Alkaline earth metals important reactions

Phosphides are binary compounds containing anionic phosphorus (P ). Heavy metal, alkali, and alkaline earth metal phosphides exist but few of them are commercially important. Phosphides hydrolyze to the flammable and toxic gas phosphine (PH3). The hydrolysis reaction of aluminum phosphide is given below ... 

The large amounts of natural gas (mainly methane) found worldwide have led to extentive research programs in the area of the direct conversion of methane [1-3]. Ihe oxidative transformation of methane (OTM) is an important route for the effective utilization of the abundant natural gas resources. How to increase catalyst activity is a common problem on the activation of methane. The oxidation of methane over transition m al oxides is always high active, but its main product is CO2, namely the product of deep oxidation. It is because transition metal oxides have high oxidative activity. So, they were usually used as the main corrqtonent of catalysts for the conqilete oxidation of alkane[4]. The strong oxidative activity of CH4 over tran on metal oxides such as NiO indicates that the activation of C-H bond over transition metal oxides is much easier than that over alkaline earth metal oxides and rare earth metal oxides. Furthermore, the activation of C-H bond is the key step of OTM reaction. It is the reason that we use transition metal oxides as the mam conq>onent of the OTM catalysts. However, we have to reahze that the selectivity of OTM over transition metal oxides is poor. 

The compositions of biomass among fuel types are considerably varied, especially with respect to inorganic constituents important to the critical problems of fouling and slagging. Alkali and alkaline earth metals, in combination with other fuel elements such as silica and sulfur, and facilitated by the presence of chlorine, are responsible for many imdesirable reactions in combustion furnaces and power boilers. 

Alkaline earth metal oxides have been used as solid base catalysts for a variety of organic transformations. Excellent reviews by Tanabe 4) and Hattori 2,3,7) provide detailed information about the catalytic behavior of alkaline earth metal oxides for several organic reactions of importance for industrial organic synthesis. In this section, we describe in detail reactions that have been reported recently to be catalyzed by alkaline earth metal oxides. 

The Guerbet reaction is an important industrial process for increasing the carbon numbers of alcohols. Thus, a primary or secondary alcohol reacts with itself or another alcohol to produce a higher alcohol (Scheme 23). Alkaline earth metal oxides have been used as catalysts for the condensation of alcohols. Ueda et al. (158,159) reported the condensation of methanol with other primary or secondary alcohols having a methyl or methylene group at the )S-position they used MgO, CaO, and ZnO as catalysts. The reactions were performed with gas-phase reactants at 635 K only MgO was found to be both active and selective (>80%). 

Complexes of alkali metals and alkaline-earth metals with carbohydrates have been reviewed in this Series,134 and the interaction of alkaline-earth metals with maltose has been described.135 Standard procedures for the preparation of adducts of D-glucose and maltose with the hydroxides of barium, calcium, and strontium have been established. The medium most suitable for the preparation of the adduct was found to be 80% methanol. It is of interest that the composition of the adducts, from D-glucose, maltose, sucrose, and a,a-trehalose was the same, namely, 1 1, in all cases. The value of such complex-forming reactions in the recovery of metals from industrial wastes has been recognized. Metal hydroxide-sugar complexes may also play an important biological role in the transport of metal hydroxides across cell membranes. 

Nitroalkanols are intermediate compounds of /1-amino alcohols that are used extensively in many important syntheses. They are obtained by Henry s reaction through the condensation of nitroalkanes with aldehydes. Different nitro compounds have been reacted with carbonyl compounds in reactions catalysed by alkaline earth metal oxides and hydroxides/621 Among the catalysts examined, MgO, CaO, Ba(OH)2, and Sr(OH)2, exhibited high activity for the reaction of nitromethane with propionaldehyde. The yields were between 60 % (for MgO) and 26 % [for Sr(OH)2] at 313 K after 1 h in a batch reactor. The study of the influence of the pretreatment temperature of the solid showed that for MgO and CaO a... 

While the latter reactions are no longer used for nitrogen fixation, the reaction of dinitrogen with dihydrogen to form ammonia is among the most important industrial processes. The alkaline-earth metals react readily with dinitrogen at elevated temperatures to form nitrides lithium reacts even at room temperature with dinitrogen. 

Table 18.8 summarizes some important reactions involving the alkaline earth metals. 

The reactions of alkaline earth metal atoms with halogen molecules, either forming alkaline earth metal monohalides or leading to chemi-ionization, represent an important case study in the reaction dynamics of divalent systems [91, 92, 95-100]. Let us take as an example the reaction... 

Measuring the polarization of the reaction product is also an important issue in stereodynamics. A lot of the activity in this field concerns the reactivity of alkaline earth metal atoms since the corresponding reaction products are easy to probe by optical techniques. A full account of methods to measure product alignment and orientation in bimolecular collisions has been given by Orr-Ewing and Zare [18]. Such measurements, with the help of simple models such as the DIPR-DIP model considered Section 2.3.2, give insight into the shape of the reactive system at the moment where forces are released [86, 87, 184, 195, 233, 234]. 

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