DD146945A5 - PROCESS FOR PREPARING 3,3-DIMETHYL-2-OXOBUTTERIC ACID - Google Patents

Abstract

The invention relates to a process for the preparation of 3,3-dimethyl-2-oxobutyric acid in high yield and purity by catalytic oxidation of 3,3-dimethyl-2-hydroxybutyric acid in alkaline-aqueous medium. As the oxidizing agent sodium hypochlorite is used, serve as a catalyst ruthenium salts or oxides, in particular ruthenium dioxide hydrate. The solid catalyst is filtered off and can be reused; the filtrate containing a salt of 3,3-dimethyl-2-oxobutyric acid can be further processed immediately.

Description

Berlin, May 12, 1980 } _ _A _ AP C 07 C / 216 802 ^u 56 386/18

Process for the preparation of 3,3-dimethyl-2-oxobutyric acid

Field of application of the invention

The invention relates to a process for the preparation of 3,3-dimethyl-2-oxobutyric acid and its salts by catalytic oxidation of 3,3-dimethyl-2-hydroxybutyric acid.

The compound prepared according to the invention is a valuable intermediate for the production of herbicides.

Characteristic of the known technical solutions

3,3-Dimethyl-2-oxobutyric acid is required as an intermediate for large-scale production - by reaction with thiocarbohydrazide and subsequent S-IvIethylierung of 4 - ^ mino-6-tert-butyl-3-methylthio-1,2,4- triazine-5 (4H) -one (metribuzin), a selective herbicide used primarily in soybean, tomato and potato crops (see Chem. Ber., 97, 2173-8 (1964), U.S. Patent No. 3,671,523 and U.S. Patent 3,905,801). 3,3-Dimethyl-2-oxobutyric acid can be prepared by oxidation of 3,3-dimethyl-2-hydroxybutyric acid with potassium permanganate (see DE-OS 26 48 300).

Although this method is also suitable for large-scale implementation and has been used for the production of large quantities of metribuzin, but it is very expensive because of the high price of potassium permanganate; In addition, large amounts of manganese dioxide (manganese dioxide) as a by-product, which must be landfilled and may possibly contribute to environmental pollution.

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Object of the invention

The aim of the invention is therefore to provide an improved and economical process for the preparation of 3,3-dimethyl-2-os: obutyric acid and / or their salts.

Explanation of the essence of the invention

The invention has for its object to find oxidizing agents that are cheaper than potassium permanganate and cause no environmental impact.

According to the invention, 3,3-dimethyl-2-o: xobutyric acid is prepared in the manner that 3,3-dimethyl-2-hydroxybutyric acid e

(CHOoC-CH-OOOH ("hydroxy acid") OH

in aqueous alkaline solution with the at least stoichiometric amount of a salt of the hypochlorous acid (hypochlorite) in the presence of a ruthenium catalyst oxidized and the 3,3-dimethyl-2-oxobutyric acid

(CHO) OO-C-COOH ("keto acid") O

optionally also sets the initially obtained solution of their salts in freedom.

Favorably, the sodium salts of said acids are used for this purpose, but it is also possible to use other alkali metal and alkaline earth metal salts, with the proviso that they are soluble in the aqueous reaction medium.

The reaction medium advantageously has a pH of about 9 to 13, preferably from about 10 to 12. Since some of the hydroxyl ions appear to be consumed in the course of the reaction, alkali is either in excess

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used or added during the oxidation to maintain the desired pH. When the pH of the solution of the salt of 3,3-dimethyl-2-hydroxybutyric acid ("hydroxy acid") falls below 6.0, or the content of the free potassium caustic soda solution drops to less than about 1.3%, the desired one proceeds Oxidation does not proceed to the extent required and further addition of hypochlorite will only result in the cleavage of optional keto acid. In addition, the Ru catalyst is converted into a water-soluble form, which is difficult to separate from the solution.

The hypochlorite is preferably used in an excess of about 5-15 % to ensure complete oxidation of the 2-hydroxy acid to 2-keto acid. The hypochlorite can be prepared in situ, for example by introducing chlorine gas into an aqueous, alkaline solution of "hydroxy acid" containing the catalyst.

The reaction may be carried out at room temperature, but is carried out to accelerate more favorably at elevated temperature, preferably in the range of about 40 to 60 ° C. Temperatures above 60 ^° C. are unfavorable and should be avoided since pivalic acid is formed as a by-product in this region as a result of decarbonylation.

The ruthenium catalyst is oxidized by the hypochlorite to a mixture of ruthenate, perruthenate and ruthenium tetroxide, wherein the ruthenate predominates. At the end of the reaction, the ruthenium oxide is in the form of a solid in one of the originally used essentially 21

C _ 4 -

  'Chen appropriate amount, so that it can be used by filtration UQd even without treatment in a further oxidation approach. The ruthenium may be introduced into the reaction solution in the form of a salt or oxide, with ruthenium dioxide and in particular ruthenium dioxide hydrate being preferred. The oxide could e.g. in situ from a salt, e.g. Ruthenium trichloride.

The ruthenium oxide is used in catalytic amounts, e.g. 10 '0.01 to about 1.0 g / mol, preferably about 0.1 to 0.5 g / mol of "hydroxy acid" used.

The catalyst-containing aqueous "hydroxy acid" salt solution is brought to the desired pH and temperature. Then, aqueous sodium hydroxide solution are added and chlorine introduced or previously prepared sodium hypochlorite, NaOCl, added dropwise in the form of an aqueous solution or added in portions. After completion of the addition of the entire oxidant, the reaction mixture is allowed to stand until the end of the reaction and then filtered off to separate the catalyst from the solution containing the desired product, i. a salt of 3,3-dimethyl-2-oxobutyric acid, in high yield and purity.

From this solution, the "keto acid" can be purified in the usual way by acidification with a mineral acid, e.g. Hydrochloric acid, set free and also isolated in high yield and purity.

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The oxidation is rapid and addition of the hypochlorite within only 5 minutes already leads to very high yields. Advantageously, however, longer reaction times of from 30 minutes to 1 hour are maintained to allow the ruthenium catalyst to be converted to a suitable insoluble form so that it can be filtered off and reused in a further reaction mixture. The solution obtained by simple filtration can be used directly for the reaction with thiocarbohydrazide to form 4-amino-6-tert-butyl-3-thio-1,2,4-triazine-5 (4H) -one.

In "Chemical Communications", 1420 (1970) it is described that compounds which have the group -CHOH-CO-, in the course of the oxidation using ruthenium as a catalyst of a carbon-carbon cleavage and not the conversion into -CO- CO- subject, z. B .:

-CHOH-CO-> -CHO + OHC-

-CHOH-CO- __j> -CO-CO-

Surprisingly, however, using the inventively provided -A-Ausgangsgangsverbindungen in alkaline-aqueous reaction medium, the oxidation under conversion of the 2-hydroxy group in a 2-carbonyl group without cleavage between the hydroxyl or carbonyl-bearing carbon atoms C-1 and C-2 before yourself.

embodiment

The invention will be explained in more detail below with reference to embodiments.

ag - -w - -

example 1

a) In a 2 liter capacity round-bottomed flask equipped with a mechanical stirrer, thermometer, condenser and dropping funnel, 559 g of an 11.8% aqueous solution of 3,3-dimethyl-2-hydroxybutyric acid (" Hydroxy acid ") in the form of the sodium salt (0.5 mol) and 0.2 g of ruthenium dioxide hydrate (RuOp.HpO). The pH was adjusted to 12 and the temperature auf.40 ⁰ C · adjusted. Then, with rapid stirring, 330.5 g of 12.1% strength NaOCl (0.5 mol + 7.5 % excess) in water were added dropwise over the course of 30 minutes and the temperature was kept at 40 ^° C. by means of an ice bath during this period. Upon completion of the addition, the ice bath was removed, the solution stirred for 1 hour and then filtered to remove the catalyst. 879 g of a 7.5% aqueous solution of 3,3-dimethyl-2-oxobutyric acid ("keto acid") as the sodium salt were obtained. Yield: about 100 %.

b) After completion of the oxidation, the Ru catalyst was in the form of the black, water-insoluble Rutheniumdioxidhydrats. It was filtered off using celite filtration aid. The wet, consisting of catalyst and filtration aid filter cake was introduced directly into another subset of hydroxy acid salt solution and as described above, was carried out with the addition of hypochlorite further oxidation.

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c) 956 g of a 15.8% strength Thiocarbohydrazidlösung in dilute HCl was within 10 minutes under "rapid stirring at 7O ⁰ C with 2682 g of 7.27% sodium""-filtrat keto acid (heated to 70 ⁰ C) was added, the as described under a) had been prepared.

After maintaining the temperature at 70 ^° C. for four hours at a pH of 1.3, the solution was cooled and filtered off. The resulting solid was washed with water and air dried. There were obtained 272.2 g (99.3 % pure) of 4-amino-6-tert-butyl-3-thio-1,2,4-triazine-5 (4H) -one.

Example 2

In a provided with stirrer, thermometer and feed funnel four-necked round bottom flask with a capacity of 1 liter 52 4 g of an aqueous solution containing 0.5 mol of "hydroxy acid" and 100 mg Rutheniumdioxidhydrat were introduced. The temperature was kept at 15 ° C by means of ice bath, 294 g of 11.9% NaOCl solution were added dropwise with stirring over 1.5 hours. Thereafter, the solution was brought to room temperature with stirring within 1 hour. After filtration through glass fiber filter paper (trade name GFA) and washing the RuOp with a small amount of dilute sodium hydroxide solution, 829 g of a solution containing 7.25 % "keto acid" were obtained. Despite the low reaction temperature and the small amount of catalyst, the yield was 94.4 %.

Example 3 (comparative example )

The procedure was as described in Example 1, but at a temperature of 80 ⁰ C worked.

427.4 g (3.5 % excess) 9.0% NaOCl became 555 g 11.7% within about 30 minutes

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"Hydroxy acid" added at a level of 0.4 g. After filtration, 982 g of a solution containing 5.82 % "keto acid" (87.9 %), 0.44% unreacted "hydroxy acid" (6.5 %) and 0.32% (6.6%) were added. Yield) pivalic acid in the form of its salt. It can be seen that at higher temperatures, small amounts of pivalic acid are obtained as a by-product.

Example 4

The procedure was as in Example 1; the NaOCl was added at a constant rate over 5 minutes while maintaining the temperature of the reaction mixture at 40 ° C. 982 g of a solution containing 6.36 % "keto acid" (96.1 % yield) containing no unreacted "hydroxy acid" were obtained. 0.3 g of RuOp-H 2 D was used. Due to the low temperature, the formation of pivalic acid was avoided, but the faster addition compared to Example 1 resulted in a low yield loss.

Example 5

Example 4 was repeated except that the NaOCl solution was added over 2 hours and 983 g of a solution containing 6.55 % "keto acid" (yield 99 %) were obtained.

Example 6

Example 1 was repeated using glass and platinum electrodes attached to a pH meter (model Sargent-Welch LS) and a 10 mV recorder. The NaOCl was fed at constant speed with a metering pump. The potential of the solution was maintained at 330-400 mV. Near the end of the implementation rose

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the voltage to 500 mV, at which point the NaOCl addition was adjusted. There were obtained from 559 g of 11.8% hydroxy acid "solution 921 g of a solution containing 6.7%" keto acid "(yield 95 %) .

Example 7

To a mixture of 120 ml of water, 100 ml of 50 % IV sodium hydroxide solution, 1 g of RuO ₂ .HpO and 0.5 mol of "hydroxy acid" (559.3 g of a 11.8% solution) was added chlorine gas (about 0.5 g / Minute). The temperature was maintained at 0-5 ⁰ C, and after about 0.7 mole of Cl _{2 was} added, the solution was warmed to room temperature and filtered, and there were 839 g of a solution containing 7.05 % "keto acid" (Yield 91 %) and 0.38% "hydroxy acid" (yield 4.8 %) .

Example 8

Example 1 was repeated, but using ruthenium trichloride hydrate. 350.5 g of 11.4% NaOCl were added dropwise to a solution of 511.6 g of 12.9% "hydroxy acid" containing 0.3 g RuCI ^ oHpO. 818.7 g of a solution containing 7.25 % "keto acid" (yield 91.3 %) were obtained.

Example 9

The procedure was as described in Example 1, but in the flask 279.7 g of 11.8% "hydroxy acid" were introduced and the pH was adjusted to 12. Then, 0.3 g of RuOp-H ₂ O was added and 76.8 g of a 26% NaOCl solution was added dropwise. There were obtained 341 g of a solution containing 9.53 % "keto acid" (yield 100 %) .

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Claims (9)

-10- 12.5.1980 AP C 07 C / 216 56 386/18 Invention claim. 1. A process for preparing 3,3-dimethyl-2-oxo-butyric acid and its salts by oxidation of 3,3-dimethyl-2-hydro: xybutt er acid, characterized in that the reaction in aqueous alkaline solution with the at least stoichiometric amount of a salt of the hypochlorous acid as the oxidizing agent in the presence of a ruthenium catalyst and optionally releases the 3,3-dimethyl-2-oxobutyric acid from the solution of its salts, 2, Method according to item 1, characterized in that one carries out the reaction in sodium-alkaline solution. 3 · Method according to item 1, characterized by the fact that
performs · the reaction at 'J.'empei-a.turen between 40 and 60 C 4 · Method according to item 1, characterized in that adjusting the pH of the reaction medium to about 9 to 13, preferably about 10 to 12. 5, method according to item 1, characterized in that one uses the salt of hypochlorous acid in an excess of 5 to 15 / S, 6, Process according to item 1, characterized in that one uses the ruthenium catalyst in amounts of about 0.01 to 1 g, preferably from about 0.1 to 0.5 g per mole of 3,3-dimethyl-2-hydroxybutyric acid. -11- 12.5.1980 AP C 07 C / 216 802 56 386/18 7. The method according to item 1, characterized in that is used as the ruthenium catalyst Rutheniumdioxidhydrat or ruthenium trichloride hydrate. 8. The method according to item 1, characterized in that initially introducing a mixture of 3,3-dimethyl-2-hydroxy'buttersäure and ruthenium catalyst in aqueous alkaline solution and adding the salt of the hypochlorous acid. Process according to item 1, characterized in that the salt of the hypochlorous acid is generated in situ by introducing chlorine gas into the aqueous-alkaline reaction medium containing a salt of 3,3-dimethyl-2-hydroxybutyric acid and the ruthenium catalyst,