PROCESS FOR THE PREPARATION OF 1,1-DIHALO-1,3-DIENES

PROCEDE POUR LA PREPARATION DE 1,1-DIHALO-1,3-DIENES

English Abstract

ABSTRACT
A process for the preparation of a 1,1-dihalo-1,3-diene of the
general formula
<IMG> (I)
in which Hal represents a chlorine, bromine or iodine atom, and R1, R2,
R3 and R4 each represents a hydrogen atom or an alkyl group, which comprises
reacting a tetrahaloalkane of the general formula:
<IMG> (II)
with a tertiary amine at a temperature of at least 100°C. The process of
the invention is useful in the preparation of intermediates in the production
of pyrethrin-type insecticides.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for the preparation of a 1,1-dihalo-1,3-diene of the
general formula:
<IMG> (I)
in which Hal represents a chlorine, bromine or iodine atom, and R1, R2, R3
and R4 each represents a hydrogen atom or an alkyl group, which comprises
reacting a tetrahaloalkane of the general formula:
<IMG> (II)
wherein R1, R2, R3, R4 and Hal are as defined above with a tertiary amine
at a temperature of at least 100°C.
2. A process as claimed in claim 1 in which the tertiary amine is a
trialkylamine, a dialkylaniline or an optionally alkyl- or phenyl-substi-
tuted pyridine or quinoline.
3. A process as claimed in claim 2 in which the tertiary amine is tri-
butylamine or quinoline.
4. A process as claimed in any one of claims 1 to 3 in which the molar
ratio of tertiary to compound of formula II is from 2:1 to 3:1.
5. A process as claimed in any one of the claims 1 to 3 in which the
temperature is from 150° to 200°C.
6. A process as claimed in any one of claims 1 to 3 in which the com-
pound of formula II is 1,1,1,3-tetrachloro-4-methylpentane.
7. A process as claimed in any one of claims 1 to 3 in which R1, R2,
R3 and R4 each represents hydrogen or an alkyl group of 1 to 6 carbon atoms.

Description

~7~333
This invention relates to a process for the preparation of
1,1-dihalo-1,3-dienes from 1,1,1,3-tetrachloroalkanes.
It is known from "Collection Czechoslov. Chem. Comm." 24 (1959),
2230-6 that the reaction of 1,1,1,3-tetrachloroalkanes with alkalis such as
lime in water or potassium hydroxide in ethanol, gives l,l-dichloro-1,3-
dienes in low yield.
It has now been found that under certain conditions other basic
reagents may be used to produce l,1-dichloro-1,3-alkadienes in higher yields.
Accordingly the invention provides a process for the preparation
of a 1,1-dihalo-1,3-diene of the general formula:-
R2 R3 R4
1 (I)
R - C = C - C = CHal2
in which Hal represents a chlorine, bromine or iodine atom and Rl, R2, R3, R4
each represents a hydrogen atom or an alkyl group, preferably of 1 to 6 carbon
atoms, which comprises reacting a 1,1,1,3-tetrahaloalkane of the general
formula:-
R R3 R4
Rl _ C - C - C - CHal3 (II)
H Hal H
wherein Rl, R , R , R4 and Hal are as defined above with a tertiary amine
at a te~perature of at least 100C.
Surprisingly, using the process of the invention two molecules of
hydrogen halide are eliminated from one molecule of the compound of the
formula II with formation of the compound of formula I in a yield of usually
more than 80%.
The process is preferably carried out at a temperature from 150 to
200C. The reaction time is preferably from 0.5 to 5 hours.
The molar ratio of tertiary amine to 1,1,1,3-tetrahaloalkane of
formula II is preferably at least 2:1, for example from 2:1 to 3:1 and in
particular from 2:1 to 2.5:1.
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~070333
The tertiary amine may be a trialkylamine, a dialkylaniline or
an optionally alkyl^ or phenyl-substituted pyridine or quinoline, the alkyl
in each case being preferably of 1 to 6 carbon atoms. Quinoline is
particularly preferred. The process is preferably carried out
...^;
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1070333
under atmospheric pressure usin a tertiary amine which has a boiling
point at atmospheric pressure above the reaction te~perature.
The process of the invention i3 of particular interest Por the
preparation o~ dichloro-4~methyl-1,3-pentadiene from 1,1,1,3-tetra-
chloro-4-methylpentane. 1,1-Dichloro-4-methyl-1,3-pentadiene is a
precursor o~ 2-(2,2-dichlorovinyl)-3 t 3-dimethylcyclopropanecarboxylic
acid, esters Or which are pyrethrin-type insecticides (see published
Netherlands patent application 7307130).
The in~ention is ~urther illustrated in ~he following Exam~les.
EXAMPLE I
A mixture of one mol of 1,1,1,3-tetrachloro-4-methylpentane
and 2.5 mol Or quinoline was vigorously stirred under nitrogen for
a period of two hours at a temperature of 160 C. The crude 1,1-dichloro-4-
methyl-1,3-pentadiene was then distilled at 180C and atmospheric
pressure. An equal volume of carbon tetrachloride was added to the
distillate which was then ~iltered. The ~iltrate was washed with
25 ml o~ 0.1 N aqueous hydrochloric acid and dried over anhydrous
calcium chloride. The solvent was then removed under reduced pressure
to give pure 1,1-dichloro-4-methyl-1,3-pentadiene, yield 97%, ca]culated
on starting 1,1,1,3-tetrachloro-4-methylpentane.
EXAMPLE II
The procedure described in Example I waY repeated using 2.2
mol Or quinoline. The same results were obtained.
EXAMPLE III
The procedure described in Example I was repeated using 2.5
mol Or tributylamine instead Or quinoline. In this case the yield
of 1,1-dichloro-4-methyl-1,3-pentadiene was 85%.
EXAMPLE IV
The procedure described in Example I was repeated using 1,1,1,3-tetra-
chloropentane as starting material. The yield of 1,1-dichloro-1,3-pen-
tadiene obtained was 90%.
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