Magnesium forms

Fabricating Magnesium, Form No. 141-477, The Dow Chemical Co., Midland, Mich., 1984. 

Lime is among a family of chemicals which are alkaline in nature and contain principally calcium, oxygen and, in some cases, magnesium. In this grouping are included quicklime, dolomitic lime, hydrated lime, dolomitic hydrated lime, limestone, and dolomite. The most commonly used additives are quicklime and hydrated lime, but the dolomitic counterparts of these chemicals (i.e., the high-magnesium forms) are also widely used in wastewater treatment and are generally similar in physical requirements. 

Magnesium forms few halide complexes of the type MX4 , though [NEt4]2[MgCl4] has been reported examples of for the heavier... 

Whether or not the highly electropositive alkali metals or magnesium form an ionic instead of a covalent bond to the oxygen of the enolate is less important. Even if there is a contact ion pair of the metal cation and the oxygen anion, the geometry of the six-membered chair transition state, as outlined above, will be maintained. 

Caution Potassium is highly reactive. Although it may be handled safely in air if it is covered with a hydrocarbon solvent such as heptane or mineral oil, it will spark and ignite flammable organic vapors on contact with water. The magnesium formed in this reaction is highly reactive and pyrophoric (Note 1). Accordingly, Parts C and D of this procedure should be carried out behind a safety shield. 

The ratio of the two forms depends on the cation as well as on a. Ba has a greater tendency to make linkages of the COO-Me-OOC type than Mg and this difference is accentuated when the density of COO" in the polyanion is low. Thus, at a = 025 more Ba ions are in the COO-Ba-OOC form than in the COO-Ba form, while the reverse is true for Mg ions. Moreover, the structure COO-Mg is more stable and soluble than COO-Ba because Mg is more hydrophilic than Ba. For these reasons, Ba is precipitated at a = 0-25 while Mg is not. This interpretation is supported by titration experiments in the presence of divalent cations (Jacobsen, 1962). Magnesium forms very stable hydrates and would be expected to be more difficult to desolvate. 

Magnesium forms hydride when heated with hydrogen under pressure ... 

Magnesium forms an array of silicates having varying structures. Such a wide variety of silicates include metasilicate, orthosilicate, pyrosilicate, polysilicates, and a number of complex silicates, such as asbestos and talc in combination with other metal ions. Many such silicates occur in nature either as complex silicates or as discrete magnesium silicate. Some important magnesium silicates are listed below ... 

These titrations arc used in the estimation of metal salts. Ethylenediamine tetracetic acid (EDTA) shown in Figure 3.10 is the usual titrant used. It forms stable 1 1 complexes with all metals except alkali metals such as sodium and potassium. The alkaline earth metals such as calcium and magnesium form complexes which are unstable at low pH values and are titrated in ammonium chloride buffer at pH 10. The general equation for the titration is ... 

Hydrolysis and decarboxylation in the usual way lead to keto-esters or keto-acids. Of the more common metals used to form enolates, lithium is the most likely to give good C-acylation as it> like magnesium, forms a strong O-Li bond. It is possible to acylate simple lithium enolates with enoliz-able acid chlorides,... 

Magnesium compounds retard cellulose depolymerization by deactivating the transition metal catalysts. In alkaline media where hydroxy-acids or products of polysaccharide degradation are present, magnesium forms stable complexes with transition metals. The formation of iron-magnesium complexes in particular is supported by interactions approximating the coordination number of iron (6) and one half the coordination number (3). 

Tables 2.12 and 2.13 list the logarithm of the stability constants for the complexes of these chelating agents with various metal ions. Note that with the exception of Chel-138, calcium and magnesium form rather stable complexes with these chelating agents Fe3+ forms the most stable chelate of any metal listed. Generally, ferric iron is followed by Cu2+, Zn2+, Mn2+, Fe2+, Ca2+, and Mg2+. The weak acid properties of these chelating agents must be considered in any evaluation of their behavior. Because they are weak acids, the hydrogen ion tends to compete with the metal ions for association with the active groups.

Magnesium forms the bivalent cation Mg2+. Its oxide, hydroxide, carbonate, and phosphate are insoluble the other salts are soluble. They taste bitter. Some of the salts are hygroscopic. 

Plant foods contain relatively large amounts of inositol phosphates, including the hexaphosphate, phytic acid. Phytate chelates minerals, such as calcium, zinc, and magnesium, forming insoluble complexes that are not absorbed. However, both intestinal phosphatases and endogenous phosphatases (phytase) in many foods dephosphorylate a significant proportion of dietary phytate. The inositol released can be absorbed and utilized for phosphatidylinositol synthesis. 

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