138616-16-7Relevant articles and documents
Addition versus oxygenation of alkylbenzenes with 10-methylacridinium ion via photoinduced electron transfer
Fujita, Morifumi,Ishida, Akito,Takamuku, Setsuo,Fukuzumi, Shunichi
, p. 8566 - 8574 (2007/10/03)
Addition of alkylbenzenes with 10-methylacridinium ion (AcrH+) occurs efficiently under visible light irradiation in deaerated acetonitrile containing H2O to yield 9-alkyl-10-methyl-9,10-dihydroacridine selectively. On the other hand, the photochemical reaction of AcrH+ with alkylbenzenes in the presence of perchloric acid in deaerated acetonitrile yields 10-methyl-9,10-dihydroacridine, accompanied by the oxygenation of alkylbenzenes to the corresponding benzyl alcohols. The photooxygenation of alkylbenzenes occurs also in the presence of oxygen, when AcrH+ acts as an efficient photocatalyst. The studies on the quantum yields and fluorescence quenching of AcrH+ by alkylbenzenes as well as the laser flash photolysis have revealed that the photochemical reactions of AcrH+ with alkylbenzenes in both the absence and presence of oxygen proceed via photoinduced electron transfer from alkylbenzenes to the singlet excited state of AcrH+ to produce alkylbenzene radical cations and 10-methylacridinyl radical (AcrH·). The competition between the deprotonation of alkylbenzene radical cations and the back electron transfer from AcrH· to the radical cations determines the limiting quantum yields. In the absence of oxygen, the coupling of the deprotonated radicals with AcrH· yields the adducts. The photoinduced hydride reduction of AcrH+ in the presence of perchloric acid proceeds via the protonation of acridinyl radical produced by the photoinduced electron transfer from alkylbenzenes. In the presence of oxygen, however, the deprotonated radicals are trapped efficiently by oxygen to give the corresponding peroxyl radicals which are reduced by the back electron transfer from AcrH· to regenerate AcrH+, followed by the protonation to yield the corresponding hydroperoxide. The ratios of the deprotonation reactivity from different alkyl groups of alkylbenzene radical cations were determined from both the intra- and intermolecular competitions of the deprotonation from two alkyl groups of alkylbenzene radical cations. The reactivity of the deprotonation from alkylbenzene radical cations increases generally in the order methyl ethyl isopropyl. The strong stereoelectronic effects on the deprotonation from isopropyl group of alkylbenzene radical cations appear in the case of the o-methyl isomer.
Electron-transfer oxidation of 9-substituted 10-methyl-9,10-dihydroacridines. Cleavage of the C-H vs C-C bond of the radical cations
Fukuzumi, Shonichi,Tokuda, Yoshihiro,Kitano, Toshiaki,Okamoto, Toshihiko,Otera, Junzo
, p. 8960 - 8968 (2007/10/02)
Electron-transfer oxidation of various 9-substituted 10-methyl-9,10-dihydroacridines (AcrHR) by Fe(ClO4)3 and [Fe(phen)3](PF6)3 (phen = 1,10-phenanthroline) results in cleavage of the C(9)-H or C(9)-C bond of AcrHR?+ depending on the substituent R. Transient electronic absorption spectra as well as electron spin resonance (ESR) spectra of AcrHR?+ have been detected by using a stopped-flow spectrophotometer and a rapid mixing flow ESR technique, respectively. The hyperfine splitting constants (hfs) are determined by comparing the observed ESR spectra with those from the computer simulation. Comparison of the hfs values with those expected from the molecular orbital calculations indicates the structural change of AcrHR?+ with the substituent R, which is reflected in the selectivity of the C-H vs C-C bond cleavage of AcrHR?+ depending on the substituent R. The decay rates of AcrHR?+ obey the mixture of first-order and second-order kinetics due to the deprotonation (or the C-C bond cleavage) and disproportionation reactions, respectively. Both the first-order and bimolecular second-order decay rate constants of AcrHR?+ are reported. The first-order decay rate constant for the deprotonation of AcrHR?+ by the C-H bond cleavage decreases with the substitution in order R = primary > secondary > tertiary alkyl groups, while the first-order decay due to the C-C bond cleavage becomes dominant with tertiary alkyl groups. The one-electron oxidation potentials of various AcrHR have been determined directly by applying fast cyclic voltammetry. The pKa values of AcrHR?+ (R = H and Me) have also been evaluated by analyzing the dependence of the first-order deprotonation rate constants on the concentrations of HClO4.
