48 research outputs found
Distinguishing between abstraction and addition as the first step in the reaction of a nitroxyl radical with cyclohexene
An unambiguous method for distinguishing between abstraction-addition and addition-abstraction mechanisms (and mixtures thereof) in the reaction of 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl with a specifically deuterated cyclohexene, 1,2-dideuteriocyclohexene, is demonstrated.Peer reviewed: YesNRC publication: Ye
Mechanisms of reaction of aminoxyl (nitroxide), iminoxyl, and imidoxyl radicals with alkenes and evidence that in the presence of lead tetraacetate, N-hydroxyphthalimide reacts with alkenes by both radical and nonradical mechanisms
1,2-Dideuterio-cyclohexene, 1,2-dideuterio-cyclooctene, and trans-3,4-dideuterio-hex-3-ene were reacted with three >NO. radicals: 4-hydroxyTempo, di-tert-butyliminoxyl, both used as the actual radicals, and phthalimide-N-oxyl (PINO) generated from N-hydroxyphthalimide (NHPI) by its reaction with tert-alkoxyl radicals (t-RO.) and with lead tetraacetate. In all cases, except the NHPI/Pb(OAc)4 system, only mono >NO.-substituted alkenes were produced. The 2H NMR spectra imply that 88-92% of monoadducts were formed by the initial abstraction of an allylic H-atom, followed by capture of the allylic radical by a second >NO., while the remaining 12-8% appear to be formed by an initial addition of >NO. to the double bond followed by H-atom abstraction by a second >NO.. A substantial and sometimes the major product formed with the NHPI/Pb(OAc)4 system has two PINO moieties added across the double bond. Since such diadducts are not formed with the NHPI/t-RO. system, a heterolytic mechanism is proposed, analogous to that known for the Pb(OAc)4-induced acetoxylation of alkenes. A detailed analysis of the NHPI/Pb(OAc) 4/alkene products indicates that monosubstitution occurs by both homolytic and heterolytic processes. \ua9 2005 American Chemical Society.Peer reviewed: YesNRC publication: Ye
Maximizing the yield of water-soluble cellouronic acid sodium salt with high carboxyl content by 4-acetamide-TEMPO mediated oxidation of parenchyma cellulose from bagasse pith
The source of conductivity and proton dynamics study in TEMPO-oxidized cellulose doped with various heterocyclic molecules
New N-aryloxy-phthalimide derivatives. Synthesis, physico-chemical properties, and QSPR studies
Influence of different oxidizing systems on cellulose oxidation level: introduced groups versus degradation model
Bleached cotton yarns were oxidized by
potassium periodate and TEMPO-mediated oxidation
systems, with different concentrations and treatment
time, to obtain aldehyde and carboxyl oxy-cellulose
with different oxidation levels. Oxidized celluloses
were further treated with sodium chlorite to convert
the created aldehyde to carboxyl groups. The oxidation
level was evaluated by assessing the amount of
introduced aldehyde and carboxyl groups, the changes
in surface morphology and incurred degradation.
Functional groups were determined by titration methods,
while surface morphology by FTIR-ATR and
SEM analyses. Degradation was analysed by determining
the mechanical properties, degree of polymerization,
alkali solubility and whiteness stability of the
cotton samples. It has been established that a properly
selected oxidation system, with appropriate working
conditions, can provide satisfactory results for achieving
low, medium and extensively oxidized celluloses,
with a defined degradation profile. For a short
treatment time, a higher oxidation level could be
achieved by potassium periodate and TEMPO-mediated
oxidation with sodium bromide, while by using
the bromide-free TEMPO system a longer time was
necessary to reach the same oxidation level. The type
and oxidation level of the obtained oxy-celluloses
influenced their mechanical properties, degree of
polymerization, alkaline and whiteness stability.
Low-level oxidized celluloses are suitable for producing
stable, long-lasting materials with high added
value, while extensively oxidized ones are more
appropriate for developing disposable products