Halogenated hydrocarbons and a method for their preparation

A halogenated hydrocarbon having the general formula: ##STR1## wherein Y represents fluorine, chlorine, bromine or --(CF.sub.2).sub.m W, R represents hydrogen or lower alkyl, R.sup.1 represents lower alkyl, X represents chlorine, bromine or iodine, W represents hydrogen, fluorine or chlorine and m is 1 or 2, is prepared by heating a compound having the general formula: ##STR2## wherein R, R.sup.1, X, Y, W and m have the meanings given above and Z represents chlorine, bromine or iodine, in a polar aprotic solvent together with an alkanolamine, optionally in the presence of a copper salt.

This invention relates to halogenated hydrocarbons, useful as insecticide 
intermediates, and to a method for their preparation. 
According to the present invention there is provided a halogenated 
hydrocarbon having the general formula: 
##STR3## 
wherein Y represents a fluorine, chlorine or bromine atom, or 
(CF.sub.2).sub.m W, R represents a hydrogen atom or a lower alkyl group, 
R.sup.1 represents a lower alkyl group, X represents a chlorine, bromine 
or iodine atom, W represents hydrogen, fluorine or chlorine and m is 1 or 
2. 
Preferably X and Y represent chlorine or bromine atoms, especially chlorine 
atoms. 
By "lower alkyl group" we mean an alkyl group containing from 1 to 6 carbon 
atoms, preferably a methyl group. 
A specific example of a halogenated hydrocarbon of formula (I) is 
2,4-dichloro-5-methyl-1,1,1-trifluorohex-2-ene. 
According to a further feature of the invention there is provided a process 
for the manufacture of a halogenated hydrocarbon of formula (I) which 
comprises heating in a polar aprotic solvent, together with an 
alkanolamine, optionally in the presence of a copper salt, a halogenated 
hydrocarbon having the general formula: 
##STR4## 
wherein R, R.sup.1, X, Y, W and m have the meanings defined above and Z 
represents a chlorine, bromine or iodine atom. 
Examples of polar aprotic solvents which may be used in the above process 
are diethylformamide, hexamethylphosphoramide and especially 
dimethylformamide and dimethylacetamide. 
The amount of polar aprotic solvent which is used may be from 1 to 100 
moles, preferably 3 to 15 moles per mole of the starting material of 
formula (II). 
Examples of the alkanolamines which may be used are monoethanolamine, 
monoisopropanolamine and diethanolamine. 
The amount of alkanolamine which is used may be from 1 to 100 moles, 
preferably 1 to 10 moles per mole of the compound of formula (II). 
An example of a copper salt which may be included is cuprous chloride. 
The copper salt may be used in a amount from 10.sup.-4 to 10.sup.-1 moles, 
conveniently 10.sup.-3 to 10.sup.-2 moles per mole of the compound of 
formula (II). 
The reaction may be carried out at a temperature from 20.degree. to 
200.degree. C., conveniently from 50.degree. to 150.degree. C., and may 
require a reaction time of several minutes to several days. 
The progress of the reaction can be followed by analytical sampling of the 
reaction mixture, for example, by gas-liquid chromatographic (GLC) 
analysis. 
Reaction is preferably carried out under an inert atmosphere, for example, 
nitrogen. 
Isolation of the reaction product is carried out by conventional means. For 
example, the product may be precipitated from solution in the polar 
aprotic solvent by addition of a solvent which is miscible with the polar 
aprotic solvent but in which the reaction product of formula (I) is 
insoluble. A suitable solvent for this purpose is water. The precipitated 
product may then be extracted from the aqueous mixture with an organic 
solvent, for example, dichloromethane, followed by removal of the organic 
solvent, if desired under reduced pressure, to give the product of formula 
(I). 
The starting materials of formula (II), may be prepared by suitable 
classical processes of organic chemistry. However, especially useful 
processes comprise reacting an alkyl substituted butene with a 
polyhalogenated alkane having 2 to 4 carbon atoms, in the presence of a 
suitable catalyst, as more fully described in our copending United Kingdom 
patent Application of earlier date. 
The halogenated hydrocarbons of formula (I) are useful as intermediates in 
the preparation of insecticides based on certain cyclopropanecarboxylic 
acids. Thus, the compounds of formula (I) may be dehydrohalogenated by 
heating in a polar aprotic solvent, for example, dimethylformamide 
preferably in the presence of an alkali metal halide, for example, lithium 
chloride, to give dienes of the general formula: 
##STR5## 
wherein R, R.sup.1,Y,W and m have the meanings defined above. This process 
is more fully described in a copending United Kingdom patent application 
of earlier date. 
A specific example of a compound of formula (III) which may be prepared as 
described above is 2-chloro-5-methyl-1,1,1-trifluorohexa-2,4-diene. The 
latter compound (1 mol proportion) may be reacted, for example, with ethyl 
bromocyanoacetate (1.5 mol proportions) in the presence of cuprous 
chloride (0.1 mol proportion) as catalyst and calcium carbonate (1.5 mol 
proportions) as base, in ethanol at reflux for ca. 12 hours, to give ethyl 
3-(2-chloro-3,3,3-trifluoropropenyl)-1-cyano-2,2-dimethylcyclopropane-1-ca 
rboxylate, which may itself be converted by known methods into 
3-(2-chloro-3,3,3- 
trifluoropropenyl)-2,2-dimethylcyclopropane-1-carboxylic acid or a lower 
alkyl ester thereof. This cyclopropane carboxylic acid or ester may be 
further esterified or transesterified respectively with, for example, 
m-phenoxybenzyl alcohol, to give a compound which is a potent insecticide.

The invention is illustrated but not limited by the following Examples. 
EXAMPLE 1 
A mixture comprising 5-methyl-2,2,4-trichoro-1,1,1-trifluorohexane (51.5 
g), monoethanolamine (6.1 g), cuprous chloride (0.1 g) and 
dimethylformamide (100 ml) is stirred and heated at 96.degree. C. 
(internal temperature) under a nitrogen atmosphere. When the initial green 
colour of the mixture is discharged further aliquots of monoethanolamine 
are added until a geen colour persists and GLC analysis shows that the 
starting material has been consumed. The reaction is complete after 5 
hours. The crude product is isolated by precipitation with water, 
extraction with dichloromethane and removal of the solvent under reduced 
pressure. Distillation affords 
2,4-dichloro-5-methyl-1,1,1,trifluorohex-2-ene (71%), b.p. 
79.degree.-82.degree. C./100 mm Hg; 'Hnmr (CDCl.sub.3).tau.9.2-8.8 (q, 
6H); 8.2-7.8 (m, H); 5.6-5.3 (m, H); 3.9-3.4 (pair of doublets, H). 
EXAMPLE 2 
A mixture comprising 5-methyl-2,2,4-trichloro-1,1,1-trifluorohexane (5.0 
g), monoethanolamine (1.7 g) and dimethylforamide (10 ml) is heated under 
nitrogen in an oil bath at 105.degree. for 2 hours. Examination of the 
reaction mixture by GLC shows the product to consist mainly of 
2,4-dichloro-5-methyl-1,1,1-trifluorohex-2-ene. 
EXAMPLE 3 
A mixture comprising 5-methyl-2,2,4-trichloro-1,1,1-trifluorohexane (5.0 
g), monoethanolamine (1.7 g) and dimethylacetamide (10 ml) is heated under 
nitrogen in an oil bath at 105.degree. C. for 2 hours. The cooled reaction 
mixture is added to a large volume of water to precipitate the product. 
The crude product is washed with water, dried over anhydrous sodium 
sulphate and shown by 'Hnmr to consist almost entirely of 
2,4-dichloro-5-methyl-1,1,1-trifluorohex-2-ene. 
EXAMPLE 4 
This is not an example of the invention but illustrates the 
dehydrohalogenation of the product obtained in Example 1. 
2,4-Dichloro-5-methyl-1,1,1-trifluorohex-2-ene (22.1 g) in 
dimethylformamide (100 ml) containing lithium chloride (5.0 g) is heated 
under a nitrogen atmosphere in an oil bath at 160.degree. C. for 1.5 
hours. The cooled mixture is added to water (1.5 l), extracted with 
dichloromethane and the extracts dried over anhydrous sodium sulphate and 
distilled to afford 2-chloro-5-methyl-1,1,1-trifluorohexa-2,4-diene (76%). 
The identity of the product was proved by comparison to 'Hnmr and 
infra-red spectra with those of authentic material.