Radicals, from hypochlorites

Followed by C-C bond formation. Cekovic reported sequential reactions involving generation of alkoxyl radicals from hypochlorites and nitrite esters followed by... 

The homolysis of tertiary hypochlorites for the production of oxy radicals is well known." The ease with which secondary hypohalites decompose to ketones has hampered the application of hypohalites for transannular reactions. However the tendency for the base-catalyzed heterolytic decomposition decreases as one passes from hypochlorites to hypobromites tohypoidites. Therefore the suitability of hypohalites for functionalization at the angular positions in steroids should increase in the same order. Since hypoidites (or iodine) do not react readily with ketones or carbon-carbon double bonds under neutral conditions hypoiodite reactions are more generally applicable than hypochlorite or hypobromite decompositions. 

Hll. Hawkins, C. L., and Davies, M. J., Hypochlorite-induced damage to proteins Formation of nitrogen-centred radicals from lysine residues and their role in protein fragmentation. Biochem. J. 332, 617-625 (1998). 

Another possibility for the formation of free radical species from hypochlorite is through its reactions with transition metal ions. Thus, Guilmet and Meunier (1980) reported a manganese-promoted epoxidation of olefins such as styrene (Equation 5.13) and cyclohexene in a two-phase dichloromethane-water solvent mixture. The epoxide oxygen was derived from HOCl, not from air, but no mechanistic details were speculated upon. Further evidence needs to be obtained on the possibility of free-radical reactions in water and wastewater chlorination. 

Intramolecular hydrogen abstraction by alkoxy radicals generated from hypochlorites has also been observed ... 

One-electron cleavage of the oxaziridine ring is especially useful in the case of the oxaziridine (114), easily obtained from cyclohexanone, methylamine and hypochlorite. The radical formed from (114) by uptake of one electron from the iron(II) ion can be trapped, for example, by acrylonitrile to form products derived from radical (297) (68TL5609). 

Alpha-l-antiprotease (ai-AP) limits tissue damage arising from the actions of the leucocyte protease, elastase (Carrell and Travis, 1985), and there is much evidence available for the oxidative inactivation of this protein by oxygen-derived free-radical species and hypochlorous acid/hypochlorite anion (HOCl/OCP). The mechanism of this inactivation appears to involve the oxidation of a critical methionine residue (Met-358) to its corresponding sulphoxide and methionine sulphoxide has been detected in ai-AP samples isolated from the lungs of cigarette smokers (Carp et al., 1982) and rheumatoid synovial fluids (Wong and Travis, 1980). 

The f-butoxy radicals thus formed then abstract hydrogen from hydrocarbons to generate hydrocarbon radicals and f-butyl alcohol. The hydrocarbon radicals in turn generate more r-butoxy radicals by attacking the t-butyl-hypochlorite ... 

HOCl-mediated protein oxidation accelerates under pathophysiological conditions. Thus, proteins from extracellular matrix obtained from advanced human atherosclerotic lesions contained the enhanced levels of oxidized amino acids (DOPA and dityrosine) compared to healthy arterial tissue [44], It was also found that superoxide enhanced the prooxidant effect of hypochlorite in protein oxidation supposedly by the decomposition of chloramines and chlor-amides forming nitrogen-centered free radicals and increasing protein fragmentation [45], In addition to chlorination, hypochlorite is able to oxidize proteins. The most readily oxidized amino acid residue of protein is methionine. Methionine is reversibly oxidized by many oxidants including hypochlorite to methionine sulfide and irreversibly to methionine sulfone [46] ... 

Experiments designed to utilize spin trapping to monitor free-radical chemistry in the gas phase were first reported by Janzen and Gerlock (1969). In these, radicals generated by photolysis in a stream of carrier gas were passed over solid PBN. The PBN was then dissolved in benzene, and the solution was found to contain spin adducts of radicals present in the gas stream. Photolysis of t-butyl hypochlorite vapour in this way leads to a nitroxide whose spectrum reveals splitting from two chlorine atoms. This proved to be due to butyl nitroxide (Janzen, 1971 Janzen et al., 1970), and recalls the observation of other nitroxides which apparently result from further reaction of the initial spin adducts. 

The possibility that significant amounts of 2-phenylpropyl-l-peroxy (POO ) radicals were formed via CO abstraction from the -position of CH was investigated using cumyl hypochlorite as the source of CO radicals. At 56°C. with 3.6M [CH] in chlorobenzene, (ku)a/(ku)p = 23 and therefore the formation of POO radicals via Reaction 14 can be neglected under these conditions. Since COO radicals are more selective than CO radicals, POO will not be formed in Reaction 2. The hypochlorite experiments gave k /k12 = 0.75 Mole"1 at 56°C.]... 

Benzylic halides can be prepared by the same radical-halogenating agents that give allylic halides from alkenes. These include Cl2, Br2, N-bromo-succinimide (Section 14-3A), S02C12, and im-butyl hypochlorite (see Exercise 4-18) ... 

This is present in neutrophils, and catalyzes the production of hypochlorite from hydrogen peroxide and chloride. The hypochlorite then reacts with superoxide to generate hydroxyl radical... 

Assuming all alkoxy radicals abstract hydrogen from cyclohexane at the same rate, and that there is no interference by chlorine atom chains in the hypochlorite decompositions. See Reference c. 

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