Advances in gas-phase electrophilic aromatic substitution reaction

Recent advances in the gas - phase reaction of aromatics with cationic electrophiles are reviewed. The overall substitution reaction is analyzed in terms of its elementary steps. Mechanistic studies have been focused on the structure and reactivity of covalent and non - covalent ionic intermediates, which display a rich chemistry and provide benchmark reactivity models. Particular attention has been devoted to proton transfer reactions, which may occur intra or intermolecularly in arenium intermediates.

Synthesis and characterization of aromatic dianhydrides and polyesterimides derived from 4-hydroxyphthalic anhydride

4-Hydroxyphthalic anhydride, prepared from 4-chlorophthalic anhydride, was reacted with trimellitic anhydride monoacid chloride or arylene diacid chloride to give aromatic ester-containing dianhydrides (EDAs). These dianhydrides were characterized by element analysis, melt point, FTIR and H-1-NMR. A series of aromatic poly (amic ester acid)s was synthesized by polycondensation of these EDAs and various diamines in polar organic solvent. The inherent viscosity of poly (amic ester acid)s ranged from 0.55 to 0.89 dL/g, indicating the intermediate to higher molecular weight. Polyesterimides having glass transition temperatures between 184-219degreesC were produced by thermal imidization of corresponding poly (amic ester acid)s. These polymers were fairly resistant to organic solvent, but some of them were soluble in phenol solvents. Thermogravimetric analyses revealed that these polyesterimides were stable up to 400degreesC, and the 5% weight loss temperatures were recorded in the range of 432-483degreesC in air atmosphers and 451-490degreesC in nitrogen.

Synthesis and characterization of optically active aromatic polyimides derived from 2,2 '-bis(2-trifluoro-4-aminophenoxy)-1,1 '-binaphthyl and aromatic tetracarboxylic dianhydrides

Optically active 2,2'-bis(2-trifluoro-4-aminophenoxy)-1,1'-binaphthyl and its corresponding racemate were prepared by a nucleophilic substitution reaction of 1,1'-bi-2-naphthol with 2-chloro-5-nitrotrifluorotoluene and subsequently by the reduction of the resulting dinitro compounds. a series of optically active and optically inactive aromatic polyimides also were prepared therefrom, These polymers readily were soluble in common organic solvents such as pyridine, N,N'-dimethylacetamide, and m-cresol and had glass-transition temperatures of 256 similar to 278 degrees C. The specific rotations of the chiral polymers ranged from 167 similar to 258 degrees, and their chiroptical properties also were studied. (C) 1999 John Wiley & Sons Inc.

Synthesis of a new kind of polyamide and polyester including aromatic spirodilactone

A new kind of monomers including aromatic spirodilactone-5, 5'-carboxy-7,7'-dioxo-2,2'-spirobi(benzo-[c]tetrahydrofuran) is synthesized from m-xylene and paraformaldehyde. It is converted to a series of polyamides and polyesters by means of low-temperature solution polycondensation and interfacial polycondensation. NMR and IR spectra, solubility, mechanical and thermal properties of all these polymers are investigated. The polymers have high glass transition temperatures and good thermal oxidative properties. All polyamides have high viscosity and good solubility in strong polar organic solvents such as DMSO, DMAc, DMF and NMP. All polyamides can be cast into transparent, flexible and tough films possessing good tensile properties.

End-column electrochemical detection for aromatic amines with high performance capillary electrophoresis

Electrochemical detection of five species of aromatic amines at a carbon fiber microdisk electrode after separation by capillary electrophoresis is described. Under the optimum conditions, the detection limit for 3,4-dihydroxybenzylamine, N,N-dimethylaniline, p-phenylenediamine, p-aminophenol and aniline sulfate was 0.9, 0.03, 0.075, 1.2 and 0.15 mu M (S/N = 3), respectively. The linear response range was 5-1000, 0.1-500, 0.5-500, 5-500 and 1-200 mu M, respectively The effect of the electrode position and buffer pH on the detection was also studied. This method is very simple, sensitive and stable for the detection of these compounds.

New optically active aromatic polyimides II: Synthesis and properties of optically active aromatic polyimide based on (R)-(+)-2,2 '-bis(2-trifluoro-4-aminophenoxy)-1,1 '-binaphthyl

Optically active (R)-(+)-2, 2'-bis(2-trifluoro-4-aminophenoxy)-1, 1'-binaphthyl was prepared from 1, 1'-bi-2-naphthol. The optically active aromatic polyimide was also successfully synthesized. This new polymer has good solubility, thermal stability etc. Its specific rotation was found to be +174 degrees, and its chiroptical property was also studied.

Synthesis and properties of aromatic polyimides derived from 2,2,' 3,3 '-biphenyltetracarboxylic dianhydride

2,2,'3,3' -Biphenyltetracarboxylic dianhydride (2,2,'3,3'-BPDA) was prepared by a coupling reaction of dimethyl 3-iodophthalate. The X-ray single-crystal structure determination showed that this dianhydride had a bent and noncopolanar structure, presenting a striking contrast to its isomer, 3,3,'4,4'-BPDA. This dianhydride was reacted with aromatic diamines in a polar aprotic solvent such as N,N-dimethylacetamide (DMAc) to form polyamic acid intermediates, which imidized chemically to polyimides with inherent viscosities of 0.34-0.55 dL/g, depending on the diamine used. The polyimides from 2,2,'3,3'-BPDA exhibited a good solubility and were dissolved in polar aprotic solvents and polychlorocarbons. These polyimides have high glass transition temperatures above 283 degrees C. Thermogravimetric analyses indicated that these polyimides were fairly stable up to 500 degrees C, and the 5% weight loss temperatures were recorded in the range of 534-583 degrees C in nitrogen atmosphere and 537-561 degrees C in air atmosphere. All polyimides were amorphous according to X-ray determination. (C) 1999 John Wiley & Sons, Inc.

Synthesis of aromatic polyimides in DMAc containing large amount of water and the properties thereof

A series of polyamic acids were prepared in N,N-dimethylactamide (DMAc) containing large amount of water, some of which contain the amount of water up to 25%. Their inherent viscosities decreased with the increase of water in DMAc, depending on the electronic properties of dianhydride and reaction condition. The molecular weights and mechanical properties of the polyimides thermally imidized from the polyamic acids were almost independent on the water content in solvent. The decomposition-resynthesis of polyamic acids during the curing was also investigated.

Intramolecular energy transfer mechanism between ligands in ternary rare earth complexes with aromatic carboxylic acids and 1,10-phenanthroline

A series of binary and ternary rare earth (Gd, Eu, Tb) complexes with aromatic acids and 1,10-phenanthroline have been synthesized. The lowest triplet state energies of ligands have been obtained by measuring the phosphorescence spectra of binary gadolinium complexes. By comparing the phosphorescence spectra of binary complexes with those of ternary ones, it is found that there exists another intramolecular energy transfer process from the aromatic acids to 1,10-phenanthroline besides the intramolecular energy transfer process between the aromatic acids and the central rare earth ions. The intramolecular energy transfer efficiencies have been calculated by determining phosphorescence lifetimes of binary and ternary gadolinium complexes. The luminescence properties of corresponding europium and terbium complexes are in agreement with the prediction based on energy transfer mechanism. (C) 1998 Elsevier Science S.A. All rights reserved.

Spectroscopic study of luminescence and energy transfer of binary and ternary complexes of rare earth with aromatic carboxylic acids and 1,10-phenanthroline

A series of rare earth (Gd, Eu, Tb) complexes with different substituent group carboxylic acids (ortho-hydroxylbenzioc acid, ortho-aminobenzoic acid and ortho-methoxy benzoic acid) and 1,10-phenanthroline were synthesized. The spectroscopic studies of the photophysical properties such as luminescence properties, energy match and intramolecular energy transfer were carried out. The lowest triplet state energies of ligands and the intramolecular energy transfer efficiencies were determined with the measurement of low phosphorescence spectra and lifetimes of Gd complexes.

Synthesis, luminescence and intramolecular energy transfer of binary and ternary rare earth complexes with aromatic carboxylic acids and 1,10-phenanthroline

A series of binary and ternary rare earth complexes with para-substitued benzoic acids and 1,10-phenanthroline were synthesized. The phosphorescence spectra were measured and the lowest tripler state energies of ligands were determined, the phosphorescence lifetimes were obtained and intramolecular energy transfer mechanism between ligands was studied. The luminescence properties were also measured and were in agreement with the prediction. The energy match and intramolecular energy transfer process in these binary and ternary complexes were discussed in detail.

Gas separation with organo-soluble high performance aromatic polyimide films

An organo-soluble polyimide based on 4,4'-(1,4-phenylenedioxy)diphthalic anhydride and 2,2'-dimethyl-4,4'-methylenedianiline was synthesized by two-step polycondensation accompanied by chemical imidization. Polyimide films were prepared by spray casting onto glass substrates. The study focused on the separation of carbon dioxide (CO2) from natural gas and the enrichment of methane (CH4) from butane (C4H18). The permeability and permselectivity coefficients of these gases were determined.

Synthesis and properties of optically active aromatic polyimides derived from optically pure 1,1'-bi-2-naphthol

A series of new optically active aromatic polyimides containing axially dissymmetric 1,1'-binaphthalene-2,2-diyl units were prepared from optically pure (R)-(+)-or (S)-(-)-2,2'-bis(3,4-dicarboxyphenoxy)-1,1'-binaphthalene dianhydrides and various aromatic diamines via a conventional two-step procedure that included ring-opening polycondensation and chemical cyclodehydration. The optically pure isomer of dianhydride was prepared by a nucleophilic substitution of optically pure (R)-(+)or (S)-(-)1,1'-bi-2-naphthol with 4-nitrophthalonitrile in aprotic polar solvent and subsequent hydrolysis of the resultant tetranitrile derivatives, followed by the dehydration of the corresponding tetracarboxylic acids to obtain the dianhydrides. These polymers were readily soluble in common organic solvents such as N,N-dimethylacetamide, N-methyl-2-pyrrolidone, and m-cresol, etc., and have glass transition temperatures of 251-296 degrees C, and 5% weight loss occurs not lower than 480 degrees C. The specific rotations of the optically active polyimides ranged from +196 degrees to +263 degrees, and the optical stability and chiroptical properties of them were also studied. (C) 1997 John Wiley & Sons, Inc.

Synthesis, luminescence properties and energy transfer of binary and ternary rare earth complexes with aromatic acids and 1,10-phenanthroline

A series of binary and ternary rare earth (Gd, Eu, Tb) complexes with ortho hydroxyl benzoic acid, pam aminobenzoic acid, nicotinic acid and 1,10-phenanthroline were synthesized. Phosphorescence spectra and lifetimes of Gd complexes were measured and the lowest triplet state energies of gadolinium binary complexes end the intramolecular energy transfer efficiencies were determined. The luminescence properties and energy transfer process of Eu3+ and Tb3+ complexes were discussed.

Synthesis and miscibility studies of rodlike flexible polyimide molecular composites via para-para linked aromatic poly(amic ester) precursors

Para-para linked aromatic poly(amic ester) precursors of rodlike polyimide (PI) BPDA-PDA and polyetherimide (PEI) HQDPA-ODA were synthesized. The para-para linked poly(amic ester)s were employed in this work to obtain, in theory, full-imidized polyimides. The two precursors were mixed by dissolving them in N, N'-dimethyl acetamide and subsequently coagulating in methanol. After thermal imidization, the miscibility behaviour of the resulting composites has been studied by means of dynamic mechanical analysis (d.m.a.) and differential scanning calorimetry (d.s.c.). The composites show a single glass transition temperature (T-g) at both d.m.a. and d.s.c. in which the T-g increases with increasing PI content. These Tg values are reproducible in repeated heating cycles, suggesting the true miscibility of the blends. (C) 1997 Elsevier Science Ltd.