Bleaching oxidising

Ageing as well as bleaching oxidises the components, which increase their water solubility. The material will have a higher tendency to stay in the aqueous phase. Volatile extractives evaporate further reducing the extractive content. This is what smells from freshly cut trees. Ageing of wood and chip before cooking considerably reduce the pitch problems. 

The presence of chloric(I) acid makes the properties of chlorine water different from those of gaseous chlorine, just as aqueous sulphur dioxide is very different from the gas. Chloric(I) acid is a strong oxidising agent, and in acid solution will even oxidise sulphur to sulphuric acid however, the concentration of free chloric(I) acid in chlorine water is often low and oxidation reactions are not always complete. Nevertheless when chlorine bleaches moist litmus, it is the chloric(I) acid which is formed that produces the bleaching. The reaction of chlorine gas with aqueous bromide or iodide ions which causes displacement of bromine or iodine (see below) may also involve the reaction... 

Liquid chlorine dioxide, ClOj, boils at 284 K to give an orange-yellow gas. A very reactive compound, it decomposes readily and violently into its constituents. It is a powerful oxidising agent which has recently found favour as a commercial oxidising agent and as a bleach for wood pulp and flour. In addition, it is used in water sterilisation where, unlike chlorine, it does not produce an unpleasant taste. It is produced when potassium chlorate(V) is treated with concentrated sulphuric acid, the reaction being essentially a disproportionation of chloric(V) acid ... 

Chloric(III) acid is a fairly weak acid, and is an oxidising agent, for example it oxidises aqueous iodide ion to iodine. Sodium chlorate(III) (prepared as above) is used commercially as a mild bleaching agent it bleaches many natural and synthetic fibres without degrading them, and will also bleach, for example, oils, varnishes and beeswax. 

Because pulp bleaching agents are, for the most part, reactive oxidising agents, appropriate precautions must be taken in their handling and use. For example, it is important to ensure that the threshold limit values (TLV) (20) in Table 2 are not exceeded in the workplace air. These are airborne concentrations in either parts per million by volume under standard ambient conditions or mg per cubic meter of air. They "represent conditions under which it is beUeved that nearly all workers may be repeatedly exposed, day after day, without adverse effect" (20). TWA refers to a time-weighted average for an 8-h workday STEL is a short-term exposure limit or maximum allowable concentration to which workers can be continuously exposed for 15 minutes. 

Table 10.12 AOX values for cotton bleached with various oxidising agents [223]...

A substance added to latex in the preparation of pale crepe rubber sodium bisulphate prevents darkening of the crepe due to the presence of oxidising enzymes, xylyl mercaptan is an effective bleaching agent proper. 

There are two approaches to the bleaching of mechanical pulps. They may be either reductive or oxidative in nature. The reductive bleaching agents are usually bisulfite, dithionite or borohydr.de, and the oxidising agents are normally peroxide, hypochlorite, peracetic... 

Chiral irara-cyclohexane- 1,2-diamine was used as the bridging diamine and this led to a successful catalyst [14], often referred to as Jacobsen s catalyst (Figure 14.12). The oxidising agent is household bleach ( ) diluted and buffered... 

The main application of the perdisulphates is in analytical chemistry other directions in which they find use are mentioned under the description of their properties. Because of their oxidising and bleaching action they are used in the textile and dyeing industries, and for bleaching soap. They are also used for deodorising whale and fish oils and animal fats in order to render them suitable for soap making. 

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