SU568642A1 - Method of obtaining pyridine carbon acids - Google Patents

Description

one

The invention of Otosit to an improved method for the synthesis of pyridiparboxylic acids (2,6-pyridinedicarboxylic and 2,4,6-pyridine tricarboxylic acid).

These acids are the raw material for the synthesis of physiologically active substances, heterocyclic compounds of more complex structure and high-quality polymeric materials. Pyridinecarboxylic acids are used in the same way as analytical reagents.

A method of producing pyridinecarboxylic acids by the method of catalytic carboxylation of pyridine or salts of pyridinecarboic acids using free CO2 or COz, obtained by decarboxylation of another acid, for example, trimellitic or hememellitic acids

one.

The disadvantage of this method is the relatively low yield of the target product, as well as high pressures (up to 1800 atm) and the reaction temperature.

There is also known a method for producing these compounds by liquid-phase oxidation of the corresponding alkyl pyridines in aqueous solution at 50-100 ° C with sodium or potassium permanganate 2.

This method is characterized by a number of disadvantages: a relatively expensive and regenerated oxidant — permanganate, a considerable process duration and a complicated technology for the selection of target products, since manganese oxides are fine-crystalline and difficult to filter. The yield of the target product by the known and the proposed method is comparable.

According to the invention, a method for producing pyridinecarboxylic acids of general formula I is described.

R

about

-"DON

N where or -COOH

liquid phase oxidation. m

alkylpyridines of general formula II

N-, C

sn.

25

Claims (2)

where RH or CH3 in an aqueous solution when heated, which consists in using sodium bichromate as an oxidant and the process is carried out under a pressure of 20-94 atm, preferably 25-35 atm, at a temperature of 225-275 ° C, preferably at 230-250 ° С, the initial concentration of alkylpyridines (II) is 1-2 mol per 1 liter of water and the molar ratio of alkylpyridines (II): sodium bichromate is 1: 1.8-4.5, mostly 1: 3- 4.5. The advantages of the proposed method are: a significantly smaller excess of the oxidizing agent than in the well-known germanium method (alkylamine ratio: KMnO4 - 1: 4.5-5.8); Cr20z is a large scattering precipitate, it is easily filtered, while manganese oxides are fine-crystalline and difficult to filter; easy regeneration of the bichromate oxidizer, concludes, and with Cg203 electrochemical oxidation, the permaiganate-oxidant is unregenerable, and the reduced method is characterized by a 2–4-fold reduction in dilution of the reaction mixture than the non-manganate method. Example 1. 18.7 g (0.175 mol) of 2,6-lutidiene (2.6 - dimethylpyridine), 153.6 g (0.515 mol) of Na2Cr207-2H2O and 160 ml of water are loaded into the reactor. The reaction is carried out by irradiation of the temperature up to 250 ° C for 1 h and iri 250 ° C for 2 h (the pressure in the reactor is 38 atm). The reactor is cooled. The reaction mixture is discharged from the reactor and diluted with water to 530 ml. The precipitate is filtered off. 67.4 g of Cr 2 O 3 are obtained. The oxide contains 0.18 g (0.0023 mol, 1.3 mol.%) Pyridine, 0.48 g (0.0045 mol, 2.6 mol.%) 2,6-lutidine. Under intensive stirring, the potassium oxide is acidified with concentrated HC1 to pH 1 and left at 6 ° C for 2 hours. The precipitate is filtered and washed with water. The precipitate is dried at 100 ° C. 31.94 g of 2,6-yiridine dicarboxylic acid (crude) are obtained, containing 19.37 g (0.1 mol) of 2,6-iiridine dicarboxylic acid (yield 57 mol%). After crystallization of the raw material, 2,6-yiridine dicarboxylic acid is obtained with a purity of 95.6% of the desired product (in the form of C5H3 (COOH) 2-1.5H2O). The loss of 2,6-pyrndindi “arboic acid during crystallization does not exceed 8%. Example 2. 21.2 g (0.175 mol) of 2,4,6-collidine, (2,4,6-trimethylpyridine), 208.6 g (0.7 mol) of Ma2Cr2O7-2H20, 160 ml of water are charged to the reactor. The reaction is carried out with a gradual increase in temperature to 236 ° C for 1 h and a temperature of 236 ° C for 2 h (reactor pressure 28 atm). The reactor is cooled. The reaction mixture is discharged from the reactor and diluted with water to 510 ml. The precipitate is filtered off with Cr20z (111 g), which contains significant amounts of the sodium salt of 2,4,6 pyridon-tri-carboxylic acid. The filtrate, while vigorous stirring, is acidified with concentrated HC1 before and leaves at 6 ° C for 2 hours. The precipitate is filtered and the filter is 100 ° C. 15.51 g of crude 2,4,6-pyridine-tricarboxylic acid are obtained, containing 5.98 g (0.026 mol) of 2,4,6-pyridine tri-carboxylic acid as a dihydrate. Cg20z precipitate containing 2,4,6-pyridine-tricarboic acid sodium salt, cues and tons with 1500 ml of water. The CrO2 precipitate is filtered off, the solution is cooled, the acid is taken up with concentrated HC1 and kept at 6 ° C for 2 hours. The precipitate is filtered and dried at 100 ° C. 20.15 g2,4,6-niridi-tricarboxylic acid crude are obtained, containing 18.22 g (0.079 mol) of 2,4,6-pyridine-tricarboxylic acid. Precipitates of 2,4,6-irindintricarboxylic acid raw, and the rays of the filtrate and after treatment with Cr2O3, are combined. 24.2 g (0.105 mol) of 2,4,6 nitride tri (carboxylic acid) dihydrate are obtained (yield 55.2 mol%). The precipitate of crude acid and recrystallized from water. Example 3. 19.27 g (0.159 moles) of 2,4,6-collidia, 198 g (0.66 moles) of Na2Cr2O7-2H20, 153 ml of water are loaded into the reactor. The reaction is carried out at a gradual increase in temperature to 250 ° C for 1 h and at 250 ° C for 2 h (reactor pressure 34 atm). The reactor is cooled. The reaction mixture is discharged from the reactor and diluted with water to 465 ml. The precipitate is filtered off with Cr2Oz (110 g), which contains significant amounts of the sodium salt of 2,4,6-iiridine tricarboxylic acid. The filtrate, with vigorous stirring, is acidified with concentrated HC1 before and left at 6 ° C for 2 hours. The precipitate is filtered and dried at 100 ° C. 8.24 g of 2,4,6-iiridine tricarboxylic acid-raw material are obtained, containing: 2.84 g (0.012 moles) of 2,4,6-iiridine tri-carboxylic acid as a dihydrate. Cg2Oz precipitate containing 2,4,6-iiridine tricarboxylic acid sodium salt cia t with 1500 ml of water. The Cg20z precipitate is filtered off, the solution is cooled, acidified with HC enduitration and left at 6 ° C for 2 h. The precipitate is filtered, dried at 100 ° C. 21.47 g of crude 2,4,6-pyridine-tricarboic acid, containing 20.40 g (0.083 mol) of 2,4,6-pyridine tri-carboxylic acid, are obtained. 23.24 g (0.101 mol) of 2,4,6-iiridine tricarboxylic acid dihydrate are obtained (yield 63.5 mol%). The claims of the invention 1. Method of obtaining niridinecarboxylic acids of general formula I (: ooT de R-P or -SOOI, liquid phase oxidation of the corresponding alkyl pyridines of the general formula II AT tlli VAT N where RH or -Snz, in aqueous solution under heating, characterized in that, in order to simplify the process technology, sodium dichromate is used as an oxidizer and the process is carried out under a pressure of 20-94 atm at a temperature of 225-275 ° C, the initial concentration of alkylpyridines (II) is 1- 2 mol per 1 liter of water and molar ratio of alkylpyridines (II):: sodium dichromate 1: 1.8-4.5. 2. A method according to claim 1, characterized in that the process is carried out at a temperature of 230-250 ° C, a pressure of 25-35 atm, and a molar ratio of alkylpyridines (II): sodium bichromate is 1: 3-4.5. Sources of information taken into account in the examination 1. The patent of Czechoslovakia No. 102727, cl. 12p 10/01, published 1960 2.I. Supniewski, T. Wapu, I. Krupinska Bull. Acad. polon Sci., classe 11, 3, 1955.