Cesare Rol

Carbon silicon bond cleavage in the oxidation of benzylic silanes by cerium(IV) ammonium nitrate

Abstract Benzyltrimethylsilanes react with cerium(IV) ammonium nitrate in AcOH to give products of C-Si cleavage (benzyl nitrate and acetate), under very mild conditions and in quantitative yields. The reaction rate is very sensitive to the nature of the ring substituents (???= −5.4), which clearly suggests the operation of one electron transfer mechanism. x

TiO2-catalyzed photooxygenation of methylaromatic compounds in the presence of Ag2SO4 in CH3CN

Methylaromatic compounds have been photooxygenated in CH3CN, at room temperature, in the presence of TiO2 and Ag2SO4, to form benzaldehydes and, in some cases, benzoic acids, in yields up to 50%

The role of nitrate free radicals in the photochemical side-chain nitrooxylation of alkylbenzenes by cerium(IV) ammonium nitrate in acetonitrile

Abstract It is suggested that the reactive species in the CAN-induced photochemical side-chain nitrooxylation of alkylbenzenes is the nitrate radical, which probably acts as one-electron oxidant.

Photo-oxidation of some benzylic alcohols sensitized by colloidal TiO2 in CH3CN. A kinetic mechanistic study through quantum yield determinations

The quantum yields (ϕobs) relating to the colloidal TiO2-sensitized photo-oxidation of ring methoxy-substituted benzylic alcohols (D) were determined. The true quantum yields (ϕ0) were obtained from a Langmuir–Hinshelwood isotherm treatment of ϕobs at different [D]. In the light of the suggested photo-oxidation mechanism, an equation was deduced where ϕ0 is expressed as a function of the electron transfer (ket), back electron transfer (k−et) and benzylic deprotonation (kp) rate constants. In particular, the lower ϕ0 value of 3-CH3O-vs 4-CH3O-benzyl alcohol (1, with lower Ep) should principally depend on the difference in ket, while the decrease in ϕ0 on going from alcohol 1 to the α-methyl derivative (4) should be due to the difference in kp (stereoelectronic effect). The adsorption equilibrium constants under irradiation (KD) were also obtained from the above equation and the values are similar for the considered substrates, except for 4. In fact, this substrate shows a lower KD value, probably because of the steric hindrance of the methyl group to the OH adsorption (preferential site) on TiO2. Finally, both the inter- and intramolecular deuterium isotope effect (kH/kD = 1.8 and 1.6, respectively) are consistent with a kinetically significant Cα—H bond breaking following the electron-transfer step. Copyright

Photochemical nitrooxylation of methylbenzenes by cerium(IV) ammonium nitrate in acetonitrile

Abstract The photochemical reaction of substituted toluenes with CAN in CH 3 CN leads to good yields of benzyl nitrates under very mild conditions.

Oxidation of aromatic compounds by metal ions. Part 8. Structure and selectivity in anodic and metal ion oxidations of polyalkylbenzenes

Positional selectivity and the partition deuterium isotope effect (k/sub H//k/sub D/) have been determined in the chemical (with cerium(IV) ammonium nitrate (CAN), cobalt(III) acetate, and N-bromosuccinimide (NBS)) and electro-chemical side-chain oxidation of alkyl aromatics by using 5-R-hemimellitenes (R = H, t-Bu) and 1,3-dimethyl-2-(trideuterimethyl)-5-tert-butylbenzene as the substrates. Considering also the already available data for isodurene, it has been found that the positional selectivity is strongly influenced by the substrate structure in the anodic and CAN-promoted oxidations, both reactions exhibiting a very similar pattern. In conrast, Co(OAc)/sub 3/ selectivities do not correlate with those of the anodic oxidation but with the selectivities of the side-chain bromination promoted by NBS. These results have been interpreted by suggesting that, as in the anodic oxidations, CAN-induced reactions involve first the formation of a radical cation intermediate which then loses a proton to give a benzylic free radical in the selectivity-determining step. The data for Co/sup III/ would instead suggest a mechanism involving a hydrogen atom transfer, but this conclusion cannot yet be considered definitive. No simple correlation exists between selectivity data and the k/sub H//k/sub D/ values.

The photoelectrochemical oxidation of benzyl derivatives at Ti/TiO2 anodes. A mechanistic approach through current efficiency and density measurementst

The mechanism of the photoelectrochemical sensitised oxidation of 4- and 3-methoxybenzyl alcohols and silanes at Ti/TiO2 ‘anatase’ and ‘rutile’ photoanodes has been investigated through current efficiency and density measurements.

One electron oxidations of benzyl and 2-phenylethyl phenyl ethers: the fate of the intermediate radical cations

Abstract The one electron oxidations of benzyl phenyl ether ( 1 ), 2-phenylethyl phenyl ether ( 2 ) and 2-(4-methoxyphenyl)ethyl phenyl ether ( 3 ) promoted (a) by cerium(IV) ammonium nitrate (CAN) in AcOH, (b) electrochemically in AcOH-MeCN/AcOK and (c) photochemically in MeCN, in the presence of 9,10-dicyanoanthracene (DCA), have been investigated. With 1 benzaldehyde forms, under all the reaction conditions, accompanied by products of acetoxylation at the phenoxy ring (conditions a and b) or by phenyl benzoate (condition c). The CAN-promoted and the electrochemical oxidation of 2 exclusively lead to substitution at the phenoxy ring, whereas only-side-chain attack at the benzylic carbon occurs in all of the reactions of 3 , with formation of 4-methoxybenzaldehyde and products of side-chain oxidation. Phenyl 4-methoxybenzoate is also formed (conditions b and c). However, when the electrochemical oxidation is carried out in the absence of AcOK, only a product of intramolecular ring closure forms. These results allow one to draw some interesting conclusion on the competition between the various reaction pathways available to the cation radicals which are the first formed reaction intermediates in these one electron processes.

Cerium (IV) ammonium nitrate catalyzed photochemical autoxidation of alkylbenzenes

Abstract The autoxidation of alkylbenzenes can be promoted photochemically in the presence of catalytic amounts of cerim (IV) ammonium nitrate (CAN) under very mild conditions, the efficiency of the process being significantly increased by added acids. It is suggested that the reaction is promoted by NO 3 , radicals formed in the light induced decomposition of CAN and that Ce(III) may be reoxidized to Ce(IV) by benzylperoxy radicals.

Dark adsorption equilibrium constants of benzylic derivatives on TiO2 and their implications in the sensitised heterogeneous photooxidation

The “dark” adsorption equilibrium constants of different series of benzylic derivatives on TiO2 suspended in CH3CN were determined through a Langmuir-type adsorption isotherm. In particular, the similarity of the K values of differently ring substituted α-OH derivatives within the same series confirms the previously suggested preferential adsorption of the hydroxyl group (at the oxygen atom) with respect to the aromatic moiety.