DE952634C - Process for the preparation of compounds of the pyridine series - Google Patents

Description

Process for the preparation of compounds of the pyridine series The patent 94425o relates to a process for the preparation of compounds of the pyridine series, in which one glutaraldehyde as such or in the form of their acetals, in particular the cyclic enol acetals, d. H. the 2-alkoxy-3, [-dihydro-i, 2-pyrans, or the corresponding 2-acyloxy-3, 4-dihydro-i, 2-pyrane gradually in to about 9o to 13o ° heated aqueous solutions of hydroxylammonium salts with thorough mixing of the Reactants can run in or the components together by about 100 to 130 ° heated pressure tube conducts.

It has now been found that compounds of the pyridine series can also be used can be prepared in such a way that one mono- or dioximes of glutaraldehyde, if necessary in pressure vessels, with excess strong acid if possible quickly heated to temperatures above 90 °.

As strong acids come z. B. in question hydrochloric acid, sulfuric acid, Phosphoric acid or sulfonic acids.

One can proceed in such a way that the solid or molten Oxirn or his solution, e.g. B. in water, with stirring in a kept at temperatures above 9o °, ani is most easily introduced into a boiling, aqueous solution of the strong acid, with care is taken that there is always an excess of acid present. One can .also a solution of the oxime in excess prepared at ordinary temperature Acid through heated Pipelines, expediently with random packings are provided; the last-mentioned mode of operation can be used particularly advantageously increased pressure.

Attempts have already been made to treat with glutaraldehyde oxime To convert mineral acids into pyridine (see 1st reports of the German Chem. Ges., Vol. 46 (1913), p. 11o, and journ. Chem. Society London, Vol. 127 (1925), p. 215, or 1937, p. 3o2) by gradually heating mixtures of oxime and mineral acid or laughed to the boil. It never succeeded in increasing the pyridine yield than 211% increase; the main product was tarry masses. With the present Process in which the oximes with excess strong acid as quickly as possible Temperatures above 911 ° are obtained, pyridine compounds in 511 bis 70% and even higher yield.

The parts mentioned in the examples are parts by weight.

Example 100 parts of crystallized glutaraldehyde dioxime are used concentrated in the course of 2 hours in a boiling mixture of T511 parts Hydrochloric acid and 45o parts of water entered. Then the reaction mixture becomes alkaline made, the pyridine is distilled off together with water and from the distillate in usually isolated. The yield is 35 parts = 5611 / o of theory.

Dissolve the same amount of the dioxime in the amount given above Hydrochloric acid and the mixture heated to the boil in the usual way, one obtains after 2 hours of boiling and usual work-up, only 12.5 parts of pyridine, accordingly about 2111 / o of theory.

Example 2 A solution of 118 parts of β-methyl-glutaraldehyde monoxime (e.g. prepared by dissolving 142 parts of 2-ethoxy-4-methyl-3, 4-dihydro-i, 2-pyran in a mixture of 25 parts of concentrated hydrochloric acid and 511o parts Water and addition of 711 parts of hydroxylammonium chloride) within 2 hours sent through a coiled pipe heated externally with xylene vapor. You get 58 parts of y-picoline, corresponding to a yield of 62%.

EXAMPLE 3 A solution of 130 parts of glutaraldehyde dioxime in 5110 parts of 1811 /% hydrochloric acid is passed over the course of 4 hours through a pressure tube heated with xylene vapor. Working up the reaction mixture as in Example i gives 44 parts of pure pyridine, corresponding to a yield of 56% of theory.

Claims (1)

PATENT CLAIM: Further development of the process according to patent 944 25o for the preparation of compounds of the pyridine series from glutaraldehyde derivatives, characterized in that one mono- or dioximes of glutaraldehyde, if necessary in pressure vessels, with excess strong acid as quickly as possible. on temperatures heated to over 911 °.