After hydrolysis, the carbon tetrachloride is separated from the aqueous phase, washed with potassium hydroxyde to remove traces of phosgene, and finally distilled. The distillate is dried over calcium chloride and weighed. Infrared analysis showed that a single distillation from aqueous potassium hydroxide and drying over calcium chloride suffice to give a product which is purer than commercial technical grade carbon tetrachloride. Hexachloroethane could not be detected in significant amounts. The catalyst may be prepared by direct vaporization of thechlorides of the transition metals of Groups V to VIlI onto the activated carbon. Alternatively, the carbon can be impregnated with solutions of salts of the transition metals, dried, reduced with hydrogen, and finally chlorinated (preferably at room temperature) with phosgene or chlorine. With tungsten hexachloride on Katepon F 12 (Degussa's activated carbon) the conversion of phosgene into carbon tetrachloride was 60 "/, at a phosgene feed rate of 0.93 liter/h and a temperature of 500 "C. With a mixed MoCl5 and W C l 6 catalyst on Katepon F 12 at 400 "C, we made the surprising observation that the performance of the catalyst is actually improved despite a decrease in the phosgene conversion. Here the performance is judged by the grams of C C l 4 formed per gram of catalyst per hour (cf. Figure 2). As can be seen from the graph, even at a feed rate of 10 liters of phosgene per hour the conversion is still 24 %.Longer contact times, achieved by increasing the catalyst volume, increase the conversion of phosgene into carbon tetrachloride further even at high feed rates.It is interesting to note that the same quantities of ammonium molybdate give different conversions of phosgene into carbon tetrachloride when deposited on different activated carbons, even though the reaction conditions (temperature, catalyst volume, feed rate) remain the same. A linear dependence of the phosgene conversion on the surface areas of the various activated carbon catalyst carriers used (as determined by the iodine adsorption method) was obtained; this is shown in Figure3. It is assumed that the formation of carbon tetrachloride from phosgene proceeds via the steps outlined below, although it remains uncertain whether radical reactions are involved.
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