Showing papers in "Transactions of The Faraday Society in 1967"
TL;DR: In this article, the reactions of e-aq, H· and OH· with phenol have been studied and the corresponding rate constants were 1.8 × 107, 1.6 × 109 and 1.4 × 1010 M−1 sec−1, respectively.
Abstract: The reactions of e–aq, H· and OH· with phenol have been studied. The corresponding rate constants were 1.8 × 107, 1.8 × 109 and 1.4 × 1010 M–1 sec–1, respectively. The product detected after e–aq and H· attack was the H adduct (Iµ3300A= 3800 M–1 cm–1). The initial product of OH· attack was the OH adduct (Iµ3300A= 4400 M–1 cm–1). Both H and OH adducts are probably mixtures of isomers. OH adducts subsequently undergo either unimolecular elimination of water to form the more resonance-stabilized phenoxyl radical, ϕO·(Iµ4000A= 2200 M–1 cm–1), or bimolecular radical-radical reactions. The elimination is catalyzed by H+, OH– and HPO2–4 ions. There are indications of different rates of catalysis for different isomers of the OH adduct. The uncatalyzed rate of elimination is ⩽103 sec–1. The elimination was also detected from OH adducts of p-cresol (to give p-CH3C6H4O-, Iµ4050A= 2400 M–1 cm–1) and tyrosine. The ability to eliminate water appears to be a general property of OH adducts of phenols.
329 citations
TL;DR: In this article, phase diagrams have been determined for the systems MI+AgI (M = Na, K, Rb, Cs, Tl or NH4), MBr+AgBr(M = K,Rb or Cs) and MI+CuI (m = K or Rb).
Abstract: Phase diagrams have been determined for the systems MI+AgI (M = Na, K, Rb, Cs, Tl or NH4), MBr+AgBr (M = K, Rb or Cs) and MI+CuI (M = K or Rb). A group of isomorphous compounds MAg4I5(M = K, Rb, NH4) with exceptionally high ionic conductivity has been identified. At 20°C the conductivity of polycrystalline RbAg4I5 is 0.124 ± 0.006 ohm–1 cm–1, i.e., higher than the ionic conductivity of any other known solid. At this temperature RbAg4I5 is stable, but KAg4I5 and NH4Ag4I5 slowly disproportionate to AgI and K2AgI3 or (NH4)2AgI3. The ternary system KI+RbI+AgI contains a complete range of solid solutions (K,Rb) Ag4I5. Analogous bromides have not been found, but a compound KCu4I5 is stable between 257 and 332°.
227 citations
TL;DR: The absolute intensity and quenching constants of the NO2 emission in the chemiluminescent reaction between nitric oxide and ozone have been determined using a large capacity-flow reactor at low pressures.
Abstract: The absolute intensity and quenching constants of the NO2 emission in the chemiluminescent reaction between nitric oxide and ozone have been determined using a large capacity-flow reactor at low pressures. These studies have confirmed the mechanism previously proposed: NO+O3= NO*2(2B1)+O2(1a) NO+O3= NO2(2A1)+O2(1b) NO*2= NO2+hv(2) M+NO2= NO2+M (3) The rate constants of the primary steps are k1a=(7.6 ± 1.5)× 1011 exp (–4180 ± 300/RT) and k1b=(4.3 ± 1.0)× 1011 exp (–2330 ± 150/RT) cm3 mole–1 sec–1. The half-quenching pressures (k2/k3m) of electronically excited NO2 produced are: Ar = 13.0 ± 1.0 µ, O2= 8.3 ± 0.5 µ, NO = 5.2 ± 0.3 µ, NO2= 3.7 ± 0.1 µ. The detailed mechanism of reactions (1a) and (1b) is discussed.
177 citations
TL;DR: In this article, the authors determined the change Δtext-decoration:overlineV2 in partial molar volumes on micelle formation by molecular structure, and showed that the hydration of the methylene groups adjacent to the hydrophilic group is retained.
Abstract: The partial molar volumes text-decoration:overlineV2 of some ionic and non-ionic surface-active agents have been determined above and below the critical micelle concentrations. The change Δtext-decoration:overlineV2 in partial molar volumes on micelle formation is determined by molecular structure. Thus, additional methylene groups in the alkyl chain remote from the hydrophilic group give an increase in Δtext-decoration:overlineV2, while additional methylene groups in close proximity to a hydrophilic centre give a small decrease in Δtext-decoration:overlineV2. These results indicate that in the process of micelle formation the hydration of the methylene groups adjacent to the hydrophilic group is retained.
164 citations
TL;DR: A number of transient free-radical spectra produced during the pulse radiolysis of benzoquinone and hydroquinone, have been observed and characterized in this article, where the extinction coefficients of the various species and the reaction rate constants for their formation and decay have been measured.
Abstract: A number of transient free-radical spectra produced during the pulse radiolysis of benzoquinone, and hydroquinone, have been observed and characterized. The semiquinone radical and radical-anion are produced directly by reactions of e–aq and H atoms with benzoquinone and also by the unimolecular elimination of water from trihydroxycyclohexadienyl radicals. The latter species arise directly by OH addition to hydroquinone. The extinction coefficients of the various species and the reaction rate constants for their formation and decay have been measured. The equilibrium constant for the benzsemiquinone radical and radical-anion equilibrium is 10–4 M.
161 citations
TL;DR: In this article, the infra-red spectra from 4000 to 750 cm-1 of various carbonato species adsorbed on magnesium oxide are presented, and the interaction on the MgO surface of CO2 with H2O and D2O results in the unidentate carbonate species when CO2 is adsoribed first but a bi-carbonate species HO-CO-2 is formed when water is adsored first.
Abstract: The infra-red spectra from 4000 to 750 cm–1 of various carbonato species adsorbed on magnesium oxide are presented. When CO2 is adsorbed at temperatures above 300°C a bidentate species is formed. The interaction on the MgO surface of CO2 with H2O and D2O results in the unidentate carbonate species when CO2 is adsorbed first but a bi-carbonate species HO—CO–2 is formed when water is adsorbed first. Correlations have been made of the low-frequency carbonate bands (1200–800 cm–1) and the carbonate bands in the region 1800–1200 cm–1. Infra-red absorption bands in the region 1200–800 cm–1, are better defined when D2O rather than H2O is used for the interaction studies.
133 citations
TL;DR: In this article, real free energies of solvation have been measured in several non-aqueous and mixed solvents and the results are discussed in terms of the bulk and surface contributions.
Abstract: Real free energies of solvation have been measured in several non-aqueous and mixed solvents. The results are discussed in terms of the bulk and surface contributions. Changes in these can be deduced in mixed solvents by comparison with the known surface composition. Hence it is proposed that most of the non-aqueous solutions studied have negative χ-potentials and approximate values are suggested which fit the available facts. The sign of the χ-potential of water is still uncertain although the range of possible values has been narrowed. Methanol, unlike the higher alcohols, appears to be oriented differently at the air and uncharged mercury interfaces.
131 citations
TL;DR: In this paper, the effects of the absorption of the chromophoric group of thymine on irradiation in aqueous solution with γ-rays has been studied under a variety of conditions.
Abstract: The loss of absorption of the chromophoric group of thymine on irradiation in aqueous solution with γ-rays has been studied under a variety of conditions. The effects of thymine and oxygen concentrations, of pH and of the presence of N2O have been investigated. In solutions containing oxygen, the loss of absorption is the result of initial OH radical attack on the pyrimidine molecule; radiation-induced electron attachment to thymine does not lead to destruction of the chromophoric group if oxygen is present in the system. Aerated thymine solutions (8 × 10–5-2 × 10–4 M) have been used to determine, spectrophotometrically, the relative reactivities of solutes towards OH radicals; because of an unusual pH effect observed in neutral solutions, the competition experiments were carried out below pH 6. The reactivities of a number of organic solutes have been obtained. Similar rate constant ratios were obtained in solutions containing N2O, indicating that N2O– was not an oxidizing species under the conditions of the experiments.
124 citations
TL;DR: In this paper, the authors used spin resonance to study the reaction of oxygen atoms in a nitrogen carrier and of hydrogen atoms in an argon carrier with simple hydrocarbons in a fast flow system at total pressures around 2 mm Hg.
Abstract: Electron spin resonance has been used to study the reaction of oxygen atoms in a nitrogen carrier and of hydrogen atoms in an argon carrier with simple hydrocarbons in a fast flow system at total pressures around 2 mm Hg. The reaction between oxygen atoms and acetylene occurs predominantly by the mechanism: O+C2H2= CH2+CO (3) O+CH2= CO+2H (6) CH2+C2H2= C3H4(12) where k3=(9.2 ± 0.4)× 1010 cm3 mole–1 sec–1 and k6=(2.7 ± 1.0)k12 both at 298°K. The initial step in the reaction of oxygen atoms with methyl acetylene is O+CH3 . C CH = CH3 . CH : + CO (13) with k13=(4 ± 1)× 1011 cm3 mole–1 sec–1 at 298°K; the total rate constant for the disappearance of oxygen atoms being 3–4 times greater.
The mechanisms of the O+C2H4 and O+CH4 reactions have been deduced from their overall stoichiometries and the hydrogen atom yields. For the initial steps O+C2H4= CH3+HCO (15) O+CH4= CH3+OH (23)k15=(3.2 ± 0.4)× 1011 cm3 mole–1 sec–1 at 298°K and k23=(7 ± 2)× 1012 exp (–7700 ± 300/RT) cm3 mole–1 sec–1 between 450 and 600°K. The addition of hydrogen atoms to methyl acetylene and to ethylene were second order processes, H+C3H4= C3H5(4) H+C2H4= C2H5(17) with k4=(2.4 ± 0.3)× 1011 cm3 mole–1 sec–1 and k17=(8.8 ± 0.4)× 1010 cm3 mole–1 sec–1 at 298°K.
115 citations
TL;DR: In this article, a modified characteristic time constant containing constants which characterize geometrical and equilibrium properties of the system was proposed to characterize the rate processes in diffusion-controlled sorptive processes.
Abstract: In diffusion-controlled sorptive processes, Fick's second equation can be solved analytically only for special functional forms of an immobilization isotherm. The dissimilarity in the formal appearance of attainable solutions hides common features of physical behaviour. The rate processes can, however, be broadly characterized by adopting a modified characteristic time constant containing constants which characterize geometrical and equilibrium properties of the systems. In the absence of information concerning the shape of the immobilization isotherm, diffusion coefficients of the mobile species can then be derived from observed “apparent diffusivities” within ±30 % of uncertainty in magnitude.
98 citations
TL;DR: In this article, the solution and trapping of helium and neon in cristobalite in the range 293-857°K and in tridymite between 293 and 838°K were studied.
Abstract: The solution and trapping of helium and neon has been studied in cristobalite in the range 293–857°K and in tridymite between 293 and 838°K. These temperatures cover regions in which α- and β-cristobalite and α-, β1- and β2-tridymite are found. The solubilities are considerable, those in tridymite being close to solubilities in silica glass and those in cristobalite rather less. Heats of solution were evaluated from isotherms and had the same signs as those in silica glass. The results were discussed in terms of an oscillator model for dissolved atoms. For some of the systems approximate diffusion coefficients were obtained which could be represented by the Arrhenius equation: He in α-tridymite (236–336°K): D= 7·7×10–4 exp –12000/RT cm2 sec–1, He in α-cristobalite (244–335°K): D= 2·0×10–2 exp –13800/RT cm2 sec–1, Ne in α-tridymite (336–366°K): D= 6·7×10–2 exp –22500/RT cm2 sec–1, Ne in β1-tridymite (418–474°K): D= 9·9×10–1 exp –24100/RT cm2 sec–1, Ne in β2-tridymite (513–577°K): D= 4·5×10–4 exp –19100/RT cm2 sec–1. Energies of activation are about twice their values in silica glass and diffusion coefficients are smaller.
TL;DR: In this paper, the homologous series of acids from n-propyl to n-octadecyl has been synthesized, the transition temperatures of each member of the series measured by means of a heated-stage, polarizing microscope, and the corresponding transition energies determined by differential scanning calorimetry.
Abstract: The alkoxy benzoic acids, above n-propyl, exhibit liquid crystal properties. The homologous series of acids from n-propyl to n-octadecyl has been synthesized, the transition temperatures of each member of the series measured by means of a heated-stage, polarizing microscope, and the corresponding transition energies determined by differential scanning calorimetry. Some of the acids showed solid state transitions not previously reported.
TL;DR: In this paper, equipment for the measurement of the magnetic double refraction, or Cotton-Mouton effect, in compressed gases is described for twelve gases, including Argon, methane and sulphur hexafluoride, which have effective spherical symmetry, and significant coefficients which are interpreted in terms of a fourth order tensor describing the effect of magnetic field on the usual optical polarizability tensor.
Abstract: Equipment is described for the measurement of the magnetic double refraction, or Cotton-Mouton effect, in compressed gases. The results are given for twelve gases. Argon, methane and sulphur hexafluoride, which have effective spherical symmetry, have significant coefficients which are interpreted in terms of a fourth order tensor, η, describing the effect of the magnetic field on the usual optical polarizability tensor. For the non-spherical molecules the anisotropy of the magnetic susceptibility, (χ∥–χ⊥), is derived and the approximations used in the derivation are discussed.
TL;DR: In this article, a magnetic float technique has been developed for the measurement of densities of dilute aqueous solutions to within ± 1 part in 106. The results are discussed in terms of deviations from the Debye-Huckel limiting law, and it is shown that for the salts R4NBr, the concentration dependence of ϕv does not conform to the trends normally observed for univalent electrolytes.
Abstract: A magnetic float technique has been developed for the measurement of densities of dilute aqueous solutions to within ±1 part in 106. Apparent molal volumes ϕv at 5 and 25° are presented for alkali chlorides and tetra-alkylammonium bromides in the molar concentration range 0.002 < c < 0.1. The results are discussed in terms of deviations from the Debye-Huckel limiting law, and it is shown that for the salts R4NBr, the concentration dependence of ϕv does not conform to the trends normally observed for univalent electrolytes. The ϕv(c½) behaviour is interpreted in terms of cation-cation interactions, induced by co-operative ion-water interactions. Mean apparent molal expansibilities ϕE at 15° are presented, and the ϕE(c½) plots for NaCl and KCl show good agreement with predicted limiting law behaviour. For the series R4NBr (except where R = Me) increasingly large positive excess expansibilities are observed.
TL;DR: The adsorption of nitro-compounds on the surface of MgO powder has been studied by e.s.r. and reflectance spectrophotometry as discussed by the authors.
Abstract: The adsorption of nitro-compounds on the surface of MgO powder has been studied by e.s.r. and reflectance spectrophotometry. Radical anions are formed on clean MgO surfaces prepared in vacuo whereas this no longer occurs if the MgO surface is contaminated with water and carbon dioxide. Several possibilities for the source of electrons in MgO are discussed and it is suggested that some of the lattice oxygen ions on the surface may act as electron donors. The nitrobenzene radical ion appears to lie flat on the surface and the e.s.r. data indicate considerable rotational freedom at 20°C.
TL;DR: The crystal structure of MAg4I5(M = K, Rb, NH4) is cubic with a= 11.2 A, z= 4 and space group of the enantiomorphic pair P4132 and P4332 as mentioned in this paper.
Abstract: The crystal structure of MAg4I5(M = K, Rb, NH4) is cubic with a= 11.2 A, z= 4 and space group of the enantiomorphic pair P4132 and P4332. The locations of the I– and M+ ions have been deduced from symmetry and packing considerations. The Ag+ ions do not occupy distinct single sites, but are distributed randomly over a number of interstitial positions. This model is consistent with the expectionally high mobility of the Ag+ ions and the high entropy of formation of the compound. The absence of Na or Cs analogues is explained by the steric requirements of the proposed structure.
TL;DR: In this article, it was suggested that the selectivity of reactions of this type is controlled largely by the stereochemistry of the activated transition-state structure of the organic molecule, and that these compounds react largely 1 : 1 with the single surface hydroxyls although 1 : 2 bridging reactions occur on preheating the solid to temperatures of the order of 500°C.
Abstract: Methyl chlorosilane vapours react with the surface hydroxyls of Aerosil silicas at temperatures above about 250°C. Infra-red spectroscopic studies on deuterium exchanged samples show that only the external hydroxyl-groups are affected. The trimethyl- and dimethyl-substituted chlorosilanes react selectively but completely with the isolated or single surface hydroxyls, whereas the monomethyl and tetrachloro compounds also react with some of the interacting hydrogen-bonded surface groups. Analyses of the solid reaction products from the dimethyl and trimethyl chlorosilane + silica reactions suggest that these compounds react largely 1 : 1 with the single surface hydroxyls although 1 : 2 bridging reactions occur on preheating the solid to temperatures of the order of 500°C. By comparing these results with those reported earlier1 it is suggested that the selectivity of reactions of this type is controlled largely by the stereochemistry of the activated transition-state structure of the organic molecule.
TL;DR: In this article, the total vapour pressure of liquid mixtures of argon and krypton has been measured over the whole range of composition at 115.77°K and at 103.94°K.
Abstract: The total vapour pressure of liquid mixtures of argon and krypton has been measured over the whole range of composition at 115.77°K (the triple-point of krypton) and at 103.94°K from an argon mole fraction of ∼0.4 to unity. The volume increase VE on mixing per mole has also been determined (at 115.77°K). The excess Gibbs energy GE of mixing per mole has been evaluated, and for a given mixture is only about half that estimated from earlier experimental studies of this system. For the equimolar solution, GE is 20.06 cal at 115.77°K, and 19.71 cal at 103.94°K. VE is negative, and has an unsymmetrical dependence on mole fraction.
The experimental GE has been compared with values calculated from statistical theories of solutions. Theories based on the “two-liquid” or “refined average potential” model predict GE values too high by a factor of about 2. The calculated values are relatively little affected by the choice of intermolecular energy parameters or by the precise form of the intermolecular potential adopted. Values calculated on the “three-liquid” or “separate interaction” model are in much closer agreement with experiment. None of the ways of calculating VE at present available is satisfactory when applied to the argon + krypton system. A possible reason for the unsymmetrical variation of VE with composition is briefly considered.
Details are given of a simple but efficient low-temperature fractionating column.
TL;DR: In this paper, a number of cyanocarbons and related compounds have been studied by the magnetron technique and observed to capture electrons directly, showing evidence for an additive relationship between the number of CN subsituents and the electron affinity.
Abstract: A number of cyanocarbons and related compounds have been studied by the magnetron technique and observed to capture electrons directly. These molecules have electron affinities in the range 1–3.5 eV and show evidence for an additive relationship between the number of CN subsituents and the electron affinity. The measured electron affinities are related to the energy of the charge-transfer band in charge-transfer complexes with pyrene and to the reversible one electron-polarographic reduction potentials. The electron affinities measured are related to the work done in bringing the electron up to the molecule against the external field of the dipolar substituents.
TL;DR: In this article, rotational analysis of the 2-0 and 3-0 bands of the A-X system and of the 0-0 band of the B -X system has been carried out from plates of the absorption spectrum of gold vapour at about 2000°C.
Abstract: The rotational analysis of the 2—0 and 3—0 bands of the A—X system and of the 0—0 band of the B—X system has been carried out from plates of the absorption spectrum of gold vapour at about 2000°C. The bands of both systems consist of simple R and P branches, and both transitions are considered to be 0+u–1Σ+g. The internuclear distance r″e in the ground state is 2.472 A.
TL;DR: In this paper, the anomalous charge and field distributions in the diffusion layer and the diffuse double layer at the limiting current are resolved by means of two matching expansions valid in the two regions.
Abstract: Apparent anomalies in charge and field distributions in the diffusion layer and the diffuse double layer at the limiting current are resolved by means of two matching expansions valid in the two regions. The region of appreciable deviation from electroneutrality is thicker, and in this region the electric field is expected to be smaller, than at currents below the limiting current. Modified zeta potentials are calculated for a cation-discharge reaction.
TL;DR: In this paper, the formation of anion vacancies at the surfaces of unirradiated and irradiated oxides is discussed, which play a dual role in the irreversible adsorption of oxygen by providing a trap for an electron at the surface.
Abstract: A fast irreversible adsorption of oxygen at 20°C on γ- or neutron-irradiated MgO or CaO is correlated with observable surface paramagnetic centres (S centres) and colour centres. The S centre in MgO with gav= 2.0007 is believed to be an intrinsic defect consisting of an electron trapped at a surface anion vacancy. An additional oxygen-sensitive signal SH is related to the presence of some hydrogen contamination on the surface. The S centre in CaO, with g∥= 1.9992 and g⊥= 1.9969 after γ-irradiation to low doses, is similar in behaviour to that on MgO; however, at high γ-doses or after neutron irradiation a complex signal is produced. A surface centre with gav= 1.9798 and of low intensity has been detected on γ- and neutron-irradiated SrO, but this accounts for only a small fraction of the total oxygen adsorption on SrO.
The formation of anion vacancies at the surfaces of unirradiated and irradiated oxides is discussed. These defects play a dual role in the irreversible adsorption of oxygen by providing a trap for an electron at the surface and a site capable of stabilizing the adsorbed oxygen species; other sites for oxygen adsorption are increasingly important in CaO and SrO and account for adsorption on the unirradiated oxides.
TL;DR: In this article, the authors used the etch-pit technique and analysis of cleavage patterns to characterize dislocations in single crystals of melt-grown, solution-grown and vapour-grown anthracene.
Abstract: Dislocations in single crystals of melt-grown, solution-grown and vapour-grown anthracene have been characterized using the etch-pit technique and from an analysis of cleavage patterns. From the observed alignments of emergent dislocations (at (00l) faces) to form small-angle boundaries (of twist, tilt and mixed character), deductions are made concerning the planes and directions in which the dislocations move. The most widely occurring dislocations are those that glide in the (010) plane along the [001] direction. Dislocations that glide in the[100] direction in this plane are also feasible. Although less widely occurring, dislocations in the (100) plane exist, there being slight preference for those that glide along [010] to dominate, but those that move in the [001] direction definitely occur. The geometry of two kinds of emergent edge dislocations is outlined, and the relevance of lattice distortion at dislocation cores is considered in relation to the photodimerization of the solid.
TL;DR: In this paper, an apparatus of the Burnett type has been built with which to measure accurately the second virial coefficients of gases at low temperatures, and the principal feature is a mercury manometer with which pressures up to 1 bar can be measured with an accuracy of 2 × 10-6 bar.
Abstract: An apparatus of the Burnett type has been built with which to measure accurately the second virial coefficients of gases at low temperatures. The principal feature is a mercury manometer with which pressures up to 1 bar can be measured with an accuracy of 2 × 10–6 bar. The second virial coefficients B of argon (80–190°K) and of krypton (110-225°K) have been measured with absolute accuracies of from 0.001 to 0.01 m3 kmol–1, and are discussed in relation to the pair potential of the intermolecular forces. The rapid fall of B at low temperatures implies, in each case, a deeper well in the potential than has been proposed heretofore.
TL;DR: In this article, the potential energy as a function of the orientation of n-paraffin molecules in the urea channel was calculated and an Ising treatment was used with an approximation similar to that of Weiss being applied to the interactions between paraffin molecule in neighbouring channels using reasonable values for the parameters of intermolecular potentials.
Abstract: Calculations have been made of the potential energy as a function of the orientation of the n-paraffin molecules in the urea channel An Ising treatment was then used with an approximation similar to that of Weiss being applied to the interactions between paraffin molecules in neighbouring channels Using reasonable values for the parameters of the intermolecular potentials, gradual transitions involving extra heat absorption were found in the temperature region in which they are found experimentally The relatively higher transition temperatures of the adducts of “odd” n-paraffins were also successfully predicted
TL;DR: In this paper, the general kinetics of radiation-induced ionic polymerization are discussed and the effects resulting from impurity termination are analyzed quantitatively, and a method is described for the calculation of the propagation rate constants kp by combining measurements of polymerization rates with conductivity determinations of the ionic lifetime in the stationary state.
Abstract: The general kinetics of radiation-induced ionic polymerization are discussed and the effects resulting from impurity termination are analyzed quantitatively. A method is described for the calculation of the propagation rate constants kp by combining measurements of polymerization rates with conductivity determinations of the ionic lifetime in the stationary state. The rate constant for cationic propagation by free ions is ca. 4 × 106 M–1 sec–1 for both styrene and α-methylstyrene in the bulk monomer. This large value suggests that the lower results obtained previously for styrene by the use of chemical cationic catalysts refer mainly to ion pairs of varying reactivity.
TL;DR: In this paper, a dynamic approach to study chemisorbed species during the course of catalytic reaction was applied to the catalytic dehydration of formic acid over alumina and silica gel.
Abstract: A new dynamic approach to study chemisorbed species during the course of catalytic reaction was applied to the catalytic dehydration of formic acid over alumina and silica gel. Formic acid is chemisorbed on alumina surface and dissociates to formate ion and a proton. Formate ions on the alumina do not decompose directly to the reaction products and a fraction desorbs rapidly by exchange with formic acid. The rate of the reaction over the alumina is proportional to the number of protons from the dissociative adsorption of formic acid on the alumina surface, and also to the partial pressure of formic acid. Consequently, the decomposition proceeds between formic acid molecules and the surface protons supplied from the dissociative adsorption of formic acid, i.e., protons from formic acid behave as he reaction sites on the catalyst surface, while the formate ion on the catalyst surface does not behave as the reaction intermediate.
For the formic acid dehydration on a silica gel, the adsorption of formic acid on silica gel is non-dissociative, and the rate of the decomposition is proportional to the pressure of formic acid and is independent of the amount of formic acid adsorbed. The silica gel treated with methanol to methoxylate its surface OH to OCH3 had no catalytic activity for the decomposition, which suggests that the surface OH is the reaction site for the decomposition. It is, accordingly, concluded that the decomposition of formic acid on the dehydrating metal oxide catalysts proceeds via the protonic sites on the surface, as with sulphuric acid in the liquid phase.
TL;DR: The diffusion of various liquids in natural rubber vulcanizates has been studied by following the kinetics of the mass uptake of a sheet of rubber while immersed in the liquid as discussed by the authors.
Abstract: The diffusion of various liquids in natural rubber vulcanizates has been studied by following the kinetics of the mass uptake of a sheet of rubber while immersed in the liquid. An anomaly in the mass uptake-time relation is due to the stresses set up in the sheet during swelling and to their variation as the swelling proceeds. This anomaly has been eliminated by using samples constrained laterally, by bonding to metal backing plates, which maintains the boundary conditions constant during the swelling. At the liquid concentrations used, the diffusion coefficient depends mainly on the liquid viscosity rather than the compatability of the rubber and the liquid. Neither the amount of carbon black filler not the degree of crosslinking of the rubber has a significant effect on the diffusion coefficient measured at relatively high liquid concentrations.
TL;DR: In this article, the authors used mass spectrometry, u-v. spectroscopy, gas chromatography, and pressure measurements to study the homogeneous gas-phase pyrolysis of 1,4-cyclohexadiene.
Abstract: The homogeneous gas-phase pyrolysis of 1,4-cyclohexadiene has been shown to obey the pattern of reactivity of cyclic olefins [graphic omitted] where X is O, CH2, CH2—CH2, or CHCH. The reaction was studied using mass spectrometry, u.-v. spectroscopy, gas chromatography, and pressure measurements. The process is first order to at least 80 % decomposition. The rate constant has been measured over a range of seven powers of ten, in packed and unpacked, static and flow reactors between 250 and 620°C and between 10–3 and 102 torr. Between 330 and 390°, log k=(12.36 ± 0.13)–(43.8 ± 0.4)/θ, where θ is 2.3 RT kcal mole–1, in good agreement with Ellis and Frey. The absence of hydrogen atoms has been shown by the lack of exchange with hexadeuterobenzene and toluene. The chain decomposition involving cyclohexadienyl radicals is, therefore, not important, probably due to the endothermicity and low A-factor of the bimolecular initiation [graphic omitted] From the Arrhenius parameters for the intramolecular elimination of hydrogen from 1,4-CH, and from estimates of the entropy and heat changes we have calculated the rate constant for the dienophilic 1,4-hydrogenation of benzene to be k= 108.7–50.2θ mole–1 l. sec–1, where θ is 2.3 RT kcal mole–1. Butene-2 probably eliminates H2 by a 1–4 molecular mechanism with an activation energy of 65 kcal.
TL;DR: In this article, the shift and change in intensity of the OH stretching bands of decationated near-faujasite (Y) zeolites have been studied with respect to the physical adsorption of N2, O2, CH4, Ar and Kr.
Abstract: The shift and the change in intensity of the OH stretching bands of decationated near-faujasite (Y) zeolites have been studied with respect to the physical adsorption of N2, O2, CH4, Ar and Kr. The high-frequency OH stretching was assigned to hydroxyls in the supercage and the low-frequency OH stretching to hydroxyls in the cubo-octahedron. A simple electrostatic model allows one to correlate the shift and the change in intensity of the high-frequency OH band to the dielectric constant of adsorbed species. The reaction field of the OH dipole in an ellipsoidal cavity surrounded by the adsorbed molecules seems to be responsible for the perturbation undergone by the OH oscillator when the dielectric constant around the cavity is modified.