Renhua Liu

TEMPO/HCl/NaNO2 catalyst: a transition-metal-free approach to efficient aerobic oxidation of alcohols to aldehydes and ketones under mild conditions.

Hydrochloric acid, a very inexpensive and readily available inorganic acid, has been found to cooperate exquisitely with NaNO(2)/TEMPO in catalyzing the molecular-oxygen-driven oxidation of a broad range of alcohol substrates to the corresponding aldehydes and ketones. This transition-metal-free catalytic oxidative conversion is novel and represents an interesting alternative route to the corresponding carbonyl compounds to the metal-catalyzed aerobic oxidation of alcohols. The reaction is highly selective with respect to the desired product when carried out at room temperature in air at atmospheric pressure. Notably, the use of very inexpensive NaNO(2) and HCl in combination with TEMPO for this highly selective aerobic oxidation of alcohols in air at ambient temperature makes the reaction operationally and economically very attractive. The results of mechanistic studies, performed with the aid of electrospray ionization mass spectrometry (ESI-MS), are presented and discussed. TEMPO, TEMPOH, and TEMPO(+) were observed in the redox cycle by means of ESI-MS. On the basis of these observations, a mechanism is proposed that may provide an insight into the newly developed aerobic alcohol oxidation.

Copper-Catalyzed Aerobic Oxidative Coupling of Aromatic Alcohols and Acetonitrile to β-Ketonitriles

A practical, convenient, and cheap copper-catalyzed aerobic oxidative coupling of aromatic alcohols and acetonitrile to β-ketonitriles has been developed. The green C-C bond formation involving the loss of two hydrogen atoms from the corresponding two carbons, respectively, unlocks opportunities for markedly different synthetic strategies.

A highly enantioselective phase-transfer catalyzed epoxidation of enones with a mild oxidant, trichloroisocyanuric acidElectronic supplementary information (ESI) available: experimental details. See http://www.rsc.org/suppdata/cc/b3/b308042k/

The enantioselective epoxidation can be carried out using trichloroisocyanuric acid (TCCA) as oxidant in the presence of chiral quaternary ammonium salt as a phase-transfer catalyst; treatment of chalcone derivatives with TCCA under mild conditions afforded the corresponding epoxy ketones in good yields with moderate to excellent enantioselectivities of up to 96%.

NaNO2/FeCl3 catalyzed wet oxidation of the azo dye Acid Orange 7

A combination of ferric chloride and sodium nitrite significantly improved the wet oxidation of the azo dye Acid Orange 7 (AO7) in acid aqueous media (pH 2.6) under moderate conditions (T=150 degrees C; oxygen pressure=0.5 MPa). To evaluate the catalytic system, wet oxidation of AO7 was carried out at temperatures between 90 and 150 degrees C and oxygen pressures ranging from 0.1 to 0.5 MPa. The effect of initial solution pH from 2.6 to 11.4 and the amount of catalyst on the degradation of AO7 were also investigated. AO7 initial concentration was kept 200 mg L(-1). The degradation process was monitored by UV-visible spectroscopy, HPLC, IC (ion chromatography), GC-MS and TOC analysis. At 150 degrees C and 0.5 MPa oxygen pressure, 56% TOC was removed after 4h of treatment, while no obvious TOC removal were achieved without catalyst at the same experimental condition. The main degradation products were some small organic acids: formic acid, acetic acid, pyruvic acid, oxalic acid, succinic acid (identified and quantified by IC) and phthalic acid (identified by GC-MS).

A novel click lysine zwitterionic stationary phase for hydrophilic interaction liquid chromatography

A novel type of zwitterionic HILIC stationary phase was prepared by covalently bonding the l-azido lysine on silica gel via click chemistry. The key intermediate azido lysine was synthesized by transformation the amino group in l-Boc-lysine to corresponding azido group and subsequent removal of the N-protected group (Boc). Finally, the azido lysine was covalently bonded to silica beads by click chemistry to get click lysine. Its structure was confirmed by FT-IR and elemental analysis. The new stationary phase showed good HILIC characteristics, when it was applied to separate polar and hydrophilic compounds, such as organic acids, cephalosporins and carbapenems. Compared with the commercial stationary phases, such as Atlantics HILIC and ZIC-HILIC, click lysine displayed better or similar chromatographic behaviors.

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.

C–H Functionalization via Remote Hydride Elimination: Palladium Catalyzed Dehydrogenation of ortho-Acyl Phenols to Flavonoids

Although deprotonation of electron-poor C-H bonds to carbon anions with bases has long been known and widely used in organic synthesis, the hydride elimination from electron-rich C-H bonds to carbon cations or partial carbocations for the introduction of nucleophiles is a comparatively less explored area. Here we report that the carbonyl β-C(sp3)-H bond hydrogens of ortho-acyl phenols could be substituted by intramolecular phenolic hydroxyls to form O-heterocycles, followed by dehydrogenation of the O-heterocycle into flavonoids. The cascade reaction is catalyzed by Pd/C without added oxidants and sacrificing hydrogen acceptors.

Click N-benzyl iminodiacetic acid: Novel silica-based tridentate zwitterionic stationary phase for hydrophilic interaction liquid chromatography

Iminodiacetic acid (IDA) is dicarboxylic acid amine, which may produce stronger interaction with polar or charged compounds than bidentate α,β-amino acid. In this article, a novel type of tridentate zwitterionic HILIC stationary phase was prepared by covalently bonding N-benzyl IDA on silica gel via copper(I) catalyzed Huisgen azide-alkyne 1,3-dipolar cycloaddition (CuAAC). The structure of this stationary phase and all related intermediates was confirmed by NMR, FT-IR, MS spectrum and elemental analysis. The new stationary phase showed good HILIC characteristics and high column efficiency (the theoretical plate number is up to 44000 plates m(-1) in the case of guanosine) in the application of separation of polar compounds, including organic acids, organic bases, as well as highly polar and hydrophilic compounds, such as cephalosporins and carbapenems. Most of them displayed good peak shape and selectivity.

One-pot, three-component reaction using modified Julia reagents: a facile synthesis of 4,5-disubstituted 1,2,3-(NH)-triazoles in a wet organic solvent.

A new one-pot, three component reaction involving the use of Julia reagent, aldehyde, and sodium azide was developed for the efficient synthesis of N-unsubstituted 1,2,3-triazoles. This reaction could be carried out under mild reaction conditions without any precaution, and broad scope of substrates, both respect to Julia reagents and aldehydes, could be applied in this reaction system in generation of a small library of title compounds.

Concurrent destruction strategy: NaNO2-catalyzed, trichlorophenol-coupled degradation of p-nitrophenol using molecular oxygen

Oxidative degradation of p-nitrophenol (PNP) was investigated with NaNO(2) as the catalyst and dioxygen as the oxidizing agent in the presence of trichlorophenol (TCP). Although degradation of PNP alone was proved to be inefficient toward the NaNO(2)-mediated oxidative degradation system, when PNP in combination with TCP was used as the substrate, NaNO(2) showed relatively high catalytic activity for eradicating both PNP and TCP with molecular oxygen. Reaction conditions to the degradation system, e.g., temperatures, reaction time, pH, NaNO(2) and TCP concentrations were optimized. PNP could be highly efficiently degraded in the NaNO(2)/TCP/O(2) system (more than 99% removal for PNP) and the TOC removal of the mixture of PNP and TCP could reach 71% at 150 degrees C, 0.5 MPa oxygen pressure. Degradation products were determined, and 93% carbon atom was clarified. A plausible overall mechanism for the formation of active species is described, in which peroxylnitrite was believed to be a dominating active intermediate being responsible for destroying the substrates, PNP and TCP. The novel NaNO(2)-based concurrent oxidation system for PNP and TCP provides a potential application in treatment of multi-component industrial effluents.