Hydrolysis of complexes

In aqueous solution, all vacant coordination positions are fully occupied by water molecules. However, much body chemistry occurs at the pH near neutrality, e.g. blood plasma pH = 7.4. At such a pH, it is possible for protons to be liberated from some of these water molecules in order to produce hydroxy complexes, e.g. 

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Another way of applying the selective extraction method directly on the initial solution is to produce a solution of low acidity. This can be achieved by using the hydrofluoride method for fluorination and decomposition of raw material. As was discussed in Paragraph 8.2.2, the raw material is fluorinated by molten ammonium hydrofluoride yielding soluble complex fluorides of ammonium and tantalum or niobium. The cake obtained following fluorination is dissolved in water, leading to a solution of low initial acidity that is related for the most part to the partial hydrolysis of complex fluoride compounds. The acidity of the solution is first adjusted to ensure selective tantalum extraction. In the second step, the acidity of the raffinate is increased to provide the necessary conditions for niobium extraction. 

The interaction between fluorotantalic or oxyfluoroniobic acids and ammonia solution initiates the hydrolysis of complex fluoride compounds. The complete process can be represented as follows ... 

Equations (141) and (142) describe the equilibrium between the hydrolysis of complex fluoride acids (shift to the right) and the fluorination of hydroxides (shift to the left). Near complete precipitation of hydroxides can be achieved by applying an excessive amount of ammonia. Typically, precipitation is performed by adding ammonia solution up to pH = 8-9. However, the precipitate that separates from the mother solution can be contaminated with as much as 20% wt. fluorine [490]. Analysis of niobium hydroxides obtained under different precipitation conditions showed that the most important parameter affecting the fluorine content of the resultant hydroxide is the amount of ammonia added [490]. Sheka et al. [491] found that increasing the pH to 9.6 toward the end of the precipitation process leads to a significant reduction in fluorine content of the niobium hydroxide. 

Roasted and ground coffee is packed into columns and percolated by the passage of hot water under pressure at about 340°F. The use of pressurized boiling water not only brings about the dissolution of the most readily water-soluble coffee extractables, it also causes the solubilization and possibly the hydrolysis of complex carbohydrates. Water-soluble compounds of a smaller molecular weight are produced. The extent of possible... 

Anions can promote hydrolysis of complex cations by producing ion pairs of enhanced reactivity (see 2.178). Usually however, ligands accelerate the removal of a coordinated ligand by entering the metal coordination sphere with it and thereby labilizing it towards hydrolysis. We have already seen the effect of coordinated OH on the enhanced labilities of Fe(III) and Cr(III). Dissociative mechanisms and considerable acceleration are promoted by CFlj, CN , SOj and other groups on inert Cr(III), Co(III) and Pt(IV) complexes. Nitrate ions, for example, reduce the half-life for replacement of water in Cr(H20)g by dmso from —380 h to 10 s ... 

Metal ions can assist in the dissociation (hydrolysis) of complexes containing multidentate ligands. The metal ion may not necessarily complex with the detached ligand, for example, in the metal-assisted acid-catalyzed aquation of Cr(C204)3. Ref. 112. Usually however the metal ion removes and complexes the ligand as in... 

In 5, coordination through O polarizes the C = O bond producing the incipient carbonium ion, which is more susceptible to nucleophilic attack. In 6, there is intramolecular attack by coordinated OH on the N-bonded monodentate amino acid. In 7, only a small rate enhancement would be anticipated from intermolecular attack on the N-bonded monodentate. In these representations, X is OR, but anticipating the next section, it might also be NHR. These interpretive problems are illustrated in the hydrolysis of complexes of the type 8, where again any of three mechanisms corresponding to 5-7 could apply. 

Structures have been determined for [Fe(gmi)3](BF4)2 (gmi = MeN=CHCF[=NMe), the iron(II) tris-diazabutadiene-cage complex of (79) generated from cyclohexanedione rather than from biacetyl, and [Fe(apmi)3][Fe(CN)5(N0)] 4F[20, where apmi is the Schiff base from 2-acetylpyridine and methylamine. Rate constants for mer fac isomerization of [Fe(apmi)3] " were estimated indirectly from base hydrolysis kinetics, studied for this and other Schiff base complexes in methanol-water mixtures. The attenuation by the —CH2— spacer of substituent effects on rate constants for base hydrolysis of complexes [Fe(sb)3] has been assessed for pairs of Schiff base complexes derived from substituted benzylamines and their aniline analogues. It is generally believed that iron(II) Schiff base complexes are formed by a template mechanism on the Fe " ", but isolation of a precursor in which two molecules of Schiff base and one molecule of 2-acetylpyridine are coordinated to Fe + suggests that Schiff base formation in the presence of this ion probably occurs by attack of the amine at coordinated, and thereby activated, ketone rather than by a true template reaction. ... 

Biogas or synthetic natural gas production can be accomplished by utilizing the process of anaerobic digestion to convert biomass into methane. This multistage process of anaerobic decomposition involves hydrolysis of complex organic compounds by multiple bacterial species. The bacteria are grouped into the following classes ... 

Hydrolysis of complex molecules to their component building blocks... 

Hydrolysis of complex molecules In the first stage, complex molecules are broken down into their component building blocks. For example, proteins are degraded to amino acids, polysaccha rides to monosaccharides, and triacylglycerols to free fatty acids and glycerol. 

When the mechanism of the reaction is more complex then an analysis of the initial state and transition state must take account of all the individual steps. A reaction which involves more than one step is the base hydrolysis of complexes of Co111, Rh111 and Crm, which are believed to react via the, SNl(cb) mechanism.29 This mechanism involves an initial pre-equilibrium to form the conjugate base, illustrated for [Co(NH3)5C1]2+ in equation (19) ... 

In an effort to develop new chiral BINOL-Ti complexes, chemical modifications of the chiral complex (f )-BINOL-Ti(OPr )2 (R-2) that can easily be prepared by simply mixing ( PrO)4Ti and (/ )-BINOL in the absence ofMS4A have been studied [37c-e]. A dimeric form has been reported for the single-crystal X-ray structure of complex R-2 [38], (I )-BINOL-Ti-p3-oxo complex, prepared via hydrolysis of complex R-2 has been shown to serve as an efficient and moisture-tolerable asymmetric catalyst [37d,e]. It is noteworthy that the (/ )-BINOL-Ti-)i3-oxo catalyst [37e] shows a remarkable level of (+)-NLE (asymmetric amplification), thereby attaining the maximum enantioselectivity for this system by using (/ )-BINOL with only 55-60% ee as the chiral source (consult Scheme 8C. 14). 

As in the case of anandamide, 2-AG is derived from the hydrolysis of complex membrane lipids. The direct precursors of 2-AG can either be 1-acyl, 2-arachidonoyl-diacylglycerols (DAGs) or 2-arachidonoyl-lysoglycerophospholi-pids (e.g., lysophosphatidic acid, LPA). 

One should distinguish between hydrolysis of cations and hydrolysis of complexes. The former process is described as a process of a successive loss of protons... 

IR spectroscopy can also be used to monitor the progress of biological reactions. For example, the hydrolysis of complex lipids (esters of glycerol) causes a characteristic decrease in intensity of the ester carbonyl absorption at 1735 cm-1, with a corresponding appearance of a carboxylic acid absorption near 1710 cm-1. 

Hydrolysis of starch as in tenderization of peas Hydrolysis of complex carbohydrate cell walls Hydrolysis of cellulose during drying of beans Removal of graininess of pears peeling of apricots, tomatoes... 

The kinetics of substitution of bipy or phen into Co (467, 574), Ni (144), and Pt (697) complexes have been reported. Several studies of the hydrolysis of complexes of form [Co(III)(bipy)2XY] may be found. For both cis and trans isomers where X = Y = CY, hydrolysis is instantaneous (581), whereas for the cis isomer with X = acetate and Y = acetate or OH , reaction is very slow as a conjugate base mechanism cannot operate and the first-order reaction is therefore independent of [OH ] (124). One NO2 group in acid dependent and under acidic conditions is thought to proceed via protonation of one nitro group (289, 472). The interconversion of the cis and trans isomers, where X = N02 and Y = H2O, has an overall rate constant equal to + A [H+], implying reactions for both OH and... 

Since the common intermediate A is the only one for the trans isomer, this allows the statement of a rule that for base hydrolysis of complexes of the type [Co en)2LX] the cis isomer mitst never give less cis product than does the trans form. The data in Table III show that this rule is obeyed. 

Anaerobic treatment, a multistep complex process, can be described from a kinetic viewpoint as a three-step process involving (1) hydrolysis of complex organic material (2) organic acid production (3) methane fermentation (2). In the first step complex organics are converted to less complex soluble organic compounds by enzymatic hydrolysis. In the... 

The aim is to form a less soluble or nonsoluble solid deposited onto a support by decomposition, disproportionation, or hydrolysis of complexes or other organic compounds. 

Complex formation and hydrolysis of complexes. In acidic solutions, hydrolysis of group 5 elements is competing with complex formation. For group 5 complexes, it is described by the following equilibrium ... 

Hydrolysis in the silicones is usually just a special case of the reaction with organic halides. The most important reaction is the preparation of siloxanes by the hydrolysis of chlorosilanes and the subsequent condensation to form the commercially important polysiloxanes (see Chap. 15). Diethyl silane diol, (CjHs)2Si(OH)s, and the corresponding di-n-propyl and di-n-butyl diols have been made by hydrolyzing the dichlorosilanes. The trimethyl and triethyl silicon hydroxides have been prepared by the hydrolysis of complex organic silicon compounds containing the aceto and the amino group, respectively. ... 

Hydrolysis of complexes of the type MFe is catalysed not only by acid but also by a series of metal ions. Kinetic data have been obtained for catalysis of hydrolysis of PFe, AsFg", AsFgCOH)- and also of BF4-, by beryllium(ii), aluminium(iii), zirconium(iv), and thorium(rv). Again this may be seen as an extension of studies on cation catalysis of hydrolysis of transition-metal complexes, e.g. the numerous studies of mercury(ii)-catalysed aquations of cobalt(iii)-ammine-halide complexes, or the recent study of metal ion catalysis of chloro(ethylenediaminetriacetato)-cobaltate(m). ... 

Hydrolysis of complex polymers by extracellular enzymes to simpler soluble products. 

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