Hypohalous acid additions

Formation of oxiranes on the sterically more hindered side of the steroid ring system is usually carried out via /raw -halohydrins which afford oxiranes on treatment with base (c -Halohydrins yield ketones on exposure to base). Two general methods are available for the synthesis of tm s-halohydrins (1) the reduction of a-halo ketones and (2) the addition of a hypohalous acid to unsaturated steroids. 

This section concludes with a reminder that, in addition to the hypohalous acids HOX and metal hypohalites M(OX) , various covalent (molecular) hypohalites are known. Hypochlorites are summarized in Table 17.22. All are volatile liquids or gases at room temperature and are discussed elsewhere (see Index). Organic hypohalites are unstable and rapidly expel HX or RX to form the corresponding aldehyde or ketone ... 

In addition to the applications indicated on p. 858. hypohalous acids are useful halogenating agents for Ixjth aromatic and aliphatic compounds. HOBr and HOI are usually generated in silii. The ease of aromatic halogenation increa.ses in the sequence OCl < OBr < Ol and is facilitated by salts of Pb or Ag. Another well-known reaction of hypohalites is their cleavage of methyl ketones to form carboxylates and haloform ... 

Addition of Hypohalous Acids to Alkenes Halohydrin Formation... 

ThomsorWOW Click Organic Interactive to use a web-based palette to predict products of the addition of hypohalous acid to alkenes. 

Yet another example of an electrophilic addition is the reaction of alkenes with the hypohalous acids HO—Cl or HO-Br to yield 1,2-halo alcohols, called halohydrins. Halohydrin formation doesn t take place by direct reaction of an alkene with HOBr or HOC1, however. Rather, the addition is done indirectly by reaction of the alkene with either Br2 or Cl2 in the presence of water. 

The addition of mineral acids to hypohalous acids produces a large increase in the rate at which these latter acids halogenate and reaction under these conditions is usually referred to as positive haiogenation which has been subjected to intensive kinetic studies. Whilst there is ample evidence supporting the existence... 

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

Cleavage of epoxides with hydrogen halides Addition of hypohalous acids to alkenes... 

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 ... 

It wh nearly a century ago—in fact only a few yean after Wurtz discovered ethylene oxide1 64—that Garina184 effected the earliest additions of hypohalous acids to olefins. In the yoara that followed, many celebrated chemists were among those who investigated thin reaction, which has been of great interest because of the parallelism between it and olefin h logenation. 

Mechanism. Addition of hypohalous acids to olcfinic double bonds is generally regarded as a typical electrophilic substitution reaction, and therefore subject- to the same governing principles v. others of the same typo. 

Many of the common laboratory methods for the preparation of alcohols have been discussed in previous chapters or will be considered later thus to avoid undue repetition we shall not consider them in detail at this time. Included among these methods are hydration (Section 10-3E) and hydroboration (Section 11-6D), addition of hypohalous acids to alkenes (Section 10-4B), SN1 and Sn2 hydrolysis of alkyl halides (Sections 8-4 to 8-7) and of allylic and benzylic halides (Sections 14-3B and 14-3C), addition of Grignard reagents to carbonyl compounds (Section 14-12), and the reduction of carbonyl compounds (Sections 16-4E and 16-5). These methods are summarized in Table 15-2. 

Sec. 7.3) from alkenes by electrophilic addition of hypohalous acid (HOX)... 

MPO (Myeloperoxidase) [EC 1.11.1.7] catalyzes the hydrogen peroxide dependent two-electron oxidation of halides (CD, I, Br ) and thiocyanate to the corresponding hypohalous acids and hypothiocyanate which are cytotoxic to invading pathogens. In addition, MPO is capable of the singleelectron oxidation of a wide variety of aromatic alcohols and amines. " ... 

The diastereoselectivity of the addition of hypohalous acids and esters to alkenes is potentially even more susceptible to polar effects than peracid epoxidations124 they correlate to the electronegativity of the halogen and of the oxygen substituent. The derived epoxide normally has the opposite configuration to that resulting from the polar effect on peracid epoxidation, e.g., formation of the epoxide 2 with various acyl hypohalites38. 

Olefins, addition—Continued of diazoacetic ester, 498 of halo ethers, 232 of halogen, 106 of hydrogen cyanide, 603 of hydrogen halide, 105 of hypohalous acid, 109 of polyhalides, 107 to cyanides, 571 allylic bromination, 36, 104 condensation, with halides, 108 with phenols, 179 conversion to amides (Wi 11 gerodt),... 

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