- Quenching of singlet oxygen by tertiary aliphatic amines. Structural effects on rates and products
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A kinetic and product study of the reaction of a series of α-methyl-substituted N-methylpiperidines with thermally generated 1O2 in MeCN was carried out. It was found that as the number of α-methyl groups (Me in α-position relative to the N-atom) increases, the rate of 1O2 quenching (physical plus chemical) slightly decreases. This finding shows that, with respect to the reaction rate, steric effects are much more important than electronic effects as the latter should have produced the opposite result. The opposite outcome was instead found for the chemical quenching that leads to the N-demethylation products and N-formyl derivatives. The same trend was observed for the ratio between N-demethylation and formation of the N-formyl derivatives (NH/NCHO ratio). All these results are consistent with the mechanism reported in Scheme 1 where an exciplex is first formed that by a H-atom transfer process produces an α-amino-substituted C-radical. The latter forms the product of N-demethylation by one electron oxidation, or affords the N-formyl derivative by radical coupling (Scheme 1). Similar results were obtained with N,N-dimethylcyclohexanamine. However, this 'acyclic' amine exhibited behaviors quite distinct from those of the N-methylpiperidines series, with respect to reaction rate, extent of chemical quenching, and NH/NCHO ratio.
- Baciocchi, Enrico,Del Giacco, Tiziana,Lapi, Andrea
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p. 2273 - 2280
(2007/10/03)
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- Diesters of carbonic acid endowed with antiviral and anti-inflammatory activity
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Diesters of carbonic acid disubstituted with primary, secondary or tertiary amine groups, pharmaceutically acceptable salts thereof, and their use as antiviral and inti-inflammatory agents.
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- LITHIUM DIALKYLAMIDES. 13C PARAMETERS AND SLOW PROTON TRANSFER
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The changes in 13C chemical shifts for the structural change R2NH -> R2N-Li have been measured for a series of dialkylamines.These lithiation shifts are largest at the alpha carbon (3.7-9.7 ppm) and decrease in the order α > β > χ > δ.The rates of lithium-hydrogen interchange between R2NH and R'2N-Li have been determined.The activation energies are large (9 - 17 kcal/mole) and increase as the size of R or R' increases.The slow exchange permits the direct measurement of acidity differences between pairs of amines using 13C nmr.
- Fraser, Robert R.,Baignee, Alison,Bresse, Monique,Hata, Kazumi
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p. 4195 - 4198
(2007/10/02)
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