共查询到20条相似文献,搜索用时 15 毫秒
1.
B. Hammouti H. Oudda A. El Maslout A. Benayada 《Fresenius' Journal of Analytical Chemistry》1999,365(4):310-313
A potentiometric method at imposed weak current between two paste electrodes, ferrocene and chloranil, permits the in situ determination of sulfuric acid concentrations (0.5–11.0 M). The different factors affecting the potential at imposed current
as current intensity, temperature and H+ ion concentration are studied. The potentials measured between ferrocene and chloranil electrodes are directly linked to
the acid concentration. The acidity Ri(H) function, which represents the determination of the H+ activity has been determined and compared to Strehlow Ro(H), Janata HGF and Hammet Ho functions. Ri(H) is numerically equal to the thermodynamic Ro(H).
Received: 19 October 1998 / Revised: 22 March 1999 / Accepted: 23 March 1999 相似文献
2.
《Annales de Chimie Science des Materiaux》2001,26(5):79-84
The corrosion of a carbon steel in (0.5 – 9.0 M) HCl media using weight loss, electrochemical polarization and polarization resistance measurements was investigated. The corrosion data are discussed as function of the Strehlow acidity function Ro(H) which is the extension of pH in concentrated solutions. Weight loss, corrosion current densities and resistance polarization values show a linear behaviour with the Ro(H) acidity function. The corrosion potential-Ro(H) plot is also linear using the ferricinium (Fc+) / ferrocene (Fc) reference electrode in concentrated acid solutions. 相似文献
3.
《Analytical letters》2012,45(11):937-946
Abstract Electroactivity ranges at polished Platinum, vitreous Carbon, and Mercury electrodes are determined in H2O - H3PO4 mixtures (0.1 -14 M H3PO4). The Ferrocene system is considered as a comparison system. Ag+/Ags and AgCl/Ags systems are considered as reference systems. The Ro(H) acidity function is determined. It varies from -2.0 to -6.0 when H3PO4 varies from 5.5 to 11.5 M. 相似文献
4.
The electro chemical systems of chloranil (quinone/semiquinone and semiquinone/hydroquinone) are shown to be usable as pH indicators in anhydrous hydrogen fluoride and in the superacid mixtures HF + MFn (where MFn = PF5, BF3, TaF5, NbF5, AsF5 and SbF5). The combined use of both hydrogen and chloranil electrodes has allowed the establishment of a complete potential-pH diagram of chloranil in the whole acidity range of HF. The quinone/semiquinone system can be used at very high acidity levels (solutions of AsF5 or SbF5) where the hydrogen electrode does not function correctly. A new value of the autoprotolysis constant of HF is reported (Ki = [H+. [F-] = 10-13.7 mol2 l-2) and compared with earlier values. The equilibrium constants of acid-base systems of the quinone (Q/QH+) and hydroquinone (QH2/QH3+ and QH2+4) forms of chloranil, and the disproportionation constant of the semiquinone (QH2+ form are also reported. The indicator system allows the acidity levels reached in HF to be placed on an R(H) scale (where R(H) = 0 corresponds to pH = 0 in aqueous solution). These levels were found to lie between R(H) = -14.2 for 1 M KF solution and R(H) = -27.9 for 1 M SbF5 (i.e. 18% by weight). 相似文献
5.
《Polyhedron》1999,18(21):2737-2747
Nucleophilic substitution reactions of various acetylides on substituted tricarbonyl(η6-fluoroarene)chromiums were pursued. The reaction presumably underwent a more complicated mechanism rather than the direct substitution on the fluorine-bearing carbon. The organometallic compounds (η6-C6H3R1R2R3)Cr(CO)3 (R1: CC–C6H4CH3, R2: o-Me, R3: H (5a), R1: CC–C6H4CH3, R2: o-OMe, R3: H (6a), R1: CC–C6H4CH3, R2: m-OMe, R3: H (6b), R1: CCPh, R2: o-Me, R3: o-OMe (8b), R1: CCPh, R2: m-Me, R3: m-OMe (8c), R1: CCSiMe3, R2: o-Me, R3: H (9a), R1: CC–C6H4CCH, R2: H, R3: H (12), R1: CC–C6H4CCH, R2: o-Me, R3: H (13)) as well as the organometallic dimmer [{(η6-o-Me-C6H4)Cr(CO)3(di-ethynyl)] (di-ethynyl: CC–C6H4CC (14)) have been synthesized from nucleophilic substitution reactions of tricarbonyl(η6-fluoroarene)(chromium) compounds with suitable acetylides. The products have been characterized by spectroscopic means. In addition, (8b) and (8c) were characterized by X-ray diffraction studies. Further reactions of (9a) and (12) with appropriate amount of Co2(CO)8 yielded μ-alkyne bridged bimetallic complexes, Co2(CO)6{μ-Me3SiCC–(o-tolueneCr(CO)3} (10) and (Co2(CO)6)2{μ-HCC–C6H4–CC–(benzene)Cr(CO)3)}(15), respectively. Both (10) and (15) were characterized by spectroscopic means as well as single crystal X-ray crystallography. The core of these molecules is quasi-tetrahedron containing a Co2C2 unit. A two-dicobalt-fragments coordinated di-enyls complex, (Co2(CO)6)2{μ-HCC–C6H4–CC–H} (17), was synthesized from the reaction of 1,3-diethynylbenzene with Co2(CO)8. Crystallographic studies of (17) also show that it exhibits a distorted Co2C2 quasi-tetrahedral geometry. 相似文献
6.
Eight new R1CpTiCl2(OC(C6H4R2)Ph2) complexes were synthesized by the reaction of R1CpTiCl3 with Ph2(R2C6H4)COH (R2C6H4 = phenyl or o‐methyl‐phenyl) in the presence of Et3N in good yield and characterized by 1H NMR, elemental analysis, IR and mass spectrometry. A suitable single crystal of complex 2 (R1: CH3, R2: H) was obtained and the structure determined by X‐ray diffraction. When activated by methylaluminoxane (MAO), all complexes were active for the polymerization of ethylene and styrene. The effect of variation in temperature, catalyst concentration and MAO/catalyst molar ratio was also studied. Complex 5 (R1: n‐C4H9, R2: H) showed a moderate conversion (37.4%) for the polymerization of methyl methacrylate. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
7.
Deprotonation constants of phthalic (H2A) and biphthalic (HA−) acids and of mono-protonated (BH+) and di-protonated (BH22+) piperazine acids have been determined at 25 °C by measuring the Emf of galvanic cells comprising H+-sensitive glass GE(H+) and Ag,AgCl electrodes in non-aqueous isodielectric mixtures of protic ethylene glycol (EG) and dipolar aprotic N,N-dimethylformamide
(DMF). Solvent effects on deprotonation of the acids: ∂(ΔG
disso)=2.303RT[p(s
K
a)−p(R
K
a)], have been dissected into transfer Gibbs energies, ΔG
to
, of the species involved by evaluating ΔG
to of the uncharged phthalic acid and base piperazine (B) from the measured solubilities of the acid and base, respectively,
and using ΔG
to of H+ based on the TATB reference electrolyte assumptions, as evaluated earlier. The contributions of the different species involved
in the protolytic equilibria i.e., H+,H2A,HA−,BH22+ and BH+ and their respective conjugate bases HA−,A2−,BH+ and B have been discussed in terms of their solvation behavior as guided by the ‘acid-base’, dispersion, structural and electronic
characteristics of the acid-base species and of the co-solvent molecules and binary mixtures, ignoring the Born-type electrostatic
interactions on the ionic species as the solvent system is quasi isodielectric. 相似文献
8.
《Analytical letters》2012,45(10):1975-1989
ABSTRACT Electroanalytical methods have been widely used for determination of Se(IV), but the nature of the reduction processes involved is not well understood. Polarographic reduction occurs in three waves (i1, i2, and i3) the height of which changes with pH. We proved that in wave i1, H3SeO3 + is reduced, in i2 H2SeO3, and in i3 HSeO3 -. SeO3 2? is not reducible. All reductions involve a transfer of six electrons and yield selenides. Limiting currents are controlled by the rate of protonation. As proton donors, in addition to H3O+, the acid forms of the buffer present also act. Limiting currents increase markedly with increasing concentration of the buffer. Tenfold increase in buffer concentration can result in up to 200% increase in limiting current. 相似文献
9.
The enthalpies of formation (ΔH f o) for 24 hydrocarbon radicals (R?), mainly polycyclic aromatic radicals with the complex structure, were determined from the published data on bond dissociation energies. The ΔH f o values of the corresponding molecules were calculated, in the majority of cases, by the macroincrement method. Calculations by the group contribution method were performed. Some ΔH f o(R?) values were compared to those calculated by the additive-group method. Calculations were performed, and the conjugation energies of the radicals were discussed. The errors of determination of the ΔH f o(R?) values found were estimated. Due to this work, the database for ΔH f o values of hydrocarbon radicals was increased more than by 25%. 相似文献
10.
Cecil F. Wells 《Thermochimica Acta》1982,53(1):67-87
The acid dissociation constants of a wide range of acids in water+acetone mixtures have been combined with values for the free energy of transfer of the proton. ΔG0t(H+ to calculate values for the free energy of transfer of ions which derive only from the charge on the ion. ΔG0t(i)c. As the values of ΔG0t(H+) have been revised, revised values for the total free energies of transfer of cations and anions, ΔG0t(M+) and ΔGot(X-), are given. New data for ΔGot(MXn) is also split into values for ΔG0t(Mn+) (where n=1 and 2) and ΔG0t(X?). These free energies of transfer, both total and those deriving from the charge alone, are compared with similar free energies in other mixtures water+co-solvent. Values for ΔGot(i)c do not conform to a Born-type relationship and show the importance of structural effects in the solvent even when only the transfer of the charge is involved. 相似文献
11.
Pyridine N-imine complexes of methylcobaloxime, CH3Co(Hdmg)2(R1— C5HnN+N?H) (n = 4; R1 = H, 2-CH3, 3-CH3, 4-CH3: n = 3; R1 = 2,6-CH3), have been synthesized by the reaction of CH3Co(Hdmg)2S(CH3)2 with a pyridine N-imine which is generated from a pyridine, hydroxylamine-O-sulfonic acid and K2CO3. The reactions of CH3Co(Hdmg)2(C5H5N+N?H) with acid anhydrides form new methylcobaloxime complexes with N-substituted pyridine N-imines, CH3Co(Hdmg)2(C5H5N+N?R2) R2 = COPh, COMe, COEt). With maleic anhydride, (pyridine N-acryloylimine)carboxylic acid is formed. With acetylenedicarboxylic acid dimethyl ester, 1,3-dipolar cycloaddition of the ligand gives pyrazolo[1,5-a]pyridine-2,3-dicarboxylic acid dimethyl ester. 相似文献
12.
G. I. Borodkin A. Yu. Vorob’ev M. M. Shakirov V. G. Shubin 《Russian Journal of Organic Chemistry》2011,47(6):889-896
Treatment of 2-X-substituted pyrazines [X = H, Me, Et, Pr, i-Pr, t-Bu, MeCH(OH), H2N, AcNH] with O-mesitylenesulfonylhydroxylamine gave the corresponding 2-X- and 3-X-(1-amino)pyrazin-1-ium mesitylenesulfonates. 2-Alkylpyrazines
(X = Me, Et, Pr, i-Pr) displayed a correlation between the logarithms of the concentration ratio of 2- and 3-substituted cations and substituent
steric constants. Wider series of substituted pyrazines [X = H, Me, Et, Pr, i-Pr, MeCH(OH), H2N, AcNH] conformed to a multiparameter correlation between the logarithms of the concentration ratio of 2- and 3-substituted
cations, on the one hand, and substituent constants σI, σRo, and E
so, on the other. The obtained data on the regioselectivity of amination of pyrazines were interpreted in terms of DFT/PBE/3Z
quantum-chemical calculations. 相似文献
13.
In this communication are presented exact quantum mechanical nonadiabatic electronic transition probabilities for the collinear reaction Ar+ + H2(vi = 0) → ArH+(vf) + H. The calculations were performed using a potential surface calculated by the DIM method. It is established that large probabilities (≈ 1.0) can be obtained only if there is enough translational energy to overcome a potential barrier formed due to the crossing between vi = 0 of the Ar+ + H2 system and vi = 2 of the Ar + H+2 system. The threshold for the reaction is found to be 0.06 eV. 相似文献
14.
Nadia Marino Giuseppe Bruno Archimede Rotondo Giovanna Brancatelli Francesco Nicol 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(10):o587-o589
The title compound, C8H8NO4+·Cl−·H2O, is the chlorohydrated form of 2‐aminobenzene‐1,4‐dicarboxylic acid, the basic crystal structure of which is still not known. Molecules are linked by classical N—H⋯O, O—H⋯O, N—H⋯Cl and O—H⋯Cl hydrogen bonds, mainly along the molecular plane, into sheets built by unusual R64(26), R64(22) and R43(22) rings. The stacking between layers is stabilized by another N—H⋯Cl hydrogen bond and by π–π interactions between aromatic rings facing each other. 相似文献
15.
The use of the complex acid HAlCl4 (HCl+AlCl3) permits the detemrination of the standard potential of the hydrogen electrode in nitromethane. The result (E0(Hs+/H2)=0.5 V vs. Fc/Fc+, Fc=ferrocene) shows that nitromethane is very weakly basic. This measurement is confirmed by showing that the standard potential of the hydrogen electrode in various solvents is linked to Gutmann's donor numbers of these solvents. The E0(Hs+/H2) value obtained in nitromethane belongs to the correlation line. 相似文献
16.
Graham Smith Urs D. Wermuth 《Acta Crystallographica. Section C, Structural Chemistry》2011,67(7):o259-o264
The structures of the 1:1 proton‐transfer compounds of isonipecotamide (piperidine‐4‐carboxamide) with 4‐nitrophthalic acid [4‐carbamoylpiperidinium 2‐carboxy‐4‐nitrobenzoate, C6H13N2O8+·C8H4O6−, (I)], 4,5‐dichlorophthalic acid [4‐carbamoylpiperidinium 2‐carboxy‐4,5‐dichlorobenzoate, C6H13N2O8+·C8H3Cl2O4−, (II)] and 5‐nitroisophthalic acid [4‐carbamoylpiperidinium 3‐carboxy‐5‐nitrobenzoate, C6H13N2O8+·C8H4O6−, (III)], as well as the 2:1 compound with terephthalic acid [bis(4‐carbamoylpiperidinium) benzene‐1,2‐dicarboxylate dihydrate, 2C6H13N2O8+·C8H4O42−·2H2O, (IV)], have been determined at 200 K. All salts form hydrogen‐bonded structures, viz. one‐dimensional in (II) and three‐dimensional in (I), (III) and (IV). In (I) and (III), the centrosymmetric R22(8) cyclic amide–amide association is found, while in (IV) several different types of water‐bridged cyclic associations are present [graph sets R42(8), R43(10), R44(12), R33(18) and R64(22)]. The one‐dimensional structure of (I) features the common `planar' hydrogen 4,5‐dichlorophthalate anion, together with enlarged cyclic R33(13) and R43(17) associations. In the structures of (I) and (III), the presence of head‐to‐tail hydrogen phthalate chain substructures is found. In (IV), head‐to‐tail primary cation–anion associations are extended longitudinally into chains through the water‐bridged cation associations, and laterally by piperidinium–carboxylate N—H...O and water–carboxylate O—H...O hydrogen bonds. The structures reported here further demonstrate the utility of the isonipecotamide cation as a synthon for the generation of stable hydrogen‐bonded structures. An additional example of cation–anion association with this cation is also shown in the asymmetric three‐centre piperidinium–carboxylate N—H...O,O′ interaction in the first‐reported structure of a 2:1 isonipecotamide–carboxylate salt. 相似文献
17.
The electrochemical behavior of ferrocene has been studied in a number of room temperature ionic liquids. Diffusion‐controlled, well‐defined anodic and cathodic peaks were found for the Fc/Fc+ (ferrocene/ferrocenium) oxidation/reduction on the gold electrode. Ohmic resistance R between working and auxiliary electrodes was deduced from impedance measurements. Cyclic voltammograms were corrected for the base line current as well as for the ohmic drop (IR). The formal potential 1/2(Epa+Epc) for ferrocene reduction/oxidation in aprotic ionic liquids tested is within a relatively narrow range and may be approximated by the value of 0.527±0.018 V (against the cryptate Ag/Ag+222 in acetonitrile reference). Ferrocene diffusion coefficients, calculated from the peak current dependence on the sweep rate, were of the order of 10?7 cm2 s?1. 相似文献
18.
Prof. Carl Redshaw Mark Walton Dr. Lucy Clowes Dr. David L. Hughes Dr. Anna‐Marie Fuller Dr. Yimin Chao Dr. Alex Walton Dr. Victor Sumerin Dr. Pertti Elo Dr. Igor Soshnikov Dr. Weizhen Zhao Prof. Wen‐Hua Sun 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(27):8884-8899
The reactions of MCl5 or MOCl3 with imidazole‐based pro‐ligand L1H, 3,5‐tBu2‐2‐OH‐C6H2‐(4,5‐Ph2‐1H‐)imidazole, or oxazole‐based ligand L2H, 3,5‐tBu2‐2‐OH‐C6H2(1H‐phenanthro[9,10‐d])oxazole, following work‐up, afforded octahedral complexes [MX(L1, 2)], where MX=NbCl4 (L1, 1 a ; L2, 2 a ), [NbOCl2(NCMe)] (L1, 1 b ; L2, 2 b ), TaCl4 (L1, 1 c ; L2, 2 c ), or [TaOCl2(NCMe)] (L1, 1 d ). The treatment of α‐diimine ligand L3, (2,6‐iPr2C6H3N?CH)2, with [MCl4(thf)2] (M=Nb, Ta) afforded [MCl4(L3)] (M=Nb, 3 a ; Ta, 3 b ). The reaction of [MCl3(dme)] (dme=1,2‐dimethoxyethane; M=Nb, Ta) with bis(imino)pyridine ligand L4, 2,6‐[2,6‐iPr2C6H3N?(Me)C]2C5H3N, afforded known complexes of the type [MCl3(L4)] (M=Nb, 4 a ; Ta, 4 b ), whereas the reaction of 2‐acetyl‐6‐iminopyridine ligand L5, 2‐[2,6‐iPr2C6H3N?(Me)C]‐6‐Ac‐C5H3N, with the niobium precursor afforded the coupled product [({2‐Ac‐6‐(2,6‐iPr2C6H3N?(Me)C)C5H3N}NbOCl2)2] ( 5 ). The reaction of MCl5 with Schiff‐base pro‐ligands L6H–L10H, 3,5‐(R1)2‐2‐OH‐C6H2CH?N(2‐OR2‐C6H4), (L6H: R1=tBu, R2=Ph; L7H: R1=tBu, R2=Me; L8H: R1=Cl, R2=Ph; L9H: R1=Cl, R2=Me; L10H: R1=Cl, R2=CF3) afforded [MCl4(L6–10)] complexes (M=Nb, 6 a – 10 a ; M=Ta, 6 b – 9 b ). In the case of compound 8 b , the corresponding zwitterion was also synthesised, namely [Ta?Cl5(L8H)+] ? MeCN ( 8 c ). Unexpectedly, the reaction of L7H with TaCl5 at reflux in toluene led to the removal of the methyl group and the formation of trichloride 7 c [TaCl3(L7‐Me)]; conducting the reaction at room temperature led to the formation of the expected methoxy compound ( 7 b ). Upon activation with methylaluminoxane (MAO), these complexes displayed poor activities for the homogeneous polymerisation of ethylene. However, the use of chloroalkylaluminium reagents, such as dimethylaluminium chloride (DMAC) and methylaluminium dichloride (MADC), as co‐catalysts in the presence of the reactivator ethyl trichloroacetate (ETA) generated thermally stable catalysts with, in the case of niobium, catalytic activities that were two orders of magnitude higher than those previously observed. The effects of steric hindrance and electronic configuration on the polymerisation activity of these tantalum and niobium pre‐catalysts were investigated. Spectroscopic studies (1H NMR, 13C NMR and 1H? 1H and 1H? 13C correlations) on the reactions of compounds 4 a / 4 b with either MAO(50) or AlMe3/[CPh3]+[B(C6F5)4]? were consistent with the formation of a diamagnetic cation of the form [L4AlMe2]+ (MAO(50) is the product of the vacuum distillation of commercial MAO at +50 °C and contains only 1 mol % of Al in the form of free AlMe3). In the presence of MAO, this cationic aluminium complex was not capable of initiating the ROMP (ring opening metathesis polymerisation) of norbornene, whereas the 4 a / 4 b systems with MAO(50) were active. A parallel pressure reactor (PPR)‐based homogeneous polymerisation screening by using pre‐catalysts 1 b , 1 c , 2 a , 3 a and 6 a , in combination with MAO, revealed only moderate‐to‐good activities for the homo‐polymerisation of ethylene and the co‐polymerisation of ethylene/1‐hexene. The molecular structures are reported for complexes 1 a – 1 c , 2 b , 5 , 6 a , 6 b, 7 a, 8 a and 8 c . 相似文献
19.
Metal‐Free Dihydrogen Oxidation by a Borenium Cation: A Combined Electrochemical/Frustrated Lewis Pair Approach
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Elliot J. Lawrence Thomas J. Herrington Dr. Andrew E. Ashley Dr. Gregory G. Wildgoose 《Angewandte Chemie (International ed. in English)》2014,53(37):9922-9925
In order to use H2 as a clean source of electricity, prohibitively rare and expensive precious metal electrocatalysts, such as Pt, are often used to overcome the large oxidative voltage required to convert H2 into 2 H+ and 2 e?. Herein, we report a metal‐free approach to catalyze the oxidation of H2 by combining the ability of frustrated Lewis pairs (FLPs) to heterolytically cleave H2 with the in situ electrochemical oxidation of the resulting borohydride. The use of the NHC‐stabilized borenium cation [(IiPr2)(BC8H14)]+ (IiPr2=C3H2(NiPr)2, NHC=N‐heterocyclic carbene) as the Lewis acidic component of the FLP is shown to decrease the voltage required for H2 oxidation by 910 mV at inexpensive carbon electrodes, a significant energy saving equivalent to 175.6 kJ mol?1. The NHC–borenium Lewis acid also offers improved catalyst recyclability and chemical stability compared to B(C6F5)3, the paradigm Lewis acid originally used to pioneer our combined electrochemical/frustrated Lewis pair approach. 相似文献
20.
Dominik Cin
i Branko Kaitner 《Acta Crystallographica. Section C, Structural Chemistry》2008,64(2):o101-o104
In the title compounds, C7H8NO2+·Br−, (I), and C7H8NO2+·I−, (II), the asymmetric unit contains a discrete 3‐carboxyanilinium cation, with a protonated amine group, and a halide anion. The compounds are not isostructural, and the crystal structures of (I) and (II) are characterized by different two‐dimensional hydrogen‐bonded networks. The ions in (I) are connected into ladder‐like ribbons via N—H...Br hydrogen bonds, while classic cyclic O—H...O hydrogen bonds between adjacent carboxylic acid functions link adjacent ribbons to give three characteristic graph‐set motifs, viz. C21(4), R42(8) and R22(8). The ions in (II) are connected via N—H...I, N—H...O and O—H...I hydrogen bonds, also with three characteristic graph‐set motifs, viz. C(7), C21(4) and R42(18), but an O—H...O interaction is not present. 相似文献