Process for the preparation of 2,3,5,6-tetrachloropyridine

Details Process for the preparation of 2,3,5,6-tetrachloropyridine Process for the preparation of 2,3,5,6-tetrachloropyridine

1994-08-22

1997-01-07

Ivy, C. Warren

Organic compounds -- part of the class 532-570 series

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

C07D21361, C07D21369

Patent

active

055918573

DESCRIPTION:

BRIEF SUMMARY
This application is a 371 of PCT/DK93/00392, filed Dec. 1, 1993.
The present invention relates to an improved process for the preparation of 2,3,5,6-tetrachloropyridine of formula I ##STR3## from 3,3,5-trichloroglutarimide of formula II ##STR4##
2,3,5,6-Tetrachloropyridine is a useful intermediate product in the preparation of various herbicides, fungicides and insecticides, e.g., (3,5,6-trichloro-2-pyridyloxy)acetic acid [BR patent No. 74,02900] and O,O-diethyl-O-3,5,6-trichloro-2-pyridylphosphorothioate [U.S. Pat. No. 3,244,586].
Various processes for the preparation of 2,3,5,6-tetrachloropyridine (I) are known, including the following:
2,3,5,6-Tetrachloropyridine can be prepared from glutarimide by chlorination with phosphorus pentachloride. Thereby, a mixture of chlorinated pyridines is formed which can then be further chlorinated with chlorine to 2,3,4,5,6-pentachloropyridine which can thereafter be selectively reduced by zinc to 2,3,5,6-tetrachloropyridine.
2,3,5,6-Tetrachloropyridine can also be prepared by chlorination of pyridine or pyridine derivatives as, e.g., 2,6-dichloropyridine, .alpha.-picoline or 3,5-dichloro-2-trichloromethylpyridine in a vapour phase at a high temperature.
The starting material can also be glutaric acid dinitrile, pentenenitrile, .epsilon.-caprolactam or cyclohexanone oxime which by chlorination at a high temperature (400.degree.-600.degree. C.) can be converted into 2,3,5,6-tetrachloropyridine.
These high-temperature processes are usually not selective as they likewise result in the formation of other highly chlorinated by-products which are to be removed.
One such by-product is 2,3,4,5,6-pentachloropyridine which as mentioned can be converted, however, into 2,3,5,6-tetrachloropyridine by selective reduction of the chlorine atom in the 4-position.
3,5,6-Trichloropyridin-2-ol or mixtures thereof with 2,3,5,6-tetrachloropyridine can be prepared from trichloroacetyl chloride and acrylonitrile.
These processes primarily concern the preparation of 3,5,6-trichloropyridin-2-ol, and tetrachloropyridine is a by-product in the application of the procedures.
Trichloropyridinol is preferably used for the preparation of O,O-diethyl-O-3,5,6-trichloro-2-pyridylphosphorothioate, whereas tetrachloropyridine has a wider field of application, including, inter alia, the preparation of the above-mentioned phosphorothioate via hydrolysis of tetrachloropyridine to trichloropyridinol.
2,3,5,6-Tetrachloropyridine can be prepared from 3,3,5-trichloroglutarimide by reaction with phosphorus trichloride, phosphorus oxytrichloride or phosphorus pentachloride.
The present invention relates to an improved process for the preparation of 2,3,5,6-tetrachloropyridine (I) from 3,3,5-trichloroglutarimide (II), and said process is characterized in that the 3,3,5-trichloroglutarimide is reacted either thereof in the presence from the start of catalytic amounts of hydrogen chloride, followed by a conversion of polyphosphorus compounds formed into phosphorus oxytrichloride by supplying chlorine, optionally only after supplying further phosphorus trichloride, or phosphorus oxytrichloride as a solvent, followed by a dehydrochlorination of the reaction mixture and finally conversion of polyphosphorus compounds formed into phosphorus oxytrichloride by supplying chlorine, optionally only after supplying further phosphorus trichloride.
Use can be made of various expedient embodiments of process a. of the invention as stated in claims 2-7.
The reaction of 3,3,5-trichloroglutarimide (II) with phosphorus trichloride or phosphorus oxytrichloride or mixtures thereof by process a. of the invention, which is preferably carried out at 160.degree. C. to 200.degree. C. for, e.g., 1/2 to 3 hours, takes place substantially according to the reaction scheme: ##STR5## It has surprisingly been found that the latter process proceeds only in the presence of catalytic amounts of hydrogen chloride from the start of the reaction.
The hydrogen chloride can be supplied to the reaction mixture in the form of dry hydrogen chloride gas, or it

REFERENCES:
patent: 4360676 (1982-11-01), Martin et al.

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