Catalytic bleach: Most valuable applications for smart oxidation chemistry

The extraordinary interest of the chemical industry in oxidation catalysts is described. Regarding the use of such substances in catalytic bleaching, the washing process is employed to illustrate the pertinent phenomena and to quantify the current state of the art. Bleaching of stains, an essentially heterogeneous process, and of migrating dyes, basically a homogeneous oxidation reaction, are both discussed in quantitative terms. Likewise, the extent of damage to fibers and dyes, i.e. concomitant adverse effects inherent to any laundry bleaching system, is indicated. The essentials of the corresponding screening procedures are reviewed. With regard to chemical structures, results for complexes of diverse sorts of chelating agents are reported. These comprise 1,4,7-trimethyl-1,4,7-triazacyclononane-, salene-, saltrene- and terpyridine-type ligands and manganese, in different oxidation states, as the heavy metal cation. A qualitative model is presented to characterize the role of a bleach catalyst in activating hydrogen peroxide, i.e. at present the standard latent oxidant incorporated in modern detergent formulations. Relying on diverse experimental methods, critical aspects of catalytic bleaching have been studied. The ensemble of the corresponding results renders it possible to properly assess the technology per se and to indicate most promising routes for future pertinent research.

Interacting with H2O2 in a catalytic cycle any bleach catalyst gives rise to a specific ensemble of active intermediates. Their steady state concentrations are available for chemical reactions. Depending on the process conditions and on the test material used in practice, this chemistry transforms into specific levels of bleaching, damage, disproportionation and catalyst decay. Figure optionsDownload as PowerPoint slide