A new catalytic oxidation system using catalytic amounts of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and tert-butyl nitrite with molecular oxygen serving as the environmentally benign, terminal oxidant has been developed. This aerobic catalytic system was established for the selective oxidation of non-sterically hindered benzylic alcohols and electron-rich benzyl methyl ethers, and successfully extended to an application in the oxidative deprotection of PMB ethers to the alcohols in high selectivity.

A metal-free catalytic system consisting of 2,2,6,6-tetramethylpiperidine N-oxyl (TEMPO) and tert-butyl nitrite has been developed to activate molecular oxygen for the aerobic oxidation of alcohols. A variety of active and non-active alcohols were oxidized to their corresponding carbonyl compounds in high selectivity and yields.Keywords: alcohols; tert-butyl nitrite; molecular oxygen; oxidation; TEMPO; 2,2,6,6-tetramethylpiperidine N-oxyl (TEMPO) Selective oxidation of alcohols is an important reaction in organic chemistry. [1,2] Among the stoichiometric oxidants, molecular oxygen is a preferred terminal oxidant from both economical and environmental perspectives. We have previously developed a three-component catalyst system, consisting of 2,2,6,6-tetramethylpiperidine N-oxyl (TEMPO), Br 2 and NaNO 2 , to activate molecular oxygen for the selective aerobic oxidation of alcohols to their corresponding carbonyl compounds.[3] The method hinges upon a key finding that the inorganic salt, NaNO 2 , could serve as an NO equivalent to activate molecular oxygen under acidic conditiona. This concept has been extended and applied for a broad array of substrates with good selectivities.[4] However, most of these methods require a Br source as the co-catalyst to bridge the two catalytic cycles between TEMPO cation/TEMPOH and NO/ NO 2 . As a result, those substrates bearing an olefin moiety are not favored due to side reactions of HBr or Br 2 with the carbon-carbon double bonds.[5] Moreover, the aerobic oxidation of aliphatic primary alcohols remains a challenge because their propensity toward being overoxidized into acids and/or ortho esters under these conditions. [6] Therefore, it is desirable to develop of an efficient and selective catalyst system for the aerobic oxidation of a broad range of alcohols. Although the catalytic system TEMPO/NaNO 2 /HCl was recently developed for selective aerobic oxidation of a variety of primary and secondary alcohols under mild conditions, [7] its application to substrates containing acid-sensitive functional groups might be limited because a high loading of HCl (10-16 mol%) was used. Very recently, we have reported an efficient aerobic oxidation of various active alcohols with high turnover number (TON) under almost neat condition with TEMPO/ tert-butyl nitrite (TBN)/aqueous HBr as the catalytic system. [8] In this system, the organic nitrite, TBN, served as an efficient NO equivalent to activate molecular oxygen and enabled the aerobic oxidation at very high-volume efficiency.Generally, the TEMPO cation, which was initially formed via oxidation of TEMPO, acts as the active oxidant in the TEMPO-catalyzed oxidation of alcohols. According to the literature, the electrode potential (E 0 ) of TEMPO cation/TEMPO is 0.75 V, [2h] while E 0 of N 2 O 4 /NO is 1.03 V. [9] Based on this information, we reckoned that NO 2 can oxidize TEMPO into the TEMPO cation to initialize the oxidation (Scheme 1). Under high temperatures TBN can release NO or NO 2 because of its thermal instability. NO...

SummaryA general and facile one-pot protocol for the preparation of a broad range of alkyl and aryl isothiocyanates has been developed from their corresponding primary amines under aqueous conditions. This synthetic process involves an in situ generation of a dithiocarbamate salt from the amine substrate by reacting with CS2 followed by elimination to form the isothiocyanate product with cyanuric acid as the desulfurylation reagent. The choice of solvent is of decisive importance for the successful formation of the dithiocarbamate salt particularly for highly electron-deficient substrates. This novel and economical method is suitable for scale-up activities.

The phase behavior of a kind of pseudogemini surfactant in aqueous solutions, formed by the mixture of sodium dodecyl benzene sulfonate (SDBS) and butane-1,4-bis (methylimidazolium bromide) ([mim-C4-mim]Br2) or butane-1,4-bis(methylpyrrolidinium bromide) ([mpy-C4-mpy]Br2) in a molar ratio of 2 : 1, is reported in the present work. When [mim-C4-mim]Br2 or [mpy-C4-mpy]Br2 is mixed with SDBS in aqueous solutions, one cationic [mim-C4-mim]Br2 or [mpy-C4-mpy]Br2 molecule "bridges" two SDBS molecules by noncovalent interactions (e.g. electrostatic, π-π stacking, and σ-π interactions), behaving like a pseudogemini surfactant. Vesicles can be formed by this kind of pseudogemini surfactant, determined by freeze-fracture transmission electron microscopy (FF-TEM) or cryogenic-transmission electron microscopy (cryo-TEM) and dynamic light scattering (DLS). The mixed system of sodium dodecyl sulfate (SDS) with [mim-C4-mim]Br2 or [mpy-C4-mpy]Br2 was also constructed, and only micelles were observed. We infer that a pseudogemini surfactant is formed under the synergic effect of electrostatic, π-π stacking, and σ-π interactions in the SDBS/[mim-C4-mim]Br2/H2O system, while electrostatic attraction and hydrophobic interactions may provide the directional force for vesicle formation in the SDBS/[mpy-C4-mpy]Br2/H2O system.

Ionic liquid crystals (ILCs) with hexagonal and lamellar phases were successfully fabricated by the self-assembly of a polymerizable amphiphilic zwitterion, which is formed by 3-(1-vinyl-3-imidazolio)propanesulfonate (VIPS) and 4-dodecyl benzenesulfonic acid (DBSA) based on intermolecular electrostatic interactions. The microstructures and phase behaviors of ILCs were studied by polarized microscope (POM) and small-angle X-ray scattering (SAXS). The ILC topological structures can be considered as proton pathways and further fixed by photopolymerization to prepare nanostructured proton-conductive films. The introduction of highly ordered and well-defined ILC structures into these polymeric films radically improves the ionic conductivities.