Organic Chelates of Silicon

Chelates of silicon have already been discussed in some detail in Chapter I in connection with the effects of organic compounds on the solubility of silica and also on the rate of dissolution of silica. Further discussion will be limited to some of the compounds that have been formed. 

Our understanding of silicon chelates with organic ligands is still insufficient, and research in this area is sparse. 

The anionic nature of pectin is yet another important aspect, which prevents the pol5mierization of organic silicon compounds. Thus pectin always makes crosslinked complexes with proteins under suitable conditions and act as a powerful chelator of allergens such as cobalt, nickel, copper (Table 8.1). 

Liquid phase modifications. Alternatively a porous membrane can be reduced in pore size by a liquid deposition prcx ess where the membrane is dipped into a solution or sol to form deposits inside the membrane pores. For example, a silicon nitride tube with a mean pore diameter of 0.35 pm is first immersed in a solution of aluminum alcoholate (aluminum isopropylate or 2aluminum tris(ethyl acetoacetate) or ethyl acetoacetate aluminum diisopropylate) in an organic solvent (hexane, cyclohexane, benzene, isopropanol, etc.). It is then treated with saturated water vapor to hydrolyze the alcoholate or chelate to form bochmite inside the pores, thus changing the pore diameter to as small as 20 nm [Mitsubishi Heavy Ind., 1984a and 1934b]. Upon calcining at 800X, boehmite transforms into transition-alumina. 

The presence of this reaction sometimes could affect the crystallization of zeolites. Silicon could form a 5-coordinated chelate with organic ligands ... 

The trimethylsilylated silicic acids formed in this instance are soluble in conventional organic solvents, and their volatility is sufficiently high for them to be analysed by gas chromatography. Carzo and Hoebbel [411] carried out a comprehensive study of the chromatographic retention of various trimethylsilylated silicic acids on different stationary phases Apiezon L and silicone OV-1 and OV-17. The analysis of metals in the form of volatile complexes continues to attract attention, and have been described for analysing sodium [412], potassium [412], radium [413], caesium [413], barium [414], calcium [414], strontium [415], beryllium [416, 417], magnesium [418], zinc [419, 420], nickel [419], mercury [421], copper [422, 423], silver [424, 425], cadmium [421], indium [426, 427], g ium [428], scandium [217], cobalt [421], thallium [426], hafnium [429, 430], lead [431, 432], titanium [430], vanadium [433], chromium [434-436], manganese [426], iron [437], yttrium [438], platinum [439,440], palladium [439, 441, 442], zirconium [430], molybdenum [443], ruthenium [444], rhodium [445], rare earths [446—449], thorium [221, 450, 451] and uranium [221, 452]. The literature on GC analysis of metal chelates was reviewed by Sokolov [458]. 

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