Hypohalous acids and hypohalites

Hypohalous acids either preformed or prepared in situ readily add to carbon-carbon multiple bonds.142-144 The addition is an electrophilic reaction with the positive halogen attaching itself predominantly to the less substituted carbon. The Markov-nikov rule, therefore, is followed in most cases. The addition of the elements of hypohalous acids may be carried out by the use of reagents serving as positive 

Limited data are available on hypofluorous acid, which is a very reactive, explosive reagent.145 Exceptionally among hypohalous acids, it is polarized in the sense H08+-F8. It converts alkenes into fluoroalkanols with regioselectivites opposite to other hypohalous acids [Eq. (6.24)] the large amount of HF present may affect the actual mechanism of addition  

Hypochlorous acid and hypobromous acid react with acyclic alkenes to give Mar-kovnikov products. In striking contrast, exclusive anti-Markovnikov orientation was observed in the transformation of methylenecycloalkanes with HOBr, and mixtures of chlorohydrins were formed with HOC1 146 

This was attributed to the fact that the open tertiary carbocation leading to Markov-nikov products are unfavorable in these ring systems. 

A convenient synthesis of chlorohydrins is based on the use of Chlorine T (TosNCINa) as the positive chlorine source in water-acetone.147 It adds to a variety of alkenes to form Markovnikov and anti-Markovnikov products in a ratio of 4 1. 

All of the halogens form acids having the formula HOX, and all are oxidizing agents. Of these, only HOF appears to be stable outside of aqueous solutions, and it decomposes easily into HF and 02. The HOX acids can all be prepared by the general reaction 

These acids can also be prepared by the reaction of the appropriate halogen with a base, 

However, the solutions must be cold and dilute or else the competing reaction 

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The manner and rate of decomposition of hypohalous acids (and hypohalite ions) in solution are much influenced by the concentration, pH and temperature of the solutions, by the presence or absence of salts which can act as catalysts, promotors or activators, and by light quanta. The main competing modes of decomposition are ... 

Other uses of hypohalous acids and hypohalites are described in the Panel. 

Addition of Hypohalous Acids and Hypohalites (Addition of Halogen, Oxygen)... 

Fluorination of ice yields milligram amounts of hypofluorous acid, HOF, which is unstable at RT . Solutions of the other hypohalous acids and hypohalites are formed via disproportionative hydrolysis of the halogens ... 

Oxidation with Hypohalites in Alkaline Solutions. In alkaline solution the halogens exist as hypohalous acid and hypohalite ions. The oxidation is likely to be more drastic than for the free halogens. Thus, whereas free iodine will not act as an oxidant, hypoiodite is a powerful oxidizing agent. Hypobromite and hypochlorite particularly are likely to produce oxidation of primary and secondary alcoholic groups and cause cleavage of carbon-carbon bonds. As noted above, the processes are complicated by the tendency of hypohalite to be converted to halate ions. 

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