19829-61-9Relevant articles and documents
Substituent effects on the photocleavage of benzyl-sulfur bonds. Observation of the "Meta effect"
Fleming, Steven A.,Jensen, Anton W.
, p. 7040 - 7044 (1996)
Benzyl phenyl sulfide has been used to investigate the photocleavage mechanism for benzyl-sulfur bonds. Four experiments have shown that the reaction goes through a radical intermediate. First, the photoproducts observed can all be justified by radical mechanisms. Second, the radical intermediate was trapped with a five hexenyl tether. Third, UV analysis of analogs for the 4-NO2 derivative indicate no exciplex or electron transfer pathway. Fourth, no strong correlation is observed between a values and the quatum yields for loss of substituted benzyl phenyl sulide. The effect of oxygen on quantum yields is best observed after samples are thoroughly outgassed with consecutive freeze-pump-thaw cycles. It is shown that oxygen diminishes the substituent effect. Upon photolysis of the outgassed samples, the meta-substituted derivatives showed more significant variances than the para derivatives. The meta derivatives are most efficiently cleaved in the following order: 3-CN > 3-NO2 > 3-CF3 > 3-CH3 > 3-OCH3. These findings are justified by an increase in electron density of the radical ipso to the forming benzyl radical for the 3-OCH3 derivative and a decrease in the electron density of the radical ipso to the forming benzyl radical for the 3-CN derivative.
REACTIVITY OF THE ACIDS OF TRIVALENT PHOSPHORUS AND THEIR DERIVATIVES. PART IV. THE REACTION OF DIALKYLPHOSPHITE ANIONS WITH NITROBENZYL BROMIDES
Witt, Dariusz,Rachon, Janusz
, p. 33 - 48 (2007/10/03)
The reaction of o-, m- and p-nitrobenzyl bromide with sodium dimethylphosphite as well as sodium diisopropylphosphite in THF and alcohols as the solvent is described.According to the constitution of the starting materials and the solvents used, the formation of the P-C bond, debromination or dimerization occurs.The principal process in o- and p-nitrobenzyl bromide and >P-O- anion systems is believed to be X-philic substitution, the dimer is formed through a secondary process via SET from the nitrobenzyl anion to nitrobenzyl bromide.Electron-transfer and proton-transfer processes in the nitrobenzyl bromide->P-O- systems are also discussed.Key words: o-, m- and p-nitrobenzyl bromides, dialkyl phosphites, Michaelis-Becker reaction, X-philic substitution, SET.
Sructure an Mechanism in the Photo-Retro-Aldol Type Reactions of Nitrobenzyl Derivatives. Photochemical Heterolytic Cleavage of C-C Bonds
Wan, Peter,Muralidharan, S.
, p. 4336 - 4345 (2007/10/02)
The photo-retro-aldol type reactions of several nitroaromatic compounds have been studied in aqueous solution over the pH 1-14 range.These reactions are observed only in aqueous or in predominantly aqueous solution.Catalysis of reaction due to hydroxide ion is observed for several derivatives.Quantum yields of reaction and product ratios (of nitrotoluene vs dinitrobibenzyl) are reported as a function of pH.The proposed mechanism of reaction involves heterolytic cleavage of the benzylic C-C bond from the triplet excited state in the primary photochemical step to generate a nitrobenzyl carbanion and a carbocation-equivalent fragment, except for the nitrophenylacetates 24-26, which eliminate CO2 in place of such a fragment.Photogenerated nitrobenzyl carbanions are efficiently trapped by molecular oxygen to give isolable hydroperoxides at pH 9 M-1 s-1.The results show that photochemical C-C bond heterolysis requires favorable stabilization of both the carbanion and carbocation-derived fragments.Hydroxide ion catalysis may also facilitate the process.The use of the nitrobenzyl moiety as the carbanion-stabilizing group appears to be generally applicable, as demonstrated by the systems studied.
