The reaction between NO3' and polyalkylbenzenes was studied using 308-nm laser flash photolysis of cerium- (IV) ammonium nitrate in the presence of the alkylbenzenes in acetonitrile solution. For all benzenes, with the exception of monoalkylbenzenes and 0- and m-xylene, the reaction with NO3* was found to yield the corresponding radical cations and to proceed in an apparently straightforward bimolecular manner. For monoalkylbenzenes and 0- and m-xylene, radicals were seen which are derived from the parents by formal loss of H' from the side chain of the aromatic. This reaction proceeds via a complex between the aromatic and NO,' with the decomposition of the complex being rate determining at higher concentrations of aromatic (rate constants for decomposition between 6 X IO5 and 4 X lo7 s-l). In the complex, electron transfer from the aromatic to NO3* is suggested to be concerted with deprotonation of the incipient radical cation. Formation of a complex between NO3* and aromatic is likely even in those cases where radical cations are observed, with the assumption that in these cases the complex decomposition rate is 16 X lo7 s-l.
One-electron oxidation of alkylbenzenes in acetonitrile by photochemically produced nitrate radical: evidence for an inner-sphere mechanism
DEL GIACCO, Tiziana;
1993
Abstract
The reaction between NO3' and polyalkylbenzenes was studied using 308-nm laser flash photolysis of cerium- (IV) ammonium nitrate in the presence of the alkylbenzenes in acetonitrile solution. For all benzenes, with the exception of monoalkylbenzenes and 0- and m-xylene, the reaction with NO3* was found to yield the corresponding radical cations and to proceed in an apparently straightforward bimolecular manner. For monoalkylbenzenes and 0- and m-xylene, radicals were seen which are derived from the parents by formal loss of H' from the side chain of the aromatic. This reaction proceeds via a complex between the aromatic and NO,' with the decomposition of the complex being rate determining at higher concentrations of aromatic (rate constants for decomposition between 6 X IO5 and 4 X lo7 s-l). In the complex, electron transfer from the aromatic to NO3* is suggested to be concerted with deprotonation of the incipient radical cation. Formation of a complex between NO3* and aromatic is likely even in those cases where radical cations are observed, with the assumption that in these cases the complex decomposition rate is 16 X lo7 s-l.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
