Hydroxide functions

The structure of [TpBut Me]ZnOH has been determined by x-ray diffraction, confirming the presence of a terminal zinc hydroxide functionality, with a Zn-OH bond length of 1.850(8) A (Fig. 40). The Zn-OH moiety has also been characterized by a variety of spectroscopic techniques, including IR, 1H, 2H, and 170 NMR spectroscopies, as summarized in Table VI. For example, the H NMR spectrum of [TpBut,Me]ZnOH, shown in Fig. 41, illustrates that the [Zn-OH] moiety is observed as a sharp signal at 8 - 0.07 ppm in C6D6. The importance of using a sterically... 

In the above reactions, hOH represents a solid surface with its hydroxide functional group. Depending... 

As described in US patent 6,777,552, an atorvastatin ester derivative is converted to atorvastatin hemicalcium by mixing the ester derivative with more than 70% excess (molar basis) of calcium hydroxide (see Fig. 1.3). Calcium hydroxide functions as a basic catalyst for the hydrolysis of ester and also supplies calcium ion to form the hemi calcium salt. A significant advantage of this method is that the amount of calcium hydroxide does not have to be as carefully controlled in contrast to the amount of sodium hydroxide and calcium acetate generally controlled in other processes. 

A similar monolith was also used in the Horner-Wadsworth-Emmons (HWE) olefmation (Scheme 4.60). Initial reactions using the hydroxide-functionalized column 19 resulted in partial hydrolysis of the ester groups, but it was found that thorough drying of the column (under vacuum with P2O5) and the use of anhydrous TH F prevented this... 

Chloroperbenzoic acid (MCPBA) has been frequently applied to sulfide oxidation (Figure 3.96). MCPBA has been the oxidant of choice for the diastereoselective oxidation of 2-exo-hydroxynorbornyl systems containing a sulfide group in the 10 position and a diastereomeric excess (d.e.) of 80-90% is obtained. However, if the hydroxide function is protected as the ether, the d.e. drops to 30%.387 388... 

The epoxide method can be used with epoxides of acyclic [ 165-168] and cyclic [169-172] alkenes with a visible bias for cyclohexene oxide as the epoxide of choice. The epoxide is usually reacted with unsubstituted imidazole creating a neutral molecule. If the epoxide is reacted with an N-substituted imidazole, a zwitterionic molecule is created as the hydroxide functional group in the sidearm lacks the imidazole NH hydrogen atom to be proto-nated. In this case, addition of one equivalent of acid provides protonation to the alcohol and the counteranion for the formation of the imidazolium salt. 

In the present case the acyl migration is easily understood if the hydroxide function becomes an alkoxide by the intervention of sodium hydride. Its approach to the carbonyl groups of the urethane unit is facilitated by its positioning in the axial conformation, as shown in III (see Scheme 1.1). 

Another more mineralogically relevant example is crystal growth by assembly of polynuclear clusters or nanoparticles in aqueous solution (Penn and Banfield 1998). As the particles or clusters approach each other, hydrolysis of outer hydroxide functional groups yields water molecules that are eliminated progressively from the interfacial region. At some later time, the particles are attached and no longer require an atomistic description at the shared interface. The oxidation of a metallic nanoparticle such as... 

Replacing a hydrogen atom in any of the methylene groups by a hydroxide function significantly reduces the retention time. The position of the hydroxide function exerts a noticeable influence on the resulting retention time. Fig. 5-35 shows the separation of two Ci6-hydroxyalkane sulfonates, which are hydroxy-substituted in the 2- and 3-pos-ition of the alkyl chain. In comparison to non-substituted alkane sulfonates, the retention decrease corresponds to the loss of 2 to 3 methylene groups from the solvophobic alkyl groups. 

Functionalization of SWCNTs and MWCNTs was shown to alter significantly the ability of these materials to induce oxidative stress. The addition of polyethylene glycol (PEG), sulfur (SH), or amine (NH2) groups reduced the biological oxidative damage, while it was slightly increased in the presence of carboxylic or hydroxide functionalization [14]. 

Section 1 considers the methods of synthesis and physico-chemical properties of new types of inorganic sorbents (complex carbon-mineral sorbents, co-precipitated hydroxides, functional polysiloxane sorbents, porous glasses with controlled porosity, colloidal silicas, aluminium oxyhydroxide colloids, apatites). These sorbents are widely used in scientific investigations, in chemical practice and are important from a technological point of view. The presented results provide additional possibilities for the preparation of inorganic sorbents possessing unique adsorption and catalytic properties. Moreover, Section 1 presents the possibilities of the computational studies on the design of synthetic materials for selective adsorption of different substances. 

The use of the NilNiO metal oxide electrode for potentiometric investigations of hydroxide-ion dissociation makes it possible to neglect the so-called, hydroxide function of the conventional oxygen electrodes. Indeed, since the slope of the E-pO calibration plots obtained with the use of the metal-oxide electrode is close to 1.15R77F, both in dry and in wet atmospheres, it is obvious that hydroxide ions do not participate in the electrode process. If this were not the case, the slope should be equal to... 

HYDRAQL (10) treats adsorption as surface complexation with bound hydroxide functional groups, SOH, and their ionization products, SO and SOH2. The calculations in this paper use HYDRAQL in its triple layer mode. Surface charge and countercharge accumulate in three layers (1) at the surface itself, i.e., in the plane of the SOH groups where the surface potential is T o (2) in the outer Helmholtz plane (OHP), where adsorbed ions retain their inner hydration sheaths (26) and the potential is and (3) in the diffuse layer. The triple layer model is ideal for our purposes because of its ability to compute an estimate of Pp. The computed T p can be compared with experimental measurements of the zeta potential, providing an additional means of constraining models. 

The principle found for zinc(II) was applied to copperdi) complex models by Young et al. (25). The hydroxyl function of copper complex 27a deprotonates with a pK value of 8.8 to yield 27b, which cleaves phosphodiester bis(2,4-dinitrophenyl) phosphate (BDP ) by transesterification to produce 28 (A(BDP ) = 7.2 x 10 M" sec at 25°C see Scheme 5). The analogous complex with a hydroxyethyl pendent cleaves the diester predominantly by hydrolysis, which suggests that the reactive species is not Cu -alkoxide, but Cu —OH . The rate ife(BDP ) of 9.5 X 10" M sec is about two orders of magnitude smaller than the phosphoryl-transfer reaction. This copper model study shows that metal-alkoxide species may be more effective nucleophiles, as has been seen with zincdD-model complex 24. Thus, future models may be designed that are composed of a metal-alkoxide function and a proximate metal-hydroxide function. 

The reagents are strong bases and poorly soluble metal hydroxides. In the above equations, the metal hydroxides function as acids, in agreement with the modern theory of their amphoteric behavior. As far as is presently known, the following metals (arranged in order of increasing valence) form hydroxo salts ... 

Magnesium hydroxide functions in a manner similar to ATH. It liberates water from crystallization in a fire situation and in so doing it forms a barrier to the ingress of oxygen required for combustion. The material is also capable of absorbing heat, although the heat capacity value of 77.0 J/K mol (crystalline) is lower than that for ATH. 

Draw a mechanism for each of the three steps in the preparation of the 6-ethoxycarbonyl-3,5-diphenyl-2-cyclohexenone. You may assume that sodium hydroxide functions as a base and ethanol serves as a proton source. 

Alkaline-based polymer electrolyte membranes are relative newcomers on the scene. It has been widely believed that the quaternary ammonium hydroxide functional group (RN4 , OH ), which is the one used in most anion exchange membranes, is self-destructive, because the OH- ion is likely to attack the RN4 cation. In addition, the specific conductivity of an OH conducting ionomer was suspected of being at least a factor 3-A lower than that of the H" conducting... 

In the final step of the mechanism, water (not hydroxide) functions as a base and abstracts a proton from the oxonium ion. Like all proton transfer steps, this process requires two curved arrows. One curved arrow is drawn with its tail on a lone pair of water and its head on the proton, while the second curved arrow is drawn with its tail on the O—H bond and its head on the oxygen atom ... 

In the first step, hydroxide functions as a nucieophiie and opens the ring in an S vj2 process... 

Hydroxide functions as a base and deprotonates the aromatic ring... 

Hydroxide functions as a nucleophile and attacks the cartx)nyl group... 

Hydroxide functions as a base and deprotonates phthahmide. The proton is relatively acidic (pA j=8.3), because it is flanked by two C—O groups (similar to a P-keto ester). Potassium phthalimide can function as a nucleophile and is readily alkylated to form a C—N bond (directly analogous to the acetoactetic ester synthesis. Section 22.5) ... 

The conversion of triglycerides into biodiesel can be achieved in the presence of either catalytic acid or catalytic base. We have seen a mechanism for transesterification with catalytic acid. In contrast, the mechanism for base-catalyzed transesterification has fewer steps. The base, such as hydroxide, functions as a catalyst by establishing an equilibrium in which some alkoxide ions are present. 

In the base-catalyzed mechanism, the hydroxide functions as the nucleophile. Water then protonates the intermediate adduct, a hydroxy alkoxide, to give the product diol and to regenerate the catalyst. 

The focus here will be on anhydrous HCl, since, (i) it is a strong Br0nsted acid (at least in water), (ii) in principle it can behave as a Brpnsted acid by dissociative adsorption at a surface that contains oxide (hydroxide) functioning as a Br0nsted base and (iii) it could function as a weak Lewis base as a result of associative adsorption at a surface that contains (strong) Lewis acid sites. From this analysis, it would be expected that the behaviour of HCl towards fluorides would be different from its behaviour towards oxides. This comparison is less clear cut however if oxyfluorides and partially hydrolysed (hydroxylated or hydrated) fluoride surfaces are included. Schematic representations of dissociatively adsorbed HCl at medium strong and weak Lewis acid sites of 7/-alumma are shown in Figures 4.6 and 4.7. These are based on spectroscopic observations. 

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