Calcium alkoxides synthesis

Calcium, tetrakis(methanol)dinitrato-structure, 1, 89 Calcium alkoxides synthesis, 2, 336... 

Calcium alkoxides synthesis, 336 Calcium complexes acetylacetone, 372 amides, 164 malonic acid, 444... 

The synthesis of precursors A and B (see Figure 12.10) has been described by Michalczyk et al. [102]. These compounds can be synthesised from platinum-catalysed hydrosilylation reactions, that is addition reactions between Si—H and C=C groups in the presence of a catalyst. Once the pure precursors are obtained, BSG can be synthesised by incorporation of calcium alkoxide during polycondensation of the precursors. 

A numbers of calcium alkoxides have been synthesized to date [7], Because their derivatives possess groups such as MeO , EtO , and PrO , they often form insoluble, large aggregates that have a tendency to continuously equilibrate in solution [8], Because of this, the synthesis of calcium alkoxides of low nuclearity is cumbersome and usually requires the use of sterically large chelating ligands [9] or Lewis acids to prevent aggregation. 

In the past, many variations of the sol-gel process have been developed and used to produce powders with different Ca/P ratios, by altering not only the quantity and composition of precursors but also the processing variables. As the synthesis of HA requires a calcium to phosphorus molar ratio of 1.67 1 in the final product, a number of caldum/phosphorus precursor combinations have been used in the preparation of HA powders. For example, calcium nitrate or different calcium alkoxides and 2-ethyl-hexyl phosphate, triethyl phosphate or orthophos-phoric acid, have been used as the calcium and phosphoras precursors, respectively. The major limitation for appUcation of the sol-gel process was shown to be the very poor solubility of the calcium alkoxides in organic solvents, and the poor reactivity of the phosphorous compounds. The effective control of stoichiometry due to the volatility of the phosphorous compounds used also represented a challenge. 

BG-PVAL hybrid materials are formed because the organic component (in this case PVAL) is crosslinkable with the inorganic component through H-bonds or van der Waals interactions. The synthesis of these hybrids is carried out through the sol-gel synthesis under acidic conditions. For this purpose the hydrolysis of organically modified silicon and/or phosphorus alkoxides together with a calcium salt is a one-pot method, in the presence of dissolved PVAL. Figure 12.5 collects the most relevant steps of this kind of synthesis. 

Condensing agents are basic catalysts such as alkali carbonates, hydrogen carbonates, hydroxides, or alkoxides, or primary aliphatic amines or calcium hydroxide zinc chloride may also be used with aromatic aldehydes. Ethylene-diamine was introduced by Lerner972 for use in the synthesis of unsaturated nitriles in the aromatic series and he gave a large number of examples in which yields were around 95%. 

Sol-gel and precipitation methods are simple and commonly used wet-chemical synthesis methods of ceramic nanoparticles such as calcium phosphates, iron oxides, silica, titanium oxides, and zinc oxides. Basically, the sol-gel method uses inorganic precursors (i.e., meal salts or organometalhc molecules) that react in aqueous environment and subsequently form integrated network (gel). For example, metal oxide nanoparticles are often synthesized via the hydrolysis and condensation reactions of metal alkoxides ... 

Interest in the synthesis and structural characterisation of less common metalloorganophosphide systems has continued. A range of alkali metal complexes of the phosphide anion (48) has been prepared from the lithio-phosphide by simple metathesis with alkali metal alkoxides. The lithio-phosphide exists as a dimer, but crystallisation of the sodium and potassium drivatives in the presence of TMEDA results in the formation of monomeric species. The caesium triphosphenide (49), involving a phosphorus analogue of the allyl anion, has been prepared from the previously described sodium complex. Unlike the sodium and potassium complexes, which are monomeric, the caesium complex has a polymeric structure. A variety of arylphosphide complexes of magnesium, calcium, strontium and barium have been prepared and their solid state structures characterised. Cop-per(I)-, silver(I)- and gold(I)-complexes of the cyclo-(P ion have also... 

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