Oxidizing agents auxiliary

The first possibility for aromatization of the cr -adduets of azine iV-oxides is their oxidation with oxidizing agents, resulting in the eorresponding substituted azine iV-oxides with the retention of the iV-oxide group (Seheme 1, pathway A). When (T -adduets eontain an auxiliary leaving group, autoaromatization takes... 

In systems of this type, the electrochemical reactions can be realized or greatly accelerated when small amounts of the components of another redox system are added to the solution. These components function as the auxiliary oxidizing or reducing intermediates of the primary reactants (i.e., as electron or hydrogen-atom transfer agents). When consumed they are regenerated at the electrode. 

EDTA titration solutions frequently need to be buffered to a high pH to ensure stoichiometric formation of the complex. Unfortunately many metals will precipitate as hydroxides or hydrated oxides under these conditions. Use can be made of secondary or auxiliary complexing agents to retain the metal ion in solution. Typical reagents for this purpose are... 

Often, auxiliary complexing agents must be used in EDTA titrations to prevent precipitation of the analyte as a hydrous oxide. Such reagents cause the end points to be less sharp. 

Many cations form hydrous oxide precipitates when the pH is raised to the level required for their successful titration with EDTA. When this problem is encountered, an auxiliary complexing agent is needed to keep the cation in solution. For example, zinc(II) is ordinarily titrated in a medium that has fairly high concentrations of ammonia and ammonium chloride. These species buffer the solution to a pH that ensures complete reaction between cation and titrant in addition, ammonia forms ammine complexes with zinc(II) and prevents formation of the sparingly soluble zinc hydroxide, particularly in the early stages of the titration. A somewhat more realistic description of the reaction is then... 

The analyte in an oxidation/reduction titration must be in a single oxidation state at the outset. Often, however, the steps that precede the titration, such as dissolving the sample and separating interferences, convert the analyte to a mixture of oxidation states. For example, when a sample containing iron is dissolved, the resulting solution usually contains a mixture of iron(II) and iron(III) ions. If we choose to use a standard oxidant to determine iron, we must first treat the sample solution with an auxiliary reducing agent to convert all of the iron to iron(II). If we plan to... 

Basotol . [BASF] Auxiliary for protecting dyes against reductmn oxidizing agent fm vat dyes. 

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