Elucidation of the role of the complex in hydride transfer reaction between methylene blue and 1-benzyl-1,4-dihydronictinamide by effect of γ-cyclodextrin

The kinetics of the hydride transfer reaction between Methylene Blue (MB+) and&#12288;1-benzyl-1,4-dihydronicotinamide (BNAH) were studied in 10 % ethanol-90 % water mixed solvents containing &#946;- and &#947;-cyclodextrins (&#946;-CD and &#947;-CD). The pseudo-first order rate constant shows kinetic saturation at high initial concentration of BNAH. This indicates the formation of a complex between MB+ and BNAH. The reaction was suppressed by addition of &#946;-CD, but enhanced by addition of &#947;-CD. MB+ and BNAH were separately accommodated within the &#946;-CD cavity and the cavity walls may protect the activity site of the reactants. On the other hand, in the MB+-BNAH-&#947;-CD system, the inclusion of the complex between MB+ and BNAH with &#947;-CD occurred. This effect of &#947;-CD can distinguish between the productive and non-productive nature of the complex.</p

Generation, Characterization, and Deprotonation of Phenol Radical Cations1

A variety of methoxy- and methyl-substituted phenol radical cations have been generated and characterized by laser flash photolysis in solution under ambient conditions. The radical cations were generated by either photosensitized electron transfer using 1,4-dicyanonaphthalene with biphenyl as a cosensitizer in acetonitrile or by direct excitation of the phenol at 266 nm. The phenol radical cations have absorption maxima between 410 and 460 nm, with the exception of the 3,5-dimethoxyphenol which absorbs at 580 nm. The assignment of the observed transients to phenol radical cations is based on their spectral similarity to matrix spectra for the same species and to the corresponding methoxybenzene radical cations, as well as their characteristic reactivity. In the presence of small amounts of water the radical cations are not detected and the phenoxyl radical is the only observed transient in the photosensitized electron transfer. For those phenols for which authentic phenoxyl spectra are not available, the identity of the radical was confirmed by its generation by hydrogen abstraction by the tert-butoxyl radical. Although several of the phenols can be photoionized in either 1:1 aqueous ethanol or in acetonitrile, this is a less general route for the formation and characterization of the phenol radical cations. The rate constants for deprotonation of the phenol radical cations by water were measured and fall within the range (0.6-6) ? 108 M-1 s-1; the 2-methoxyphenol radical cation is more reactive than the 4-methoxy, consistent with a recent estimate of the pKa for these species.Peer reviewed: YesNRC publication: Ye

Photochemical Reactivity of 2-Azido-1,3-thiazole and 2-Azido-1,3- benzothiazole: A Procedure for the Aziridination of Enol Ethers

Direct irradiation of a mixture of the azido\u2013tetrazole tautomers of 2-azido-1,3-thiazole and 2-azido-1,3-benzothiazole in toluene solution gives products arising from the intermediate nitrene, which in turn undergoes ring opening in the case of 2-azido-1,3-thiazole to give a polymer, and dimerization in the case of 2-azido-1,3-benzothiazole to give [1,3]benzothiazolo[ 2',3':3,4][1,2,4,5]tetraazino[6,1b][1,3]benzothiazole in low yields. When irradiation is performed in the presence of methyl acrylate or various enol ethers, aziridination of the double bond is observed, with good yields in the case of enol ethers. Among these, 1-(6-methyl-3,4-dihydro-2H-pyran-2- yl)ethanone undergoes aziridination with complete diastereoselectivity to give the (1RS,3RS,6SR) diastereomer