Processes for preparing pesticidal intermediates

Details Processes for preparing pesticidal intermediates Processes for preparing pesticidal intermediates

2002-01-04

2002-06-25

Davis, Zinna Northington (Department: 1625)

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

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

C564S305000, C564S442000

Reexamination Certificate

active

06410737

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to novel processes for preparing intermediates (particularly certain arylamine compounds and arylhydrazine derivatives) useful in the preparation of pesticides.
DESCRIPTION OF THE RELATED ART
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. 4-Trifluoromethylaniline, 2-chloro-4-trifluoromethylaniline and 2,6-dichloro-4-trifluoromethylaniline are valuable compounds used for the synthesis of pesticidally active phenylpyrazole compounds. A number of methods are known for preparing these compounds. However these procedures are expensive and the compounds are difficult to prepare requiring multi-step synthetic procedures. For example US patent publication number 4096185 describes the preparation of 4-trifluoromethylaniline by the reaction of 4-chlorobenzotrifluoride with ammonia at 200° C. in the presence of potassium fluoride and cuprous chloride in a Hastelloy vessel. There remains a need to develop new methods for obtaining these compounds.
SUMMARY OF THE INVENTION
The present applicants have surprisingly discovered novel processes for the preparation of certain substituted arylamines and arylhydrazines, thus providing a new method for preparing important 5-amino-1-aryl-3-cyanopyrazole compounds which are valuable intermediates for the preparation of pesticides.
The present invention accordingly provides a process (A) for the preparation of a
compound of formula (I):
wherein R
1
is haloalkyl (preferably trifluoromethyl), haloalkoxy (preferably trifluoromethoxy) or −SF
5
;
W is N or CR
3
; and
R
2
and R
3
are each independently hydrogen or chlorine; or an acid addition salt thereof; which process comprises the hydrogenolysis of a compound of formula (II):
 or an acid addition salt thereof, with a metal or metal compound (for example a metal salt) under reducing conditions.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Certain compounds of formula (I) and (II) are novel and as such form a feature of the present invention.
Unless otherwise specified in the present invention ‘haloalkyl’ and ‘aloalkoxy’ are straight- or branched- chain alkyl or alkoxy respectively having from one to three carbon atoms substituted by one or more halogen atoms selected from fluorine, chlorine and bromine.
The acid addition salts referred to in the invention are preferably the salts formed from strong acids such as mineral acids, for example sulphuric acid or hydrochloric acid.
The hydrogenolysis may be performed using a metal or metal salt selected from Raney nickel (a nickel-aluminium alloy) optionally in the presence of iron, manganese, cobalt, copper, zinc or chromium; stannous chloride; zinc in the presence of acetic acid; and a molybdenum (III) salt. The reaction may also be carried out using Raney nickel, platinum or palladium (which may be supported on charcoal or other inert material) in the presence of hydrogen gas. When the reaction is performed with hydrogen gas a pressure of 2 to 20 bars (preferably 5 to 10 bars) is generally used. The hydrogenolysis is preferably performed using Raney nickel.
The reaction is generally conducted in a solvent which may be selected from alcohols such as methanol or ethanol; ethers; and aromatic hydrocarbons (methanol and ethanol are preferred solvents).
The reaction temperature is generally from 20° C. to 1 50° C., preferably from 20° C. to 90° C., more preferably from 50° C. to 80° C. The amount of catalyst employed is generally from 0.01 to 3 molar equivalents (preferably from 0.05 to 2 molar equivalents), although when the reaction is carried out under an atmosphere of hydrogen, a smaller amount generally gives satisfactory results.
In formulae (I) and (II) and in-the formulae depicted hereinafter R
1
preferably represents trifluoromethyl, trifluoromethoxy or −SF
5
, more preferably trifluoromethyl.
Particularly preferred compounds of formula (I) are 2,6-dichloro-4-trifluoromethylaniline; 2-chloro-4-trifluoromethylaniline; and 4-trifluoromethylaniline. Process (A) seeks to enable arylamine 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 can be straightforward. Another advantage of this method is that the compounds of formula (I) may be prepared at moderate temperatures and pressures, whereas prior art methods require high temperatures.
If necessary the compounds of formula (I) may be purified by crystallisation, for example from petroleum ether, to remove unwanted isomer products which may be present in small amounts. Alternatively crystallisation at a later stage in the synthetic scheme may be effective.
The compounds of formula (II) can be obtained by a process (B) wherein a compound of formula (III):
is reacted with hydrazine or an acid addition salt or source thereof.
Compounds of formula (III) are known or may be prepared by known methods.
According to a further feature of the invention process (A) can be combined with a process (B) to prepare a compound of formula (I) from a compound of formula (III).
Preferably hydrazine hydrate is used in the process (B).
When an acid addition salt of hydrazine is employed a base such as a trialkylamine (for example triethylamine) is optionally present.
Particularly preferred compounds of formula (II) are 2,6-dichloro-4-trifluoromethylphenylhydrazine; 2-chloro-4-trifluoromethylphenylhydrazine; and 4-trifluoromethylphenylhydrazine.
The process (B) may be conducted in a solvent chosen from cyclic or aliphatic ethers such as tetrahydrofuran, 1,4-dioxan or 1,2-dimethoxyethane; N-methylpyrrolidone; dimethyl sulphoxide; N,N-dimethylformamide; sulpholane; N,N,N′,N′-tetramethylurea; aromatic hydrocarbons which may be substituted with one or more alkyl groups or chlorine atoms, such as chlorobenzene or xylene;
alcohols such as isopropanol; and pyridine. Preferred solvents include pyridine, tetrahydrofuran, N,N,N′,N′-tetramethylurea and 1,4-dioxan (pyridine and tetrahydrofuran are especially preferred). The amount of solvent used is generally from 1 to 10 ml (preferably from 4 to 8 ml). per gramme of compound of formula (III).
The process (B) is generally performed in an autoclave or other sealed vessel. A pressure of from 1-8 bars (preferably 2-6 bars) is generally used.
The reaction temperature for process (B) is generally from 50° C. to 250° C., preferably from 120° C. to 180° C. A most preferred reaction temperature is from 120° C. to 150° C., when vessel corrosion and thermal decomposition of the product is minimal.
The reaction is generally conducted using from 1 to 20 molar equivalents (preferably 4 to 8 molar equivalents) of the hydrazine source.
A catalyst may optionally be used in the process (B), and when present is generally chosen from alkali and alkaline earth metal fluorides such as potassium fluoride. The amount of catalyst employed is generally from 0.05 to 2 molar equivalents (preferably from 0.5 to 1 molar equivalents). The reaction may also be effected in the presence of copper or a copper salt, preferably copper (I) chloride.
According to a further feature of the invention, process (A), or the combined processes (A) and (B), to give a compound of formula (I), which is purified by precipitation of the salt formed by treatment with a strong acid in the presence of an organic solvent.
The combined process (A) and (B) of the invention is particularly valuable when used for the preparation and reaction of the important intermediate 2-chloro-4-trifluoromethylphenylhydrazine, because the process step (B) proceeds in high yield and provides together with the other processes of the present inve

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