Reducing agent alkaline earth agents

Other Bromides. Alkali and alkaline earth bromides can be prepared by neutralizing a solution of the corresponding hydroxide or carbonate with hydrobromic acid. Alternatively, bromine and a reducing agent such as ammonia are used in the van der Meulen process (13) ... 

The general method for preparing the alkaline earth elements is to convert the mineral to a chloride or a fluoride by treatment with HC1 or HF. Then the molten salt is electrolyzed or, as in the case of BeF2, reduced with a chemical reducing agent such as Mg. 

The position of hydrogen in the activity series is particularly important because it indicates which metals react with aqueous acid (H + ) to release H2 gas. The metals at the top of the series—the alkali metals of group 1A and alkaline earth metals of group 2A—are such powerful reducing agents that they react even with pure water, in which the concentration of H+ is very low ... 

The alkaline earth elements in group 2A—Be, Mg, Ca, Sr, Ba, and Ra—are similar to the alkali metals in many respects. They differ, however, in that they have ns2 valence-shell electron configurations and can therefore lose two electrons in redox reactions. Alkaline earth metals are thus powerful reducing agents and form ions with a +2 charge. 

Alkali and alkaline earth metals dissolve in liquid ammonia with the formation of solvated electrons. These solvated electrons constitute a very powerful reducing agent and permit reduction of numerous conjugated multiple-bond systems. The technique, named for Birch provides selective access to 1,4-cydohcxiidicnes from substituted aromatics.8 In the case of structures like 21 that are substituted with electron-donating groups, electron transfer produces a radical anion (here 22) such that subsequent protonation occurs se lectively in the ortho position (cf intermediate 23) A second electron-transfer step followed by another protonation leads to com pound 24... 

The development of extensive uses for the alkaline-earth metals has been retarded by their high cost of production. Nevertheless, these metals are very useful in the chemical laboratory and are used commercially to a limited extent as reducing agents in the production of other metals. 

The tetrahydroborate salts of alkali metals, M[BH4] (M = Li, Na, K),1 are important because they serve as starting materials for the preparation of other boron hydrides2,3 and because they are used frequently as reducing agents.4 The lithium and sodium salts are prepared on a technical scale.5 9 The tetrahydroborate salts of the alkaline earth metals, M[BH4]2 (M = Mg, Ca, Sr, Ba), have not as yet been used extensively however, calcium bis[tetrahydroborate(l-)], Ca(BH4)2,10 is very soluble in tetrahydrofuran (THF) and it therefore has considerable potential application as a substitute for the lithium and sodium salts. 

The standard electrode potentials for all the rare earths have similar values and are comparable with the redox potentials of alkaline earth metals [144], Thus the lanthanides are strong reducing agents, and form trivalent ions easily. Both europium and samarium can exist in both trivalent and divalent states and the divalent states are not stable in aqueous solutions. Cerium can exist in both tetravalent and trivalent states in solution but Ce(III) is the most stable. 

The addition of an easily ionized substance such as cesium, which is usually not an analyte of interest in air pollution work, can reduce problems in alkali metal determination. A releasing agent, such as lanthanum, is useful for overcoming problems in analyzing for alkaline earth elements, and rare earth elements. Information on the use of these additives is given for specific cases in Table 1. 

---