The kinetics of the chromic acid oxidation of diphenylmethane

The kinetics of the chromic acid oxidation of diphenylmethane in aqueous acetic acid solution has been studied. The rate law is v = k[φCH₂φ][CrO₃]h₀ a kinetic isotope effect, k_H/k_D = 6·4 at 30°, was noted, and electron releasing groups were found to moderately facilitate the reaction (⁺ = −1·17). These, and related data, suggest that the initial reaction is the abstraction of a hydrogen atom forming a benzhydryl radical. The latter may then be further oxidized to give the product, benzphenone. It is noted that the chromic acid oxidations which must involve hydrogen abstraction all show a kinetic dependence on the total chromium (VI) concentration, whereas those which are believed to proceed via an ester mechanism have a kinetic dependence on only the acid chromate ion. This difference is suggested as a possible method of distinguishing between these two mechanisms. The effect of the water content of the solvent on the rate of the reaction is discussed, and a tentative, relative, H₋ scale for some of these solutions is suggested. This may permit one to determine the number of molecules of water which are involved in a reaction.     

Metal complexes of biologically important ligands: Synthesis of amino acidato complexes of Pd containing a C,N-cyclometallated group as an ancillary ligand

New amino acidato complexes of Pd^II of stoichiometry [Pd(C---N)(Aa)] (C---N=C,N-cyclometallated ligand, Aa = N,O-amino acidato ligand) have been obtained by reaction of [Pd(C---N)(acac)] (C---N=N,N-dimethylbenzylamine-C²,N (dmba) (1) or N,N-dimethyl(S--phenylethyl)amine-C²,N (S-dmphea) (2)) with glycine, chiral amino acids (alanine, phenylalanine and valine), and amino acid derivatives (N-acetylglycine and N-acetyl-,β-dehydroalanine) in MeOH. The compounds are characterized by IR, ¹H and ¹³C NMR. The geometry of these complexes has been unambiguously determined by NOE difference experiments and NOESY measurements.     

Equilibrium, FTIR, scanning electron microscopy and small wide angle X-ray scattering studies of chromates adsorption on modified bentonite

The study presents a discussion about the adsorption mechanism of chromate anions on bentonite modified by hexadecyltrimethylammonium bromide (HDTMA-Br). The formation of alkylammonium chromates: HDTMAHCrO₄, (HDTMA)₂Cr₂O₇ and to the lesser extent (HDTMA)₂CrO₄ at the water–bentonite interface is examined based on the Scanning Electron Microscopy and surface tension measurements. The histograms of HDTMA/Cr(VI) molar ratio on the bentonite surface, found from Scanning Electron Microscopy (SEM) measurements, show that for the majority of points of bentonite surface the value of this ratio is in 1–2 range. FTIR spectra of modified bentonite samples show the change from gauche to trans conformation in the surfactant arrangement in the clay interlayer accompanying its concentration increase.

In turn Small Wide Angle X-Ray Scattering (SWAXS) patterns evidently suggest incorporation of chromate anions into the interlamellar space of bentonite structure.     

Characterization and crystal structures of copper(II), cobalt(II), and nickel(II) complexes with two kinds of piperidine carboxylic acids

Copper(II) complex with -piperidine-3-carboxylic acid ( -Hpipe-3):[Cu( -pipe-3)₂(H₂O)] and cobalt(II) and nickel(II) complexes with piperidine-4-carboxylic acid (Hpipe-4):[M(Hpipe-4)₂(H₂O)₄]Cl₂ (M: Co, Ni) have been prepared and characterized by means of IR and powder diffuse reflection spectra, thermal analysis, and magnetic susceptibility. The crystal structures of these complexes have been determined by X-ray diffraction. The crystal of [Cu( -pipe-3)₂(H₂O)] is orthorhombic with the space group Pbcn. The copper atom is in a square pyramidal geometry, ligated by two carboxylato oxygen atoms, two nitrogen atoms, and a water molecule. One molecule of this complex consists of either -piperidine-3-carboxylic acid or -piperidine-3-carboxylic acid. The crystals of [M(Hpipe-4)₂(H₂O)₄]Cl₂ are monoclinic with space group P2₁/n. In these complexes the metal atom is in an octahedral geometry ligated by two carboxylato oxygen atoms and four water molecules.     

Synthesis and characterization of new thermally stable copoly(ester–amide)s from diester–dicarboxylic acids

Three new aromatic diester–dicarboxylic acids containing furan rings, namely, benzofuro[2,3-b]benzofuran-2,9-dicarboxyl-bis-phenyl ester-4,4^′-dicarboxylic acid, benzofuro[2,3-b]benzofuran-2,9-dicarboxyl-bis-phenyl ester-3,3^′-dicarboxylic acid and benzofuro[2,3-b]benzofuran-2,9-dicarboxyl-bis-naphthyl ester-2,2^′-dicarboxylic acid were synthesized by the reaction of benzofuro[2,3-b]benzofuran-2,9-dicarbonyl chloride with 4-hydroxybenzoic acid, 3-hydroxybenzoic acid and 3-hydroxy-naphthalene-2-carboxylic acid, respectively. Diester–dicarboxylic acids were characterized by FT-IR and NMR spectroscopy and elemental analyses. Then, these monomers were converted to aromatic copoly(ester–amide)s by their reaction with various aromatic diamines via the direct polycondensation. These polymers were characterized by viscosity measurements, solubility tests, FT-IR, Ultraviolet and ¹H-NMR spectroscopy and thermogravimetry. The polymers with inherent viscosities in the range of 0.16–0.37 dl/g in dimethyl sulfoxide at 30 °C were obtained in high yield. Most of them dissolved readily at room temperature in polar solvents. The synthesized copoly(ester–amide)s possessed glass-transition temperatures from 210–255 °C. The copoly(ester–amide)s exhibited excellent thermal stabilities and had 10% weight loss at temperature above 295 °C under nitrogen atmosphere.     

Formation of S-[2-carboxy-1-(1H-imidazol-4-yl) ethyl]glutathione, a new metabolite of L-histidine, from cis-urocanic acid and glutathione by the action of glutathione S-transferase

Exposure of the skin to sunlight results in an increase of the content of epidermal trans-urocanic acid, a key metabolite of L-histidine, and also in occurrence of the isomerization of trans-urocanic acid to the cis isomer. S-[2-Carboxy-1-(1H-imidazol-4-yl)ethyl]glutathione (GS(CIE)), an adduct of urocanic acid and glutathione, is a presumed origin of a urinary compound S-[2-carboxy-1-(1H-imidazol-4-yl)ethyl]-L-cysteine (Cys(CIE)). The formation of GS(CIE) is stimulated by exposing the skin to sunlight irradiation. In this study we investigated an enzymatic formation of GS(CIE) from glutathione and cis-urocanic acid by incubation with rat liver extract that contained glutathione S-transferase (GST) at high activity. The formation of GS(CIE) was suppressed significantly when a liver extract depleted of GST activity was used. Enzymatic degradation of GS(CIE) with gamma -glutamyl transpeptidase resulted in the formation of N-[S-[2-carboxy-1-(1H-imidazol-4-yl)ethyl]-L-cysteinyl]glycine, a metabolic intermediate between the glutathione adduct and Cys(CIE). A hydrolyzed product of GS(CIE) by HCl was identical with the urinary Cys(CIE). Compounds were analyzed by high-voltage paper electrophoresis, capillary electrophoresis, and fast atom bombardment mass spectrometry. From these results, we suggest that GS(CIE) formed from cis-urocanic acid and glutathione is an origin of the urinary compound Cys(CIE) and that the formation reaction is catalyzed mostly by the action of GST.     

Coordination geometry of chromium(VI) species. The first example of cis-bridging chromate ions in helically structured catena(μ-CrO4-O,O′)[Ni(HIm)3H2O]

Nickel(II) chromate complex with imidazole (HIm) was isolated from the [Ni²⁺–HIm–CrO₄²⁻] system in various experimental conditions, i.e. reagent molar ratios and nickel(II) salts. The catena(μ-CrO₄-O,O′)[Ni(HIm)₃H₂O] (1) crystallizes in monoclinic crystal system—space group P2₁/n with cell parameters: a=11.784(2), b=8.899(2), c=13.934(3) (Å), β=95.19(3) (°). The unit cell contains two independent helixes, left- and right-handed, stabilized by intrahelical and interhelical hydrogen bonds (HB) and π–π interactions. The cis coordination of the CrO₄²⁻ anions and the HB systems appeared to be the main determinants of the helical architecture. To the best of our knowledge the cis-chromate coordination was observed for the first time. The cis coordination causes the distortion of the nickel octahedron, which was analysed by 4 K single crystal electronic spectra with D_4h symmetry approximation (gaussian resolution and crystal field parameters). This symmetry was also confirmed with the polarised electronic spectra. The magnetic properties of the complex suggest the occurrence of weak intrachain antiferromagnetic interactions between the magnetic Ni^II center. The computational DFT studies of complex 1 assuming three possible isomers mer[(HIm)₃]–cis[(CrO₄²⁻)₂], mer–trans and fac–cis suggested that the main contribution to the stability of 1 might have interhelical and intrahelical hydrogen bonds.     

1-烷基-3-甲基咪唑氯化物焓变的热重分析

The structures of ionic liquids (ILs) based on 1-alkyl-3-methylimidazolium chloride [C_nmim]Cl (n = 2, 4, 6), (1-ethyl-3-methylimidazolium chloride [C₂mim]Cl, 1-butyl-3-methylimidazolium chloride [C₄mim]Cl, and 1-hexyl-3-methylimidazolium chloride [C₆mim]Cl) were elucidated by ¹H NMR and ¹³C NMR experiments. The vaporization characteristics of these ILs were studied by thermogravimetric analysis. Dynamic and isothermal thermogravimetric experiments were conducted in this study. The purpose of the dynamic experiments was to determine the initial decomposition temperature of the experimental sample and the temperature range for the isothermal thermogravimetric experiments. The purpose of the isothermal experiments was to record the mass dependence of the sample on time in the experimental temperature range. The Langmuir equation and Clausius-Clapeyron equation were used to fit the experimental data and obtain the vaporization enthalpies of these ILs at the average temperature within the experimental temperature range. However, in order to expand the applicability of the estimated values and to compare them with the literature data, the vaporization enthalpy ΔH_vap(T_av) measured at the average temperature was converted into vaporization enthalpy ΔH_vap(298) at ambient temperature. The difference between the heat capacities of the ILs in the gaseous and liquid states at constant pressure, Δ_l^gC_pm^ө proposed by Verevkin, was used in this conversion process. The experimental data for substance density and surface tension at other temperatures were obtained by referring to the literature. In addition, the data for density and surface tension at T = 298.15 K were obtained by applying the extrapolation method to the literature values for other temperatures. The vaporization enthalpy of the 1-octyl-3-methylimidazolium chloride IL [C₈mim]Cl was estimated by using the new vaporization model we had proposed in our previous work and compared with the reference value. The estimated value for [C₈mim]Cl was on the same order of magnitude as the reference value. We compared the vaporization enthalpies in the present study with those for the carboxylic acid imidazolium and amino acid imidazolium ILs ([C_nmim]Pro (n = 2-6) and [C_nmim]Thr (n = 2-6), respectively in our previous work. The results revealed that a change in the anion type affects the vaporization enthalpy of the ILs in the order amino acid imidazolium > carboxylic acid imidazolium > halogen imidazolium, when the cation is the same. Considering the structural differences between the three kinds of ILs, the abovementioned order may be related to the intermolecular hydrogen bonds. There were no intermolecular hydrogen bonds in the [C_nmim]Cl (n = 2, 4, 6) ILs studied here. Therefore, the vaporization enthalpy of [C_nmim]Cl (n = 2, 4, 6) was the lowest among the three kinds of ILs considered.     

Capillary electrophoresis for measuring major and trace anions in thermal water and condensed-steam samples from hydrothermal springs and fumaroles

A new application of capillary electrophoresis for measuring major and trace anions in thermal water and condensed-steam samples is presented. Ten fluid samples were collected from hydrothermal springs and fumaroles located in a volcanic zone of Deception Island, Antarctica. Anion separation was achieved in less than 6 min using indirect UV detection at 254 nm with a negative power supply (−15 kV). The electrolyte consisted of 4.7 mM sodium chromate, 4.0 mM electroosmotic flow modifier (OFM) hydroxide, 10 mM 2-(N-cyclohexylamino)ethanesulfonic acid and 0.1 mM calcium gluconate (pH 9.1). Major anions (Cl⁻, SO₄², PO₄H²⁻, and CO₃H⁻) were measured using hydrostatic injection (10 cm for 30 s) at 25°C. Trace amounts of anions (F⁻, Br⁻, and NO₃⁻) were better determined by electromigration injection (4 kV, 10 s) at 15°C. Good reproducibility of the migration times (<0.72% RSD), a satisfactory linear response and accuracy as well as acceptable detection limits were successfully obtained.     

High-performance liquid chromatographic analysis of glutathione and its thiol and disulfide degradation products

A rapid and sensitive high-performance liquid chromatographic method for quantitation of picomole levels of glutathione, glutathione disulfide, cysteine, cystine, cysteinylglycine, cysteinylglycine disulfide and cysteine glutathione-mixed disulfide in biological samples is described. The compounds were separated isocratically on a reversed-phase column by ion-pair chromatography. The mobile phase consisted of an aqueous buffer containing 0.1 M monochloroacetic acid and 3.3 mM 1-heptanesulfonic acid (pH 2.60)-methanol-N,N-dimethylformamide (96.5:3.0:0.5). After chromatographic separation, the disulfides were reduced by a potential (-1.0 V) from a battery, with subsequent detection of all thiols by electrochemical oxidation (+0.15 V) with a dual gold-mercury electrode. Thiol and disulfide concentrations were determined in tissue extracts (liver and kidney) and fluids (bile and plasma) from control rats and rats treated with acivicin, an inhibitor of gamma-glutamyltranspeptidase. A marked increase in biliary glutathione concentration was observed in treated animals with a corresponding decrease in cysteine and cysteinylglycine concentrations. The results demonstrate that this method is useful for measuring glutathione and its degradation products in tissues and fluids.     

Solid-phase extraction of the chromium(III)-diphenylcarbazone complex prior to ion-pair chromatography and application to geological samples

A method for the pre-treatment of acid samples prior to ion chromatography is described. In a strong acid medium, Cr(VI) oxidizes diphenylcarbazide, the resulting products forming a stable complex which can be transferred in a methanolic medium by solid-phase extraction using polyethylene as sorbent. This methanolic sample solution can be injected directly into a chromatographic system with a silica-based column. The separation and determination of the chromium complex can be performed by HPLC-using a mobile phase of 15% (v/v) acetonitrile containing 1 mmol/L tetrabutyl ammonium hydroxide (TBAH). The detection limit is estimated to be 2 microg/L chromate and the linear range is at least 0.05-2 mg/L chromate.     

A comparison of ferroelectric liquid crystals containing diastereomeric propionic acids derived from natural ethyl lactate

Two diastereomeric carboxylic acids, 2(S)-[2(R)-methylhexyloxy]propionic acid and 2(S)[2(S)-methylhexyloxy]propionic acid, were prepared from ethyl (S)-lactate and (R)-1-iodo2-methylhexane or (S)-1-iodo-2-methylhexane in the presence of Ag₂O. From these acids two liquid crystals, 2 and 3 , whose configurations are (S , R ) and (S, S) were synthesized and their liquid crystal properties investigated. Although both LCs have the same phase sequence Cr-SmC*-N*-I as well as a wide SmC* phase range, the influence of the relative stereochemistry on their physical properties is clear. The liquid crystal with (S, S)-configuration possesses better properties: lower SmC* phase transition temperature, wider SmC* phase range and higher P_s value. The P_s value difference between the ferroelectric LCs 2 and 3 (97 and 131nCcm^-2, respectively, at T_c - T = 10°C) is unexpectedly large. The consideration, alone, of a zigzag conformation at the chiral molecular part of 2 and 3 is insufficient to explain such a difference.     

螺[二苯并[a,j]氧杂蒽-14,9'-芴]的合成及性质

芴酮与2-萘酚在硫酸和3-巯基丙酸的作用下反应得到化合物螺[二苯并[a,j]氧杂蒽-14,9'-芴]. 采用核磁共振、 质谱、 红外光谱和元素分析等对该化合物进行了表征, 并通过X射线衍射法测得了其晶体结构, 确定该化合物是通过二苯并[a,j]氧杂蒽中的含氧六元杂环和芴中的五元环共用一个碳原子形成一个螺环. 利用荧光光谱和热分析等手段对该化合物的性质进行了研究, 结果表明其最大荧光发射峰为366 nm, 熔点为297 ℃, 热分解温度为329 ℃, 具有较高的热稳定性.     

Studies on the syntheses of heterocycles from 3-arylsydnone-4-carbohydroximic acid chlorides with N-arylmaleimides, [1,4]naphthoquinone and aromatic amines

3-Arylsydnone-4-carbohydroximic acid chlorides (1) could react with N-arylmaleimides (3a–b) or 2-methyl-N-phenylmale-imide (3c) to give 3-(3-arylsydnon-4-yl)-5-aryl-3a,6a-dihydro-pyrrolo[3,4-d]isoxazole-4,6-diones (4a–h) or 6a-methyl-3-(3-arylsydnon-4-yl)-5-phenyl-3a,6a-dihydro-pyrrolo[3,4-d]isoxazole-4,6-diones (4i–l), respectively. However, 3-(arylsydnon-4-yl)-naphtho[2,3-d]isoxazole-4,9-diones (6a–d) were obtained in good yield by the reaction of carbohydroximic acid chlorides 1 with [1,4]naphthoquinone. Furthermore, 2-(3-arylsydnon-4-yl)benzoxazoles (9a–d) and 2-(3-arylsydnon-4-yl)benzothiazoles (9e–h) were obtained via the reaction of carbohydroximic acid chlorides 1 with ortho-substituted aromatic amines 7a and b.     

氮、氧为配位原子的铅(Ⅱ)混合配合物的稳定性研究Ⅳ.铅(Ⅱ)-芳香氮碱-苯烷基丙二酸体系

混合配体配合物中配体间的相互作用在金属酶化学及其生物识别过程中具有重要意^[1,2].以往的研究,主要针对具有部分填充的3d过渡金属离子与芳香氮碱、氨基酸或一元羧 配合物体系^[3,4].铅(Ⅱ)为非过渡的主族金属离子,我们在对其PbLA型配合物的研究时 ,配合物中也存在配体间的相互识别作用^[5～7].     

Analysis of lipid hydroperoxides and long-chain conjugated keto acids by negative ion electrospray mass spectrometry

Lipid hydroperoxides are important products of enzymatic processes and autooxidation products of polyunsaturated fatty acids. Analysis of such compounds has proved difficult in the past, but negative ion electrospray ionization mass spectrometry was found to be suitable for direct analysis. Abundant [M - H]⁻ ions were observed in full scan mode for hydroperoxyeicosatetraenoic (HPETE), hydroperoxyoctadecenoic acid isomers, and 5,12-diHPETE. Loss of water was observed for all species. Collisional activation and tandem mass spectrometry generated unique and characteristic spectra that shared some common features such as loss of small neutral molecules. More importantly, fragment ions that were indicative of the position of the hydroperoxide were observed. Collision-induced decomposition (CID) of [M - H₂O]⁻ for the HPETE isomers was found to be virtually identical to the CID mass spectra of the [M - H]⁻ anions from corresponding keto-eicosatetraenoic acids, which suggests that the hydroperoxide anions decompose via a dehydration intermediate that resembles the keto acid molecular anion. Cleavage of the double bond allylic to the hydroperoxide formed structurally characteristic ions at m/z 129 from 5-HPETE, m/z 153 from 12-HPETE, and m/z 113 from 15-HPETE. Charge-driven allylic fragmentation led to formation of m/z 203 from 5-HPETE, m/z 179 from 12-HPETE, and m/z 219 from 15-HPETE. Mechanisms consistent with the decomposition of stable isotope analogues are proposed for the formation of these and other characteristic ions. These specific decompositions can be used in multiple reaction monitoring to measure picomolar concentrations of hydroperoxides by direct high performance liquid chromatography tandem mass spectrometry.     

Reactivity of several deactivated 3-aminobenzo[b]thiophenes in the Buchwald–Hartwig C–N coupling. Scope and limitations

Di(hetero)arylamines were prepared in moderate to high yields by Buchwald–Hartwig C–N coupling of bromobenzenes bearing electron-withdrawing groups and of a bromobiphenyl with several methyl 3-aminobenzo[b]thiophene-2-carboxylates, using the coupling conditions for heteroaromatic amines [Pd(OAc)₂, Xantphos, Cs₂CO₃ in dioxane, 120 °C]. The use of these aminobenzo[b]thiophenes as coupling components avoids the step of changing the amino group into a bromine atom, like we have done before to perform C–N couplings using the corresponding 3-bromobenzo[b]thiophenes. Nevertheless, the couplings using the methyl 3-aminobenzo[b]thiophene-2-carboxylates were only successful with bromobenzenes bearing electron-withdrawing groups and a bromobiphenyl or with electron deficient rings such us as bromopyridines. Using the latter compounds, different substituted 6H-benzothieno[3,2-d]pyrido[1,2-a]pyrimid-6-ones were obtained by C–N coupling followed by an intramolecular cyclization. These tetracyclic compounds may have interesting biological activity like it was already demonstrated by us for the non substituted derivative.     

Control of carboxylic acid and ester groups on chromium (VI) binding to functionalized silica/water interfaces studied by second harmonic generation

Resonantly enhanced surface second harmonic generation (SHG) measurements carried out at pH 7 and room temperature were performed to study how surface-bound carboxylic acid and methyl ester functional groups control the interaction of chromate ions with fused silica/water interfaces. These functional groups were chosen because of their high abundance in humic and fulvic acids and related biopolymers commonly found in soils. They were anchored to the silica surface using organosilane chemistry to avoid competing complexation processes in the aqueous solution as well as competitive adsorption of the organic compounds and chromate. The SHG experiments were carried out at room temperature and pH 7 while using environmentally representative chromate concentrations ranging from 1 x10(-6) to 2 x 10(-4) M. Chromate is found to bind to the acid- and ester-functionalized silica/water interfaces in a reversible fashion. In contrast to the plain silica/water interface, chromate binding studies performed on the functionalized silica/water interfaces show S-shaped adsorption isotherms that can be modeled using the Frumkin-Fowler-Guggenheim (FFG) model. This model predicts a coverage-dependent binding constant of K(ads) x exp(gtheta). Values for g are found to be 3.2(2), 2.1(2), and 1.3(2) for the carboxylic acid-, the ester-, and the nonfunctionalized silica/water interfaces, respectively, and are consistent with stabilizing lateral adsorbate-adsorbate interactions among the Cr(VI) species adsorbed to the functionalized surfaces. The FFG model allows for the parametrization of the solid-liquid partition coefficient and chromate retardation factors in silica-rich soil particles whose surfaces contain organic adlayers rich in carboxylic acid and methyl ester groups. The straightforward model presented here predicts that chromate retardation increases by up to 200% when carboxylic acid functional groups are present at the silica/water interface. Increases up to 50% are predicted for methyl ester-containing organic adlayers, and the retardation factor remains effectively near unity for the plain silica/water interface (no siloxanes present).     

Syntheses of heparin - like pentamers containing “opened” uronic acid moieties

The syntheses of four analogues of pentasaccharide Ia, which corresponds to the minimal AT III binding region of heparin, are presented and the biological activities of these analogues will be discussed. Three of these analogues (i.e. compounds II, III and IV) contain an R-glyceric acid oxymethylene residue (i.e. B in fig.3) instead of -L-iduronic acid and in the other analogue (i.e. compound V) the β-D-glucuronic acid unit has been replaced by an s-glyceric acid oxymethylene residue (i.e. A in fig3). The R and S-glyceric acid oxymethylene residues represent an “opened” iduronic acid unit and an “opened” glucuronic acid unit, respectively, containing the essential carboxylate function in the appropriate configuration. The crucial step in the syntheses of these “opened” uronic acid pentamer analogues, was the preparation of the required glyceric acid oxymethylene residues 8a, 8b and 8c.

Analogues II and III, containing an “opened” iduronic acid moiety, display a significant AT III mediated Xa activity. Compound III contains two extra sulphate groups at unit 2. Removal of the contributing O-sulphate groups at position 3 and 6 of unit 6 of compound II (i.e. compound IV) results in a seven-fold drop in Xa activity. Replacement of the β-D-glucuronic acid unit by an S-glyceric acid oxymethylene residue (i.e. compound V) leads to almost a complete loss of Xa activity, notwithstanding the fact that all the essential and contributing charged groups are present in the molecule.     

The synthesis and transition temperatures of 5-(4-alkyl- and 4-alkoxy-phenyl)-2-cyanobenzo[b]furans and a 5-(4'-alkylbiphenyl-4-yl)-2-cyanobenzo[b]furan: a comparison with their biphenyl and terphenyl analogues

The synthesis and transition temperatures of a series of 5-(4-alkyl- and 4-alkoxy-phenyl)2-cyanobenzo[b]furans and a 5-(4'-alkylbiphenyl-4-yl)-2-cyanobenzo[b]furan are presented. The 2-cyanobenzo[b]furans show similar mesophase types to the analogous biphenyl and terphenyl compounds, which are obtained by replacing the benzo[b]furan unit with a phenyl ring. The transition temperatures for the 2-cyanobenzo[b]furan compounds are always higher than for their biphenyl and terphenyl counterparts, but they are much lower than for the corresponding phenylnaphthalenes. Five mesogenic benzo[b]furans without a cyano group were prepared as intermediates and these compounds have lower clearing points than their biphenyl analogues.