Condensation with metals

The sol-gel synthesis of siloxane-based hybrid organic-inorganic implants usually involves di- or trifunctional organosilanes co-condensed with metal alkoxides, mainly Si(OR)4 and Ti(OR)4. As we will see in this section, the incorporation of Ca salts is a common strategy to provide bioactivity at the systems. Each of these components has specific roles that will be reviewed and discussed. 

The interaction of metal atoms with cyclopentadiene is characterized by a tendency toward formation of a stable electronic configuration for the metal. Thus, cyclopentadiene undergoes the following reactions on condensation with metal vapors at -196°C (21, 115, 127, 136) ... 

This work raises the possibility that some eryfAro-selective aldol condensations with metal enolates may actually involve the a-metallo ketone. 

In contrast amphibole asbestos consists of Si40n-bands as the supporting entities. These are condensed with metal hydroxide bands to double bands, which are held together... 

The increase in activity in the field of organotin hydrides is mostly due to the facility of addition of the tin-hydrogen bond to unsaturated systems and to the multiple mechanistic investigations of the hydrostannation reaction. Hev is a number of organometallic reactions, i.e., addition to transition metal complexes7 condensation with metal alkyls yielding tin-metal derivatives and with metal amides for synthesis of compounds with longer tin chains. 

In the presence of an alkali metal hydroxide at about 50°C, chloroform condenses with acetone to give l,l,l-trichloro-2-methyl-2-propanol, [57-15-8] ie, chlorobutanol, chloretone, or acetone—chloroform (9,10). Chlorobutanol is a white crystalline substance with a campborlike odor its sedative, anesthetic, and antiseptic properties have given the compound some importance in the pharmaceutical industry. 

Ethyl chloride can be dehydrochlorinated to ethylene using alcohoHc potash. Condensation of alcohol with ethyl chloride in this reaction also produces some diethyl ether. Heating to 625°C and subsequent contact with calcium oxide and water at 400—450°C gives ethyl alcohol as the chief product of decomposition. Ethyl chloride yields butane, ethylene, water, and a soHd of unknown composition when heated with metallic magnesium for about six hours in a sealed tube. Ethyl chloride forms regular crystals of a hydrate with water at 0°C (5). Dry ethyl chloride can be used in contact with most common metals in the absence of air up to 200°C. Its oxidation and hydrolysis are slow at ordinary temperatures. Ethyl chloride yields ethyl alcohol, acetaldehyde, and some ethylene in the presence of steam with various catalysts, eg, titanium dioxide and barium chloride. 

The result of condensation of (3-dicarbonyl compounds with 3,4-diaminofurazan depends on the reaction conditions. With metal ions as templates, 14-membered rings 188 were formed exclusively (91MI2), whereas in the absence of these ions, only fused diazepines 189 were formed (Scheme 122) (89UKZ1064). 

Macrocyclic coordination compounds formed bv condensation of metal amine complexes with aliphatic carbonyl compounds. N. F. Curtis, Coord. Chem. Rev., 1968, 3, 3-47 (78). 

Generally, in the nucleophilic addition to carbonyl groups, either magnesium compounds or alkali metal compounds (such as the Li, Na and K derivatives) are used. In some cases even potassium carbonate or piperidine were used as the base for condensation with sulfones. Good results were obtained when concentrated aqueous NaOH was used under phase-transfer conditions288,297,333. 

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