GB869273A - Purification of fluorinated hydrocarbons - Google Patents

Abstract

Saturated perfluorocarbons and perfluorochlorocarbons are freed from hydrogen-containing impurities and/or olefinic impurities by subjecting the impure compound to free radical oxidising conditions including the presence of an oxygen donor, such as molecular oxygen, ozone or oxides of nitrogen, whereby the impurities are oxidized, and then separating purified perfluorocarbon or perfluorochlorocarbon from the products of oxidation. The reaction is preferably carried out in the presence of ultra-violet light, but other energy sources such as thermal energy, X-rays, radio-active material energy sources, irradiation by high energy particles, and exposure to strong electron fields may also be used. A chemical initiator, capable of forming free radicals from the impurities, may be used, e.g. a halogen (other than iodine), a halogen fluoride (other than iodine fluoride), an organic peroxide, or an azo or diazo compound. In Example 1, a sample of perfluorodimethylcyclohexane C8F16 (20 g.), containing 0,07% hydrogen, was sealed in a silica tube with chlorine (0,5 g.) and oxygen (5 atm. pressure); and the tube was shaken at room temperature whilst exposed to ultraviolet radiation. After 48 hours, the tube was opened, and excess of chlorine was removed by treatment with mercury. The liquid product was then washed with aqueous alkali, and distilled in vacuo to give C8F16 containing only 0,002 to 0,005% hydrogen. Example 2 relates to the purification of perfluorodimethylcyclohexane by treatment with oxygen and chlorine, using visible light from filament light bulbs as a source of energy, the irradiation lasting 4 days. In Example 5, perfluoroheptane (12 g.), containing 0,08% hydrogen, was sealed with chlorine trifluoride (0,5 g.) and oxygen (3 atm.) in a silica flask, and exposed to U.V. light for 14 hours. After removal of the more volatile products by treatment with dilute aqueous sodium hydroxide, the residual liquid was distilled in vacuo to give C7F16 containing less than 0,004% hydrogen. In Example 11, a fluorochloro-oil of high boiling-point, consisting of a chain of (-CF2CFCl-) units with perhalogenalkyl end groups, but containing 0,08% hydrogen, was diluted with purified C7F14, sealed with chlorine and oxygen, and irradiated with U.V. light for 24 hours. Removal of the solvent and distillation gave a purified oil which contained only 0,006% hydrogen. In Example 13, a product obtained by the vapour-phase fluorination of toluene with fluorine, in the presence of a gold-plated copper catalyst, contains hydrogenous and olefinic impurities. This product is mixed with chlorine and oxygen, and irradiated with U.V. light. A mixture of perfluoromethylcyclohexane, perfluorocyclohexane and perfluoroheptane is then separated. Example 15 relates to the treatment of crude perfluorodimethylcyclohexane with oxygen alone (i.e. no initiator is used), the source of C10F18 (containing 0,05% H2) from the vapourphase fluorination of naphthalene, was passed through a platinum tube, heated electrically to 350 DEG -400 DEG C., together with a mixture of chlorine and oxygen. The condensed product was washed and distilled to give a purified product containing 0,007% hydrogen.