Reducing agents auxiliary

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... 

The initial reduction step does not necessarily rely on the nucleophilic substrate as the reducing agent. It can also be induced by addition of catalytic amounts of copper as an auxiliary reducing agent [14] (Scheme 2.171). The whole reaction sequence follows supposedly an Sr I mechanism [15]. 

Hydride reductions of C = N groups are well known in organic chemistry. It was therefore obvious to try to use chiral auxiliaries in order to render the reducing agent enantioselective [88]. The chiral catalyst is prepared by addition of a chiral diol or amino alcohol, and the active species is formed by reaction of OH or NH groups of the chiral auxiliary with the metal hydride. A major drawback of most hydride reduction methods is the fact that stoichiometric or higher amounts of chiral material are needed and that the hydrolyzed borates and aluminates must be disposed of, which leads to increased costs for the reduction step. 

Environmental problems are often caused by the use of auxiliary materials, e.g. processes using Clemmensen reduction with amalgamated Zn as reducing agent [31, 35]. 

A new US EPA air pollution ruling will drastically restrict the flexible PU foam industry s use of the auxiliary blowing agent methylene chloride. Methylene chloride has been identified as 98% of the flexible PU foam industry s toxic emissions, and foam facilities have until 7 October 2001 to comply with the new standards. Under a rule from the OSHA, PU foam makers must reduce methylene chloride emissions in the workplace to 25ppm by 10 October 1999. 

In the leuco process, auxiliaries, dye, sodium hydroxide solution, and reducing agent are added to the dyebath. The textile is introduced into the bath after vatting. Depending on the depth of shade, dyeing is performed for 30-60 min and completed in the usual manner (rinsing, oxidation, soaping). 

In the two-phase process dyes and chemicals are applied in separate steps first dyes and thickener ( solid phase ) are printed, then chemicals and auxiliaries are added as an aqueous solution by padding. Sodium dithionite (Hydrosulfite) is used as reducing agent, and steaming time is kept short (20-40 s). For stabilized reducing agents, see [5, p. 296-298],... 

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