Organic reactions in ionic liquids:ionic liquids ethylammonium nitrate promoted Knoevenagel condensation of aromatic aldehydes with active methylene compounds

The Knoevenagel condensation of aromatic aldehydes with active methylene compounds proceeded efficiently in a reusable ionic liquid, ethylammonium nitrate, at room temperature in the absence of any catalyst with high yields.

Organic reactions in ionic liquids:Ionic liquid promoted Knoevenagel condensation of aromatic aldehydes with (2-thio)barbituric acid

The Knoevenagel condensation of aromatic aldehydes with (2-thio)barbituric acid proceeded efficiently in reusable ionic liquids, EAN, BmimBF4, and BmimPF6 at room temperature in the absence of any catalyst with high yields.

Organic reactions in ionic liquids: ionic liquid-accelerated nucleophilic substitution reaction of alpha-tosyloxyketones with potassium salts of aromatic acids

The room temperature ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) is used as a ‘green' recyclable alternative to classical molecular solvents for the nucleophilic substitution reaction of a-tosyloxy ketones with potassium salts of aromatic acids. Significant rate enhancement and improved yields have been observed.

The adsorptive separation of aromatic hydrocarbon mixtures

A detailed study has been made of the feasibility of adsorptive purification of slack waxes from traces of aromatic compounds using type 13X molecular sieves to achieve 0.01% aromatics in the product. The limited literature relating to the adsorption of high molecular weight aromatic compounds by zeolites was reviewed. Equilibrium isotherms were determined for typical individual aromatic compounds. Lower molecular weight, or more compact, molecules were preferentially adsorbed and the number of molecules captured by one unit cell decreased with increasing molecular weight of the adsorbate. An increase in adsorption temperature resulted in a decrease in the adsorption value. The isosteric heat of adsorption of differnt types of aromatic compounds was determined from pairs of isotherms at 303 K to 343 K at specific coverages. The lowest heats of adsorption were for dodecylbenzene and phenanthrene. Kinetics of adsorption were studied for different aromatic compounds. The diffusivity decreased significantly when a long alkyl chain was attached to the benzene ring e.g. in dodecylbenzene; molecules with small cross-sectional diameter e.g. cumene were adsorbed most rapidly. The sorption rate increased with temperature. Apparent activation energies increased with increasing polarity. In a study of the dynamic adsorption of selected aromatic compounds from binary solutions in isooctane or n-alkanes, naphthalene exhibited the best dynamic properties followed by dibenzothiophene and finally dodecylbenzene. The dynamic adsorption of naphthalene from different n-alkane solvents increased with a decrease in solvent molecular weight. A tentative mathematical approach is proposed for the prediction of dynamic breakthrough curves from equilibrium isotherms and kinetic data. The dynamic properties of liquid phase adsorption of aromatics from slack waxes were studied at different temperatures and concentrations. The optimum operating temperature was 543 K. The best dynamic performance was achieved with feeds of low aromatic content. The studies with individual aromatic compounds demonstrated the affinity of type NaX molecular sieves to adsorb aromatics in the concentration range 3% - 5% . Wax purification by adsorption was considered promising and extension of the experimental programme was recommended.

Detection of organic aromatic compounds in paraffin by a long-period fiber grating optical sensor with optimized sensitivity

A long-period grating (LPG) sensor is used to detect small variations in the concentration of an organic aromatic compound (xylene) in a paraffin (heptane) solution. A new design procedure is adopted and demonstrated to maximize the sensitivity of LPG (wavelength shift for a change in the surrounding refractive index, (dλ/dn3)) for a given application. The detection method adopted is comparable to the standard technique used in industry (high performance liquid chromatograph and UV spectroscopy) which has a relative accuracy between ∼±0.5% and 5%. The minimum detectable change in volumetric concentration is 0.04% in a binary fluid with the detection system presented. This change of concentration relates to a change in refractive index of Δn ∼ 6 × 10-5. © 2001 Elsevier Science B.V.

Phenols and aromatic amines as thermal stabilizers in polyolefin processing

Scavenging of C- and O-centered free radicals is mandatory in processing stabilization of polypropylene. Phenolic antioxidants act principally as O-radical scavengers only. Aromatic amines, N,N'-disubstituted 1,4-phenylenediamines (PD) and 4,4'disubstituted diphenylamines (DPA), scavenge both C- and O-centered radicals and have consequently a broader activity spectrum. PD cannot be used, however, in polypropylene because of formation of strongly discoloring and staining sacrificial transformation products. Such products formed from DPA have even more discoloring properties. A good processing stability and acceptable extent of discoloration can be achieved by blends of phenols with 4,4'-di-tert.octyl DPA. The effect is considered as a beneficial cooperation between the two chain-breaking antioxidants involving interactions with amine-based transformation products.

Octahedral molybdenum cluster complexes with aromatic sulfonate ligands

This article describes the synthesis, structures and systematic study of the spectroscopic and redox properties of a series of octahedral molybdenum metal cluster complexes with aromatic sulfonate ligands (nBu4N)2[{Mo6X8}(OTs)6] and (nBu4N)2[{Mo6X8}(PhSO3)6] (where X- is Cl-, Br- or I-; OTs- is p-toluenesulfonate and PhSO3 - is benzenesulfonate). All the complexes demonstrated photoluminescence in the red region and an ability to generate singlet oxygen. Notably, the highest quantum yields (>0.6) and narrowest emission bands were found for complexes with a {Mo6I8}4+ cluster core. Moreover, cyclic voltammetric studies revealed that (nBu4N)2[{Mo6X8}(OTs)6] and (nBu4N)2[{Mo6X8}(PhSO3)6] confer enhanced stability towards electrochemical oxidation relative to corresponding starting complexes (nBu4N)2[{Mo6X8}X6].