TEMPO-catalyzed aerobic oxidation of alcohols to aldehydes and ketones in ionic liquid [bmim][PF6]

A copper complex bearing a TEMPO moiety as catalyst for the aerobic oxidation of primary alcohols

A new bifunctional, triazine-based ligand has been designed with the aim to generate a copper(II) complex holding a TEMPO (2,2,6,6-tetramethylpiperidinyloxy) moiety. The coordination compound obtained from the ligand 4-(2-(3-(pyridin-2-yl)-1H-pyrazol-1-yl)ethoxy)-6-(4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl)-N,N-diphenyl-1,3,5-triazin-2-amine (pypzt-1) and copper(II) bromide (i.e. complex 8) is capable of catalysing the selective, aerobic oxidation of benzyl alcohol to 84% of benzaldehyde in 24 h. This "galactose oxidase activity" of the copper/TEMPO complex is observed as well for the conversion of the non-activated alkyl alcohol octan-1-ol to octanal with a yield of 29% after the same reaction time. The single-crystal X-ray structure of 8 shows that its crystal lattice contains [Cu(I)Br(2)](-) anions which appear to be stabilised by means of both anion-pi and hydrogen bonding interactions. In addition, the solid state structure of 8 exhibits (lone-pair)-pi interactions between the nitrogen atom of an acetonitrile molecule and a triazine ring. The magnetic properties of 8 have been investigated by EPR and magnetic susceptibility measurements.

Highly efficient selective oxidation of alcohols to carbonyl compounds catalyzed by ruthenium (III) meso-tetraphenylporphyrin chloride in the presence of molecular oxygen

Efficient selective oxidation of alcohols to carbonyl compounds by molecular oxygen with isobutyraldehyde as oxygen acceptor in the presence of metalloporphyrins has been reported. Ruthenium (III) meso-tetraphenylporphyrin chloride (Ru(TPP)Cl) showed excellent activity and selectivity for oxidation of various alcohols under mild conditions. Moreover, different factors influencing alcohols oxidation, for example, catalyst, solvent, temperature, and oxidant, have been investigated. In large-scale oxidation of benzyl alcohol, the isolated yield of benzaldehyde of 89% was observed.

Copper(II)-Catalyzed Aerobic Oxidation of Primary Alcohols to Aldehydes in Ionic Liquid [bmpy]PF6

A room-temperature aerobic oxidation of primary alcohols to aldehydes catalyzed by the three-component system acetamido-TEMPO/Cu(ClO(4))(2)/DMAP in the ionic liquid [bmpy]PF(6) has been developed, and the catalysts can be recycled and reused for five runs without any significant loss of catalytic activity. [reaction: see text]

Development and comparison of the substrate scope of Pd-catalysts for the aerobic oxidation of alcohols

[reaction: see text] Three catalysts for aerobic oxidation of alcohols are discussed and the effectiveness of each is evaluated for allylic, benzylic, aliphatic, and functionalized alcohols. Additionally, chiral nonracemic substrates as well as chemoselective and diastereoselective oxidations are investigated. In this study, the most convenient system for the Pd-catalyzed aerobic oxidation of alcohols is Pd(OAc)(2) in combination with triethylamine. This system functions effectively for the majority of alcohols tested and uses mild conditions (3 to 5 mol % of catalyst, room temperature). Pd(IiPr)(OAc)(2)(H(2)O) (1) also successfully oxidizes the majority of alcohols evaluated. This system has the advantage of significantly lowering catalyst loadings but requires higher temperatures (0.1 to 1 mol % of catalyst, 60 degrees C). A new catalyst is also disclosed, Pd(IiPr)(OPiv)(2) (2). This catalyst operates under very mild conditions (1 mol %, room temperature, and air as the O(2) source) but with a more limited substrate scope.

NaNO2-activated, iron–TEMPO catalyst system for aerobic alcohol oxidation under mild conditions

FeCl3-TEMPO-NaNO2 catalyses the selective and mild aerobic oxidation of a broad range of alcohols to the corresponding aldehydes and ketones.

Aerobic Oxidation of 2,3,6-Trimethylphenol to Trimethyl-1,4-benzoquinone with Copper(II) Chloride as Catalyst in Ionic Liquid and Structure of the Active Species

TMQ is an important precursor in industrial vitamin E synthesis. We report a "green chemistry approach" with respect to the highly selective and environmentally friendly oxidation of 2,3,6-trimethylphenol (TMP) to trimethyl-1,4-benzoquinone (TMQ) with molecular oxygen as oxidant and a copper catalyst immobilized in a molten salt. n-Butanol as co-solvent has a positive effect on the activity and selectivity. The structurally characterized catalyst, a 1-n-butyl-3-methylimidazolium oxotetracuprat, is formed in situ via hydrolysis of CuCl2 in the presence of imidazolium chloride. We propose a mechanism of oxidative phenolate activation at a [Cu4(mu4-O)]6+ core as electronically coupled electron acceptor, formation of a copper-bound phenolate radical anion, spin delocalization into the aromatic ring, and attack by triplet oxygen at the para position. Attack of Cu(I) as reduction equivalent at the peroxy radical, proton-mediated elimination of a copper(II)-hydroxo species, will either substitute a copper(I) site in the reduced oxo cluster or take up an electron from the reduced mixed valent cluster [Cu4(mu4-O)]6+ to regenerate the oxidized cluster as the active electron acceptor.