Alkaline-earth hydrides

Another aspect of the hydrolysis of hydrides is the alkalinity that results, especially from alkaU metal and alkaline-earth hydrides. This alkalinity can cause chemical bums in skin and other tissues. Affected skin areas should be flooded with copious amounts of water. 

Eu—D system. — Europium deuteiide was found to be isostructural [236] with alkaline earth hydrides and ytterbium deuteride. The sample of the deuteride was prepared by reacting deuterium with the europium and had a maximum composition of EuDi.95. The lattice constants of europium deuteride are a = 6.21, b = 3.77, c = 7.16 A ( 0.02 A). The deuterides of europium and ytterbium are believed to be predominantly ionic rather than interstitial. 

The ionic hydrides are white solids with high melting points, and all of the alkali metal hydrides have the sodium chloride crystal structure. Because they resemble the salts of the alkali and alkaline earth metals, the ionic hydrides are often referred to as saline or salt-like hydrides. The properties of the alkali metal hydrides are shown in Table 6.3, and those of the alkaline earth hydrides are shown in Table 6.4. 

Table 6.4 Some Properties of Alkaline Earth Hydrides...

The conditions for preparing LiH are different from those of the other alkali hydrides because of its high stability, making it similar to the alkaline-earth hydrides. This hydride, therefore, is discussed separately. 

Direct reaction of Ca, Sr, Ba and presumably Ra with forms hydrides that are ionic, like the alkali-metal hydrides. Direct reaction with Mg also forms a hydride which may be synthesized by other methods. Alkaline-earth hydrides are discussed in 1.8.3. 

The third subgroup consists of Eu and Yb dihydrides, which have an orthorhombic structure and resemble the alkaline-earth hydrides, CaHj, SrHj and BaHj (see 1.8.3.3). 

Syntheses that exploit the solubility of the alkaline-earth metals in liquid ammonia have proven practical for alkoxide work, as they generate high yields, reaction rates, and purity (Table 8, Equation (3)). In a refinement of this approach, Caulton and co-workers have used dissolved ammonia in an ethereal solvent, usually THF, to effect the production of a number of alkoxides of barium, and this method has also been examined with calcium and strontium (Table 8, Equations (4a) to (4c)). Displacement reactions using alkali metal alkoxides and alkaline-earth dihalides (Table 8, Equation (5)), and between alkaline-earth hydrides or amides and alcohols (Table 8, Equations (6) and (7)), have been examined, but alkali-metal halide impurities, incomplete reactions, and unexpected equilibria and byproducts can affect the usefulness of these approaches. 

The alkaline-earth hydrides all have a PbCl2 type of structure in which the metal atoms are arranged approximately in hexagonal closest packing. Of the two sets of non-equivalent H atoms one occupies tetrahedral holes while the other H atoms have (3 + 2)-coordination ... 

Studies of the photodecompositions of alkaline earth hydrides (MgHj, CaHj, SrHj and BaHj) — Metal + [9] showed that all exhibited generally similar behaviour. 

The more saltlike barium compound decomposes when distilled. Complete thermal breakdown of the alkaline earth bis(tetraethylalanates) gives triethylalane, ethylene, and alkaline earth hydride ... 

From alkaline earth hydrides and rhodium metal by sintering powder mixtures at 1073 K under 5 bar hydrogen pressure powder of black-red (Sr) and black (Ca)... 

Recent patent disclosures by the Standard Oil Co. of Indiana indicate that their process for the polymerization of ethylene is also a relatively low-pressure process, and the following process information is based on these disclosures. The polymerization process is a fixed-bed process employing a prereduced catalyst, ethylene pressures of 809-1,000 psi, and temperatures somewhat greater than 200°C. The metal oxides (such as nickel, cobalt, and molybdenum) can be supported on either charcoal or alumina, and materials such as lithium aluminum hydride, boron, alkali metals, and alkaline-earth hydrides may be used as promotors. Variations of this process are reported to produce polyethylene resins with densities from 0.94-0.97. 

Condensation of acetone with alkali or alkaline-earth hydrides, ... 

---