Halous acid

Only four of the acids listed in Table 19.8 have been isolated in pure form perchloric acid (HC104), iodic acid (HIO3), and the two periodic acids, metaperiodic acid (HI04) and paraperiodic acid (H5IC>6). The others are stable only in aqueous solution or in the form of their salts. Chlorous acid (HCIO2) is the only known halous acid. 

The basic (nucleophilic) reagents in the reactions of the preceding paragraph were the iodide and thiosulfate ions, respectively. If chlorine, bromine, or iodine is dissolved in aqueous alkali, the halogen color disappears, and an apparent self-oxidation takes place. Half of the halogen is converted to the — 1 state, the remainder to the +1 state (as a hypo-halous acid, HOX, or its ion). Such a reaction is similar to those above ... 

The only definitely known halous acid, chlorous acid, is obtained in aqueous solution by treating a suspension of barium chlorite with sulfuric acid and filtering off the precipitate of barium sulfate. It is a relatively weak acid (KA <= 10 2) and cannot be isolated in the free state. Chlorites (MC102) themselves are obtained by reaction of C102 with solutions of bases ... 

Chlorous acid, HCIO2, is the only known halous acid. All the halogens except fluorine form halic and perhalic acids. The Lewis structures of the chlorine oxoacids are... 

It remains now to consider the equilibria of the oxo anions not yet mentioned and their kinetic relations to those we have discussed. Halite ions and halous acids do not arise in the hydrolysis of the halogens. HI02 apparently does not exist, HBr02 is doubtful, while HC102 is not formed by disproportionation of ClOH if for no other reason than that the equilibrium constant is quite unfavorable ... 

An in-depth study of the industrially important hydrolysis of titanium alkoxides has been carried out by Bradley. A number of intermediate complexes were isolated and characterized. The alcohol exchange reaction has been discussed previously. The addition of hydro halous acids to alkoxides is clearly related to the reverse reaction, the addition of alcohols to metal halides, In general, the products of these two reactions will be the same (equation 59). Hence, complete substitution will occur to give metal halides that are known to form only alcoholates with alcohols (equations 60 and 61). ... 

X = Cl, Br + 3 HXO2 halous acid NaXOj sodium halite... 

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