CS267906B1 - Method of aryloxyalkanecarboxyl acids preparation - Google Patents

Abstract

The solution relates to the method of preparation of aryloxyalkanecarboxylic acids by oxidation aryloxyalcohols with oxygen or oxygen containing gas in the aqueous-alkaline medium at 50-110 ° C and a pressure of 0.1 to 1.0 MPa in the presence of 0.5 % to 20 wt. of the catalyst relative to it to an aryloxyalcohol which is palladium in the form of medium diameter crystallites 1.5 to 16 mm applied in quantity 2 to 10 wt. on an inorganic support. The solution can be used in chemical industry.

Description

The present invention relates to a process for the preparation of aryloxyalkanecarboxylic acids by the oxidation of aryloxyalcohols with oxygen or an oxygen-containing gas in an aqueous-alkaline medium in the presence of a palladium catalyst.

Of the aryloxyalkanecarboxylic acids, many have found wide application in the form of salts and esters as herbicidal active ingredients (2-methyl-4-chlorophenoxyacetic acid, 2-methyl-4-chlorophenoxypropionic acid, 2,4-dichlorophenoxyacetic acid, 2,4,5- 1richlorophenoxyacetic acid), phenoxyacetic acid is a precursor for the production of V-penicillin, 3-chlorophenoxyacetic acid and trifluoromethylphenoxyacetic acid are the starting materials for the production of some very effective preparations in human and veterinary practice and 2-methylphenoxyacetic acid and 2-methylpropionic acid for the synthesis of herbicides.

These compounds are essentially prepared in a stepwise manner. In the first process, which has long been known from the literature (Ullman: Encyclopaedia of Technical Chemistry, 4th edition Band 9, 578/1975), aryloxy acids are prepared by heating the corresponding aryloxy compounds (phenol or its derivatives) and chloroacetic acid in excess aqueous hydroxide solution. sodium. In this process, it is necessary to use an excess of chloetic acid, which is degraded when the product is isolated.

The second process, which is more environmentally advantageous, is based on the oxidation of arylaxyethanols by oxygen or air in the presence of Pt / C catalysts (SU 1 30510; Ž. 125-128 and Kinetics and Catalysis 2 (1961) 245. However, the results are unsatisfactory in view of the yields and catalyst life obtained. 5 to 10% of platinum (Ž. Fiz. Chim. 42 (1968) 266-268) However, the disadvantage of this process is that a freshly prepared catalyst must be used and at the same time low concentrations of phenoxyethanol in the reaction mixture The reaction takes place at high pressures (14 MPa) and temperatures of 100 DEG to 140 DEG C. The product yield drops to 60% of theory with repeated use of the catalyst. CO2 and phenol.

GB 1590 614 describes the use of palladium alone as a catalyst for the oxidation of monoalkyl or monoalkyl aryl ethers of polyethylene glycol or polypropylene glycol or mixtures thereof, chemically significantly different from simple substituted phenyl-2-hydroxyethyl ethers, respectively. phenyl 2-hydroxy-1-methylethyl ethers.

EP 73 545 relates to a process for the preparation of ether carboxylates by oxidation of ether alcohols with 88% conversion, but in the presence of a mixture of Pt and Pd catalyst.

A significant increase in the activity and selectivity of the catalyst is reported in WO 2851 788, according to which the oxidation of aryloxyethanes takes place in the presence of a Pt or Pd catalyst doped with activators which are lead or bismuth compounds alone or in combination with cadmium or cadmium. its compounds. At the same time, 0E 2851 788 states that Pd catalysts are almost inactive and non-selective in the absence of activators. In Example 3, the authors used a catalyst for the oxidation of Pd / C. The reaction was carried out at 90 ° C and atmospheric pressure for 10 hours. with a phenoxy acid yield of only 40%. The catalyst used is not specified. ·

It has now been found that aryloxyalkanecarboxylic acids of formula I

CS 267 906 Bl

2 wherein R is hydrogen or methyl and R and R are the same or spit and are hydrogen, chlorine or methyl, can be prepared by oxidation of aryloxyalcohols of formula II

2 'wherein R, R and R are as defined above, with oxygen or an oxygen-containing gas in an aqueous-alkaline medium at a temperature of 50 to 110 ° C and a pressure of 0.1 to 1.0 MPa in the presence of 0.5 to 20% by weight, of catalyst, based on the aryloxyl alcohol with which palladium is applied in an amount of 2 to 10% by weight, to the inorganic support according to the invention. The essence of the invention is that palladium in the form of crystallites with a mean diameter of 1.5 to 16 mm is used to catalyze the oxidation.

The advantage of the process for the preparation of aryloxyalkanecarboxylic acids of the formula I according to the process of the invention is that the Pd supported on an inorganic support and used as an oxidation catalyst has a high selectivity, activity and longevity. This achieves very high yields, the amount of catalyst used, calculated on the oxidized alcohol, is considerably reduced, the reaction is carried out at low pressure with the possibility of carrying out the reaction at a high concentration of oxidized alcohol in the batch (up to 30%).

The Pd used as a catalyst can be applied to various supports, such as activated carbon, Al 2 O 3, CaCO 3.

The concentration of the aryloxy alcohol in the aqueous-alkaline reaction medium is chosen so that the resulting aryloxy acid remains dissolved during the reaction and does not appear as a solid phase. Concentrations of 5 to 30% by weight are suitable.

The oxidation according to the invention is carried out predominantly in the presence of alkalis, e.g. NaOH, KOH but also Na ,, C0-j, K ₂ C0 · ,. The amount of alkali is chosen such that 0.5 to 5 moles of alkali, preferably 1 to 3 moles of alkali, are used per mole of -COOH group formed.

The oxidation of aryloxyalcohols according to the invention can be carried out at a temperature of 20 to 150 ° C and a pressure of 0.01 to 1.5 MPa, while from a practical point of view it is suitable to work at a temperature of 50 to 110 ° C and a pressure of 0.1 to 1 MPa. .0 MPa.

The following examples illustrate but do not limit the scope of the invention.

Example 1

0.3 g of a catalyst containing 5 l of Pd on activated carbon, in which the mean diameter of the palladium crystallites was 1.5 to 8.7 nm, was metered into a stirred stainless steel reactor containing 100 cm @ 2 equipped with a temperature meter and an outer jacket for heating. , 1.4 g of sodium hydroxide dissolved in 65 ml of water and 3.8 g of 2-methylphenoxyethanol. After expelling air from the reaction vessel by blowing with a gas containing 60% oxygen, stirring was started and the reaction mixture was heated to 80 ° C. At this temperature, it passed over the surface of the reaction mixture gas of 60% 0 ₂ at a pressure of 0.1 bar. The progress of the reaction was monitored at regular intervals by analyzing the oxygen in the reactor off-gas. The reaction was terminated when the oxygen content of the off-gas was the same as at the reactor inlet. The catalyst was filtered off while hot and, after appropriate work-up, the reaction mixture was analyzed by gas chromatography. 4.2 g of a white crystalline substance were obtained, which contained 95.7 wt. 2-methyl • CS 267 906 B1 3 phenoxyacetic acid, 3.0% by weight, unreacted starting 2-methylphenoxyethanol and 0.5% by weight of o-cresol. The yield of 2-methylphenoxyacetic acid is 96.8% of theory.

Example 2

The procedure was as in Example 1, except that 1.2 g of a catalyst containing 5% Pd / CaCO 3 in which the mean diameter of the palladium crystallites was 6.0 to 12.1 nm, 5.2 g of NaOH dissolved in 45 ml of water and 18.6 g of 2-methyl-4-chlorophenoxyethanol. 21.6 g of a white crystalline substance with a content of 90.1% by weight were obtained. Of 2-methyl-4-chlorophenoxyacetic acid, 4.6% by weight. 2-methylphenoxyacetic acid, 4.5% by weight, unreacted phenoxyethanol and 0.4% by weight. 2-methyl-4-chlorophenoxyethanol. Thus, the yield of 2-methyl-4-chlorophenoxyacetic acid is 97% of theory.

Example 3

The procedure was as in Example 1, but 1.2 g of a catalyst containing 5% Pd / C was used, in which the mean diameter of the palladium crystallites was 4.8 to 14 nm, 6.9 g of Na ₂ CO 2 dissolved in 40 ml of water. 18.6 g of 3-methyl-4-chlorophenoxyethanol and a gas content of 96% by volume was used for the oxidation. oxygen at a pressure of 0.25 MPa. 20.9 g of a white crystalline substance were obtained, which contained 92.5% by weight. Of 3-methyl-4-chlorophenoxyacetic acid, 2.4% by weight. Of 3-methylphenoxyacetic acid, 0.4% by weight of unreacted starting phenoxyethanol and 0.7% by weight of 3-methyl-4-chlorophenol. Thus, the yield of 3-methyl-4-chlorophenoxyacetic acid is 96.3% of theory.

Example 4 The procedure was the same as in Example 1, but using 1.2 g of a catalyst containing 5% Pd / C, in which the mean diameter of the palladium crystallites was 1.5 to 5.9 nm, which had already been used 16 times. for oxidation, 5.2 g of NaOH dissolved in 45 ml of water, 15.2 g of 2-methylphenoxyethanol and for oxidation pure oxygen at a pressure of 0.1 MPa was used. 17.4 g of a white crystalline substance were obtained, which contained 93.2% by weight. 2-methylphenoxyacetic acid, 1.2% by weight of unreacted starting 2-methylphenoxyethanol and 0.2% by weight of o-cresol. The yield of 2-methylphenoxyacetic acid is 97.7% of theory.

Example 5

The procedure was as in Example 1, except that 2.6 g of a catalyst containing 2.3 3 Pd / C, in which the mean diameter of the palladium crystallites was 2.2 to 6.8, was metered into the reactor. tun ,. 5.2 g of NaOH dissolved in 45 ml of water, 13.8 g of phenoxyethanol and air were used for the oxidation at a pressure of 1.0 MPa and a temperature of 90 ° C. 15.2 g of white crystals are obtained, containing 98.2% by weight of phenoxyacetic acid, 0.7% by weight of unreacted starting phenoxyethanol and 0.8% by weight of phenol. The yield of phenoxyacetic acid is 98.2% of theory.

Example 6 '

The procedure was as in Example 1, except that 0.6 g of a catalyst containing 7.4 g of Pd / C, in which the mean diameter of the palladium crystallites was 4.9 to 16 nm, 6.0 g of Na 2 CO 3 dissolved, was metered in. in 40 ml of water, 15.2 g of 2- (2-methylphenoxy) propanol and pure oxygen at 0.1 MPa and 60 ° C were used for the oxidation. 16.8 g of a white crystalline substance were obtained, which contained 86.2% by weight. 2- (2-methylphenoxy) propanecarboxylic acid, 6.9% by weight of unreacted phenoxypropanol and 2.0% by weight of o-cresol. The yield of 2- (2-methylphenoxy) propanecarboxylic acid is 87.7% of theory.

CS 267 906 Bl

Example 7

The procedure was as in Example 1, except that 1.2 g of a catalyst containing 5% Pd / CaCO 3 in which the mean diameter of the palladium crystallites was 6.0 to 12.1 nm, 5.2 g of NaOH were metered in. dissolved in 45 ml of water, 20.7 g of 2,4-dichlorophenoxyethanol and pure oxygen at a pressure of 0.1 MPa was used for the oxidation. 21.9 g of a white crystalline substance were obtained, which contained 98.4% by weight. 2,4-dichlorophenoxyacetic acid, 0.1% unreacted 2,4-dichlorophenoxyethanol and 0.5% 2,4-dichlorophenol. The yield of 2,4-dichlorophenoxyacetic acid is 97.5% of theory.

Claims (1)

OBJECT OF THE INVENTION Process for the preparation of aryloxyalkanecarboxylic acids of general formula I ’12 * wherein R is hydrogen or methyl and R and R are the same or different and are hydrogen, chlorine or methyl, by oxidation of aryloxyalcohols of formula II Wherein R 1, R 2 and R 3 are as defined above, with oxygen or an oxygen-containing gas in an aqueous-alkaline medium at a temperature of 50 to 110 ° C and a pressure of 0.1 to 1.0 MPa, in the presence of 0.5 to 20% by weight. , catalyst, based on the aryloxyl alcohol with which palladium is applied in an amount of 2 to 10% by weight, on an inorganic support, characterized in that the palladium is used in the form of crystallites having a mean diameter of 1.5 to 16 nm.