Water-redispersible and high-yield α-chitin nanocrystals isolated using electron-beam irradiation as adsorbents to remove heavy metals and dye.

An innovative approach to fabricate transparent and redispersible α-chitin nanocrystals (ChNCs) with high overall yields was developed in this work for eventual commercial use. The nanomanufacturing process included electron-beam irradiation (EBI) of chitin for oxidation and degradation in the dried state, high-pressure nanoscale homogenization via swelling, CO2 absorption, and spray-drying to obtain dehydrated products. The resulting EBI-disassociated chitins contained increased amounts of carboxylate (0.19-0.27 mmol g-1) and a negligible fraction of D-glucosamine moiety (from ca. 6.5 to <1.0%) with an intrinsic structure identical to α-chitin derived from shrimp shell prior to purification by conventional methods, such as deproteination. The resulting EBI-induced ChNC series exhibited nano-sized and rod-like morphology with tunable lengths averaging 608-259 nm, uniform widths of ca. 16-12 nm, a high isolation yield of max. 81%, and sufficient anionic surface charges, as zeta potentials of -32 to -34 mV indicate that it is homogenously water-dispersible and stable with background transparency. Unlike ChNC prepared by HCl-hydrolysis, the dehydrated particles of EBI-induced ChNCs were clearly redispersible in water and retained the characteristics of the original nanomaterials. We also tested the redispersible EBI-induced ChNCs as effective adsorbents. Their anionic groups interacted with cationic heavy metals (Cu2+ and Fe3+) and organic blue dye via electrostatic attraction, forming robust hydrogels, which were self-supporting after centrifugation. The EBI-induced ChNCs produced with low environmental impact in this work offer a promising choice of adsorbents for the removal of undesirable chemicals during wastewater treatment.

Selective C-H Functionalization of Methane and Ethane by a Molecular SbV Complex.

Owing to the strong nonpolar bonds involved, selective C-H functionalization of methane and ethane to esters remains a challenge for molecular homogeneous chemistry. We report that the computationally predicted main-group p-block SbV (TFA)5 complex selectively functionalizes the C-H bonds of methane and ethane to the corresponding mono and/or diol trifluoroacetate esters at 110-180 °C with yields for ethane of up to 60 % with over 90 % selectivity. Experimental and computational studies support a unique mechanism that involves SbV -mediated C-H activation followed by functionalization of a SbV -alkyl intermediate.

Homogeneous Functionalization of Methane.

One of the remaining "grand challenges" in chemistry is the development of a next generation, less expensive, cleaner process that can allow the vast reserves of methane from natural gas to augment or replace oil as the source of fuels and chemicals. Homogeneous (gas/liquid) systems that convert methane to functionalized products with emphasis on reports after 1995 are reviewed. Gas/solid, bioinorganic, biological, and reaction systems that do not specifically involve methane functionalization are excluded. The various reports are grouped under the main element involved in the direct reactions with methane. Central to the review is classification of the various reports into 12 categories based on both practical considerations and the mechanisms of the elementary reactions with methane. Practical considerations are based on whether or not the system reported can directly or indirectly utilize O2 as the only net coreactant based only on thermodynamic potentials. Mechanistic classifications are based on whether the elementary reactions with methane proceed by chain or nonchain reactions and with stoichiometric reagents or catalytic species. The nonchain reactions are further classified as CH activation (CHA) or CH oxidation (CHO). The bases for these various classifications are defined. In particular, CHA reactions are defined as elementary reactions with methane that result in a discrete methyl intermediate where the formal oxidation state (FOS) on the carbon remains unchanged at -IV relative to that in methane. In contrast, CHO reactions are defined as elementary reactions with methane where the carbon atom of the product is oxidized and has a FOS less negative than -IV. This review reveals that the bulk of the work in the field is relatively evenly distributed across most of the various areas classified. However, a few areas are only marginally examined, or not examined at all. This review also shows that, while significant scientific progress has been made, greater advances, particularly in developing systems that can utilize O2, will be required to develop a practical process that can replace the current energy and capital intensive natural gas conversion process. We believe that this classification scheme will provide the reader with a rapid way to identify systems of interest while providing a deeper appreciation and understanding, both practical and fundamental, of the extensive literature on methane functionalization. The hope is that this could accelerate progress toward meeting this "grand challenge."

P-modified and carbon shell coated Co nanoparticles for efficient alkaline oxygen reduction catalysis.

Described herein is the development of a novel Co-based oxygen electrode catalyst coupled with unique carbon structures. The present carbon shell coated Co nanoparticles of which the surface composites are modified by phosphorus incorporation, exhibit efficient oxygen reduction activities as well as oxygen evolving properties.

Mechanistic studies of the rhodium-catalyzed direct C-H amination reaction using azides as the nitrogen source.

Direct C-H amination of arenes offers a straightforward route to aniline compounds without necessitating aryl (pseudo)halides as the starting materials. The recent development in this area, in particular in the metal-mediated transformations, is significant with regard to substrate scope and reaction conditions. Described herein are the mechanistic details on the Rh-catalyzed direct C-H amination reaction using organic azides as the amino source. The most important two stages were investigated especially in detail: (i) the formation of metal nitrenoid species and its subsequent insertion into a rhodacycle intermediate, and (ii) the regeneration of catalyst with concomitant release of products. It was revealed that a stepwise pathway involving a key Rh(V)-nitrenoid species that subsequently undergoes amido insertion is favored over a concerted C-N bond formation pathway. DFT calculations and kinetic studies suggest that the rate-limiting step in the current C-H amination reaction is more closely related to the formation of Rh-nitrenoid intermediate rather than the presupposed C-H activation process. The present study provides mechanistic details of the direct C-H amination reaction, which bears both aspects of the inner- and outer-sphere paths within a catalytic cycle.

Rhodium-catalyzed direct C-H amination of benzamides with aryl azides: a synthetic route to diarylamines.

No muss, no fuss: A rhodium-catalyzed direct intermolecular C-H amination of benzamides and ketoximes using aryl azides as the amine source has been developed. The reaction exhibits a broad substrate scope with excellent functional-group tolerance, requires no external oxidants, releases N(2) as the only by-product, and produces diarylamines in high yields.

Rhodium-catalyzed intermolecular amidation of arenes with sulfonyl azides via chelation-assisted C-H bond activation.

We report the direct amidation of arene C-H bonds using sulfonyl azides as the amino source to release N(2) as the single byproduct. The reaction is catalyzed by a cationic rhodium complex under external oxidant-free conditions in the atmospheric environment. A broad range of chelate group-containing arenes are selectively amidated with excellent functional group tolerance, thus opening a new avenue to practical intermolecular C-N bond formation.

Sulfonyl and phosphoryl azides: going further beyond the click realm of alkyl and aryl azides.

Whereas alkyl and aryl azides readily react with terminal alkynes to afford 1,4-disubstituted-1,2,3-triazoles in excellent yields and selectivity in the presence of a copper catalyst, sulfonyl, phosphoryl, and certain acyl azides allow additional chemistry upon ring-opening of the corresponding copper-triazole intermediates. The amazingly versatile new chemistry stems from the high reactivity of a ring-opened ketenimine intermediate, with which a wide range of nucleophiles react to give multicomponent products. Among those nucleophiles, amines, alcohols, water, and heterocyclic compounds are especially capable of being involved in this new chemistry.

Intramolecular aromatic carbenoid insertion of biaryldiazoacetates for the regioselective synthesis of fluorenes.

The rhodium- or copper-catalyzed intramolecular aromatic carbenoid insertion of biaryldiazoacetates offers a convenient route to fluorene carboxylates with high yields. Whereas, thermal conditions provided a mixture of two regioisomeric products when substituted biaryldiazoacetates were employed as substrates. The developed catalytic conditions displayed an excellent level of regioselectivity, presumably owing to steric effects. The insertion mechanism was assumed to be an electrophilic aromatic substitution, which was supported by preliminary mechanistic studies. A chloro-substituted fluorene derivative was efficiently synthesized and utilized as a base-sensitive protecting group of amines.

Rhodium-catalyzed selective olefination of arene esters via C-H bond activation.

A new catalytic procedure of ortho-olefination of benzoates and benzaldehydes has been developed. Ester and carboxaldehyde units were revealed to be effective chelating groups in focusing the activation of aryl C-H bonds ortho to the directing moieties under the Rh-catalyzed oxidative conditions. The reaction is highly regioselective with a range of benzoates and benzaldehydes enabling the efficient olefination with acrylates, acrylic acid, and styrenes.

A new entry of copper-catalyzed four-component reaction: facile access to alpha-aryl beta-hydroxy imidates.

Alpha-aryl beta-hydroxy imidates are efficiently obtained by the four-component reaction of ethyl glyoxylates, aryl acetylenes, sulfonyl azides, and alcohols using a copper catalyst. The developed procedure is characterized by high selectivity, mild reaction conditions, a wide substrate scope, and an excellent functional group tolerance. Facile transformations of the obtained sulfonylimidate moiety to other carbonyl groups such as sulfonamides or esters were also demonstrated.