GB570869A - Improvements in or relating to the manufacture of halogen-substituted alkenes - Google Patents

Abstract

Terminally halogen-substituted alkenes are prepared by reacting a 1,3-diene or 2,5-dihydrothiophene-1-dioxide with at least the molecular equivalent of a polyhalo-ethane or methane having at least two halogen atoms attached to one carbon atom, at an elevated temperature, in the presence of an iron-containing substance, and a peroxygen compound or a polyhydroxybenzene or both. The polyhydroxybenzene is essential unless freshly distilled polyhalo-compounds are used. A pressure vessel may be charged with the freshly distilled halo-compound, e.g. carbon tetrachloride, 2,5-dihydrothiophene-1-dioxide, which forms the 1,3-diene in situ, a diacyl peroxide or ammonium or alkali metal persulphate, pyrogallol, and a solvent for pyrogallol such as ethanol. After heating for 4-6 hrs. at 60-150 DEG C., the mixture is cooled, sulphur dioxide blown off, steam distilled, and the products separated. An iron or steel vessel may be used or iron filings or ferric chloride added. Peroxygen compounds include acyl, e.g. acetyl, propionyl, lauroyl and benzoyl peroxides, persulphates, perborates, and percarbonates, and peroxides of hydrogen, diethyl, cyclohexanone and tetrahydronaphthalene, and ascaridole. Other polyhydroxybenzenes specified are hydroquinone, resorcinol and catechol. A molecular excess of polyhalo-compound over the diene is generally used and the molar ratio may be up to 10 : 1. Inert solvents, e.g. saturated aliphatic or cycloaliphatic hydrocarbons, and ethers, water, alcohols, ketones and aromatic hydrocarbons may replace part of the excess of poly-halo compound. The presence of small amounts of atmospheric oxygen is sometimes permissible. Polyhalo-ethanes or methanes specified are carbon tetrachloride or tetrabromide, chloroform, bromoform, iodoform, methylene chloride, bromide, iodide or chloriodide, hexachlorethane, 1,1-dichlorethane and 1,1,1-trichlorethane. 1,3-Dienes include butadiene, 2-chlor-, 2-methyl- or 2-cyano-1,3-butadiene, and 2,3-dimethyl - 1,3 - butadiene. The corresponding 2,5-dihydrothiophene-1-dioxides, prepared by reacting the 1,3-dienes with sulphur dioxide, give better yields. The products may be used as solvents or as plasticizers and softeners for cellulose derivatives and resins. Examples describe the reaction of 2,5-dihydrothiophene-1-dioxide and carbon tetrachloride to yield 1,1,1,5 - tetrachlorpentene - 3. Higher boiling products, chiefly tetrachlornonadiene, may also be formed. A steel or stainless steel or, when iron or ferric chloride is added, a silver-lined reactor is used. The additional catalyst is benzoyl peroxide or pyrogallol or both. A further example employs 1,3-butadiene.