CH620185A5 - Process for the preparation of 1,1-dihalo-1,3-dienes - Google Patents

Description

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Claims (6)

CLAIMS 1. Process for preparing l,l-dihalo-l,3-dienes of the general formula R t R- t 4 R-C=C-C= CHal2 in which Hal represents a chlorine, bromine or iodine atom and R1, R2, R3 and R4 each represent a hydrogen atom or an alkyl group, characterized in that a tetrahaloalkane of the general formula R i i R - C R t C - hello R t - CHal, at a temperature of at least 100°C with a tertiary amine. 2. The method according to claim 1, characterized in that the tertiary amine is a trialkylamine, a dialkylaniline or an optionally alkyl- or phenyl-substituted pyridine or quinoline. 3. The method according to claim 2, characterized in that the tertiary amine is tributylamine or quinoline. 4. The method according to any one of claims 1-3, characterized in that the molar ratio of tertiary amine to the compound of formula II is 2:1 to 3:1. 5. The method according to any one of claims 1-4, characterized in that it is carried out at a temperature of 150-200°C. 6. Process according to any one of claims 1-5, characterized in that 1,1,1,3-tetrachloro-4-methylpentane is used as the compound according to formula II. The invention relates to a process for preparing 1,1-dihalo-1,3-dienes from 1,1,1,3-tetrahaloalkanes. From «Collection Czechoslov. Chem. Comm." 24 (1959), 2230-6, it is known that the reaction of 1,1,1,3-tetrachloroalkanes with alkalis, such as lime in water or potassium hydroxide in ethanol, leads to l,l-dichloro-l,3-dienes, however, the yield is low. It has now been found that under certain conditions the use of other basic reactants leads to higher yields of l,l-dichloro-l,3-alkadienes. The process according to the invention for the preparation of 1,1-dihalo-1,3-dienes of the general formula: R I R-! 4 1 f (1) R-C = C-C = CHal2 wherein Hal represents a chlorine, bromine or iodine atom and R\ R2, R3, R4 each represents a hydrogen atom or an alkyl group, preferably one with 1-6 carbon atoms, is therefore characterized in that a 1,1, 1,3-Tetrahaloalkane of the general formula: R2 R3 4 R ? ; ! C - C - C ! } \ H shark H (ii) at a temperature of at least 100°C with a tertiary amine. Surprisingly, when the process according to the invention is carried out, two molecules of hydrogen halide are split off from one molecule of the compound of formula II, the compound of formula I being formed in a yield of usually more than 80%. The process is preferably carried out at a temperature of 150-200°C and the reaction time is preferably between half an hour and five hours. The molar ratio of tertiary amine to 1,1,1,3-tetrahaloalkane according to formula II is preferably at least 20:2:1 and is, for example, from 2:1 to 3:1, in particular from 2:1 to 2.5: 1. The tertiary amine may be a trialkylamine, a dialkylaniline or a pyridine or quinoline optionally substituted by alkyl or phenyl groups, the alkyl groups in each case preferably containing 1 to 6 carbon atoms. Quinoline is particularly preferred. The process is preferably carried out at atmospheric pressure, using a tertiary amine which boils above the reaction temperature at atmospheric pressure. The process according to the invention is of particular interest for preparing l,l-dichloro-4-methyl-l,3-pentadiene from l,l,l,3-tetrachloro-4-methylpentane. 1,1-Dichloro-4-methyl-1,3-pentadiene is a precursor of 2-(2,2-dichloro-vinyl)-3,3-dimethylcyclopropanecarboxylic acid, the esters of which are pyrethrin-type insecticides (see the published Dutch patent application no. 7 307 130). The examples serve to explain the invention in more detail. example 1 40 A mixture of one mole of 1,1,1,3-tetrachloro-4-methylpentane and 2.5 moles of quinoline was stirred vigorously at 160° C. under nitrogen for two hours. The crude 1,1-dichloro-4-methyl-1,3-pentadiene was distilled off at 180° C. under atmospheric pressure. The distillate was filtered after adding an equal volume of carbon tetrachloride and the filtrate was washed with 25 ml of 0.1 N aqueous hydrochloric acid and dried over anhydrous calcium chloride. After driving off the solvent under reduced pressure, pure 1,1-dichloro-4-methylpentadiene was obtained in such a yield of 97%, calculated on the 1,1,1,3-tetrachloro-4-methylpentane from which one started. example 2 The procedure was as in Example 1, but 2.2 mol of 55 quinoline were used. The same result was obtained. Example 3 The procedure was as in Example 1, but 2.5 moles of tributylamine were used instead of quinoline. The yield of 1,1-dichloro-4-methyl-1,3-pentadiene was 85% in this case. example 4 The procedure was again as in Example 1, but the starting material used was 1,1,1,3-tetrachloropentane. The yield of 1,1-dichloro-1,3-pentadiene was 90%. s