Group 14 reagents method

Although acetyl chloride is a convenient reagent for deterrnination of hydroxyl groups, spectroscopic methods have largely replaced this appHcation in organic chemical analysis. Acetyl chloride does form derivatives of phenols, uncompHcated by the presence of strong acid catalysts, however, and it finds some use in acetylating primary and secondary amines. 

The preformed (BC) method is a one-step process used in this case to introduce high multiplicity of terminal hydroxy groups. The method involves direct coupling of branch cell reagents (i.e. tris(hydroxymethyl)aminomethane (Tris-)) by amidation of ester terminated PAMAM dendrimers. Advancement to the next generation of branch cells occurs in one step. 

Trimethylsilyldiazomethane, as a stable and safe substitute for hazardous diazomethane, is useful both as a reagent for introducing a Cj-unit and as a C-N-N synthon for the preparation of azoles. Many methods are described in the literature for the preparation of trimethylsilyldiazomethane, including the trimethylsilylation of diazomethane (7-74S), the alkaline decomposition of N-nitroso-N-(trimethylsilylmethyl)amides (25-61%) and the diazo group transfer reaction of trimethylsilylmethyllithium with p-toluenesulfonyl azide (38%). The present modified diazo group transfer method appears to be the most practical, high-yield, and large scale procedure for the preparation of... 

Another important application of the polymer reagent method is in the synthesis of cyclic peptides. In this approach, the amino-protected linear peptide (7(5) is converted into the corresponding polymeric active ester (17) by coupling it to a cross-linked hydroxyl function containing polymer (eg. 12) on deprotection of the amino group and subsequent neutralization, the cyclic peptide (18) is obtained in good yields 109 110> ... 

Thus, in this method the stepwise synthesis proceeds on the soluble polymer, as in the liquid phase method the only difference is in the coupling step where the carboxyl component is an insoluble polymeric active ester. The use of the solubilizing C-terminal macromolecular protecting group overcomes the limitations encountered in the original application of the polymer reagent method of peptide synthesis. However, due to the steric limitations characteristic of the polymer-polymer interactions, the attainment of quantitative coupling in each step of the synthesis can be difficult in this method. 

Cleavage of t-butyidimethylsilyl ethers. Aqueous hydrofluoric acid (5-30% of a 40% aqueous solution of HF) is an excellent reagent for removal of t-butyl-dimethylsilyl and trimethylsilyl groups. The method is particularly useful for... 

There are few spectrophotometric methods published to determine ezetimibe in pharmaceutical dosage forms. The first one was established by Mishra et al. [17] by applying colorimetric assay of phenol group. This method was developed based on the reaction between Folin-Ciocalteu s (FC) phenol reagent and phenol group of ezetimibe, which results in a blue chromogen that was then observed at 760 nm. 

The next group of methods to be considered represents a far more recent development than the Rosenmund the use of the anionic metal complexes [Fe(CO)4] , [HFe(CO)4] , [HCr(CO)s]", [HW(CO)5] and [CpV(CO)3H] . Although it is only the first of these reagents which is clearly a nonhydride reducing agent, they are all considered here because of their close structural relationship and because of possible mechanistic similarities vide infra). 

In this group, too, the first observations were made by Thiele 192), who found that cuprous and silver ions are precipitated from aqueous ammoniacal solution by cyclopentadiene, but gave no analytical data. Thallium was later found to be precipitated similarly. Copper (I), however, also yields a white crystalline cyclopentadienyl-triethylphosphine complex, C5H5CuP(C2H5)3, which is stable to water 215) this was, in fact, analogous to an earlier method described by van Peski and Melsen. Attempts to make a complex by the Grignard reagent method or by the action of cyclopentadienyl sodium on cuprous halides were unsuccessful. 

The dynamic characteristics of adsorbed molecules can be determined in terms of temperature dependences of relaxation times [14-16] and by measurements of self-diffusion coefficients applying the pulsed-gradient spin-echo method [ 17-20]. Both methods enable one to estimate the mobility of molecules in adsorbent pores and the rotational mobility of separate molecular groups. The methods are based on the fact that the nuclear spin relaxation time of a molecule depends on the feasibility for adsorbed molecules to move in adsorbent pores. The lower the molecule s mobility, the more effective is the interaction between nuclear magnetic dipoles of adsorbed molecules and the shorter is the nuclear spin relaxation time. The results of measuring relaxation times at various temperatures may form the basis for calculations of activation characteristics of molecular motions of adsorbed molecules in an adsorption layer. These characteristics are of utmost importance for application of adsorbents as catalyst carriers. They determine the diffusion of reagent molecules towards the active sites of a catalyst and the rate of removal of reaction products. Sometimes the data on the temperature dependence of a diffusion coefficient allow one to ascertain subtle mechanisms of filling of micropores in activated carbons [17]. 

Only a slight excess of the Grignard reagent is required, and the reaction tolerates keto, ester, amide and nitrile groups. This method is especially suited for large-scale preparations. ... 

In this method, specific functional groups reagents containing a marker - halogens, radioactive isotopes, fluorescent moieties... 

Although the number of known specific reagents is rather small, there exist some methods based on the use of group reagents (that react with many elements), which in the presence of suitable masking agents and at proper pH have a specific action. Examples of such systems may be the determination of Zn with dithizone at pH 4-5 in the presence of... 

Although oxine is a group reagent and reacts with many metals, the use of appropriate masking agents makes the method specific for aluminium. There are many variants of the oxine method, depending on the kinds of metals that accompany aluminium in the analyte... 

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