Hydrolysis and condensation

Hydrolysis, condensation and neutralisation by either a batchwise or continuous process. 

Henry M, Jolivet JP, Livage J (1991) Aqueous Chemistry of Metal Cations Hydrolysis, Condensation and Complexation. 77 153-206 Hider RC (1984) Siderophores Mediated Absorption of Iron. 57 25-88 Hill HAO, Rdder A, Williams RJP (1970) The Chemical Nature and Reactivity of Cytochrome P-450. 8 123-151... 

Many of the structural features of sol-gel-derived inorganic polymers are rationalized on the basis of the stability of the M-O-M condensation products in their synthesis environments. Structures which emerge in solution reflect a successive series of hydrolysis, condensation and, depending on the acid or base concentration, restructuring reactions. M-O-M bonds which are unstable with respect to hydrolysis or alcoholysis are generally absent. During... 

The structures of sol-gel-derived inorganic polymers evolve continually as products of successive hydrolysis, condensation and restructuring (reverse of Equations 1-3) reactions. Therefore, to understand structural evolution in detail, we must understand the physical and chemical mechanisms which control the sequence and pattern of these reactions during gelation, drying, and consolidation. Although it is known that gel structure is affected by many factors including catalytic conditions, solvent composition and water to alkoxide ratio (13-141, we will show that many of the observed trends can be explained on the basis of the stability of the M-O-M condensation product in its synthesis environment. 

Water is both the solvent in which metabolic reactions occur and a reactant in many biochemical processes, including hydrolysis, condensation, and oxidation-reduction reactions. 

As deduced from the TEM micrographs of the products after hydrolysis, condensation and calcination, tubular structures comparable to that found with [Pt(NH3)4](HC03)2 were only obtained by use of the complex compound [Pd(NH3)4](HC03)2. 

Sol-gel chemistry has been extensively studied during the past decade. The basic reactions, hydrolysis, condensation, and complexation, involved in the formation of oxide networks from molecular precursors are now quite well described. The sol-gel process brings new opportunities in the field of materials science. It allows a powderless processing of glasses and ceramics. Coatings can be easily deposited directly from the solution onto a wide variety of substrates. Many patents have been taken and several products are now on the market. Other industrial applications will undoubtedly be developed during the next few years. 

Henry, M., J. P. Jolivet, Livage, J. Aqueous Chemistry ofMetal Cations Hydrolysis, Condensation and Complexation. Vol. 77, pp. 153-206. 

Henry, M., Jolivet, J.-P, and Livage, J., Aqueous chemistry of metal cations hydrolysis, condensation and complexation. Struct. Bonding, 77, 154, 1992. 

Figure 3. Illustration of the pH dependence of the hydrolysis, condensation, and dissolution rates of silica. Condensation rates are judged by the reciprocal of gel times. RLCA denotes reaction-limited cluster aggregation. (Reproduced with permission from reference 30. Copyright 1988.)...

The silicone fluids form a range of colorless liquids with viscosities from 1 to 1,000,000 centistokes (cs). The conversion of chlorosilane intermediates into polymer is accomplished by hydrolysis with water, which is followed by spontaneous condensation. In practice, the process involves three important stages (1) hydrolysis, condensation, and neutralization (of the HCl evolved on hydrolysis) (2) catalytic equilibration and (3) devolatilization. 

The relative rates of reaction between the hydrolysis, condensation, and polycondensation directly affect the type and quality of sol-gel produced. For instance, in base-catalyzed sol-gel synthesis, the rate of the hydrolysis reaction is much slower than the polycondensation step, which tends to form a polymeric structure that is highly branched with relatively large particles. In contrast, in acid-catalyzed sol-gel synthesis, the rate of the hydrolysis reaction is much faster than the polycondensation step, which favors the formation of linear polymers. This also tends to form much smaller particles that the gel is composed of, which results in materials with much higher porosities and higher surface areas than is formed with sol-gels formed in base-catalyzed reactions. Therefore, acid-catalyzed synthesis tends to produce materials that have properties that are preferable for microfluidic applications. 

The characterization of the hybrid particles H by NMR and FTIR spectroscopies confirmed that the organic structure was maintained during the hydrolysis-condensation and quenching reaction. The surface area of these hybrid particles, determined by BET N2 sorption [4], were low (52 mVg) (Table 1). 

The change in electronegativity controls hydrolysis, condensation and other nucleophilic reactions. 

Figure 9.7 Organofunctional silane hydrolysis, condensation and covalent bonding with inorganic substrate e.g. glass fibre).

Silanes are multifunctional molecules which are used as coupling agents to modify fiber surfaces and create a chemical link between the fiber and matrix through a siloxane bridge. They go through various stages of hydrolysis, condensation and bond formation during the fiber treatment process. This treatment is used to stabilize... 

The hydrolysis, condensation, and polymerization reactions are governed by several factors, including the molar ratio of water to alkoxides, choice of solvents, temperature and pH (or concentration of add or base catalysts). Depending on these factors, either a hnear polymeric gel or a more crosshnked polymeric gel can be formed. A homogeneous network is built up as the polymerization reaction continues. 

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