Synthesis and characterization of novel fluorinated polyimides derived from 4,4′‐[2,2,2‐trifluoro‐1‐(3‐trifluoromethylphenyl)ethylidene]diphthalic anhydride and aromatic diamines

A novel fluorinated aromatic dianhydride, 4,4′‐[2,2,2‐trifluoro‐1‐(3‐trifluoromethyl‐phenyl)ethylidene]diphthalic anhydride (TFDA) was synthesized by coupling of 3′‐trifluoromethyl‐2,2,2‐trifluoroacetophenone with o‐xylene under the catalysis of trifluoromethanesulfonic acid, followed by oxidation of KMnO₄ and dehydration. A series of fluorinated aromatic polyimides derived from the novel fluorinated aromatic dianhydride TFDA with various aromatic diamines, such as p‐phenylenediamine (p‐PDA), 4,4′‐oxydianiline (ODA), 1,4‐bis(4‐aminophenoxy)benzene (p‐APB), 1,3‐bis(4‐amino‐phenoxy)benzene (m‐APB), 4‐(4‐aminophenoxy)‐3‐trifluoromethylphenylamine (3FODA) and 1,4‐bis(4‐amino‐2‐trifluoromethylphenoxy)benzene (6FAPB), were prepared by polycondensation procedure. All the fluorinated polyimides were soluble in many polar organic solvents such as NMP, DMAc, DMF, and m‐cresol, as well as some of low boiling point organic solvents such as CHCl₃, THF, and acetone. Homogeneous and stable polyimide solutions with solid content as high as 35–40 wt % could be achieved, which were prepared by strong and flexible polyimide films or coatings. The polymer films have good thermal stability with the glass transition temperature of 232–322 °C, the temperature at 5% weight loss of 500–530 °C in nitrogen, and have outstanding mechanical properties with the tensile strengths of 80.5–133.2 MPa as well as elongations at breakage of 7.1–12.6%. It was also found that the polyimide films derived from TFDA and fluorinated aromatic diamines possess low dielectric constants of 2.75–3.02, a low dissipation factor in the range of 1.27–4.50 × 10^?3, and low moisture absorptions <1.3%. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4143–4152, 2004     

Substituent effects of phosphorus and arsenic containing groups in aromatic substitution—II : Nitration of benzylphosphonic acid and related compounds

The reactivities of benzylphosphonic acid (protonated and unprotonated) and β-phenylethylphosphonic acid have been determined for nitration. The highly selective para/ortho orientation has been confirmed. The relative reactivities of systems PhX and PhCH₂X for some substituents are discussed.     

NHC-catalyzed generation of difluorocarbene and its application to difluoromethylation of oxygen nucleophiles

Controlled generation of difluorocarbene was effected by an NHC catalyst under mild conditions starting from trimethylsilyl 2,2-difluoro-2-fluorosulfonylacetate (TFDA). Cyclohexenones and tetralones were treated with TFDA in the presence of catalytic amounts of N,N′-dimesitylimidazolium chloride and sodium carbonate. The ketones were difluoromethylated with the generated difluorocarbene to afford enol difluoromethyl ethers without difluorocyclopropanation. The ethers thus obtained were dehydrogenated with DDQ to furnish aryl difluoromethyl ethers in high yield. Under similar conditions, secondary amides underwent difluoromethylation selectively on the oxygen atom to give difluoromethyl imidates, which allows the formation of 2-difluoromethoxypyridines.     

Activation of Methane and Ethane as Mediated by the Triatomic Anion HNbN−: Electronic Structure Similarity with a Pt Atom

Investigations of the intrinsic properties of gas‐phase transition metal nitride (TMN) ions represent one approach to gain a fundamental understanding of the active sites of TMN catalysts, the activities and electronic structures of which are known to be comparable to those of noble metal catalysts. Herein, we investigate the structures and reactivities of the triatomic anions HNbN^? by means of mass spectrometry and photoelectron imaging spectroscopy, in conjunction with density functional theory calculations. The HNbN^? anions are capable of activating CH₄ and C₂H₆ through oxidative addition, exhibiting similar reactivities to free Pt atoms. The similar electronic structures of HNbN^? and Pt, especially the active orbitals, are responsible for this resemblance. Compared to the inert NbN^?, the coordination of the H atom in HNbN^? is indispensable. New insights into how to replace noble metals with TMNs may be derived from this combined experimental/computational study.     

Selective Synthesis by Use of Lewis Acids in the Presence of Organocopper and Related Reagents. New Synthetic Methods (61)

Organometallic compounds with pronounced nucleophilicity such as organocopper and organolithium compounds, and powerful electrophiles, such as BF₃ and AlCl₃, are generally thought to be incompatible under normal, homogeneous reaction conditions. As a matter of course, it is anticipated that the two species cannot coexist and undergo transmetalation reactions. To our surprise, however, RCu and BF₃ are compatible at low temperature. RCu·BF₃ and related organocopper-Lewis acid reagents exhibit new and unique reactivities and selectivities: in conjugate additions, e.g., not only activation but also high regio-, stereo-, and chemo-selectivity as well as very high asymmetric induction is observed; allylic derivatives are alkylated regioselectively, and reaction towards carbonyl groups, imines, epoxides, aziridines, ethers, acetals, orthoformates, and pyridinium salts is in each case found to be selective. RLi·BF₃ and related organolithium-Lewis acid reagents also exhibit noteworthy selectivities and reactivities. These complex reagents are utilized in the key steps of the total synthesis of many important natural products, such as certain terpenes, steroids, and alkaloids.     

Copolymeric nano/microgels of N-isopropylacrylamide and carboxyalkyl methacrylamides: Effect of methylene chains and the ionization state of the weak acids on size and sensitivity to pH and temperature

ABSTRACT

We prepared nano/microgels by precipitation copolymerization of N-isopropylacrylamide (NIPAAm), and one of three different carboxyalkyl methacrylamides [methacryloylamido hexanoic acid (M₅), 8-methacryloylamido octanoic acid (M₇), and 11-methacryloylamido undecanoic acid (M₁₀)], either in the acid forms or as carboxylates (potassium salts). The hydrodynamic diameter (Dh) of the nano/microgels prepared with the carboxylates was smaller (≈100 nm for M₁₀ copolymers), compared to the size of homopolymeric NIPAAm microgels prepared by dispersion polymerization (around 600 nm), indicating that the carboxylates act as surfactants reducing the size of the seeds during the polymerization process. These materials presented a swollen-shrunken transition temperature (T _tr) similar to the T _tr of the homopolymeric NIPAAm microgels, without pH sensitivity. On the other hand, the copolymeric microgels prepared from the acid form of the comonomers have a similar or bigger size than NIPAAm microgels. For these copolymers, the T _tr can be tuned by the type and proportion of acid comonomer used and present pH sensitivity. This is important for biomedical applications such as positive temperature control release. Polyelectrolyte titration demonstrates that the nano/microgels prepared with the carboxylates behave as hard spheres, while the microgels prepared with the weak acid behave as porous materials.     

Reaction of difluorocarbene with propargyl esters and efficient synthesis of difluorocyclopropyl ketones

Difluorocarbene generated from FSO₂CF₂CO₂SiMe₃ (TFDA) at 120 °C could reacted with terminal alkynes having an ester group at the α position to the triple bond. Difluorocyclopropenes were further converted to difluorocyclopropyl ketones under alkaline condition. Mechanism for the conversion was studied.     

Influence de la solvatation par le tert-butanol sur la structure et la reactivite de l'enolate de potassium de l'acetylacetate d'ethyle en presence de couronne ou de cryptand. etude par spectrometrie infra-rouge et cinetique

The structure and the nucleophilic reactivity of crowned (18-crown-6) or cryptated {cryptand (2.2.2)} potassium ethyl acetoacetate enolate have been compared in tert-butanol and in DME (or THF). In the protic solvent tert-butanol, the crowned and the cryptated potassium enolate species both exist as loose ion pairs in which the enolate anion, strongly hydrogen-bonded to the solvent, is in a “transoid” (non chelating) conformation. Both species show similar reactivities towards alkylating agents but completely different reactivities are observed in aprotic weakly dissociating media (THF, DME). In contrast to what is observed in tert-butanol, the cryptated species and the crowned species have very different nucleophilic reactivities in THF or DME; in those solvents only the cryptated species retains a loose ion pair structure; the crowned species is a contact ion pair in which the enolate anion chelates the potassium cation. The solvation of this crowned chelate species by tert-butanol has been demonstrated in binary mixtures of solvents (C₆D₆-t-BuOH, THF-t-BuOH). The oxygen basicity of the enolate anion is very different in the crowned chelated ion pair compared with the cryptand separated ion pair.     

Studies on human proinsulin C-peptide radioimmunoassay method--preparation of antiserum and its specificity-- (author's transl)]

The antisera using at final dilution of 1 : 10,000 have been prepared by immunizing synthetic human proinsulin connecting peptide to rabbits for human proinsulin C-peptide radioimmunoassay. The cross reactivities of human proinsulin C-peptide derivatives with the prepared antisera were reduced by leaving amino acid residues from N terminal, although this phenomenon was a little different among antisera. Those results suggested that main antigen determinant in N terminal 31-38 of human proinsulin connecting peptide. The cross reactivities of other animal proinsulin C-peptide and other peptide hormones with the prepared antissera were not recognized at 10(3) p mole/ml.     

Synthesis of (R)-3-Methylpyrrolidine Alkaloids Using (S)-Malic Acid as a Chiral Pool

Previous work in our laboratory was around the development of chiral 2-pyrrolidinone synthon A. Malimides 1 and 2, which can be easily prepared from (S)-malic acid, have been shown to be versatile chiral synthetic intermediates. All the reactivities showed in synthon A have been exploited.1     

Characterization of vanadium-based olefin polymerization catalyst precursors by solid-state 51v-nmr

Several VOCL₃-based ethylene polymerization catalyst precursors were prepared on silica and studied by solid-state ⁵¹V-NMR. The structure of the vanadium species in these samples, as determined by ⁵¹V-NMR, did not have any significant effect on the resultant polyethylene MI or MWD. This result is significant since conventional wisdom says the attachment of the transition metal to the silica plays a key role in polymer properties. VOCl₃ reacted with hexamethyldisilazane-treated silica and with 250°C dried silica results in double attachment of the vanadium to the silica, yet the catalysts which formed had different reactivities and produced polyethylene with different HLMIs. On the other hand, VOCl₃ reacted with 600°C dried silica results in single attachment of the vanadium to the silica, yet this catalyst had a similar reactivity and produced polymer properties similar to the doubly attached vanadium on 250°C dried silica. Two theories are offered to explain the lack of correlation between catalyst precursor structure and catalyst performance. © 1995 John Wiley & Sons, Inc.     

Palladium supported on urea-containing porous organic polymers as heterogeneous catalysts for C–C cross coupling reactions and reduction of nitroarenes

The novel palladium nanoparticles (Pd@POPs) were successfully prepared with controllable sizes and dispersity through the introduction of H₂PdCl₄ into urea-linked porous organic polymers (POPs) in an aqueous environment followed by reducing Pd(II) to Pd(0) by NaBH₄. The newly prepared Pd@POPs were thoroughly characterized by FT-IR, ICP-AES, BET, XRD, SEM and TEM. Furthermore, the catalytic reactivities of this novel Pd@POPs were investigated via Heck, Suzuki-Miyaura cross-coupling reaction and nitroarene reduction, and they exhibited superior catalytic performances in all these three reactions, producing the corresponding products in up to quantitative yields. Additionally, the Pd@POPs had excellent recyclability in both Heck and Suzuki-Miyaura cross-coupling reactions with the repeating time up to four times and ten times, respectively, along with no obvious decrease of catalytic reactivities.     

Development of N,N-bis(perfluoroalkanesulfonyl)squaramides as new strong Brønsted acids and their application to organic reactions

New strong Brønsted acids derived from a squaric acid scaffold bearing different perfluoroalkanesulfonyl groups have been developed and applied to several organic reactions. These squaramides are bench-stable and exhibit much higher reactivities in several organic reactions than squaric acid itself. N,N-Bis(trifluoromethanesulfonyl)squaramide 2a was applied to the Mukaiyama aldol reaction and Mukaiyama Michael reaction. Mechanistic studies revealed that the Brønsted acid might be the predominant catalyst through direct protonation of carbonyl compound by the acid itself rather than the silylated Brønsted acid. The utility of this acid 2a was further extended to Hosomi-Sakurai allylation of aldehydes and a carbonyl-ene reaction. Furthermore, other squaramides 2b and c bearing longer perfluoroalkyl chains have been developed, which are also bench-stable and displayed similar reactivities with squaramide 2a in several organic reactions.     

Kinetics and mechanism of ligand substitution in binuclear nickel(II) and cobalt(II) complexes

The kinetics and mechanism of the removal of M²⁺ from bis-(heptane-2,4,6-trionato)M(II) [M = Ni, Co] by ethylenediminetetraacetic acid (EDTA), nitrilotriacetic acid (NAT), 1,2-cyclohexanediamine-N, N, N′, N′-tetraacetic acid (C_yDTA), and ethylenebis(oxyethylenenitrilo)tetraacetic acid (EGTA) have been investigated using stopped-flow spectrophotometry in methanol-water at 25°C and ionic strength 0.1 mol dm^?3 KNO₃. The reactions were investigated at a number of different pHs. An associative mechanism is proposed to account for the kinetic data. Although all the ligands have similar functional groups, their reactivity towards the parent complex is quite different. The pH dependence of the rate constants has been used to determine the relative reactivities of the various ligand species present. In the case of nitrilotriacetic acid, a nonlinear dependence on ligand concentration is observed, thus confirming the mechanism proposed. © 1995 John Wiley & Sons, Inc.     

Relation between the reactivities of vinyl monomers in ionic polymerizations and their 1H NMR spectra

¹H NMR chemical shifts of the protons in the vinyl groups of monomers are correlated with their reactivities in anionic, coordinated anionic, and cationic polymerizations. The relative reactivities of styrenes in anionic addition reactions with living polystyrene increase linearly with the chemical shift of the proton trans to the substituent (δ_H1). Only the plot for 2,4,6-trimethylstyrene deviates very much from the linear relation because of the large steric hindrance. The relative reactivities of methacrylates in anionic copolymerizations increase with increasing chemical shifts of protons attached to the β-carbon of methacrylates. In cationic polymerizations of styrenes, the relative reactivities decrease with increasing δ_H1. The relative reactivities in coordinated anionic polymerizations with Ti-containing Ziegler initiators show a typical feature of cationic polymerization, and those with V-containing initiators show a typical feature of anionic polymerization, indicating the importance of the coordination process in the propagation reaction with Ti-containing initiator systems. From the results, it can be concluded that the chemical shifts of the protons attached to the β-carbon of vinyl monomers can be used as a practical measure of the reactivity of vinyl monomers in ionic polymerizations and also as a tool for understanding the mechanism of polymerization. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2134–2147, 2002     

Biomolecular materials based on sol-gel encapsulated proteins

The proteins copper-zinc superoxide dismutase (CuZnSOD), cytochrome c, myoglobin, hemoglobin, and bacterio-rhodopsin are encapsulated in stable, optically transparent, porous, silica glass matrices prepared by the sol-gel method such that the biomolecules retain their characteristic reactivities and spectroscopic properties. The resulting glasses allow transport of small molecules into and out of the glasses at reasonable rates but retain the protein molecules within their pores. The transparency of the glasses enables the chemical reactions of the immobilized proteins to be monitored by means of changes in their visible absorption spectra. Silica glasses containing the immobilized proteins have similar reactivities and spectroscopic properties to those found for the proteins in solution. The enzymes glucose oxidase and peroxidase were also encapsulated in transparent silica glass matrices. Upon exposure to glucose solutions, a colored glass is formed that can be used as the active element in a solid state optically based glucose sensor.     

A new synthesis of 2-fluoro-1-naphthols

A general synthesis of 2-fluoro-1-naphthols in two steps from 1-indanones is reported. The 1-indanones are first converted to difluoromethyl 2-fluoro-1-napthyl ethers by reaction with difluorocarbene source, trimethylsilyl 2-fluorosulfonyl-2,2-difluoroacetate (TFDA). These ethers are then converted in high yield to the respective naphthols by heating with a mixture of acetic acid and 48% HBr.     

Electron spin resonance study of copolymerization of hexafluoroisobutylene with vinylidene fluoride

The Copolymerization reaction of hexafluoroisobutylene (HFIB) and vinylidene fluoride (VF₂) was studied using X-band electron spin resonance (ESR) by applying a photo-in situ method. Owing to the toxicity of HFIB monomer, the flow ESR method could not be directly applied without extensive modification. The observed ESR signal with 21-line hyperfine structure was assigned to the copolymer radical with head-to-head configuration. Although the HFIB monomer radical possesses the same hyperfine pattern, the ambiguity has been removed by using CF₃ as an initiator radical. Owing to the high steady-state concentration of the observed copolymer radical with head-to-head configuration as well as the nature of the static photo-in situ ESR method, we believe the actual molecular configuration for HFIB/VF₂ copolymer must be head-to-tail. The observed hyperfine constant for A_βF = 1.74 mT suggests that the geometry for HFIB/VF₂ copolymer radicals with both head-to-head or head-to-tail configurations is possibly similar to that of (CF₃)₃C· radical. The small value for A_βH indicates steric hindrance to rotation about the C_α? C_β bond, and this is also supported by the experimental results of nonalteration in linewidth during the temperature dependence study from ?40 to about 90°C. Attempts to measure directly the monomer reactivities have been unsuccessful owing to the fact that not all the possible radicals were detected, but nevertheless the relative reactivities of VF₂ and HFIB could be estimated. The relative reactivities of VF₂ and HFIB monomers and the steric hindrance effect indicate that the conformation of the copolymer is head-to-tail; this has been further confirmed by infrared analysis.     

1‐Thiacyclooct‐4‐yne (=5,6‐Didehydro‐3,4,7,8‐tetrahydro‐2H‐thiocin), and Its Sulfoxide and Its Sulfone

1‐Thiacyclooct‐4‐yne (=5,6‐didehydro‐3,4,7,8‐tetrahydro‐2H‐thiocin; 9 ) can be prepared from thiocan‐5‐one ( 6 ) in three steps by applying the so‐called selenadiazole method. The heterocyclic alkyne can be oxidized to the corresponding sulfoxide 16 and sulfone 17 . Due to their geometrical strain, all three cyclic alkynes show high reactivities in Diels? Alder and 1,3‐dipolar cycloadditions. Moreover, tetrathiafulvalenes can be prepared from 9 and 16 by the reaction with CS₂.