Thermal conversion of hydroxy-containing polyimides to polybenzoxazoles. Does this reaction really occur?

Hydroxy-containing polyimides with a low level of structural defects have been produced by the reaction of aromatic tetra-carboxylic acids with hydroxy containing aromatic diamines in water, as this method avoids the normal ester impurities formed by the standard polyimide synthesis techniques using tetra-carboxylic dianhydrides in dry polar solvents. Detailed FTIR studies focused on the controlled thermolysis of these purified alpha-hydroxypolyimides and their model compounds has revealed that the hydroxy groups are lost at significantly lower temperatures and times than the imide groups. This observation does not support previous literature reports which suggested that benzoxazole formation occurs and has implications for the style of materials ultimately produced. We propose a new mechanism and provide evidence to indicate that the polymers initially produced by the thermolysis reaction of alpha-hydroxypolyimides are actually crosslinked, imide containing biphenylene derivatives.     

与煤结构和煤液化有关的五个模型化合物热解反应动力学的研究

本文对二苯甲烷、二苯乙烷、二苯醚、苯基苄基醚和二苄醚等五个与煤的化学结构和煤液化有关的模型化合物在供氢溶剂四氢萘中、N_2压力为50—60大气压下的热解反应动力学及反应机理进行了研究。结果表明: (1) 二苯甲烷和=苯醚在435 ℃/2 h条件下依然比较稳定, 这意味着, 在实际煤液化过程中, C—C、C—O键的断裂不能靠这些简单结构方式的裂解加以解释; (2) 二苯乙烷和苯基苄基醚的热解有一级反应特征, 其反应机理为自由基过程, 反应速度方程和速度常数的理论计算与实验结果完全一致; (3) 二苄醚的热解可用分子内氢转移模型得到较好解释, 热解产物苯甲醛进一步脱氧生成甲苯, 这可能是煤液化中除氧的一条很重要的途径。     

N-[1-(取代苯基)乙基]-2-羟基苯甲酰肼的合成、表征及抑菌活性

依据邻羟基二苯醚及芳香肼类化合物的抗菌特性, 以邻羟苯基为分子核心, 酰肼键为桥基, 设计合成了7种未见报道的N-(取代苯基)乙基-2-羟基苯甲酰肼类化合物. 以水杨酸甲酯为原料, 经肼解反应后与取代苯乙酮缩合, 再与硼氢化钠反应制得目标化合物, 化合物结构经IR, ¹H NMR和元素分析等证实. 抗菌活性测试结果表明, 该类化合物对不同菌株的抑菌活性具有明显的选择性和特异性. 当质量浓度为1×10^-4 g/mL时, 化合物3b和3e对大肠杆菌和白色念珠菌的抑菌率高达100%, 有极强的抑菌活性; 所有化合物对金黄色葡萄球菌的抑菌率均大于70%, 有一定的抑菌活性. 构效关系分析结果表明, 苯基中引入Cl或Br等卤原子能显著增强化合物的抑菌活性, 而引入-NO₂及-CH₃基团则会降低其抑菌活性.     

Acidity trends in alpha,beta-unsaturated sulfur, selenium, and tellurium derivatives: comparison with C-, Si-, Ge-, Sn-, N-, P-, As-, and Sb-containing analogues

The gas-phase acidity of CH3-CH2XH (X=S, Se, Te), CH2=CHXH (X=S, Se, Te) and PhXH (X=S, Se) compounds was measured by means of Fourier transform ion cyclotron resonance mass spectrometry. To analyze the role that unsaturation plays on the intrinsic acidity of these systems, a parallel theoretical study, in the framework of the G2 and the G2(MP2) theories, was carried out for all ethyl, ethenyl (vinyl), ethynyl, and phenyl O-, S-, Se-, and Te-containing derivatives. Unsaturated compounds are stronger acids than their saturated analogues, because of the strong pi-electron donor ability of the heteroatoms that contributes to a large stabilization of the unsaturated anions. Ethynyl derivatives are stronger acids than vinyl compounds, while phenyl derivatives have an intrinsic acidity intermediate between that of the corresponding vinyl and ethynyl analogues. The CH2=CHXH vinyl compounds (enol-like) behave systematically as slightly stronger acids than their CH3-C(H)X (keto-like) tautomers. Vinyl derivatives are stronger acids than ethyl compounds, because the anion stabilization attributable to unsaturation is greater than that undergone in the neutral compounds. Conversely, the enhanced acidity of the ethynyl derivatives with respect to the vinyl compounds is due to two concomitant effects, the stabilization of the anion and the destabilization of the neutral compound. The acidities of ethyl, vinyl, and ethynyl derivatives containing heteroatoms of Groups 14, 15, and 16 of the periodic table are closely related, and reflect the differences in electronegativity of the CH3CH2-, CH2=CH-, and CH[triple chemical bond]C- groups.     

Rearrangements in the haloalkoxy(mercapto,amino)-sym-triazine series

It is shown by means of an O¹⁸ label that the thermolysis of 2-methoxy-4-(2-chloroethoxy)-6-dialkylamino-sym-triazines to give oxazolo-sym-triazines in an inert medium proceeds without the formation of intermediate N-2-chloroethyl derivatives. In contrast to this, the thermolysis of 2-ethoxy(propoxy)-4-(2-chloroethoxy) derivatives gives N-2-chloroethyl derivatives, which upon prolonged heating are converted to oxazolo-sym-triazines. Triazinium salts are formed when both 2-chloroethoxy and N-2-chloroethyl derivatives are heated in water. The triazinium salts undergo rearrangement to N-2-chloroethyl derivatives when the water is removed. On the basis of the data obtained it is assumed that the thermolysis of 2-chloroethoxy-sym-triazines in an inert medium proceeds via a concerted mechanism, whereas thermolysis proceeds via an ionic mechanism in water. Data from the UV, IR, and PMR spectra are presented.See [1] for communication 3.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 124–127, January, 1979.     

Homolytic reactions of polyfluoroaromatic compound. Part XI. Confirmation of the proposed mechanism of phenylation of polyfluoroaromatic substrates

The derivatives of dihydrobiphenyl, which were predicted [1,2] to be formed in the thermolysis of benzoyl peroxide in polyfluoroaromatic compounds and which arose from transesterification, have been identified in the reactions of hexafluorobenzene and of octafluorotoluene with this peroxide. The presence of 1,4-dihydro-1,2,3,4,4,5,6-heptafluorobiphenyl (or its positional isomer, 1,2-dihydro-1,2,2,3,4,5,6-heptafluorobiphenyl) in such reaction mixtures also explains the formation of 3,4′-$\text{bis}$(phenyl)-octafluorobiphenyl in the dehalogenation products of the polynuclear residue from the reaction in hexafluorobenzene. Fluorine migration [3] does not need to be postulated.The yield of 2,3,4,5,6-pentafluorobiphenyl from the thermal decomposition of phenylazotriphenylmethane (PAT) in hexafluorobenzene at 80° is generally increased by the presence of a variety of hydrogen donors. Larger amounts of additive increase the yield of biaryl with respect to PAT, but not usually with respect to the additive.These results are consistent with the mechanism of arylation of polyfluoroaromatic compound previously suggested [1,2].     

Synthesis and Antibacterial Activities of N-[(1-Aryl-3-phenyl-pyrazol-4-yl)methylene]-2-(halo-o-hydroxyphenyl)hydrazide Derivatives

A series of novel N-[(1-aryl-3-phenyl-pyrazol-4-yl)methylene]-2-(halo-o-hydroxyphenyl)hydrazide derivatives was synthesized and the antibacterial activity of each of them was evaluated. The supposed reaction mechanism of acquiring compounds 3a—3d is that catalytic activity is enhanced by the electron-donating groups of the first phenyl ring while decreased by electron-withdrawing groups of that ring. The result of preliminary bioassay shows that the lowest minimal inhibitory concentration(MIC) of the title compounds against Escherichia coli is 2 μg/mL. MIC values against Monilia albican and Staphlococcus aureus are as low as 4 μg/mL. They will be a series of potential antibacterial compounds against fungi and gram-negative bacteria.     

Isocyanate-, isothiocyanate-, urea-, and thiourea-substituted boron dipyrromethene dyes as fluorescent probes

Boron dipyrromethene dyes (Bodipy) bearing a meso-phenyl substituent carrying a variety of functional groups can be prepared under mild conditions. A single-crystal X-ray structure determination for the 3,5-dinitrophenyl compound shows the phenyl ring to be almost orthogonal (dihedral angle 84 degrees) to the plane of the Bodipy core, with one nitro group almost coplanar with the ring and the other tilted by approximately 21 degrees. Nitro substituents at the 3-, 4-, and 5- positions of the phenyl group are readily reduced to the corresponding amino groups and then converted to isocyanato, isothiocyanato, urea, thiourea, and some polyimine derivatives, the last providing additional functionality (phenazine and pyridylindole units) suitable for chelation of metal ions. All compounds are redox active, the electron-transfer processes being assigned on the basis of comparisons with model compounds. Their fluorescence properties are sensitive to the phenyl group substituents. The Bodipy unit excited state appears to be a strong reductant (Eo approximately -1.4 V) and a modest oxidant (Eo approximately +1.0 V). Quenching processes in the nitro and phenazine derivatives appear to involve intramolecular photoinduced electron transfer.     

Photooxidation and reproduction of pentacene derivatives substituted by aromatic groups

Pentacene derivatives substituted by aromatic groups at the 6,13-positions were prepared and investigated for their electronic properties and the photoaddition reaction with oxygen. The pentacene derivatives substituted by 2-thienyl and phenyl groups reacted with oxygen in solution under light and afforded their endoperoxides. These first-order kinetic constants were evaluated to be 1.5×10⁻³ s⁻¹ and 2.7×10⁻³ s⁻¹. The pentacene derivative with pentafluorophenyl groups was relatively stable in solution. The thermolysis and photolysis of the endoperoxide with 2-thienyl groups in solution afforded the pentacene derivative with yields of 30 and 44%, respectively. In addition, UV irradiation (254 nm) of the thin film of the endoperoxide was studied, which indicated the reproduction of the pentacene derivative.     

Investigation of free base, Mg, Sn, and Zn substituted porphyrin LB films as gas sensors for organic analytes

The visible absorption spectra of various substituted porphyrin compounds both in chloroform solution and as Langmuir-Blodgett (LB) solid-state films have been investigated. The porphyrin compounds examined were the Zn, Sn, Mg, and free base derivatives of 5,10,15,20-tetrakis[3,4-bis(2-ethylhexyloxy)phenyl]-21H,23H-porphine (EHO). Changes in the absorption spectra of these materials induced by their exposure to various organic compounds are reported with a view toward determining whether this is a useful approach toward an optical gas sensor.     

Carboxyketenes from 4-hydroxy-1,3-oxazin-6-ones and Meldrum's acid derivatives

New 4-hydroxy-1,3-oxazin-6-ones 8 and 16 were prepared from chlorocarbonyl(phenyl)ketene and amides. The flash vacuum thermolysis (FVT) reactions of these compounds and the 4-methoxy derivative 17 were investigated by Ar matrix isolation IR spectroscopy and online mass spectrometry including MS/MS analysis. Carboxy(phenyl)ketene 10 is formed as the major product by thermal fragmentation of 4-hydroxy-1,3-oxazin-6-one 8. This takes place via the unstable 6-hydroxy tautomer 9. Another tautomer, the 5H-isomer 12, leads to the formation of benzoyl isocyanate 13 as a minor product together with phenylketene 14. Carboxy(phenyl)ketene 10 remains detectable at high FVT temperatures but undergoes thermal decarboxylation to phenylketene 14. The same carboxy(phenyl)ketene 10 is also produced in significant amounts by FVT of 5-phenyl-Meldrum's acid 18 via the unstable enol tautomer 19. A small amount of the unsubstituted carboxyketene 20 is observable on FVT of Meldrum's acid 1 itself.     

Diastereoselective remote C-H activation by hydroboration

Hydroboration of tetrasubstituted or trisubstituted alkenes with BH(3) and subsequent thermolysis allows remote diastereoselective C-H activation of neighboring aryl rings. Tetrasubstituted and trisubstituted 1,1-diphenylethylene derivatives undergo a highly stereoselective 1,2-rearrangement followed by remote C-H activation to lead, after oxidative workup, to a diol in which the relative stereochemistry of two stereocenters has been controlled. The mechanism of this remote activation has been studied and extended to related molecules that undergo this stereoselective C-H activation, namely alkenylbiphenyl systems or alkenes with only one phenyl ring, such as alkenylbenzenes, or bicyclic systems. We have shown that this reaction allows diastereoselective synthesis of molecules with up to three contiguous chiral centers.     

Thermal and Photofragmentation of N-Benzoylhydrazone Derivatives

Two selected benzoylhydrazones I and II were subjected to thermolysis by reflux at 200 °C. Benzil, benzoic acid, biphenyl, benzanilide together with the corresponding ketones, nitriles and imines were isolated. Similar treatment of the third hydrazone III at 250 °C afforded, in addition to the previous products, bibenzyl, stilbene, and 2-phenylindole. Photolysis of the same hydrazones I-III in acetonitrile gave the previously reported products but in different ratios along with azine derivatives and substituted methanes. A free radical mechanism involving homolysis of the N-N and C-N bonds is suggested, substantiated by trapping of phenyl radical with isoquinoline, to account for the formation of the identified products.     

Thermolysis of 3-phenyl-5-arylamino-1,2,4-oxadiazole and thiadiazole derivatives

Thermal reactions of 3-phenyl-5-arylamino-1,2,4-oxadiazoles I and II were investigated. Neat heating at ca. 250°C for 6 hours afforded H₂O, benzonitrile, arylcyanamides, arylamines, azobenzene, benzimidazole derivatives, and 3,3′-diphenyl-5,5′-bis[1,2,4-oxadiazolyl]. Analogous results were obtained by the thermolysis of 3-phenyl-5-anilino-1,2,4-thiadiazole III at ca. 200°C for 2 hours. In addition to H₂S, NH₃, and HNCS, phenyl isothiocyanate and thiocarbanilide were obtained. Thermolysis of III in quinoline as a radical trap gave analogous resuLts but also 2-anilinoquinoline. A free-radical mechanism has been suggested to account for the identified products. © 1997 John Wiley & Sons, Inc.     

Aryl calcium compounds: syntheses, structures, physical properties, and chemical behavior

Organocalcium chemistry is still in its infancy. The direct synthesis of activated calcium and (substituted) iodobenzenes allows for the large-scale and high-yield synthesis of aryl calcium iodides. The influence of the substitution patterns of the phenyl group, halogen atom, and solvent is discussed. Aryl calcium iodides show a Schlenk equilibrium that enables the isolation of diaryl calcium derivatives. Owing to the high reactivity of aryl calcium halides, low temperatures have to be maintained throughout the preparative procedures in order to avoid side reactions. A decrease of reactivity and, hence, an enhanced stability at higher temperatures can be achieved by shielding of the calcium atom by increasing the coordination number of the metal center or by substitution of the iodide anion by bulky groups.     

Pyridinium derivatives of histamine are potent activators of cytosolic carbonic anhydrase isoforms I, II and VII

A series of positively-charged derivatives has been prepared by reaction of histamine with substituted pyrylium salts. These pyridinium histamine derivatives were investigated as activators of the zinc enzyme carbonic anhydrase (CA, EC 4.2.1.1) and more precisely the human isoforms hCA I, II and VII. Activities from the subnanomolar to the micromolar range were detected for these compounds as activators of the three isoforms, confirming the validity of current and previous designs. The substitution pattern at the pyridinium ring was the main factor influencing activity, the three isoforms showing different structural requirements for good activity, related with the number of pyridinium substituting groups and their nature, among various alkyl, phenyl and para-substituted styryl moieties. We were successful in identifying nanomolar potent and selective activators for each isozyme and also activators with a relatively good activity against all isozymes tested--valuable lead compounds for physiology and pathology studies involving these isozymes.     

High resolution capillary gas chromatography and gas chromatography–mass spectrometry of protein and non-protein amino acids,amino alcohols,and hydroxycarboxylic acids as their tert-butyldimethylsilyl derivatives

A simple, single-step derivatization technique is presented for capillary GC-FID and GC-MS separation and identification of common protein and non-protein constituents of natural peptides as their tert-butyldimethylsilyl (TBDMS) derivatives. The tert-butyldimethyl-silylation of more than sixty compounds was accomplished with high yields and a single peak observed for each component. The TBDMS derivatives of both the protein and non-protein substances, moreover, exhibit excellent separation on apolar capillary columns and can be resolved completely using a polydimethylsiloxane or 5 % phenyl polydimethylsiloxane column and, complementarily, a 50 % phenyl polydimethylsiloxane column. Retention data and molar responses of the TBDMS derivatives on the polydimethylsiloxane column are compiled. Direct coupling of the 5 % phenyl polydimethylsiloxane column to an ion trap mass spectrometer enabled fast separation and identification of the investigated components, at nanomole to picomole levels, on the basis of retention and mass spectral data. The general usefulness of the method is demonstrated by research into new biologically active peptides isolated from entomopathogenic fungi.     

Trialkylphosphine-stabilized copper(I) gallium(III) phenylchalcogenolate complexes: crystal structures and generation of ternary semiconductors by thermolysis

A series of organometallic trialkylphosphine-stabilized copper gallium phenylchalcogenolate complexes [(R(3)P)(m)Cu(n)Me(2-x)Ga(EPh)(n+x+1)] (R = Me, Et, (i)Pr, (t)Bu; E = S, Se, Te; x = 0, 1) has been prepared and structurally characterized by X-ray diffraction. From their molecular structures three groups of compounds can be distinguished: ionic compounds, ring systems, and cage structures. All these complexes contain one gallium atom bound to one or two methyl groups, whereas the number of copper atoms, and therefore the nuclearity of the complexes, is variable and depends mainly on size and amount of phosphine ligand used in synthesis. The Ga-E bonds are relatively rigid, in contrast to flexible Cu-E bonds. The lengths of the latter are controlled by the coordination number and steric influences. The Ga-E bond lengths depend systematically on the number of methyl groups bound to the gallium atom, with somewhat shorter bonds in monomethyl compounds compared to dimethyl compounds. Quantum chemical computations reproduce this trend and show furthermore that the rotation of one phenyl group around the Ga-E bond is a low energy process with two distinct minima, corresponding to two different conformations found experimentally. Mixtures of different types of chalcogen atoms on molecular scale are possible, and then ligand exchange reactions in solution lead to mixed site occupation. In thermogravimetric studies the complexes were converted into the ternary semiconductors CuGaE(2). The thermolysis reaction is completed at temperatures between 250 and 400 °C, typically with lower temperatures for the heavier chalcogens. Because of significant release of Me(3)Ga during the thermolysis process, and especially in case of copper excess in the precursor complexes, binary copper chalcogenides are obtained as additional thermolysis products. Quaternary semiconductors can be obtained from mixed chalcogen precursors.     

新型含吡唑环的N-甲氧基氨基甲酸甲酯类化合物的设计、合成及生物活性

以苯(吡啶)乙/丙酮类化合物为原料, 经酯化、环化和缩合三步制得新型含吡唑环的N-甲氧基氨基甲酸甲酯类化合物3a~3r, 化合物及其中间体的化学结构经红外光谱、核磁共振谱及元素分析确认. 生物活性结果表明, 化合物3在400 mg/L下分别对水稻稻瘟病、黄瓜霜霉病和小麦白粉病具有很好的防治效果. 对水稻稻瘟病, R₁为甲基或甲氧基取代的苯基时活性最好; 对于黄瓜霜霉病和小麦白粉病, R₁为苯基或甲基取代苯基的化合物杀菌活性优于其它化合物, R₂为甲基的化合物杀菌活性优于R₂为氢的化合物.     

Application of Phase Transfer Catalysis in Heterocyclic Synthesis: Synthesis of Some New Polyfunctional Thiophenes,Thiopyrans, Pyridines and Oxazines

The reaction of compound 1 with CS 2 and different active halo compounds gave the corresponding thiophene derivatives 2a,b-4a,b , whereas treatment of compound 1 with CS 2 and active methylene compounds afforded the corresponding thiopyran derivatives 5a,b , 6a,b , 7 , and 8 . Also, 1,3-thioxane derivatives 9 and 10 were obtained by reacting compound 1 with CS 2 and different cycloalkanones. Thiophene and pyrrolidene derivatives 11 , 12a,b , and 13a,b were obtained by reacting compound 1 with phenyl isothiocyanate and different halo compounds. The active methylene compounds and/or cycloalkanones were treated with compound 1 in the presence of phenyl isothiocyanate to give pyridines, thiopyran and oxazine derivatives 14a,b-16a,b , 17a-19a , and 19b , respectively.