Hydroxides of alkaline earth metals

In this case asbestos is the only suitable material for diaphragms being fully resistant against caustic while at least partially resistant against chlorine. Asbestos diaphragms are particularly suitable for electrolyzers with horizontal diaphragms as they are entirely surrounded by caustic solution (see Fig. 88). In such a medium the durability of asbestos is almost unlimited and the diaphragm requires replacement only after its permeability has been considerably impaired by precipitated hydroxides of alkaline-earth metals. 

As to the reaction catalyst, Malinowski and Kehl, in 1960 to 1962, reported that the hydroxides of alkaline-earth metals, such as barium hydroxide, calcium hydroxide, magnesium hydroxide, strontium hydroxide, certain alkali-metal hydroxides, and some heavy-metal oxides are all effective as catalysts for the aldol reaction. Likewise, the hydroxides of tri- and tetra-valent rare-earth metals were shown to be active by Berlin and coworkers in the formation of formose under conditions of high temperature (110°) and pressure (1.8 atm.). Some organic bases, as well as certain inorganic bases, were also shown effective by Mizuno and co-... 

A number of catalysts for the formose reaction are known (see Table I). They are mostly inorganic and organic bases. In particular, the hydroxides of alkaline-earth metals (for example, calcium hydroxide) are most effective, because of their particular ability to form stable complexes with enediol compounds (see formula 1). The reaction occurs not only in aqueous solution but also in anhydrous ethyl alcohol, glycerol, and glycol, or in solutions of organic acids, although less actively. 

TABLE 4.8.7 Solubility Product of the Hydroxides of Alkaline Earth Metals [18,101-103]... 

The oxides and hydroxides of alkaline earth metals are active catalysts for the polymerization of ethylene oxide at 340 — 380 K. As for the hydroxides, the activity decreases in the series Be(OH)2 to Ba(OH)2. Strontium carbonate is several fold more active than calcium or barium oxide.Carbonates and oxalates are also active catalysts. The molecular weight is 10 — 10 for the oxides and hydroxides of alkaline earth metals.The presence of protons on the catalysts leads to a lowering of molecular weight because of participation in the breaking reaction. 

The most general methodology followed to prepare alkaline earth metal oxides as basic catalysts consists of the thermal decomposition of the corresponding hydroxides or carbonates in air or under vacuum. Decomposition of hydroxides is frequently used to prepare MgO and CaO, whereas BaO and SrO are prepared from the corresponding carbonates as precursor salts. Preparation of alkaline earth metal... 

Peterson and Scarrah 165) reported the transesterification of rapeseed oil by methanol in the presence of alkaline earth metal oxides and alkali metal carbonates at 333-336 K. They found that although MgO was not active for the transesterification reaction, CaO showed activity, which was enhanced by the addition of MgO. In contrast, Leclercq et al. 166) showed that the methanolysis of rapeseed oil could be carried out with MgO, although its activity depends strongly on the pretreatment temperature of this oxide. Thus, with MgO pre-treated at 823 K and a methanol to oil molar ratio of 75 at methanol reflux, a conversion of 37% with 97% selectivity to methyl esters was achieved after 1 h in a batch reactor. The authors 166) showed that the order of activity was Ba(OH)2 > MgO > NaCsX zeolite >MgAl mixed oxide. With the most active catalyst (Ba(OH)2), 81% oil conversion, with 97% selectivity to methyl esters after 1 h in a batch reactor was achieved. Gryglewicz 167) also showed that the transesterification of rapeseed oil with methanol could be catalyzed effectively by basic alkaline earth metal compounds such as calcium oxide, calcium methoxide, and barium hydroxide. Barium hydroxide was the most active catalyst, giving conversions of 75% after 30 min in a batch reactor. Calcium methoxide showed an intermediate activity, and CaO was the least active catalyst nevertheless, 95% conversion could be achieved after 2.5 h in a batch reactor. MgO and Ca(OH)2 showed no catalytic activity for rapeseed oil methanolysis. However, the transesterification reaction rate could be enhanced by the use of ultrasound as well as by introduction of an appropriate co-solvent such as THF to increase methanol solubility in the phase containing the rapeseed oil. 

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. 

Dialysis experiments" have shown that Ca2 , Mg2 , Ba2 , and Sr2 form soluble chelates in aqueous alkaline solution with D-galactose, D-glucose, D-fructose, D-arabinose, D-ribose, maltose, and lactose. The absence of any precipitation of alkaline-earth metal hydroxide when an aqueous solution containing D-fructose and an alkaline-earth metal salt is made alkaline... 

A review by Mackenzie and Quin,19 on complexes of alkaline-earth metal hydroxides, is recommended to those who desire a more thorough description of the methods of preparation. 

There have been no studies of adducts of alkaline-earth metal hydroxides with a view to determining the position, or positions, of attachment of alkaline-earth metal hydroxide on carbohydrates. 

Corma A. and Iborra, S. Optimization of alkaline earth metal oxide and hydroxide catalysts for base-catalyzed reactions, Adv. Catal. 2006, 49, 239-302. 

Remember what we discussed in the context of Figure 13.44 ketones usually do not undergo aldol additions if they are deprotonated to only a small extent by an alkaline earth metal alkox-ide or hydroxide. The driving force behind that reaction simply is too weak. In fact, only a very few ketones can react with themselves in the presence of alkaline earth metal alkoxides or alkaline earth metal hydroxides. And if they do, they engage in an aldol condensation. Cyclopentanone and acetophenone, for example, show this reactivity. 

The major part of hydroxides are poorly soluble or insoluble in water, except well-soluble hydroxides of alkaline metals and thallium, and much worse soluble hydroxides of alkaline earths. 

Potassium hydroxide solution may also be used as a regenerent for the analysis of alkaline-earth metals, as long as a detection sensitivity in the ppm range is sufficient. 

All of these catalysts were active for ethylene polymerization. The average activity values are shown in Table 44. The activity was mostly unaffected by the presence of alkaline earth metal hydroxide, with the exception of barium hydroxide, which lowered the polymer yield by about 50%. Magnesium hydroxide caused a major change in the physical structure of the catalyst, which is an indication that a new material, perhaps magnesium silicate, was formed, with smaller primary particles. It is not clear whether the Cr(VI) becomes attached to the new material or whether it remains with the silica phase, perhaps now etched or otherwise changed. 

CjHjCljOj Noncombustible solid. Reacts with strong bases, amines, amides, inorganic hydroxides alkalis, alkaline earth metals alkali carbonates ammoniacal silver nitrate strong oxidizers soluble barbiturates producing chloroform and formate. Incompatible with camphor, menthol, or thymol. Contact with hydroxylamine produces poisonous hydrogen cyanide gas. Attacks metals in the presence of moisture. In heat of decomposition or fire, releases hydrogen chloride and other toxic fumes. 

In 1952, Pfeil and Schroth reported that, in formose formation, the Cannizzaro reaction takes part, simultaneously and competitively, with the addition reaction. Whereas alcohols of low molecular weight, 1,4-dioxane, tetrahydrofuran, and other compounds repress the Cannizzaro reaction, the hydroxides of alkaline-earth and alkali metals activate the reaction, with only one exception, namely, thallium hydroxide, which catalyzes the addition reaction specifically. In 1971, the two reactions, namely, the addition reaction and the Cannizzaro reaction, were quantitatively and differentially measured by Fujino. When measured for the... 

The most common soluble strong bases are the ionic hydroxides of the alkali metals, such as NaOH, KOH, and the ionic hydroxides heavier alkaline earth metals, such as Sr(OH)2. These compounds completely dissociate into ions in aqueous solution. Thus, a solution labeled 0.30 M NaOH consists of 0.30 MNa ([Pg.665]

Lux S, Siebenhofer M (2013) Synthesis of lactic acid frran dihydroxyacetone use of alkaline-earth metal hydroxides. Catal Sd Technol 3(5) 1380-1385... 

Duan Y, Sorescu DC (2010) CO2 capture properties of alkaline earth metal oxides and hydroxides a combined density functional theory and lattice phonon dynamics study. J Chem Phys 133 074508-074511... 

Further studies of the formose reaction have been reported. Alkaline-earth metal hydroxides initiated zero-order reactions at intermediate conversions of formaldehyde, and the formation of glyceraldehyde or tetroses and pentoses, etc., from formaldehyde in the presence of calcium hydroxide depended on whether or not glycolaldehyde was present. Self-condensation of formaldehyde in the presence of alkaline-earth metal hydroxides has also been studied in the absence and in the presence of a co-catalyst such as D-glucose and in the presence of glycolaldehyde. Self-condensation of formaldehyde in the presence of lead(ii) oxide appears to involve a soluble complex in which the lead atom co-ordinates with the carbonyl oxygen atom of formaldehyde. " The catalytic functions of calcium ion species in a homogeneous formose reaction and the distribution of products in a photochemical formose reaction have been investigated. 

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