Photochemische Carbonylierung und Oxydation von wässerigem Methanol bei 1470 Å

Zusammenfassung Das photochemische Verhalten von wässerigem Methanol, gesättigt mit Argon, CO bzw. O₂ wurde bei 1470 Å als Funktion der VUV-Dosis und der Methanolkonzentration untersucht. Als Reaktionsprodukte wurden Wasserstoff, Formaldehyd, Glykolaldehyd, Glykol, Ameisensäure und in Gegenwart von Sauerstoff auch Peroxyd nachgewiesen. In 10^–2 m-Methanol, gesättigt mit Argon, betrug (H₂)=0,69 und (HCHO)=0,22, in Gegenwart von 7·10^–4 m-CO war (H₂)=0,10 und (HCHO)=0,29, während bei Sättigung mit O₂ (10^–3 mO₂) (H₂)=0,01, (HCHO)=0,33, (HCOOH)=0,20 und (H₂O₂)=0,22 gefunden wurde. Die -Werte der übrigen Produkte, die unter den angegebenen Bedingungen erhalten wurden, waren <0,07. Durch Erhöhung der Methanolkonzentration bis zu reinem Methanol, gesättigt mit Argon, stieg die Ausbeute von H₂, HCHO und (CH₂OH)₂ entsprechend an, während die von HCOOH und CH₂OHCHO sich praktisch nicht änderte. Bei reinem, mit Argon gesättigtem Methanol war (H₂)=0,89 und (HCHO)=0,73. Das Glykol erreichte bei etwa 2m-Methanol eine Höchstausbeute von =0,38. Reaktionsmechanismen werden diskutiert.

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Photochemical carbonylation and oxidation of aqueous methanol at 1470 Å

The photochemical behaviour of aqueous methanol saturated with argon, CO and O₂, resp., has been investigated at 1470 Å as a function of the v.u.v. dose and the methanol concentration. Hydrogen, formaldehyde, glycolaldehyde, glycol, formic acid and, in the presence of oxygen, also peroxide were detected. In 10^–2 M-CH₃OH saturated with argon (H₂)=0,69 and (HCHO)=0,22 were found; in the presence of 7·10^–4 M-CO the yields are (H₂)=0,10 and (HCHO)=0,29, whereas under saturation with oxygen (10^–3 M O₂) (H₂)=0,01, (HCHO)=0,33, (HCOOH)=0,20 and (H₂O₂)=0,22. The quantum yields of all other products obtained under the conditions mentioned above are <0.07. With increasing methanol concentration up to pure argon saturated methanol, the quantum yields of H₂, HCHO and (CH₂OH)₂ increase correspondingly, whereas the yields of HCOOH and CH₂OHCHO remain practically unchanged. When irradiating pure, argon saturated methanol, (H₂)=0,89 and (HCHO)=0,73 were found. A maximum yield of (CH₂OH)₂=0,38 was achieved using 2M-CH₃OH. Reaction mechanisms are discussed.

     

Seawater—A test of multicomponent electrolyte solution theories. I. The apparent equivalent volume,expansibility, and compressibility of artificial seawater

The apparent equivalent volume _V, expansibility _E, and compressibility _K of an artificial seawater solution containing10 ionic components (Na⁺, Mg²⁺, Ca²⁺, K⁺, Sr²⁺, Cl^–, SO ₄ ^2– , HCO ₃ ^– , Br^–, and F^–) and one nonionic component (H₃BO₃) has been determined from0 to40°C (in5° intervals) and from0.1 to0.8 m ionic strength at1 atm. The concentration dependence (I_v=volume ionic strength) of the _V's, _E's, and _K's have been examined by using a Masson-type equation, = ^° +S'I _V ^1/2, and a Redlich-type equation, = ^° +SI _V ^1/2 +BI _V, where ^° is the infinite-dilution value, S is the empirical Masson slope, S is the theoretical Debye-Hückel slope, and B is an empirical deviation constant. By using Young's rule, = E_i(i), the apparent equivalent volumes, expansibilities, and compressibilities for sea salt have been estimated from the ionic and nonionic components making up the mixture. The estimated apparent molal quantities agree very well with the directly measured values providing the concentration terms, S _i and B_i, are weighted according to the methods of Wood and Reilly.Contribution Number 1599 from the University of Miami.     

VUV-Photolyse von Methanol bei 1236 Å

Zusammenfassung Es wird über die indirekte und die direkte VUV-Photolyse von luftfreiem Methanol in flüssiger Phase bei 1236 Å berichtet. Bei der Bestrahlung von wäßr. 0,01m-Methanol wurden folgende Produkte und Ausbeuten erhalten: (H₂)=1,00, (HCHO)=0,27, (CH₂OH)₂=0,12, (CH₂OH·CHO)=0,04 und (HCOOH)=0,02. Die Photolyse von flüssigem Methanol lieferte die gleichen Produkte, jedoch mit höheren Ausbeuten: (H₂)=1,50, (HCHO)=0,98, (CH₂OH)₂=0,28 und (CH₂OH·CHO)=0,06. Unter Anwendung von Methanol als Radikalfänger konnte auch die Quantenausbeute der Wasserphotolyse bei 1236 Å, (H,OH)=1,025 verifiziert werden. Wahrscheinliche Reaktionsmechanismen werden diskutiert.

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V.U.V.-Photolysis of methanol at 1236 Å

The indirect and the direct v.u.v.-photolysis of air free methanol in liquid phase at 1236 Å is reported. After irradiation of aqueous 0.01M-methanol the following products were obtained: (H₂)=1.00, (HCHO)=0.27, (CH₂OH)₂=0.12, (CH₂OH·CHO)=0.04 and (HCOOH)=0.02. The photolysis of liquid methanol yielded the same compounds, however with higher amount as follows: (H₂)=1.50, (HCHO)=0.98, (CH₂OH)₂=0.28 and (CH₂OH·CHO)=0.06. Using methanol as a scavenger for the H and OH radicals the quantum yield of the water photolysis at 1236 Å could be verified to be (H,OH)=1.025. Probable reaction mechanisms are discussed.

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Mit 3 Abbildungen

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Herrn Prof. Dr.E. Broda zum 60. Geburtstag gewidmet.     

Primärprodukte der Wasserphotolyse bei 1849 Å

Zusammenfassung Die Photolyse des Wassers bei 1849 Å wurde unter Verwendung von 0,01m-Formiat als Fänger für die H-Atome und OH-Radikale untersucht. Dabei diente 5m-Äthanol als Aktinometer mit einem korrigierten Wert für (H₂)=0,50. In diesem Fall wurde eine Quantenausbeute der Wasserphotolyse (H, OH)=0,36±0,01 bestimmt. Bezieht man die exper. Daten auf das N₂O-Aktinometer bei (–N₂O)=1,0, dann ist (H, OH)=0,29±0,01. In diesem Wert ist auch die Quantenausbeute der reaktionsfähigen angeregten Wassermoleküle, die mit Formiat reagieren, inbegriffen. Auf Grund von experimentellen Daten wurde ferner die Bildung von solvatisierten Elektronen (e ^–aq) vorgeschlagen. Durch Sättigung der Formiatlösung mit Kohlensäure, die sowohl vone ^–aq als auch von H₂O^* reduziert werden kann, wurde (e ^–aq, H₂O^*)>0,02<0,04 bestimmt.

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Liquid water photolysis at 1849 Å was investigated by using 0,01m-formate as scavenger for the H and OH radicals. 5M-ethyl alcohol serviced as actinometer with a corrected value of (H₂)=0,50. The quantum yield of water photolysis was determined in this case to be (H, OH)=0,36±0,01. When the experimental results are related to N₂O actinometer with (–N₂O)=1,0, a quantum yield of (H, OH)=0,29±0,01 is obtained. This value includes also the quantum yield of the excited water molecules which react with the formate. Based on experimental data the formation of solvated electrons (e ^–aq) is proposed. By saturation of the formate solution with carbon dioxide, which can be reduced bye ^–aq as well as by H₂O^*, (e ^–aq, H₂O^*>0,02<0,04 was determined.

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Mit 4 Abbildungen     

The Influence of Dimerization of Water-Soluble Metalloporphyrins as Photosensitizers on the Efficiency of Generation of Singlet Oxygen

Quantum yields () for the generation of singlet oxygen sensitized by Pd(II) complexes of water-soluble porphyrins: meso-tetrakis(4-N-methylpyridyl)porphine [PdTMPyP]⁴⁺ ( = 0.9), meso-tetrakis(4-N,N,N-trimethylaminophenyl)porphine [PdTTMAPP]⁴⁺ ( = 0.8), meso-tetrakis(4-carboxyphenyl)porphine [PdTCPP]^4– ( = 0.7), and meso-tetrakis(4-sulfonatophenyl)porphine [PdTSPP]^4– ( = 0.5) were determined using a chemical method. It was found that the dimerization and aggregation of metalloporphyrins greatly influence the value. The quantum yields evaluated for the formation of singlet oxygen sensitized by metalloporphyrin monomeric and dimeric forms are _{, M} 0.9 and _{, D} 0.2, respectively, and do not depend on the porphyrin nature.     

EXAFS Study of Ph3GeMn(CO)5 Structure Evolution on Exposure to X-Radiation

Ge K-edge and Mn K-edge EXAFS spectroscopy was used to study changes in the local environment of germanium and manganese atoms during radiolysis of the Ph₃GeMn(CO)₅ complex. On exposure to X-radiation, the metal complex undergoes a number of transformations depending on the radiant exposure (). It was shown that at = (6–8) × 10⁶ J/m², the initial metal complex decomposes into the [Ph₃Ge] and [Mn(CO) _n ] fragments with partial detachment of the CO groups from Mn atoms. When = 1.3 × 10⁷ J/m², Mn atoms lose completely the CO groups to form finely dispersed metal nanoparticles, which interact with the surrounding atoms (carbon or nitrogen). With further increase in , the local environment of the Mn atoms no longer changes. The Ge atoms remain coordinated to the Ph groups as increases up to 2 × 10⁷ J/m², but starting with = 1.6 × 10⁷ J/m², metal–metal bonds are formed; subsequently, the amount of this phase increases and when = 2.6 × 10⁸ J/m², it becomes predominant. Since manganese and germanium atoms lose their ligands at different values, one can conclude that germanium and manganese nanoparticles are the final products in the radiolysis of Ph₃GeMn(CO)₅.     

r 12-Dependent terms in the wave function as closed sums of partial wave amplitudes for large l

The ansatz = (1+1/2r₁₂)+ with the bare nuclear (or screened nuclear) wave function and expanded in products of one-electron functions is explored for second-order perturbation theory and for variational calculations of the ground state of Helium-like ions.The energy increments E _l ⁽²⁾ corresponding to the partial wave expansion of go asymptotically as l^–8, while conventional partial wave increments go as l^–4. is coupled to by a residual interaction U₁₂ that has no singularity for r₁₂=0. With the present ansatz it is sufficient to include l-values up to 5 in order to get the second-order energy accurate to one microhartree. For the same accuracy l4 is sufficient in a CI with correlated reference function while in conventional CI one must go to l50. The surprisingly faster convergence of the variational approach as compared to second-order perturbation theory is explained. The slow convergence of the traditional partial wave expansion is entirely due to the attempt to represent the quantity 1=¦r₁₂r₁₂ ^–1¦ by its partial wave expansion. The best reference function shows very little shielding and resembles closely the eigenstate of the bare nuclear Hamiltonian. The generalization to arbitrary systems is discussed and it is pointed out that the calculation of difficult integrals can be avoided without a significant loss in accuracy.     

3, 3, 3-Trifluoropropyl(methyl)cyclosiloxanes

The influence of the number of 3, 3, 3-trifluoropropyl(methyl)siloxane links (/) in the cyclotetrasiloxanes _mD_4-m, where D represents the dimethylsiloxane link and m=0–4, on the rearrangement of these compounds in acetone solution under the action of sodium siloxanolate has been studied. The rearrangement takes place with the formation of a linear polysiloxane the degradation of which yields, in addition to the initial ring, cyclosiloxanes with a different structure. The rate of rearrangement of _mD_4-m and of the formation of a linear polysiloxane rises with an increase in m from 0 to 3. The equilibrium concentration of the linear polysiloxane formed from _mD_4-m is inversely proportional to m. Results have been obtained on the kinetics of the formation of the cyclosiloxanes _mD_n, where m=0–5, n=0–5, and m+n=3–6, in the rearrangement of the rings D₃, ₂D₂, ₃D, and ₄. The reactivity of the siloxane links rises in the sequence (CH₃)₂Si-O-Si(CH₃)₂ < (CF₃CH₂CH₂)-(CH₃) Si-O-Si(CH₃)₂ <(CF₃CH₂CH₂) (CH₃)Si-O-Si(CH₃) (CH₂CH₂CF₃) . Because of the negative inductive effect transferred through the siloxane links, the 3, 3, 3-trifluoropropyl groups strongly activate the siloxane ring with respect to nucleophiiic reagents.For part I, see [3].     

Radiolysis of [EtC5H4Mn(CO)2NO]+(PF6)– and Evolution of the Nearest Environment of the Manganese Atoms in the Complex

X-ray emission and EXAFS spectroscopies were used to examine changes in the nearest environment of manganese atoms upon radiolysis of [EtC₅H₄Mn(CO)₂NO]⁺(PF₆)^– at different energy exposures (). It was found that the initial complex loses the CO and NO ligands at = 4.5 × 10⁶ J/m². An increase in to 7.5 × 10⁶ J/m² gives rise to Mn–Mn bonds with lengths characteristic of Mn dimers. At = 9.0 × 10⁶ J/m², Mn nanoparticles are formed; they interact with the carbon atoms of EtC₅H₄ and the fluorine atoms of PF₆ anions. Further increase in = 2.6 × 10⁷ J/m² yields manganese-containing nanoparticles structured like metallic Mn; their surface atoms interact with carbon atoms formed in the disintegration of the EtC₅H₄ ligands. The formation of manganese carbides and fluorides at = 2.6 × 10⁸ J/m² reduces the content of the metal constituent in nanoparticles; this content is zero at = 4.4 × 10⁸ J/m². The final radiolysis products are manganese carbides and fluorides (or fluorocarbides).     

Apparent molar volumes of aqueous calcium chloride to 250°C, 400 bars,and from molalities of 0.242 to 6.150

Relative densities of CaCl ₂ (aq) with 0.22ml(mol-kg^–1)6.150 were measured with vibrating- tube densimeters between 25 and 250°C and near 70 and 400 bars. Apparent molar volumes V calculated from the measured density differences were represented with the Pitzer ioninteraction treatment, with appropriate expressions chosen for the temperature and pressure dependence of the virial coefficients of the model. It was found that the partial molar volume at infinite dilution V ^o , and the second and third virial coefficients B ^V and C ^V , were necessary to represent V near the estimated experimental uncertainty. The ionic-strength dependent ^(1)v term in the B ^V coefficient was included in the fit. The representation for V has been integrated with respect to pressure to establish the pressure dependence of excess free energies over the temperature range studied. The volumetric data indicate that the logarithm of the mean ionic activity coefficient, ln ±(CaCl ₂ ), increases by a maximum of 0.3 at 400 bars, 250°C, and 6 mol-kg^–1 as compared with its value at saturation pressure.     

On a variational method for determining excited state wave functions

A variational method is proposed which results in an approximate wave function for an excited state which has the maximum overlap with the true excited state eigenfunction. The method involves the calculation of the quantities E=¦H¦ and =¦(H-E)²¦, but is free of the constraint that the trial function must remain orthogonal to all states of the same symmetry which lie beneath it. One must know, however, an approximation to the true eigenvalue. A discussion is given on how one might gain the latter information, lacking knowledge of the spectrum, from the repeated application of the method.

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Zusammenfassung Es wird eine Variationsmethode vorgeschlagen, die auf eins genäherte Wellenfunktion für einen angeregten Zustand führt, welche sich maximal mit der wahren Eigenfunktion des angeregten Zustandes überlappt. Die Methode ermöglicht die Berechnung der Größen: E=¦H¦ und =¦(H-E)²¦, ist aber frei von der Nebenbedingung, daß die Versuchsfunktion orthogonal zu allen benachbarten Zuständen mit derselben Symmetrie bleiben muß. — Man will jedoch eine Näherung des wahren Eigenwertes wissen. — Eine Diskussion darüber, wie man durch wiederholte Anwendung der Methode letztere Information gewinnen kann, ohne Kenntnisse über das Spektrum zu besitzen, wird durchgeführt.

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Résumé Méthode variationnelle pour la détermination d'une fonction d'onde d'un état excité présentant le recouvrement maximum avec la fonction d'onde exacte. La méthode implique le calcul de E=¦H¦ et =¦(H-E)²¦ mais ne comporte pas la contrainte d'orthogonalité de la fonction d'essai à tous les états inférieurs de même symétrie. On doit cependant connaître une valeur approchée de la valeur propre exacte. Discussion sur la manière dont on peut obtenir cette valeur approchée sans connaître le spectre, par application répétée de la méthode.

     

Partial molal expansibilities of organic compounds in aqueous solution. I. Alcohols and ethers

The temperature dependence of limiting apparent molal volumes ° in water for some alcohols (methanol, ethanol, 1-propanol, 2-butanol, 3-pentanol, 3-hexanol, 2,5-hexanediol, cyclopentanol, cyclohexanol, cycloheptanol, and 1,4-cyclohexanediol) and ethers (trimethylene oxide, tetrahydrofuran, tetrahydropyran, 1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, 1,3-dioxepane, 1,3,5-trioxane, dimethoxymethane, 1,2-dimethoxyethane, diethoxymethane, and diethyl ether) has been studied in the temperature range 10–50°C by means of an automatic digital-readout dilatometer. Values of the thermal expansion coefficient * = (1/°)(°/T)_p have been obtained at several temperatures and discussed together with literature data on expansibilities of related compounds. The data show a wide spectrum of values of ^* at low temperatures which is narrowed at the higher ones. The expansibilities of monofunctional alcohols increase with increasing temperature; the opposite effect is observed for polyhydric alcohols. The ^*'s of ethers are very slightly temperature dependent and are much higher, at low temperature, than those of alcohols having the same ratio ofn _o/n_c. These results are discussed in terms of solutewater interactions, and a possible interpretation is put forward.     

Volumes and heat capacities of anionic-nonionic surfactant mixtures

Density, heat capacity and surface tension measurements of sodium decylsulfate (NaDeS)-dodecyldimethylamine oxide (DDAO)-water mixtures were carried out as functions of the surfactants total molality m_t at fixed stoichiometric mixture compositions X_NaDeS. From the surface tension data, the critical micelle concentration of NaDeS-DDAO mixtures as a function of X_NaDeS were obtained. From density and heat capacity data, the apparent molar volume V_,2 and heat capacity C_,2 of NaDeS-DDAO mixtures in water were calculated, respectively. At a given mole fraction, V_,2 and C_,2 monotonically increases and decreases, respectively, with increasing mt. However, anomalies were observed at X_NaDeS=0.1 and 0.3 for both V_,2 and C_,2 vs. mt curves. The nonideal contributions to the thermodynamic properties for the formation of surfactant-surfactant mixed micelles in water by mixing aqueous solutions of pure NaDeS and DDAO micelles were calculated at 0.3 mol-kg^–1 for the micellized surfactants mixture. The excess volume V^exc and heat capacity as functions of X_NaDeS are concave and S-shaped curves, respectively. All the properties are compared to those for sodium dodecylsulfate-DDAO mixture. In addition, to clarify the effect of the change in the hydrophobicity of the surfactants mixtures V^exc for the dodecyltrimethylammonium bromide-decyltrimethylammonium bromide mixture were calculated from literature data.     

Vibrational isotope effect of linear and planar molecules: Deuterated bromoethenes

Linear (planar) molecules A and B which are identical except for isotopic substitutions at the atomic sites are considered. Stretching (bending, out-of-plane) frequencies _k and normal modes _k of the isotopically perturbed molecule B are expressed in terms of stretching (bending, out-of-plane) frequencies _i and the corresponding normal modes _i of the unperturbed molecule A. Complete specification of the unperturbed normal modes is not required. All that is needed are stretching (bending, out-of-plane) amplitudes | _i of the normal modes _i at those sites that are affected by isotopic substitution. The rule which interlaces frequencies _k of molecule A with frequencies _i of molecule B is derived. Given two isotopic molecules A and B that differ by a single isotopic substitution at site , the inversion relation is derived. This relation expresses unperturbed stretching (bending, out-of-plane) amplitudes at the site in terms of stretching (bending, out-of-plane) frequencies of molecules A and B . As an example, out-of-plane vibrations of deuterated bromoethene were considered. In the simplest method 12 out-of-plane frequencies of four polydeuterated bromoethenes were calculated from 12 out-of-plane frequencies of bromoethene and three monodeuterated bromoethenes. Standard deviation of thus calculated frequencies from experimental frequencies is =2.74 cm^–1. In another method, 15 out-of-plane frequencies of four polydeuterated bromoethenes and selected monodeuterated bromoethene are calculated from 9 out-of-plane frequencies of bromoethene and the remaining two monodeuterated bromoethenes. Depending on which monodeuterated bromoethene is selected (1-, cis- or trans-), standard deviation of thus obtained frequencies from experimental frequencies is 1=2.84 cm^–1, c=2.96 cm^–1 and t=2.72 cm^–1.     

3, 3, 3-Trifluoropropyl(methyl)cyclosiloxanes

The catalytic rearrangement of the cyclopentasiloxanes _mD_5-m, where represents a 3, 3, 3-trifluoropropyl(methyl)siloxane link and D a dimethylsiloxane link, and m=2–5 has been studied by the method described previously [1]. The rate of rearrangement and the rate of formation of a linear polysiloxane rise with an increase in m from 2 to 4. The equilibrium concentration of the linear polysiloxane formed from _mD_5-m and from _mD_4-m (m=0–4) [1] is inversely proportional to the molar fraction of links in the ring and rises with an increase in the total concentration of siloxane links in solution. Results have been obtained on the kinetics of the formation of the cyclosiloxanes _mD_n (where m=0–5, n=0–5, and m+n=3-6) during the rearrangement of the cyclopentasiloxanes _mD_5-m. It has been established that at equilibrium a mixture of cyclosiloxanes _mD_n containing practically constant ratios of tetramers, pentamers, and hexamers (m+n=4, 5, and 6) is obtained, regardless of the composition and structure of the initial cyclosiloxane and of the conditions of rearrangement (polymerization). The cyclopentasiloxanes _mD_5-m are less active in the process of rearrangement than the cyclotetrasiloxanes _mD_4-m. The activity of the cyclosiloxanes in rearrangement in the presence of a base rises in the sequence D₄D_{3 2}D₃<₃D₂<₄D < ₂D₂ < ₃D.For part II, see [1].     

Vibrational isotope effect by the low rank perturbation method

Mathematical formalism of the low rank perturbation method (LRP) is applied to the vibrational isotope effect in the harmonic approximation. A pair of two n-atom isotopic molecules A and B which are identical except for isotopic substitutions at atomic sites is considered. Relations which express vibrational frequencies _k and normal modes _k of the perturbed isotopic molecule B in terms of the vibrational frequencies _i and normal modes _i of the unperturbed molecule A are derived. In these relations complete specification of the unperturbed normal modes _i is not required. Only amplitudes | _i of normal modes _i at sites affected by the isotopic substitution are needed.     

An Alternative Method of Introducing Fugacity

In current textbooks fugacity is introduced according to its differential or integral mathematical formulation. In this article an alternative method of explanation is offered. It is suggested that the real state of a pure gas can be described by comparing it to a hypothetical idealized state. The differences between these two states can then be expressed in terms of a function, , defined as (T,P) = _real(T,P) - _ideal(T,P) where _real and _ideal are the chemical potentials of the gas in its real and ideal states, respectively. The function is a molar excess quantity and is expressed as (T,P) = RT1n where is the fugacity coefficient. This approach introduces fugacity deductively through the function, which leads to , the fugacity coefficient. This method is also appropriate for introducing the activity of solution components and the fugacity of a real gas in gaseous mixtures.     

Large-sample neutron activation analysis: Present status and prospects

Neutron activation analysis is attractive for trace-element determinations in large samples. Facilities for reactor irradiation and -ray spectrometry of kilogram-size cylindrical samples are described. The thermal neutron flux is ca. 5·10¹²m^–2·s^–1 with a _th/ _epi>10⁴, so neutron self-thermalization can be neglected. The correction for the neutron attenuation within the sample is derived from measurement of the neutron flux depression just outside the sample. Correction for -attenuation in the sample is performed via linear attenuation coefficients derived via transmission measurements. Also the natural radioactivity in the sample is taken into account. Examples are given of materials to which large sample INAA has been applied successfully, and further lines of development and exploration are indicated.     

Kinetics of substitution of aqua ligands from cis-diaqua(ethylenediamine)platinum(II) perchlorate by DL-penicillamine in aqueous medium

The kinetics of the interaction of DL-penicillamine with [Pt(en)(H₂O)₂]²⁺ have been studied spectrophotometrically as a function of [Pt(en)(H₂O)₂]²⁺, [DL-penicillamine] and temperature at pH 4.0. The reaction proceeds via rapid outer sphere association complex formation, followed by two slow consecutive steps. The first is the conversion of the aforementioned complex into the inner sphere complex and the second is the slower chelation step whereby another aqua ligand is replaced. The association equilibrium constant (K _E) for the outer sphere complex formation has been evaluated together with rate constants for the two subsequent steps. Activation parameters have been calculated for both steps using the Eyring equation (H ₁ = 46.5 ± 5.0 kJ mol^–1, S ₁ = – 143.0 ± 15.0 J K^–1 mol^–1, H ₂ = 44.3 ± 1.3 kJ mol^–1, S ₂ = –189.0 ± 4.2 J K^–1 mol^–1). The low enthalpy of activation and large negative entropy of activation values indicate an associative mode of activation for both aqua ligand substitution processes.     

Headspace-gas chromatography: The influence of sample volume on analytical results

Summary The role of the volume of the sample and the sample vial in equilibrium headspace-gas chromatography is discussed. A new term, thesample phase fraction (_S) is introduced. It is shown that if the value of _S is kept constant, the vial's volume has no influence on the sensitivity of the headspace analysis (which is proportional to the concentration of the analyte in the headspace). In a given headspace sampling system, concentration of the compound of interest in the headspace (c _G ^* ) at equilibrium is related to the value of _S: a higher _S will increase c _G ^* . However, the influence is important only in the case of low distribution coefficients: in the case of higher distribution coefficients this influence is negligible. This conclusion is also true for small changes in the sample volume in duplicate analyses: exact reproducibility of the sample volume is important only in the case of low distribution coefficient values.