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Hydrocarbons electrochemical determination

For saturated hydrocarbons, exchange is too slow and reference points are so uncertain that direct determination of pAT values by exchange measurements is not feasible. The most useful proach to obtain pK data for such hydrocarbons involves making a measurement of the electrochemical potential for the reaction... [Pg.410]

Brewis et al. used TOF-SIMS to determine the surface composition of hydrocarbon polymers after electrochemical pretreatment with nitric acid alone or in the presence of silver ions [58J. AgNO was generated by electrolysis of a 0.1 M solution of silver nitrate in 3.25 M nitric acid in the anode compartment of a... [Pg.308]

Electrochemical promotion has also been used to determine the optimal alkali promoter coverage on Ag epoxidation catalysts as a function of chlorinated hydrocarbon moderator level in the gas phase (Chapter 8). [Pg.516]

Because process mixtures are complex, specialized detectors may substitute for separation efficiency. One specialized detector is the array amperometric detector, which allows selective detection of electrochemically active compounds.23 Electrochemical array detectors are discussed in greater detail in Chapter 5. Many pharmaceutical compounds are chiral, so a detector capable of determining optical purity would be extremely useful in monitoring synthetic reactions. A double-beam circular dichroism detector using a laser as the source was used for the selective detection of chiral cobalt compounds.24 The double-beam, single-source construction reduces the limitations of flicker noise. Chemiluminescence of an ozonized mixture was used as the principle for a sulfur-selective detector used to analyze pesticides, proteins, and blood thiols from rat plasma.25 Chemiluminescence using bis (2,4, 6-trichlorophenyl) oxalate was used for the selective detection of catalytically reduced nitrated polycyclic aromatic hydrocarbons from diesel exhaust.26... [Pg.93]

Electrochemical reduction of carbon monoxide in dry nonaqueous media at moderate to low pressures leads to the formation of the 1,3-cyclobutanedione dianion (squarate) at current efficiencies, up to about 45% depending on the cathode material [1,2]. In aqueous solution, electroreduction can lead to the formation of methane and other hydrocarbon products. The role of the metal/adatom in determining the extent of CO and hence hydrocarbon formation during the reduction of carbon dioxide is related to the ability of the electrode material to favor CO formation (Cu, Au, Ag, Zn, Pd, Ga, Ni, and Pt) and stabilize HCCO [3, 4]. [Pg.226]

MacCrehan, W. A., W. E. May, S. D. Yang, and G. A. Benner, Jr., Determination of Nitro Polynuclear Aromatic Hydrocarbons in Air and Diesel Particulate Matter Using Liquid Chromatography with Electrochemical and Fluorescence Detection, Anal Chem., 60, 194-199 (1988). [Pg.538]

Use of Isotopic Effects in the Determination of Electro-Organic Reaction Mechanisms. Much work has been carried out on the mechanism by which hydrocarbons can be clectrochemically oxidized. Were that easy, it might be possible to use available oil in electrochemical devices (fuel cells) to convert chemical to electrical energy 2—3 times more efficiently than do heat engines (Chapter 13). [Pg.439]

In principle, the A 0(H) function is of limited interest for kinetic applications because the indicators are chemically very different from the organic substrates generally used. On the other hand, as the measurements are based on pH determination, the length of the acidity scale is limited by the pA" value of the solvents. However, very interesting electrochemical acidity studies have been performed in HF by Tremillon and co-workers, such as the acidity measurement in anhydrous HF solvent and the determination of the relative strength of various Lewis acids in the same solvent. By studying the variation of the potential of alkane redox couples as a function of acidity, the authors provide a rational explanation of hydrocarbon behavior in the superacid media.48... [Pg.20]

The determination of the strength of the Lewis acids MF , has been carried out in various solvents using the conventional methods. Numerous techniques have been applied conductivity measurements, cryoscopy, aromatic hydrocarbon extraction,53,84 solubility measurements,85-87 kinetic parameters determinations,52,88,89 electroanalytical techniques (hydrogen electrode),90-93 quinones systems as pH indicators,94-97 or other electrochemical systems,98 99 IR,100,101 and acidity function (//,) determinations with UV-visible spectroscopy,8 9 14 19 102-105 or with NMR spectros-copy.20-22,44-46,106-108 Gas-phase measurements are also available.109-111 Comparison of the results obtained by different methods shows large discrepancies (Table 1.2). [Pg.24]

In a landmark paper, Breslow and coworkers described the determination of pA), values of weak hydrocarbon acids by use of thermochemical cycles involving electrochemical reduction data for triarylmethyl, cycloheptatrienyl, and triphenyl- and trialkylcyclopropenyl cations and radicals [9aj. Later, they derived pATa data from standard oxidation potentials and bond-dissociation energies [9b, c]. The methodology was further developed by Nicholas and Arnold [10a] for the determination of cation radical acidities, and later modified and extensively used by Bordwell and coworkers [10b, c] so that homolytic bond-dissociation energies and cation radical... [Pg.1342]

An alternative approach to pK determination for very weak hydrocarbon acids is the electrochemical method of Breslow " . This method is thermodynamic in origin employing voltammetric reduction/oxidation of the cation (or anion) to radical thence to anion (or cation) and comparing the energetics of these steps to the triphenylmethyl system (including bond dissociation energies of the respective hydrocarbons). Values of p aS obtained for some weak carbon acids by this method are given in Table 1 for comparison with the Streitwieser results. [Pg.258]

It has been reported that the concentration of proton and adsorbed hydrogen can be controlled by adjusting the anodic and cathodic bias in the pulsed method [7]. The hydrogen adsorbed on the electrode surface seems to interrupt the reaction for the electrochemical reduaion of COj. The CO2 coverage on the electrode surface may be increased by the elimination of adsorbed hydrogen during anodic period. In the subsequent cathodic period, the electron transfer to CO2 was promoted, yielding CO2 radical anions. The selectivity of products for the electrochemical reduction of CO2 was determined in association with electrode material and CO2 radical anion [10,11]. CO is intermediate species in the reaction process of hydrocarbonization [8]. [Pg.576]

In the area of electron affinities of organic molecules, other electrochemical measurements were made and compared with half-wave reduction potentials. Quantum mechanical calculations for aromatic hydrocarbons were carried out using self-consistent field calculations. Many advances were made in the determination of the acidity of organic molecules. The effect of substitution and replacement on electron affinities and bond dissociation energies was recognized. This work is summarized in Chapters 10 and 12. A. S. Streitweiser provides an excellent review of the role of anions in organic chemistry up to 1960 [12]. [Pg.27]

Allylic conjugation stabilizes carbanions and pA values of 43 (in cyclohexy-lamine) and 47 8 (in THF-HMPA) have been determined for propene. On the basis of exehange rates with cesium cyclohexylamide, cyclohexene and cycloheptene have been found to have pAT values of about 45 in cyclohexylamine3 The hydrogens on the sp carbons in benzene and ethylene are more acidic than the hydrogens in saturated hydrocarbons. A pAT of 43 has been estimated for benzene on the basis of extrapolation from a series of fluorobenzenes. Electrochemical measurements have been used to establish a lower limit of about 46 for the pAT of ethylene. ... [Pg.372]


See other pages where Hydrocarbons electrochemical determination is mentioned: [Pg.354]    [Pg.61]    [Pg.270]    [Pg.213]    [Pg.74]    [Pg.17]    [Pg.56]    [Pg.97]    [Pg.407]    [Pg.651]    [Pg.790]    [Pg.235]    [Pg.162]    [Pg.948]    [Pg.313]    [Pg.819]    [Pg.213]    [Pg.498]    [Pg.256]    [Pg.128]    [Pg.300]    [Pg.38]    [Pg.17]    [Pg.56]    [Pg.21]    [Pg.331]    [Pg.1168]    [Pg.294]    [Pg.162]    [Pg.948]    [Pg.82]    [Pg.301]    [Pg.1225]    [Pg.252]   
See also in sourсe #XX -- [ Pg.372 , Pg.584 ]




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Hydrocarbons determination

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