1062-99-3Relevant articles and documents
Competitive decay pathways of the radical ions formed by photoinduced electron transfer between quinones and 4,4′-dimethoxydiphenylmethane in acetonitrile
Del Giacco, Tiziana,Baciocchi, Enrico,Lanzalunga, Osvaldo,Elisei, Fausto
, p. 3005 - 3013 (2001)
The reactivity of the cation radical of (4-MeOC6H4)2CH2 photosensitized by 1,4-benzoquinone (BQ), 2,5-dichloro-1,4-benzoquinone (Cl2BQ), and tetrachloro-1,4-benzoquinone (chloranil, CA) was investigated in acetonitrile. The main photoreaction products obtained by steady-state irradiation were identified to be: (4-MeOC6H4)2CHOC6H4OH, sensitized by BQ; (4MeOC6H4)2CHCl, sensitized by Cl2BQ; (4-MeOC6H4)2CHOH, sensitized by CA. The mechanism of their formation was investigated by nanosecond laser flash photolysis that allowed transient species (radical ions, neutral radicals, and ions) to be detected and characterized in terms of absorption spectra, formation quantum yields, and decay rate constants. For all systems, the interaction between the triplet quinone (Q) and (4-MeOC6H4)2CH2 produced the corresponding radical ions (quantum yield φ ≥ 0.72) which mainly decay by back electron transfer processes. Less efficient reaction routes for the radical ions Q.- and (4-MeOC6H4)2CH2.+ were also: i) the proton-transfer process with the formation of the radical (4MeOC6H4)2CH. by use of Cl2BQ; ii) the hydrogen-transfer process with the formation of the cation (4-MeOC6H4)2CH+ in the case of CA. Instead, BQ sensitized a much higher yield of BQH. and (4MeOC6H4)2CH., mainly by the direct interaction of triplet BQ with (4MeOC6H4)2CH2. It was also shown that the presence of salts decreases significantly the rate of the back electron transfer process and enhances the quantum yields of formation of the neutral radicals and ions when Cl2BQ and CA are used, respectively. The behavior of BQ.-, Cl2BQ.-, and CA.- appears to be mainly determined by the Mulliken charges on the oxygen atom obtained from quantum mechanical calculations with the model B3LYP/6-311G(d,p). Spin densities seem to be much less important.
Iodine-catalyzed transformation of aryl-substituted alcohols under solvent-free and highly concentrated reaction conditions
Jereb, Marjan,Vra?i?, Dejan
, p. 747 - 762 (2018/01/17)
Iodine-catalyzed transformations of alcohols under solvent-free reaction conditions (SFRC) and under highly concentrated reaction conditions (HCRC) in the presence of various solvents were studied in order to gain insight into the behavior of the reaction intermediates under these conditions. Dimerization, dehydration and substitution were the three types of transformations observed with benzylic alcohols. Dimerization and substitution reactions were predominant in the case of primary- and secondary alcohols, whereas dehydration prevailed in the case of tertiary alcohols. The relative reactivity of substituted 1-phenylethanols in I2-catalyzed dimerization under SFRC provided a good Hammett plot ρ+ = -2.8 (r2 = 0.98), suggesting the presence of electron-deficient intermediates with a certain degree of developed charge in the rate-determining step.
Iodine-catalyzed disproportionation of aryl-substituted ethers under solvent-free reaction conditions
Jereb, Marjan,Vrazic, Dejan
, p. 1978 - 1999 (2013/05/22)
Iodine was demonstrated to be an efficient catalyst for disproportionation of aryl-substituted ethers under solvent-free reaction conditions. Variously substituted 1,1,1′,1′-tetraaryldimethyl ethers were transformed into the corresponding diarylketone and diarylmethane derivatives. I 2-catalyzed transformation of 4-methoxyphenyl substituted ethers yielded mono- and dialkylated Friedel-Crafts products as well. Treatment of trityl alkyl and trityl benzyl ethers with a catalytic amount of iodine produced triphenylmethane and the corresponding aldehydes and ketones. The electron-donating substituents facilitated the reaction, while the electron-withdrawing groups retarded it; the difference in reactivity is not very high. Such an observation may be in favour of hydride transfer, predominantly from the less electron rich side of the ether with more stable carbocation formation. With the isotopic studies it was established that a substantial portion of the C-H bond scission took place in the rate-determining step, while the carbonyl oxygen atom originated from the starting ether, and not from the air. The transformation took place under air and under argon, and HI was not a functioning catalyst.
Anomalous reactivity of radical cations produced by photosensitized oxidation of 4-methoxybenzyl alcohol derivatives: Role of the sensitizer
Del Giacco, Tiziana,Faltoni, Annalisa,Elisei, Fausto
, p. 200 - 210 (2008/09/20)
Steady-state and nanosecond laser flash photolysis measurements of 4-methoxybenzyl alcohol (1a), 4-methoxy-α-methylbenzyl alcohol (1b), 4,4′-dimethoxydiphenylmethanol (1c) and 4-methoxy-α,α′- dimethylbenzyl alcohol (1d) were carried out in air-equilibrated CH 2Cl2 and CH3CN solutions, in the presence of 9,10-dicyanoanthracene (DCA) and N-methylquinolinium tetrafluoroborate (NMQ +BF4-) as sensitizers. In particular, steady-state irradiation with DCA produced carbonyl compounds and, with NMQ +BF4-, carbonyl compounds, ethers (substrates 1a-c) and styrene (substrate 1d) while time-resolved investigations gave evidence of charged species produced upon irradiation. The effect of solvent polarity on the reactivity was investigated; in the case of DCA, the reactivity increased with the solvent polarity, while the opposite was obtained when NMQ+BF4- was used. Quantum mechanical calculations at semiempirical (INDO/1-CI) and DFT (B3LYP/6-311G(d)) levels were used to support transient assignments and to obtain the charge and spin density distributions, respectively. The different photooxidation mechanisms operative with the neutral and charged sensitizer were rationalized in terms of the reactivity of free and complexed radical cations, respectively. the Owner Societies.
