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5.The Action of Alkyl Iodides on Copper-oxide.
[Read before the Philosophical Institute of Canterbury, 12th July, 19 11.]
The existence of cupric iodide in aqueous solution was first demonstrated by Moritz Trautz (Ber. d. D. Chem. Gessell, 1884, vol. 17, 1866), while Carnegie (Chem. News, 1889, vol. 59, 57) showed that any attempt to obtain solid cupric iodide by the evaporation of a solution containing Cu++ and I-ions always led to the separation of iodine and cuprous iodide. Walker and Dover (Jour. Chem. Soc., 1905, vol. 87, 1584) obtained a compound of the formula CuI, but all efforts to obtain cupric iodide itself have up to the present proved futile. The presence of the slightest trace of moisture is sufficient to cause the decomposition of the unstable cupric iodide, and it is to this fact that our failure to prepare this salt is due.
The action of dried methyl-iodide vapour on heated copper-oxide appeared to the author to form a promising method for securing cupric iodide, and, as the vapour of the alkyl iodides can be readily dried over phosphorus-pentoxide, it was hoped that the iodide, once formed, would not suffer the usual decomposition.
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The apparatus consisted of a distillation-flask containing the alkyl iodide and phosphorus-pentoxide, two U tubes containing the same drying reagent, a further U tube containing carefully dried copper-oxide, and an upright condenser connected to a receiver with suitable guard-tubes. Between the distillation-flask and the first drying-tube was interposed a T piece that allowed the entry of dry carbonic acid. After the whole apparatus had been sealed together, glass to glass, the various U tubes were heated to the required temperature and the apparatus exhausted. Dried carbonic-acid gas was then allowed to stream in, and, in order to insure the complete absence of oxygen, as well as complete drying, this operation was repeated about thirty times.
A preliminary experiment showed that at a temperature of 310° C. the oxide reacted quickly with the iodide, while at this temperature the vapour of the volatile alkyl compound suffered no decomposition. The rate at which the iodide distilled could be readily controlled, and it was generally so regulated that about 80 grammes were distilled over in 45 minutes.
A few experiments sufficed to show that the reaction, instead of taking the course represented by the equation CuO + 2 CH3I = CuI2 + (CH3)2O, took a much more complex path, the ultimate solid product invariably being cuprous iodide. Since not the slightest liberation of iodine was noted. as would occur were the cuprous iodide formed by the decomposition of the unstable cupric salt, it is to be concluded that cuprous iodide is the primary product of the reaction.
Numerous other products of the reaction were also obtained. The distillate always gave a strong aldehyde reaction, and it was also possible to collect a considerable quantity of gas. This proved to contain oxygen, carbon-monoxide, ethylene, methane, and its homologues. When methyliodide was used, the first three gases were contained to the extent of about 3 per cent., while the methane series bulked very largely in the total. The substitution of ethyl-iodide for methyl-iodide caused a marked change in the ratio of saturated to unsaturated hydrocarbons, for the percentage of ethylene rose to about 50 per cent., while the saturated hydrocarbons fell from about 90 to 45 per cent.