DE852244C - Process for the production of pyridine and pyridinecarboxylic acids - Google Patents

Description

Process for obtaining pyridine and pyridinecarboxylic acids It has been found that tnan homologs of the 1'yri <lins in a simple way in pyridine or pyridinecarboxylic acids can be converted if they are heated to an elevated temperature below Pressure treated with dilute nitric acid. It is expedient to use 5 to 4o % igc, preferably about 20% acid. The side chains are in the oxidation initially degraded to carboxyl groups. One can now, especially with ß- and Y-substituted Pyridines, stop the reaction at this point or by further heating at higher temperatures cause splitting off of the carboxyl groups, whereby pyridine is obtained. «-Substituted pyridines usually give pyridine immediately, since the carboxyl group in the position of the nitrogen atom occurs during the oxidation, which occurs, for example, at i8o to 22o °, is easily split off. By addition Oxidation-accelerating catalysts, such as iron, manganese, copper and vanadium compounds and the like, the reaction temperature can be lowered. Are substituents in a- and in the ß- or Y-position, so one can depending on the treatment conditions Win ß- or Y-pyridinecarboxylic acids or P_vridin.

With suitable conversion conditions that can be easily determined by experiment can be obtained from. Each pyridine homologue pyridine, z. B. from the very cheap crude pyridine base mixtures. Under relatively mild implementation conditions can one in a technically simple manner from mixtures of variously substituted, z. B. also containing higher alkyl radicals pyridine homologues, relatively simple composite, namely only P- or γ-pyridinecarboxylic acid or both containing Products received.

The process can be carried out batchwise; advantageous but one works continuously by, for example, under the reaction mixture Let pressure trickle through a heated pressure-resistant tube provided with packing elements and the resulting gases through a valve set to a certain pressure lets escape.

The parts given in the following examples are parts by weight. Example 1 87 parts of a crude pyridine base mixture boiling from 115 to 128 ° (average molecular weight determined by perchloric acid titration: 87), which consists mainly of picolin, are heated in a pressure vessel with 720 parts of 20% nitric acid. At around 19o °, the pressure begins to rise above the pressure caused by the vapor pressure of the starting materials as a result of the conversion taking place. After further slow heating to 21o to 215 °, the pressure and temperature rise by themselves until the reaction subsides again at around 235 °. The reacted mixture only reacts weakly after cooling. The pyridine formed is distilled off with steam from the aqueous solution which has been made alkaline; from the distillate 58 parts of pyridine are recovered from the boiling range 1 1 5 to 12o ° by salting out and drying with caustic soda.

Used in place of the specified crude pyridine base mixture those with a higher boiling range that contain more ß- and ^ r-substituted pyridines, in this way one also obtains pyridine and, depending on the amount of β- and Y-substituted ones present Pyridines correspond to amounts of pyridinecarboxylic acids. Example 2 121 parts of 2-methyl-5-ethylpyridine are, as indicated in Example 1, treated with 1795 parts of 20% nitric acid. By evaporating the resulting solution and recrystallizing the dry residue nicotinic acid is obtained in very good yield. The ethyl group is therefore to the carboxyl group been oxidized, while the substituent in the 2-position is split off during the oxidation has been.

Claims (1)

PATENT CLAIM Process for the production of pyridine and pyridinecarboxylic acids; characterized in that homologous pyridines are treated with dilute nitric acid at elevated temperature under pressure.