On the loss of a benzyl radical from the molecular ion of α,ω -dibenzyloxyalkanes : Evidence for a benzyl cation transfer in an SNi-type reaction,revealed by a simultaneous D- and 18O-labelling

The molecular ions of the title compounds appear to lose a benzyl radical, which must be due to the presence of two benzyloxy groups, as benzylalkyl ethers do not exhibit such an expulsion upon electron impact. The results of the partition of the labels deuterium and ¹⁸O in the ions m/e 107 (protonated benzaldehyde) and [M-benzyl-benzaldehyde]⁺ put forward evidence that this process is initiated by a successive migration of a benzylic H atom to the opposite ether function and transfer of the benzyl cation from this protonated O atom to the uncharged O atom in an S_Ni-type reaction (cf Scheme 5).     

Mechanism of Thermal Toluene Autoxidation

Aerobic oxidation of toluene (PhCH₃) is investigated by complementary experimental and theoretical methodologies. Whereas the reaction of the chain‐carrying benzylperoxyl radicals with the substrate produces predominantly benzyl hydroperoxide, benzyl alcohol and benzaldehyde originate mainly from subsequent propagation of the hydroperoxide product. Nevertheless, a significant fraction of benzaldehyde is also produced in primary PhCH₃ propagation, presumably via proton rather than hydrogen transfer. An equimolar amount of benzyl alcohol, together with benzoic acid, is additionally produced in the tertiary propagation of PhCHO with benzylperoxyl radicals. The “hot” oxy radicals generated in this step can also abstract aromatic hydrogen atoms from PhCH₃, and this results in production of cresols, known inhibitors of radical‐chain reactions. The very fast benzyl peroxyl‐initiated co‐oxidation of benzyl alcohol generates HO₂^. radicals, along with benzaldehyde. This reaction also causes a decrease in the overall oxidation rate, due to the fast chain‐terminating reaction of HO₂^. with the benzylperoxyl radicals, which causes a loss of chain carriers. Moreover, due to the fast equilibrium PhCH₂OOH+HO₂^.?PhCH₂OO^.+H₂O₂, and the much lower reactivity of H₂O₂ compared to PhCH₂OOH, the fast co‐oxidation of the alcohol means that HO₂^. gradually takes over the role of benzylperoxyl as principal chain carrier. This drastically changes the autoxidation mechanism and, among other things, causes a sharp decrease in the hydroperoxide yield.     

Recent discoveries on the structure of iodine(iii) reagents and their use in cross-nucleophile coupling

This perspective article discusses structural features of iodine(iii) compounds as a prelude to presenting their use as umpolung reagents, in particular as pertains to their ability to promote the selective coupling of two nucleophilic species via 2e⁻ oxidation.

This perspective article discusses structural features of iodine(iii) compounds as a prelude to presenting their use as umpolung reagents, to promote the selective coupling of two nucleophilic species via 2e⁻ oxidation.     

Iodine/DMSO promoted oxidation of benzylic Csp3–H bonds to diketones – A mechanistic investigation

This article describes a mechanistic investigation into the I₂/DMSO mediated benzylic C_sp³–H oxidation of an α-methylene ketone. The electron paramagnetic resonance (EPR) spectrum centred at g = 2.0011 supports the involvement of iodine and benzylic radicals, as the α-iodinated compound 2-iodo-1,2-diphenylethanone was isolated as a key reactive intermediate. The oxidation reaction relies, primarily, on DMSO as a source of oxygen in benzil, proven by the reaction of benzyl phenyl ketone with diphenyl sulfoxide (DPSO).     

Ag/SBA-15低温气相选择性催化氧化苯甲醇合成苯甲醛

以SBA-15为载体,采用浸渍法制备了不同Ag含量的Ag/SBA-15,通过N₂吸附-脱附、X射线衍射、扫描电子显微镜、高分辨透射电子显微镜、X射线光电子能谱和电感耦合等离子体质谱对催化剂进行了表征。将Ag/SBA-15用于苯甲醇气相选择性催化氧化合成苯甲醛,研究了反应条件对转化率和选择性的影响。结果表明,Ag/SBA-15具有均一的一维孔道结构、较厚的孔壁（3-5 nm）及较大的比表面积（411-541 m²/g）,其规整纳米空间的限域作用使一定负载量的Ag以纳米尺寸均匀分散于介孔SBA-15孔道内,增加了活性组分的比表面积。亲核性氧物种从Ag到SBA-15表面的氧溢流,提高了低温下Ag/SBA-15对苯甲醇气相选择性氧化合成苯甲醛的催化性能。5.3% Ag/SBA-15中的Ag粒径为5-6 nm,且均匀分散于载体孔道中,反应温度为220℃时,苯甲醇转化率为87%,苯甲醛选择性为95%;240℃时,苯甲醇转化率和苯甲醛选择性分别高达94%和97%;并在240-300℃范围内,其催化活性和选择性保持不变,表现出了良好的温度耐受能力。催化剂经活化再生可以连续使用40 h,选择性基本保持不变。     

Reagents and synthetic methods—40 : Halosilanes/chromium trioxide as efficient oxidizing reagents

Synthetic utility of halosilanes-chromium trioxide reagents as excellent new oxidizing agents is described. They are highly efficient for the oxidation of alcohols to carbonyl compounds, for the oxidative coupling of mercaptans into disulfides and for a mild cleavage of oximes to carbonyl compounds. Chlorotrimethylsilane-chromium trioxide has been shown to be an efficient oxidizing agent for the conversion of arylmethanes to benzaldehydes. The reagent is applied to the oxidative cleavage of some benzyl esters. A mild procedure for the iodination of organic compounds by means of in situ generated iodonium species from this reagent and molecular iodine is also described.     

Reactions of dioxygen with benzylnickel complexes

The benzyl complexes Ni(X)(CH₂C₆H₅)(PCy₃) (X = Cl, CN; Cy = cyclohexyl) react with molecular oxygen to give benzaldehyde and benzyl alcohol as main oxidation products. The ratio of the two products is strongly dependent on the nature of X and is also influenced by the solvent and the temperature. Isotopic labelling and mass spectra show that the hydrogen atoms necessary for the formation of the benzyl alcohol are supplied by the phosphine ligands. Isolation and characterization of the chloride complex by conventional spectroscopic techniques (IR, ¹H ³¹P NMR, visible spectra) provide evidence in favour of a η³-τ-benzyl structure for the compound.     

Biomimetic oxidation of N-nitrosodibenzylamine with molecular oxygen catalysed by chemical cytochrome P-450 in AOT reverse micelles

Moderate yields of benzaldehyde, benzyl alcohol and benzylamine are obtained by the biomimetic oxidation of N-nitrosodibenzylamine with molecular oxygen catalysed by water soluble anionic manganese(III) 5,10,15,20-tetraphenylporphyrin acetate/sodium dithionite/methylene blue in aerosol-OT (AOT) reverse micelles, under phase transfer conditions with AOT concentration higher than 10⁻³M. The formation of α-hydroxy-N-nitrosodibenzylamine and its decomposition products, benzaldehyde and benzyl alcohol in reverse micellar systems are governed by the ratio of water and AOT, pH and other changes in the microenvirpnment.     

A new square planar mononuclear Mn complex for catalytic epoxidation of stilbene

The manganese(III) complex (2) with a diamide ligand has been synthesized. This complex was found to catalyze both the epoxidation of (Z)- and (E)-stilbene with high conversion and the oxidation of benzyl alcohol to benzaldehyde.     

Oxidation of benzyl alcohol by novel peripherally and non-peripherally modular C2-symmetric diol substituted cobalt (II) phthalocyanines

In this study, a modular ligand structure was designed by altering the binding position of the phenyl group at backbone of hydrobenzoin. A series of regio isomeric substituted phthalonitriles derived from this modular C₂-symmetric ligand was synthesized and characterized. Then, eight cobalt (II) phthalocyanines (CoPc) were obtained from the reaction of phthalonitrile derivatives with cobalt (II) chloride. The catalytic activities of synthesized cobalt (II) phthalocyanines were tested for benzyl alcohol oxidation in acetonitrile using tert-butylhydroperoxide as the oxygen source and in the presence of N-bromosuccinimide as an additive at 80 °C for 5 hr of the reaction. In this sense, the effect of substrate to catalyst ratio and oxidant to catalyst ratio have been studied in detail for getting the highest benzaldehyde selectivity (up to 83%). The effect of structural design of substituents at peripheral or non-peripheral positions of phthalocyanine skeleton on the catalytic activity performance of cobalt (II) phthalocyanines in benzyl alcohol oxidation was also clarified. All newly synthesized compounds are characterized by FT-IR, ¹H NMR, IR, UV–Vis and MALDI-TOF MS spectral data.     

Kinetics and mechanism of benzyl <Emphasis Type="Italic">para</Emphasis>-chlorophenyl ketone oxidation

The oxidation of benzyl para-chlorophenyl ketone in chlorobenzene at 100°C occurs through the formation of short chains. Non-peroxide reaction products (1-(4-chlorophenyl)-2-hydroxy-2-phenyl-1-ethanone, para-chlorobenzyl, benzaldehyde, and para-chlorobenzoic acid) are formed not only by the transformation of hydroperoxide (1-(4-chlorophenyl)-2-hydroxy-2-phenyl-1-ethanone) but also (or solely) through the recombination of α-ketoperoxyl radicals with or without chain termination. α-Hydroperoxide decomposes predominantly through a heterolytic route to form para-chlorobenzoic acid and benzaldehyde. Benzaldehyde and 1-(4-chlorophenyl)-2-hydroxy-2-phenyl-1-ethanone undergo radical chain oxidation in the reaction medium to form benzoic acid (benzaldehyde), para-chlorobenzyl, and benzoic and para-chlorobenzoic acids (1-(4-chlorophenyl)-2-hydroxy-2-phenyl-1-ethanone). The homolytic decomposition of α-hydroperoxy ketone and α-hydroxy-α-hydroperoxy ketone causes the self-acceleration of the process and affords 1-(4-chlorophenyl)-2-hydroxy-2-phenyl-1-ethanone or, to a lesser extent, benzaldehyde and para-chlorobenzoic acid (α-hydroperoxy ketone). para-Chlorobenzoic acid substantially accelerates the heterolytic decomposition of α-hydroxy-α-hydroperoxy ketone and the oxidation of benzyl para-chlorophenyl ketone with peroxy acids to ester according to the Baeyer-Villiger mechanism. The rate constants of the main steps of the process and kinetic parameters are calculated by solving the inverse kinetic problem.     

Radical-Pair Formation in Hydrocarbon (Aut)Oxidation

The reaction profiles for the uni- and bimolecular decomposition of benzyl hydroperoxide have been studied in the context of initiation reactions for the (aut)oxidation of hydrocarbons. The unimolecular dissociation of benzyl hydroperoxide was found to proceed through the formation of a hydrogen-bonded radical-pair minimum located +181 kJ mol⁻¹ above the hydroperoxide substrate and around 15 kJ mol⁻¹ below the separated radical products. The reaction of toluene with benzyl hydroperoxide proceeds such that O−O bond homolysis is coupled with a C−H bond abstraction event in a single kinetic step. The enthalpic barrier of this molecule-induced radical formation (MIRF) process is significantly lower than that of the unimolecular O−O bond cleavage. The same type of reaction is also possible in the self-reaction between two benzyl hydroperoxide molecules forming benzyloxyl and hydroxyl radical pairs along with benzaldehyde and water as co-products. In the product complexes formed in these MIRF reactions, both radicals connect to a centrally placed water molecule through hydrogen-bonding interactions.     

Catalytic wet air oxidation of aromatic compounds: degradation in molybdovanadophosphoric polyoxometalates micellar system under room temperature conditions

Catalytic wet air oxidation process, enable to eliminate organic pollutants with non toxic by-product formation, was investigated in micellar system under room condition. Degradation of a series of aromatic compounds, including aromatic hydrocarbons, benzyl alcohol, benzaldehyde, benzoic acid, and some N-containing compounds was carried out based on molybdovanadophosphoric polyoxometalates [(C₁₆H₃₃)N(CH₃)₃]_3+x PV _x Mo_12?x O₄₀ (x = 1, 2, 3) catalysts and surfactants. Outstanding results (60–96 % degradation efficiencies) were achieved for most of the tested substrates. And the POM micellar catalysts have an excellent stability and can be used as heterogeneous catalysts for about six times.     

Studies on kinetics and thermodynamics of oxidation of 3,4,5-trimethoxy benzaldehyde,benzaldehyde and N,N-dimethylamino benzaldehyde by tetraethylammonium bromochromate in dimethyl formamide and acetic acid mixture

The oxidation of 3,4,5-trimethoxy benzaldehyde (TMBA), benzaldehyde (BA) and dimethylamino benzaldehyde (DMABA) in N,N-dimethyl formamide (DMF) by tetraethylammonium bromochromate (TEABC) resulted in the formation of the corresponding acids. The reaction is first order with respect to both TEABC and the aldehydes. The reaction is catalyzed by toluene-p-sulfonic acid (p-TsOH). The hydrogen ion dependence has the form: k_obs = a + b [H⁺]. The reaction has been studied in different percentage of DMF–acetic acid mixture. The effect of dielectric constant of the medium indicates the reaction to be of ion–dipole type. Various thermodynamic parameters for the oxidation have been reported and discussed along with the validity of isokinetic relationship. Reason for high rate in the case of oxidation of N,N-dimethylamino benzaldehyde is also described. A mechanism involving formation of a chromate ester intermediate in the slow step has been proposed.     

Rotating-disc electrode studies of the anodic oxidation of iodide in concentrated iodine + iodide solutions

The anodic oxidation of iodide on platinum in concentrated iodine + iodide solutions has been investigated using a rotating disc electrode. The conventional limiting diffusion current, which is produced by the diffusion of iodide ions towards the electrode, was not observed due to the formation of an iodine film on the electrode. On the other hand, the steady-state anodic current after a current/time transient is the genuine limiting diffusion current in the anodic oxidation due to diffusion of iodine species from the electrode surface towards the bulk solution. Thus, the dissolution-diffusion control mechanism of the iodine film is confirmed. This is interesting as a typical example of an anodic process in a redox system governed by diffusion of the anodic product species from the electrode surface towards the bulk solution. When an iodine film is formed on the electrode, the maximum driving force of the iodine species is Δm_I2,max, which is defined as the extent of unsaturation of the iodine, and the limiting current of the anodic oxidation of iodide is always directly proportional to Δm_I2,max, regardless of the forms of iodine species in the solution, which may be I₂, I⁻₃, i₅⁻, etc. δm_I2,max is clearly determined by the solution composition and temperature, and it is different in definition and value from the usual degree of unsaturation of iodine.     

A Copper(II) Schiff base complex immobilized onto SBA-15 silica for selective oxidation of benzyl alcohol

A copper(II) Schiff base complex has been immobilized onto SBA-15 silica through a stepwise procedure and tested as an oxidation catalyst. BET surface area, total pore volume and average pore width of the SBA-15 all decrease after stepwise modification of SBA-15, while the structure of the support remains intact. The molar ratio of Cu²⁺/Schiff base is ca. 1/2 in the synthesized material. Catalytic tests showed that the supported copper complex catalyzes the oxidation of benzyl alcohol with 30 % conversion and 89 % selectivity to benzaldehyde when water is used as the solvent.     

Evidence of protonation during the oxidation of some aryl alcohols by permanganate in perchloric acid medium and mechanism of the oxidation processes

The oxidation of benzyl alcohol and methoxy-, chloro-, and nitro- substituted benzyl alcohols by permanganate has been studied in aqueous and acetic acid medium in presence of perchloric acid. The reaction is first-order in [MnO₄^?] and [XC₆H₄CH₂OH], but the order is complex with respect to [H⁺]. Different thermodynamic parameters have been evaluated. The reaction occurs through the protonation of alcohol in a fast preequilibrium followed by a slow rate-determining oxidation step. A two-electron transfer oxidation step has been suggested for benzyl alcohol and chloro- and nitro- substituted alcohols, while the oxidation of methoxy compounds involves a one-electron transfer via a free-radical mechanism. © 1995 John Wiley & Sons, Inc.     

In alkaline media,Fremy’s salt oxidizes alkanols by a hydrogen atom transfer mechanism

In aqueous alkali, Fremy’s salt (potassium nitrosodisulfonate dimer), homolyses nearly exclusively to the monomer radical anion, nitrosodisulfonate (NDS). In this media, NDS almost quantitatively oxidizes benzyl alcohol (PhCH₂OH) to benzaldehyde (PhCHO), itself being reduced to hydroxylamine disulfonate (HNDS). The reaction is very nearly first-order in [NDS], [alkanol] and in [OH⁻]. However, with progressive addition of HNDS, decay kinetics of NDS gradually deviates from first-order. Ultimately, with sufficient excess of HNDS, the reaction becomes second-order in [NDS]. The consumption ratio, (ΔPhCH₂OH]/Δ[NDS]), is ∼2. PhCD₂OH manifests a large primary kinetic isotope effect (k_H/k_D = 11.6). Substituted benzyl alcohols (RBzCH₂OH) with R-groups withdrawing electron density from the O–H bond accelerated the reaction; those with R-groups donating electron density to the O–H bond retarded the reaction. The conversion of 2-propanol to 2-propanone is much slower compared to that of benzyl alcohol to benzaldehyde. An alpha-H atom transfer mechanism seems logical.     

Persistence Enhancement of a Promising Tick Repellent,Benzyl Isothiocyanate,by Yeast Microcarriers

Phenethyl isothiocyanate isolated from Armoracia rusticana root oil and its derivatives were tested at different doses in a bioassay designed to evaluate repellency against individual Haemaphysalis longicornis nymphs. Among the tested compounds, benzyl isothiocyanate exhibited repellency against H. longicornis nymphs at the lowest dose of 0.00625 mg/cm², followed by phenethyl isothiocyanate (0.0125 mg/cm²) and phenyl isothiocyanate (0.025 mg/cm²). The behavioral responses of H. longicornis nymphs exposed to benzyl isothiocyanate and phenethyl isothiocyanate indicated that the mode of action of these compounds can be mainly attributed to the vapor phase. Encapsulated benzyl isothiocyanate showed repellency up to 120 min post-application at 0.1 mg/cm², whereas pure benzyl isothiocyanate showed repellency up to 60 min post-application at 0.1 mg/cm². The present study suggests that benzyl isothiocyanate is a potential repellent for protection against H. longicornis nymphs, and encapsulation in yeast cells may enhance the repellency effect.     

Effect of water on the functionalization of substituted anisoles with iodine in the presence of F-TEDA-BF4 or hydrogen peroxide

Water was found to be a convenient reaction medium for functionalization of substituted anisoles using iodine in the presence of Selectfluor F-TEDA-BF(4) or hydrogen peroxide as mediators and oxidizers. Two types of functionalization were observed: iodination or oxidation. In the iodination process, two reaction routes were established. In the case of the first route, a high iodine atom economy was achieved for selective and effective iodo functionalization with a stoichiometric ratio of substrate/iodine/(mediator/oxidizer) = 2:1:1.2. An electrophilic iodination reaction process was suggested for this route, with the oxidizer converting the liberated iodide anion to iodine. For the second reaction route, a stoichiometric ratio of substrate/iodine/(mediator/oxidizer) = 1:1:1 and a lower iodine atom economy were observed; in this case, ion radical formation in the first step of the reaction was suggested. Iodine was found to be an effective catalyst for the oxidation of a hydroxy benzyl functional group to benzaldehyde using F-TEDA-BF(4). Water is an effective medium for functionalization of anisole, p-methoxy benzyl alcohol, 1-(4-methoxyphenyl)ethanone, o-dimethoxy benzene, m-dimethoxy benzene, and p-dimethoxy benzene, whereas F-TEDA-BF(4) as a mediator/oxidizer could be replaced by hydrogen peroxide in the case of the functionalization of 1-(4-methoxyphenyl)ethanone, o-dimethoxy benzene, m-dimethoxy benzene, and p-dimethoxy benzene. Water changes the type of transformation of p-methoxy benzyl alcohol.