Selective Oxidation Of Secondary Alcohols Research Articles

Taming Bromine Azide for Use in Organic Solvents─Radical Bromoazidations and Alcohol Oxidations.

The formation of bromine azide from the bisazidobromate(I) anion or alternatively from Zhdankin's reagent, using a phosphonium bromide salt as a common starting point, is reported. After homolytic cleavage in the presence of alkenes or alcohols either 1,2-functionalization or alternatively the selective oxidation of secondary alcohols in the presence of primary alcohols occur. The scopes and limitations of the use of BrN3 are covered.

Chemoselective Electrochemical Oxidation of Secondary Alcohols Using a Recyclable Chloride-Based Mediator

AbstractSelective anodic oxidation of alcohols in the presence of other functional groups can be accomplished by using nitroxyl radical mediators. However, the electrochemical chemoselective oxidation of secondary alcohols in the presence of primary alcohols is an unsolved issue. Herein, we report an electrochemical procedure for the selective oxidation of secondary alcohols by using an inexpensive chloride salt that acts as a redox mediator and supporting electrolyte. The method is based on the controlled anodic generation of active chlorine species, which selectively oxidize secondary alcohols to the corresponding ketones when primary hydroxy groups are present. The method has been demonstrated for a variety of substrates. The corresponding ketones were obtained in good to excellent yields. Moreover, the chloride salt can be easily recovered by a simple extraction procedure for reuse, rendering the method highly sustainable.

Catalytic oxidation of alcohols using Fe-bTAML and NaClO: Comparing the reactivity of Fe(V)O and Fe(IV)O intermediates

We demonstrate the selective oxidation of secondary alcohols and activated primary alcohols to their corresponding aldehydes or ketones using Fe-bTAML as the catalyst and sodium hypochlorite (NaClO) as the oxidant. Good to excellent yields of 80%–99% for the carbonyl compounds and turnover numbers up to ∼500 was obtained with this catalytic system. The reactions are clean, performed under mild conditions (air, room temperature) and yielded sodium chloride as the only by-product. The yield and turnover number were dependent on the pH of the reaction and this difference was attributed to the different reactive intermediates that was formed at pH 7 and pH 12 (FeV(O) and FeIV(O) respectively). Reactions involving the FeV(O) intermediate oxidize secondary alcohols more efficiently than its FeIV(O) analog. This trend was reversed for the oxidation of activated primary alcohols where reactions involving FeIV(O) afforded much higher TON’s. This reactivity trend can be explained from the differences in bond dissociation energy (BDE) of their corresponding one electron reduced species ([FeIV-OH], ∼99 kcal/mol; [FeIII-OH], ∼83 kcal/mol) as well as their relative stabilities in the solvent during reaction. This catalytic system was found to be unsuitable for nonconjugated primary alcohol due to the formation of the inactive FeIV(OMe) intermediate after one catalytic cycle.

Ag2O Nanoparticles-Doped Manganese Immobilized on Graphene Nanocomposites for Aerial Oxidation of Secondary Alcohols

Ag2O nanoparticles-doped MnO2 decorated on different percentages of highly reduced graphene oxide (HRG) nanocomposites, i.e., (X%)HRG/MnO2–(1%)Ag2O (where X = 0–7), were fabricated through straight-forward precipitation procedure, and 400 °C calcination, while upon calcination at 300 °C and 500 °C temperatures, it yielded MnCO3 and manganic trioxide (Mn2O3) composites, i.e., [(X%)HRG/MnCO3–(1%)Ag2O] and [(X%)HRG/Mn2O3–(1%)Ag2O], respectively. These nanocomposites have been found to be efficient and very effective heterogeneous catalysts for selective oxidation of secondary alcohols into their respective ketones using O2 as a sole oxidant without adding surfactants or nitrogenous bases. Moreover, a comparative catalytic study was carried out to investigate the catalytic efficiency of the synthesized nanocomposites for the aerobic oxidation of 1-phenylethanol to acetophenone as a substrate reaction. Effects of several factors were systematically studied. The as-prepared nanocomposites were characterized by TGA, XRD, SEM, EDX, HRTEM, BET, Raman, and FTIR. The catalyst with structure (5%)HRG/MnO2–(1%)Ag2O showed outstanding specific activity (16.0 mmol/g·h) with complete conversion of 1-phenylethanol and >99% acetophenone selectivity within short period (25 min). It is found that the effectiveness of the catalyst has been greatly improved after using graphene support. A broad range of alcohols have selectively transformed to desired products with 100% convertibility and no over-oxidation products have been detected. The recycling test of (5%)HRG/MnO2–(1%)Ag2O catalyst for oxidation of 1-phenylethanol suggested no obvious decrease in its performance and selectivity even after five subsequent runs.

Chemoselective Continuous Ru-Catalyzed Hydrogen-Transfer Oppenauer-Type Oxidation of Secondary Alcohols

A continuous flow method for the selective oxidation of secondary alcohols is reported. The method is based on an Oppenauer-type ruthenium-catalyzed hydrogen-transfer process that uses acetone as both solvent and oxidant. The process utilizes a low loading (1 mol%) of the commercially available ruthenium catalyst [Ru(p-cymene)Cl2]2 and triethylamine as a base and can be successfully applied to a range of different substrates, with a good level of functional group tolerance.

A rapid and convenient oxidation of secondary alcohols

A rapid (normally 20 min to 2 h) and selective oxidation of secondary alcohols to ketones can be achieved using 0.4 equivalents trichloroisocyanuric acid and 1.2 equivalents pyridine at room temperature in ethyl acetate. A likely mechanism for the reaction is proposed.

Synthesis, Characterization, and Relative Study on the Catalytic Activity of Zinc Oxide Nanoparticles Doped MnCO3, –MnO2, and –Mn2O3 Nanocomposites for Aerial Oxidation of Alcohols

Zinc oxide nanoparticles doped manganese carbonate catalysts [X% ZnOx–MnCO3] (where X = 0–7) were prepared via a facile and straightforward coprecipitation procedure, which upon different calcination treatments yields different manganese oxides, that is, [X% ZnOx–MnO2] and [X% ZnOx–Mn2O3]. A comparative catalytic study was conducted to evaluate the catalytic efficiency between carbonates and oxides for the selective oxidation of secondary alcohols to corresponding ketones using molecular oxygen as a green oxidizing agent without using any additives or bases. The prepared catalysts were characterized by different techniques such as SEM, EDX, XRD, TEM, TGA, BET, and FTIR spectroscopy. The 1% ZnOx–MnCO3 calcined at 300°C exhibited the best catalytic performance and possessed highest surface area, suggesting that the calcination temperature and surface area play a significant role in the alcohol oxidation. The 1% ZnOx–MnCO3 catalyst exhibited superior catalytic performance and selectivity in the aerial oxidation of 1-phenylethanol, where 100% alcohol conversion and more than 99% product selectivity were obtained in only 5 min with superior specific activity (48 mmol·g−1·h−1) and 390.6 turnover frequency (TOF). The specific activity obtained is the highest so far (to the best of our knowledge) compared to the catalysts already reported in the literatures used for the oxidation of 1-phenylethanol. It was found that ZnOx nanoparticles play an essential role in enhancing the catalytic efficiency for the selective oxidation of alcohols. The scope of the oxidation process is extended to different types of alcohols. A variety of primary, benzylic, aliphatic, allylic, and heteroaromatic alcohols were selectively oxidized into their corresponding carbonyls with 100% convertibility without overoxidation to the carboxylic acids under base-free conditions.

Rapid and Selective Oxidation of Alcohols in Deep Eutectic Solvent

Deep eutectic solvent (DES) has been identified as a highly efficient catalyst and reaction medium, for rapid oxidation of alcohols to aldehydes and ketones using N-bromosuccinimide as the oxidant. This mild procedure utilizes biodegradable and readily available choline chloride/urea-based DES for high-yield oxidation at room temperature or at 60 °C. Selective oxidation of secondary alcohols in the presence of primary alcohols can be achieved. Furthermore, the catalyst-free synthesis of 2-bromoacetophenone was achieved through DES-mediated tandem oxidation and bromination of alcohol.

Cooperative metal-ligand assisted E/Z isomerization and cyano activation at Cu(II) and Co(II) complexes of arylhydrazones of active methylene nitriles.

New (E/Z)-2-(2-(1-cyano-2-methoxy-2-oxoethylidene)hydrazinyl)benzoic acid (H2L(4)) and known sodium 2-(2-(dicyanomethylene)hydrazinyl)benzenesulfonate (NaHL(1)), 2-(2-(dicyano-methylene)hydrazinyl)benzoic acid (H2L(2)), and sodium (E/Z)-2-(2-(1-cyano-2-methoxy-2-oxoethylidene)hydrazinyl)benzenesulfonate (NaHL(3)) were used in the template synthesis of a series of Cu(II) and Co(II) complexes [Cu(H2O)2L(1a)]·H2O (1), [Cu(H2O)(3-pyon)L(1b)]·H2O (2), [Cu(H2O)(4-pyon)L(1b)] (3), [Co(H2O)((CH3)2NCHO)(μ-L(2a))]2·(CH3)2NCHO (4), [Cu3(μ3-OH)(NO3)(CH3OH)(μ2-X)3(μ2-HL(3))] (5), [Cu(H2O)(py)L(3)]·H2O (6), [Cu(H2O)2(μ-L(4))]6·6H2O (7), [Cu(2-cnpy(b))2(L(1b))2]·2H2O (8), [Cu(2-cnpy(a))2(L(1a))2]·2H2O (9), and [Cu(H2O)(4-cnpy)(L(1a))2] (10), where 3-pyon = 1-(pyridin-3-yl)ethanone, 4-pyon = 1-(pyridin-4-yl)ethanone, py = pyridine, HX = syn-2-pyridinealdoxime, 4-cnpy = 4-cyanopyridine; 2-cnpy(a), 2-cnpy(b), L(1a), L(1b), L(2a) are the ligands derived from nucleophilic attack of methanol (a) or water (b) on a cyano group of 2-cyanopyridine (2-cnpy), L(1) or L(2), respectively, giving the corresponding iminoesters (2-cnpy(a), L(1a) or L(2a)) or carboxamides (2-cnpy(b) or L(1b)). An auxiliary ligand, namely syn-2-pyridinealdoxime or pyridine, acting cooperatively with the metal ion (Cu(II) in this case), induced an E/Z isomerization of the H2L(4) ligand; the E- and Z-isomers were isolated separately and fully characterized (compounds 9 and 10, respectively). A one-pot activation of nitrile groups in different molecules was achieved in the syntheses of 8 and 9. Complexes 1-10 are catalyst precursors for the solvent-free microwave (MW)-assisted selective oxidation of secondary alcohols to the corresponding ketones, with typical yields in the 29-99% range (TOFs up to 4.94 × 10(3) h(-1)) after 30 min of MW irradiation.

Selective liquid phase oxidation of secondary alcohols into ketones by tert-butyl hydroperoxide on nano-fibrous Ag-OMS-2 catalyst

Selective oxidation of secondary alcohols to ketones using tert-butyl hydroperoxide was accomplished over active and reusable silver incorporated octahedral molecular sieve (Ag-OMS-2) catalyst. Different loadings of Ag (5–15% w/w) were incorporated in OMS-2 by the precipitation method among which 15% w/w Ag-OMS-2 was found to be the best. The catalyst was fully characterized. It possesses nanofibrous crystalline structure with high surface area. Oxidation of 1-phenylethanol, as a model compound, was conducted at 75°C into acetophenone by tert-butyl hydroperoxide over 15% w/w Ag-OMS-2. Effects of various parameters were investigated in detail. A mathematical model is built to interpret the experimental data and develop mechanism. The reaction is intrinsically kinetically controlled and follows second order kinetics. The modeling will help reactor design and scale-up. As an extension to the studies, oxidation of various aliphatic and aromatic alcohols was studied in the liquid phase over 15% w/w Ag-OMS-2 catalyst under optimized conditions. The catalyst is reusable up-to five runs without any loss in catalytic activity. The results obtained are novel.

Manganese‐Catalyzed Selective Oxidation of Aliphatic CH groups and Secondary Alcohols to Ketones with Hydrogen Peroxide

An efficient and simple method for selective oxidation of secondary alcohols and oxidation of alkanes to ketones is reported. An in situ prepared catalyst is employed based on manganese(II) salts, pyridine-2-carboxylic acid, and butanedione, which provides good-to-excellent conversions and yields with high turnover numbers (up to 10 000) with H2 O2 as oxidant at ambient temperatures. In substrates bearing multiple alcohol groups, secondary alcohols are converted to ketones selectively and, in general, benzyl C-H oxidation proceeds in preference to aliphatic C-H oxidation.

ChemInform Abstract: Lacunary Derivative [HPW9O34]8‐ as Reusable and Active Catalyst for Alcohol Oxidation in Water.

AbstractAn environmentally friendly and efficient procedure for the selective oxidation of secondary alcohols to corresponding ketones is developed.

ChemInform Abstract: Chromium-Substituted Aluminophosphate-5: A Recyclable Catalyst for the Selective Oxidation of Secondary Alcohols.

Isomorphous substitution of aluminium by chromium in the aluminophosphate-5 framework by hydrothermal synthesis leads to an active, selective and recyclable catalyst for the liquid phase oxidation of secondary alcohols, to the corresponding ketones, using moleular oxygen or tert-butyl hydroperoxide as the terminal oxidant.

Oppenauer Oxidation of Secondary Alcohols with 1,1,1-Trifluoroacetone as Hydride Acceptor

1,1,1-Trifluoroacetone (2a) reacts as a hydride-acceptor in the Oppenauer oxidation of secondary alcohols (1) in the presence of diethylethoxyaluminum. The oxidant allows for selective oxidation of secondary alcohols in the presence of primary alcohols.

A Simple, Efficient and Recyclable Copper(II) Acetylacetonate Catalytic System for Oxidation of sec-Alcohols in Ionic Liquid

A selective oxidation of secondary alcohols to the corresponding ketones in room temperature ionic liquid was achieved by using copper acetylacetonate/tert-butylhydroperoxide system. The catalytic system can be recycled and reused for five runs without any significant loss of catalytic activity and products are obtained in excellent yield.

Highly Efficient and Selective Oxidation of Secondary Alcohols to Ketones under Organic Solvent and Transition Metal Free Conditions.

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Highly efficient and selective oxidation of secondary alcohols to ketones under organic solvent and transition metal free conditions

The aqueous HBr/H 2 O 2 was found to be highly efficient and green catalytic system for the selective oxidation of the secondary alcohols to ketones in excellent yields under organic solvent free conditions. The results of the oxidation of the secondary alcohols with solid alternatives of the aqueous hydrogen peroxide like SPC or SPB are also described.

Efficient aerobic oxidation of alcohols in water catalysed by microgel-stabilised metal nanoclusters

Noble metal nanoclusters stabilised by N , N -dimethylacrylamide-based soluble cross-linked polymers (microgels) have been prepared and tested as catalysts in the selective oxidation of secondary alcohols to the corresponding carbonyl compounds with molecular oxygen in water. Pd nanoclusters turned out to be superior catalysts compared with nanoclusters of other noble metals, such as Pt or Au; they are efficient (TOF up to 70 h −1) and easily recoverable by simple extraction of the reaction product from the aqueous phase.

IBX/ n-Bu 4NBr/CH 2Cl 2–H 2O: a new mild system for selective oxidation of secondary alcohols

A new alternative system for the chemoselective oxidation of secondary hydroxyl group to ketone with IBX/ n-Bu 4NBr in CH 2Cl 2–H 2O has been developed. Under the reaction conditions, the secondary hydroxyl group was highly chemoselectively oxidized to the corresponding ketone, in moderate to good yields at rt, in the presence of primary hydroxyl group within the same molecule.

Oxidation of alcohols over Fe 3+/montmorillonite-K10 using hydrogen peroxide

Oxidation of various primary and secondary alcohols is studied in liquid phase at atmospheric pressure over Fe 3+/montmorillonite-K10 catalyst prepared by ion-exchange method at a pH of 4 in an environmentally friendly protocol using hydrogen peroxide. The catalyst and the method are found to be suitable for the selective oxidation of secondary alcohols to the corresponding ketones. Aromatic alcohols form mainly secondary or over oxidation products. Presence of CH 3 group at the OH bearing carbon is deleterious to the oxidation. The catalyst activity increases with increase in reaction time due to the slow activation of the catalyst. The reaction mechanism is expected to involve the intermediate formation of binuclear, peroxide ion-bridged iron complex by reaction of iron and the activated peroxide followed by oxygen transfer to the alcohol. The catalyst is also found to be easily separable and recyclable.