Replacement of alkoxy groups

With Replacement of Alkoxy Groups and Rednction of Tellurium... 

AIO5 groups in the precursor results from the replacement of alkoxy groups by hydrazide species, and once formed, AIO5 appears to facilitate the incorporation of nitrogen during heat treatment (Kim et al. 2000). 

Subject to the alkoxide/water ratio, stoichiometric or complete replacement of alkoxy groups can be achieved (Equation (2)). The variation and control of the degree of hydrolysis ( in M(OR) ,. (OH) ) profoundly influences the morphology and structure of the resulting gels. ... 

The hydrolysis rate can be controlled by replacement of alkoxy group with the help of a chelating group. 

Preferential replacement of alkoxy groups by amino groups OR -> N<... 

The sol-gel hydrolysis of alkoxysUanes, the most intensively explored one, basically proceeds in two steps. The first step is the hydrolytic replacement of alkoxy groups, OR, by hydroxyl groups, OH, shown schematically in Equation (1.1) for the first alkoxy group ... 

Partial and total replacement of alkoxy groups of oxalylketeneacetals by amino groups... 

Phosphorus oxide chloride (s. also under CgH NRs, C H N, and PCl ) Replacement of alkoxy groups by chlorine... 

In addition to conversion to chloro compounds, -ones and diones have given thiones with phosphorus pentasulfide, whilst in some cases replacement by amine of alkoxy groups in preference to a chloro group has been observed (68JHC13). 

A similar reaction mechanism was proposed by Chin et al. [32] for the hydrolysis of the biological phosphate monoester adenosine monophosphate (AMP) by the complex [(trpn) Co (OH2)]2+ [trpn = tris(ami-nopropyl)amine]. Rapid cleavage is observed only in the presence of 2 equiv metal complex. It is evident from 31P NMR spectra that on coordination of 1 equiv (trpn)Co to AMP a stable four-membered chelate complex 4 is formed. The second (trpn)Co molecule may bind to another oxygen atom of the substrate (formation of 5) and provide a Co-OH nucleophile which replaces the alkoxy group. The half-life of AMP in 5 is about 1 h at pD 5 and 25 °C. 

An elegant method for the replacement of hydroxy groups in alcohols by hydrogen is the addition of alcohol to dialkylcarbodiimide followed by catalytic hydrogenation of the intermediate 0-alkoxy-A,A -dialkylisoureas over palladium at 40-80° and 1 -60 atm (yields 52-99%) [606]. 

The Corey group has reported that Cp2TiCl2/nBuLi effectively catalyzes the high yield alcoholysis of primary, secondary, and tertiary silanes with a variety of alcohols under mild reaction conditions.160 All Si-H functionalities are replaced with alkoxy groups in reactions of ethanol and phenol, although increased temperatures and/or reaction times are required for highly substituted hydrosilanes. The system also appears to be influenced... 

So far, we have seen that an enolate anion is able to act as a nucleophile in an SN2 reaction (Sections 20.3 and 20.4) and also in an addition reaction to the carbonyl group of an aldehyde in the aldol condensation (Section 20.5). It also can act as a nucleophile in a substitution reaction with the carbonyl group of an ester as the electrophile. When an ester is treated with a base such as sodium ethoxide, the enolate ion that is produced can react with another molecule of the same ester. The product has the a-carbon of one ester molecule bonded to the carbonyl carbon of a second ester molecule, replacing the alkoxy group. Examples of this reaction, called the Claisen ester condensation, are provided by the following equations ... 

Next, replace the a proton that was lost, and replace the alkoxy group that was lost from the carbonyl. Two molecules of methyl 3-phenylpropionate result. 

As outlined in Section III. A.3. a, the strength of the Lewis acid with mixed chloride and alkoxy derivatives decreases as the number of chloride ligands are replaced with alkoxy groups. Titanium chloride with one alkoxy group polymerizes styrene and a-methylstyrene Lewis acid with two alkoxy groups is too weak to initiate polymerization of styrene, but will initiate polymerization of a-methylstyrene and vinyl ethers. The Lewis acidity of titanium chloride derivatives with three alkoxy groups are so low that only vinyl ether polymerizations reach reasonable conversions. 

Soluble low-valent metal alkoxides can also be synthesized by replacing small alkoxy group OR by bulky polydentate ligands such as 2-methoxyethanol CH3OC2H4OH. This solvent is currently used to prevent polymerization and get soluble molecular precursors with low-valent metal cations such as Cu + in the sol-gel synthesis of advanced ceramics such as high Tc superconductors YBa2Cu307 j (see Sulfur Organic Polysulfanes) ... 

To begin with, phosphates come in various kinds. Phosphoric acid contains three hydroxy groups and can form esters in which one, two, or three of these have been replaced by alkoxy groups. Phosphoric acid is highly acidic, and so are the... 

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