New direct hydroxylation of benzene with oxygen in the presence of hydrogen over bifunctional ion-exchange resins

Benzene was hydroxylated directly to phenol with oxygen in the presence of hydrogen over Pt/Pd containing acid resins such as Amberlyst and Nafion/silica composites; over the latter materials the best results were obtained.     

纳米钼钒砷杂多酸盐催化苯羟化合成苯酚的研究

过氧化氢作为一种清洁氧化剂,在苯的直接羟化的研究中受到重视。催化剂主要有含钛催化剂系列、含铁催化剂系列和含铜催化剂系列、含钒催化剂系列和其它杂原子催化剂。杂多化合物是一类酸性和氧化性较强的双功能催化剂,但由于受其低比表面积的限制,导致杂多化合物固有的高催化活性在苯的过氧化氢羟化反应中难以充分发挥。本文对所制得的4种过渡金属钼钒砷杂多酸盐纳米催化剂应用于苯的过氧化氢直接羟化合成苯酚的反应,取得了苯酚收率〉50％,选择性〉98％的结果。     

The colour reaction of phenols with the Gibbs reagent

Summary Indophenols and indophenolates resulting from the Gibbs reaction were prepared in the pure state and their properties studied under the conditions used in the photometric reactions. The results obtained and previous investigations allowed determination of the optimum conditions for the photometric procedure. Reproducible results are obtained when 2×10^–6–2×10^–5 M phenol reacts with a 30–501 ratio of the reagent. The optimum pH range is 8.0–10.0, obtained with a suitable buffer. It is not possible to use a glycocoll buffer (quantitative reaction with the reagent) and ammoniacal buffers cannot be used for quantitative purposes. If extraction into an organic solvent is necessary, 1-butanol should be used without previous acidification of the reaction mixture. The first step of the colour reaction is the formation of the corresponding quinoneimine. Two molecules of this reactive species react immediately with one molecule of phenol.

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Zusammenfassung Die Indophenole und Indophenolate, die bei der Reaktion nach Gibbs entstehen, wurden in reinem Zustand dargestellt und ihre Eigenschaften unter den Bedingungen der photometrischen Reaktion studiert. Die erhaltenen Resultate und vorherige Untersuchungen¹ ermöglichten die Definition optimaler Bedingungen für die photometrische Analyse. Reproduzierbare Ergebnisse werden erhalten, wenn 2×10^–6 bis 2×10^–5 M Lösungen von Phenol mit einem 30–501-Überschuß an Reagens umgesetzt werden. Der optimale pH-Bereich ist 8,0 bis 10,0 und wird mit einer geeigneten Pufferlösung eingestellt. Es ist nicht möglich, Glykokoll als Puffer anzuwenden (quantitative Reaktion mit dem Reagens) und ammoniakalische Pufferlösungen können nicht für quantitative Zwecke verwendet werden. Wenn die Extraktion mit einem organischen Lösungsmittel nötig ist, sollte man 1-Butanol ohne vorheriges Ansäuern der Reaktionslösung anwenden. Die erste Reaktionsstufe ist die Bildung von 2,6-Dihalogenchinonimin. Zwei Moleküle dieser reaktiven Verbindung reagieren sofort mit einem Molekül Phenol.

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Dedicated to Prof. RNDr. Arnot Oká, Dr. Sc., member of the Czechoslovak Academy of Science, on the occasion of his 75th birthday.     

The question of the oxidation of α-hydroxypyridine and nicotinic acid by Fenton's reagent

The oxidation of nicotinic acid and -hydroxypyridine by Fenton's reagent (H₂O₂ + Fe⁺⁺) takes place with the decomposition of the pyridine ring to form oxalic acid. In this process, half the label from the -hydroxypyridine passes into one of the oxygen atoms of the oxalic acid and the other oxygen atoms are derived from the hydrogen peroxide. The oxalic acid isolated from the oxidation of the nicotinic acid contains oxygen from the oxidizing agent. The results obtained show that the hydroxylation of the pyridine ring, apparently preceding its decomposition, takes place with the addition of an OH group containing oxygen from the oxidizing agent to the nucleus.     

The Hendrickson reagent and the Mitsunobu reaction: a mechanistic study

The alkoxytriphenylphosphonium ion intermediate of the Mitsunobu reaction can be generated using the Hendrickson reagent, triphenylphosphonium anhydride trifluoromethanesulfonate, 1. Strangely, while the reagent 1 can be used in place of the Mitsunobu reagents (triphenylphosphine and a dialkylazodicarboxylate) for the esterification of primary alcohols, secondary alcohols such as menthol undergo elimination. Evidence is presented to show that this unexpected result is due to the presence of trialkylammonium triflate salts. Such salts lead to a dramatic decrease in the rate of esterification relative to competing elimination. The Mitsunobu esterification of menthol with p-nitrobenzoic acid was re-examined and the occurrence of elimination reported for the first time. The presence of traces of tetrabutylammonium triflate led to a dramatic reduction in the yield of inverted ester and a corresponding increase in the yield of anti elimination product 2-menthene. The mechanism of the Mitsunobu reaction is discussed in the light of the dramatic salt effect on both the rate and outcome of the reaction and the possible involvement of ion pair clustering. In contrast, use of the reagent 1 resulted in syn elimination to give a 1:2 mixture of 2- and 3-menthenes. Finally, 1 and sodium azide can be used to convert a primary alcohol into an azide in high yield. There was no reaction under Mitsunobu conditions.     

The reaction of Lawesson's reagent with trihydroxy compounds

Lawesson's reagent (1a) reacts with pyrogallol (2) to give 1,3,2‐benzodioxaphospholane‐2‐sulfide (3) and with 1,8,9‐trihydroxyanthracene to give 13. The structures of the products have been established either chemically, using methanolysis and methylation, or spectroscopically. © 1999 John Wiley & Sons, Inc. Heteroatom Chem 10: 25–30, 1999     

Catalytic activity of iron-containing polymers in hydroxylation of benzene with hydrogen peroxide

Hydroxylation of benzene with hydrogen peroxide in aqueous acetonitrile at 50°C was studied. The KU-2-8 and KU-1 cation exchangers, and also specially synthesized cation exchangers and phenolformaldehyde resins derived from pyrocatechol and resorcinol, all modified with Fe(III) cations, were used as catalysts. The macrocomplex KU-2-8/Fe³⁺ showed the highest catalytic activity and ensured 32% yield of phenol in 15 min. The formation of phenol depends in a complex fashion on the initial concentration of hydrogen peroxide, content of Fe(III) ions in the polymer, and reaction time.     

Oxygen measurement via phosphorescence: reaction of sodium dithionite with dissolved oxygen

A homemade instrument for the measurement of oxygen concentration in aqueous solutions measures the decay rate of the phosphorescence of a Pd-porphyrin complex (phosphor) dissolved in the solution, which is flashed every 0.1 s with 630 nm light. The concentration of O2 is a linear function of the decay rate. The instrument is used to study the reaction of dithionite (S2O42-) with O2 at 25 degrees C and 37 degrees C. It is found that the ratio of dithionite to oxygen consumed in the reaction is 1.2 +/- 0.2 at 25 degrees C and 1.7 +/- 0.1 at 37 degrees C, suggesting a temperature-dependent stoichiometry. At both temperatures, the initial rate of O2 consumption, -d[O2]/dt, is found to be 1/2 order in S2O42- and first order in O2. This finding is consistent with a previously proposed mechanism: S2O42- <--> 2SO2- comes to a rapid equilibrium, and SO2- reacts with O2 in the rate-determining step.     

The role of chelating ligands and central metals in the oxygen reduction reaction activity: a DFT study

A detailed investigation of oxygen reduction reaction (ORR) catalyzed by various metal chelates has been performed by DFT study. The results indicate that the ORR activity is determined by both of the central metal ions and chelating ligands, among which the former play a key role. For the same ligand, the central metal ions Fe, Co, or Mn give higher ORR activity, while the others almost have no catalytic activity, which is due to the fact that the O₂ and oxygen containing species are either excessively adsorbed (on central Cr) or difficult to be adsorbed on the active sites (for central Zn, Cu, or Ni). Furthermore, the ORR activity for Fe chelates is slightly increased with the increase of ligand field strength, while for other metal chelates there seems to be no clear trends between ligand field strength and ORR activity. The origin of the ORR activity for the studied metal chelates is mainly attributed to the appropriate energy gaps between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO).     

The role of Acid catalysis in the baeyer-villiger reaction. A theoretical study

Quantum mechanical calculations at the B3LYP/6-311+G(d,p) level have examined the overall mechanism of the Baeyer-Villiger (BV) reaction with peroxyacetic acid. A series of reactions that include both the addition step and the subsequent alkyl group migration step included ketones, acetone, t-butyl methyl ketone, acetophenone, cyclohexyl methyl ketone, and cyclohexyl phenyl ketone. The combined data suggested that the first step for addition of the peroxyacetic acid oxidation catalyst to the ketone carbonyl to produce the Criegee or tetrahedral intermediate is rate-limiting and has activation barriers that range from 38 to 41 kcal/mol without the aid of a catalyst. The rate of addition is markedly reduced by the catalytic action of a COOH functionality acting as a donor-acceptor group affecting both its proton transfer to the ketone C═O oxygen in concert with transfer of the OOH proton to the carboxylic acid carbonyl. The second or alkyl group migration step has a much reduced activation barrier, and its rate is not markedly influenced by acid catalysis. The rate of both steps in the BV reaction is greatly influenced by the catalytic action of very strong acids.     

The reaction of triplet nitrenes with oxygen: a computational study

Triplet carbenes react much more rapidly with oxygen than do triplet nitrenes. This trend is explained by DFT and MO calculations. [reaction: see text]     

吸电子基团取代的苯和三氧化硫的反应研究

研究了室温下多种吸电子基团取代的苯和三氧化硫的反应, 用^1H NMR测定反应产物. 苯甲醛, 苯甲酸, 苯磺酸, 二苯砜, 二苯甲酮等均首先得到3-磺酸衍生物, 进一步反应得到少量的3,5-二磺酸衍生物. 苯磺酸还得到少量的3,3'-二磺酸二苯砜和3,5,3'-三磺酸二苯砜. 硝基苯只能进行单磺化反应. 苯甲酸甲酯则得到磺酸取代的苯甲酸和硫酸甲酯     

The constitution of the Grignard reagent: X. Complexes of some organomagnesium compounds with an electron donor in benzene

Measurements of association of RMgBr (R = Me, Et, i-Bu) with one (or slightly more than one) equivalent of an electron donor E (E = Et₃N, Et₂O or THF) revealed that the complexes formed were partly dimeric. Further addition of E causes a decrease in the degree of association.     

析氧反应中催化剂-电解质界面的质子动力学研究

电催化水分解是一种可持续的绿色产氢技术,该技术在工业化的大规模应用急需开发高效稳定的非贵金属催化剂,用于提高析氧反应(OER)的反应速率.研究发现,钙钛矿氧化物是优异的OER催化剂,但是对于发生在催化剂-电解质固液界面上的反应机理仍有争论.目前普遍认为,在OER反应过程中,水分子吸附在金属氧化物催化剂表面的金属活性中心...     

Stereochemical study of the reaction of molecular oxygen with alkylcobaloximes

The insertion of molecular oxygen into the cobaltcarbon bond of a secondary alkylcobaloxime takes place with racemisation.     

Oxygen thermodesorption and role of oxygen diffusion in bulk silver

The activity of V-W-Ti-O catalysts for selective NO reduction by ammonia has been studied as a function of the physicochemical and catalytic properties of the support (TiO₂) produced in a number of ways and of the chemical nature of initial V and W compounds. We have formulated principal requrements for the chemical composition of a raw material for the development of a technology for producing honeycomb monolith catalysts with the necessary properties.