Organic hypohalite

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 ... 

The mechanism of the haloform reaction has been extensively studied, and it can be concluded that it is a very complex process. The exact mechanistic pathway is dependent on the structure of the substrate and the specific reaction conditions. The scheme depicts the oxidation of a methyl carbinol to the corresponding methyl ketone via an organic hypohalite. The methyl ketone then undergoes deprotonation, and three sequential a-halogenations take place to afford the trihalomethyl ketone. This compound undergoes rapid hydrolysis to afford the haloform and a carboxylate. 

For reviews, see (a) Anbar, M. and Ginsburg, D., Organic hypohalites, Chem. Rev., 54, 925,1954 (b) Heusler, K., and Kalvoda, J., Selective functionalisation of the angular methyl group and further transformation to 19-norsteroids, in Organic Reactions in Steroid Chemistry, Fried, J. and Edwards, J.A., Eds., van Nostrand Reinhold, New York, 1972, chap. 12. 

Anbar, M. and Dostrovsky, I., Ultraviolet absorption spectra of some organic hypohalites, /. Chem. Soc., 1105, 1954. 

Cl (hypohalite), -CIO3 (chlorate), -CIO4 (perchlorate), -OCIO2 and -OCIO4 connected to inorganic or organic radicals ... 

Superior antimicrobial activity in alkaline pH (seawater is always above pH 8), in the presence of nitrogenous organic matter, and due to lower volatility has been documented for bromine antimicrobials3 4. The pKa acid dissociation constants for HOC1 and HOBr are 7.4 and 8.7, respectively the dissociated acids are less effective antimicrobials4,5. Undissociated hypohalous acids are more effective because they are far better halogenating agents compared to the dissociated anion (hypohalite). Table 1 shows the effect of acid dissociation on antimicrobial performance in well-controlled laboratory experiments. 

Organic crosslinkers have also been used. These include glyoxal (215) and formaldehyde. Use of hypohalite salts (216,217) and epichlorohydrin (218,219) have been found to increase gel stability. 

The most widely used, and often most convenient reagents for such one-pot reactions are sodium hypochlorite (45) or hypobromite (16). These reactions are performed in the presence of an organic base (generally triethylamine) that normally enhances the yield of cycloaddition products (45). This method was employed for many intermolecular reactions (71) and also seems especially suited for intramolecular ones (72-77) as well as for the solid-phase synthesis (78) of 2-isoxazolines. Hypohalite can also be replaced by sodium broruite in combination with a catalytic amount of tri-u-butyltin chloride (79). In a related method, O-tributylstannyl oximes were treated with tert-butyl hypochlorite to produce nitrile oxides that were trapped with aUcenes or alkynes to afford the corresponding isoxazolines or isoxazoles in moderate to good yield (80). 

Some Recent Developments in the Photochemistry of Organic Nitrites and Hypohalites... 

Until recently, in the chemistry of hypochlorites, there has been particular emphasis on the chemistry of -butyl hypochlorite. Hypochlorites in general were ignored. However, in their classical paper on the photolysis of organic nitrites,48 Barton et al. adumbrated a photochemical rearrangement of hypohalites of the type (A) —> (B) (X = any halogen). A year later applications of this principle were described... 

See other ORGANIC PEROXIDES, POLYMERISATION INCIDENTS See related HYPOHALITES... 

A minor explosion in the use of gaseous acetyl hypofluorite was caused by inadvertent contact of the gas inlet tube with a cooling bath, which condensed liquid hypofluorite which subsequently exploded on contact with organic material or air [ 1 ]. More detail on the isolation of this compound of limited stability, particularly in the liquid phase, is given [2]. See other ACYL HYPOHALITES, OXIDANTS... 

The photolysis of alkyl hypohalites, especially alkyl hypoiodites [29], can be used in a manner similar to the organic nitrites for functionalization of an unactivated carbon atom. Scheme 25 outlines a general scheme for remote functionalization by the hypoiodite reaction. Readers requiring more information on this subject are advised to refer to review articles [2c, 16, 20],... 

The hypohalites and their parent acids decompose to release oxygen (equation 114) and thus serve as very strong oxidizers in inorganic and organic chemistry. The hypohalites oxidize oxalates to carbon dioxide, nitrites to nitrates, sulfites to sulfates, divalent manganese to permanganate, halides to halates, and ketones to carboxylic acids, and so on. 

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