Oxyacids with halogens

With the exception of perchloric acid, the halogen oxyacids are reduced through the corresponding halogen elements to the hydracids in the case of iodic acid3 the formation of free iodine after a definite interval forms a striking example of a time reaction. 4 The formation of the element is not observed until after the disappearance of the whole of the sulphite. The mechanism of the reaction is probably as follows ... 

The oxidation of arsine may be accomplished by means of the halogen oxyacids and their salts,8 although not so readily as with the halogens themselves. Hypochlorites and hypobromites cause complete oxidation to arsenic acid, but side reactions are liable to occur, especially if the gas is present in excess. Chloric add slowly oxidises arsine to arsenious acid a trace of silver nitrate catalyses the reaction. Chlorates are quite inactive. More complete oxidation results with solutions of bromic acid and bromates, iodic acid and iodates, especially in the presence of catalysts. The reactions are of the type represented by the equation8... 

A comprehensive review of the pre-1976 literature on the decompositions of the salts of halogen oxyacids has been provided by Solymosi [1]. Another important review (1974) by Stem [2] is concerned with the high temperature properties of oxyhalides. 

A relatively large number of oxyacids of the halogens exist. Because of the extensive redox chemistry of these compounds, there is an enormous number of reactions involving them. We will give only an overview in keeping with the spirit and space requirements of this survey. 

HF b.p. 19°C HCl b.p. -85°C). Unlike the other halogens, fluorine does not form higher oxides or oxyacids oxygen difluoride in fact reacts with water to give hydrogen fluoride. 

The halogens and their oxyacids probably are the most important oxidants used in the carbohydrate field. They are widely used as bleaching agents, but the mechanism of this action remains to be clarified. As reagents for preparatory purposes (particularly for aldonic acids and lactones) and for analytical procedures, they are very important. Periodic acid, discussed in a later section, has an important application for the elucidation of structures of carbohydrates. A number of valuable commercial products are made by treatment of polysaccharides with halogens, particularly chlorine or hypochlorous acid, but the nature of these actions, such as the modification of starch, has not been clarified. 

All the halogens except fluorine combine with various numbers of oxygen atoms to form a series of oxyacids, as shown in Table 20.10. The strengths of these acids vary in direct proportion to the number of oxygen atoms attached to the halogen, as we discussed in Section 14.9. 

---