Building a Better Bleach
A stain is a color where you don’t want it. It might surprise you to find out that getting rid of the unwanted color is not a matter of removing the offending molecules, like detergents acting to remove soil. Instead, the stain molecules are altered chemically so that they no longer reflect light in just the same way as before. We’ll call it decolorizing, or bleaching—words that imply the chemistry going on in the process. sodium percarbonate
The active ingredient in ordinary household bleach, sodium hypochlorite (NaOCl), keeps white clothing white and your bathtub sparkling. But handle with care. If you’ve ever spilled bleach, you know it can also add white blotches to a favorite pair of blue jeans. sodium percarbonate
The color of the stain is a physical property caused by the chemical structure of its molecules. When an oxidizing agent removes electrons from a molecule, the chemical structure of the molecule is changed, and the physical properties (like color) are altered.
Chlorine bleaches are oxidizing agents that work efficiently and cheaply in the laundry. Any excess is washed away in the rinse water. This solves the problem you created by washing white socks with your red T-shirt, but oxidation with chlorine bleach sometimes adds chlorine atoms to the colored stain molecules rather than just removing electrons. Adding chlorine to an organic-rich waste stream (like rinse water) leads to the formation of environmentally hazardous byproducts, such as dioxins.
Nonchlorine bleaches to the rescue
Because H2O2 is a liquid, it is not actually present in solid nonchlorine laundry bleaching products. These solid bleaches contain ingredients like perborate or percarbonate— compounds that react in water to release hydrogen peroxide. Thus, H2O2 is the nonchlorine bleaching agent common to almost all of these products. sodium percarbonate
In the process of decomposing, H2O2 releases free radicals—highly reactive intermediates that oxidize other molecules by removing electrons or hydrogen atoms from them. If these other molecules are colored stains or pigments, the chemical changes accompanying their oxidation may alter their physical properties, rendering them colorless—bleached. sodium percarbonate
Best of all, hydrogen peroxide does not contain any chlorine atoms. It oxidizes by either adding oxygen or removing hydrogen atoms. As a result, the oxidized compounds do not include organochlorine-type pollutants, and the problem of hazardous pollution is prevented at the source. sodium percarbonate
Why not stop using chlorine bleach altogether and replace it with hydrogen peroxide alternatives? There are two reasons. First, any molecules in the vicinity that are exposed to decomposing hydrogen peroxide get exposed to reactive free radicals, so some unwanted chemistry might accompany the desired oxidation. Second, successful bleaching with H2O2 requires higher temperatures and pressures and longer reaction time than those required for chlorine bleach. sodium percarbonate
A research group led by Professor Terry Collins at the Institute for Green Oxidation Chemistry (we’ll get to the Green part in a minute) at Carnegie Mellon University may have solved our bleaching problems by developing some heroic molecules with names to match. Collectively, they are called tetraamido macrocyclic ligands or TAML for short. These versatile molecules function as catalysts in the hydrogen peroxide bleaching process. Their presence allows hydrogen peroxide oxidation to proceed at much lower temperatures and pressures. And like all catalysts, they are not consumed in the process. sodium percarbonate
Bleaching with TAML-activated H2O2 is ideal example of "green chemistry" in action. Made from naturally occurring biochemicals, TAML catalysts reduce energy costs and not only prevent pollution, but are also useful in cleaning up pollutants that other processes have left behind. sodium percarbonate
That’s the kind of good news the Environmental Protection Agency rewards with the annual Presidential Green Chemistry Challenge Awards, a program that recognized Prof. Collins’s research team for their innovative research in 1999.
You’ll be happy to know that TAML technology has been applied to laundry. Commercial laundries and homeowners in drought-stricken areas are looking for ways to reduce water usage. But using less water leads to problems with dye transfer. The highly selective TAML activators use the peroxide present in some detergents to hunt and destroy free dye molecules, while leaving fabric-bound dye molecules unchanged. Check the product labels—this "green" technology could make your laundry much whiter. sodium percarbonate
Shangyu Jiehua Chemical Co.,Ltd (Page last updated Mar 21,2007)
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