Methylation of softwood and hardwood kraft lignins with chloromethane.

Methylation is a well-established means of enhancing the thermal stability, improving the compatibility in polymer blends, and lowering the glass-transition temperature of lignins. This process normally involves reagents that are costly, associated with poor atom economy and/or highly toxic. Herein, we report the methylation of softwood and hardwood kraft lignins using chloromethane in alkaline aqueous media. This reaction proceeds in high yields at 90-110 °C under moderate pressure (40 psi) while generating environmentally benign sodium chloride and water as by-products.

Predictably Ordered Open Hydrogen-Bonded Networks Built from Indeno[1,2-b]fluorenes.

Predictably ordered materials can be constructed by a modular strategy in which properly designed molecular components are positioned in space by reliable interactions. In principle, this approach can be used to control the arrangement of adjacent systems of π-conjugation, thereby creating molecular materials with valuable optoelectronic properties. To explore this possibility, we have synthesized compounds in which 2,4-diamino-1,3,5-triazinyl groups are attached to derivatives of 6,12-dihydroindeno[1,2-b]fluorene to produce molecules with well-defined cruciform topologies, extended π-conjugated aromatic cores, and an ability to form multiple hydrogen bonds. These compounds crystallize to form robust open hydrogen-bonded networks with parallel indenofluorenyl cores, significant volume (64-70%) available for accommodating guests, and characteristic luminescence. Our results will help permit the rational design of complex new molecular materials in which multiple optoelectronically active components are arranged in productive ways.

Chiral Self-Sorting of [2+3] Salicylimine Cage Compounds.

An inherently chiral C3 -symmetric triaminotribenzotriquinacene was condensed in racemic and enantiomerically pure form with a bis(salicylaldehyde) to form [2+3] salicylimine cage compounds. Investigations on the chiral self-sorting revealed that while entropy favors narcissistic self-sorting in solution, selective social self-sorting can be achieved by exploiting the difference in solubility between the homochiral and heterochiral cages. Gas sorption measurements further showed that seemingly small structural differences can have a significant impact on the surface area of microporous covalent cage compounds.

Chirality-Assisted Synthesis of a Very Large Octameric Hydrogen-Bonded Capsule.

The strategy of chirality-assisted synthesis, which makes use of enantiomerically pure building blocks that are designed to associate in a single geometric orientation, was applied to synthesize an octameric hydrogen-bonded capsule with a cavity volume of 2300 Å3 . This cube-shaped capsule forms even host-guest complexes with tetraalkylammonium ions, and accommodates the large tetrahexadecylammonium cation in its cavity. The use of an enantiopure building block was shown to be highly beneficial for capsule formation, whereas its racemate also generates a large amount of ill-defined aggregates in solution and crystallizes as a hydrogen-bonded network.

Dimerization of Aromatic C-Nitroso Compounds.

Aromatic C-nitroso compounds (Ar-N═O) and related species have a rich chemical history, and they continue to interest researchers in many fields. Among the most distinctive and puzzling properties of these compounds is their ability to dimerize reversibly to form azodioxy compounds. The present review subjects this intriguing phenomenon to comprehensive analysis. All aspects of the subject are examined in detail, including the structures of monomeric and dimeric forms, the mechanism of dimerization, features that favor or disfavor dimerization, thermodynamic and kinetic factors, dimerization under specific conditions (including in solution, in the solid state, and on surfaces), and the special associative behavior of dinitroso and polynitroso compounds. By summarizing the current state of knowledge, the review promises to spur further advances in the evergreen field of C-nitroso chemistry, including the discovery of new ways to exploit the reversible dimerization of nitrosoarenes.

Building Giant Carbocycles by Reversible C-C Bond Formation.

We describe a simple way to build giant macrocyclic hydrocarbons by the reversible formation of carbon-carbon bonds. Specifically, extended spirobifluorene-substituted derivatives of Wittig's hydrocarbon were synthesized and found to undergo oligomerization, giving the largest hydrocarbon that has been crystallized and characterized by X-ray diffraction to date.

Constructing monocrystalline covalent organic networks by polymerization.

An emerging strategy for making ordered materials is modular construction, which connects preformed molecular subunits to neighbours through interactions of properly selected reactive sites. This strategy has yielded remarkable materials, including metal-organic frameworks joined by coordinative bonds, supramolecular networks linked by strong non-covalent interactions, and covalent organic frameworks in which atoms of carbon and other light elements are bonded covalently. However, the strategy has not yet produced covalently bonded organic materials in the form of large single crystals. Here we show that such materials can result from reversible self-addition polymerizations of suitably designed monomers. In particular, monomers with four tetrahedrally oriented nitroso groups polymerize to form diamondoid azodioxy networks that can be fully characterized by single-crystal X-ray diffraction. This work forges a strong new link between polymer science and supramolecular chemistry by showing how predictably ordered covalent or non-covalent structures can both be built using a single modular strategy.

Dual fluorescence and electrochemical detection of the organophosphorus pesticides--ethion, malathion and fenthion.

Organophosphorus (OP) based pesticides are known powerful inhibitors of cholinesterases, thus the toxicity of this class of compounds causes serious environmental and human health concerns. We report that benzodipyrido[3,2-a:2',3'-c]phenazine (BDPPZ) and 3,6-dimethylbenzodipyrido-[3,2-a:2',3'-c]phenazine (DM-BDPPZ) provide independent fluorescent and electrochemical signal transductions in the presence of the organophosphorus (OP) pesticides; fenthion, malathion and ethion. The presence of the methyl groups at the 3 and 6 positions in DM-BDPPZ was found to significantly influence the sensor performance. The difference in the fluorescence and electrochemical signals produced by the interaction of the sensor compound with each of the OP pesticides provides a means for differentiating between the three pesticides. Detection limits of 10(-8)M, 10(-9) and 10(-12)M were obtained for fenthion, malathion and ethion, respectively. Due to the high sensitivity and ability to minimize false positives these new sensors will be useful for potential integration for future environmental use.

[4+2] Cycloaddition of 2-substituted 1,2-dihydropyridines with nitrosobenzene: asymmetric synthesis of trans-2-substituted 3-amino-1,2,3,6-tetrahydropyridines.

[reaction: see text] A new methodology for the stereoselective synthesis of trans-2-substituted 3-amino-1,2,3,6-tetrahydropyridines is reported. The preparation of these 3-aminopiperidines is achieved by cycloaddition of nitrosobenzene with 2-substituted 1,2-dihydropyridines followed by chemoselective reduction of the cycloadducts. Enantioenriched 1,2-dihydropyridine derivatives are easily prepared from pyridine and a chiral amide following a previous report from our laboratories. Moreover, the in situ hydrogenation of these cycloadducts over palladium in a solution of hydrogen chloride in methanol led to tetrahydropyrroloimidazoles.