Ru(PPh3)(OH)-salen complex: a designer catalyst for chemoselective aerobic oxidation of primary alcohols

Based on the analysis of the mechanism of aerobic oxidation of alcohols using Ru(NO)-salen catalyst, we designed a new complex, Ru(PPh₃)(OH)-salen 3, which was proved to be an excellent catalyst for chemoselective aerobic oxidation of primary alcohols to the aldehydes in the presence of secondary alcohols under ambient and non-irradiated conditions. Complex 3 was also successfully applied to the oxidation of 1-phenyl-1,n-diols to the lactols or the n-hydroxy aldehyde. It is of note that selective oxidation of primary alcohols was achieved even in the presence of activated secondary alcohols.     

Photocatalytic oxidation of primary and secondary benzylic alcohols to carbonyl compounds catalyzed by H3PW12O40/SiO2 under an O2 atmosphere

An efficient, selective and green procedure for the photocatalytic oxidation of primary and secondary benzylic alcohols to the corresponding aldehydes and ketones has been achieved using silica-encapsulated H₃PW₁₂O₄₀ as a recyclable heterogeneous photocatalyst in acetonitrile under oxygen gas as the sole reoxidant of the catalyst.     

RuCl3-DCHA Catalyst System: A Selective Aerobic Oxidation of Primary Benzylic Alcohols Under Mild Conditions

The aerobic oxidation of benzylic alcohols to their corresponding aldehydes was performed in a RuCl₃ · 3H₂O–dicyclohexylamine (DCHA) catalyst system under ambient atmosphere at room temperature. It is noteworthy that the RuCl₃ · 3H₂O–DCHA system displayed a preference for the primary versus secondary benzylic alcohols in both intermolecular and intramolecular competition experiments.     

A Convenient and Selective Palladium‐Catalyzed Aerobic Oxidation of Alcohols

An efficient procedure for the oxidation of primary and secondary alcohols to aldehydes and ketones, respectively, with molecular oxygen under ambient conditions has been achieved. By applying catalytic amounts of Pd(OAc)₂ in the presence of tertiary phosphine oxides (O?PR₃) as ligands, a variety of substrates are selectively oxidized without formation of ester byproducts. Spectroscopic investigations and DFT calculations suggest stabilization of the active palladium(II) catalyst by phosphine oxide ligands.     

A TEMPO‐Free Copper‐Catalyzed Aerobic Oxidation of Alcohols

The copper‐catalyzed aerobic oxidation of primary and secondary alcohols without an external N‐oxide co‐oxidant is described. The catalyst system is composed of a Cu/diamine complex inspired by the enzyme tyrosinase, along with dimethylaminopyridine (DMAP) or N‐methylimidazole (NMI). The Cu catalyst system works without 2,2,6,6‐tetramethyl‐l‐piperidinoxyl (TEMPO) at ambient pressure and temperature, and displays activity for un‐activated secondary alcohols, which remain a challenging substrate for catalytic aerobic systems. Our work underscores the importance of finding alternative mechanistic pathways for alcohol oxidation, which complement Cu/TEMPO systems, and demonstrate, in this case, a preference for the oxidation of activated secondary over primary alcohols.     

Na4H3[SiW9Al3(H2O)3O37]·12H2O/H2O: a new system for selective oxidation of alcohols with H2O2 as oxidant

This work describes a catalytic system consisting of both Na₄H₃[SiW₉Al₃(H₂O)₃O₃₇]·12H₂O(SiW₉Al₃) and water as solvents (a small quantity of organic solvents were used as co-solvent for a few substrates) that can be good for selective oxidation of alcohols to ketones (aldehydes) using 30% H₂O₂ without any phase-transfer catalyst under mild reaction conditions. The catalyst system allows easy product/catalyst separation. Under the given conditions, the secondary hydroxyl group was highly chemoselectively oxidized to the corresponding ketones in good yields in the presence of primary hydroxyl group within the same molecule, and hydroxides are selectively oxidized even in the presence of alkene. Benzylic alcohols were selectively oxidized to the corresponding benzaldehydes in good yields without over oxidation products in solvent-free conditions. Nitrogen, oxygen, sulfur-based moieties, at least for the cases where these atoms are not susceptible to oxidation, do not interfere with the catalytic alcohol oxidation.     

Efficient and selective oxidation of alcohols with <Emphasis Type="Italic">tert</Emphasis>-BuOOH catalyzed by a dioxomolybdenum(VI) Schiff base complex under organic solvent-free conditions

The catalytic activity of dioxidobis{2-[(E)-p-tolyliminomethyl]phenolato}molybdenum(VI) complex was studied, for the first time, in the selective oxidation of various primary and secondary alcohols using tert-BuOOH as oxidant under organic solvent-free conditions at room temperature. The effect of different solvents was studied in the oxidation of benzyl alcohol in this catalytic system. It was found that, under organic solvent-free conditions, the catalyst oxidized various primary and secondary alcohols to their corresponding aldehyde or ketone derivatives with high yield. The effects of other parameters such as oxidant and amount of catalyst were also investigated. Among different oxidants such as H₂O₂, NaIO₄, tert-BuOOH, and H₂O₂/urea, tert-BuOOH was selected as oxygen donor in the oxidation of benzyl alcohol. Also, it was found that oxidation of benzyl alcohol required 0.02 mmol catalyst for completion. Dioxomolybdenum(VI) Schiff base complex exhibited good catalytic activity in the oxidation of alcohols with tert-BuOOH under mild conditions. In this catalytic system, different primary alcohols gave the corresponding aldehydes in good yields without further oxidation to carboxylic acids.     

Oxidation of alcohols by TBHP in the presence of sub-stoichiometric amounts of MnO2

Commercially available activated MnO₂ has been investigated as a catalyst for the oxidation of alcohols (phenylethanol, 4-methyl- and 4-methoxybenzyl alcohol, trans-cinnamyl alcohol, cyclohexanol, menthol, perillyl alcohol and myrtenol) by TBHP/decane or TBHP/water in MeCN. The activity is highest for benzylic and allylic alcohols. Secondary alcohols yield ketones with good selectivities, while the aldehydes generated from primary alcohols are further oxidized. The process competes with the TBHP catalyzed decomposition. It thus requires the use of excess TBHP and high catalyst loadings to achieve high conversions. However, the low cost of the reagents makes this new protocol convenient for the oxidation of reactive secondary alcohols. The study also suggests that MnO₂ should be proscribed as a reagent to quench excess TBHP in oxidative processes when the synthetic target contains easily oxidizable alcohol functions and when carrying our detailed kinetic monitoring of oxidation processes.     

[Sn(TPP)(BF4)2]: An efficient and reusable catalyst for chemoselective trimethylsilylation of alcohols and phenols with hexamethyldisilazane

Tin(IV)tetraphenylporphyrinato tetrafluoroborate, [Sn^IV(TPP)(BF₄)₂], was used as an efficient catalyst for trimethylsilylation of alcohols and phenols with hexamethyldisilazane (HMDS). High-valent [Sn^IV(TPP)(BF₄)₂] catalyzes trimethylsilylation of primary, secondary and tertiary alcohols as well as phenols, and the corresponding TMS-ethers were obtained in high yields and short reaction times at room temperature. While, under the same reaction conditions [Sn^IV(TPP)Cl₂] is less efficient to catalyze these reactions. One important feature of this catalyst is its ability in the chemoselective silylation of primary alcohols in the presence of secondary and tertiary alcohols and phenols. The catalyst was reused several times without loss of its catalytic activity.     

Oxidation of primary and secondary alcohols catalyzed by a pentamethylcyclopentadienyliridium complex

The oxidation of primary and secondary alcohols is carried out in acetone under mild conditions using catalytic amounts of [Cp*IrCl₂]₂ and K₂CO₃. Primary alcohols are converted into the corresponding aldehydes with high selectivity in good yields. Secondary alcohols are readily oxidized to ketones with smaller amounts of the catalyst.     

Efficient oxidation of alcohols with tert-butyl hydroperoxide catalyzed by Mo(CO)6 supported on multiwall carbon nanotubes

Efficient oxidation of alcohols with tert-butyl hydroperoxide catalyzed by Mo(CO)₆ supported on multiwall carbon nanotubes modified with 4-aminopyridine is reported. The effect of various parameters such as catalyst amount, solvent and oxidant was studied. The catalyst, [Mo(CO)₅@APy-MWCNT], showed high activity not only in the oxidation of benzylic and linear alcohols but also in the oxidation of secondary alcohols. The catalyst can be reused several times without significant loss of its activity.     

A BINOL-terpyridine-based multi-task catalyst for a sequential oxidation and asymmetric alkylation of alcohols

Treatment of a BINOL-terpyridine compound with RuCl₃ generates a Ru(II) complex (R)-6. This complex is found to be a novel multi-task catalyst capable of conducting a sequential oxidation and asymmetric alkyl addition to convert primary alcohols to chiral secondary alcohols. The terpyridine-Ru(II) site of (R)-6 catalyzes an efficient oxidation of primary alcohols to aldehydes which then undergo an enantioselective alkylation to generate chiral secondary alcohols when the BINOL site of (R)-6 is combined with ZnEt₂ and Ti(OⁱPr)₄.     

Alumina Perchloric Acid (Al 2 O 3 -HClO 4 ) as an Efficient Heterogeneous Catalyst for Modified Preparation of Trimethylsilyl Ethers

A highly efficient and mild procedure for the trimethylsilylation of a wide variety of alcohols, including primary, benzylic, secondary, hindered secondary, tertiary, phenols, and oximes with hexamethyldisilazane (HMDS) using alumina perchloric acid (Al ₂ O ₃ -HClO ₄ ) as recyclable heterogeneous catalyst in excellent yields with short reaction times (3?65 min) under ambient conditions is described.     

Selective oxidation of alcohols with hydrogen peroxide catalyzed by tungstate ions (WO4) supported on periodic mesoporous organosilica with imidazolium frameworks (PMO-IL)

Tungstate ions supported on the periodic mesoporous organosilica with ionic liquid frameworks (WO₄⁼@PMO-IL) were found to be a recoverable catalyst system for the highly selective oxidation of various primary or secondary alcohols to the corresponding aldehydes or ketones by 30% H₂O₂ as green oxidant under neutral aqueous reaction conditions. The catalyst can be also recovered and efficiently reused in seven subsequent reaction cycles without any remarkable decreasing in the catalyst activity and selectivity. Moreover, N₂ sorption analysis, transmission electron microscopy (TEM) images, and thermal gravimetric analysis (TGA) showed that the structure regularity and functional groups loaded of the catalyst were not affected during the reaction process.     

H2O2 Oxidation by Ce(IV) Contained Weakley-Type Heteropolyoxometalate for Various Alcohols

Catalytic activity of Ce(IV) contained Weakley-type heteropoly-oxometalate for the H₂O₂ oxidation of primary and secondary alcohols was evaluated for the first time. It was found that this catalyst exhibited a mild and thus quite selective activity, especially for benzylalcohols.     

Magtrieve™: a convenient catalyst for the oxidation of alcohols

We find that Magtrieve™ (CrO₂) catalyzes the oxidation of a wide variety of alcohols with periodic acid as the terminal oxidant. Mild conditions, short reaction times, and facile aqueous work-up make this a most attractive method. Olefins are not oxidized under these conditions; thus alcohols react selectively in the presence of alkenes. Conditions have been optimized with respect to catalyst loading, solvent, and co-oxidant; and the scope of the reaction includes primary and secondary benzylic, allylic, and aliphatic alcohols.     

Aerobic oxidation of alcohols using bismuth bromide as a catalyst

We developed an environmentally friendly method for aerobic oxidation of alcohols using a commercially available, relatively benign bismuth salt as a catalyst. We found that the catalytic combination of BiBr₃ with nitric acid is key for enhancing the reactivity. The reaction proceeds well under air, making the use of pure oxygen unnecessary. Each of the primary or secondary alcohols tested was oxidized to the corresponding aldehydes or ketones using this protocol.     

A Mild,Simple, Efficient,and Selective Protection of Hydroxyl Groups Using Silica-Supported Sodium Hydrogen Sulfate as a Heterogeneous Catalyst

A mild, simple, novel, and highly efficient method for the rapid protection of various primary, secondary, tertiary aliphatic alcohols, aromatic alcohols, and oximes using hexamethyldisilazane (HMDS) in the presence of silica-supported sodium hydrogen sulfate (NaHSO ₄ -SiO ₂ ), as an active, inexpensive, nontoxic, heterogeneous, and readily available catalyst under ambient conditions is described. Timethylsilyl ethers were prepared in high to excellent yields, with short reaction times under mild and almost neutral reaction conditions at room temperature.     

Selective aerobic oxidation of allylic and benzylic alcohols catalyzed by N-hydroxyindole and copper(I) chloride

In the presence of copper(I) chloride, tert-butyl 1-hydroxy-2-methyl-6-trifluoromethyl-1H-indole-3-carboxylate acted as a catalyst for the chemoselective aerobic oxidation of allylic and benzylic alcohols. A variety of primary and secondary allylic and benzylic alcohols were oxidized into the corresponding α,β-unsaturated carbonyl compounds in good yields without affecting non-allylic alcohols.     

Ruthenium Complexation in an Aluminium Metal–Organic Framework and Its Application in Alcohol Oxidation Catalysis

A ruthenium trichloride complex has been loaded into an aluminium metal–organic framework (MOF), MOF‐253, by post‐synthetic modification to give MOF‐253‐Ru. MOF‐253 contains open bipyridine sites that are available to bind with the ruthenium complex. MOF‐253‐Ru was characterised by elemental analysis, N₂ sorption and X‐ray powder diffraction. This is the first time that a Ru complex has been coordinated to a MOF through post‐synthetic modification and used as a heterogeneous catalyst. MOF‐253‐Ru catalysed the oxidation of primary and secondary alcohols, including allylic alcohols, with PhI(OAc)₂ as the oxidant under very mild reaction conditions (ambient temperature to 40 °C). High conversions (up to >99 %) were achieved in short reaction times (1–3 h) by using low catalyst loadings (0.5 mol % Ru). In addition, high selectivities (>90 %) for aldehydes were obtained at room temperature. MOF‐253‐Ru can be recycled up to six times with only a moderate decrease in substrate conversion.