The Solvating Power of Anhydrous Magnesium Bromide as a Possible Function of Its Preparation Temperature

Before undertaking a study of the solvates of magnesium bromide, a method for preparing a reproducibly active anhydrous salt must be found. A suitable method is by the direct union of magnesium and bromine in ether, according to the procedure of Zelinsky. This results in the formation of etherates, from which the anhydrous salt can be obtained by desolvating at a moderately high temperature in a vacuum. It is known that if too high a temperature is used in the preparation of anhydrous aluminum oxide or calcium sulfate, the resulting product will not recombine with water. It is conceivable that the solvating power of anhydrous magnesium bromide, prepared from its etherates, might in an analogous way be a function of the preparation temperature. To test the possible effect of temperature on the solvating property of magnesium bromide, samples were desolvated under reduced pressure at 100°, 200°, 300° and 400° C. A constant stream of air saturated with ether at 20° was then passed over the samples, which were kept at 25° and weighed at intervals. The rates of solvation for the various samples were found to be equal within experimental error. It is conceded that the necessity of using interchangeable ground-glass joints permitted the entrance of traces of moisture, but within the temperature ranges studied, we feel justified in stating that the solvating power of anhydrous magnesium bromide is not a function of its preparation temperature