DE1620174C - Process for the oxidative production of pyridine ^ .o-dicarboxylic acid - Google Patents

Description

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Example 2 passed. Yield: 41 g of pyridine-2,6-dicarboxylic acid

= 49% of theory, with an acid number of 645.

It is carried out as in Example 1. Are used. 11.3 ml of free water are used from the water of reaction

53 g of 2,6-dimethylpyridine, 500 ml of 1,2,4-trichlorobenzene base isolated, so that the yield based on

and Ig SeO ₂ . At 150 ⁰ C. 0.5 g _NO2 / h 5 mono- needed pyridine is 70% of theory.

Claims (1)

1 ... '■ · .. ■ "■' ■ '■■■ - ^:. 2 ' ^χ that this is also not a technical one Claim: Production of pyridine ^ ö-dicarboxylic acid are suitable. U.S. Patent 2,513,251 describes the oxy- Process for the production of pyridine: 2,6-dation of alkylpyridines, including lutidines, carboxylic acid by oxidation of 2,6-dialkyl-5 with nitrogen tetroxide in concentrated sulfuric acid pyridines, their salts or a 2,6-dialkyl- at temperatures containing 225-350 ⁰ C in Gegenpyridine technical Group claimed waiting means of selenium dioxide. Examples and a nitrogen oxide, thereby marked yield data for the reaction with dialkylpyrizeichnet that the dines to be oxidized are missing. Working in concentrated sulfur-2,6-dialkylpyridines or their salts in an io acid as solvent, especially in the case of such organic inert solvents at relatively high temperatures, is known to dissolve 1: 1 to 1:10 or dilute it and with preparative methods and complex and expensive in terms of equipment. 130 to 160 ° C in the presence of selenium dioxide When the process was reworked using nitrogen dioxide from 2,6-dimethylpyridine as a catalyst, only resinous treatments were obtained until this was no longer absorbed are. ; Finally, U.S. Patent 2524957 mentions that instead of nitric acid one also uses Use nitrogen tetroxide as an oxidizing agent 20 could. The invention is therefore based on the object It is known to be oxidative. Production of pyridine-2,6-dicarboxylic acid in high yields of pyridine-2,6-dicarboxylic acid from 2,6-dialkylpyridine technically more advantageous way from 2,6-dialkylpyridine to use various oxidizing agents. dinen using nitrogen oxides as According to Reports, 67 (1934), p. 751 below, Reports, 25 To Obtain Oxidants. 88: 157 (1955) and J. Pharm. Soc. Japan, 70 It has now been found that the problem posed (1950), p. 156 to 161, reported in CA., 1950, p. 5878, is achieved by the fact that the [cf. also E. Klings berg, "Pyridine and its 2,6-dialkylpyridine or the corresponding technical derivatives", 1962, 3rd part, p. 186, 2nd paragraph of fraction in an organic inert solvent below], is z. B. selenium dioxide with or without dilution in a ratio of 1: 1 to 1:10 dissolves or diluted with it as a diluent. However, the yields of pyridine and, at 130 to 160 ^° C., preferably 150 ^° C., 2,6-dicarboxylic acid by this process are treated with nitrogen dioxide until no more gas is unsatisfactory. is taken up, then the reaction. Furthermore, potassium permanganate was cooled as an oxy mixture to 100 to 140 ° C and the ausdans proposed (cf. J. Org. Chem., 14 [1949], 35 precipitated pyridine-2,6-dicarboxylic acid The Reaction page 17, 3rd paragraph from below, and J. Am. Pharm ). dioxide carried out. Instead of the 2,6-dialkylpyri, long reactive bases can also be oxidized, and their salts can also be oxidized, which requires 17 and 24 to 48 hours which, as inert organic solvents, are not acceptable for industrial production. For example, chlorinated benzenes or nitrobenzenes in US Pat. No. 2,522,163 are questionable. Instead of the inert solution sulfates of alkyl pyridines with concentrated salt, the technical pyridine base fraction in question, pitric acid, in the presence of concentrated sulfur in excess can also be used. The versic acid according to the invention oxidizes. This process requires a great deal of effort. It is explained below with reference to the 2,6-dimethyl amount of nitric acid and, in terms of apparatus, because of the use of pyridine or its hydrochloride as a starting material, working with the hot concentrated acids is very much explained. laborious. In addition, in the case of the example B, ρ ie 1 1
specified temperature of preferably 170 ⁰ C in the oxidation of 2,6-dialkylpyridines in considerable- A mixture consisting of 72 g of 2,6-dimethyl- Lich extent already shows decomposition. 50 pyridine hydrochloride, 500 ml 1,2,4-trichlorobenzene and Another method is used with 1 g of SeO ₂ , while stirring in a cylindrical Manganese dioxide, in concentrated sulfuric acid (see flask, which is equipped with a reflux condenser, water U.S. Patent 2109,954). Because of the high separator and inlet pipe is provided on Apparatus expense due to the hot concentrated 150 ⁰ C heated. While maintaining this temperature trated acid, this process would produce 0.5 g NO ₂ / h _{until NO 2 uptake is complete} Niche production of pyridine-2,6-dicarboxylic acid just initiated. After 5 to 7 hours the reaction is complete if not considered. completed. All the methods listed so far have also. The reaction mixture is cooled to 100 to the substantial disadvantage that a considerable 14O ⁰ C., the precipitated acid filtered off, washed Consumption of expensive oxidizing agents is given. 60 with 1,2,4-trichlorobenzene, then with petroleum Since then, the cheapest method of oxidation has been the ethereal and dries at 100 ° C. ·
Dampfphasenpxydation of alkylpyridines known Yield: 48 g of pyridine-2,6-dicarboxylic acid = 57.5 ° / ₀ in the oxygen or air as an oxidizing agent of the theory, with an acid number of 660. - Theo is employed (see German Patent Specification 733,298. rie: 670. and U.S. Patent 2,437,938). In each case, 3 g of the water of reaction are not converted game4 in both patents the oxidation set 2,6-dimethylpyridine is isolated, so that the of 2,6-lutidine. The yields according to booty, based on the pyridine base consumed, 63% however, both methods are so unsatisfactory that the theory is.