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21.
A protocol has been developed for the reliable titration of aqueous sulfite solutions which minimizes photodecomposition effects.
This procedure has been used to measure the protonation constants of the sulfite ion in aqueous solution by glass electrode
potentiometry at 25.0‡C and ionic strengths (I) from 0.1 to 5.0M in NaCI media and atI = 1.0M in KC1 and Me4NCl media. These measurements provided evidence of weak but significant ionpairing between SO2/3 -and Na+ with a formation constant of logK
Na = 0.431 in 1.0M Me4NCl. This was in very good agreement with the value logK
Na = 0.410 measured directly by Na+ ion-selective electrode potentiometry. Evidence is also presented for an extremely weak association of K+ and SO
2
3
-with logK
k
= 0.22 in 1.0M Me4NCl. 相似文献
22.
Schiff-base (SB) derivatives of Ni(II) and Cu(II) porphyrins endowed with various amine functions (R−NH2),n-butylamine,p-anisidine andm-nitroaniline have been prepared from corresponding formyl porphyrins. Protonation studies of these SB derivatives reveal
a marked red shift of the optical absorption bands in the visible region relative to the unprotonated imines. The magnitude
of the observed red shifts in the protonated derivatives, (SBH+) are found to depend on the electron-withdrawing or electron-donating nature of the R group of the amines. The results of
the optical absorption,1H NMR, EPR, and cyclicovoltammetric studies are illustrative of the fact that protonation of the SB derivatives results in
a localized positive charge,
in the periphery of the porphyrin (p) system. The dibenzo-18-crown-6 interspersedbisporphyrin schiff bases have been prepared fromtrans 4,4′-diamino dibenzo-18-crown-6 and formyl porphyrins. The protonation of these SB derivatives is found to proceed in a concerted
fashion. The cation complexation studies by the crown ether entity in thebisporphyrin systems have been investigated using optical absorption, magnetic resonance and electrochemical methods. The redox
characteristics of the protonated dimeric SB porphyrins reveal that the first oxidation step involves a two-electron transfer
reaction. This is important in view of their possible usage in multielectron transfer reactions of biological and catalytic
interest. 相似文献
23.
Alexander G. Grechin Hans-Jürgen Buschmann Eckhard Schollmeyer 《Thermochimica Acta》2005,430(1-2):47-51
The heats of protonation of n-pentylamine, dipentylamine, tributylamine and heats for the first protonation step of 1,8-diamino-3,6-dioxaoctan, diazacrownether 22 and cryptand 222 in pure acetonitril and propylene carbonate and of diazacrownether 22 and dibenzosubstituted ligand 22BB in water + acetonitrile mixtures have been measured at 298.15 K using calorimetric titrations. The values of the reaction enthalpies in the solvents as well as the data in aqueous and methanol solutions reported in literature are analysed in terms of the simple electrostatic model and thermodynamic parameters of transfer (solvation) of the reactants. Estimation of the electrostatic and covalent contributions to standard enthalpy of transfer of the reactions from water to non-aqueous and mixed solvents has been made. 相似文献
24.
25.
S. O. Bondareva V. V. Lisitskii N. I. Yakovtseva Yu. I. Murinov 《Russian Chemical Bulletin》2004,53(4):803-807
The kinetics of hydrolysis of 1,2-disubstituted imidazolines in aqueous media was studied (pH 2.0—12.5, T = 25—90 °C) by UV spectroscopy. The hydrolysis products were identified. The introduction of a branched substituent into position 2 of the imidazoline ring increases the hydrolytic stability of the compounds. The effect of the pH on the hydrolysis rate of imidazolines is discussed. 相似文献
26.
Koridze A. A. Kuklin S. A. Petrovskii P. V. Dolgushin F. M. Ezernitskaya M. G. 《Russian Chemical Bulletin》2002,51(2):350-353
The Os3(-H)2(CO)7(-C6H4){3-Ph2PCH2P(C6H4)Ph} complex, which was isolated from the products of thermolysis of Os3(CO)10(-dppm) (dppm is Ph2PCH2PPh2) in toluene, was characterized by X-ray diffraction analysis. Protonation of the resulting complex with trifluoroacetic acid afforded the cationic complex [Os3(-H)3(CO)7(-C6H4){3-Ph2PCH2P(C6H4)Ph}]+. 相似文献
27.
Elhabiri M Siri O Sornosa-Tent A Albrecht-Gary AM Braunstein P 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(1):134-141
We present a detailed study on the acid-base behaviour of a family of "potentially antiaromatic" p-benzoquinonediimine ligands. These 12pi electron molecules can be considered as constituted of two chemically connected but electronically not conjugated 6pi-electron subunits. Upon successive protonation, "mono" and "double" cyanine-type chromophores are generated in solution and allow a precise and sensitive spectrophotometric detection. These molecules represent a new class of tunable quinones whose electronic and structural properties can be triggered by proton input, as established by a complete physico-chemical study involving a combination of potentiometric and spectrophotometric methods (absorption and emission). 相似文献
28.
O. A. Kizas V. V. Krivykh V. V. Vorontsov A. A. Koridze 《Russian Chemical Bulletin》1993,42(6):1102-1103
Protonation of triosmium clusters Os3(-H)(CO)9(3-,2-CC-R) (R=CMe2OH, C(Me)=CH2) affords a cationic complex containing a six-electron propargyl ligand which has been detected for the first time.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1144–1145, June, 1993. 相似文献
29.
Ab initio molecular orbital calculations employing a 4-31G basis set have been used to study the minimum energy paths for the formation of HCO+, COH+, and HCOH2+ from CO by protonation. The protonation of N2 to give NNH+ and HNNH2+ and of NO+ to form HNO2+ and NOH2+ have also been investigated. All species formed have linear equilibrium geometries and the minimum energy path for approach of the proton is along the line-of-centers of the heavy atoms. Energy barriers to the formation of the various species are given, where appropriate, and changes in geometry, ordering of molecular orbitals and orbital occupancy are discussed. 相似文献
30.
用AM1MO方法计算了质子化卟吩的构型,并通过结构分析、电荷布局分析和前线轨道分析,讨论了其质子化过程的构型变化及Raman光谱变化的原因。 相似文献