Chimisorption de l'hydrogene par les composes d'insertion graphite-potassium

At low temperature, graphite-potassium intercalation compounds of stage higher than one behave as molecular sieves as regards hydrogen [1,2]. At ambient and higher temperature, however, these compounds including the first stage one, chemically fix hydrogen by a completely different process. This reaction, which has been the object of previous papers [3,4], has been further studied so as to remove some of the previous uncertainties and imprecisions.The brown compound KC₈ after fixing hydrogen becomes blue, and saturates for an $\text{H}\text{K}$ ratio of $\text{2}\text{3}$. The reaction is reversible but does present noticeable hysteresis. Radiocrystallographic examination of the hydrogenated product shows that it involves a pure ternary phase of formula $\text{KC}{}_8\text{H}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}$. The indexing of the 00l reflections indicates a second stage compound: each intercalated layer is composed of two metallic planes in the presence of hydrogen (Fig. 1). This stage change can be interpreted by the pleating of the graphite layers [5]. Neutrocrystallographic studies confirm the preceding results and allow (Table 2) to conclude that the hydrogen forms a layer between the two potassium planes (Fig. 2). The belonging to the second stage of the phase $\text{KC}{}_8\text{H}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}$ is further confirmed by the fact that the free graphite spacings are susceptible of fixing new alkaline metal layers (K, Rb or Cs) to form new compounds referred to as “bi-insertion compounds” [6].Attempts at hydrogen physisorption on the product during the course of chemical hydrogenation (Fig. 3), and the radiocrystallographic and kinetic measurements, clarify the finer points of the reaction. The hydrogen starts to be chemisorbed into the lattice of the compound KC₈ without any stage change (0A), then there appears progressively a second stage phase, unsaturated with hydrogen (AB). Saturation is only attained when the first stage phase has disappeared (BC).Low temperature hydrogen physisorption tests have been carried out on the second stage compound KC₂₄ during chemical hydrogenation. Figure 4 shows a linear decrease in the physisorption capacity, when the hydrogenation ratio increases. By extrapolation it is seen that this capacity should become zero for a chemisorption ratio $\text{H}\text{K}$ in the neighbourhood of $\text{2}\text{3}$.The results suggest the following hydrogenation model. Under the action of the gas, the intercalated metal forms double, hydrogenated layers, identical to those in the ternary $\text{KC}{}_8\text{H}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}$. There also appear three types of graphitic spacings: free intervals, those occupied by lacunar single layers and those occupied by hydrogenated double layers. These spacings are distributed in such a manner that there appears a binary phase KC_12n coexisting with a ternary phase $\text{KC}{}_{\mathrm{4N}}\text{H}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}$ of equal or neighbouring stages n and N. Stoichiometry imposes a relationship between n and N. Figure 5 represents the variation of N as a function of n for various values of the hydrogenation ratio. At saturation the system would once again become single phase: a ternary, $\text{KC}{}_{24}\text{H}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}$ of sixth stage.In Table 3 are given the strongest 00l reflections and the corresponding interplanar distances, characteristic of the compound KC_12n and $\text{KC}{}_{\mathrm{4N}}\text{H}\text{2}\text{3}$. The experimental data taken from the X-ray diagrams, obtained for three KC₂₄H_y, compounds are compared to the values predicted by our model in Table 4. It is seen that the positions of the observed peaks are in good agreement with the 00l reflections of the model, confirming the interpretation we propose.In conclusion, hydrogenation of the potassium layers of KC₈ or of KC₂₄ always leads to the formation of dense and hydrogenated metallic double layers of formula $\text{KH}\text{2}\text{3}$. This process thus creates ternaries of higher stage than the starting binary.     

Contribution de la voltammetrie a l'etude du comportement electrochimique sur electrode de mercure,de certains ortho- et para-nitrophenylazobenzenes

The electroreduction mechanism of ortho- and para-nitrophenylazo-para-cresols, in basic media, at a mercury electrode is studied specially by the means of cyclic voltammetry. It is possible to explain the formation, during preparative runs, of nitrogen heterocyclic compounds of the type benzotriazole N-oxyde easily reducible to the parent benzotriazole, in the case of the ortho isomer, and of an azoxy derivative in the case of the para isomer.     

Contribution a l'etude des sulfures de cuivre non stoechiometriques

The anodic oxidation of cuprous sulphide has been studied using a carbon paste electrode. Typical voltammetric curves are obtained. At slow rates, the oxidation of Cu₂S in CuS and Cu²⁺ occurs via the formation of non stoichiometric compounds: Cu_1,92S, Cu_1,77S, Cu_1,60S and Cu_1,31S.     

Application de la thermoluminescence a l'etude de l'hydratation du silicate bicalcique

Hydraulic properties differences between β and γ dicalcium silicate varieties are well known. In this work, a water vapour chemisorption on the surface of both solid phases is shown by thermoluminescence and by quadrupole mass spectrometry.The similar behaviour of β and γ dicalcium silicate varieties in those experiments means that the fundamental difference between their hydraulic reactivities is not due to this hydration step.     

Equilibres acide-base donnes par les 1–4 benzodiazepines en solution hydro-alcoolique; incidence sur leur comportement a l'electrode de mercure

The electrochemical behaviour at the mecury electrode of 1, 4-benzodiazepines and 1, 4-benzodiazépines-2-one was investigated. Medazepam, diazepam and desmethyldiazepam were reducibles according to a 2 F.mol^?1 process. The plot of half-wave potentials vs pH is in agreement with the results of the spectrophotometric uv analysis: the more basic atom of the diazepine ring was that of the imine bond (C₅ = N₄).The introduction of an OH substituent on the carbon 3 resulted in 4 F.mol^?1 process (oxazepam and lorazepam). The 2 F.mol^?1 reduced intermediate was isolated. It underwent an acid-catalysed dehydration reaction and yielded in slightly basic solution a dimeric insoluble product. For oxazepam, the dimerisation initiated a disproportionation reaction.     

Etude theorique de mecanismes de regeneration du deuxieme ordre en voltammetrie en couche mince ou en surface—application a l'etude de la regeneration catalytique de l'iode par les iodates

A theoretical study of current-potential curves in thin layer or in surface potential sweep voltammetry is presented for second order regeneration mechanisms. The theory is applied to the study of the catalytic reduction of iodate by thin layer potential sweep voltammetry. A trace of iodine is added to the iodate solution and the electroreduction of iodine to iodide initiates the catalytic reduction of iodate. The rate constant of the reaction of iodate with iodide which is determined is in good accord with values given in the literature.     

Etude de la reduction sur electrode de mercure de l'acide β-bromopyruvique et de son ester ethylique

In aqueous or water/alcohol media, reductive cleavage of the carbonbromine bond of β-bromopyruvic acid 1 and its ethylester 2 occurs at the mercury electrode. In aqueous solution, the carbonyl group is strongly hydrated and cathodic current strength is small. In water/alcohol media, the electrode process is complicated by adsorption of bromide ions at the mercury electrode. When the electrode potential is in accordance with a positive value of the electrode charge a prewave appears corresponding to the adsorption of bromide ions. The electrocapillary curve is not affected by such an adsorption phenomena. The prewave does not represent the reduction of an organomercuric compound. No reaction occurs between 1 or 2 and the electrode material. When ethanol is added, the increase in adsorpion of bromide ions arises from the reduced solubility of bromide ions in the bulk of the solution.     

Etude de la reduction sur electrode de mercure de thioethers et de sulfoniums derives de l'acide β-mercaptopyruvique

Thioethers with general formula RSCH₂COCOOR′ where R is paratolyl, methyl or ethyl, and sulfonium salts like Br^?,(CH₃)₂$\text{S}\text{+}$-CH₂COCOOR′ which proceed from β-mercaptopyruvic acid or its ethylester, have been investigated polarographically and by means of controlled potential electrolysis, in aqueous or aquo—alcoholic media.Reduction of sulfonium salts at the mercury electrode is in accordance with the general rule a reductive cleavage of the substituting group RS— occurs. Behaviour of thioethers is not uniform. When R is aryl, cleavage of the carbone—sulphur bond still occurs; when R is alkyl, the carbonyl group undergoes the reduction and the substituted secondary alcohol is formed.     

Contribution a l'etude de la reduction polarographique de l'anion Re3Cl123−

The polarographic reduction of Re₃Cl₁₂^3? anion gives a single polarographic wave corresponding to a two-electrons reversible process. Classical polarographic measurements and instantaneous current—time curves show that the limiting current is diffusion controlled. Plotting the half-wave potential vs pH and pCl, it appears that one chloride ion is released in the reduction of one atom of rhenium, and that H⁺ ion is not involved in the reduction. The overall electrochemical reaction is:

     

Reduction electro-chimique a l'electrode de mercure de composes α hydroxycarbonyles en solution aqueuse—III. composes du type R-CO-C(OH)2-R′, cas de la ninhydrine

At the dme, the first step of the reduction (2F mol^?1) of dihydroxy 2,2 indanedione 1,3 (ninhydrin $\text{1}$) consists in the reduction of the CO group adjacent to the aromatic nucleus in α position and yields tryhydroxy 1,2,2 indanone 3 ($\text{2}$).

$\text{2}$ is furthermore reduced according to an original pathway: the second two electrons transfer implies the cleavage of a C-O bond of the gem-diol group in β position. It results in the formation of the enediol tautomer reversibly oxidized according to the gross reaction:

Cyclic voltammetry enables the determination of ε′^o (ε′^o = ?190 mV at pH = 3.00).A similar process was previously observed in the case of phenyl glyoxal and rhodizonic acid. So it can be concluded that the reduction of organic compounds bearing a —COC(OH)₂— group involves the same process.Whenever introduction of a third carbonyl group (—COC(OH₂CO—) results in change of mechanism. The presence of such a group increases the reactivity of the median carbonyl to nucleophilic addition, in particular to hydration, and then the CO bond cleavage cannot occur.     

L'electrolyse de l'alumine dans la cryolithe fondue. Etude du mecanisme de decharge cathodique a l'aide de l'electrode a disque tournant

The use of a rotating disk platinum electrode, on which aluminium has been previously deposited, has allowed us to determine the mechanism of the cathodic reaction during the electrolysis of cryolite—alumina melts. This mechanism requires three stages within the Nernst's diffusion layer. The first of these is the dissociation of the ion AlF^3?₆, at δ′ from the electrode, forming the ions Al³⁺ and F^?. The second one is the discharge of ions Al³⁺ diffusing towards the cathode and the third one, at δ″ from the electrode, is the reaction of the ions F^? with the ions AlF^?₄ to give again the ions AlF^3?₆. The ions Na⁺, which transport most of the current serve to maintain electro-neutrality.     

Generalisation de la theorie de l'electrode dite “electrode a disque-anneau’, dans un fluide d'otswald. Calcul des facteurs de collection

Supposing that in the diffusional boundary layer, the tangential component V_x and radial component V_r of the relative fluid velocity are respectively written in the form V_xS₀x^by and V_ra₀r^by (S₀, a₀ are independent coefficient of the normal coordinate y, tengential coordinate x, radial coordinate r;b is a numerical exponent that is expressed in terms of the behaviour law and of the flow), the authors calculate a analytical expression for the collection factor N defined as the quotient, with the sign inverted, of the limiting diffusional flux on the downstream active surface by the limiting diffusional flux on the upstream active surface. This factor N is dependent only on geometrical characteristics of system and on exponent b.     

Etude par thermoluminescence de l'hydration de l'aliminate tricalcique

Thermoluminescence shows that the hydration of tricalcium aluminate is deeply influenced by structural defects of the solid. Hydration reaction excites centers of the solid detected by thermoluminescence; this energy storage is related to trapped electrons. Hydration of tricalcium aluminate in the presence of gypsum is not influenced by traps but thermoluminescence allows to corroborate the well-known mechanism of this reaction.     

Mesure de l'impedance faradique pour l'etude de mecanismes EC. Application a l'oxydation de la N,N-dimethyl-p-phenylenediamine

Faradaic impedance measurements have been used to study an EC mechanism involving an irreversible chemical reaction. This technique has proved quite successful to determine kinetic constants ranging from 1 to 10³ s^?1. It has been applied to the hydrolysis reaction, in basic aqueous media, of theN-N-dimethylquinone-diimine resulting from the electrochemical oxidation of the N,N-dimethyl-p-phenylenediamine. The kinetic constant has been determined from pH values 10.5 to 12.5.     

Cinetique du couple redox ferro-ferricyanure a des electrodes d'oxyde et de graphite. Effets de la nature de l'electrode et du cation alcalin

At an electrode made of graphite or of the mixed oxide La_0.8Sr_0.2CoO₃, it is shown with the rotating disk method that the limited current of oxidation of ferrocyanide is governed by the diffusion of a participating species only with K ⁺ and Cs ⁺. Conversely, with Na ⁺ and Li ⁺, it is governed by the diffusion and by a heterogenous reaction which takes place before the charge-transfer. This step is apparently catalysed by the surface of the oxide. By scanning potential cyclic voltametry, it is shown that, with Na ⁺ and Li ⁺, the oxidation reaction is semifast, though it is an order of magnitude faster with K ⁺. By conductibility measurements, we have verified that the number of ion pairs formed is larger with K ⁺ than with Na ⁺ and Li ⁺. A mechanism in term of “contact” and “non contact” ion pairs is proposed.     

Determination du courant limite d'electrodialyse par conductivite pour les faibles nombres de reynolds. Cas des solutions de tartrate acide de potassium

In the case of an electrodialysis operation, it is possible to obtain the limiting current by measuring the conductivity of the solution undergoing dilution. Starting from the equation of the constant flux of matter, when the concentration at the membrane falls to zero, (i/σ_d)_crit = δ relates the current density i and the conductivity of the diluate σ_d. The critical value of (i/σ_d) is easily obtained from the drawing of σ _dvs the potential applied to the apparatus. Experiments carried on aqueous solutions of KHC₄H₄O₆ at 8 g/l show that (i/σ_d)_crit) is well related to the Reynold's number by the relation αRe^β. It is then possible to calculate the thickness δ of the diffusion layer as a function of the Reynold's number.     

Influence de l'adsorption du depolarisant ou d'un produit de la reaction electrochimique sur les courants polarographiques—XVIII. Etude de la dimerisation de radicaux mercuroorganiques par voltammetrie a variation lineaire de tension

Compounds with the general formula ArHgX, adsorbed on a mercury electrode are reduced to free radicals, which dimerize on the surface of the electrode. A study by linear potential sweep voltammetry shows that the dimerization involves two free radicals and establishes the validity of the theory elaborated previously for that type of reaction.     

Etude de la reduction de l'oxygene sur les phtalocyanines monomeres et polymeres—I. principes fondamentaux,choix de l'ion central

The catalytic activity of compounds of the phthalocyanine type can be predicted by means of present theories of catalysis. Study of the activity of iron, cobalt, nickel and copper phthalocyanines shows that the Fe(II) compounds are the most active, the order being PcFe > PcCo > PcNi > PcCu. Molecular orbital theory can be used to relate the order of activity to the filling of the d-levels. The electrocatalysis of oxygen reduction has been experimentally examined.     

Contribution a l'etude du comportement electrochimique du nickel en milieu hydrazine

A potentiostatic set up with three electrodes was used to study the electrochemical behaviour of nickel electrodes in hydrazine. In acid medium it was possible to show a nickel corrosion. But in neutral saline medium no attack of the metal could be shown in hydrazine.