Their tendency to linger in the environment has prompted the U. Environmental Protection Agency to work with industry to find ways to limit their usage. Chlorine on the large scale is deadly to an environment. Other alternatives or nonchlorine bleaches are available. The nonchlorine bleaches contain hydrogen peroxide or solids like perborate or percarbonate that react with water to release hydrogen peroxide.
Hydrogen peroxide decomposes into oxygen gas and water, shown in Equation 1. In the process of decomposing, H 2 O 2 releases free radicals, highly reactive intermediates that oxidize other molecules by removing electrons from them. If these other molecules are colored stains or pigments, the chemical changes occurring from their oxidation may change their physical properties, making them colorless.
Hydrogen peroxide is a greener and more environmentally friendly alternative to the chlorine bleaching reagents. However, the challenge to replacing chlorine bleaches with hydrogen peroxide comes with two problems. The peroxide oxidation process can be indiscriminate; any molecule can react with the free radicals. The second problem with the use of hydrogen peroxide is the requirement of higher temperatures and pressures with longer reactions times to attain the same results as with chlorine bleaching.
A number of these compounds are stable solids that hydrolyze readily to give hydrogen peroxide in solution, the most important being sodium perborate and sodium percarbonate. Solid oxygen bleaches, as in the case of halogen bleaches, are preferred for stability and compatibility with other sensitive ingredients. Another solid oxygen bleach, peroxymonosulfuric acid the peroxygen product of hydrogen peroxide and sulfuric acid is a powerful oxidizing agent.
A commercially available salt, potassium peroxymonosulfate, is a white solid having a satisfactory shelf life and an active oxygen content of about 4.
Peracids are compounds containing the functional group -OOH derived from an organic or inorganic acid functionality. Peracids have superior cold water bleaching capability versus hydrogen peroxide due to the greater electrophilicity of the peracid peroxygen group. The cold water bleaching performance and phosphate reductions in detergent systems accounts for their emergent utilization and vast literature of peracids in textile bleaching.
Peracids can be introduced into the bleaching system by two methods. Peracids can be manufactured separately and delivered to the bleaching bath with the other components or as an adjunct. Peracids can also be formed in situ utilizing the perhydrolysis reaction shown in Equation 10 where L denotes a leaving group. The two main peracid precursors in general use are tetraacetylethylenediamine TAED , which generates peracetic acid in the wash, and nonanoyloxybenzene sulfonate NOBS , which produces pernonanoic acid when combined with hydrogen peroxide in the wash water.
As bleaching agents, oxygen bleaches are much less effective than hypochlorite. However, they do have some advantages over halogen bleaching agents, such as less potential damage to textile fibers and dyes, and lack of a strong odor.
Attempts have been made to increase the laundry bleaching power of hydrogen peroxide-based laundry bleaches by the addition of heavy metal catalysts. However, the effectiveness of these systems remains controversial; an early attempt to incorporate a catalyst into a laundry detergent led to fabric damage and was consequently withdrawn. Though catalysts have not been incorporated into commercial products in the U.
Reducing Bleaches Reducing agents generally used in bleaching include sulfur dioxide, sulfurous acid, bisulfites, sulfites, hydrosulfites dithionites , sodium sulfoxylate formaldehyde and sodium borohydride. These materials are used mainly in industrial processes such as pulp and textile bleaching, however they have been used in a small number of consumer products. Sulfur dioxide and its derivatives have been used to bleach textiles since earliest times.
Besides being an important bleaching agent in the pulp and paper industry, sulfur dioxide is also used in the manufacture of chlorine dioxide, sodium hydrosulfite, and sodium sulfite. The composition of the mixture depends on the concentration of the sulfur dioxide in the water, the pH, and the temperature. Sodium sulfite, which is used in pulp and paper bleaching, is usually produced by the reaction of sulfur dioxide with either caustic soda or soda ash Equations 11 and 12 :.
Free dithionous acid, H2S2O4, has never been isolated; however the salts of the acid in particular zinc and sodium dithionite have been prepared and are widely used as industrial reducing agents. The dithionite salts can be prepared by the reduction of sulfites, hydrosulfites, and sulfur dioxide with metallic substances such as zinc, iron, or zinc or sodium amalgams or by electrolytic reduction.
So what, exactly, happens to that ketchup stain on your white t-shirt when you bleach it? In order to understand how chlorine bleach makes a stain "disappear," we need to understand how colors work. Light is both a particle and a wave; its particles, called photons, travel in waves that have a particular length. Not all wavelengths of light are visible to the human eye: infrared light wavelengths are too long for our eyes to see, and ultraviolet wavelengths are too short. The wavelengths we can see are between and nanometers, and they appear as color to us.
For example, when light with a wavelength of about nanometers hits the retina in your eye, you perceive the color blue. The light that comes from the ketchup stain on your t-shirt to your retina has a wavelength of about nanometers, which makes it appear red [source: Atmospheric Science Data Center ].
The reason the ketchup stain reflects light with a wavelength of nanometers has to do with its chemical makeup. Like most other substances, ketchup is made up of multiple elements joined together by chemical bonds to form molecules. The electrons involved in some of these bonds are capable of absorbing light of certain wavelengths, depending on the characteristics of the chemical bond.
The light that the electrons in a substance can't absorb determines the substance's color. So the ketchup stain is absorbing all of the wavelengths of normal light that hit it -- except the nanometer light, which it reflects back to your eye, making it appear red.
Many stains have a network of double bonds between carbon atoms, and this network absorbs light. Chlorine bleach is able to oxidize many of these bonds, breaking them and taking away the substance's ability to absorb light.
When this happens, the stain "disappears. It then appears white, like the rest of the shirt. The remains of the ketchup can still be there; you just won't see the stain anymore.
Soaking and washing the shirt can remove the now-invisible stain [source: Barrans ]. Since sodium hypochlorite is a powerful oxidizing agent, it is able to oxidize chemical bonds not only in stains on your clothing, but also in the dyes that give the clothing its color. Anyone who has accidentally dripped chlorine bleach on their favorite pair of jeans has experienced just how effective bleach is as an oxidizing agent.
A non-chlorine bleach that uses a weaker oxidizing agent, such as hydrogen peroxide, can break the chemical bonds in certain stains without breaking the stronger chemical bonds in clothing dye [source: Barrans ]. The use of chlorine bleach as a medical disinfectant was first recorded in Austria in Staff at the Vienna General Hospital began using it to keep "childbed fever," a severe infection that killed countless women after they gave birth, from spreading throughout the maternity ward [source: American Chemistry Council ].
The food processing industry uses chlorine bleach to kill hazardous bacteria such as Listeria , Salmonella and E. Sodium hypochlorite also is added to municipal drinking water to kill dangerous waterborne organisms like the bacterium Salmonella typhi , which causes typhoid fever and killed many people before water disinfection and antibiotic treatment became common [source: American Chemistry Council ].
Chlorine bleach kills Vibrio cholerae , the bacterium that causes cholera, a disease that killed in epidemic proportions before water treatment. It can still kill in countries where clean drinking water is not available.
Chlorine bleach can also kill dangerous bacteria and viruses on surfaces, such as methicillin-resistant Staphylococcus aureus MRSA , influenza and HIV.
Chlorine bleach is especially valuable as a disinfectant, since germs are not able to develop immunity against it, as they have done against certain drugs [source: Lenntech ]. To kill germs, sodium hypochlorite uses the same quality that makes it such a great stain remover -- its power as an oxidizing agent. When sodium hypochlorite comes in contact with viruses, bacteria, mold or fungi, it oxidizes molecules in the cells of the germs and kills them.
Scientists also believe that the hypochlorous acid that forms when sodium hypochlorite is added to water can break down the cell walls of some germs [source: Lenntech ]. The hypochlorous acid also seems to be able to cause certain proteins to build up in bacteria, making their cells unable to function [source: Winter ]. Non-chlorine bleaches that are oxidizing agents can also act as disinfectants on some surfaces, but they are less potent than chlorine bleach.
Chlorine bleach, when used properly, is a practical and effective disinfectant. Since chlorine bleach is a strong oxidizing agent, it's hazardous if not used properly.
You should never mix chlorine bleach with any other household product, because it can react to form very hazardous substances. For example, mixing chlorine bleach with ammonia or vinegar can release poisonous chlorine gas. Cleaning and disinfecting products that aren't called "bleach" may also contain sodium hypochlorite as one of their active ingredients, so you should always read the label before using a cleaning product.
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