Organic compounds -- part of the class 532-570 series – Organic compounds – Nitriles
Reexamination Certificate
2000-12-22
2002-05-21
Rotman, Alan L. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Nitriles
Reexamination Certificate
active
06392081
ABSTRACT:
This invention relates to novel processes for preparing intermediates (particularly 2-(arylhydrazino)succinonitrile compounds and 3-(arylhydrazono)propionitrile derivatives) useful in the preparation of pesticides.
European Patent Publication Nos. 0295117 and 0234119 describe the preparation of pesticidally active phenylpyrazole compounds and of 5-amino-1-aryl-3-cyanopyrazole intermediate compounds used in their synthesis.
Various methods for preparing these compounds are known. The present invention seeks to provide improved or more economical methods for the preparation of pesticides and the intermediate compounds useful in preparing them.
German Patent Publication No.3612940 discloses the preparation of 5-amino-1-arylpyrazole derivatives of general formula:
wherein Ar represents substituted phenyl or pyridyl, which can be used as intermediates in the preparation of compounds possessing herbicidal or pesticidal properties, by the reaction of arylhydrazine hydrochloride salts with formylacetonitrile sodium salt of formula:
NaOCH═CH—CN
to give hydrazone compounds of general formula:
Ar—NH—N═CH—CH
2
—CN
wherein Ar is as hereinbefore defined; which are then cyclised in the presence of a base.
However it may be desirable to obtain the hydrazone compounds in a pure form useful for their further conversion into pesticides. Known procedures may result in the formation of hydrazones which are contaminated with the cyclised 5-amino-1-arylpyrazole product.
The present applicants have surprisingly discovered a novel process for the preparation of the hydrazone compounds without cyclisation occurring. The hydrazone compounds may then be used either to provide a new method to prepare the 5-amino-1-arylpyrazole compounds, or in a novel process which involves addition of a cyanide to provide 2-(arylhydrazino)succinonitrile derivatives which may be further processed to provide important 5-amino-1-aryl-3-cyanopyrazole compounds which are valuable intermediates for the preparation of pesticides.
U.S. Pat. No.4,824,960 describes the preparation of 5-amino-1-arylpyrazole derivatives of general formula:
wherein Ar represents substituted phenyl or pyridyl, which can be used as intermediates in the preparation of compounds possessing herbicidal or pesticidal properties, by the reaction of arylhydrazines of formula:
Ar—NH—NH
2
wherein Ar is as hereinbefore defined, with acrylonitrile of formula:
NC—CH═CH
2
in a first stage in the presence of a diluent and optionally a catalyst to give the 3-arylhydrazinopropionoitrile compounds of formula:
Ar—NH—NH-CH
2
-CH
2
—CN
wherein Ar is as hereinbefore defined, followed by oxidation and cyclisation in a second process stage.
However if it is desired to perform an oxidation of the above 3-arylhydrazinopropilonitriles (without cyclisation to the 5-amino-1-arylpyrazoles) in order to obtain 3-arlylhydrazonopropionitriles, which may then be further processed to provide important 5-amino-1-aryl-3-cyanopyrazole compounds which are valuable intermediates in the preparation of pesticides, a different process must be employed.
The present invention accordingly provides a process (A) for the preparation of a compound of formula (I):
wherein W represents nitrogen or —CR
3
;
R
1
represents halogen, haloalkyl (preferably trifluoromethyl), haloalkoxy (preferably trifluoromethoxy), R
4
S(O)
n
—, or SF
5
;
R
2
represents hydrogen or halogen (for example chlorine or bromine);
R
3
represents halogen (for example chlorine or bromine);
R
4
represents alkyl or haloalkyl; and
n represents 0,1 or 2; which process comprises the reaction of a compound of formula (II):
wherein R
5
and R
6
independently represent alkyl or together represent an alkylene chain containing two or three carbon atoms, with an acid addition salt of an arylhydrazine compound of formula (III):
wherein R
1
, R
2
and W are as hereinbefore defined. Compounds of formula (I) may exist as a mixture of syn and anti isomers or as individual isomers.
Unless otherwise specified in the present specification ‘alkyl’ means straight- or branched-chain alkyl having from one to six carbon atoms (preferably one to three). Unless otherwise specified ‘haloalkyl’ and ‘haloalkoxy’ are straight- or branched-chain alkyl or alkoxy respectively having from one to six carbon atoms (preferably one to three) substituted by one or more halogen atoms selected from fluorine, chlorine or bromine.
Generally R
5
and R
6
in formula (II) represent the same alkyl group, preferably methyl or ethyl.
The acid addition salts of the compounds of formula (III) are preferably the salts formed from strong acids such as mineral acids, for example sulphuric acid, or preferably hydrochloric acid. Generally the salts are pre-formed but may optionally be generated in situ. The reaction may be conducted in a polar or a non-polar solvent in the presence of water. Examples of polar solvents include water; alcohols such as methanol or ethanol; nitriles such as acetonitrile; N-methylpyrrolidone or sulphoxides such as dimethyl sulphoxide. Examples of non-polar solvents include chlorinated hydrocarbons, preferably carbon tetrachloride; and hydrocarbons such as cyclohexane. The reaction temperature is generally from 20° C. to 100° C., preferably from 50° C. to 90° C. Equimolar amounts of the compounds of formula (II) and (III) are generally employed. The amount of water which may be present is from a catalytic amount to a large excess.
In formulae (I), (III) and in the formulae depicted hereinafter, preferred values of the symbols are as follows:
R
1
represents haloalkyl (preferably trifluoromethyl), haloalkoxy (preferably trifluoromethoxy) or —SF
5
;
W represents —CR
3
; and R
3
represents halogen;
A most preferred compound of formula (I) is 3-(2,6-dichloro-4-trifluoromethylphenylhydrazono)propionitrile.
A further preferred compound of formula (I) is 3-(2-chloro-4-trifluoromethylphenylhydrazono)propionitrile.
Compounds of formula (II) and (III) are generally known in the literature.
The process of the invention is characterised by a number of advantages. Thus, it seeks to enable 3-arylhydrazono-propionitrile compounds of formula (I) to be obtained in high yield from readily available starting materials. Furthermore the reaction can be very simple and economical to perform, and product isolation is very straightforward. Furthermore the compounds of formula (I) can be obtained without substantial cyclisation occurring.
According to a further feature of the present invention there is provided a process (B) for the preparation of a compound of formula (I), wherein W, R
1
and R
2
are as hereinbefore defined, which comprises the reaction of a compound of formula (IV):
wherein R
7
represents alkyl (preferably methyl or ethyl), with a compound of formula (III), wherein R
1
, R
2
and W are as hereinbefore defined. The reaction conditions which are generally employed are the same as those used for the above preparation of a compound of formula (I) from the reaction of a compound of formula (II) with an acid addition salt of a compound of formula (III).
Compounds of formula (IV) are generally known in the literature.
According to a further feature of the present invention there is provided a process (C) for the preparation of a compound of formula (I) wherein W, R
1
and R
2
are as hereinbefore defined; which process comprises the oxidation of a compound of formula (V):
wherein R
1
, R
2
and W are as hereinbefore defined.
Suitable oxidants for the above reaction to form compounds of formula (I) include quinones such as benzoquinone, peroxides such as hydrogen peroxide, hypohalites such as sodium hypochlorite; or preferably a metal salt or oxide for example cupric chloride or mercuric oxide. The oxidation is generally conducted in a solvent. Solvents suitable for use include aromatic halogenated or non-halogenated hydrocarbons such as toluene or chlorobenzene, nitrites such as acetonitrile or amides such as N,N-dimethylformamide. The reaction temperature is generally from about 20° C. to about 150° C., and preferably from about
Aventis Agriculture Ltd.
Burns Doane Swecker & Mathis L.L.P.
Robinson Binta
Rotman Alan L.
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