The effect of the bridge group on the thermal stability of nitro-substituted aromatic polyamides

The effect of introducing a bridge group into the diamine moiety on the thermal stability of aromatic polyamides substituted with nitro group in the diamine ring at the ortho position to the amide group was studied. Our present work showed that the bridge group, whether it was electron withdrawing or releasing, did not have a significant effect on the activity of the nitro group for the intramolecular cyclization reaction to poly(benzoxazole)s.     

Novel cardo polyamides with high solubility,thermally stability,and flame retardancy

Abstract

A new monomeric building block was prepared via three consecutive reactions. 4-(4-Nitrobenzyl)pyridine was catalytically reduced to 4-(4-aminobenzyl)pyridine by converting the nitro to amino group. In second step, the later compound was reacted with 3,5-dinitrobenzoyl chloride to obtain a dinitro compound which finally was converted to a new diamine by reduction of nitro groups. Polycondensation reactions of the diamine with diacidchlorides led to preparation of novel cardo polyamides with high thermal stability and flame retardancy, as well as improved solubility. The structure-property relations were studied by varying the diacidchlorides to investigate the effect of symmetry and aromaticity on the polymers.     

Synthesis and characterization of heat resistant, pyridine-based polyimides with preformed ether and ester groups

A pyridine-based diamine as a building block for the preparation of heat resistant polyimides was prepared. Reaction of 1,5-dihydroxy naphthalene with 4-nitrobenzoyl chloride resulted in preparation of 5-hydroxy-1-naphthyl-4-nitrobenzoate (HNNB). 5-Hydroxyl-1-naphthyl-4-aminobenzoate (HNAB) was prepared via reduction of nitro group of HNNB. The diamine with built-in ether and ester groups was synthesized by nucleophilic substitution reaction of HNAB with 2,6-dichloropyridine in the presence of K₂CO₃. The obtained diamine was fully characterized and its polycondensation reaction with different aromatic dianhydrides led to preparation of novel heat resistant poly (ether ester imide)s. All the polymers were characterized and their physical and thermal properties were studied.     

Novel thermally stable poly(sulfone ether ester imide)s

A novel sulfone ether ester diamine was prepared by a three-step method. Reaction of 1,5-dihydroxy naphthalene with 4-nitrobenzoyl chloride afforded 5-hydroxy-1-naphthyl-4-nitrobenzoate. Reduction of nitro group by iron powder and HCl resulted in preparation of 5-hydroxyl-1-naphthyl-4-aminobenzoate. Reaction of this compound (two moles) with bis (4-chlorophenyl) sulfone led to preparation of a novel sulfone ether ester diamine. Three novel aromatic poly(sulfone ether ester imide)s were synthesized by polycondensation reactions of the prepared diamine with aromatic dianhydrides. Conventional methods were used to characterize the structure of the monomer and polymers. Physical properties of the polymers were also studied. The polyimides showed high thermal stability.     

Novel pyridine-based ether ester diamine and resulting thermally stable poly (ether ester amide)s

A novel pyridine-based ether ester diamine was prepared in three steps. Reaction of 1,5-dihydroxy naphthalene with 4-nitrobenzoyl chloride afforded 5-hydroxy-1-naphthyl-4-nitrobenzoate (HNNB). Reduction of nitro group resulted in preparation of an amino compound named 5-hydroxyl-1-naphthyl-4-aminobenzoate (HNAB). The diamine was synthesized by nucleophilic substitution reaction of 5-hydroxyl-1-naphthyl-4-aminobenzoate with 2,6-dichloropyridine in the presence of K₂CO₃. The obtained diamine was fully characterized and used to prepare novel thermally stable poly (ether ester amide)s via polycondensation reaction with different aromatic and aliphatic diacid chlorides. All the polymers were characterized and their physical and thermal properties were studied.     

Novel thermally stable polyimides based on flexible diamine: synthesis, characterization, and properties

A novel diamine with built-in sulfone, ether, and amide structure was prepared via three-step reactions. Nucleophilic reaction of 4-aminophenol with 4-nitrobenzoyl chloride in the presence of propylene oxide led to preparation of N-(4-hydroxy phenyl)-4-nitrobenzamide (HPNB). The nitro group of this compound was reduced with hydrazine and Pd/C to afford 4-amino-N-(4-hydroxy phenyl)benzamide (AHPB). Two moles of AHPB were reacted with bis-(4-chloro phenyl)sulfone to provide a novel sulfone ether amide diamine (SEAD). All the prepared compounds were characterized by common spectroscopic methods. The prepared diamine (SEAD) used to prepare related polyimides by reaction with different aromatic dianhydrides. The obtained poly(sulfone ether amide imide)s were characterized and their properties were studied.     

Potential Building Blocks for 1,4-Dihydro-N-heteroacenes

Studies have been performed aimed at the synthesis of N-heteroacenes via substitution reactions of 4,5-difluoro-1,2-dinitrobenzene with a diamine. The fluorine atoms are displaced first, followed by an activated nitro group. Two intermediates have been characterised by X-ray single-crystal structure determinations. Their intermolecular interactions were examined by Hirshfeld surfaces to assess their suitability for organic molecular electronics. The high reactivity of the phenazine, which is prone to oxidise and rearrange, as are displacement products prepared from it, is explained by the formation of a cis-aci-nitro form from the secondary amine of the phenazine and a nitro group.     

Modulating the Photochemistry of Bipyridylic Compounds by Symmetric Substitutions

A quantum electronic study of the effect of substituents on (2,2′‐bipyridyl)‐3,3′‐diol and (2,2′‐bipyridyl)‐3,3′‐diamine is presented. A large difference in the photochemical behavior between the original and the substituted selected systems is expected. For the sake of simplicity, the study is restricted to the symmetrically bi‐substituted compounds: fluorine, the more electronegative atom and thus a strong σ‐acceptor but also a weak π‐donor group, and NO₂, a strong π‐acceptor substituent. Among the large set of compounds studied, two receive special attention: 5,5′‐dinitro‐(2,2′‐bipyridyl)‐3,3′‐diamine and 6,6′‐difluoro‐(2,2′‐bipyridyl)‐3,3′‐diol. While in the former case the nitro substitution transforms (2,2′‐bipyridyl)‐3,3′‐diamine, previously suggested to behave as a photomemory material, into a simple fluorescent species, the latter substitution turns (2,2′‐bipyridyl)‐3,3′‐diol into a fresh new candidate for a photomemory device.     

ORGANOSOLUBLE,THERMALLY STABLE POLYAMIDES CONTAINING SULFONE AND SULFIDE UNITS

A new diamine containing sulfone,sulfide and amide groups was synthesized via a three-step reaction process. The nucleophilic substitution reaction of 4-aminothiophenol with 4-nitrobenzoyl chloride in the presence of propylene oxide (PO) afforded N-(4-mercaptophenyl)-4-nitrobenzamide(MPNB).The catalytic reduction of the nitro group in MPNB to amino group was accomplished by using Pd/C and hydrazine monohydrate to produce 4-amino-N-(4-mercapto phenyl)benzamide(AMPB).Reaction of two moles of AMPB with bis(...     

Polarographic study of the conduction of the polar effect of a substituent through the furan ring and side bridge groupings

The coefficients of conduction of the polar effect of a substituent through the furan ring and side bridge groupings were calculated by comparison of the polarographic half-wave potentials for the electroreduction of the nitro group in series of 5-substituted derivatives of 2-nitrofuran and p-substituted nitrobenzene derivatives by means of the - method. The polarographic method can be successfully used for this purpose in media in which the electrochemical process is not limited by the kinetics of the side process of surface protonation of the nitro group. It follows from the polarographic data and hyperfine structure of the ESR spectra of the anion radicals that the furan ring conducts the polar effect of substituents better (by a factor of 1.1–1.2) than the benzene ring. Depending on the electronic structure of the bridge groups, the introduction of bridge groups between the furan ring and the substituent decreases the conduction of the effect of substituents.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1309–1312, October, 1972.     

Concise and stereocontrolled synthesis of pseudo-C2-symmetric diamino alcohols and triamines for use in HIV protease inhibitors

A new protocol is described for the stereocontrolled synthesis of pseudo-C(2)-symmetric core units of interest as candidates for HIV protease inhibition. Addition of unbranched and branched organolithium reagents to cyanohydrins from l-phenylalaninal and l-isoleucinal, followed by in situ reduction of the intermediate imines and CHT deprotection under MW irradiation, led to 1,3-diamino alcohols 6a and 8a as the major products in satisfactory to good yields. The first preparation of a previously unreported pseudo-C(2)-symmetric triamino derivative was accomplished expeditiously via high-yielding nitro-Mannich addition of the silylnitronate, from 2-phenyl-1-nitroethane, to the PMP imine derived from l-phenylalaninal. Reduction of the nitro group in the moderately unstable nitro diamine adduct, followed by chromatographic separation of the required diastereoisomer and CHT debenzylation under MW irradiation, led to the 2-PMP-protected triamine 19 isolated as a bis(sulfonamide).     

Heat-resistant, pyridine-based polyamides containing ether and ester units with improved solubility

<正>A diamine containing ether and ester units,as basic monomer for the preparation of polyamides,was prepared via three consecutive reactions.Nucleophilic substitution reaction of 1,4-dihydroxy benzene with 4-nitrobenzoyl chloride produced 4-hydroxyphenyl 4-nitrobenzoate(HPNB).Reduction of nitro groups to amino groups using Fe and HC1 resulted in preparation of 4-hydroxyphenyl 4-aminobenzoate(HPAB).The diamine was synthesized through nucleophilic substitution reaction of HPAB with 2,6-dichloropyridine The precursors and diamine were fully characterized by common methods,and the diamine was polycondensed with different diacid chlorides in the presence of an acid scavenger to prepare new polyamides.The polyamides were characterized,and their physical properties including thermal stability and behavior, inherent viscosity and solubility were studied.     

Novel species of soluble thermally stable poly(keto ether ether amide)s: preparation,characterization, and properties

A new diamine containing one keto and four ether groups was prepared through a three‐step reaction: first, hydroquinone was reacted with 1‐fluoro‐4‐nitrobenzene and 4‐(4‐nitrophenoxy) phenol was obtained. The next step was reduction of nitro group to amino group in which 4‐(4‐aminophenoxy) phenol was prepared. In the final step, the new diamine named as bis(4‐(4‐(4‐aminophenoxy)phenoxy)phenyl) methanone was synthesized through reaction of the later compound with 4,4′‐difluoro benzophenone. All prepared materials were fully characterized by spectroscopic methods and elemental analysis. Novel species of poly(keto ether ether amide)s were synthesized via polymerization reaction of the diamine with different diacid chlorides including terephthaloyl chloride, isophthaloyl chloride, and adipoyl chloride. All polyamides were characterized, and their properties such as thermal behavior, thermal stability, solubility, viscosity, water uptake, and crystallinity were investigated and compared together. The glass transition temperatures of the polymers were about 204–232°C, and their 10% weight losses were in the range of 396–448°C. Polymers showed high thermal stability and enhanced solubility that mainly resulted from incorporation of the diamine structure containing keto, ether, and aromatic units into polyamide backbones. Copyright © 2014 John Wiley & Sons, Ltd.     

Poly(sulfone ether amide amide)s as a new generation of soluble, thermally stable polymers

A new sulfone ether amide diamine was synthesized via three steps, starting from reaction of 4-aminophenol with 4-nitrobenzoyl chloride in the presence of propylene oxide afforded N-(4-hydroxy phenyl)-4-nitrobenzamide (HPNB). In the next step, reduction of nitro group resulted in preparation of 4-amino-N-(4-hydroxy phenyl) benzamide (AHPB). Final step in the preparation of diamine was the reaction of AHPB with bis(4-chlorophenyl) sulfone in the presence of K₂CO₃. All the materials were characterized using conventional spectroscopic methods. Poly(sulfone ether amide amide)s were synthesized by polycondensation reactions of prepared diamine with different diacid chlorides (aromatic and aliphatic ones). The obtained polymers were fully characterized and their physical properties including thermal behavior, thermal stability, solubility, and inherent viscosity were studied.     

Use of copper(II)/diamine catalysts in the desymmetrisation of meso-diols and asymmetric Henry reactions: comparison of (−)-sparteine and (+)-sparteine surrogates

Four new copper(II)/diamine complexes comprising some (+)-sparteine surrogates and a cyclohexane-derived diamine were prepared and evaluated as chiral catalysts in desymmetrisation of meso-diols and asymmetric Henry reactions. Mono-benzoylation reactions generated two products with high enantioselectivity (90:10 to 97:3 er). Asymmetric Henry reactions gave nitro alcohols in 90:10 to 98:2 er. Notably, the sense of induction with the (+)-sparteine surrogates was opposite to that obtained using the copper(II)/(−)-sparteine complex. One of the nitro alcohol products was utilised in a concise synthesis of a chiral morpholine.     

Preparation,characterization, and properties of novel category of processable thermally stable poly(ether ether imide)s

New poly(ether ether imide)s were synthesized based on an aromatic diamine containing pyridine and four ether groups. Diamine was designed to induce desirable properties to final polymer such as flexibility and processability in addition to thermal stability. The diamine was synthesized via a three-step procedure. Firstly, 1-fluoro-4-nitrobenzene was reacted with hydroquinone to obtain a nitrophenol compound. Next, the catalytic reduction was performed to convert nitro to amino group. Finally, the resulted aminophenol was reacted with 2,6-dichloropyridine and the diamine was synthesized. Polycondensation reactions of the diamine with three dianhydrides led to the preparation of novel poly(ether ether imide) films. All prepared materials and polymers were completely characterized. Thermal stability and glass transition temperature of polyimides were measured and compared. Mechanical properties and cross-section morphology of films were also investigated. Poly(ether ether imide)s revealed unique balance of physical and thermal properties including very high flexibility along with outstanding thermal stability.     

A fundamental study on the fluorescence-quenching effect of nitro groups in tetraphenylethene AIE dyes with electron-withdrawing groups

A nitro group is a common fluorescence quencher, but its quenching efficiency can be easily affected by the surrounding environment. To date, there has been no systematic study on the effects of electronwithdrawing groups on the quenching efficiency of nitro groups. Herein, by virtue of experimental validation and theoretical calculations, we found that strong electron-withdrawing groups, such as pyridinium and dicyanovinyl groups, are detrimental to the quenching effect of nitro groups. Decreasing the electron-withdrawing ability could restore the nitro group's quenching effect.     

Synthesis of 2,2′-diamino-7-tert-butyl-9,9′-spirobifluorene starting from 4,4′-di-tert-butylbiphenyl

Abstract  

A novel spirobifluorene diamine monomer, 2,2′-diamino-7-tert-butyl-9,9′-spirobifluorene, was obtained starting from the readily available reagent 4,4′-di-tert-butylbiphenyl. The key step of the synthesis is the introduction of a nitro group into the 2-position of the spirobifluorene through the loss of tert-butyl at the 2-position.     

Basicity of nitropyrazoles and their simultaneous spectrophotometric determination

The protonation constants of some 1-, 3(5)-, 3-, 4- and 5-nitropyrazoles have been determined, and compared with those of nitroimidazoles. The effect of the position of the nitro group in the pyrazole and imidazole ring is discussed. The ortho effects of the nitro group in pyrazole and imidazole are compared and found to have identical values. The effect of the nitro group on protonation constants is greater when the nitro group is close to the pyridine nitrogen atom. This, together with the ability of N-unsubstituted nitropyrazoles to dissociate to give nitropyrazole anions, with an accompanying shift of the spectra to longer wavelengths, permits the simultaneous spectrophotometric determination of nitropyrazoles.     

Synthesis of nonlinear optical polyimides containing azodiamine derivative chromophores and their electrooptic and thermal properties

Some thermally stable second‐order nonlinear optical (NLO) polyimides were synthesized. The polyimides were prepared by the ring‐opening polyaddition of 4,4′‐(hexafluoroisopropylidene) diphthalic anhydride and pyromellitic dianhydride with two aromatic azodiamine derivatives as the NLO chromophores. These chromophores, based on a nitro group connected with azobenzene as the acceptor end of a donor–π‐bridge–acceptor chromophore and a diamine group as the donor end, had specific chemical stability. On the basis of ZERNER'S INDO methods, according to the sum‐over‐states formula, a program for the calculation of nonlinear second‐order optical susceptibilities was devised. The resulting polyimides had high number‐average and weight‐average molecular weights of up to 26,000 and 53,500, respectively, and a large glass‐transition temperature of 248 °C. With an in situ poling and temperature ramping technique, the optimal temperatures (T_opt's) for corona poling were obtained for the largest second‐order NLO response. The electrooptic coefficient (γ₃₃) of a polyimide at a wavelength of 830 nm was up to 21 pm/V after corona poling under its T_opt, and the value remained at elevated temperatures (>90.6% was retained at 240 °C for >120 h). The thermal stability of the NLO polyimides was studied with UV spectrometry after poling of the films. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2478–2486, 2002