David J. Edge

Nitroxide chemistry. Part VI. N-trifluoromethylsulphamate N-oxyl

Purple solutions containing N-trifluoromethylsulphamate N-oxyl can be prepared by treatment of trifluoronitrosomethane with aqueous alkali-metal hydrogen sulphite in the presence of lead dioxide; addition of tetraphenylarsonium chloride to such a solution results in precipitation of the pale purple tetraphenylarsonium salt [CF3·N(O)·SO3–Ph4As+].

Nitroxide chemistry. Part XII. Free radical formation in the reactions between trifluoronitrosomethane and some 1,3-diketones

The 1,3-diketones RCO·CH2·COR′(R = R′= CH3 or CF3, and R = CH3, R′= CF3) react with trifluoronitrosomethane to generate the nitroxide radicals CF3·N(Ȯ)·CH(COR′)·COR and their tautomers CF3N(Ȯ)·C(COR′):C(OH)R together with the iminoxy-radicals (RCO)(R′CO)C:N·O, all detected by e.s.r. spectroscopy. Diethyl 2-methyl-3-oxosuccinate affords only the radical CF3·N(Ȯ)·CMe(CO2Et)CO·CO2Et under similar conditions. Intermediate hydroxylamine anions CF3·N(Ō)·CH(COR)·COR′, are proposed as intermediates which can undergo further reaction by two different pathways to give the observed radicals. The e.s.r. parameters of the various nitroxide radicals are given, and these are interpreted in terms of a deviation from planarity at the nitrogen atom.

Electron spin resonance studies of radical addition to alkynes and intramolecular reactions of vinyl radicals

E.s.r. spectra are described of radicals formed by the reactions of some alkynes both with hydroxyl and also with radicals formed from a variety of ethers in the presence of hydroxyl. Vinyl radicals, though not normally detected, are apparently involved, and evidence is presented for their intermolecular addition and intramolecular abstraction reactions. For example, the vinyl radical produced by addition of ·CHMeOEt to HO2CCCCO2H reacts to form the allyl radical ·CHMeC(CO2H)CHCO2H, evidently via a 1,5 carbon-to-carbon hydrogen shift and fragmentation. Other instances of ready 1,5-shifts (including an oxygen-to-carbon example) are described.

Nitroxide chemistry. Part XI. Reaction of trifluoronitrosomethane and bis(trifluoromethyl)nitroxide with some cobalt(II) species

Trifluoronitrosomethane reacts with alkaline solutions of the cobalt(II) species [Co(CN)5]3– and [Co(dmg)2·H2O] to afford solutions of the relatively stable nitroxide radicals [CF3·N(O·)Co(CN)5]3– and [CF3·N(O·)·Co(dmg)2· H2O] respectively, the e.s.r. parameters of which are discussed. E.s.r. spectroscopic evidence suggests that under similar conditions the reaction between [Co(CN5)]3– and bis(trifluoromethyl)nitroxide leads to the formation of the compound [(CF3)2NO·Co(CN)5]3–: attempts to isolate this particular complex free from impurities were unsuccessful.

Trimethylsilyloxy-radicals from peroxides: electron spin resonance study of homolytic substitution on silicon

The photolysis of trimethylsilyl t-butyl peroxide results in homolytic fission of the O–O bond. In the presence of alkenes the e.s.r. spectra of adducts of trimethylsilyloxy-radicals are observed, together with those of allylic radicals derived from hydrogen abstraction. In the absence of reactive substrates, trimethylsilyloxy-radicals are involved in an induced decomposition of the silyl peroxide by an SH2 reaction at silicon, and the e.s.r. spectrum of the displaced t-butylperoxy-radical can be observed. The latter can also be trapped by 1,3-butadiene and the resultant allylic radical is involved in a further SH2 reaction with the silyl peroxide. The e.s.r. spectrum observed in this case is due to cis-α-trimethylsilylallyl radical produced by the secondary photolysis of the butadiene adduct with loss of formaldehyde. The possibility of homolytic rearrangement of an allylic intermediate is ruled out.