The reaction between diethyl succinylsuccinate (1,4-diethoxycarbonyl-2,5-dihydroxy-1,4-cyclohexadiene) and amines and its application to polymer synthesis

Polymers having polyamine structures were obtained by the condensation reaction between diethyl succinylsuccinate (1,4-diethoxycarbonyl-2,5-dihydroxy-1,4-cyclohexadiene) and aliphatic diamines. The reactions were carried out in high polar solvents such as N-methylpyrrolidone (NMP) and N,N-dimethylformamide (DMF). The mode of the polymerization reaction and the structure of the polymers were verified by studies of model compounds. The polymers thus obtained were conveniently utilized as coating and adhesive materials and were able to be cast into films.     

Synthesis and crystal structure of cyclopentadienyl(1,4-dimethyl-1,4-dibora-2,5-cyclohexadiene)cobalt

The synthesis of the organometallic derivative cyclopentadienyl(1,4-dimethyl-1,4-diboracyclohexa-2,5-diene)cobalt is described. This complex, [(CH₃BC₄H₄BCH₃)Co(η-C₅H₅)], forms red-oranged monoclinic crystals, space group P2₁/a with Z = 4 in a unit cell of dimensions a 11.362(7), b, 7.467(7), c 13.290(12) Å, β 103.76(6)°. The structure has been elucidated by heavy-atom methods from 1732 reflections (I > 2σ(I)) measured on a Syntex P2₁ four-circle diffractometer and refined to R = 0.055. In the coordination complex all six atoms of the cyclohexadiene ring are within bonding distance of the metal atom, but the two boron atoms bend away from the metal atom, and the ring elongates slightly in the B---B direction. As a standard of comparison the known geometry of the free ligand [1,4-difluoro-1,4-dibora-2,3,5,6-tetramethylcyclohexa-2,5-diene] is used. The terminal methyl groups on the boron atoms, by contrast, bend slightly back towards the metal atom. The cyclopentadienyl ring remains planar but is positionally disordered.     

Spectrophotometric determination of Si(IV) with 3,6-dichloro-2,5-dihydroxy-1,4-benzoquinone

A new rapid spectrophotometric method for the determination of Si is described. Chloranilic acid (CA) reacts with Si(IV) forming a complex, which is stable for several hours. The procedure is suitable for the determination of Si in the concentration range of 0.5–5.0 μmol/ml, at pH 1.25 ± 0.05 measured at 370 nm. The relative standard deviation at the level of 1.0 μmol/ml Si is ± 3.5%. Of the foreign ions investigated, Fe, Ti, Mo, and PO₄³⁻ interfere significantly.     

Inelastic neutron scattering (INS) studies on 2,5-dihydroxy-1,4-benzoquinone (DHBQ)

Inelastic neutron scattering (INS) spectra of solid 2,5-dihydroxy-1,4-benzoquinone were measured and compared with IR and Raman data. The INS spectrum is very well reproduced in the region below 1000 cm(-1) by DFT calculations on the B3LYP/6-311++G** level using Gaussian and Climax programs. To get a better agreement one should take into account additional interactions of OH groups in the solid state leading to an increase of the gamma(OH) frequency and to a decrease of frequencies for modes in which the delta(OH) participates. The studies of the deuterated compound in IR enabled to correct the assignment of gamma(OH) vibrations. Highly asymmetric nu(OH) band observed in IR spectrum with sharp maximum at about 3300 cm(-1) is discussed in terms of a stochastic approach to the analysis of hydrogen bonded systems.     

Spectral-luminescence properties of some 2,5-dihydroxy-1,4-di(azol-2-yl)benzenes

The influence of the type of azole fragments and substituents on the spectral-luminescence properties of a series of 2,5-dihydroxy-1,4-di(azol-2-yl)benzenes, possessing an anomalously high Stokes shift, was investigated.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 242–245, February, 1993.     

Determination of zirconium,thorium and scandium with 2,5-dihydroxy-1,4-benzoquinone

Zirconium is quantitatively precipitated by 2,5-dihydroxy-1,4-benzoquinone and is separated from scandium in 1 N hydrochloric acid solution. Thorium is separated at pH 0.5 from uranium(VI), cerium(IV), lanthanum, yttrium and scandium. Scandium is quantitatively precipitated by this reagent in the pH range 1.4–2.0 and at pH 1.5 equivalent amounts of lanthanum do not interfere; small amounts of yttrium cause interference.     

Electrochemically synthesized polymer of the plant substance embelin (2,5-dihydroxy-3-undecyl-1,4-benzoquinone)

Among the possible new materials for microelectronics, quinones have a number of significant advantages. Similarly, polymers with quinone functionality possess biodegradability. Because natural polymers are promising candidates for functional materials for the future, we have initiated studies on the polymers of natural products. In the present study, a natural quinone (a plant substance) extracted from Embelier libes distributed in the Kerala state of India was electrochemically polymerized and its properties were investigated. The redox activity, electrical conductivity, and biodegradability are discussed.     

Structural phenomena in polymers arising at low temperatures and by the action of high forces

New structural phenomena which can be produced in polymers at low temperatures or by the action of high forces are described and discussed. Experimental evidence supports the argument that the deformation of polymers can develop not only as a result of conformational changes of the macromolecules proper but also by transformation of more complex structural formations. The consequence of this phenomenon is the possibility of large deformations far below the glass-transition temperature in a crystalline polymer with well-developed supermolecular structure. This type of deformation takes place without molecular orientation. Another phenomenon discussed is the sharp change of supermolecular structure in crystalline polymers caused by the action of a shock wave. These effects ought to be connected with an energetic rather than entropic deformation mechanism because the transformations occur at a supermolecular level. Thus, there can be two extreme types of deformation processes: the well-known conformation changes that occur at a molecular level, and the deformation of supermolecular structures. Examples of the pure form of the latter type of mechanism obtained under extreme conditions are given.     

Tunnelling effects in the double proton transfer reaction of 2,5-dihydroxy-1,4-benzoquinone

Two dynamic models were used to investigate the double proton transfer reaction of 2,5-dihydroxy-1, 4-benzoquinone. The stationary points of the potential energy surface were located using the AM1 method. A model two-dimensional potential surface based on the Cartesian coordinates of the protons is constructed. According to the first model, the synchronous and asynchronous mechanisms of the reaction are treated separately. In the second model the two-dimensional vibrational problem is solved on the corresponding potential energy surface. The unimolecular rate constants are calculated in terms of the RRKM theory and the one- and two-dimensional approximations are compared. The second model predicts the dominant role of tunnelling and the synchronous and asynchronous processes can hardly be separated.     

Syntheses and molecular structures of half-sandwich iridium metallarectangles containing bridging 2,5-dihydroxy-1,4- benzoquinonato (dhbq) ligands

Binuclear complex (Cp∗IrCl)₂(dhbq) (dhbq = 2,5-dihydroxy-1,4-benzoquinonato) (1) was obtained by the reaction of (Cp∗IrCl₂)₂ with bridging ligand 2,5-dihydroxy-1,4-benzoquinone(H₂dhbq) in the presence of the base n-BuNH₂. After treatments of 1 with AgX (X = ) and then with N-linkers (pyrazine, 4,4′-bipyridine), the corresponding tetranuclear metallarectangular complexes [(Cp∗Ir)₄(dhbq)₂(pyrazine)₂] (NO₃)₄·CH₂Cl₂·5H₂O (2) and [(Cp∗Ir)₄(dhbq)₂(4,4′-bipyridine)₂](SO₃CF₃)₄(3) were obtained in good yields. Both the products were characterized by IR, ¹H NMR and single crystal X-ray analyses and revealed that these tetranuclear complexes were constructed from half-sandwich metal corners with both dhbq and N-linkers to form rectangular cavities with the dimensions 8.0 × 6.9 Å (Ir-Ir separations) for 2, 8.0 × 11.2 Å (Ir-Ir separations) for 3, respectively. In additionally, in the solid structure of 2 the counteranions are located out of the cavities with the observed water molecules by hydrogen bonding of the type N-O?H-O-H?O-N. One-dimensional channels are observed in 3 along the b axis with intramolecular stacking, the similar arrangement is not found in the solid of 2.     

Adsorption voltammetric techniques for the determination of uranium(VI) with 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone as complex forming reagent

Uranium (VI) can be determined by adsorptive voltammetric techniques, as its chloranilic acid complex, over a wide concentration range. Differential pulse polarography is useful for quantification of uranium between 0.1 and 1.5 mg/l; for the range from 10 to 500 g/l differential pulse voltammetry and for ultra-trace analysis between 0.024 and 40 g/l adsorptive stripping voltammetry are preferred. The standard deviation for the 3-detection limit of 24 ng/l uranium was found to be 8%. In the trace analysis of metals in aquatic environmental systems by adsorptive stripping voltammetry it is normally necessary to decompose polluted water samples by UV irradiation or microwave digestion. The advantage of the developed method is the fact that no sample pretreatment is necessary.Dedicated to Professor R. Geyer on the occasion of his 80th birthday     

2,5-dihydroxybenzyl and (1,4-dihydroxy-2-naphthyl)methyl, novel reductively armed photocages for the hydroxyl moiety

Irradiation of alcohols, phenols, and carboxylic acids "caged" with the 2,5-dihydroxybenzyl group or its naphthalene analogue results in the efficient release of the substrate. The initial byproduct of the photoreaction, 4-hydroxyquinone-2-methide, undergoes rapid tautomerization into methyl p-quinone. The UV spectrum of the latter is different from that of the caging chromophore, thus permitting selective irradiation of the starting material in the presence of photochemical products. These photoremovable protecting groups can be armed in situ by the reduction of photochemically inert p-quinone precursors.     

Complexes of 2,5-dihydroxy-1,4-benzoquinone and chloranilic acid with second and third row transition elements

The synthesis of new 2,5-dihydroxy-1,4-benzoquinone (H2DHBQ) and chloranilic acid (H2CA) complexes cis-[Mo2O5L2]2– (L = DHBQ, CA), [W2O5(DHBQ)2]2–, [WO2(CA)2]2–, trans-[UO2(DHBQ)]·H2O, and trans-[UO2(CA)2]2– is described. Raman, i.r., 1H and 13C n.m.r spectra of the ligands and their complexes are reported and their structures discussed.     

Degradation of poly(terphenylenephthalide) at high temperatures

The thermal and thermooxidative degradation of poly(terphenylenephthalide) has been studied by thermal analysis, IR and UV spectroscopy, and mass spectrometry. On the basis of the spectral data and the chemical composition of degradation products, it has been shown that both the thermal and thermooxidative degradations of poly(terphenylenephthalide) are characterized by intramolecular cyclization reactions. Depending on the mode of closure of intermediates generated in the course of thermal decomposition of neighboring phthalide groups (head-to-head or head-to-tail), either phenyl-substituted anthraquinones, fluorenones, and fluorenes or symmetric and nonsymmetric dicyclic compounds containing end anthraquinone, fluorenone, and fluorene groups may be formed. The oxidation of poly(terphenylenephthalide) likewise gives rise to cyclic products—the compounds of xanthone and dibenzofuran series.     

Diversity of lanthanide(iii)-2,5-dihydroxy-1,4-benzenedicarboxylate extended frameworks: syntheses, structures, and magnetic properties

Six lanthanide(iii)-2,5-dihydroxy-1,4-benzenedicarboxylate frameworks, namely, [Ln(H(2)-DHBDC)(1.5)(H(2)O)(2)](n) (Ln = La (1) and Pr (2); H(4)-DHBDC = 2,5-dihydroxy-1,4-benzenedicarboxylic acid), {[Nd(H(2)-DHBDC)(1.5)(H(2)O)(3)](H(2)O)}(n) (3), {[Eu(H(2)-DHBDC)(NO(3))(H(2)O)(4)](H(2)O)(2)}(n) (4), and {[Ln(2)(H(2)-DHBDC)(2)(DHBDC)(0.5)(H(2)O)(3)](H(2)O)(4)}(n) (Ln = Gd (5) and Dy (6)), with four different structural types ranging from 1D chain, 2D layer to 3D networks have been synthesized and structurally characterized. Compounds La (1) and Pr (2) are isomorphous and exhibit 3D frameworks with the unique 1D tubular channels. Compounds Nd (3) and Eu (4) are 2D layer and 1D zigzag chain, respectively, which are further extended to 3D supramolecular frameworks through extensive hydrogen bonds. Isomorphous compounds of Gd (5) and Dy (6) are 3D frameworks constructed from secondary infinite rod-shaped metal-carboxylate/hydroxyl building blocks. While the hydroxyl groups as secondary functional groups in the 1D chain of Eu (4) and 2D layer of Nd (3) are not bonded to the lanthanide centers, the hydroxyl groups in the 3D frameworks of La (1), Pr (2), Gd (5), and Dy (6) participate in coordinating to lanthanide centers and thus modify the structural types of theses compounds. The magnetic data of compounds Pr (2), Nd (3), Gd (5), and Dy (6) have been investigated in detail. In addition, elemental analysis, IR spectra, powder X-ray diffraction (PXRD) patterns and thermogravimetric analysis of these compounds are described.     

Stabilization of ortho-quinone methides by a bis(sulfonium ylide) derived from 2,5-dihydroxy-[1,4]benzoquinone

The zwitterionic intermediates (2a) in the oxidation of ortho-alkylphenols (1) and bis(sulfonium ylide) 3 form reasonably stable 2:1-complexes (4), in which the ortho-quinone methide (oQM) moieties are not present in quinoid form with the exocyclic in-plane methylene group, but as zwitterionic, aromatic conformer having an out-of-plane exocyclic methylene group. The complex 7 derived from the α-tocopherol model compound PMC (5) was comprehensively characterized. As exemplarily demonstrated, the adducts can be advantageously employed in organic synthesis as ‘stabilized oQMs’.     

Synthesis of 2,5-dihydroxy-3-(indol-3-yl)benzoquinones by acid-catalyzed condensation of indoles with 2,5-dichlorobenzoquinone

Three methods for the conjugate addition of indoles to 2,5-dichlorobenzoquinone have been developed. A wide variety of indoles substituted with halogen, alkyl, alkoxy, and aryl groups participate in anaerobic condensation reactions promoted by HCl, H2SO4, or CH3CO2H. The hydroquinone product is partially oxidized by excess dichlorobenzoquinone and fully converted to the 2,5-dichloro-3-(indol-3-yl)benzoquinone targets by DDQ or Ag2CO3 oxidation. 2,5-Dihydroxy-3-(indol-3-yl)benzoquinones can be obtained from the dichlorides by alkaline hydrolysis. The rotational characteristics of the biaryl bond created in these reactions have been examined by theoretical and spectroscopic methods.