Aerobic oxidation of 1,3,5-triisopropylbenzene using N-hydroxyphthalimide (NHPI) as key catalyst

The first systematic study on the aerobic oxidation of 1,3,5-triisopropylbenzene was examined by the use of N-hydroxyphthalimide (NHPI) as a key catalyst. It was found that 1,3,5-triisopropylbenzene was efficiently oxidized with O₂ in the presence of a catalytic amount of NHPI and azobisisobutyronitrile (AIBN) at 75 °C. Upon treatment of the resulting products with sulfuric acid followed by acetic anhydride led to 5-acetoxy-1,3-diisopropylbenzene and 3,5-diacetoxy-1-isopropylbenzene as major products and a small amount of 1,3,5-triacetoxybenzene. When t-butylperoxypivalate (BPP) was employed as a radical initiator, the oxidation could be achieved in good yield even at 50 °C. This oxidation provides a facile method for preparing phenol derivatives bearing an isopropyl moiety, which can be used as pharmaceutical starting materials.     

Synthesis of 6-hydroxy-2-naphthoic acid from 2,6-diisopropylnaphthalene using NHPI as a key catalyst

A new strategy to 6-hydroxy-2-naphthoic acid (HNPA) and 4-hydroxybenzoic acid from 2,6-diisopropylnaphthalene and p-cymene, respectively, was developed using the NHPI-catalyzed aerobic oxidation as a principal reaction. 2,6-Diisopropylnaphthalene was oxidized by the oxidation with O₂ (1 atm) by NHPI (10 mol %) combined with Co(OAc)₂ (0.5 mol %) to give 6-acetyl-2-isopropylnaphthalene, which then was converted to 6-isopropyl-2-naphthoic acid under O₂ (1 atm) in the presence of Co(OAc)₂ (0.5 mol %) and Mn(OAc)₂ (0.5 mol %). Esterification of the resulting acid followed by the aerobic oxidation produced methyl 6-hydroxy-2-naphthoate whose hydrolysis led to the desired HNPA. An alternative route involves the oxidation of 6-acetyl-2-isopropylnaphthalene to 6-acetyl-2-naphthol on which subsequent oxidation and deacetylation gave HNPA. This method was successfully extended to the synthesis of 4-hydroxybenzoic acid from p-cymene.     

Synthesis of aromatic aldehydes by aerobic oxidation of hydroaromatic compounds and diarylalkanes using N-hydroxyphthalimide (NHPI) as a key catalyst

Aerobic oxidation of hydroaromatic compounds and diarylalkanes by N-hydroxyphthalimide (NHPI) under mild conditions afforded the corresponding hydroperoxides in high selectivity. Treatment of the resulting hydroperoxides with sulfuric acid followed by neutralization by a base resulted in phenol and aromatic aldehydes in high selectivity. This method provides a convenient synthetic route to aldehydes involving an aromatic moiety.     

Highly efficient and metal-free oxidation of olefins by molecular oxygen under mild conditions

Highly efficient and metal-free aerobic oxidations of cyclohexene and styrene were successfully performed under mild conditions in the presence of 1,4-diamino-2,3-dichloro-anthraquinone and N-hydroxyphthalimide. When cyclohexene was oxidized, an 89% conversion and 71% selectivity for 2-cyclohexen-1-one was obtained under 0.3 MPa at 80 °C for 5 h. In the oxidation of styrene, a 77% conversion and 69% selectivity for benzaldehyde was obtained for 10 h. Furthermore, more olefins were efficiently oxidized to corresponding oxygenated products under mild conditions. All kinds of factors that affected cyclohexene oxidation were well investigated, and the possible reaction mechanism was provided.     

Binuclear complexes for aerobic oxidation of primary alcohols and carbohydrates

The influence of electron-donating and electron-accepting properties of three pentadentate ligands was determined in connection with the aerobic oxidation ability of the corresponding binuclear copper(II) complexes for benzyl and allyl alcohols; additionally, the catalytic performance of their palladium and platinum analogs was characterized under comparable conditions. Quantitative aerobic oxidation of benzyl alcohol at 40 °C was achieved with a binuclear copper(II) complex—TEMPO catalyst in 2.5 h, while the regioselective aerobic oxidation of underivatized methyl-β-d-glucopyranoside was accomplished in about 35% yield at 60 °C after 24 h.     

N-羟基邻苯二甲酰亚胺及其类似物催化下的分子氧氧化反应

本文综述了近年来N-羟基邻苯二甲酰亚胺（NHPI）及其类似物催化下分子氧氧化的各种反应,并对它们的催化机理作了简要介绍。NHPI与过渡金属离子组成的催化体系能高效的催化乙烷氧化为乙酸、环烷烃氧化为二元羧酸、甲苯氧化为苯甲酸、烯烃氧化为环氧化物、炔烃氧化为炔酮、酰胺氧化为酰亚胺;NHPI单独使用能催化金刚烷发生氧化羰基化反应、催化氧化醇制取过氧化氢;NHPI与有机助催化剂如：偶氮二异丁腈、溴化季铵盐、蒽醌、醇等也能催化分子氧氧化反应。     

Facile hydroboration of (Z)-1-trimethylsilyl-1-alkenes with dichloroborane-dioxane complex: An easy access to gem-dimetalloalkanes containing boron and silicon

(Z)-1-trimethylsilyl-1-alkenes easily prepared by the hydroboration of the corresponding 1-trimethylsilyl-1-alkynes followed by protonolysis with acetic acid, readily react with dichloroborane-dioxane complex in dichloromethane for 6 h. The resulting solution is then treated with 1,3-propane diol in dichloromethane at 0 °C for half an hour to provide the corresponding gem-dimetalloalkanes containing boron and silicon. These α-trimethylsilylalkylboronate esters are purified by vacuum distillation in high yields (72-84%) and the structures of these novel intermediates are further confirmed by selective oxidation with alkaline hydrogen peroxide to provide the corresponding alcohols containing α-trimethylsilyl group in 78-88% isolated yields.     

Oxidations by the system ‘hydrogen peroxide-[Mn2L2O3][PF6]2 (L=1,4,7-trimethyl-1,4,7-triazacyclononane)-carboxylic acid’. Part 10: Co-catalytic effect of different carboxylic acids in the oxidation of cyclohexane, cyclohexanol, and acetone

Hydrogen peroxide oxidation of cyclohexane in acetonitrile solution catalyzed by the dinuclear manganese(IV) complex [LMn(O)₃MnL](PF₆)₂ (L=1,4,7-trimethyl-1,4,7-triazacyclononane, TMTACN) at 25 °C in the presence of a carboxylic acid affords cyclohexyl hydroperoxide as well as cyclohexanone and cyclohexanol. A kinetic study of the reactions with participation of three acids (acetic acid, oxalic acid, and pyrazine-2,3-dicarboxylic acid, 2,3-PDCA) led to the following general scheme. In the first stage, the catalyst precursor forms an adduct. The equilibrium constants K₁ calculated for acetic acid, oxalic acid, and 2,3-PDCA were 127±8, (7±2)×10⁴, and 1250±50 M⁻¹, respectively. The same kinetic scheme was applied for the cyclohexanol oxidation catalyzed by the complex in the presence of oxalic acid. The oxidation of cyclohexane in water solution using oxalic acid as a co-catalyst gave cyclohexanol and cyclohexanone, which were rapidly transformed into a mixture of over-oxidation products. In the oxidation of cyclohexanol to cyclohexanone, varying the concentrations of the reactants and the reaction time we were able to find optimal conditions and to obtain the cyclohexanone in 94% yield based on the starting cyclohexanol. Oxidation of acetone to acetic acid by the system containing oxalic acid was also studied.     

Convenient synthesis of porphine from β-tetra(tert-butyl)porphyrin

β-Tetra(tert-butyl)porphyrin was prepared from 2-dimethylaminomethyl-4-tert-butylpyrrole and converted into porphine, the mother compound of porphyrins, in 64% yield. The dealkylation smoothly proceeded in aqueous sulfuric acid over 15 min at 190 °C under nitrogen.     

Aerobic oxidation of trimethylbenzenes catalyzed by N,N′,N″-trihydroxyisocyanuric acid (THICA) as a key catalyst

The oxidation of trimethylbenzenes was examined with air or O₂ using N,N′,N″-trihydroxyisocyanuric acid (THICA) as a key catalyst. Thus, 1,2,3-, 1,2,4-, and 1,3,5-trimethylbenzenes under air (20 atm) in the presence of THICA (5 mol %), Co(OAc)₂ (0.5 mol %), Mn(OAc)₂, and ZrO(OAc)₂ at 150 °C were oxidized to the corresponding benzenetricarboxylic acids in good yields (81-97%). In the aerobic oxidation of 1,2,4-trimethylbenzene by the THICA/Co(II)/Mn(II) system, remarkable acceleration was observed by adding a very small amount of ZrO(OAc)₂ to the reaction system to form 1,2,4-benzenetricarboxylic acid in excellent yield (97%). In contrast, no considerable addition effect was observed in the oxidation of 1,3,5-trimethylbenzene. This aerobic oxidation by the present catalytic system provides an economical and environmentally benign direct method to benzenetricarboxylic acids, which are very important polymer materials.     

Thermal degradation of polyaniline films prepared in solutions of strong and weak acids and in water - FTIR and Raman spectroscopic studies

Polyaniline (PANI) films were prepared in situ on silicon windows during the oxidation of aniline with ammonium peroxydisulfate in aqueous solutions of strong (0.1 M sulfuric) or weak (0.4 M acetic) acid or without any acid. In solutions of sulfuric acid, a granular PANI is produced, in solutions of weak acids or without any acid, PANI nanotubes are obtained. The thermal stability and structural variation of the corresponding films produced on silicon windows during treatment at 80 °C for three months were studied by FTIR and Raman spectroscopies. The morphology of the films is preserved during the degradation but the molecular structure changes. The results indicate that the spectral changes correspond to deprotonation, oxidation and chemical crosslinking reactions. The films of PANI salts loose their protonating acid. PANI bases are more stable than the salt forms during thermal ageing. The films obtained in water or in the presence of acetic acid are more stable than those prepared in solutions of sulfuric acid. The protonated structure is more prone to crosslinking reactions than deprotonated one. The molecular structure corresponding to the nanotubular morphology, which contains the crosslinked phenazine- and oxazine-like groups, is more stable than the molecular structure of the granular morphology.     

N-羟基邻苯二甲酰亚胺和二氧化锰高效催化对硝基甲苯氧化

采用N-羟基邻苯二甲酰亚胺(NHPI)和二氧化锰(MnO2)作为催化剂催化对硝基甲苯的氧化反应以制备对硝基苯甲酸;对反应条件进行了优化.结果表明,采用10%(与原料的摩尔比)NHPI和10%(与原料的摩尔比)MnO2作为催化剂,在110℃、氧气压力0.4 MPa下反应4 h,对硝基甲苯的转化率为97%,对硝基苯甲酸的分...     

A novel and efficient synthesis of porphine

meso-Tetra(n-hexyloxycarbonyl)porphyrin was found to be converted into porphine, the mother compound of porphyrins, in a 77% yield when heated in aqueous sulfuric acid at 180 °C over 30 min under an inert atmosphere. The observation demonstrates that the substituted porphyrin serves as a novel and useful precursor for porphine.     

Microwave-assisted combined Mitsunobu reaction-Claisen rearrangement and microwave-assisted phenol oxidation: rapid synthesis of 2,6-disubstituted-1,4-benzoquinone natural products

Microwave irradiation of a phenol, an allylic alcohol, di-isopropyl azodicarboxylate and triphenylphosphine at 220-240 °C for 30 min results in a combined Mitsunobu reaction and Claisen rearrangement to give the rearranged 2-allylphenol. Following the first detailed study of microwave-assisted phenol oxidation, rapid syntheses of the natural products primin and 2-methoxy-6-pentadecyl-1,4-benzoquinone (four reaction steps, total reaction time 1 h) were achieved using this combined Mitsunobu-Claisen strategy in combination with two further microwave-assisted steps (alkene hydrogenation and phenol oxidation).     

An electropolymerized aniline-based fiber coating for solid phase microextraction of phenols from water

An aniline-based polymer was electrochemically prepared and applied as a new fiber coating for solid phase microextraction (SPME) of some priority phenols from water samples. The polyaniline (PANI) film was directly electrodeposited on the platinum wire surface in sulfuric acid solution using cyclic voltammetry (CV) technique. The efficiency of new coating was investigated using a laboratory-made SPME device and gas chromatography with flame ionization detection for the extraction of some phenols from the headspace of aqueous samples. The scanning electron microscopy (SEM) images showed the homogeneity and the porous surface structure of the film. The results obtained proved the ability of this polymer as a suitable SPME fiber coating for trapping the selected phenols. Influential parameters affecting the extraction process were optimized and an extraction time of 50 min at 50 °C gave maximum efficiency, when the aqueous sample was saturated with NaCl and adjusted at pH 2. This new coating can be prepared easily in a reproducible manner and it is rather inexpensive and stable against most of organic solvents. The PANI thickness can be precisely controlled by the number of CV cycles. At the optimum conditions, the R.S.D. for a double distilled water spiked with phenol and chlorophenols at ppb level were 4.8-17% (n = 3) and detection limits for the studied compounds were between 0.69 and 3.7 ng ml⁻¹, except for phenol and 4-chlorophenol. The optimized method was successfully applied to some real-life water samples.     

Selective one-pot synthesis of various phenols from diarylethanes

Various substituted phenols were selectively synthesized by a one-pot reaction through the NHPI-catalyzed aerobic oxidation of 1,1-diarylethanes followed by treatment with dilute sulfuric acid.     

Determination of methanol in o,o-dimethyldithiophosphoric acid (DMDTPA) of technical grade by UV/vis spectrophotometry and by HPLC

Two procedures are proposed in this work for the determination of methanol impurities in o,o-dimethyldithiophosphoric acid (DMDTPA). To avoid possible interferences from the main component, DMDTPA was precipitated in the form of insoluble lead complex. Free Pb(II) ions were eliminated with sulfuric acid and methanol was oxidized to formaldehyde with potassium permanganate in methanesulfonic acid medium. Finally, the excess of oxidizing agent was neutralized with saturated sodium oxalate. The above pretreatment procedure was identical for spectrophotometric assay and for chromatographic determination. In the first case, the solution obtained was treated with Nash reagent to form 3,5-diacetyl-1,4-dihydrolutidine (λ_max = 415 nm). In the calibration range 0.1-1.0% (methanol in DMDTPA), the analytical figures of merit were: R² = 0.9993, quantification limit 0.02% methanol in DMDTPA coefficient of variance (n = 5) for 0.1% and 0.4% methanol respectively 6.7% and 2.4%. Recoveries obtained in the sample fortified with 0.1, 0.2, 0.4% of methanol (in DMDTPA) were in the range 99-105%. For chromatographic procedure, formaldehyde was derivatized with 2,4-dinitrophenylhydrazine and separation was achieved on Luna C18(2) column using the isocratic elution with acetonitrile-water (70:30, v/v) and spectrophotometric detection at 360 nm. In the calibration range 0.05-0.25% (methanol in DMDTPA), R² was always higher than 0.999, the quantification limit was 0.004% and the recoveries in these same fortified samples in the range 98-101%. No statistically significant differences were observed between the results obtained in the analysis of technical grade DMDTPA by the two procedures (ANOVA, p < 0.05)     

Alkane oxidation by the H2O2-NaVO3-H2SO4 system in acetonitrile and water

A simple system is described, which oxidizes saturated hydrocarbons either in acetonitrile or (less efficiently) in water. The system consists of 50% aqueous hydrogen peroxide as an oxidant, sodium metavanadate, NaVO₃, as a catalyst and sulfuric (or oxalic) acid as a co-catalyst. The reactions were carried out at 20-50 °C. In the oxidation of cyclohexane in acetonitrile, the highest yield (37% based on cyclohexane) and turnover number (TON=1700) were attained after 3 h at 50 °C. The corresponding parameters were 16% and 1090 for n-heptane oxidation under the same conditions. The oxidation of higher alkanes, RH, in acetonitrile gives almost exclusively the corresponding alkyl hydroperoxides, ROOH. Light alkanes (n-butane, propane, ethane, and methane) have been also oxygenated by the system under consideration. The highest TON (200) was attained for ethane and the highest yield (19%) was obtained in the case of n-butane. The selectivity parameters measured for the oxidation of linear and branched alkanes are low, the reaction with cis- and trans-1,2-dimethylcyclohexanes is not stereoselective. These facts lead us to conclude that the oxidation occurs with the formation of hydroxyl radicals in the crucial step.     

Aerobic oxidation with N-hydroxyphthalimide catalysts in ionic liquid

N-Hydroxyphthalimide (NHPI)-catalyzed aerobic oxidations in the ionic liquids were examined for the first time. Both NHPI and its ionic derivative, 3-pyridinylmethyl-N-hydroxyphthalimide (Py-NHPI), were found to have better performance in the ionic liquid than in the conventional organic solvents for the aerobic oxidation of N-alkylamides to imides. On the other hand, Py-NHPI was found to be a much better catalyst than NHPI for the aerobic oxidation of benzylic compounds in the ionic liquid.     

Alkane Oxidation with Molecular Oxygen Using a New Efficient Catalytic System: N-Hydroxyphthalimide (NHPI) Combined with Co(acac)(n)() (n = 2 or 3)

A novel class of catalysts for alkane oxidation with molecular oxygen was examined. N-Hydroxyphthalimide (NHPI) combined with Co(acac)(n)() (n = 2 or 3) was found to be an efficient catalytic system for the aerobic oxidation of cycloalkanes and alkylbenzenes under mild conditions. Cycloalkanes were successfully oxidized with molecular oxygen in the presence of a catalytic amount of NHPI and Co(acac)(2) in acetic acid at 100 degrees C to give the corresponding cycloalkanones and dicarboxylic acids. Alkylbenzenes were also oxidized with dioxygen using this catalytic system. For example, toluene was converted into benzoic acid in excellent yield under these conditions. Ethyl- and butylbenzenes were selectively oxidized at their alpha-positions to form the corresponding ketones, acetophenone, and 1-phenyl-1-butanone, respectively, in good yields. A key intermediate in this oxidation is believed to be the phthalimide N-oxyl radical generated from NHPI and molecular oxygen using a Co(II) species. The isotope effect (k(H)/k(D)) in the oxidation of ethylbenzene and ethylbenzene-d(10) with dioxygen using NHPI/Co(acac)(2) was 3.8.