Production of 2,3,5,6-tetrachloropyridine

Details Production of 2,3,5,6-tetrachloropyridine Production of 2,3,5,6-tetrachloropyridine

1996-03-15

1997-04-08

Ivy, C. Warren

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

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

C07D21346, C07D21353

Patent

active

056189427

DESCRIPTION:

BRIEF SUMMARY
This application is a 371 of PCT/US94/10010, filed Sep. 2, 1994 published as WO95/06639 on Mar. 9, 1995.
The present invention relates to a novel, improved process for the production of 2,3,5,6-tetrachloropyridine, also known as Symtet.
2,3,5,6-tetrachloropyridine is useful as an intermediate in the production of various herbicides, fungicides and insecticides, for example the important insecticide O,O-diethyl-O-3,5,6-trichloro-2-pyridyl phosphorothioate.
Various processes are -known for the production of 2,3,5,6tetrachloropyridine. For example, it can be prepared by the liquid phase chlorination of .beta.-picoline (U.S. Pat. No. 4,483,993) or pyridine (U.S. Pat. No. 4,515,953) or by vapor phase chlorination of 2-chloropyridine or 2,6-dichloropyridine (U.S. Pat. No. 3,251,848).
Israel Patent 61581 describes a process whereby a mixture of 2,3,5,6-tetrachloropyridine and 3,5,6-trichloropyridin-2-ol is obtained by reacting trichloroacetyl chloride and acrylonitrile in a solvent at ca 170.degree. C. using various metals as catalysts (yields were not reported).
European Patent Application 0 030 215 describes the preparation of 3,3,5-trichloroglutaric acid imide and its subsequent conversion with dehydrating agents such as POCl.sub.3 to 2,3,5,6-tetrachloropyridine.
Unexpectedly, we have discovered that 2,2,4-trichloro-4cyanobutyrate esters, e.g. the ethyl ester, undergo a one-step conversion to 2,3,5,6-tetrachloropyridine as described in the following equation, where R is an alkyl, aralkyl or aryl group: ##STR1##
As used herein "aryl" means an aromatic hydrocarbon radical of C.sub.6 to C.sub.10 carbon atoms which may optionally be substituted with lower alkyl and/or halo. As used herein "aralkyl" means a C.sub.1 -C.sub.6 alkyl group substituted with an aryl radical as defined above.
This novel and remarkably simple transformation results in yields of 60-90% of 2,3,5,6-tetrachloropyridine, depending on the chemical nature of R. The reaction is carried out using POCl.sub.3, a readily available commercial material, at a temperature of 100.degree. to 160.degree. C., preferably at 120.degree.-140.degree. C., in the presence of a catalytic amount of hydrogen chloride. At this preferred temperature range, the reaction time is 5-10 hours. The molar ratio of POCl.sub.3 to the 2,2,4-trichloro-4-cyanobutyrate ester is in the range of 10:1 to 1:1. The preferred range is 2:1 to 3:1. If a high ratio is used, it is recommended to distill out and recycle the excess POCl.sub.3 at the end of the reaction. After the reaction is completed, excess POCl.sub.3 is distilled off, water is added to the residue and the mixture is extracted with a suitable organic solvent, containing now crude 2,3,5,6-tetrachloropyridine. The pure product is isolated by conventional methods, such as sublimation, crystallization or steam distillation. The product thus obtained exhibited a m.p. 89.degree.-90.degree. C.; .sup.1 H-NMR (CDCl.sub.3): .delta.7.88 ppm (singlet), and was found to be identical in all respects with an authentic sample of 2,3,5,6-tetrachloropyridine.
Dry HCl gas in the amount of 0.5-5% by weight of the combined reactant and solvent is recommended. The preferred range is 1.5-3%. The reaction is autocatalytic in the sense that HCl is being produced as the reaction is progressing.
The reaction may also be carried out in the presence of an aprotic and non-reactive solvent, such as aromatic and aliphatic hydrocarbons as well as halogenated hydrocarbons, without seriously affecting the reaction efficiency.
The starting materials of formula I above, i.e. ethyl 2,2,4-trichloro-4-cyanobutyrate and other esters of 2,2,4-trichloro-4-cyanobutyric acid, can be readily prepared according to methods known in the art which are described in the chemical literature, for example: The Journal of Organic Chemistry, Vol. 29, pp. 2104-5 (1964); and Tetrahedron, Vol. 29, pp. 827-832 (1973); Journal of Organic Chemistry, Vol. 41, pp. 396-398 (1976); and U.S. Pat. No. 5,017,705.
The simplicity of the process described herein makes it amenable to large scale pr

REFERENCES:
patent: 4996323 (1991-02-01), Pews
patent: 5017705 (1991-05-01), Becker
patent: 5106984 (1992-04-01), Halpern
patent: 5200522 (1993-04-01), Grozinger
patent: 5206372 (1993-04-01), Schrodier
patent: 5229519 (1993-07-01), Zhang
patent: 5480995 (1996-01-01), Kraus
patent: 5493028 (1996-02-01), Zhang
patent: 5508410 (1996-04-01), Murugan

Affiliated with

Also associated with

Rating

Production of 2,3,5,6-tetrachloropyridine does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Production of 2,3,5,6-tetrachloropyridine, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Production of 2,3,5,6-tetrachloropyridine will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2398658