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1.
Methylmaleic (citraconic, CTA) acid and methylfumaric (measaconic, MSA) acid in aqueous sulfuric acid solution undergo bromine-catalyzed reversible cis-trans isomerization in the presence of ceric and bromide ions. The positional isomerization of CTA or MSA to itaconic acid (ITA) is not observed. The method of high performance liquid chromatography (HPLC) was applied to study the kinetics of this catalyzed isomerization. The major catalytic species is best expressed as the Br?2 · radical anion. Under suitable catalytic conditions, there is a tendency for the [MSA]/[CTA] ratio to reach an equilibrium value of 4.10 at 25° for the CTA+Br?2 · ? MSA+Br?2 · reaction. Chloromaleic (CMA) and chlorofumaric (CFA) acids undergo similar isomerization with an equilibrium [CFA]/[CMA] ratio of 10.3 at 25°. The isomerization of maleic acid (MA) to fumaric acid (FA) is essentially irreversible with 50 as the lower limit of the equilibrium [FA]/[MA] ratio. The substituent has an important effect on the reversibility of this catalyzed isomerization of butenedicarboxylic acids. The thermodynamic parameters ΔH° and ΔS° at 25° for the CTA+Br?2 · ? MSA+Br?2 · reaction were found to be ?5.1±0.7 kj/mol and ?6.0±3.3 J/mol K, respectively. The present method gives a plausible way to measure the differences in enthalpy and entropy between the trans- and cis-isomers of butenedicarboxylic acids (CRCO2H=CR'CO2H) in aqueous solution. 相似文献
2.
Dhirendra Kumar Dr. K. R. Justin Thomas Ching‐Chiao Lin Prof. Jwo‐Huei Jou 《化学:亚洲杂志》2013,8(9):2111-2124
A series of pyrenoimidazoles that contained various functional chromophores, such as anthracene, pyrene, triphenylamine, carbazole, and fluorene, were synthesized and characterized by optical, electrochemical, and theoretical studies. The absorption spectra of the dyes are dominated by electronic transitions that arise from the pyrenoimidazole core and the additional chromophore. All of the dyes exhibited blue‐light photoluminescence with moderate‐to‐high quantum efficiencies. They also displayed high thermal stability and their thermal‐decomposition temperatures fell within the range 462–512 °C; the highest decomposition temperature was recorded for a carbazole‐containing dye. The oxidation propensity of the dyes increased on the introduction of electron‐rich chromophores, such as triphenylamine or carbazole. The application of selected dyes that featured additional chromophores such as pyrene, carbazole, and triphenylamine as blue‐emissive dopants into multilayered organic light‐emitting diodes with a 4,4′‐bis(9H‐carbazol‐9‐yl)biphenyl (CBP) host was investigated. Devices that were based on triphenylamine‐ and carbazole‐containing dyes exhibited deep‐blue emission (CIE 0.157, 0.054 and 0.163, 0.041), whereas a device that was based on a pyrene‐containing dye showed a bright‐blue emission (CIE 0.156, 0.135). 相似文献
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The isotope exchange reactions of malonic acid and a malonate ion were investigated in acidic and basic D2O solutions, respectively, using 1H NMR spectroscopy. The isotope exchange reaction of malonic acid is inhibited by the presence of DNO3 (0–3 M) and DSO4? ion (0–0.1 M), whereas it is catalyzed by the presence of DSO4? ion (> 0.2 M), D3PO4, D2PO4? ion or DPO42– ion. The order of relative reactivity for catalyzing the isotope reaction of malonic acid in D2O is DPO42– > D2PO4? > D3PO4 > DSO4? > DNO3. The rate of the isotope exchange reaction of malonate ion in D2O decreases to a minimum and then increases with increased [NaOD]0. The mechanism of the isotope exchange reaction of malonic acid in acidic D2O is different from the general acid-catalyzed mechanism generally observed for organic acids like acetic and dichloroacetic acids. The bimalonate ion plays an important role in the isotope exchange reactions of this system. 相似文献
5.
In a stirred batch reaction, Fe(phen)32+ ion behaves differently from Ce(III) or Mn(II) ion in catalyzing the bromate‐driven oscillating reaction with ethyl hydrogen malonate [CH2COOHCOOEt, ethyl hydrogen malonate (EHM)]. The effects of N2 atmosphere, concentrations of bromate ion, EHM, metal ion catalyst, sulfuric acid, and additive (bromide ion or bromomalonic acid) on the pattern of oscillations were investigated. The kinetic study of the reaction of EHM with Ce(IV), Mn(III), or Fe(phen)33+ ion indicates that under aerobic or anaerobic conditions the order of reactivity toward reacting with EHM is Mn(III) > Ce(IV) ≫ Fe(phen)33+, which follows the same trend as that of the malonic acid system. The presence of the ester group in EHM lowers the reactivity of the two methylene hydrogen atoms toward bromination or oxidation by Ce(IV), Mn(III), or Fe(phen)33+ ion. No good oscillations were observed for the BrO3−‐CH2(COOEt)2 reaction catalyzed by Ce(III), Mn(II), or Fe(phen)32+ ion. A discussion of the effects of oxygen on the reactions of malonic acid and its derivatives (RCHCOOHCOOR′) with Ce(IV), Mn(III), or Fe(phen)33+ ion is also presented. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 52–61, 2000 相似文献
6.
TiO2 Nanoparticles Produced by Electric-Discharge-Nanofluid-Process as Photoelectrode of DSSC
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Self-made TiO2 nanoparticles were used as photoelectrode material of dye sensitized solar cell. The TiO2 thin film coats through spreading nanoparticles evenly onto the ITO glass via self-made spin-heat platform, and then TiO2 thin film is soaked in the dye N-719 more than 12 h to prepare the photoelectrode device. The TiO2 nanoparticles produced by electric-discharge-nanofluid-process have premium anatase crystal property, and its diameter can be controlled within a range of 20-50 nm. The surface energy zeta potential of nanofluid is from -22 mV to -28.8 mV, it is a stable particle suspension in the deionized water. A trace of surfactant Triton X-100 put upon the surface of ITO glass can produce a uniform and dense TiO2 thin film and heating up the spin platform to 200 oC is able to eliminate mixed surfac-tant. Self-made TiO2 film presents excellent dye absorption performance and even doesn't need heat treatment procedure to enhance essential property. Results of energy analysis show the thicker film structure will increase the short-circuit current density that causes higher conversion efficiency. But, as the film structure is large and thick, both the open-circuit voltage and fill factor will decline gradually to lead bad efficiency of dye-sensitized solar cell. 相似文献
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In aqueous H2SO4, Ce(IV) ion oxidizes rapidly Arnold's base((p-Me2NC6H4)2CH2, Ar2CH2) to the protonated species of Michler's hydrol((p-Me2NC6H4)2CHOH, Ar2CHOH) and Michler's hydrol blue((p-Me2NC6H4)2CH+, Ar2CH+). With Ar2CH2 in excess, the rate law of the Ce(IV)-Ar2CH2 reaction in 0.100 M H2SO4 is expressed -d[Ce(IV)]/dt = kapp[Ar2CH2]0[Ce(IV)] with kapp = 199 ± 8M?1s?1 at25°C. When the consumption of Ce(IV) ion is nearly complete, the characteristic blue color of Ar2CH+ ion starts to appear; later it fades relatively slowly. The electron transfer of this reaction takes place on the nitrogen atom rather than on the methylene carbon atom. The dissociation of the binuclear complex [Ce(III)ArCHAr-Ce(III)] is responsible for the appearance of the Ar2CH+ dye whereas the protonation reaction causes the dye to fade. In highly acidic solution, the rate law of the protonation reaction of Michler's hydrol blue is -d[Ar2CH+]/dt = kobs[Ar2CH+] where Kobs = ((ac + 1)[H*] + bc[H+]2)/(a + b[H+]) (in HClO4) and kobs= ((ac + 1 + e[HSO4?])[H+] + bc[H+]2 + d[HSO4?] + q[HSO4?]2/[H+])/(a + b[H+] + f[HSO4?] + g[HSO4?]/[H+]) (in H2SO4), and at 25°C and μ = 0.1 M, a = 0.0870 M s, b = 0.655 s, c = 0.202 M?1s?1, d = 0.110, e = 0.0070 M?1, f = 0.156 s, g = 0.156 s, and q = 0.124. In highly basic solution, the rate law of the hydroxylation reaction of Michler's hydrol blue is -d[Ar2CH+]/dt = kOH[OH?]0[Ar2CH+] with kOH = 174 ± 1 M?1s?1 at 25°C and μ = 0.1 M. The protonation reaction of Michler's hydrol blue takes place predominantly via hydrolysis whereas its hydroxylation occurs predominantly via the path of direct OH attack. 相似文献
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W.C. Chan D.S. Jwo Y.F. Lin Y. Huang 《Physica C: Superconductivity and its Applications》1994,230(3-4):349-353
By using an ordinary electric balance, we are able to measure the magnetic levitation forces acting on a superconducting YBa2Cu3Oy (YBCO) single crystal. It is found that when the external magnetic field is parallel to the c-axis of the single crystal, the hysteretic levitation curve is similar to that of a melt-processed YBCO superconducting sample. However, when the external magnetic field is perpendicular to the c-axis of the YBCO single crystal, the levitation forces are too small to be measured by our equipment. Also, we have introduced a simple model with the Bean's approximations to explain the levitation forces. The critical current density derived from this model by fitting with experimental data is quite close to the value obtained from magnetization measurements. 相似文献
9.
Jing-Jer Jwo 《中国化学会会志》1981,28(1):34-41
The presence of small amounts of ceric and bromide ions in the aqueous sulfuric acid solution of maleic acid can catalyze the isomerization of maleic acid to fumaric acid rapidly and quantitatively at room temperature. A qualitative kinetic study was carried out to see how the rate and the yield of this reaction depend on the relative amounts of maleic acid, ceric ion, and bromide ion. In general, the rate increases asymptotically to a limiting value as the concentration of maleic acid, ceric or bromide ion increases. Sulfuric acid has both the chemical and physical effects on the rate of isomerization. If the relative amounts of the reactants is in the order of [maleic acid]≥[Br?]≥[Ce(IV)], a very high yield up to 98% can easily be obtained. Sulfuric acid does not have major effect on the yield. A mechanism was proposed to rationalize the experimental results. 相似文献
10.
The presence of ceric and bromide ions catalyzes the isomerization of maleic acid (MA) to fumaric acid (FA) in aqueous sulfuric acid. A kinetic study of this bromine-catalyzed reaction was carried out. The reaction between ceric ion and maleic acid is first order with respect to Ce(IV). For [Ce(IV)]0=5.0×10?4 M, [H2SO4]0=1.2 M, μ=2.0 M (adjusted by NaClO4), and [MA]0=(0.5–1.0)M, the observed pseudo-first-order rate constant (k03) at 25° is k03=7.622×10?5 [MA]0/(1+0.205[MA]0). The reaction between ceric and bromide ions is first order with respect to Ce(IV). For [Ce(IV)]0=5.0×10?4 M, [H2SO4]0=1.2 M, μ=2.0 M, and [Br?]0=(0.025–0.150)M, the pseudo-first-order rate constant (k02) at 25° is k02= (4.313±0.095)x10?2[Br?]2+(2.060±0.119)x10?3[Br?]. The reaction of Ce(IV) with maleic acid and bromide ion is also first order with respect to Ce(IV). For [Ce(IV)]0=5.0×10?4 M, [MA]0=0.75 M, [H2SO4]0=1.2 M, μ=2.0 M, and [Br?]0= (0.025–0.150)M, the pseudo-first-order rate constant (k03) at 25° is k03= (5.286±0.045)x10?2[Br?]2+(3.568±0.056)x10?3[Br?]. For [Ce(IV)]0=5.0 × 10?4 M, [Br?]0=0.050 M, [H2SO4]0=1.2 M, μ=2.0 M, and [MA]0=(0.15–1.0)M at 25°, k03=(2.108×10?4+2.127×10?4[MA]0)/(1+0.205[MA]0). A mechanism is proposed to rationalize the results. The effect of temperature on the reaction rate was also studied. The energy barrier of Ce(IV)—Br? reaction is much less than that of Ce(IV)—MA reaction. Maleic and fumaric acids have very different mass spectra. The mass spectrum of fumaric acid exhibits a strong metastable peak at m/e 66.5. 相似文献