Mercuration radicals from

When cation-radicals from A3-phosphorins such as 188 are formed in the presence of nucleophiles and excess of oxidant, further reaction takes place to give A5-phosphorin derivatives, e.g., 191, generated in the presence of methanol by oxidation of 188 with mercuric acetate.611-614 A crystal and molecular structure determination of a A5-phosphorin shows a planar heterocycle with spd-hybridized phosphorus.615 Anion- and cation-radicals are also obtainable from the A5-phosphorin system.606,611,612... 

When Blackley and Reinhard first isolated bistrifluoromethyl nitroxide, they found it unreactive towards mercury -a conclusion they have since revised, but perhaps not before Emeleus and Spaziante reported the formation of mercuric bistrifluoromethylnitroxide from the radical and mercury at 20 °C. ... 

CIDNP has also been reported in reactions of organomercurials. Emission is observed from the couphng product of p-methylbenzyl-mercuric bromide and triphenylmethyl bromide (Beletskaya et al., 1971), while thermolysis of organomercury derivatives of tin such as t-C4H9HgSn(CH3)3 gave mixtures of isobutene and isobutane (by disproportionation of uncorrelated pairs of t-butyl radicals) showing A/E polarization (Mitchell, 1972). 

The free-radical scheme, however, fails to account for the following (i) It cannot be easily generalised to cover the identical kinetics of the Mn(lII) sulphate oxidation if -CH(C02H) has an oxidation potential comparable with Mn(Ill)/ Mn(II) pyrophosphate then it cannot appreciably reoxidise Mn(ll) sulphate, (a) If -CH(C02H) reoxidises Mn(II) sulphate then it should be capable of re-oxidising both V(1V) sulphate (of the V(V)/V(IV) pair, potential 1.0 V) and Mn(II) sulphate in the V(V) oxidation of malonic acid that it does neither can be seen from the rate laws of these oxidations which show no Mn(II)-retardation vide infra). Hi) The not dissimilar kinetics of the Mn(III) sulphate oxidation of formic acid vide supra) and mercurous ion °. 

Formation of organometallics by radical initiated decarboxylation is largely restricted to preparations of monoorganomercurials from mercuric carboxylates (see Section IV). These reactions are used as examples in the following discussion. 

Organometallic formation may result from a chain mechanism [Eqs. (21)-(23) and (18)—(20)] and/or radical displacement [Eqs. (21)-(23), alone]. The reaction of 13C-labeled mercuric cyclohexanoate with cyclohexylcarbonyl peroxide (1 1) gave mainly unlabeled organomercu-rial, which was derived from radical displacement (122). Decarboxylation by a chain mechanism was reported for the syntheses of organomercuric carboxylates of straight chain alkyls [R = Me(CH2) , n - 0-8, 10, or 15 (123-131)], branched alkyls [R = Me2CH(CH2) , n = 0 or 2 (132) or Me3C(CH2) , n = 0-2 (133)], substituted alkyls [R = cyclopentylmethyl... 

Mercuric carboxylates, which decarboxylate by a chain mechanism when initiated by peroxides, also decarboxylate under UV irradiation (123,128,129,131-140,142,144-146,153-155). In addition, decarboxylation was observed for mercuric benzoate and mercuric a-naphthoate (123). Side reactions [Eqs. (24), (25), (109)] observed in peroxide initiated reactions also occurred on UV irradiation, and mercurous salt formation [Eq.(24)] was more extensive under the latter conditions. Decarboxylation giving methylmercuric acetate occurred on irradiation of mercuric acetate in aqueous solution and is considered to be of environmental significance (156,157). Stepwise decarboxylation giving (CF3)2Hg occurred on irradiation of solid mercuric trifluoroacetate at -196° C (158), but, at 20° C, trifluoromethyl radicals diffused from the solid and dimerized (158). No other diorganomercurial has been formed by radical decarboxylation, and the reaction is not preparatively competitive with the thermal decarboxylation synthesis of (CF3)2Hg (26,27) (Section III,A). 

DNA-DNA crosslinks develop with time following exposure to HgCl2, probably resulting from its ability to interact directly with the DNA bases [253], while single-strand breaks may result from the production of oxygen radicals by mercuric chloride and also by its interaction with DNA bases [254, 255], The single-strand breaks resemble those induced by X-rays [256]. 

The reductive decomposition of alkylmercury compounds is also a useful source of radicals.205 206 207 The organomercury compounds are available by oxymercuration (Section 4.3) or from an organometallic compound as a result of metal-metal exchange (Section 7.3.3). The mercuric hydride formed by reduction undergoes chain decomposition to generate alkyl radicals. 

The preferred position for electrophilic substitution in the pyridine ring is the 3 position. Because of the sluggishness of the reactions of pyridine, these are often carried out at elevated temperatures, where a free radical mechanism may be operative. If these reactions are eliminated from consideration, substitution at the 3 position is found to be general for electrophilic reactions of coordinated pyridine, except for the nitration of pyridine-N-oxide (30, 51). The mercuration of pyridine with mercuric acetate proceeds via the coordination complex and gives the anticipated product with substitution in the 3 position (72). The bromina-tion of pyridine-N-oxide in fuming sulfuric acid goes via a complex with sulfur trioxide and gives 3-bromopyridine-N-oxide as the chief product (80). In this case the coordination presumably deactivates the pyridine nucleus in the 2 and... 

Investigation of the use of acetyl hypofluorite in acetic acid for the regiocontrolled monofluorination of aromatic compounds starting from the corresponding mercurated derivatives has been carried out by Visser and coworkers29 (equation 19). On the basis of the observed fluorinated (7), acetoxylated (8) and methylated (9) products, a one-electron-transfer mechanism leading to an intermediate radical cation was proposed which might... 

Indeed the diversion to side products during thallation coincides with the direct obsovation of the arene radical cation as a transient intermediate both by UV-visible and ESR spectroscopy. A similar dichotomy between the products of mercuration and thallation exists with durene, albeit to a lesser degree. Finally no discrepancy is observed with mesitylene, nuclear substitution occuiring exclusively in both mercuration and thallation. Such a divergence between mercuration and thallation can be reconciled by the formulation in Scheme 6 if they difier by the extent to which di sive separation (ki) occurs in equation (31). All factors being the same, diffusive separation of the radical pair from thallium(III) should... 

However, in certain cases under photolytic conditions, spectra of the corresponding arylmercury radical cations 6 developed, whereas no mercuration occurred in dark [81] signifying collapse of the ArH +,Hg(TFA)2 radical ion pair 4, provides an alternative path way to Wheeland complex 2 and hence to ArHg(TFA) + 6. Arene radical cations can also be generated from arene and thallium(III) tris-(trifluoroacetate) in trifluoroacetic acid [82], but with a different mechanism proposed by Eberson et al. [83]. Oxidation of anthracene showed 9-trifluoroacetoxy and 9,10-bis(trifluoroacetoxy)anthracene [84, 85], benzo[a]pyrene, 7-methylbenzo-[a]pyrene and 12-methylbenzo[a]pyrene yielded radical cations of 7- and/or 12-trifluoroacetates [86], triptycene (9,10-dihydro-9,10-[l,2]benzanthracene) showed... 

Burning under reduced pressure Initiating properties of mercuric fulminate Other salts of fulminic acid Manufacture of mercuric fulminate Esters of fulminic acid I lydra >ic acid, its derivatives and salts Decomposition of azides HctcrtK yclics from azides Other react ions of azide anion amt radical Some organic azides Danger of handling a/ides Cyanic triazide... 

Organic mercurials are capable of inducing nephrotoxicity in S2 and S3 segments of the proximal tubule. Part of the S3 damage results from the biotransformation of the organic mercurial to release mercuric ions. Methylmercury (CH3Hg + ) readily concentrates in renal proximal tubular cells and alters mitochondrial function and lysosomes. At least part of methylmercury-induced nephrotoxicity may be due to homolytic scission of methylmercury to release methyl radicals and to lipid peroxidative toxicity. 

Mercury has been shown to affect hepatic microsomal enzyme activity (Alexidis et al. 1994). Intra-peritoneal administration of mercuric acetate (6.2 mol/kg/day) once daily for 6 days or once as a single dose of 15. 68 mol/kg resulted in an increase in kidney weight and a significant decrease in total cytochrome P-450 content. The single 15.68 mol/kg injection resulted in the reduction of both microsomal protein level and P-450 content, possibly resulting from the generation of free radicals during the Hg intoxication process. 

When the Cristol procedure was applied to the bridgehead acid (1), bicyclo[2.2.2]octane-l-caiboxylic acid, with bromine and mercuric oxide in carbon tetrachloride, the product was a mixture of the expected bromide (2) with an even larger proportion of the unexpected chloride (3). The chloride evidently arises by abstraction of chlorine from the solvent by an intermediate bridgehead radical. The pure bromide was obtained with use as solvent of either bromotrichloromethane or 1,2-dibromoethane. 

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