Aerobic Oxidation of Cyclohexane using N‐Hydroxyphthalimide Bearing Fluoroalkyl Chains

The N‐hydroxyphthalimide derivatives, F₁₅‐ and F₁₇‐NHPI, bearing a long fluorinated alkyl chain, were prepared and their catalytic performances were compared with that of the parent compound, N‐hydroxyphthalimide (NHPI). The oxidation of cyclohexane under 10 atm of air in the presence of fluorinated F₁₅‐ or F₁₇‐NHPI, cobalt diacetate [Co(OAc)₂], and manganese diacetate [Mn(OAc)₂] without any solvent at 100 °C afforded a mixture of cyclohexanol and cyclohexanone (K/A oil) as major products along with a small amount of adipic acid. It was found that F₁₅‐ and F₁₇‐NHPI exhibit higher catalytic activity than NHPI for the oxidation of cyclohexane without a solvent. However, for the oxidation in acetic acid all of these catalysts afforded adipic acid as a major product in good yield and the catalytic activity of NHPI in acetic acid was almost the same as those of F₁₅‐ and F₁₇‐NHPI. The oxidation by F₁₅‐ and F₁₇‐NHPI catalysts in trifluorotoluene afforded K/A oil in high selectivity with little formation of adipic acid, while NHPI was a poor catalyst under these conditions, forming K/A oil as well as adipic acid in very low yields. The oxidation in trifluorotoluene by F₁₅‐ and F₁₇‐NHPI catalysts was considerably accelerated by the addition of a small amount of zirconium(IV) acetylacetonate [Zr(acac)₄] to the present catalytic system to afford selectively K/A oil, but no such effect was observed in the NHPI‐catalyzed oxidation in trifluorotoluene.     

Preparation of Hydroperoxides by N‐Hydroxyphthalimide‐Catalyzed Aerobic Oxidation of Alkylbenzenes and Hydroaromatic Compounds and Its Application

An efficient approach to phenols and aldehydes through the formation of hydroperoxides from alkylbenzenes was successfully achieved by aerobic oxidation using N‐hydroxyphthalimide (NHPI) as a catalyst. The oxidation of various alkylbenzenes with dioxygen by NHPI followed by treatment with a Lewis acid or triphenylphosphine led to phenols or aldehydes, respectively, in good yields. For example, the aerobic oxidation of cumene in the presence of a catalytic amount of NHPI at 75 °C and subsequent treatment with H₂SO₄ gave phenol in 77% yield. 1,4‐Dihydroxybenzene (61%) and 4‐isopropylphenol (33%) were obtained from 1,4‐diisopropylbenzene. On the other hand, dibenzyl ether was converted into phenol or benzaldehyde upon treatment of the resulting hydroperoxide with InCl₃ or PPh₃, respectively.     

Highly Efficient Oxidation of Toluene to Benzoic Acid Catalyzed by Manganese Dioxide and <Emphasis Type="Italic">N</Emphasis>-Hydroxyphthalimide

Abstract  

Benzoic acid could be efficiently prepared from aerobic oxidation of toluene using manganese dioxide (MnO₂) and N-hydroxyphthalimide (NHPI) as catalysts. The conditions of oxidation, including temperature, amount of catalyst, dioxygen pressure and reaction time, were studied in details. Thus 94.4% conversion of toluene and 98.4% selectivity of benzoic acid could be obtained at 110 °C under 0.3 MPa for 3 h in the presence of 10 mol% NHPI and 4 mol% MnO₂.     

Metal‐Free: An Efficient and Selective Catalytic Aerobic Oxidation of Hydrocarbons with Oxime and N‐Hydroxyphthalimide

A non‐metal catalytic system consisting of dimethylglyoxime (DMG) and N‐hydroxyphthalimide (NHPI) for the selective oxidation of hydrocarbons with dioxygen is described. The synergistic effect of DMG and NHPI ensures its efficient catalytic ability: 82.1% conversion of ethylbenzene with 94.9% selectivity for acetophenone could be obtained at 80 °C under 0.3 MPa of dioxygen in 10 h. Several hydrocarbons were efficiently oxidized to their corresponding oxygenated products under mild conditions.     

Selective Oxidation of Acetophenones Bearing Various Functional Groups to Benzoic Acid Derivatives with Molecular Oxygen

Acetophenones substituted by alkyl, alkoxy, acetoxy, and halogen groups were selectively oxidized with molecular oxygen to the corresponding benzoic acids by using the N,N′,N′′‐trihydroxyisocyanuric acid (THICA)/cobalt(II) acetate [Co(OAc)₂] and THICA/Co(OAc)₂/manganese(II) acetate [Mn(OAc)₂]. For example, 4‐methylacetophenone was selectively oxidized with molecular oxygen to 4‐acetylbenzoic acid (85%) by THICA/Co(OAc)₂ and to 4‐methylbenzoic acid (93%) by Mn(OAc)₂, while terephthalic acid was obtained in 93% with the THICA/Co(OAc)₂/Mn(OAc)₂ catalytic system. It is interesting that the acetyl group on the aromatic ring is efficiently converted by a very small amount of Mn(OAc)₂ to the corresponding carboxylic acid, and that the present method provides a versatile route to acetylbenzoic acids which are difficult to prepare by conventional methods.     

Innovation of Hydrocarbon Oxidation with Molecular Oxygen and Related Reactions

An innovation of the aerobic oxidation of hydrocarbons through catalytic carbon radical generation under mild conditions was achieved by using N‐hydroxyphthalimide (NHPI) as a key compound. Alkanes were successfully oxidized with O₂ or air to valuable oxygen‐containing compounds such as alcohols, ketones, and dicarboxylic acids by the combined catalytic system of NHPI and a transition metal such as Co or Mn. The NHPI‐catalyzed oxidation of alkylbenzenes with dioxygen could be performed even under normal temperature and pressure of dioxygen. Xylenes and methylpyridines were also converted into phthalic acids and pyridinecarboxylic acids, respectively, in good yields. The present oxidation method was extended to the selective transformations of alcohols to carbonyl compounds and of alkynes to ynones. The epoxidation of alkenes using hydroperoxides or H₂O₂ generated in situ from hydrocarbons or alcohols and O ₂ under the influence of the NHPI was demonstrated and seems to be a useful strategy for industrial applications. The NHPI method is applicable to a wide variety of organic syntheses via carbon radical intermediates. The catalytic carboxylation of alkanes was accomplished by the use of CO and O₂ in the presence of NHPI. In addition, the reactions of alkanes with NO₂ and SO₂ catalyzed by NHPI provided efficient methods for the synthesis of nitroalkanes and sulfonic acids, respectively. A catalytic carbon‐carbon bond forming reaction was achieved by allowing carbon radicals generated in situ from alkanes or alcohols to react with alkenes under mild conditions. 1 Introduction 2 Discovery of NHPI as Carbon Radical Producing Catalyst from Alkanes 2.1 Historical Background 2.2 Catalysis of NHPI in Aerobic Oxidation 3 NHPI‐Catalyzed Aerobic Oxidation 3.1 Oxidation of Benzylic Compounds 3.2 Alkane Oxidations with Molecular Oxygen 3.3 Oxidation of Alkylbenzenes 3.4 Practical Oxidation of Methylpyridines 3.5 Preparation of Acetylenic Ketones via Alkyne Oxidation 3.6 Oxidation of Alcohols 3.7 Selective Oxidation of Sulfides to Sulfoxides 3.8 Production of Hydrogen Peroxide by Aerobic Oxidation of Alcohols 3.9 Epoxidation of Alkenes using Molecular Oxygen as Terminal Oxidant 4 Carboxylation of Alkanes with CO and O₂ 5 Utilization of NO_x in Organic Synthesis 5.1 First Catalytic Nitration of Alkanes using NO₂ 5.2 Reaction of NO with Organic Compounds 6 Sulfoxidation of Alkanes Catalyzed by Vanadium 7 Carbon‐Carbon Bond Forming Reaction via Catalytic Carbon Radicals Generated from Various Organic Compounds Assisted by NHPI 7.1 Oxyalkylation of Alkenes with Alkanes and Dioxygen 7.2 Synthesis of α‐Hydroxy‐γ‐lactones by Addition of α‐Hydroxy Carbon Radicals to Unsaturated Esters 7.3 Hydroxyacylation of Alkenes using 1,3‐Dioxolanes and Dioxygen 8 Conclusions     

Oxidation of 5-hydroxymethylfurfural to 2,5-diformylfuran with molecular oxygen in the presence of N-hydroxyphthalimide

Catalytic system Cu(NO₃)₂/NHPI can be successfully used for the mild oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran with molecular oxygen. The oxidation reaction takes place at 50 °C and 1 atm O₂ and selectively converts the primary hydroxymethyl group of HMF to the aldehyde one. The selective formation of aromatic aldehyde is observed because of the higher rate of hydrogen abstraction from primary alcohols by the phthalimide-N-oxyl radical, as compared to the rate of the hydrogen abstraction from the aldehydes.     

Manganese Dioxide and N‐Hydroxyphthalimide. An Effective Catalytic System for Oxidation of Nitrotoluenes with Molecular Oxygen

The inexpensive manganese dioxide has been proven to be an efficient auxiliary for oxidizing N‐hydroxyphthalimide (NHPI) to form the phthalimide N‐oxyl radical via reduction and reoxidation. The combination of manganese dioxide and NHPI could catalyze effectively the oxidation of nitrotulenes by molecular oxygen. Thus, the oxidation of p‐nitrotoluene with molecular oxygen (0.4 M Pa) in the presence of manganese dioxide (10 mol %) and NHPI (10 mol %) in acetic acid at 110 °C for 4 h proceeded with 97 % conversion, and gave p‐nitrotoluene in 89 % isolated yield.     

Selective oxidation of ethylbenzene by a biomimetic combination: Hemin and N-hydroxyphthalimide (NHPI)

A biomimetic catalytic system consisting of hemin and N-hydroxyphthalimide (NHPI) for the selective oxidation of ethylbenzene with dioxygen is reported. 90.32% conversion of ethylbenzene with 94.30% selectivity for acetophenone (AcPO) can be obtained at 100 °C under 0.3 MPa O₂ for 9 h. Hemin can efficiently decompose in situ formed 1-phenylethyl hydroperoxide (PEHP) with AcPO as the main product.     

A Highly Selective Pd(OAc)<Subscript>2</Subscript>/Pyridine/K<Subscript>2</Subscript>CO<Subscript>3</Subscript> System for Oxidation of Terpenic Alcohols by Dioxygen

Abstract  

Molecular sieves, complex organic bases and radical oxidants are commonly used in alcohols oxidation reactions. In this work, we have evaluated the beneficial effects of addition of K₂CO₃ to Pd(II)-catalyzed oxidation alcohols, which resulted in a remarkable increase in the oxidation reaction rates without selectivity losses. Herein, in a metallic reoxidant-free system, terpenic alcohols (β-citronellol, nerol and geraniol) were selectively converted into respective aldehydes from Pd(II)-catalyzed oxidation reactions in presence of dioxygen. High conversions and selectivities (greater than 90%) were achieved in the presence of the Pd(OAc)₂/K₂CO₃ catalyst and pyridine excess. The exogenous role of others auxiliary anionic and nitrogen compounds was appraised.     

Multi‐Site and Multi‐Ionization of Sn in the Doping of BaTiO3

This article considers the diverse substitutional effects of the Sn cations in the BaTiO₃ lattice and its impact on the electrical conduction as a function of A/B stoichiometry, oxygen partial pressure, and temperature. High‐density specimens were fabricated in the different oxygen partial pressures to control the valence state of Sn ion. Specifically, the nonstoichiometric materials were sintered in a low pO₂ atmosphere (10^?14 atm at 1320°C) and in a high pO₂ atmosphere (10^?0.21 atm at 1320°C), respectively. It is found that Sn occupying the Ti‐site acts as an acceptor dopant, and the electronic conductivity varies from a n‐type to p‐type transition, with increasing oxygen activity as mostly expected. However, there is an unusual case noted with Sn doping the A‐site where the conductivity, σ, is invariant at high pO₂'s, i.e., σ ~  with m ≈ 0 in the high pO₂ regime. The variation of the conductivity is explained by a valence changing of Sn ion from +2 to +3 to +4 with increasing oxygen partial pressure, and we model this data across all conditions within a self‐consistent defect chemistry model.     

Sunlight Induced Oxidative Photoactivation of N‐Hydroxyphthalimide Mediated by Naphthalene Imides

We report the aerobic photoactivation of N‐hydroxyphthlimide (NHPI) to the phthalimido‐N‐oxyl (PINO) radical mediated by naphthalene monoimides (NI) for promoting the selective oxidation of alkylaromatics and allylic compounds to the corresponding hydroperoxides. In the absence of either NI or NHPI no oxidation was observed, meaning that the two molecules operate in a synergistic way. Sunlight as well as artificial UV‐light irradiation was necessary in order to perform the process at low temperature (30–35 °C). EPR spectroscopy confirmed the role of NI and oxygen in promoting the formation of the superoxide radicals O₂^.− which, in turn, increased the concentration of PINO radicals during the UV light irradiation of NI/NHPI mixtures in MeCN. The investigation was extended to NI bearing different substituents on the naphthalene moiety. Finally, the synthesis and application of a unique photocatalyst including the NI and NHPI moieties linked by a suitable spacer was also considered. In this case the photocatalyst showed a substrate‐dependent behaviour with some peculiarities in comparison to the system where NI and NHPI are independent units in the same reacting system. This photocatalytic system paves the way to a non‐thermal, metal‐free approach for C H bond activation towards aerobic oxidation under very mild conditions.

     

Alkoxycarbonylation of 3,3,3‐Trifluoropropyne: an Intriguing Reaction to Prepare Trifluoromethyl‐Substituted Unsaturated Acid Derivatives

The addition of CO and methanol to 3,3,3‐trifluoropropyne is catalysed by Pd(OAc)₂ in the presence of (6‐methylpyrid‐2‐yl)diphenylphosphine and CH₃SO₃H. The main products of the reaction are the methyl esters of 2‐(trifluoromethyl)propenoic acid 1 and of 3‐(trifluoromethyl)propenoic acid 2 (4,4,4‐trifluorobut‐2‐enoic acid). The regioselectivity of the reaction can be controlled to a great extent by a suitable choice of the composition of the catalytic system and the reaction conditions. Thus, 1 can be obtained in 93% yield by using P(CO)=20 atm and high ligand/Pd and acid/Pd ratios. On the other hand, selectivity up to 85% in 2 can be achieved using P(CO)=80 atm and a low ligand/Pd ratio together with a high acid/Pd ratio. The reaction mechanism is also discussed.     

Selective oxidation of p-chlorotoluene with Co(OAc)2/MnSO4/KBr in acetic acid–water medium

Selective oxidation of p-chlorotoluene catalyzed by Co(OAc)₂/MnSO₄/KBr with molecular oxygen has been studied. Acetic acid–water is used as the reaction medium in place of pure acetic acid to avoid the nuisance of acetic acid separation. It is found that when MnSO₄ is used in place of the commonly used Mn(OAc)₂, MnO₂ barely forms and the activity of the composite catalyst greatly enhances. Under the optimized conditions (Co/(Co + Mn) mole ratio 0.2, Br/(Co + Mn) mole ratio 0.3, and reaction temperature 106 °C), 22.4% yield of p-chlorobenzaldehyde was obtained at 33.7% conversion of p-chlorotoluene with 66.6% selectivity.     

Synthesis of 2,5‐Diformylfuran and Furan‐2,5‐Dicarboxylic Acid by Catalytic Air‐Oxidation of 5‐Hydroxymethylfurfural. Unexpectedly Selective Aerobic Oxidation of Benzyl Alcohol to Benzaldehyde with Metal=Bromide Catalysts

The alcohol group of hydroxymethylfurfural (compound 1, HMF) is preferentially oxidized by dioxygen and metal/bromide catalysts [Co/Mn/Br, Co/Mn/Zr/Br; Co/Mn=Br/(Co+Mn) = 1.0 mol/mol] to form the dialdehyde, 2,5‐diformylfuran (compound 2, DFF) in 57% isolated yield. HMF can be also oxidized, via a network of identified intermediates, to the highly insoluble 2,5‐furandicarboxylic acid (compound 5, FDA) in 60% yield. For comparison, benzyl alcohol gives benzaldehyde in 80% using the same catalyst system. Over‐oxidation (to CO₂) of HMF is much higher than that of the benzyl alcohol but can be greatly reduced by increasing catalyst concentration.     

Heterogeneous Palladium Catalysts Applied to the Synthesis of 2‐ and 2,3‐Functionalised Indoles

Heterogeneous palladium catalysts ([Pd(NH₃)₄]²⁺/NaY and [Pd]/SBA‐15) were applied to the synthesis of 2‐functionalised indoles, giving generally high conversions and selectivities (>89% yield) using only 1 mol % [Pd]‐catalyst under standard reaction conditions (polar solvent, 80 °C). For the synthesis of 2,3‐functionalised indoles by cross‐coupling arylation, the [Pd]/SBA‐15 catalyst was found to be particularly interesting, producing the expected compound with =35% yield after 12 days of reaction, which is comparable to the homogeneous catalyst, Pd(OAc)₂ (=48% yield). In the course of the study, the dual reactivity of the indole nucleus was demonstrated: aryl bromides gave clean C C coupling while aryl iodides led to a clean C N coupling.     

CO2‐facilitated transport through poly(N‐vinyl‐γ‐sodium aminobutyrate‐co‐sodium acrylate)/polysulfone composite membranes

Poly(N‐vinyl‐γ‐sodium aminobutyrate‐co‐sodium acrylate) (VSA–SA)/polysulfone (PS) composite membranes were prepared for the separation of CO₂. VSA–SA contained secondary amines and carboxylate ions that could act as carriers for CO₂. At 20°C and 1.06 atm of feed pressure, a VSA–SA/PS composite membrane displayed a pure CO₂ permeation rate of 6.12 × 10^?6 cm³(STP)/cm² s cmHg and a CO₂/CH₄ ideal selectivity of 524.5. In experiments with a mixed gas of 50 vol % CO₂ and 50 vol % CH₄, at 20°C and 1.04 atm of feed pressure, the CO₂ permeation rate was 9.2 × 10^?6 cm³ (STP)/cm² s cmHg, and the selectivity of CO₂/CH₄ was 46.8. Crosslinkages with metal ions were effective for increasing the selectivity. Both the selectivity of CO₂ over CH₄ and the CO₂ permeation rate had a maximum against the carrier concentration. The high CO₂ permeation rate originated from the facilitated transport mechanism, which was confirmed by Fourier transform infrared with attenuated total reflectance techniques. The performance of the membranes prepared in this work had good stability. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 275–282, 2006     

Catalytic synthesis of toluene‐2,4‐diisocyanate from dimethyl carbonate

The process for catalytic synthesis of toluene‐2,4‐diisocyanate (TDI) from dimethyl carbonate (DMC) consists of two steps. Starting from the catalytic reaction between toluene‐2,4‐diamine (TDA) and DMC, dimethyl toluene‐2,4‐dicarbamate (TDC) is formed, and then decomposed to TDI. For the first step, the yield of TDC is 53.5% at a temperature of 250 °C, over Zn(OAc)₂/α–Al₂O₃ catalyst. For the second step, the yield of TDI is 92.6% at temperatures of 250–270 °C and under pressure of 2.7 kPa, over uranyl zinc acetate catalyst, when di‐n‐octyl sebacate(DOS) is used as heat‐carrier, and a mixture of tetrahydrofuran (THF) and nitrobenzene is used as solvent. © 2001 Society of Chemical Industry     

Production of isophthalic acid from m-xylene oxidation under the catalysis of the H3PW12O40/carbon and cobalt catalytic system

Isophthalic acid (IPA) is commercially produced from m-xylene oxidation with the catalysis of the homogeneous Co–Mn–Br catalyst system. In this study, a catalytic system consisting of HPW/C and Co(II) has been put forward to oxidize m-xylene (MX) to IPA. The experimental results prove that the HPW/C and Co catalytic system is capable of catalyzing the oxidation of MX to IPA, which can obtain a higher MX conversion and IPA concentration than the homogeneous H₃PW₁₂O₄₀/Co(OAc)₂/Mn(OAc)₂ catalytic system. The heterogeneous catalytic system is also advantageous over the homogeneous catalytic system in the inhibition of the oxidation of acetic acid and IPA. The optimal amount of phosphotungstic acid supported on carbon is 7.5% (wt). The best dosage of HPW/C is 15 g l⁻¹. The optimum Co(II) concentration in the catalytic system for IPA production is 0.064% (wt). The best HPW/C activation temperature is 220 °C.     

Practical Method for the Rhodium‐Catalyzed Addition of Aryl‐ and Alkenylboronic Acids to Aldehydes

The arylation or alkenylation of aldehydes with boronic acids is conveniently effected by a catalyst system comprising RhCl₃⋅3 H₂O (1 mol %), the sterically hindered imidazolium salt 2 (1 mol %), and a base. The N‐heterocyclic carbene 6 derived from 2 is believed to be the actual ligand to the catalytically active rhodium species formed in situ. The method is compatible with various functional groups in both reaction partners and follows a non‐chelation controlled pathway in additions to the Garner aldehyde 23 .