Chemical processes

Details Chemical processes Chemical processes

2001-06-14

2003-10-21

McKane, Joseph K. (Department: 1626)

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

Organic compounds

Nitriles

Reexamination Certificate

active

06635780

ABSTRACT:

This application is a 371 of PCT/BP99/08135 filed of Oct. 11, 1999.
This invention relates to novel processes for preparing intermediates (particuiarly 4-cyano-3-nitrobenzotrifluoride) useful in the preparation of pesticides.
Pesticidal 4-benzolisoxazoles, particularly 5-cyclopropylisoxazole herbicides and intermediate compounds in their synthesis, are described in the literature, for example in European Patent Publication Nos. 0418175, 0487353, 0527036, 0560482, 0609798 and 0682659.
Various methods for preparing these compounds are known. The present invention seeks to provide improved methods for the preparation of pesticides and the intermediate compounds useful in preparing them.
It is therefore an object of the present invention to provide novel and more economical processes for the preparation of ortho-nitrobenzonitrile compounds.
It is a further object of the present invention to provide processes for the preparation of ortho-nitrobenzonitrile compounds which proceed in high yield and/or with high selectivity.
It is a further object of the present invention to provide a process for the preparation of ortho-nitrobenzonitrile compounds which requires a low amount of copper compound as catalyst.
It is a further object of the present invention to provide a process for the preparation of ortho-nitrobenzonitrile compounds which proceeds using cuprous cyanide without the need for a catalyst.
It is a further object of the present invention to provide a process for the preparation of ortho-nitrobenzonitrile compounds which proceeds at a lower temperature than known methods and therefore easier to perform.
The present invention allows these objects to be met in whole or in part.
SUMMARY OF THE INVENTION
The present invention accordingly provides a process for the preparation of an ortho-nitrobenzonitrile compound of formula (I):
wherein:
R
1
represents C
1-4
haloalkyl (preferably trifluoromethyl), fluorine, chlorine or bromine; and R2 represents hydrogen or C
1-4
alkoxy; which process comprises the reaction of the corresponding ortho-nitrohalobenzene of formula (II):
wherein R
1
and R
2
are as hereinbefore defined and X represents a fluorine, chlorine or bromine atom, with when X represents a flourine atom:
a) an alkali metal cyanide, in a non aqueous solvent optionally in the presence of a catalyst; or
when X represents a chlorine atom:
(b) cuprous cyanide and a source of bromide selected from hydrogen bromide, bromine and a tetraalkylammonium bromide; optionally in the presence of an alkali metal bromide or an alkaline earth metal bromide; or
(c) an alkali metal cyanide or a tetraalkylammonium cyanide, in the presence of cuprous bromide and a phase transfer catalyst; or
(d) cuprous cyanide and lithium iodide; or
when X represents a bromine atom:
(e) cuprous cyanide optionally in the presence of a catalyst selected from an alkali metal bromide or an alkaline earth metal bromide; or
(f) an alkali metal cyanide in the presence of a catalytic amount of cuprous cyanide and a phase transfer catalyst.
Certain compounds of formula (I) are known and a number of processes for their preparation and conversion into herbicidal 4-benzoylisoxazole derivatives have been described in the European Patent Applications cited above.
Compounds of formula (II) are known or may be prepared by known methods.
In formulae (I) and (II) and in the formulae depicted hereinafter, preferred values of the symbols are as follows:
Preferably R
1
represents trifluoromethyl, fluorine or bromine; and R
2
represents hydrogen or methoxy.
In a particularly preferred embodiment of the invention R
1
represents trifluoromethyl and R
2
represents hydrogen.
It is to be understood that in this invention the term “alkyl” which forms part of tetralkylammonium salts represents a straight-or branched-chain alkyl group containing from one to six carbon atoms.
DETAILED DESCRIPTION OF THE INVENTION
The above preparation a) of compounds of formula (I) from compounds of formula (II) wherein X represents a fluorine atom is performed with an alkali metal cyanide (for example sodium cyanide or potassium cyanide). Sodium cyanide is preferred. The amount of cyanide used is generally from 1-2 molar equivalents, preferably from 1-1.1 molar equivalents.
A number of non-aqueous solvents are suitable, for example nitrites such as acetonitrile or benzonitrile; ethers such as tetrahydrofuran or diglyme (diethylene glycol dimethyl ether); amides such as N,N-dimethylformamide or N-methylpyrrolidone; ketones such as methyl isobutyl ketone; esters such as methyl benzoate or n-butyl acetate; dimethylsulphoxide or sulpholane. Preferably the solvent is chosen from benzonitrile, acetonitrile, tetrahydrofuran or N,N-dimethylformamide.
The reaction is generally conducted in a solvent with less than about 1% by volume water content preferably less than about 0.5%, even more preferably less than about 0.1%, typically from about 0.005 to about 0.05%. It will however be understood that in certain cases slightly more or less water may be tolerated, depending on the nature of the solvents used and the temperature of the reaction, the compound of formula (I) to be prepared and other reaction conditions.
Preferably a catalyst is used, which may be selected from ammonium salts (such as tetraalkylammonium or trialkylbenzylammonium chlorides, bromides or hydrogen sulphate salts, in which the alkyl groups are straight- or branched-chain containing from one to six carbon atoms, such as tetramethylammonium bromide); or preferably guanidinium salts (such as hexabutylguanidinium chloride or hexamethylguanidinium chloride). The amount of catalyst when employed is generally from 0.01 to 0.3 molar equivalent, preferably from 0.05-0.25 molar equivalent.
Generally the reaction temperature is from 20° C. to the boiling point of the solvent, preferably from 30° C. to 180° C., and more preferably from 60° C. to 100° C.
The above preparation (b) of compounds of formula (I) from compounds of formula (II) wherein X represents a chlorine atom is performed with cuprous cyanide and a source of bromide selected from hydrogen bromide, bromine and a tetraalkylammonium bromide, optionally in the presence of an alkali metal bromide or an alkaline earth metal bromide, preferably lithium bromide. In this process the amount of cuprous cyanide used is generally from 0.5-2 molar equivalents and preferably from 0.8-1.2 molar equivalents.
The amount of bromide source used is generally from 0.05-1 molar equivalent.
When an alkali metal bromide or an alkaline earth metal bromide is also present in the reaction mixture it is used in catalytic amount, generally from 0.01-0.5 molar equivalents and preferably from 0.02-0.05 molar equivalents.
The solvent may be chosen from nitrites such as acetonitrile or benzonitrile; ketones such as methyl isobutyl ketone; ethers such as tetrahydrofuran or diglyme (diethylene glycol dimethyl ether); esters such as methyl benzoate or n-butyl acetate; dimethylsulphoxide or sulpholane. Preferred solvents are acetonitrile, benzonitrile or diglyme.
The concentration of the compound of formula (II) used in the reaction solvent is generally in the range from 0.1 ml/mmol to 2 ml/mmol, and preferably from 0.2 ml/mmol to 1 ml/mmol.
The reaction temperature is generally from 100° C. to 200° C., preferably from 130° C. to 180° C.
The above preparation (c) of compounds of formula (I) from compounds of formula (II) wherein X represents a chlorine atom is performed with an alkali metal cyanide (for example sodium cyanide or potassium cyanide) or a tetraalkylammonium cyanide, in the presence of cuprous bromide and a phase transfer catalyst.
Preferably the alkali metal cyanide is potassium cyanide. The amount of alkali metal cyanide or tetraalkylammonium cyanide used is generally 1-1.5 molar equivalents (preferably 1-1.1 molar equivalents. The amount of cuprous bromide used is generally from 0.01-2 molar equivalents (preferably 1 molar equivalent). The reaction is conducted using solid liquid phase transfer catalysis. The phase transfer catalyst may be selected from tetr

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