent with toluene by means of a vibration motion at a temperature of 50 to 90 ° C, the ratio of the flow rates of the aqueous to the organic phase being 1.5: 1 to 3: 1.